Symposium EN03—Green Electrochemical Energy Storage Solutions—Materials, Processes and Devices

Building a healthy and wealthy society fuelled by clean energy is the most important challenge of the 21^st Century. New energy technologies rely heavily on materials, while materials production relies on energy. It is crucial we will address the fine balance between the development of emerging energy technologies and the materials we use to build them. Today, scarce metals are the most important components of energy storage and conversion systems. The current available supply for these metals cannot sustain the expansion of such technologies at a global scale. Sustainability means avoiding the depletion of natural resources to maintain an ecological balance. Sustainable development means meeting the needs of the present without compromising the well-being of future generations. Based on these definitions, the approaches we currently use to build renewable energy technologies are not sustainable, as we rely on materials choices that are limited and geographically constrained. We need to learn from past mistakes made with fossil fuels to build a future society based on clean energy. In this talk I will present new concept is making and manufacturing sustainable materials and their assembly into energy storage devices which are flexible, self healing and compostable

The massive use of lithium batteries in industries, such as automotive and electrical network accumulation, requires the development of safer electrolytes, economic and possibly made from renewable resources using eco-friendly processes. In this work, we reported the synthesis and the physico-chemical and functional characterization of a polymer gel electrolyte (GPE) based on a skeleton of polyhydroxyalcanoate
obtained from biomass by means of an easy and environmentally friendly chemical process. The GPE has an ionic conductivity of 0.8 mS cm-1 at room temperature, is thermally stable up to over 100°C and is not flammable. The electrochemical stability window is higher than 5V. The
cell Li / GPE / LiFePO4 shows specific capacity of 100 mAhg-1 at 3C with 100% coulombic efficiency. These results demonstrate that the GPE based on polyhydroxyalcanoate is very promising for use in lithium batteries of high power density.

Additive manufacturing is a promising route towards the development of mechanically resilient 3D electrodes with complex architectures, high active material loadings, and large areal capacities relative to conventional 2D film electrodes. These types of processes for fabricating lithium-sulfur (Li-S) cathode materials are beginning to be explored; currently only extrusion methods have been reported, which are limited in resolution to >150 µm and offer limited control over the final morphology and microstructure of the printed material^1,2.

We report an additive manufacturing process which enables fabrication of 3D architected lithium sulfide (Li₂S) carbon composite cathodes for Li-S batteries via digital light processing stereolithography and subsequent pyrolysis. The composites have feature sizes of ~50 µm and are comprised of a porous glassy carbon matrix containing crystalline Li₂S deposits within the pores. We 3D print porous polymer composites using water-in-oil emulsions of aqueous lithium sulfate dispersed in a UV-curable photopolymer resin. Pyrolysis converts the porous polymer matrix to glassy carbon and the lithium sulfate deposited within the pores to lithium sulfide via carbothermal reduction. We investigate the effects of surfactant concentration and emulsion composition on pore size, pore connectivity, and Li₂S morphology via SEM image analysis and show that pore size and Li₂S crystal size can vary from ~10 nm to ~5 µm and are related to the size of aqueous domains in the emulsion. We also report the effects of cathode architecture and microstructure on battery cycling performance and mechanical properties and discuss general design considerations for 3D structured electrodes.

References
1. Shen, K.; et al. 3D Printing Sulfur Copolymer-Graphene Architectures for Li-S Batteries. Adv. Energy Mater. 2018, 8, 1701527.
2. Gao, X.; et al. Toward a Remarkable Li-S Battery via 3D Printing. Nano Energy 2018, 56, 595–603.

MXenes are an emerging large family of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, that were discovered at Drexel in 2011 and have become versatile materials due to a combination of hydrophilicity and metallic conductivity. About 30 different MXenes have been experimentally synthesized already. Many more MXene compositions and their properties have been predicted computationally. Given their compositional diversity, tunable surface chemistry, existence of various ordered structures and solid solutions, MXenes may well be the largest family of 2D materials known to date. MXenes are usually produced by top-down synthesis, namely wet chemical extraction of ‘A’ atomic layers from the layered ternary carbide precursors, such as MAX phases. The resulting MXenes with surface terminations (-O, -F, -OH) impart negative surface charges, key for stable MXene dispersions in water and organic solvents which enable solution processing to ease the design of electrode architectures.
The available for intercalation 2D gallery spaces, accessible redox sites at the transition metal oxide-like surface, and metallic conductivity make MXenes promising as potential candidate materials for high rate capacitive energy storage applications. The ability of MXenes to intercalate a variety of cations while promoting fast charge transfer rates, expanding their widespread usage in a variety of electrochemical energy storage applications including hybrid metal-ion capacitors and battery applications. Besides the role of active charge storage matrix, MXenes have been explored as passive component in the form of current collectors and functional binders for designing degradable green electrochemical energy storage devices. Given the high electrical conductivity of titanium carbide MXene (beyond 10,000 S/cm), it was employed as current collector, replacing metal in fabrication of microsupercapacitors and hybrid energy storage devices. Functionalized surfaces of MXenes have shown the ability for binding carbon, silicon particles and organic systems, playing a role of conductive binder, replacing fluorinated polymers and improving the mechanical and electrochemical stability of the electrodes. Titanium carbide MXenes and also degradable in the environment, producing just titania and carbon dioxide and allowing development of green electrochemical energy storage devices.

Storage of solar radiation is currently accomplished by coupling two separate devices, one that captures and converts the energy into an electrical impulse (a photovoltaic cell) and another that stores this electrical output (a battery or a supercapacitor electrochemical cell). This configuration however has several challenges that stem from a complex coupled-device architecture and multiple interfaces through which charge transfer has to occur. As such presented here is a scheme whereby solar energy capture and storage have been coupled using a single bi-functional material. Two electroactive semiconductors BiVO₄ (n-type) and Co₃O₄ (p-type) have been separately evaluated exclusively for their energy storage capability in the presence and absence of visible radiation. Each of these have the capability to function as a light harvester and also they have faradaic capability. An unprecedented aspect has been observed in that upon photo-illumination of either of these semiconductors, in situ charge carriers being generated play a pivotal role in perturbing the electroactivity of the redox species such that the majority charge carriers, viz. electrons in BiVO₄ and holes in Co₃O₄, influence the redox response in a disproportionate manner. More importantly, there is an enhancement of ca. 30% in the discharge capacity of BiVO₄ in the presence of light and this directly provides a unique route to augment charge storage during illumination.

Supercapacitors, also called electrochemical double layer capacitors (EDLCs), store and deliver energy through ion adsorption/desorption at the electrical double layers. They have attracted intensive attention in the energy storage field in light of their fast charging capability, high power density, and long-life span. The low volumetric energy density (amount of energy stored per unit volume) is a crucial drawback index for impeding the broad application of EDLCs. The strategies used to increase EDLC energy density include developing new capacitive materials, applying high working voltage electrolytes, and designing asymmetric supercapacitors. The main task is thus to optimally match suitable positive and negative active materials with selected electrolyte. However, the optimal design of supercapacitors on device-level is still a tremendous challenge because of the high dimensional design space consisting of pore size (or packing density) and thickness of both electrodes, working voltage, and operation charging rate.
In this work, we will present that utilizing an artificial neuron network (ANN) can successfully establish the quantitative structure-property relation of supercapacitor electrodes and thus efficiently guide the supercapacitor device design. We adopted the tunable chemically converted graphene membrane (CCGM) as a suitable experimental platform with the standard KCl (1M) electrolyte. Using the capillary compression technique developed in our group, we tuned the pore size of CCGM from 1.7 down to 0.8 nm. The thickness of the electrodes was varied from 11 to 276 um. We did about 200 separated experiments to measure the capacitance of electrodes with different thickness and pore size under different charging rates. The obtained experimental database was used to train the ANN. Then, we apply the well-trained ANN model to predict the capacitance of positive and negative electrodes with various electrode structures, establishing a comprehensive and continuous quantitative relationship between CCGM structure and capacitance of both electrodes. After that, the numerical method was applied to explore the high dimensional design space modeled by ANN for the optimized matching of positive and negative electrodes on device-level. The results indicate that there are more than 1 million matching combinations for positive and negative electrodes that meet the general design rules. This result shows that it is an extremely complicated task for optimized supercapacitor design based on a conventional method. We then carried out experiments to successfully confirm the validity of our optimized supercapacitor device design. In the optimal device designs, the positive and negative electrode structures, including pore size and thickness, are hard to determine quantitatively from conventional trial-and-error experiments. Besides, the optimal designs depend on the charging rate. Our method provides a general solution to design CCGM based supercapacitor devices under different charging conditions. Our study indicates that the machine learning method offers computer models an ability to learn from the experiment database and make a reliable prediction of electrode capacitance, enabling the on-demand quantitative device-level supercapacitor design for practical applications.

The fast growing demand of portable electronics and electric vehicles has driven the rapid development of rechargeable batteries and supercapacitors in the past forty years. Energy storage devices with higher energy density is desirable for a longer using time or driving range. In pursue of higher energy density, tremendous efforts have been made in the past few decades, mainly via the developing of novel battery chemistries and/or structural engineering. Battery structural engineering is able to improve the energy density of the energy storage devices via optimizing the configurations of electrode and/or battery architecture yet without changing the electrode chemistry, representing a promising direction towards high-energy battery and supercapacitor development. One most attractive battery structural engineering strategy is thick electrode design that is able to increase the ratio of active material and reduce the manufacturing cost by reducing the use of nonactive components in batteries (e.g., current collector, separator, binder, packaging material, electrolyte, etc.). Given the opportunities thick electrode design offered, intensive efforts from the energy storage community have been dedicated, and great progresses have been made recently. However, constructing thick electrode still faces several challenges, including the delamination of electrode slurry from metal current collector during the drying process, scalable manufacturing, and the sluggish charge kinetics.

To address these challenges, Hu’s group has developed several strategies in constructing better thick electrodes for high-energy batteries and supercapacitors. One strategy is constructing three-dimensional (3D) conductive framework with low-tortuosity pores via direct carbonization of natural wood, where various active electrode materials (e.g., lithium iron phosphate, sulfur, manganese dioxide cathode, lithium metal, porous carbon anode) can be infiltrated or deposited with high active material mass loadings [1-3]. To maintain the mechanical robustness of wood, a new strategy was developed to convert natural wood into flexible wood electrode via partial delignification and multiple coating processes, where carbonization is avoided [4]. A cellulose based densified 3D electrode structure was also proposed via conformal coating of carbon black particles on each cellulose nanofiber to impart decoupled pathways for the fast transport of ions and electrons, followed by active material incorporation into the conductive framework and mechanical compression [5]. We will discuss these progresses in thick electrode development from our lab, challenges, and future research opportunities in this field.

References
[1] C. Chen, L. Hu Nanocellulose toward Advanced Energy Storage Devices: Structure and Electrochemistry Acc. Chem. Res. 2018, 51, 3154–3165. DOI: 10.1021/acs.accounts.8b00391.
[2] C. Chen, Y. Zhang, Y. Li, J. Dai, J. Song, Y. Yao, Y. Gong, I.Kierzewski, J. Xie, L. Hu, All-wood, Low Tortuosity, Aqueous, Biodegradable Supercapacitors with Ultra-High Capacitance, Energy Environ. Sci., 2017, 10, 538-545. DOI: 10.1039/C6EE03716J.
[3] Y. Zhang, W. Luo, C. Wang, Y. Li, C. Chen, J. Song, J. Dai, E. Hitz, S. Xu, C. Yang, Y. Wang, L. Hu High Capacity, Low Tortuosity and Channel-Guided Lithium Metal Anode, PNAS, 2017, 114, 3584-3589. DOI: 10.1073/pnas.1618871114.
[4] C. Chen, S. Xu, Y. Kuang, W. Gan, J. Song, G. Chen, G. Pastel, H. Huang, B. Liu, Y. Li, L. Hu Nature-Inspired Tri-Pathway Design Enabling High-Performance Flexible Li-O2 Batteries. Adv. Energy Mater. 2019, 9, 1802964. DOI: 10.1002/aenm.201802964.
[5] Y. Kuang, C. Chen, G. Pastel, Y. Li, J. Song, R. Mi, W. Kong, B. Liu, Y. Jiang, K. Yang, L. Hu Conductive Cellulose Nanofiber Enabled Thick Electrode for Compact and Flexible Energy Storage Devices. Adv. Energy Mater. 2018, https://doi.org/10.1002/aenm.201802398.

In the last few years, sodium-ion batteries (SIBs) emerged as an economical, high energy alternative to lithium-ion batteries (LIBs) for large-scale energy storage applications. Nevertheless, even after a decade of research, the anode remains the biggest challenge towards its practical applications. Consequently, for acquiring higher energy density, superior power performances, and meaningfully prolonged stability from SIBs, we need a stable, efficient and cost-effective anode material.
Here, in our proposed research work, we utilized a variety of biomass waste like fruit peels, rice husk, etc. as a precursor to synthesize some new carbon- electrode materials for their application in SIB. The carbon materials were synthesis through H₃PO₄acid treatment of the dried powdered biomass materials accompanied by washing and annealing at 900 ^oC at Ar atmosphere. The synthesized material exhibited a capacity as high as ~180 mAh/g. To further improve the electrochemical behavior of the material, we exploited different percentages of hetero-atom and found that if doping percentages are carefully optimized, they can, not only help in mitigating the material instability but also leads to significant improvement in rate performance. We further characterized thesurface of the carbon material with high-resolution scanning electron microscopy, X-ray diffraction, and Raman spectroscopy before and after cycling to investigate the structural stability. We believe that the results presented herein opens a promising direction to exploit the bio-waste as precursors to fabricate carbon materials with promising electrochemical activity.

Reference:
S. Passerini et al., Mater. Today 2019, 23, 87.
X. Li et al., Adv. Energy Mater. 2018, 8, 1703082.

Silicon has been considered as the most promising alternative for the conventional graphite anode in lithium-ion batteries, due to its high gravimetric capacity. There are tremendous approaches to alleiviate the large volume change considered as the main reason of cycle degradation upon repeated alloying reaction. In particular, hollow nano-structure is one of feasible approach, in that free voulme in hollow type of structure produces sufficient space to accomomodate the large volume change stemming from alloying reaction. Nevertheless, fabrication procedure, involving toxic reagents and complicated reactions for removing sacrificial template hinders the commercial utilization. Here in, we develop technique enabling to synthesize silicon anodes with various morphologies such as sheet, tube and hollow typed-structure without any toxic reagents and complex reactions. In this technique, SiC_x layer in which Si nanoparticles embedded in SiC passivation matrix acting as strong protection against oxidation, was coated on the carbonaceous templates (spherical, sheet and rod types) and etched via scalable one-pot thermal decomposition method using SiH₄, C₂H₄ and Air. Surprisingly, a few Si nanoparticles produced the silicon oxide even over 800°C owing to SiC passivation matrix. As a results, electrodes fabricated such anodes effectively alleviate large volume changes without pulverization during cycling with 100 cycle retention of 92%. In addition, it performs excellent initial coulombic efficiency compared with the previously reported Si hollow nanostructure. Specifically, SiC hollow nano-structure shows the high initial discharge capacity of 1862 mAh g^-1 with initial coulombic efficiency of 90.1%.

The increasing need for onboard energy supply/storage in wearable electronics, wireless sensor networks, and the upcoming Internet of Things has pushed for the miniaturization of technologies, including energy harvesting and energy storage units that could be integrated directly onto microchips to achieve energy self-sufficiency. In this context, microsupercapacitors have attracted considerable attention for their use in various emerging micropower applications. A microsupercapacitor is a miniaturized supercapacitor that can be directly mounted on a chip to power integrated circuits. These small electrochemical energy storage devices are characterized by high power and excellent cyclability. However, they have moderate energy density because they rely on a charge storage mechanisms based on interfacial reactions. In order to improve their capacitance and energetic performances while maintaining reduced footprint, more active and accessible materials have to be loaded per unit area of the electrode. This can be obtained by designing 3D electrodes with high surface-to-volume ratio that achieves charge storage over an extended surface, thereby decoupling the direct relationship between power and energy density. Various strategies exist to fabricate these 3D nano-architectured electrodes and they will be reviewed, with a special focus on disordered 3D architecture that has received increasing interest in recent years due to the impressive results obtained using this paradigm shift. These disordered 3D nano-architectured electrodes rely on the deposition of pseudocapacitive materials, known for their large specific capacitance, onto a disordered 3D high-surface-area conductive support. The areal capacitance is improved from one to three orders of magnitude compared to the planar geometry.

Rechargeable sodium-ion batteries based on non-flammable aqueous electrolytes are promising for large-scale energy storage for grid applications. Recently we reported a highly-concentrated 35 molal aqueous sodium bis(fluorosulfonyl)imide (NaFSI) electrolyte with an extended stability window of 2.6 V on stainless steel current collectors.^[1] However, such highly concentrated systems, often referred to as water-in-salt electrolytes, tend to crystallize already near room temperature, resulting in cell failure.
Here, we report a ternary 25m NaFSI + 10m NaFTFSI electrolyte, which is kinetically robust against crystallization and allows long term cycling even at -10 °C. We show that the asymmetry of the FTFSI anion is crucial for efficiently suppressing crystallization in such supercooled electrolytes.^[2]
Taking into account the raw materials supply chain as an important challenge for scaling, we developed a 2 V class aqueous sodium-ion battery employing abundant raw materials, namely NaTi₂(PO₄)₃ and Na₃(VOPO₄)₂F on the anode and cathode side, respectively. With 64 Wh kg^-1, based on the masses of active materials of both electrodes, this battery displays an energy density that is almost twice as high as that of previously reported aqueous sodium-ion batteries. The cell displays excellent cycling stability at 30 °C with a capacity retention of 85% after 100 cycles at C/5 and 77% after 500 cycles at 1C. At -10 °C, we obtain a capacity retention of 74% after 500 cycles at C/5.


References:
^[1] Kühnel, R.-S.; Reber, D.; Battaglia, C., A High-Voltage Aqueous Electrolyte for Sodium-Ion Batteries. ACS Energy Lett. 2017, 2, 2005-2006.
^[2] Reber, D.; Kühnel, R.-S.; Battaglia, C., Suppressing Crystallization of Water-in-Salt Electrolytes by Asymmetric Anions Enables Low-Temperature Operation of High-Voltage Aqueous Batteries. ACS Materials Letters 2019, 1, 44-51.

In recent years, significant attention has been paid to the development of micro-devices as innovative energy storage solutions. For instance micro-sensor networks such as sensors actuators or implantable medical devices require power densities and cyclability that are several orders of magnitude higher than those of conventional Lithium-Ion batteries. For such applications, µSCs, a developing novel class of micro/nanoscale power source are rising alternatives, and their integration “on-chip” could allow significant innovations to emerge [1]. Therefore, a great deal of attention has been focused on µSCs, for which large series of nanostructured active materials have been developed.
In this work we focused to increasing the stability and the energy performance of the supercapacitors based on silicon nanostructures electrodes (nanowires and nanotrees) and in same time used safety and green electrolytes (aqueous) without lithium and ionic liquids. The nanostructures were grown by chemical vapor deposition (CVD) through a vapor-liquid-solid (VLS) process and take here advantage of a substantial increase of the developed surface of the electrode while structured at the nanoscale [2-4]. We realized a new nanocomposites electrodes based on silicon nanostructures/ protected nanometric layer/ electronic conducting polymer. This nanocomposite electrode is a real important lever for improving performance in terms of energy density and durability of devices that becomes possible via Atomic Layer Deposition (ALD) layers of Alumina [5]. We have demonstrated a clear gains of a layer of alumina of less than four nanometers which makes it possible to reach cyclability greater than 8 million cycles and retentions of capacities close to 100%. In addition, the first key steps in the process of producing flexible composite electrodes (Si nanowires / Al₂O₃ / conductive polymers) have recently been successfully completed. Thus a remarkably simple deposition of PEDOT-PSS by drop-casting of an aqueous solution of commercial polymer was used. Despite the poor control over the thickness of the deposit, the gravimetric performances proved to be excellent with a loan capacity retention of 95% over 500 000 cycles for an initial gravimetric capacity 8.5 F. g^-1 and specific energies and powers of 8.2 mJ.cm^-2 and of 4.1 mW.cm^-2. Such cycling stability for a polymer-based nanocomposite in aqueous media combined with first-order electrochemical storage performance is unprecedented in the literature [6]
Beidaghi, M. Gogotsi, Y. Energy & Environ. Sci. 2014, 7 (3), 867-884
Thissandier, F. ; Gentile, P. ; Pauc, N. ; Brousse, T. ; Bidan, G. ; Sadki, S. Nano Energy 2014, 5, 20-27
Thissandier, F. Gentile, P. Sadki, S., 2014, Journal of Power Sources 269, 740-746
Gaboriau, D. Aradilla, D. Gentile, P. Sadki, S., RSC Advances, 2016, 6, 81017-81027
Dorian Gaboriau, Maxime Boniface, Anthony Valero, Dmitry Aldakov, Thierry Brousse, Pascal Gentile, and Said Sadki, ACS Appl. Mater. Interfaces 2017, 9, 13761−13769
Anthony Valero, Adrien Mery, Dorian Gaboriau, Pascal Gentile, and Saïd Sadki, ACS Appl. Energy Mater. 2019, 2, 436−447

I will start by giving an overview of our work on assembly and functionalization strategies of nanocellulose aimed at specific properties, with an eye toward high impact applications including energy, electronics, building materials and water treatment, including nanomanufacturing and light management in transparent nanopaper for optoelectronics (as a replacement of plastics); mechanical properties of densely packed nanocellulose for lightweight structural materials (replacement of steel, Nature 2018); artificial tree for high-performance water desalination and solar steam generations; and radiation cooling (Science, 2019).

I will then focus on our work on applying nanocellulose/wood as building blocks for advanced energy devices, including flexible, thick battery electrodes with nanocellulose binder, three-dimensional carbon derived from wood for advanced batteries (replacement of metal current collectors for beyond Li-ion batteries); nano-ionic membranes for thermoelectrics (Nature Materials, 2019).

As a new generation of supercapacitor, the Li-ion capacitor (LIC) is an advanced energy storage device which consists of an electric double-layer capacitor (EDLC) cathode and a pre-lithiated anode [1,2], between which the ions shuttle during charge and discharge processes. The LIC cell not only retains all the advantages of EDLC such as high specific power >10 kW/kg and long cycle life >100,000 cycles, but also exhibits a higher specific energy of 15-25 Wh/kg and a higher maximum cell voltage than that of the EDLC [3].
Because of using pre-lithiated and low surface anode materials, the LIC can be charged to a maximum voltage as high as 4.0 V, which is much higher than of EDLCs and comparable to Li-ion batteries (LIBs); therefore, it allows the LIC and LIB to be assembled in one package as a LIB/LIC hybrid energy storage cell.
We have demonstrated a new hybrid energy storage cell that combines the advantages of both the LIB and the LIC [4], thereby avoiding their inherent defects, while bridging the gap between the high energy densities offered by batteries and the high power densities seen in EDLCs. The energy density and power density of the hybrid cell can be designed to meet the requirements by a reasonable distribution of the ratio between LIB and LIC electrode materials in the internal hybrid cell. For example, we show a hybrid LIC consisting of a Li nickel cobalt manganese oxide (NMC)/activated carbon (AC) composite cathode in combination with an ultra-thin Li film (u-Li) pre-loaded hard carbon anode. Additionally, we show that by utilizing three design approaches: dry composite electrode fabrication method, cathode to anode capacity ratio design, and pre-lithiation method using u-Li, we can demonstrate an energy storage device with excellent cycle life, and that can be tailored by composite ratios within the cathode to fit different applications. Shown here is an in-depth look at various composite material ratios, pre-lithiation calculations and hybrid Li-ion battery-capacitor energy storage device creation based on targeting essential energy-power performance characteristics.
References
[1] W.J. Cao and J.P. Zheng, “Li-ion Capacitors with Carbon Cathode and Hard Carbon/SLMP Anode Electrodes”, J. Power Sources, 213, 180 (2012).
[2] W.J. Cao, J. Shih, J.P. Zheng, and T. Doung, “Development and characterization of Li-ion capacitor pouch cells”, J. Power Sources, 257, 388 (2014).
[3] W.J. Cao, J.F. Luo, J. Yan, X.J. Chen, W. Brandt, M. Warfield, D. Lewis, S.R. Yturriaga, D.G. Moye and J.P. Zheng, High Performance Li-Ion Capacitor Laminate Cells Based on Hard Carbon/Lithium Stripes Negative Electrodes, Journal of the Electrochemical Society, 2017, 164(2), A93-A98.
[4] Zheng, J.-S., Zhang, L., Shellikeri, A., Cao, W., Wu, Q., & Zheng, J. P. (2017). A hybrid electrochemical device based on a synergetic inner combination of Li ion battery and Li ion capacitor for energy storage. Scientific Reports, 7, 41910.

Emergent green conductive materials are pivotal to reduce harmful and long-lasting electronic waste [1, 2]. At the same time, the electronics industry has demand to transform rigid devices into soft, wearable and conformable structures [2-3]. A first achievement towards flexible and sustainable electronics would be blending biomaterials and conductive nanoparticles to produce electronic components. Following such an approach, we have realized conformable resistors, capacitors and inductors using a fibrous structural protein extracted from bio-waste as a “polymer” matrix for graphene nanoplatelets (GnPs). Furthermore, we have obtained flexible conductors (sheet resistance ≈ 10 Ω/sq) by functionalizing cellulose with bio-based conductive inks made by mixing GnPs with biopolymers and/or natural proteins. These conductive biocomposites were exploited in foldable circuits, passive electrical components (such as filters), organic photovoltaic devices, electromagnetic interference shielding films, portable antennas and electrodiagnostic sensors [2, 4, 5]. The success of conformable and sustainable conductors will simplify the fabrication of easily disposable devices with a low environmental footprint and, simultaneously, support the transition towards flexible electronics.

References:
[1] M. Irimia-Vladu, Chem. Soc. Rev., 43 (2014) 588-610
[2] P. Cataldi et al., Adv. Sust. Syst., 11 (2018) 1800069
[3] P. Cataldi et al., Adv. Sci., 2 (2018) 1700587
[4] P. Cataldi et al., Adv. El. Mat., 11 (2016) 1600245
[5] L. La Notte et al., Mater. Today Energy, 7 (2018) 105-112

Cement production is currently the largest single industrial emitter of CO₂, accounting for 8% (2.8 Gtons/year) of global CO₂ emissions in 2015. Deep decarbonization of cement manufacturing will require remediation of both the CO₂ emissions due to the decomposition of CaCO₃ to CaO, and that due to combustion of fossil fuels (primarily coal) in the calcining (~900°C) and sintering (~1,450°C) processes. Here, we demonstrate an electrochemical process that uses neutral water electrolysis to produce a pH gradient in which CaCO₃ is decarbonated at low pH and Ca(OH)₂ is precipitated at neutral to high pH, concurrently producing a high purity O₂/CO₂ gas mixture (1:2 molar ratio at demonstrated stoichiometric operation) at the anode and H₂ at the cathode. We show that the solid Ca(OH)₂ product readily decomposes and reacts with SiO₂ to form alite, the majority cementitious phase in Portland cement. Our electrochemical calcination approach produces concentrated gas streams from which the CO₂ may be readily separated and sequestered, the H₂ and/or O₂ may be used to generate electric power via fuel cells or combustors, the O₂ may be used as a component of oxyfuel in the cement kiln to further lower CO₂ and NO_x emissions, or the output gases may be used for other value-added processes including liquid fuel production. Analysis shows that in a scenario where the hydrogen produced by the reactor is combusted to heat the high temperature kiln, the electrochemical cement process can be powered solely by renewable electricity.

The strong interactions of zwitterionic polymers with ionic species and their self-assembly have been widely used for drug delivery, hydrogel materials, and membrane selective layer coatings, but little has been done to exploit their potential for electrochemical applications. Recent works within our group have focused on the development of polymer-supported ionogels containing one or more bio-inspired zwitterionic functional groups. By taking advantage of the unique interactions between zwitterionic moieties and ionic liquid ions, we have developed a new class of ionogels with highly tunable properties that could provide several potential advantages for safer electrochemical devices. An important benefit to utilizing ionic liquids is that they can be recycled due to their nonvolatile nature, leading to the development of more environmentally friendly electrolytes. This presentation will describe the synthesis of fully-zwitterionic (co)polymer scaffolds for fabrication of ionogel electrolytes and reveal the importance of polymer selection and architecture on the observed gel properties. First, random zwitterionic copolymers were prepared in situ via free radical photopolymerization in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI TFSI). Spectroscopic characterization indicated different degrees of zwitterion/ion interactions and zwitterionic dipole—dipole physical cross-links depending on the zwitterion chemical identity. A wide range of ion transport and mechanical properties were obtained by tuning the copolymer ratio, which highlighted the benefits of combining more than one zwitterion chemistry.[1] Second, fully-zwitterionic ABA triblock copolymers were synthesized using sequential addition with a controlled radical polymerization method. While both polymeric subunits are zwitterionic, a difference in solubility drives copolymer self-assembly in various environments, including ionic liquids, which allows one to fabricate ionogels. Further tuning of the mechanical and ion transport properties of these ionogels can be achieved by changing the zwitterion identities of the polymeric subunits, or by adjusting the block lengths and molar ratio between the two functional groups. Incorporation of bio-inspired zwitterionic moieties in ionic liquid-based electrolytes is still relatively unexplored, and there is much room for additional investigation in order to build a deeper understanding of zwitterion behavior within ionic liquid environments. This work highlights some of the exciting possibilities of careful selection of zwitterion chemical identities and copolymer architectures towards the development of safer materials for electrochemical energy storage.

Electrolytes are an essential component of energy storage devices. Electrolyte composition has a significant impact on the safety, price and performance of the battery. Intrinsically nonflammable aqueous electrolytes can offer safer battery operation and decreased associated toxicity but suffer from a smaller electrochemical stability window (and hence energy density) compared to traditional organic electrolytes. To circumvent the small electrochemical stability window, highly concentrated “water-in-salt”, WIS, lithium organic imide systems which demonstrate significantly wider stability windows were recently proposed.^1,2 However, the toxicity often associated with organic imides and high price make the practical implementation of current water-in-salt electrolyte chemistries into commercial energy storage devices challenging.
We address the challenge of developing new formulations of water-in-salt electrolytes caused by the lack of lithium salts having water solubility high enough to satisfy the water-in-salt condition. The proposed mixed cation strategy is whereby cheaper (by at least an order of magnitude) and more soluble salts featuring alkali cations beyond lithium, e.g. potassium acetate, are used to create the water-in-salt condition.³ We study co-dissolution of corresponding lithium and zinc acetate salts, we show that such highly concentrated electrolytes can provide the same benefits of the extended voltage window as imide-based electrolytes and, demonstrate compatibility with traditional Li-ion or Zn-ion battery electrode materials while being low-cost and environmentally benign. In addition, we demonstrate the strong effect of the solution concentration on the solvation structure of the cations and local order in the potassium acetate-based WIS systems and correlate it with the electrochemical response of different Zn-ion and Li-ion based electrode systems.

References
L. Suo, O. Borodin, T. Gao, M. Olguin, J. Ho, X. Fan, C. Luo, C. Wang and K. Xu, Science, 2015, 350, 938
Y. Yamada, K. Usui, K. Sodeyama, S. Ko, Y. Tateyama and A. Yamada, Nat. Energy, 2016, 1, 16129
MR Lukatskaya, JI Feldblyum, DG Mackanic, F Lissel, DL Michels, Y Cui, Z. Bao, Energy Environ. Sci., 2018, 11, 2876-2883

Lithium sulfur (Li-S) batteries have high theoretical specific energy for portable and stationary storage application. Sulfur is an earth abundant materials for potential green energy storage. However, Li-S batteries have many challenging issues at the materials level. Here I will present our recent progress on: 1) Nanoscale materials design for polysulfide binding, encapsulation and activation. 2) Discovery of liquid sulfur behavior at room temperature, leading to new guidance to materials design.

Sulfur-rich carbons are minimally explored for potassium ion batteries (KIBs). Here, we chemically incorporate a large amount of S (38 wt. %) into a carbon host, creating Sulfur-grafted Hollow Carbon Spheres (SHCS) for KIB anodes. The SHCS architecture provides a combination of nanoscale (ca. 40 nm) diffusion distances and C-S chemical bonding to minimize cycling capacity decay and Coulombic efficiency (CE) loss. SHCS exhibits a reversible capacity of 581 mAh g^-1 (at 0.025 A g^-1), which is the highest reversible capacity reported for any carbon-based KIB anode. Electrochemical analysis of S-free carbon spheres baseline demonstrates that both the carbon matrix and the sulfur species are highly electrochemically active. SHCS also shows excellent rate capability, achieving 202, 160 and 110 mAh g^-1 at 1.5, 3 and 5 A g^-1, respectively. The electrode maintained 93% of the capacity from the 5^th to 1000^th cycle at 3 A g^-1, with steady-state CE being near 100%. Raman analysis indicates reversible breakage of C-S and S-S bonds upon potassiation to 0.01 V vs. K/K⁺. GITT analysis provides voltage - dependent K⁺ diffusion coefficients that range 10^-10 to 10^-12 cm² s^-1 upon potassiation and depotassiation, with approximately five times higher coefficient for the former.

This presentation will compare and contrast various options in the quest for dealing with lithium ion batteries that have reached the end of their useful (first) lives. First, the economic and environmental impacts of recycling battery materials using multiple processing techniques will be examined and best practices will be suggested. We will then examine several different promising methods for direct recycling of cathode materials, as they have the most economic value and highest carbon footprint of the materials in most cells. Lastly, the durability of purposely aged second-use battery cells under several different application-specific duty cycles will be explored with the intention of understanding the likely benefits of using these aged cells in less taxing stationary applications such as intermittent renewable integration and for use in uninterruptible power supplies

Redox-active organic compounds have been attracting extensive attention as active electrode materials to replace conventional transitional metal based inorganic electrodes for rechargeable batteries.^1,2 Potential advantages of organic electrode materials include their environmental benignity, sustainability, and high theoretical energy density, which can be ideal for large-scale energy storage applications.^1,2 Despite these advantages, organic electrodes have suffered from poor cycling stability and rate performance, limiting their practical applications.^1-3 A promising strategy to overcome these issues is to incorporate redox-active molecules onto 3D conductive substrates.^1-3 In this presentation, we will discuss our recent progress in designing nanostructured organic electrodes for Li-/Na-ion storage. The assembled organic electrodes using carbon nanotube or graphene substrates have multiple redox reactions with Li-/Na-ions in high potential regions. Based on the redox reactions, these organic electrodes delivered high capacity at high potential regions with superior rate-performance and cycling stability, which can be promising cathodes for large-scale rechargeable batteries or hybrid capacitors. Next, we will introduce a new self-assembly technique using ligand exchange reactions on nanoparticles. This technique was used to convert the insulating paper or fabric to highly porous metallic current collectors. Using such metallic current collectors, we demonstrate flexible and wearable energy storage and conversion devices.

1. T. Liu, K. C. Kim, B. Lee, Z. Chen, S. Noda, S. S. Jang, and S. W. Lee, Self-Polymerized Dopamine as an Organic Cathode for Li- and Na-Ion Batteries, Energy & Environmental Science, 10, 205-215, 2017.
2. T. Liu, B. Lee, B. G. Kim, M. J. Lee, J. Park, and S. W. Lee, In Situ Polymerization of Dopamine on Graphene Framework for Charge Storage Applications, Small, 14, 1801236, 2018.
3. T. Liu, B. Lee, M. J. Lee, J. Park, Z. Chen, S. Noda, and S. W. Lee, Improved Capacity of Redox-Active Functional Carbon Cathode by Dimension Reduction for Hybrid Supercapacitors, Journal of Materials Chemistry A, 6, 3367-3375, 2018.

Supercapacitors (SCs) represents an emerging class of fast-charging and stable energy storage devices and have been extensively studied in recent years. However, most of the previous research are focused on SCs in aqueous and room temperature conditions. Improving the performance of SCs, especially at low-temperature environments, is significantly important for prolonged space exploration. This talk will report our new findings of using 3D printing method to fabricate biomass-derived carbon aerogels for supercapacitors at ultralow temperatures. The 3D printed biomass-derived carbon aerogel electrodes with periodic large pores have shown significantly improved electrochemical performance than the non-3D printed counterparts at low temperatures. More importantly, hierarchical pore structure with large periodic pores, macropores, mesopores and micropores in the 3D printed carbon aerogels enable the porous electrodes to achieve an excellent capacitance of around 150 F/g even under -70 °C. The kinetic analysis further reveals the favorable ion diffusion property in the 3D printed hierarchical porous electrodes. Moreover, the effects of each type of pore structure on capacitance at low-temperature will also be explained. This talk will for the first time demonstrate the superiority of 3D printed porous electrodes for ultralow temperature energy storage, which might open a new door for the future work on high-performance fast-charging energy storage systems for space missions.

Photo-rechargeable batteries (PRBs) have been developed as all-in-one energy devices having a merit that both energy harvesting and storage are realized in a single device. A major portion of the PRBs are based on non-faradaic processes (capacitive PRBs) for their energy storage. On the other hand, several works have focused on using faradaic processes (faradaic PRBs) because the faradaic PRBs are much superior in terms of energy densities. However, for the spontaneous electron transfer between the photo-electrode and the storage-electrode, the energy levels of the two active materials should be matched well, so that there are not so many storage materials having faradaic reaction.
In addition, dim-light performances of the faradaic PRBs have not been reported as far as we know. Herein, we present an external-power-free single-structured faradaic PRB, named dye-sensitized solar battery (DSSB), developed specifically for indoor light harvesting. The DSSB was designed to be photo-charged by the photo-anodic process of dye-sensitized solar cells (DSSCs) and the cathodic process of LiMn₂O₄ (LMO). Redox mediators in electrolyte of the compartment to the photo-electrode are oxidized to regenerate activated dye molecules. The charged DSSB can be discharged by returning to their original state of the two redox active materials. The performances of DSSBs were strongly dependent on the thermodynamic and kinetic parameters of redox mediators. At one sun condition, the kinetics of mediator determined the light-to-charge energy efficiency (η_overall). A kinetically-fast but thermodynamically-unfavorable (can make smaller cell voltage) mediator (I^-/I₃^-) showed the best results in terms of photo-charging current (J_Ch) and discharge capacity (Q_dCh). However, in dim-light condition (200 ~ 2000 lux), a thermodynamically-favorable (can make larger cell voltage) mediator (Cu⁺/²⁺(dmp)₂) delivered the highest photo-charging energy density (ED_Ch) corresponding to η_overall of 11.5 % because kinetic limitation becomes negligible. The successful demonstration of the DSSB to operate an IoT sensor node only by an indoor light (500 lux) opens the possibility of realizing indoor-light-harvesting PRBs.

Organic redox compounds are potential substitutes for transition-metal-oxide electrode materials in rechargeable batteries because of their low cost, minimal environmental footprint, and chemical diversity.[1] However, their electrochemical performances could not reach the level of currently used electrode materials due to the relatively low redox potential, low electrical conductivity and high solubility in organic solvents. Those drawbacks have not been simultaneously overcome with the single molecule-based tuning such as chemical modification and hybridization with conductive scaffolds.[2] Herein, we report the novel design paradigm of organic charge-transfer complexes for the new type of organic electrode material candidates which can solve the existing shortcomings of single-moiety-based organic electrode materials.[3] Organic charge-transfer complexes are an association of two or more types of organic molecules in which a fraction of electronic charge is transferred between the molecular entities. Well-ordered stacking of the molecular layers in charge-transfer complexes creates a charge-transport path which electrons can move freely, and the strong intermolecular interaction such as hydrogen bonding and - interaction result in high structural stability.
We first developed the donor components of organic charge-transfer complexes, 5,10-dihydro-5,10-dimethylphenazine (DMPZ)[4] and dibenzo-1,4-dioxin (DD)[5], which are ready-to-charge and have high redox potential. DMPZ and DD successfully show reversible redox reaction and high redox potential of 3.4 and 4.1 V vs. Li/Li⁺, respectively. Following with these results, organic charge-transfer complexes, a novel class of electrode materials with intrinsically high electrical conductivity and low solubility that can potentially overcome the chronic drawbacks, are constructed with the developed ready-to-charge organic electrode material.[3] Combination of DD and 7,7,8,8-tetracyanoquinodimethane (TCNQ) via a room-temperature process leads to enhancement in the electrical conductivity for 5 order magnitudes and reduction in the dissolution resulting in the high power and cycle performances that far outperform those of each single-moiety counterpart. Moreover, full redox activation of donor and acceptor molecules is revealed with the practical energy density of 560 Wh kg^-1. By applying an investigation on the relationship between the redox potential and the charge carrying ions with DMPZ and terephthalate derivatives, it is confirmed that there is still a room for enhancing energy density with optimizing the cell configuration such as electrolyte and counter metal.[4, 6] These findings demonstrate the general applicability of the charge-transfer complex and opens up an uncharged pathway toward the development of high-performance organic electrode materials via the exploration of various combinations of donor-acceptor monomers with different stoichiometry.

References
[1] M. Armand, and J.-M. Tarascon, Nature 451, 652 (2008)
[2] S. Lee, G. Kwon, K. Ku, K. Yoon, S.-K. Jung, H.-D. Lim, and K. Kang, Adv. Mater. 30, 1704682 (2018)
[3] S. Lee, J. Hong, S.-K. Jung, K. Ku, G. Kwon, W. M. Seong, H. Kim, G. Yoon, I. Kang, K. Hong, H. W. Jang, and K. Kang, Energy Storage Mater. online published (2019)
[4] M. Lee, J. Hong, B. Lee, K. Ku, S. Lee, C. B. Park, and K. Kang, Green Chem. 19, 2980 (2017)
[5] S. Lee, G. Kwon, and K. Kang, in preparation to submit.
[6] S. Lee, J. E. Kwon, J. Hong, S. Y. Park, and K. Kang, J. Mater. Chem. A 7, 11438 (2019)

As the world energy demand continues to rise and carbon dioxide emission reaching a dangerous level, many cities around the world have committed to replacing fossil energy with renewables. For this transition to take place, major improvements in current technology and investigation of new materials are essential. In this talk, I will discuss our efforts for the development of green energy storage and conversion devices including batteries, supercapacitors, and nanogenerators. We explore new materials and methods to store electricity using organic carbons and electrolytes to meet the growing demand for organic materials. The talk will be supported by several examples for green, biocompatible, biodegradable and metal-free energy storage devices. In addition, we have designed and tested supercapacitors that could make pacemakers and other implantable devices safer and more durable. On the other hand, nanogenerators have recently captured interest as an alternative for clean and sustainable energies. They could be used as a power source for self-charging batteries and supercapacitors. Here, we have developed an all-printable wearable device that can function as a stretchable energy harvester and a multifunctional sensor based on the principle of snow-electrification. These devices could potentially be integrated with solar panels to ensure continuous power supply in areas with frequent snowfall. In addition, we utilized this technology for fabricating self-powered, multifunctional electronic skin that is capable of detecting human physiological signals such as pressure, temperature, and humidity through an array of totally flat and lightweight sensors. When combined with a supercapacitor, this technology could potentially be used as a self-standing power source that is stretchable, breathable with excellent anti-bacterial properties, which is favorable for biomedical electronics.

Recent publications
V. Strauss et al., Advanced Materials 2018, 30, 1704449
D. Jung et. al, Nature Materials 2018, 17, 341.
I. Mosa et al., Advanced Energy Materials 2017, 7, 1700358
Y. Shabangoli et al., Advanced Energy Materials 2018, 8, 1802869
M. Hashemi et al., Nano energy 2018, 44, 489
A. Ahmed, et al., Nano Energy 2018, 59, 336
Y. Shabangoli et al., Energy Storage Materials 2018, 11, 282

With the increasing interest and research focus on energy storage devices such as batteries, hybrids and supercapacitors, more and more early stage materials and technologies are tested at small, usually coin cell, scale to screen materials and systems and assess their suitability for further scale-up. This small scale electrochemical testing is then often scaled through various factors and assumptions to inform likely behaviour at a larger commercial or prototype cell scale.
This approach of testing and assessing at the small scale and applying the results to a larger device generally produces reasonable agreement with what follows in prototype devices in Li-ion battery systems, where many millions of cells are produced through standard processes and using standard materials each month. The wealth of knowledge and available data on such production and scaling has allowed models to be developed and parameterised, with extensive validation resulting.
In EDLC supercapacitors, this is not the case. The vastly smaller scale of production of such devices, carried out almost exclusively in commercial entities rather than the wider academic community, has resulted in information on information on how to effectively scale from results in coin cells to larger devices being unavailable in the scientific literature. It is usually found that where a comparison is made between a coin cell (and materials properties) and how that would perform in a larger cell, parameters associated with batteries are used or parameters such as energy and power densities are quoted with no regard for the ‘parasitic’ but necessary cell components needed at a larger scale such as the mass and volume of current collectors, cans, electrolyte and the like.
In this study, the factors necessary to scale between material properties and those of prototype and commercial cells have been investigated. Commercial cells of various sizes between 100 and 3000F have been tested and characterised extensively before being disassembled into their component parts. The electrodes and separators have then been used to construct and fully characterise supercapacitor coin cells, with factors to scale between the coin cell and the original commercial cells extracted. In addition, to investigate the effect changes in parameters such as electrode thickness would have on the scaling between cell sizes, prototype 100F pouch and cylindrical cells have been produced and extensively tested in parallel with their corresponding coin cells.
Finally, through consideration of the Ragone plots generated at various sizes of cells, a realistic set of parameters to be applied to small scale tested materials is presented, along with insights into the effect of moving to larger cells on the expected lifetime of a material or system.

Stretchable and wearable electronics have been an emerging class of electronics that enable a wide range of applications such as electronic skins, implantable devices, robotics, and prosthesis. Consequently, development of stretchable power sources for such devices is highly demanded with the possibility that it can harvest energy from the environment in which the device is deployed. Triboelectric nanogenerator (TENG), a biomechanical energy harvester, possesses the advantages of low cost, light weight, high efficiency, and eco-friendly feature. However, the electrical outputs generated by TENG are pulses and sometimes with irregular magnitudes owing to the uneven strength of the mechanical motion. To enable its ability to serve as a direct power source for most electronic devices that need a constant direct-current supply, it is necessary to integrate the TENG with energy storage devices. In addition, a self-protection from the external environment is preferable for stretchable power sources so as to adapt to real-word conditions.
Here, our recent studies on the flexible/stretchable self-charging power systems to power wearable electronics sorely by harvesting biomechanical energy will be presented. The challenges, future directions and potential applications for wearable/stretchable electronics will also be discussed.

Deformable, stretchable electronics are considered as next-generation devices; however, to realize highly flexible electronics, it is first necessary to develop a deformable energy device. Herein, a crumply and highly flexible lithium-ion battery is realized by using microfiber mat electrodes in which the microfibers are wound or webbed with conductive nanowires. This electrode architecture guarantees extraordinary mechanical durability without any increase in resistance after folding 1,000 times. Its areal energy density is easily controllable by the number of folded stacks of a piece of the electrode mat. Deformable lithium-ion batteries of lithium iron phosphate as cathode and lithium titanium oxide as anode at high areal capacity (3.2 mAh cm^–2) are successfully operated without structural failure and performance loss, even after repeated crumpling and folding during charging and discharging. As another deformable batteries, we demonstrate the fabrication of highly stretchable hybrid carbon/polymer (HCP composite which was found to effectively retain its electrical conductivity, even when under high strain (~200%), due to the co-supporting network of hybrid nanofillers in its structure. We are the first to have developed a stretchable aqueous rechargeable lithium-ion battery (ARLB) that utilized this HCP composite as a stretchable current collector. The ARLB exhibited excellent rate capability (~90 mA h g⁻¹ at a rate of 20 C) and outstanding durability (capacity retention of 93% after 500 cycles).

The technological pressure on the present batteries, dominated by inorganic materials, has led to a sustainability dilemma, and therefore developing new battery chemistries has become of prime importance [1]. In this context, organic batteries are emerging as probably one of the most promising approaches to render the energy storage technology green and sustainable [2]. Presently, carbonyl-based electroactive materials are the most focused due to their potential to achieve simultaneously high energy/power density as well as extended cycling stability [3]. Within this framework, molecular engineering has played a big part in improving theirs electrochemical performances in terms of potential tuning [4] and preventing the unwanted dissolution [5]. However, these improvements usually partially penalize the gravimetric capacities and, in some cases, the exact origin of the operating potential shift as well as redox mechanism are still a matter of debates.

In this work, we will try to address both issues. Firstly, we will show how by using coordination chemistry, Ligand-Metal complexes with sustainable metals (Fe, Mn) as new multi-electron with bi-redox activity can be designed. These new materials can deliver capacities in excess of 200 mAh.g^-1 at an average working potential of 3 V vs. Li⁺/Li⁰. Secondly, we will detail on the electrochemistry of aromatic and heterocyclic dicarboxylate isomers. This study comprehends (i) the effect of N-heteroatom on the potential of the dicarboxylates, with a direct correlation between the operating potential and the ¹³C-chemical and vibration frequency shift of the carbonyl and (ii) the true redox mechanism that dictates the electrochemical activity in the case of bi-redox systems (pyrazine-dicarboxylate). This mechanistic investigation leads to the discovery of new nitrogen-related redox center that can be beneficially explored in the organic battery field.

References
[1] P. Poizot, F. Dolhem, Energy Environ Sci. 2011, 4, 2003.
[2] A. E. Lakraychi et al. Chimie Nouvelle N° 127, janvier 2018
[3] Z. Song, H. Zhou, Energy Environ Sci. 2013, 6, 2280.
[4] a) A. E. Lakraychi et al. J of Mater Chem A. 2018, 6, 19182. b) A. Jouhara et al. Nature Comm. 2018, 9, 4401. c) A. E. Lakraychi et al. Journal of Power Sources. 2017, 359, 198. d) A. E. Lakraychi et al. Electrochemistry Communication. 2018, 93, 71.
[5] a) A. E. Lakraychi et al. Electrochemistry Communication. 2017, 76, 47. b) L. Sieuw et al. Chem Sci. 2019, 10, 418.

Electrochemical energy storage systems (EESS) with high energy density, safety, low cost, and low carbon footprint have become indispensable in the modern era of ubiquitous electronics, electric vehicles, and grid storage. Current EESS lack of these characteristics due to the utilization of critical materials which are precious, flammable and difficult to recycle. Whereas, aqueous electrolytes offer higher safety and lower costs. Nevertheless, their biggest bottleneck is the narrow electrochemical window (1.23V) that is preventing from attaining higher energy and power densities in most of the aqueous EESS. For instance, aqueous rechargeable aluminum ion batteries promise high energy density due to multivalent redox chemistry of aluminum ion (Al³⁺) but they exhibit much lower energy density in real experiments due to the limited electrochemical windows of the aqueous electrolytes. The water-in-salt based electrolytes (WiSE) can potentially eliminate this barrier by offering a larger electrochemical window by reducing the overall electrochemical activity of water on the electrodes. Here, we demonstrate a new concept using aluminum perchlorate based WiSE that is showing a stable and wide electrochemical window of nearly 3 V against Ag/AgCl. The electrochemistry tests of the electrolyte are performed using carbon-based redox-active electrode materials. We employ the new electrochemical system in aqueous rechargeable aluminum ion batteries and supercapacitors, revealing superior performance to standard aqueous electrolytes. Our findings provide new possibilities for widening the electrochemical window and enhancing the energy and power density in aqueous EESS.

References
[1] Z.A. Zafar, S. Imtiaz, R. Razaq, S. Ji, T. Huang, Z. Zhang, Y. Huang, J.A. Anderson, Journal of Materials Chemistry A, 12 (2017) 5646-5660.
[2] L. Smith, B. Dunn, Science, 6263 (2015) 918.
[3] M. Kazazi, Z.A. Zafar, M. Delshad, J. Cervenka, C. Chen, Solid State Ionics, 320 (2018) 64-69.

The replacement of organic solvent-based electrode manufacturing by a water-based process offers an alternative processing route with regard to cost-reduction and more sustainability. However, the interaction of cathode materials with water changes their storage behavior and causes massive problems for electrode manufacturing and cell properties. Due to a Li⁺/H⁺ exchange reaction, the pH of the aqueous slurry is increased so that a corrosive attack of the aluminum foil takes place. The reduction of the pH value by the addition of an acid is one practical measure to prevent corrosion, but has also negative impact on slurry rheology, electrode conductivity or adhesion. These consequences are shown in an exemplary way for the addition of acetic acid. As especially the adhesion strength is influenced, this effect is investigated in detail for various acids. Best electrode properties are not found in the stable region of the aluminum foil, but at a higher pH of 9 to 10. Acetic acid treated cells show high capacities at their begin-of-life, but undergo stronger degradation than samples without acid addition.

Lithium ion batteries have become a mainstay as power storage devices with high energy densities. However, they contain heavy metal compounds such as LiCoO₂, which is constrained by limited resources and problems related to the processing of heavy metal waste. Moreover, the capacities of lithium ion battery cathodes are approaching their theoretical limit, since they rely on one-electron redox reactions of heavy transition metals. In order to increase the adoption of storage batteries in an environmentally friendly manner, the development of innovative electrode materials free of rare metals and having high output and high energy densities is necessary. In recent years, redox active organic compounds such as benzoquinone derivatives have attracted attention as candidate materials for battery electrodes. They exhibit excellent characteristics such as high capacities because of multi-electron redox reactions and their structures composed of light elements only. Moreover, their functional groups can be optimized by chemical modification. However, one of the problems in using an organic compound as cathode material is the insulating property of the organic molecule. The insulating property not only lowers the energy efficiency of the redox reaction but also requires the addition of a large amount of carbon material to ensure conductivity, which reduces the effective energy density.
In this study, we propose an organic cathode material based on a novel concept, the “Interface Charge-Transfer [1] (ICT)” phenomenon. In ICT, the electron transfer occurs at the interface between molecular solids that act as a donor and acceptor, respectively. Charge carriers are generated in the molecular solids, and electric conductivity is acquired. In order to realize an ICT “cathode,” we selected donor and acceptor molecules that are redox-active, that have a small molecular weight, so that both the donor and acceptor molecule can act as an active material, and that have a large theoretical capacity. Based on these criteria, we selected tetrathiafluvalene (donor) and 7,7,8,8-tetracyanoquinodimethane (acceptor). Powders of the molecules and polytetrafluoroethylene (PTFE) were mixed to form an electrode without adding any conductive filler such as carbon. The bulk resistivitiess were measured and it was revealed that the resistivity of the cathodes was very low (2-7 Ω cm). Then, we carried out charge-discharge cycle tests in a half cell system, and the batteries worked for at least 20 cycles while retaining more than 80% of the highest capacity value.
In summary, we succeeded in establishing a novel type of a cathode material, the “ICT cathode”, and examined its performance and characteristics. Since no additives are required to achieve electric conductivity, it is expected that this type of cathode has a high potential for future light-weight and environmentally friendly battery systems.

Reference:
[1] H. Alves, et. al., Nature Mater., 2008, 7, 574-580.

We present the development of a zinc–polymer energy storage device where we employ redox–active polymers based on naphthalenetetracarboxylic diimides (NDIs) with large electron affinities as the cathode. We observe that electrodes made of the polymer can become reduced by zinc electrodes when both electrodes are immersed in aqueous electrolytes. To enable rapid charging in aqueous electrolytes, polar side chains are attached to the polymer backbone that facilitate fast cation transport from the electrolyte into the bulk of the polymer.^[1] In addition, no additives or binders are required for the electrode to function in aqueous electrolytes which also enable to fabricate electrodes from solution. Due to the excellent charging properties of the polymers in aqueous electrolytes, we explore non–toxic aqueous electrolytes (salty water) and discuss pathways of how solid state electrolytes can be used in future devices. Finally, we will present how oxygen reduction reactions (ORRs) can be employed to develop a zinc–polymer–air energy storage devices where the redox-active polymer acts as the catalyst to reduce oxygen. We believe that our findings are of importance for the development of future zinc-air batteries, with the potential to use safe and environmentally friendly electrolytes.

[1] A. Giovannitti, I. P. Maria, D. Hanifi, M. J. Donahue, D. Bryant, K. J. Barth, B. E. Makdah, A. Savva, D. Moia, M. Zetek, P. R. F. Barnes, O. G. Reid, S. Inal, G. Rumbles, G. G. Malliaras, J. Nelson, J. Rivnay, I. McCulloch, Chem. Mater. 2018, 30, 2945.
[2] D. Moia, A. Giovannitti, A. A. Szumska, I. P. Maria, E. Rezasoltani, M. Sachs, M. Schnurr, P. R. F. Barnes, I. McCulloch, J. Nelson, Energy Environ. Sci. 2019.

It is known that the electrochemical performance of carbon-based supercapacitors depends on the porous structures of carbon-based materials. In this work, we prepare activated carbons (ACs) of different porous structures from xylose and use the prepared ACs as the electrode materials in coin-type supercapacitors with 1 mol/L Et4NBF4 solution in AN as electrolyte. The electrochemical performance of the coin-type supercapacitors is systematically studied. The largest specific capacitances obtained from the coin-type supercapacitors are 340 F/g at 0.5 A/g and 220 F/g at 50 A/g, which are much larger than the results reported for similar systems. The supercapacitors can maintain 86.8% of the capacitance after 10000 cycles at 50 A/g. The energy density is 48 Wh/kg at a power density of 13.6 kW/kg.
This work is supported by the NSF [CMMI-1634540].

One weakness of batteries is the rapid falloff in charge-storage capacity with increasing charge/discharge rate. Rate performance is related to the timescales associated with charge/ ionic motion in both electrode and electrolyte. However, no general fittable model exists to link capacity-rate data to electrode/electrolyte properties. Here we demonstrate an equation which can fit capacity versus rate data, outputting three parameters which fully describe rate performance. Most important is the characteristic time associated with charge/ discharge which can be linked by a second equation to physical electrode/electrolyte parameters via various rate-limiting processes. We fit these equations to ~200 data sets, deriving parameters such as diffusion coefficients or electrolyte conductivities. It is possible to show which rate-limiting processes are dominant in a given situation, facilitating rational design and cell optimisation. In addition, this model predicts the upper speed limit for lithium/ sodium ion batteries, yielding a value that is consistent with the fastest electrodes in the literature.

Renewable biomass-derived materials are the key to sustainable energy storage systems. Biopolymers derived from the forest have been blended with conducting polymers to produce green batteries and supercapacitors. In this work, we use cellulose, which is the most abundant biopolymer on earth, to study the critical intra-component interactions between the biopolymer and the seasoned conducting polymer poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS). We report a remarkable self-organization of PEDOT:PSS on cellulose nano-fibrils (CNF) which leads to a continuous, linear array of PEDOT:PSS nano-beads, with an average diameter of 13 nm, along the length of individual nano-fibrils. Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) studies elucidate the self-aggregation of PEDO:PSS particles on cellulose. This self-organization leads to the enhancement of long-range electronic transport in the PEDOT which is confirmed by charge transport measurements. Furthermore, we utilize Grazing-Incidence Wide-Angle X-ray Scattering (GIWAXS) to pinpoint the face-on π-stacked crystallographic orientation of the PEDOT:PSS on top of the CNF. We conclude our investigations by confirming our experimental study by the theoretical modeling of the physicochemical processes that lead to the aggregation of PEDOT:PSS on cellulose using coarse-grained molecular dynamics simulations. Significantly, the simulations also predict nano-beads of PEDOT:PSS aligned along the CNF.

The rechargeable aprotic Li-O₂ batteries hold great promise for electric vehicles because of their high energy density and environmental friendliness. However, the carbon-based cathodes commonly used in Li-O₂ batteries are not stable due to their reaction with discharge products (Li₂O₂, Li₂O), which leads to the formation of insulating lithium carbonate and fades the batteries’ efficiency and cycling stability. In this work, a WCoFe@Ni cathode consisting of sub-stoichiometric tungsten oxide (W₁₈O₄₉), cobalt oxide and ferric oxide as a carbon-free cathode for Li-O₂ batteries is presented for the first time. The resulting WCoFe@Ni cathode delivers a high specific capacity (5800 mAh g^-1 at 200 mA g^-1) and remarkable cycling stability (more than 400 cycles at a capacity of 1000 mAh g^-1 under 500 mA g^-1). The electronic structures of Co and Fe are modified upon the adding of W in the oxides. The amount of Fe²⁺ in CoFe (37 %) is higher than that in WCoFe (20.2 %), while the amount of Co²⁺ in WCoFe (66.8 %) is higher than that in CoFe (41.3 %). Furthermore, the Fe at the high-valence in WCoFe stabilizes the Co at the low-valence, which facilitates the formation of CoO-like species that is highly active for the decomposition of discharge products in the Li-O₂ batteries. The synergistic interaction between W, Co and Fe in WCoFe@Ni cathode plays a critical role in promoting the performance of Li-O₂ batteries. Moreover, the sub-stoichiometric tungsten oxide provides high electronic conductivity and the unique 3D nanowire network structure is beneficial for the storage of discharge products. The WCoFe@Ni is a promising carbon-free cathode for Li-O₂ batteries

There is currently a great need for development of scalable, sustainable and cheap storage of electrical energy in order to adapt to the power balance from the varying supply of the solar and wind electricity. In biological systems, redox reactions of quinone(Q) groups are employed for energy conversion and storage. Remarkably, lignin has been employed in charge storage devices due to the redox activity, abundance and low cost.¹ However, a challenge is that lignin itself is electronically insulating. Polymer, partially reduced graphite or graphene oxide and graphene have been investigated for energy storage devices. However, these preparation procedures are complicated and difficult for scalable production. Herein, we report a facile process to combine graphite and the lignin derivative lignosulphonate (LS) with the help of simple mechanochemistry; graphite flakes and LS are co-ground in the solid state followed by treatment with water, resulting in a readily processable lignin: graphite paste that can be coated on substrates and directly applied in electrical energy storage devices.
The materials and electrodes are characterized by UV-vis spectroscopy, FTIR spectroscopy, Raman spectroscopy, XRD, dynamic light scattering (DLS), thermogravimetric analysis (TGA), SEM, cyclic voltammetry (CVs) and galvanostatic charge-discharge measurements. The hybrid electrodes with different stoichiometry give two symmetric redox waves defined at 0.67 V and 0.34V versus Ag/AgCl, which is ascribed to the redox reactions of Q groups in LS, a conductivity range from 70 to 290 S m^-1 and a charge capacity from 30 to 35 mAhg^-1. Moreover, considering the charge capacity from Q groups and mass of LS in the LS/graphite hybrid material electrodes, the charge capacity of the hybrid materials due to LS can be as much as 70 mAhg^-1. IR results and UV-vis results prove the LS/graphite pellets and supernatant contain a mixture of LS and graphite. The Raman spectra, TEM pictures and XRD results suggest the presence of fewer layers, more defects, more disorder and smaller crystallite size of graphite in the hybrid material electrodes than in the pristine graphite. The TGA results confirm the range of the stoichiometry of the LS/graphite pellets of 0.55-1.25. The SEM results illustrate that the ball milling process can reduce the grain size of graphite and LS, and create nanoscale geometries in the hybrid materials. Furthermore, the morphology of the LS/graphite hybrid material electrodes can be effected by the stoichiometry of LS and graphite in the ball milling process.
In summary, mechanical ball milling combined with aqueous process is a way to fabricate sustainable, environmental friendly, low cost and scalable LS/graphite hybrid materials with high conductivity and moderate charge capacity. The molecular interaction and charge transfer between LS and graphite in the electrodes make these electrodes candidates for energy storage.

[1] G. Milczarek,O. Inganäs, Science 2012, 335, 1468-1471

Recently, solid lithium batteries using solid electrolytes have attracted considerable attention due to their potentially high energy density and safety. However, some key issues remain unsolved. The good interface formation between the solid polymer electrolyte and the solid active material is needed. Specifically, an adhesive and flexible electrolyte are favorable to follow the volume change of an active material in an electrode upon charging and discharging. Actually, the addition of solid polymer electrolyte (in general, around 20wt-%) into an electrode to form the above good interface causes the degradation of an energy density, hindering their commercialization.

To solve these problems, we propose in-situ radical polymerization of diallyldimethyl ammonium bis(trifluoromethanesulfonyl)imide (DADMA-NTf₂) in the presence of lithium bis(trifluoromethanesulfonyl)imide (LiNTf₂) and 1-ethyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P12NTf₂) in an electrode with an active material. The ternary mixed solution (DADMA-NTf₂/LiNTf₂/P12NTf₂) is successfully permeated into pores of an electrode layer, and a solid-state ionogel is formed in the electrode after in-situ radical polymerization under air: without decreasing the ratio of the active material. In addition, there are no observable pores or defects by SEM and EDX measurements, suggesting that an ideal interface between the ionogel and the active material is formed. The ionic conductivity of such ionogel exceeds 1.0 × 10^-3 S/cm at 50 °C, which is close to that of gel polymer electrolytes with ionic liquids as reported previously. The conversion of DADMA-NTf₂ during bulk polymerization decreases with increasing in the P12NTf₂ ratio in the feed, while the increase in P12NTf₂ leads to the improvement of the ionic conductivity. This result suggests that suitable content of the P12NTf₂ is crucial to obtain a solid-state ionogel with a high ionic conductivity. Batteries fabricated by simply stacking of a glass-fiber membrane between the positive and negative electrodes, all of which contain solvent-free in-situ formed ionogels, are successfully operated at a low current rate. Owing to no need of the volatile organic solvent and any special atmospheric control, this simple and environmentally-friendly procedure to prepare an electrode for solid batteries can help to ensure the wider practical use of solid lithium batteries.

The electrocatalytic properties of graphite felt (GF) electrodes for vanadium redox flow battery (VRFB) are studied with N and O atomic dual doping on the GF surface by urea thermolysis. Simple impregnation of GF with urea and polyethylene glycol (PEG), followed by thermal treatment at elevated temperatures, results in significant N and O dual doping on the electrode with high surface uniformity and electrocatalytic activities. The correlation analysis on the electrocatalytic properties of the GF electrodes with respect to the configuration and elemental contents of the doped N and O functionalities suggests that the pyrrolic-N species on the carbon electrodes provide significant kinetic enhancement for vanadium redox reactions. The operando studies measuring the through-plane voltage losses in the VRFB single cell reveal that the N and O dual doping by urea thermolysis gives rise to approximately 3-fold improvement in the vanadium redox kinetics, particularly on the anode side, which greatly reduces the overall cell voltage loss. At practical charge–discharge condition, the N and O dual-doped GF electrode affords about 15 % increase in voltage efficiency and 2-fold increase in charge–discharge capacity of the VRFB over that obtained from the pristine-GF electrode. These results suggest the marked electrocatalytic effects of the N and O dual-doping on carbon electrodes for vanadium redox reactions, and the high effectiveness of urea thermolysis for the electrode functionalization for VRFB.

Aqueous rechargeable sodium-ions batteries (ARSIBs) have garnered extensive research interests due to its safety and abundant sodium resources towards sustainable large-scale energy storage applications. [1, 2] Among the various transition metal oxides employed in ARSIBs, Na_0.44MnO₂ (NMO) has been considered as an attractive cathode due to its unique tunnel structure that can facilitate fast transport of Na-ions during de/insertion processes.[3-6] However, the parasitic side reactions such as dissolution of active material, H₂/O₂ evolution reactions and water protons insertion into the NMO structure undermine the cycle life of NMO.[6] Therefore, the prevailing research challenge lies in maintaining the capacity over long cycles of NMO in an aqueous media.

Herein, for the first time, we propose a novel binary electrolyte for ARSIBs by using green and low-cost 1 m sodium acetate dissolved in the optimized ethanol/water cosolvents. Electrochemical behaviors are studied on NMO plates by using our binary electrolyte. Meanwhile, the NMO electrode was also tested in a single electrolyte (1 m sodium acetate dissolved in Di water) for comparison. The overlapping cyclic voltammetry curves of NMO cycled in binary electrolyte (NMO-Et/Di) indicate a highly reversible de/insertion processes of Na-ions. Furthermore, the NMO-Et/Di electrode exhibits a superior cycle stability, while the NMO-Di sample shows an obvious capacity fading after 1000 cycles. A combination of Fourier-transform infrared spectroscopy and nuclear magnetic resonance measurements carried at various cosolvents ratio coupled with ex-situ X-ray diffraction and scanning electron microscopy were conducted to further understand the dependence of the cathode/electrolyte interface, material stability and charge storage mechanism. It is noted that the intrinsic hydrogen-bonding interaction between ethanol and water protons in binary electrolyte is one of the main contributing factors towards a superior cycle stability of NMO. The results of the study provide insights into the electrode-electrolyte interactions and highlight the significance of electrolyte design and optimization in aqueous rechargeable batteries.

References
[1] J. Huang, Z. Guo, Y. Ma, D. Bin, Y. Wang, Y. Xia, Recent Progress of Rechargeable Batteries Using Mild Aqueous Electrolytes, Small Methods 3 (2019) 1800272.
[2] M.H. Lee, S.J. Kim, D. Chang, J. Kim, S. Moon, K. Oh, K.-Y. Park, W.M. Seong, H. Park, G. Kwon, Toward a Low-Cost High-Voltage Sodium Aqueous Rechargeable Battery, Materials Today. (2019).
[3] J. Whitacre, A. Tevar, S. Sharma, Na₄Mn₉O₁₈ as a Positive Electrode Material for an Aqueous Electrolyte Sodium-Ion Energy Storage Device, Electrochemistry Communications 12 (2010) 463-466.
[4] Z. Li, D. Young, K. Xiang, W.C. Carter, Y.M. Chiang, Towards High Power High Energy Aqueous Sodium-Ion Batteries: the NaTi₂(PO₄)₃/Na_0.44MnO₂ System, Advanced Energy Materials 3 (2013) 290-294.
[5] R. Chua, Y. Cai, Z.K. Kou, R. Satish, H. Ren, J.J. Chan, L. Zhang, S.A. Morris, J. Bai, M. Srinivasan, 1.3 V Superwide Potential Window Sponsored by Na-Mn-O Plates as Cathodes Towards Aqueous Rechargeable Sodium-Ion Batteries, Chemical Engineering Journal (2019).
[6] L. Chen, Q. Gu, X. Zhou, S. Lee, Y. Xia, Z. Liu, New-Concept Batteries Based on Aqueous Li⁺/Na⁺ Mixed-Ion Electrolytes, Scientific Reports 3 (2013) 1946.

Typical fabrication methods, such as photolithography and rolling/stacking, that are commonly used in conventional electronics and energy storage systems respectively, have caused the devices to lack a variety of form factors and flexibility needed for countless new Internet-of-Things applications^[1]. In the past decade, the development of digital printing technology in the field of printed electronics, has triggered an explosion of new ideas and alternative fabrication strategies that led to lean and cost-efficient manufacturing processes. In this work, the digital nature of inkjet printer was utilised to fabricate multifunctional energy storage sources in the form of casual letters in text. A new font style of the Latin alphabet was developed so that each character assembles a planar supercapacitor, able to be aesthetically and seamlessly connected, either in series or parallel configuration. A nanoparticle-based silver current collector, a nanoparticle-based nickel (II) oxide (NiO) active electrode material and a transparent ionic liquid/ultraviolet-cured triacrylate polymer-based solid-state electrolyte, were chosen as model materials to explore the feasibility of the proposed concept. The model letter-supercapacitors were able to deliver up to 27 mF cm^-2 and handle scan rates up to 500 mV s^-1 at a voltage window of 2.5 V. This approach underlines the exceptional applicability of the inkjet-printed letter-supercapacitors as a fabrication strategy towards multifunctional power sources with versatile form factors that lie far beyond what conventional fabrication technologies can achieve. The letter-supercapacitors can be used as energy storage units for electronic books, paper electronics and smart textiles with the potential of the proposed concept to be extended beyond interconnects and energy storage to seamless printed sensors and other electronic components.

[1] Energy Environ. Sci. 2016, 9, 2812.

With the awareness of sustainable development and solving the energy storage problem, convert woody biomass into carbon products for energy storage applications has attracted enormous attention. We extract high purity lignin from four different types of biomass materials, and then control the processing conditions to produce high-value carbon products. Chemical characterizations including TGA and DSC are conducted to get the thermal properties of the lignin, such as the glass transition temperature, average decomposition temperature, and char content. The lignin functionality and chemical composition were investigated by Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy measurements. From this information, we optimized the carbonization conditions through control humidity, temperature and reducing environment needed for graphitization. Carbons after pyrolysis were activated to produce activated carbon foams. The physical and chemical activation were compared and explore the reactions during the activation. Brunauer–Emmett–Teller (BET) analysis was conducted to measure the surface area and pore size distributions (PSDs). The surface area and PSDs are significantly affected by the activation temperature and duration. Usually the higher temperature, the greater surface area and PSDs. In addition, various precursors also show different results under different activation duration. Changes in morphology were determined by SEM and TEM. Carbon morphology and composition were determined by x-ray diffraction and elemental analysis. Combined with these experiments results, the major reactions during the activation are clear and the way to control porosity through activation and produce microporous activated carbon are developed.

After decades of research, long term stability of dye sensitized solar cells (DSCs) continue to remain a questionable issue. The observed instability is caused by dye and electrolytic degradation and gradual evaporative elimination of the volatile component of the electrolyte via unavoidable faults in the sealing. Degradation of the dye and the electrolyte is mainly due to photocatalytic reactions mediated by titanium dioxide. Of familiar high-band gap oxide materials, short wavelength (< 300 nm) radiation initiated by photo-catalytic activity originating free radical generated by hole transfer to water molecules is strongest in titanium dioxide. Although DSCs made from less photo- catalytically active tin and zinc oxides are inefficient, composite tin-zinc oxide films yield efficiencies comparable to those fabricated out of titanium dioxide films. Studies conducted reveal that DSCs based tin-zinc oxide films are highly stable when moisture free high boiling point solvents are incorporated to solubilize the conventional iodide/tri-iodide redox system. Sensitized charge injection and transport in composite tin-zinc oxide films and the possible causes of enhanced stability will be discussed.

Recently, due to the tremendous demand on wearable and flexible devices, there has been an urgent requirement for future energy sources that are compact, efficient, and implementable on small footprint. Supercapacitors (SCs) can supply higher capacity per unit area compared to traditional electrostatic or electric double layer capacitors (EDLCs) while they can provide faster power delivery and longer cycling ability than lithium ion batteries (LIBs). However, one of the biggest challenge of SCs is to find an efficient way to enhance energy density comparable to LIBs without sacrificing power density loss. To address these issues, much effort has been devoted on the improvement of electrode materials and novel structures in recent years. In this work, we demonstrate Ni and Co layered double hydroxides (NiCo–LDHs) on Ni–coated textile for wearable supercapacitor (SC) applications. LDHs are a group of two dimensional layered structures and have proven to be very promising due to high performance pseudocapacitive materials, high redox activity, and environmentally friendliness. In addition, we investigate that the crystal structure and electrochemical properties of NiCo-LDH can be controlled by adjusting the reaction time using hydrothermal method. We report on controllable phase transformation of NiCo-LDH and their morphology evolution from nanosheets to nanowires with increasing growth time. Lastly, an asymmetric pseudocapacitor is assembled with the graphitic carbon as negative electrode and the NiCo LDH as positive electrode. The best device result shows a high energy density of 55.8 Wh kg^-1 at power density of 601 W kg^-1 with a 1.2 V operating voltage.

For decades, solid electrolyte thin films have opened up new avenues for power storage, as well as offering alternative applications, such as neuromorphic computing, and havepresented many benefits concerning safety, cost, and energy efficiency compared to their liquid electrolyte counterparts. The NASICON-like solid compound, lithium aluminum titanium phosphate (Li_1+xAl_xTi_2-x(PO₄)₃, LATP) has shown promise as a solid electrolyte, with a demonstrated ionic conductivity of ~3x10^-3 S cm^-1. Here, LATP thin films were deposited via RF-magnetron sputtering; this method is more suitable for large scale implementation and reproducibility, unlike the commonly utilized sol-gel method. This study focuses on the effect of thermal processing on electrical resistance for both microscale batteries and unique MIM structures created with the sputtered LATP thin films. The two thermal processes studied here are the effects of both mid-deposition heating and post-deposition annealing on these devices. During the fabrication process, a range of mid-deposition heating temperatures and post-deposition annealing temperatures are examined to determine optimal processing conditions for maximizing electrical resistivity. It has been found that optimal electrical resistivity (~150MΩ) is achieved only through post-deposition annealing at >350^oC, with notable resistivity improvements arising from mid-deposition heating. Microscale half-cell batteries(~ 100 µm x 100 µm) created with the annealed LATP films show behavior typical of half-cell batteries, with minimal to no signs of leakage.

In this study, we report the design, synthesis, and characterization of a novel, water-stable 2D sheet-like neutral Cu(I)−sulfonate metal-organic framework (MOF) having π-acidic naphthalenediimide (NDI) disulfonate as ligands. This NDI-based ligand has an ability to bind the guest lithium ions (Li⁺) with its carbonyl and sulfonate oxygen atoms, and whereas, the diffuse perchlorate anions (ClO₄^-) binds via anion−π and CH^...anion interaction. The measured ionic conductivity of this MOF [Cu₂(BPY)₂(NDIDS)] has significantly enhanced to 10⁶ times (2.3x10⁻⁴ S/m) by inserting LiClO₄ dopant.This Lithium-ion conducting (MOFs) act as an ion permeable electrode separators and useful for rechargeable batteries. For the first time, such enhancement of lithium-ion conductivity is observed in a neutral, and solvent-free, not post-synthetically modified MOF. Moreover, the determined low activation energy (E_a =0.167 eV) and high Li-transference number (τ_Li =0.749), suggest that the newly developed ion-conducting disulfonate could be a potential solid-electrolyte for battery applications. To demonstrate further the influence of the Li⁺ binding, the MOF was also treated with Bu₄NClO₄ salt which shows the poor electrical conductivity (4.55x10⁻¹⁰ S/m) similar to the pristine untreated MOF (4.65x10⁻¹⁰ S/m) at room temperature. The same conductivity properties could be attributed to the size exclusion and facile removal of large uncoordinated Bu₄N⁺ cations. The impact of ionic conductivities of this MOF upon doping with various cations such as (K⁺, Na⁺, Mg²⁺) and anions (BF₄^-, I^-, PF₆^- TfO^-) with this [Cu₂(BPY)₂(NDIDS)] MOF are under investigation in our lab.

The word is embracing a new electrification revolution sparked by the rapid development and mass deployment of lithium-ion batteries. LIBs based on lithium nickel manganese cobalt (NMC) or lithium nickel cobalt aluminum oxide (NCA) cathode materials are now dominant power sources for electric vehicles. Ni and Co are expensive heavy metals that are attractive for recycling. Currently, Ni and Co are recovered from the used batteries either by pyrometallurgy or hydrometallurgy method. Hydrometallurgy method is more widely used because it can be integrated into the production of hydroxide precursors for NMC or NCA. This is a profitable process thus goverment subsidies are no longer necessary. However, this recycling method consists of many steps (>10) and generates a large amount of heavy-metal containing acid-waste and base-waste. To better address the NMC battery recycling challenge, it is necessary to develop greener and more cost-effective mthods. We have recently developed a convenient and scalable method based on advanced molten-salt chemistry to convert the structurally damaged and lithium deficient polycrystalline NMC materials in the used batteries into high-performance single-crystal NMC cathode materials. During the conversion, it is also possible to increase the Ni content in the cathode materials to further boost the energy density and increase the value. Cost analysis are performed to confirm that the new method is a value-addition process. This work reveals a promising new path toward better recycling used battery cathode materials at a large scale and with much less environmental impact.

Although Li-ion batteries have been successful in various applications, their shortcomings with regard to high cost and global maldistribution of raw materials, as well as safety concerns have promoted alternative rechargeable batteries based on other carrier ions represented by sodium and magnesium ions, targeting grid-scale energy storage systems (ESSs). However, many electrode materials in these emerging systems often suffer from sluggish kinetics due to the larger size or bivalency of carrier ions, limiting electrochemical performance particular in specific capacity and operation voltage. In this talk, I will introduce a new approach of engaging intercalated water in layered cathode materials. The intercalated water improves the performance of the given materials substantially by shielding electrostatic interactions or maintaining the crystal frameworks over repeated cycles. Detailed effects of intercalated water will also be described, along with promising potentials towards aqueous operations. Electron microscopy characterization for in-depth understanding of these materials will also be introduced.

Room-temperature (RT) sodium-sulfur (Na-S) batteries using all earth-abundant resources as electrode materials are considered to be the next-generation cost-effective energy storage devices. However, their practical applications are still plagued by the low reversible capacity of commercial S, low Coulombic efficiency, and poor cycling stability caused by sluggish kinetics of Na-S electrochemical reactions and severe shuttle effect of polysulfides. Here we present our most recent works on developing high-performance RT Na-S batteries using facile-processed S-based cathodes. A simple and scalable approach has been developed to synthesize hollow sodium sulfide nanospheres embedded in a highly hierarchical and spongy conductive carbon matrix, forming an intriguing architecture similar to the morphology of frogspawn coral, which has shown great potential as a cathode for high-rate performance RT Na-S batteries. The shortened Na-ion diffusion pathway benefits from the hollow structures together with the fast electron transfer from the carbon matrix contributes to high electrochemical reactivity, leading to superior electrochemical performance at various current rates. A Na-metal-free Na-S battery is demonstrated by pairing the hollow sodium sulfide cathode with tin-based anode. Besides using sodium sulfide as cathode, we also develop a highly stable RT Na-S battery using a facile-processed commercial S cathode and gel polymer electrolyte, which delivers a reversible capacity of >700 mAh g⁻¹ with near 100% Coulombic efficiency and an ultrahigh capacity retention of 98.2% at 0.2C after 200 cycles.

Our society is presently facing the great challenge to switch from depleting energy sources like oil, coal, or gas, to renewables such as solar and wind. With regard to their inherent intermittency and commonly decentralized generation, however, efficient and sustainable energy storage is of utmost importance. Beside large-scale solutions like hydropower or compressed air, electrochemical energy storage, in particular secondary batteries, is currently considered to be the most suitable technology, particularly for relatively smaller applications like transportation or short- to mid-term stationary energy storage.[1–4] As a matter of fact, the number of electric vehicle (EV) sales is steadily increasing within the past years and the same trend is observed for the implementation of secondary batteries for buffering the intermittent energy supply by solar and wind.[1–4] Consequently, batteries play a vital role for moving towards a more sustainable “energy future”, raising, however, concerns about the impact that their production and disposal could have on the environment.[5]
Renewable materials, environmentally-friendly processes and safer batteries are needed for the sustainable development of electrochemical energy storage [6].
The sustainable use of natural resources is indispensable for future energy storage. As a step towards the utilisation of biowaste, hard carbon produced from waste apples is demonstrated to be a high performance active material for Na-ion batteries [7].
The aqueous processing of lithium-ion battery (LIB) electrodes has the potential to notably decrease the battery processing costs and paves the way for the sustainable production (and recycling) of electrochemical energy storage devices. In this study, we show that the addition of small quantities of phosphoric acid into the cathodic slurry yields NMC electrodes with outstanding electrochemical performance in lithium-ion cells [8]. Another example is the excellent performance of graphite/LNMO cells with both electrodes made using water-soluble binder [9].

References:
[1] B. Dunn, H. Kamath and J.-M. Tarascon, Science, 2011, 334, 928–935.
[2] Z. Yang, J. Zhang, M. C. W. Kintner-Meyer, X. Lu, D. Choi, J. P. Lemmon and J. Liu, Chem. Rev., 2011, 111, 3577–613.
[3] D. Andre, S.-J. Kim, P. Lamp, S. F. Lux, F. Maglia, O. Paschos and B. Stiaszny, J. Mater. Chem. A, 2015, 3, 6709–6732.
[4] D. Bresser, K. Hosoi, D. Howell, H. Li, H. Zeisel, K. Amine and S. Passerini, J. Power Sources 2018, 382, 176–178.
[5] C. Vaalma, D. Buchholz, M. Weil, S. Passerini, Nat. Rev. Mater. 3, 18013 (2018).
[6] J. Peters, D. Buchholz, S. Passerini and M. Weil, Energy & Environmental Science, 9 (2016) 1744.
[7] L. Wu, D. Buchholz, C. Vaalma, G.A. Giffin and S. Passerini, ChemElectroChem (2016) DOI: 10.1002/celc.201500437
[8] N. Loeffler, G.T. Kim, F. Mueller, T. Diemant, J.K. Kim, R.J. Behm, and S. Passerini, ChemSusChem (2016) DOI: 10.1002/cssc.201600353.
[9] M. Kuenzel, D. Bresser, T. Diemant, D.V. Carvalho, G.-T. Kim, R.J. Behm,
S. Passerini, ChemSusChem (2018) 11, 562-573.

MoS2 is a 2D material that has been widely used in supercapacitor applications because of its layered structure that provides a large surface area and allows for high electric double-layer charge storage. To enhance the cycling stability and capacitance of MoS2, it is usually mixed with carbon materials. However, the dependence of the charge storage mechanism on the structure of the carbon material is still unclear in the literature. Herein, the effect of the structure of the carbon material on the charge storage mechanism in 2H flower-shaped MoS2 is investigated in detail. Specifically, 2H MoS2 was mixed with either 8 nm-diameter carbon nanotubes (CNTs) or graphene nanoflakes (GNFs) in different weight ratios. Also, a composite of MoS2, CNTs, and GNFs (1:1:1) was also studied. The charge storage mechanism was found to depend on the structure and content of the carbon material. Insights into the possible storage mechanism(s) were discussed. The MoS2/CNT/GNF composite showed a predominant pseudocapacitive charge storage mechanism where the diffusion current was ∼89%, with 88.31% of the resulted capacitance being due to faradic processes.

In this study, we have demonstrated for the first-time, enable, efficient, unassisted photochemical reduction of carbon dioxide (CO₂) into syngas using wafer scale multiband InGaN/GaN nanowire structures without using any sacrificial reagent. The effective manipulation and control of charge carrier flow in nanostructured photocatalysts provides critical insight in achieving high efficiency artificial photosynthesis, which includes the efficient and selective reduction of CO₂ into solar fuels.

Supercapacitors (SC) are playing a key role within the so called Water-Energy Nexus. Indeed, SCs can improve the quality of electric energy harvested from intermittent renewable energy source and from microbial fuel cells (MFC) that are bio-electrochemical devices that convert the chemical energy of wastewater organic compounds directly into electrical energy.
In this scenario, lowering the price and minimizing the environmental and economic impact of disassembly and recycling of end-of-life SCs are is mandatory.
The use of water-processable electrode binders and new membrane production techniques like electrospinning are viable approaches to decrease cost and environmental footprint.
A study on the development of bio-inspired supercapacitors and their integration with MFCs is reported and discussed.
Specifically, a pullulan-based supercapacitor featuring carbon electrodes obtained by the pyrolysis of pepper seeds and working with ionic liquid electrolyte is hereby proposed. The use of a water soluble, biodegradable polymer as binder and separator along with a hydrophobic ionic liquid brings about a novel approach for device end-of-life management. The use of melanine as pseducapacitive electrode material is also presented.

Acknowledgments
The research has been carried out under the Italy-South Africa joint Research Programme 2018-2020 (https://site.unibo.it/isarp/en) and the Executive Bilateral Program Italy-Quebec 2017-2019, Italian Ministers of Foreign Affairs and of the Environment.


References

[1] M. Yassine, D. Fabris, Energies, 10 (2017) 1340
[2] B. Dyatkin, V. Presser, M. Heon, M. R. Lukatskaya, M. Beidaghi, Y. Gogotsi, ChemSusChem, 6 (2013) 2269 -2280.
[3] D. Bresser, D. Buchholz, A. Moretti, A. Varzi, S. Passerini, Energy & Environmental Science, 11 (2018) 3096-3127
[4] P. Kumar, E. Di Mauro, S. Zhang, A. Pezzella, F. Soavi, C. Santato, F. Cicoira, J. Mater. Chem. C, 4 (2016) 9516.
[5] S. Chen, S. He, H. Hou, Current Organic Chemistry, 17 (2013) 1402-1410
[6] F. Poli, D. Momodu, B. Mutuma, A. Terella, G.E. Spina, M. L. Focarete, N. Manyala, F. Soavi, Green Chemistry, submitted.

Sustainability for energy storage systems and environmental protection imply both the use of environmentally benign materials and the development of green processes. Rechargeable lithium ion battery (LIB) with organic electrolyte has found many applications. Its high energy density and long cycle life make it the best option compared to other secondary batteries. However, environmental impact throughout their fabrication and disposal, safety concerns during their use, and cost remain the main drawbacks for large-scale applications. Hence, interest in aqueous electrolyte rechargeable LIB (ARLB) has grown, particularly for safe and cost effective large scale devices.

To reduce the adverse environmental/human impact of LIB production, the electrode preparation process needs to be revisited. In this regard, replacing common binders (e.g. fluorine-containing polymers; polyvinylidene difluoride (PVDF)) and noxious organic solvents (e.g. N-methyl-2-pyrrolidone (NMP)) by non-toxic and aqueous processable binders is a must. Water soluble binders such as carboxymethyl cellulose (CMC) have gained considerable attention due to their natural abundance, water processability and lower cost.

Nevertheless, using water soluble binders in electrodes for aqueous batteries is challenging because of their solubility in aqueous electrolyte with low salt concentration. In our group, we successfully addressed this issue by developing a strategy to prepare electrode employing CMC usable in ARLB. A chemical modification of the electrodes prevents the loss of electronic percolation and allows the cycling over a prolonged number of cycles in low concentrated aqueous electrolytes.

In this presentation, the physiochemical properties and electrochemical performance of such electrodes were investigated and compared to that of electrodes prepared with typical binders in organic electrolytes.

Two-dimensional (2D) materials have shown promising performances as electrode materials for electrochemical energy storage devices. Most individual 2D materials, however, suffer from certain limitations and therefore, cannot be individually considered as practical electrode materials for supercapacitors or batteries.^[1] Controlled pillaring of 2D materials into multilayers and vertical stacking of different 2D layers into heterostructures have shown to be effective methods to avoid their self-restacking and overcome drawbacks of individual 2D materials. Such pillared 2D multilayers or superlattice heterostructures built by sequential stacking of single or multiple 2D layers can display new and improved electrochemical responses and offer a combination of their building blocks’ best properties. 2D metal carbides (MXenes) have recently received huge attention for energy storage applications due to their diverse compositions, ability to intercalate a variety of cations, and high rate pseudocapacitive properties. Self-restacking of MXenes and their lower capacitances compared to other pseudocapacitive materials, however, have hindered their further development. Also, because of instability and rapid structural degradation of the delaminated form of various MXene compositions, most studies on MXenes have been limited only to Ti₃C₂T_x. Here in this presentation, we demonstrate new pillared and heterostructure MXene architectures fabricated by controlled self-assembly of individual MXene sheets. The fabricated pillared MXene multilayers and MXene heterostructures show stable and superior electrochemical performances in aqueous and organic electrolytes. For example, alkali-cation pillared multilayers of V₂CT_x could deliver volumetric capacitances of over 1300 F cm^-3 and maintain ~78% of their initial capacitance after one million cycles at a rate of 100 A g^-1 in aqueous supercapacitors.^[2] In addition, all-solid-state supercapacitors based on pillared Ti₃C₂T_x electrodes fabricated by a precise layer-by-layer (LBL) self-assembly method delivered high energy and power densities of 3.0 Wh L^-1 and 4400 W L^-1, respectively.^[3] This is while Ti₃C₂T_x and V₂CT_x MXene heterostructures showed new features in their cyclic voltammetry profiles and could deliver the highest volumetric capacitance of ~1470 F cm^-3 in 3M H₂SO₄ electrolyte. This study paves the way for the preparation of high-performance pillared and hetero-layered MXene structures for electrochemical energy storage applications and beyond.
References
[1] E. Pomerantseva, Y. Gogotsi, Nat. Energy 2017, 2, 17089.
[2] A. VahidMohammadi, M. Mojtabavi, N. M. Caffrey, M. Wanunu, M. Beidaghi, Adv. Mater. 2019, 31, 1806931.
[3] W. Tian, A. VahidMohammadi, Z. Wang, L. Ouyang, M. Beidaghi, M. M. Hamedi, Nat. Commun. 2019, 10, 2558.

Lithium-ion batteries (LIBs) is widely used in every aspect of our life due to its high energy density and long cycle life. However, the large demand of LIBs will also lead to a substantial end-of-life (EOL) batteries which requiring proper treatment. Recycling EOL LIBs not only mitigates the production of hazardrous waste caused by improper disposal, it also can recover the value from strategic materials. A closed-loop recycling process developed in WPI has demonstrated its successful in synthesizing recycled NMC 111 with excellent electrochemical performance when compared with a commercially available cathode. ^[1],[2] Now, WPI moves forward to demonstrate its feasibility to synthesize high-nickel NMC cathode powder-NMC 622. Here, recycled NMC 622 shows better rate and cycle performance comparing to a commercially and chemically equivalent. In addition to that, NMC 622 cathode is coated with alumina oxide using two coating methods (dry coating and wet coating) and its cycle stability is improved.
[1] Chen, Mengyuan, et al. "Closed Loop Recycling of Electric Vehicle Batteries to Enable Ultra-high Quality Cathode Powder." Scientific reports 9.1 (2019): 1654.
[2] Zheng, Zhangfeng, et al. "High Performance Cathode Recovery from Different Electric Vehicle Recycling Streams." ACS Sustainable Chemistry & Engineering 6.11 (2018): 13977-13982.

The quest for cheaper, safer, higher-density, and more resource-abundant energy storage has driven significant battery innovations. Existing lithium-ion batteries (LIBs) use cobalt-heavy active electrode materials that are predicted to see supply constraints going down the path and can be too expensive to meet long-term capital cost goals for grid storage and electric vehicle systems ($100 kWh^-1). On the other hand, the safety issues with commercial LIBs mainly originate from the flammable and volatile nonaqueous electrolytes. Safer systems with solid-state and aqueous electrolytes are being actively developed, but today’s active electrode materials are not optimized for these electrolytes in terms of chemical and electrochemical compatibility. In the course of overcoming the above limitations, considerable innovations are taking place in the development of active materials featuring sufficiently high energy, Earth-abundant elements, and unique electrolyte-dictated properties. A notable family of such materials is organic battery electrode materials (OBEMs), which comprise electrochemically redox-active organic compounds including molecules, polymers, and organometallics where the organic components contribute to redox activity. In this talk, I will compare OBEMs with dominating/competing inorganic materials through analyses of charge storage mechanism, working potential, specific capacity, resource availability. We show that from high-energy lithium batteries to aqueous, Mg-ion, and all-solid-state batteries, OBEMs can be designed to be sufficiently capable and offer unique feature sets unmatched by other materials.

In the non-aqueous based conventional Li-ion battery (LIB) system, solid-electrolyte interphase (SEI) layer have been successfully prevented the electrolyte decomposition on the electrode surface, which enables the representative reversible electrochemical reaction, while the aqueous electrolyte could not form a stable protective layer on the electrode. However, the recent invention of highly concentrated aqueous electrolytes has outperformed conventional electrolytes by producing the SEI layer with anion decomposition and suppressing water splitting. Nevertheless, the high-concentrated aqueous electrolyte systems give a widened stability window and cycle stability with a robust protective layer, it still has a significant economic issue for their commercialization regarding the use of high-cost imide based organic solutes. In this study, we focused on finding a new low-cost high-concentrated aqueous electrolyte and studying how SEI layer forms in this newly investigated aqueous electrolyte. For evaluating these issues, we revisited all the commonly used low-cost inorganic salts and demonstrate them for their use in high-concentrated aqueous electrolytes. The reinvestigated highly concentrated aqueous electrolyte offers a wide electrochemical stability window of up to 2.7 V with forming a stable protective layer without involving the reduction of salt anions. In addition, we proposed a new mechanism of the protective layer formation on the electrode surface involving the residual gas reduction in different from the model of the anion decomposition. It was noted that the relative stability of this protective layer in the high-concentration aqueous electrolyte assists the stability of the electrode in the cell, resulting to exhibit the extraordinary electrochemical storage stability of the full-cell for over 900 hours.

Highly porous aerogels with anisotropic structural properties are highly demanded in many areas, ranging from thermal insulators in buildings to supercapacitors in electrical devices. Currently, aerogels are often made from synthetic polymers. With the depletion of fossil energy and increasing environmental concerns, the research focus has been shifted to biomass-based materials. In this work, a highly porous anisotropic wood aerogel is prepared from a top-down synthesize method. The preparation comprises removal of lignin followed by a cellulose dissolution/regeneration regime with DMAc/LiCl. The co-solvent partially dissolves the cell wall and the regeneration results in a porous cell wall with fibrillated networks inside the fibres lumen. The aerogels retain the structural anisotropy of natural wood, exhibits a high specific area of 247 m²/g, whilst remaining mechanically strong. As a demonstration, the aerogels are carbonized to yield electrodes towards supercapacitor applications. This top-down approach is found to be a novel preparation method for porous materials towards energy storage and harvesting.

Energy storage has emerged as a key technology for improving the sustainability of electricity generation by improving the efficiency of existing fossil-fuel infrastructure through load-leveling, alleviating the intermittency of renewables, and providing high-value services (frequency regulation, voltage support, or back-up power) [1]. Redox flow batteries (RFBs) are promising devices for low-cost grid energy storage due to decoupled capacity and power scaling, long operational lifetime, easy thermal management, and reliable safety features. While a variety of redox chemistries have been investigated over the years, the all-vanadium RFB has been the most successful as it is based on four stable, water-soluble oxidation states of vanadium that enable both high cell potential and crossover tolerance. Despite these favorable attributes, the technology is considered too expensive for broad adoption, motivating efforts to advance new redox chemistries, separation strategies, and reactor formats which may offer pathways to lower-cost RFB systems.

In this presentation, I will describe an alkaline polysulfide-permanganate RFB whose cell voltage, solubility, and potentially-inexpensive constituent components make it a promising candidate redox chemistry [2, 3]. Cell performance and durability will be evaluated as a function of component material selection (electrodes, membranes), electrolyte composition, and operating conditions. In addition, failure mechanisms will be asssessed and performance recovery strategies proposed.

References
[1] A. Z. Weber, M. M. Mench, J. P. Meyers, P. N. Ross, J.T. Gostick, Q. Liu, J. Appl. Electrochem. 41 (2011) 1137–1164.
[2] L. Su, A.F. Badel, C. Cao, J.J. Hinricher, F.R. Brushett, Ind. Eng. Chem. Res. 56 (2017) 9783–9792.
[3] A.N. Colli, P. Peljo, H.H. Girault, Chem. Commun. 52 (2016) 14039–14042.

To overcome the increased demand in energy consumption and fossil fuel depletion, there’s a huge requirement for sustainable energy storage devices. Supercapacitors play a vital role compared to batteries and fuel cells in terms of high-power density, long cyclic stability and environment friendly. The simple, low-cost N-containing bubbled 3D carbon sponge was prepared by the carbonization of polyaniline nanofibers coated onto pre-carbonized carbon sponge as scaffold. In this material, the 3D carbon sponge derived from kitchen sponge acts as a base framework for polyaniline fibers growth by chemical synthesis. The further carbonization of fibers on carbon sponge results in bubble formation at the nodes of network with nitrogen doping that leads to increasing the specific surface area from 75 m² g^-1 for carbon sponge to 212 m² g^-1 for bubbled carbon sponge. The morphology and N-doping of the material was confirmed by scanning electron microscope and energy dispersive spectroscopy respectively. It was found that this free-standing 3D nitrogen doped carbon sponge in symmetric cell exhibits high specific capacitance of 273 F g^-1 at 0.5 A g^-1 of current density with excellent cyclic stability. This high specific capacitance of the material was due to the interconnected microporous structure of carbon framework with bubbled structure at nodes that provides pathway for the rapid electron transfer kinetics during electrochemical reaction, N-doping and its high electrical conductivity. The high electrochemical performance makes this free-standing 3D all carbon framework a material promising for developing nanocomposites coated with metal oxides, sulfides etc. for practical potential energy storage applications.

The intermittent nature of the most reliable energy source, the Sun, requires high performance energy storage technologies [1]. Organic electrode materials operating in aqueous electrolytes offer the opportunity to use abundant, nontoxic, low cost materials, avoiding the use of critical elements. Unfortunately, organic materials often feature limited cyclability [2, 3].
Among organic materials, eumelanin is a bio-sourced, redox active, quinone-based macromolecule, ubiquitous in flora and fauna. Eumelanin originates from the oxidative polymerization of L-3-(3,4-dihydroxyphenyl)-alanine (L-dopa) via 5,6-dihydroxyindole (DHI) and 5,6-dyhydroxyindole-2 carboxyl acid (DHICA) building blocks [4]. It has fascinating properties beyond the redox activity, such as strong broadband UV-visible absorption, metal binding affinity and radical quenching [5]. The redox activity of the building blocks and the capability to reversibly bind cations constitute the foundation for the use of eumelanin in energy storage [2, 6].
In this work, we report on the electrochemical energy storage performance of composites of N-doped and pristine Carbon Quantum Dots (CQDs) with eumelanin. The composites were prepared at different weight ratios (eumelanin building block:CQD 1:0, 1:0.4, 1:1, 1:2) through a solution-based process followed by in situ polymerization [7]. From the cyclic voltammetry, galvanic charge/discharge and electrochemical impedance spectroscopy characterizations of the composite electrodes in nearly neutral aqueous electrolyte solutions, it has been possible to deduce, with respect to bare melanin electrode, that the composite electrodes feature an increase of the areal capacitance from 0.02 mF/cm² to 0.84 mF/cm² and a decrease of the charge transfer resistance from 42 Ohms to 20 Ohms. Composite electrodes also feature a capacitance retention of ca. 99.5% and coulombic efficiency of ca. 100% during 4000 cycles.

1.Augustyn, V., et al., High-rate electrochemical energy storage through Li+ intercalation pseudocapacitance. Nature materials, 2013. 12(6): p. 518.
2.Kumar, P., et al., Melanin-based flexible supercapacitors. Journal of Materials Chemistry C, 2016. 4(40): p. 9516-9525.
3.Mukhopadhyay, A., et al., Heavy Metal-Free Tannin from Bark for Sustainable Energy Storage. Nano Letters, 2017. 17(12): p. 7897-7907.
4.d'Ischia, M., et al., Melanins and melanogenesis: methods, standards, protocols. Pigment cell & melanoma research, 2013. 26(5): p. 616-633.
5.Di Mauro, E., et al., Natural melanin pigments and their interfaces with metal ions and oxides: Emerging concepts and technologies. MRS Communications, 2017. 7(2): p. 141-151.
6.Xu, R., et al., An electrochemical study of natural and chemically controlled eumelanin. APL Materials, 2017. 5(12): p. 126108.
7.Pezzella, A., et al., Stem cell-compatible eumelanin biointerface fabricated by chemically controlled solid state polymerization. Materials Horizons, 2015. 2(2): p. 212-220.

All-solid-state lithium batteries (ASLBs) are promising for next generation energy storage system with critical safety. Among various candidates, thiophosphate-based electrolytes have shown great promises because of their high ionic conductivity. However, the narrow operation voltage and poor compatibility with high voltage cathode materials impede their application in the development of high energy ASLBs. In this work, we studied the failure mechanism of Li₆PS₅Cl at high voltage through in situ Raman spectra and investigated the stability with high-voltage LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) cathode. With a facile wet chemical approach, we coated a thin layer of amorphous Li_0.35La_0.5Sr_0.05TiO₃ (LLSTO) with 15-20 nm at the interface between NMC and Li₆PS₅Cl. We studied different coating parameters and optimized the coating thickness of the interface layers. Meanwhile, we studied the effect of NMC dimension to the ASLBs performance. We further conducted the first principles thermodynamic calculations to understand the electrochemical stability between Li₆PS₅Cl and carbon, NMC, LLSTO, NMC/LLSTO. Attributed to the high stability of Li₆PS₅Cl with NMC/LLSTO and outstanding ionic conductivity of the LLSTO and Li₆PS₅Cl, at room temperature, the ASLB exhibit outstanding capacity of 107 mAh g^-1 and keep stable for 850 cycles with a high capacity retention of 91.5 % at C/3 and voltage window 2.55-4.0 V (vs. Li-In).

Sodium-ion batteries have shown potential as a cost-effective successor to lithium-ion batteries, but the performance is still limited by their low energy density and poor cycleability compared with lithium-ion analogues. The development of suitable electrode materials is crucial for the realisation of sodium-ion batteries as a feasible replacement. Disordered carbons, also known as ‘hard carbons’ (i.e. those with some degree of graphitisation but randomly oriented graphitic domains) are considered promising anode materials due to negligible volume change during the sodiation/desodiation cycles, essential for achieving a long cycle life.

A range of materials were prepared via hydrothermal carbonisation of various biomass precursors followed by further heat treatment; by tuning the carbon source, the nature and amount of dopant, the templating agent and the treatment temperature, carbon anodes with varying degrees of graphitisation and tailored pore size, wall thickness and heteroatom functionalities were obtained. The pore structure, particle size, nature of defects and degree of doping were found to have a significant effect on the storage capacity and cycleability of the batteries. The ability to tailor these hierarchical nanostructures therefore makes this process a promising route to achieving new electrode materials.

With a growing number of studies providing credible evidence that the highest capacitance in carbon nanomaterials is attainable only when the pore size is 0.7 nm, the special attention in porosity engineering is strongly biased towards micropore. Microporous carbon materials are thus extremely promising in the development of high-performing capacitive devices compared to their meso and macroporous counterparts. In this study therefore, carbon materials with extremely high micropore content was derived from parinari curatelifolia (PC) waste seeds via pyrolysis and chemical activation. Characterizatio using SEM, EDAX, TEM, Raman, and XRD techniques show that the microstructure and composition of the as-prepared carbon materials are strongly dependent on the KOH to carbon mass ratio. High BET surface area of 1898 m² g^-1, type I isotherm, and 99% micropore content were obtained for the carbon materials. The electrodes made from these carbon materials showed high specific capacitances of 423 F g^-1 at 5 mV s^-1 and cyclic stability of 98% after 50000 cycles both of which are indicative of our carbon materials huge potential in making high performance capacitive demineralization devices. The high specific capacitance the PC carbon materials deliver is due to the enhancement of diffusion and charge storage stemming from the synergetic interplay of the aforementioned textural parameters.

Hydrogen is considered as a promising alternative energy sources because it can potentially replace fossil fuel to clean energy due to its high energy density (142MJkg^-1) as well as no harmful gaseous by-products after combustion [1]. Nevertheless, the lack of efficient storage system hinders its widespread application. For the efficient hydrogen system, storage materials must readily take up hydrogen and subsequently release it again at a sufficiently high rate of hydrogenation / dehydrogenation process. Thus, understanding the kinetics of hydrogen storage materials during the process is indispensable.

Magnesium ternary hydrides Mg₂FeH₆ have been extensively studied as a candidate hydrogen storage materials due to its hydrogen gravimetric density (150 kg/m³) as well as a good cycling ability (~1000 hydrogenation / dehydrogenation cycles) [2,3]. However, kinetics during hydrogenation / dehydrogenation process in Mg₂FeH₆ is unrevealed by the limitation of in-situ observation analytical method.

In this study, we investigated the dehydrogenation kinetics of Mg₂FeH₆ by in-situ transmission electron microscopy (TEM) holder system (Fusion, Protochips). We placed nanostructured Mg₂FeH₆ sample on the chip and heated up the temperature 300 °C for 30 minutes to trigger the hydrogen decomposition in Mg₂FeH₆. We acquired high-resolution images and diffraction patterns (25 frames every second) of Mg₂FeH₆ during dehydrogenation process by one-view camera (One-view, Gatan) attached on Titan (G2, FEI). In addition, EDS analysis was performed by super-EDS embedded TEM (Talos F200X, FEI) to investigate particle size of Fe and Mg after dehydrogenation.

As expected, Mg₂FeH₆ diffraction patterns were observed in as-prepared Mg₂FeH₆ sample. Upon heating, intensities of Mg₂FeH₆ diffraction patterns decrease and eventually disappeared due to the hydrogen desorption. On the other hands, new Mg and Fe diffraction patterns were produced in the beginning of dehydrogenation process due to the phase segregation of Mg and Fe from Mg₂FeH₆. In addition, oxide phases such as MgO and Fe₂O₃ were observed possibly due to the oxidation inside TEM column.

We estimated dehydrogenation speed from the diffraction patterns of Mg₂FeH₆ and it rapidly increases up to the process temperature of 300 °C. For example, diffraction patterns of Mg₂FeH₆ were disappeared within 120 sec at 260 °C and it was shorten to 12 sec. At the process temperature of 280 °C. Also, average particle size of Fe after the dehydrogenation process was investigated through EDS results because hydrogenation speed largely depends on its dimension. It was revealed that estimated average particle size after the process is ~ 10 nm at 260 °C and 15 nm at 280 °C.

References
1. Bartali, R., et al., Sustainable Energy & Fuels, 2, 2516-2525 (2018)
2. B. Bogdanovic et al., J. Alloys Compd., 345, 77-89 (2002)
3. M. Felderhoff et al., Int. J. Mol. Sci., 10, 325-344 (2002)

Here, we report a facile method to produce sulfur-doped graphene based-carbon with three-dimensional (3D) open structure from a biomass. The 3D graphene-based carbons were produced via the transformation of glucose-derived polymers and organosulfur compounds with starting materials provide additional properties of the graphitic carbon such as sulfur doping and coral-like open structures. In-situ physical activation was performed on this method and the open structures contributed hierarchically porous and sulfur doped biomass-derived graphene-based carbon with Brunauer-Emmett-Teller theory specific surface area of 3,426 m²/g, providing a defined-mesoporosity without additional chemical activation. On organic electrolyte system, this carbon showed a high specific capacitance of 143 F/g for its high surface area, unique and interconnected structure and a highly graphitization with sulfur doping. Furthermore, this carbon-based supercapacitor electrodes exhibited high energy density of 33 Wh/kg and ultra-high power density of 1,732 kW/kg derived from its specific capacitance of 133 F/g at the high current density of 256 A/g.

Two-dimensional (2D) materials are very promising as supercapacitor electrodes due to their high specific surface area. In recent years, significant attention has been focused to environmentally friendly 2D hexagonal boron nitride (h-BN), since pristine 2D h-BN has many applications in high-temperature instruments and as a substrate for the growth of other 2D materials. However, its electrically insulating character in pristine form limits its utilization in electrochemistry and in electronic applications. Formation of nanocomposites with a conducting complementary materials offers a solution to this problem. In this study, we fabricated 2D h-BN/MoS₂ nanocomposite electrodes using solution phase synthesis routes and evaluated their electrochemical performance for supercapacitors. Prior to preparation of the electrodes both h-BN and MoS₂ were chemically exfoliated. Electrochemical properties such as specific capacity and capacity retention of the fabricated nanocomposite electrodes were examined through cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy in three electrode configuration. Obtained results were compared to that of the control sample fabricated from bare MoS₂ nanosheets. In order to determine the effect of electrolyte type on the electrochemical properties of the nanocomposite electrodes, various aqueous solutions, such as sodium sulfate (Na₂SO₄), hydrochloric acid (H₂SO₄) and potassium hydroxide (KOH) were investigated. Fabricated supercapacitor electrodes showed encouraging specific capacitance values exceeding 100 F/g. A comprehensive analysis on the electrochemical properties of the fabricated supercapacitor will be presented.

The global demand for clean energy and water combined with the rising market of supercapacitors requires materials, components, and systems to be developed with a green approach. Recently scientists making great efforts towards the development of sustainable materials for the future generation of supercapacitors, considering the environmental and economic impacts.

The present work investigates some green materials for supercapacitor such as: using Argan fruits shell (agriculture wastes) to obtain porous carbon electrodes material, ammonium acetate (salt in water electrolytes) and bacterial cellulose (biomaterial separator).

Carbon electrodes were obtained from the carbonization of Argan shells followed by activation using wet impregnation or dry physical mixing. The as-prepared samples have been subjected to textural investigations and comprehensive characterizations using SEM, XRD, Raman, FTIR, and BET. After selecting the sample with desired structural and textural proprieties, their electrochemical response was investigated ammonium acetate electrolyte with different concentration (from 1m up to 30m). Specifically, electrodes were obtained by using carbon-coated bacterial cellulose (BC) film as a current collector. The results of Electrochemical Impedance Spectroscopy (PESI), Cyclic voltammetry (CV) and Galvanostatic charge-discharge (GCPL) of the BC-electrodes and the BC-Supercapacitor making use of ammonium acetate solutions are here reported and discussed.

Acknowledgments
The research has been carried out under the support of the:
Italy-South Africa joint Research Programme 2018-2020 (https://site.unibo.it/isarp/en)., Italian Ministers of Foreign Affairs and of the Environment.
National Center for Scientific and Technical Research (CNRST), Morocco.

References
1) M. Yassine, D. Fabris, Energies, 10 (2017) 1340
2) B. Dyatkin, V. Presser, M. Heon, M. R. Lukatskaya, M. Beidaghi, Y. Gogotsi, ChemSusChem, 6 (2013) 2269 -2280.
3) D. Bresser, D. Buchholz, A. Moretti, A. Varzi, S. Passerini, Energy & Environmental Science, 11 (2018) 3096-3127
4) P. Kumar, E. Di Mauro, S. Zhang, A. Pezzella, F. Soavi, C. Santato, F. Cicoira, J. Mater. Chem. C, 4 (2016) 9516.
5) S. Chen, S. He, H. Hou, Current Organic Chemistry, 17 (2013) 1402-1410
6) F. Poli, D. Momodu, A. Terella, M. L. Focarete, N. Manyala, F. Soavi, Energy Storage Materials, submitted.
7) M. Dahbi, M. Kiso, K. Kubota, T. Horiba, T. Chafik, K. Hida, T. Matsuyama,
8) S. Komaba, Synthesis of hard carbon from argan shells for Na-ion batteries, J. Mater. Chem. A. 5 (2017) 9917–9928.
9) T. Chafik, Matériaux Carbonés Nano Poreux Préparés À Partir De La Coque Du Fruit D’argane WO/2012/050411, (2012).
10) O. Boujibar, A. Souikny, F. Ghamouss, O. Achak, M. Dahbi, T. Chafik, CO2 capture using N-containing nanoporous activated carbon obtained from argan fruit shells, Journal of Environmental Chemical Engineering 6 (2018) 1995–2002.

The widespread use of fuel cells and water splitting devices for energy generation and storage is limited by the dependence on noble metal catalysts. There is thus a tremendous need for the development of efficient electrocatalysts based on Earth-abundant elements. Nature inspired hydrogenases (HydA) are metallo-enzymes that catalyze the reversible reaction of H₂ to protons and electrons. Hydrogenases containing Fe at the active sites, known as [FeFe]-HydA, show activities comparable to that of Pt. This work addresses a new class of electrodes for [FeFe]-HydA attachment and bio-assisted catalysis based on TiO₂ nanotubes. The conducting oxide material provides suitable electronic conduction and hydrophilicity, while the nanostructure ensures tunability (tube length, crystal orientation and pore diameter) and high surface area for HydA attachment. In this work, transmission electron microscopy and atomic force microscopy are used to characterize the bio-electrodes. Based on the experimental findings, density functional theory (DFT) calculations are used to probe the catalytic reaction sites on the HydA and address the interaction between enzymes and TiO₂. The novel bioelectrode will be employed in a system of artificial photosynthesis and generation of solar fuels by simultaneous water splitting and CO₂ capture and utilization.


Financial support from the Research Council of Norway project 275058 “EnCaSE” is acknowledged. Authors also acknowledge computational resources provided by UNINETT Sigma2 – the National Infrastructure for High Performance Computing and Data Storage in Norway.

Polymer electrolytes are key components in many electrochemical devices such as dye sensitized solar cells (DSC), fuel cells, batteries super-capacitors, sensors and biomedical applications. In order to characterize such electrolytes, we developed a method to determine the charge carrier density (n), mobility (µ), and diffusion coefficient (D) of ionic conductors with the help of dielectric analysis of electrolytes [1,2]. The method previously proposed by our group is further simplified making it possible to calculate these parameters by just using electrochemical impedance analysis (EIS). The method has been tested with gel polymer electrolyte based on polyacrylonitrile host polymer and alkaline iodide at deferent temperatures. The temperature dependence of n, µ, and D have also been studied. The results are in agreements with those available for the ionic electrolytes.
[1]. T.M.W.J. Bandara M.A.K.L. Dissanayake, I. Albinsson, B.-E. Mellander, Mobile charge carrier concentration and mobility of a polymer electrolyte containing PEO and Pr4N+I− using electrical and dielectric measurements, Solid State Ionics 189 (2011) 63-68.
[2]. T.M.W.J Bandara, B.-E. Mellander, Evaluation of Mobility, Diffusion Coefficient and Density of Charge Carriers in Ionic Liquids and Novel Electrolytes. In Ionic Liquids: Theory, Properties, New Approaches Ed. Alexander Kokorin, InTech, Rijeka, Croatia, (2011), 383-406.

Silver nanowires (Ag NWs) are appealing candidates for supercapacitor electrodes due to their high conductivity in addition to their allowance for all active materials to be in close contact to facilitate charge transport. These are very important to attain maximum charge accumulation provided that Ag NWs are electrochemically stable within the utilized potential window. The potential window of bare Ag NWs was found as 0-0.5 V, where irreversible oxidation takes place at 0.6 V, limiting not only the potential window but also the power and energy density of supercapacitors in consequence. In this work, in order to extend the potential range, Ag NWs were coated with a thin platinum (Pt) shell layer using a simple solution based, green method. Fabricated core-shell nanowires were than deposited onto glass substrates in the form of networks via spray coating. Ag-Pt core-shell NW network electrodes were electrochemically tested and the potential window was found to be extended up to 1.2 V. The true potential of Ag-Pt core-shell nanowire network electrodes were further evaluated in coaxial nanocomposite form, which is simply achieved through cathodic electrodeposition of pseudocapacitive nickel hydroxide (Ni(OH)₂) layers onto the networks [1]. Capacitive behavior of the coaxial nanocomposites was investigated through cyclic voltammetry, galvanostatic charge-discharge and impedance spectroscopy. Thorough analysis on the electrochemical stability and capacitive behavior of the fabricated nanocomposite electrodes will be presented in conjunction with different electrochemical coating parameters.

[1] Yuksel, R., Coskun, S., Kalay, Y. E., & Unalan, H. E. (2016). Flexible, silver nanowire network nickel hydroxide core-shell electrodes for supercapacitors. Journal of Power Sources, 328, 167-173.

This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under grant no 117E539.

Ordered mesoporous silica materials are used as supports for various applications from catalysts, chromatography and enzyme immobilisation. In this work, the impact of surface silane functionalisation was examined by various pre-treatment methods. The surface chemistry and physical properties were examined pre and post ‘cleaning’ of the supports.
The impact of these changes were then examined by functionalisation of the support with (3-aminopropyl)triethoxysilane with potentially increasing the efficiency of attachment and robustness of the end application.
SBA-15 was synthesised, calcined and characterised. The support was then rehydroxylated or ‘cleaned’ by various routes (H₂O, H₂SO₄, H₂O₂/H₂SO₄ solution and UV/Ozonolysis) and then functionalised.
The results showed that using pre-treatment methods allowed for higher attachment of the silane.
Surface energy measurements were also determined showing the changes after pretreatment methods and after grafting with the silane.

The potential low cost and non-flammability of rechargeable batteries based on aqueous electrolytes make them a promising option for large-scale energy storage for grid applications. Using a highly-concentrated (35 molal) aqueous sodium bis(fluorosulfonyl)imide (NaFSI) electrolyte we recently reported a stability window of 2.6 V.^[1] Using asymmetric FTFSI anions as solution to suppress the commonly encountered crystallization of highly concentrated aqueous electrolytes we further demonstrated that an electrolyte consisting of 25m NaFSI + 10m NaFTFSI is robust against crystallization at low temperatures and enables long-term cycling of 2 V class full cells even at -10 °C.^[2]
Besides the electrochemical stability of an electrolyte, the chemical stability of its constituents is crucial for stable long-term performance. Here, we explore the chemical stability and physicochemical properties of aqueous solutions of FSI salts as electrolytes for lithium-ion and sodium-ion batteries. We demonstrate that the rate of hydrolysis of this anion is strongly dependent on the salt concentration as well as the nature of the cation. We relate the stability of FSI to the interaction with the cation and the charge density of the latter, and show that also at elevated temperatures highly concentrated NaFSI electrolytes are significantly more stable than their lithium analogues. Yet, hydrolysis is still observed in the NaFSI electrolytes to some degree and we emphasize that major efforts are needed to develop new, highly soluble, stable salts in order to push the long-term performance of such aqueous systems towards competitive levels. ^[3]
References:
^[1] Kühnel, R.-S.; Reber, D.; Battaglia, C., A High-Voltage Aqueous Electrolyte for Sodium-Ion Batteries. ACS Energy Lett. 2017, 2, 2005-2006.
^[2] Reber, D.; Kühnel, R.-S.; Battaglia, C., Suppressing Crystallization of Water-in-Salt Electrolytes by Asymmetric Anions Enables Low-Temperature Operation of High-Voltage Aqueous Batteries. ACS Materials Lett. 2019, 1, 44-51.
^[3] Reber, D.; Kühnel, R.-S.; Battaglia, C., Stability of Aqueous Eletrolytes Based on LiFSI and NaFSI. submitted

Lithium-ion batteries are currently being use in majority of portable applications ranging from cell phones to electric vehicles. While the use of graphite as an anode has been successful for the last 30 years, there is currently a wide variety of research in new materials and architectures that can increase a lithium-ion battery’s overall energy density, cycle life, or rate capabilities. Intermetallic alloys have been promising due to their ability to improve the energy density when compared to graphite. Of these alloys, SnSb has been heavily studied and can be a potential candidate in replacing graphite.

We herein report on the synthesis of pure phase SnSb from ethaline solution. Previous reports on electrodeposition of SnSb resulted in the presence of a Sn rich product. While the synthesis may be described simply, specific parameters (in the solution composition as well as the method of deposition) must be achieved to form this material in the pure phase. An in depth analysis with multiple characterization techniques will be used to clarify what is occurring with changes to specific parameters in the synthesis. Lithium battery cycling studies will also be presented, showing the material’s performance compared to Sn-rich production seen in previous electrodeposition reports.

Monolithic carbon xerogel with co-continuous hierarchical porosity was prepared via one-step, template-free and catalyst-free hydrothermal polycondensation reaction with resorcinol(R), formaldehyde(F) and mildly oxidized graphene oxide. The gels were prepared in a pressurized Teflon mold at 100 °C for 6 h, followed by drying at 60 °C for 36 h and then 100 °C for 12 h, generating xerogels. The R/W ratio and loading of graphene oxide were varied to optimize pore size with co-continuous hierarchical pore structure. Next, the xerogels were subjected to pyrolysis at 900 °C for 2 h, followed by KOH infiltration and activation at 800 °C for 1h. The gels, before and after the activation, were subjected to N₂ sorption study and also to electrochemical property measurement via cyclic voltammetry, while the samples for the latter were prepared via cutting the monolithic xerogels rwithout involving polymeric binder and solvent. In addition, XRD, Raman and SEM were also utilized for characterization.

Silicon graphene based composites can be very promising next generation lithium ion battery (LIB) anodes because of silicon having high capacity (4200 mA h g⁻¹ and 2400 mA h cm⁻³) and lower electrochemical potential with respect to Li (< 0.35 V vs. Li/Li⁺).¹ Unfortunately, bulk silicon anode faces other problems, e.g. poor cycle stability and great volume expansion. However, reports have suggested that silicon nanoparticles can overcome these issues by relieving larger stress/strain and facilitated by the short Li⁺/electron transfer length.
Extensive research has been performed with nano silicon-based anodes and major complexities rely with the optimization of silicon particle size, degree of crystallinity, dispersion of silicon particles in graphene matrices, nano silicon percentage in the composite etc. In this report, optimization of oxidation and degree of crystallinity of silicon nanoparticles is studied for better battery performance. A simple and scalable plasma enhanced chemical vapor deposition technique is used to produce silicon nanoparticles with variable range of crystallinity.² A detailed characterization is performed to investigate chemical, structural and morphological characteristics of these particles. Later, these particles are used as anode material in LIBs. Anodes are prepared with conductive few layers graphene and polyacrylic acid binder. These anodes showed excellent stability over 250 cycles with clear correlation between particle size, crystallinity and oxygen content. Results are very promising with these silicon NPs, with the capability of scalable production process.

1. Su, X. et al. 1-s2.0-S0039914013005584-main.pdf. Adv. Energy Mater. 4, n/a-n/a (2014).
2. Greco, E. et al. Few-layer graphene improves silicon performance in Li-ion battery anodes. J. Mater. Chem. A 5, 19306–19315 (2017).

The self-organized TiO₂ nanotube (TNTs) layers have attracted considerable scientific and technological attention for the last two decades. Nowadays, they perform very well in a wide range of applications including photo-catalysis, solar cells, hydrogen generation and energy storage [1]. The synthesis of 1D TNTs layers is carried out by a conventional electrochemical anodization of valve Ti metal sheet. The main drawback of TiO₂ is its applicability in the UV light (wavelengths < 390 nm). In order to obtain also visible light photoresponse, TiO₂ has to be doped or sensitized. For example, N [2] or C [3] were used as very effective TiO₂ dopants.
Except the extension of the VIS light response, one of the major issues to extend the functional range of nanotubes is to coat homogenously the nanotube interiors by a secondary material. It has been shown that additional ultrathin surface coating of TNTs by secondary materials using Atomic Layer Deposition (ALD) significantly improves the functionality of the resulting hetero-structure for various applications [4]. Next to the ALD, sulphur treated 1D anodic TNT layers possess improved photo-electrochemical and catalytic properties and the energy storage compared to the blank TNT layers [5, 6]. This treatment was performed in the evacuated quartz ampoules in the temperature range from 250 to 450°C. An inspection of the sulfurized nanotube layers via scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) has disclosed a gradual crystal growth within nanotube walls, represented by TiS₂ or TiS₃ phases. It was found that each application requires a different optimum condition of sulfurization.
The presentation will focus on the sulfurization process of TNTs and their characterization. The potential applications in various fields (such as batteries, photocatalysis) of prepared TiS_x/TNTs heterostructures will be discussed.

References
1. J. M. Macak et al., Curr. Opin. Solid State Mater. Sci. 1-2 (2007) 3.
2. C. Burda et al., Nano Lett. 3 (2003) 1049.
3. S. Sakthivel et al., Angew. Chem., Int. Ed. 42 (2003) 4908.
4. F. Dvorak et al., Appl. Mater. Today, 14 (2019) 1.
5. M. Krbal et al., Appl. Mater. Today 2019 – submitted
6. G. D. Salian et al. Appl. Mater. Today, 2019 accepted

In this study, low-cost, environmental friendly “water in salt (WIS)” electrolyte was introduced to replace the expensive and toxic organic electrolyte of supercapacitor. Very recently, potassium acetate (CH₃CO₂K) electrolyte was found to be able to replace the LiTFSI in LiB. To our best knowledge, this new WIS electrolyte has not been demonstrated in aqueous supercapacitor. Moreover, CH₃CO₂K is safer and cheaper than LiTFSI-based WIS electrolytes. Therefore, in this study, we open up new opportunities of using acetate-based WIS electrolyte in the supercapacitor. We demonstrated that acetate-based WIS able to obtain wide potential window up to 2.5V. We investigated several acetate-based WIS, such as CH₃CO₂K, CH₃CO₂Na, CH₃CO₂Li, and its combination. The result shows that mixing two WIS leads to wider potential window up to 3V. We investigated the performance of CH₃CO₂K-CH₃CO₂Li WIS in iron layered vanadate nanocomposite. The synergistic effect of unique properties of iron layered vanadate nanocomposite and bi-WIS resulting high energy density of 53 Wh kg^-1 at power density of 672 W kg^-1. This environmental friendly electrolyte is very promising for next generation of supercapacitor.

Small-scale energy resources become basic need for various widespread applications like implantable devices and portable electronics and internet of things (IOTs). Extensive development in supercapacitor technology aims to increase the electrical performance of electrode materials.¹ Interconnected porous graphene have gained a special attention to be use as supercapacitive material as well as current collector in developing metal-free interdigited microsupercapacitor (IMSC) due to its superior conductivity and porosity.² Herein, Electrochemical followed by laser-irradiation (LI) method gives advancement in prototyping conductive graphene-based robust MSC device. Raman spectra proves that the laser irradiation method is capable of forming fused interconnected graphene sheets within healed structural defects, resulting high conductivity and improved crystallinity of LIG sample.³ An on-chip metal free microsupercapacitor using graphene as current collector as well as electrode material shows advantages of large working voltage of 1.2 V in aqueous solid electrolyte, providing high energy-density and long-term stability.The MSC, without any metal current collector, interestingly shows unique electrical-double layer behavior and unprecedented cycling stability with 100% retention of initial capacitance after 1,00,000 continuous cycle. A large cell voltage of 10.8 V was realized by modularizing the array of devices without much degrading the rectangular shapes of the voltammogram even at higher scan rates (100 V s^-1). Based on such high voltage MSCs, a hybrid structure of commercial solar cell and metal free supercapacitor was designed to make a self-charging power system. This study provides an effective strategy to build up metal-free supercapacitor with exceptional life cycle, highly durable and high-voltage flexible MSCs to facilitate progress toward a self-sustainable energy future.

References:
1 R. S. Dey, H. A. Hjuler and Q. Chi, J. Mater. Chem. A, 2015, 3, 6324–6329.
2 T. Purkait, G. Singh, N. Kamboj, M. Das and R. S. Dey, J. Mater. Chem. A, 2018, 6, 22858–22869.
3 N. Kamboj, T. Purkait, M. Das, S. Sarkar, K. S. Hazra and R. S. Dey, Energy & Environmental Science, 2019, DOI: 10.1039/C9EE01458F.

The increasing global demand for clean and sustainable energy sources has given rise to the significant interest in the rational synthesis and design of low-cost and efficient functional nanocomposites and nanomaterials as supercapacitors in advanced electrochemical energy storage systems. Nonetheless, the design of such nanomaterials with tailored interfacial functionality and charge transport properties relies on the systematic and fundamental understanding of the processing-structure-property relations for precise tailoring of architectures and compositions of the active nanomaterials without using any undesired chemicals/surfactants/ligands that can compromise their electrochemical performance and interfacial activities. Herein, we present our most recent findings in using Laser Ablation Synthesis in Solution (LASiS) as a strategy and pathway for the facile and environment-friendly, yet efficient, synthesis of new classes of carbon-based hybrid nanocomposites (HNCs) decorated with metal-oxide nanoparticles (NPs) that exhibit unique supercapacitive properties. Initially, we report the use of LASiS coupled with two-post treatments for the fabrication of (1) Co₃O₄ NPs/reduced graphene oxide (rGO), (2) Co₃O₄ nanorods (NR)/rGO, and (3) Co₃O₄ NPs/nitrogen-doped graphene oxide (NGO). This methodology allows us to tune the selective functionalities of the HNC by adjusting their structure-property relationships. The Nitrogen doping in the NR/rGO HNCs, for instance, promotes a higher electron conductivity while enhancing the electrochemical activity and preventing the aggregation between NPs. These interfacial energetics and arrangements coupled to the presence of a network of interconnecting 1D nanostructures have indicated to yield an effective charge transport and electrolyte diffusion at the electrode-electrolyte interfaces, resulting in the enhancement of the supercapacitive properties. Secondly, we will present the screening for other potential metal oxides with supercapacitive properties and the use of the same technique for the design of their HNCs for electrical chemical storage systems. Finally, we will present our advances on the development of functional conductive inks with fluidic properties containing the aforementioned HNCs for the fabrication of all-printed solid-state supercapacitors using drop-on-demand (DoD) inkjet printing; our results have shown that by tailoring the ratio of solvent, binder, and HNCs we can obtain an ink with the viscoelastic properties required for an efficient printing, while preserving the electrochemical efficiency of the composites.

Solar fuels produced from sunlight via photocatalytic water splitting and artificial photosynthesis represent one of the most promising clean energy sources. Various semiconductors, including graphitic carbon nitride (g-C₃N₄) and transition metal oxides, have been considered as photocatalysts for the fuel production, but there lacks of the design principles for rapid screening of the best photocatalysts from numerous candidate materials. Here, we demonstrate, for the first time, a universal guiding principle that governs the photocatalytic activities of p-orbital element-doped C₃N₄-based photocatalysts for photocatalytic water splitting, which is also applicable to other doped semiconductors including ZnO and TiO₂. An activity indictor is introduced to determine the efficiency of non-metal-doped semiconductor photocatalysts for the solar fuel production. These predictions are supported by experimental results. This generalized principle could guide a broad photochemical production of solar fuels including hydrogen, hydrocarbon, and other green chemicals.

Graphene has been widely investigated for applications in supercapacitors, due to its extremely high theoretical specific surface area, excellent electrical conductivity and lightweight nature. However, most synthesis routes for graphene-based supercapacitors are highly energy-intensive and costly, utilizing harsh chemicals, multiple synthesis steps, high temperatures, and/or specialized instrumentation. In 2014, the Tour group introduced a simple method to prepare high surface area, conductive and porous graphene through the laser-induced carbonization of specific polymers such as polyimide.¹ This one-step approach is rapid, scalable, and cost-effective, utilizing commercial CO₂ infrared laser systems commonly employed for laser cutting to combine graphene production and device fabrication in a single step. This approach has been utilized to fabricate polyimide-based laser-induced graphene microsupercapacitors with specific areal capacitances of ~ 9 mF/cm².² However, thus far this approach has been limited to costly synthetic polymers prepared from coal or petroleum-based products. Methods to extend this approach to other green materials such as lignin, paper, and wood employ more costly visible or UV lasers, fabrication in inert atmospheres, or pre-treatment of the substrate materials, limiting the ease and scalability of this approach. In this work, we demonstrate for the first time the laser-induced carbonization of poly(furfuryl alcohol), a green polymer easily prepared from the one-step polymerization of furfuryl alcohol, which is a biomass waste derivative obtained from corn cobs, rice hulls, bagasse, and wood. Notably, we explore the use of graphene oxide as a carbonization catalyst, demonstrating that loadings as low as 1 wt.% facilitate the laser-induced carbonization of PFA utilizing an inexpensive CO₂ laser under ambient conditions. Furthermore, we demonstrate that composites of PFA microspheres and graphene oxide can achieve specific areal capacitances as high as 16.0 mF/cm² at 0.05 mA/cm² , which both outperforms the most commonly utilized polyimide films, and is among the highest specific capacitances achieved for supercapacitors prepared from this method. We further demonstrate that these devices cycle for over 10,000 cycles with over 97% capacitance retention. Finally, we introduce a novel method to utilize inexpensive and widely abundant salts, such as sodium chloride, as catalysts for the laser-induced carbonization of PFA. We demonstrate that these salts can enable the carbonization of the PFA into a porous, conductive carbon material and present results on the performance of supercapacitors prepared from these eco-friendly composites. Supercapacitors prepared from laser irradiation of PFA/GO and PFA/salt composites indicate the potential of uniting green materials and energy-efficient laser-induced fabrication for high-performance and sustainable next-generation supercapacitors.

References
¹ J. Lin, Z. Peng, Y. Liu, F. Ruiz-Zepeda, R. Ye, E.L.G. Samuel, M.J. Yacaman, B.I. Yakobson, and J.M. Tour, Nat. Commun. 5, 5714 (2014).
² Z. Peng, J. Lin, R. Ye, E.L.G. Samuel, and J.M. Tour, ACS Appl. Mater. Interfaces 7, 3414 (2015).

In the last decade, many efforts have been made to develop new thin films by using atmospheric pressure plasma process. In this sense, many authors have developed complex materials such as nanocomposite thin films [1.2], biodegradable coatings [3] and advanced chemical treatments on complex surfaces [4]. In parallel, the use of plasma process has also been recently proposed to improve the electro-chemical characteristic of rechargeable lithium ion batteries (LIB) [5]. In this context, atmospheric pressure dielectric barrier discharges (DBDs) could offer the possibility to strongly improve the material’s surface properties with a limited cost and a little environmental impact in the manufacturing process. Moreover, today these systems can be easily modified to scale up the process in a production line.
Through this work, we aim to present our recent results on plasma-enhance modified composite electrodes employing water soluble Carboxymethylcellulose (CMC) as a binder that are usable in aqueous electrolyte rechargeable LIB (ARLB).
Plasma-deposited coatings were then characterized by SEM-EDX, FTIR and XPS. The electrical analysis of the process shows that the discharge remains stable and homogeneous during the process. This suggests that the substrate slightly affect the physical regime of the discharge. The SEM analysis obtained on the final electro-active material, shows a homogeneous surface and the creation of a specific morphology for the coating. From the FTIR analysis, different chemical groups were observed on the surface depending on the distance from the entrance of the discharge. Finally, the physico chemical properties and electrochemical performance of such electrodes were also investigated.

[1] J. Profili et al., Plasma Processes and Polymers, volume13, issue10, October 2016, 981-989
[2] P. Brunet et al., Plasma Processes and Polymers, volume 14, issue12, December 2017, 1700049
[3] M. Laurent et al., Plasma Processes and Polymers, volume 13, issue7, July 2016, 711-721
[4] S. Asadollahi et al., Materials 2019, 12(2), 219
[5] T. Nakajima et al., Journal of Power Sources, volume 104, issue 1, 15 January 2002, 108-114

Porous electrodes exhibit impressive advantages including large surface area and fast electrolyte permeability. In the literatures, noble metals such as Au and Pt are known for electrochemical stability against different reactions and electrolytes, and therefore they are often used as the electrode materials. Unfortunately, due to their excessive cost, it is necessary to reduce their utilization. In this work, we adopt a polymeric membrane which provides a flexible and inexpensive porous substrate on which dopamine is deposited to render it hydrophilic so electroless Au deposition could be proceeded successfully to fabricate a three-dimensional microporous flexible Au conductive electrode. SEM and EDS analysis are used to characterize the surface structure and composition distribution. Electrochemical and impedance analysis are carried out to identify the electrochemical surface area (ECSA) of Au film and Solid-liquid interface resistance. In addition, we measure the resistance after multiple cycles of the bending test to determine the mechanical strength. We envision this Au-coated flexible porous electrode will become rather useful in flexible electronics.

A simple one-step method was demonstrated for the electrodeposition of phosphide-based nanostructures on nickel foam substrates. The electrodeposited materials were characterized using field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) techniques. The materials were used as supercapacitor electrodes and showed exceptional high specific capacitance and rate capability. Upon using them to fabricate asymmetric supercapacitor device, high power density and energy density were obtained, indicating the high potential of the fabricated materials for practical energy storage devices.

Non-aqueous redox flow batteries have shown great promise for grid energy storage, due to their independent scaling of power and energy, long operational lifetimes, simple manufacturing, and, when compared to their aqueous counterparts, a wider voltage window and a broader choice of electrochemical couples. Nevertheless, non-aqueous redox flow batteries must operate with high active material concentrations to exhibit high energy densities and simultaneously remain financially viable. In our previous work, we demonstrated that phenothiazine derivatives are valid candidates as posolytes for non-aqueous redox flow batteries, due to the high stability of their radical cations. The systematic chemical modification of the phenothiazine core allowed us to access an array of compounds with varying solubilities, both in neutral and radical cation state. Despite our effort to adopt simple and high-yielding synthetic routes, designing and synthesizing new redox active compounds with improved solubilities is time-demanding, often involving a trial-and-error approach. To overcome the burden of such discovery process, we proposed the study of binary and ternary mixtures of phenothiazines chosen from the active materials library developed in our group as higher-solubility alternatives to the pure constituents of such mixtures. Mixtures of solids are known to undergo the phenomenon of melting point depression – an “impure” solid exhibits a lower melting point than its pure form –, which, in turn, is associated to an overall increase in solubility of the mixture. In light of this, we first screened blends of phenothiazines to identify the ratios where a decrease in melting point is observed by thermal analysis. Subsequently, we determined the solubility of these mixtures in both states of charge – neutral and radical cation – in acetonitrile, with or without a supporting electrolyte, to correlate the extent of melting point depression to the increase in solubility. Preliminary results show significantly enhanced solubility for poorly soluble phenothiazines when present in mixtures. Also, an increase to up to three-fold has been observed for the total achievable concentration of mixtures of radical cation species. The results we report herein introduce an alternative, simpler method to achieve high concentrations of redox active materials and pave the way for a new approach to high-capacity non-aqueous redox flow batteries.

Innovation in rechargeable energy storage devices has a pivotal role in the green and sustainable energy cycle and in the portable device market. The recent trend of miniaturization of electronic devices in many fields, including remote sensors, personal electronics and medical implants, increased the demand for highly customizable, high energy-density batteries. These new demands provide opportunity for development of novel microbatteries and manufacturing processes that facilitate design of miniaturized electronic devices while maintaining a minimal ecological footprint and waste production. Such devices have the potential to be designed to be lighter, smaller and more customizable, and use more sustainable chemistries than those of current commercial batteries.
To facilitate production of microbatteries of this type, we use drop-on-demand dispensing, a highly robust printing method already in use for various types of functional materials. This method, based on piezoelectrically actuated mechanical droplet formation, enables high accuracy and repeatability in the printing of active-material inks with different properties and rheological parameters. For a sustainable production process, we use aqueous inks, avoiding the use of organic solvents for the battery printing process, thus eliminating formation of organic fumes and waste.
We have used this method to print various types of active materials for lithium-ion batteries, including cathode (lithium iron phosphate, LFP) and anode (silicon-nickel-based nanoparticles). Both yielded repeatable printability at a resolution better than 200µm, which allows customization of the printing process to produce various geometries, including 3D construction of upright electrodes for increased space efficiency and enhanced design possibilities.
We found that the electrochemical performance of the printed active materials is highly competitive with traditional manufacturing methods. Cathodes show very high specific capacity, up to 160mAhr/g_LFP, close to its theoretical capacity, and good cycleability. Electrochemical impedance spectroscopy of cathodes shows that cathode chemistry and performance are unaffected by the printing process. Hence, direct implementation of well-established equivalent-circuit models is enabled for data analysis.
Anodes also show high capacity – up to 1200mAhr/g_anode and their electrochemical behavior is similar to that of anodes prepared by traditional methods. We studied the adhesion of printed anodes to several current collectors and present methods of improving it, both by modification of the current collector and the anode ink itself. The anodes with improved adhesion gave longer cycle life and better performance of microbatteries printed in nonconventional geometries.
As a substitute for typical battery separators, we have developed a self-pore-forming ink to be printed between electrodes. The ink is based on binders similar to those of the cathode and anode, which enable improved adhesion, high uptake of liquid electrolyte, and good mechanical and electrochemical properties.
Our results inspire further studies, development of manufacturing protocols, and designs for highly customizable batteries. Such development is of particular importance for small-scale and flexible production in many fields of applications, such as in-situ 3D printing of embedded batteries during the assembly process of electronic devices.

Liquid electrolyte is inevitable to electrocatalytic transform CO₂ to liquid fuels, which will cause safety issues and energy-consumed downstream separations for pure products. Here we report an all-solid-state electrochemical CO₂ hydrogenation system, which can continuous produce pure formic acid (HCOOH) vapour without the employ of any liquid electrolyte in the full device. CO₂ and H₂ streams were separated into the cathode and anode by solid-state electrolyte (SSE), where generated HCOO^- and H⁺ were recombined to produce pure HCOOH vapour. Coupling with high activity (formate partial current densities > 440 mA cm^-2) and selectivity (Faradaic efficiencies > 97%) grain boundary-enriched bismuth catalyst, we present a record high pure HCOOH vapour (ca. 100 wt.%). A wide range concentrations of pure HCOOH solutions without mixing with other ions were obtained by tuning the flow species (N₂ or water) and flow rates in the SSE layer. A 100-hour constant production of pure HCOOH with negligible degradation in selectivity and activity was demonstrated to verify the operational stability of our all-solid-state electrochemical CO₂ hydrogenation system.

Transition metal oxide based pseudocapacitors have received significant attention as energy storage devices because of their excellent characteristics such as high power and energy density, long cycling stability etc. Among metal oxides, cobalt oxide (CoOx) is widely used; however, its low energy density compared to batteries, low conductivity along with larger volume change during the redox processes are still the limiting factors for utilizing it. A novel strategy to address these issues is to hybridize cobalt oxides with highly conductive and structurally robust materials that can improve the conductivity and the structural stability of the electrodes. In this regard, MXenes, a family of two-dimensional transition metal carbides and nitrides, are excellent candidates for the fabrication of the nanocomposite with cobalt oxides due to their high conductivity, high surface area, hydrophilic surfaces and excellent electrochemical properties. As the size and surface morphology of the metal oxides play a crucial role in the electrode’s performance because the pseudocapacitance originates from the surface-based redox reactions, we have successfully synthesized a highly porous MXene-cobalt composite nanostructure, which facilitates the movement of ions/electrons and offers extremely high electrolyte-accessible surface areas, leading to a significant improvement in the electrochemical performance. Firstly, we have spray-coated the composite thin film on a Pt-Si substrate using an air spray. Secondly, we have synthesized the MXene-cobalt oxide composite electrode by using a novel PulseForge photonic curing technique in several seconds as opposed to the traditional methods such as, hydrothermal growth, chemical vapor deposition, chemical reduction etc. which take from minutes to hours for processing. To our knowledge, the processing we are reporting is the easiest, quickest and roll-to-roll amenable, making it a high-throughput and low-cost processing method. Furthermore, because of the extremely short photonic processing time, flexible and inexpensive substrates can also be used, signifying their potential application in modern wearable, flexible and portable electronics.
Through varying processing parameters such as the number of pulses, applied voltage, pulse length etc., we have shown we can easily control the resulting nanostructure of the electrode. The as-synthesized composite electrode exhibits initial specific capacitance of 26 mF/cm2 and shows excellent improvements in electrochemical performance over the cobalt oxide electrode by retaining more than 60 % of initial specific capacitance whereas cobalt oxide electrode retains 30 % of initial specific capacitance after 15000 continuous charge-discharge cycles at 0.25 mA/cm2 areal current density. These results could be attributed to the excellent electrochemical behavior of MXene along with its synergistic effect with the cobalt oxide material. Moreover, the nanostructures are grown directly on the highly conductive substrate, which improves the conductivity of the electrode and eliminates the need for a binder.

The development of charge-storage materials for use in redox flow batteries (RFBs) requires possession of a diverse property set that will lead to high capacities, voltages, and lifetimes for large-scale stationary storage application. High capacities require high solubilities in all states of charge. High voltages stem from large differences in redox potentials. Long lifetimes require stability far greater than the timescales at which many chemists are used to operating, who rarely have the need to isolate a charged species at high concentration in diverse environments for a decade or more. None of these properties may be compromised in realizing a commercial battery, on top of which low cost and scalability are paramount. Given the demands in materials design, cost, and scale, it’s a small wonder that the variety of redox couples utilized in commercial redox flow batteries are few. While the challenge of meeting these requirements may at first seem daunting, to the right organic chemist, an opportunity is presented. The flexibility in design and tunability of properties of organic materials presents a cornucopia of choices to evaluate as electrolyte candidates. In this presentation, I will focus on the design and characterization of organic molecules as candidates for charge-storage species in non-redox flow batteries with nonaqueous electrolytes.

The possibility to intercalate anions into graphite is a well-known phenomenon, which was initially observed in 1983. However, studies of such compounds in the context of electrochemical energy storage were first reported in 2012, in connection with the coining of the term dual-ion battery (DIB). Dual-ion batteries operate through simultaneous cation and anion intercalation in the anode and cathode and they could constitute a breakthrough for large-scale, grid energy storage applications. The main benefit of all-carbon DIBs compared to other battery chemistries is their completely metal-oxide free nature. This key characteristic of DIBs would result in cheaper, environment friendly, naturally abundant and more sustainable batteries. Furthermore, the replacement of oxygen-rich cathodes with graphite would be a big leap towards increased operational safety, since electrode decomposition and evolution of flammable gases would become minimized.

The main challenge faced by all-carbon DIBs at the moment is the capacity fading related to the structural changes of the graphite upon anion intercalation; since the anion together with its solvation shell occupies a substantial volume. This will eventually lead to exfoliation of the graphitic sheets and effectively loss of active material and capacity. However, recent research as well as the preliminary results of this study indicate that the exfoliation issue can be partially supressed through careful design of both the electrolyte and carbon host material.

In this study, several carbonaceous materials with different crystallographic and morphological features are explored as potential hosts: (1) a monolithic, graphitic carbon foam which is partially turbostratically disordered (2) a flexible, expanded graphite foil and (3) a composite electrode comprised mostly of highly graphitized KS6 graphite. Additionally, the intercalated anions are varied, with the main focus being on the PF₆^- , TFSI^- and FSI^- species, which are inserted from both conventional organic solvents and from more "exotic" alternatives such as ionic liquids. The electronic and structural changes which occur in the graphite as a consequence of the cell cycling are followed through the aid of in-operando Raman spectroscopy and ex-situ X-ray diffraction. These results are thereafter coupled to the electrochemical behavior of the different carbon-salt systems in order to gain a thorough understanding of the related intercalation mechanisms.

Green or bio-sourced carbon-based materials offer sustainability in electrochemical energy storage applications. Electron transfer is a fundamental process and as such, understanding the underlying structure-function properties is critical to new technological development. In many cases, polymeric materials are blended together to create an ensemble of collective properties, such as combining redox activity with mechanical or optical properties. This blending results in spatial heterogeneity of electrochemical properties. Inspired by the ability to tune the opto-electronic properties of conductive polymers and the prospect of highly controlled photoelectrochemical processes, this work undertakes a proof-of-principle study to evaluate the charge transport-charge transfer mechanism in conductive polymer/electrolyte interfaces at the micron to nanometer length scale. Both charge transport and charge transfer will follow paths of least resistance, hypothesized to be due to local percolation pathways and intermolecular spacings. The vision to develop a collective characterization tool suite that allows for imaging of distributions in nanoscale properties, which will enable identification of key structure-function relationships leading to higher performance, and finally, leveraging these known nanoscale properties to increase photon-to-electron-to-molecule conversions.

As a model system, amorphous insulating polymethylmethacrylate (PMMA) was blended with conductive poly(3-hexylthiophene) (P3HT). The enthalpy and entropy of mixing are such that the materials phase segregate, creating an ideal spatial heterogeneity to investigate connections between macroscale and nanoscale electrochemistry approaches. Using scanning electrochemical cell microscopy, the spatially-dependent electron-transfer kinetics associated with a rapid outer-sphere electron transfer process (ferrocenedimethanol oxidation) is mapped at the nanoscale. We combine the kinetic insight with complementary conductive AFM to understand the underlying electrical charge transport properties. A new technique - synchrotron infrared nanoscale spectroscopy (SINS) - is used to image local chemical structure and evaluate composition of buried interfaces. Finally, using finite analysis, we demonstrate the limitations of macroscale electrochemical approaches to assess rate constants due to uncompensated resistances.

Due to its high natural abundance and low material cost, sodium (Na) based battery technology faces tremendous opportunities for electric vehicle and grid scale energy storage applications. Traditional Na Beta-alumina batteries (NBBs), such as Na-S and ZEBRA batteries, have been commercialized to demonstrate a variety of grid services, including power shift, renewable integration, frequency regulation, and standby power, etc. However, it is quite difficult for traditional NBBs to penetrate into larger application market due to its inevitable “barrier”-high operating temperatures (> 300^oC). In the past few years, we have been developing intermediate temperature (~190^oC) Na-metal halide (Na-MH) batteries, which present several advantages, including simple battery architecture, improved thermal management, lower operating temperature, and lower manufacturing cost over traditional NBBs. Recently, we found that the use of organic compounds as electrode materials in NBBs can provide a new pathway to further reduce the battery operating temperature to near or below 100^oC. Here, we will present the preliminary results on investigating the possible application of organic candidates for NBBs applications.

Carbon nanostructures (graphene, nanotubes)-based nanocomposite thin films applied in the field of both energy storage devices (batteries and supercapacitors) and renewable energy (photovoltaics) will be presented in this work. We developed a novel and versatile way to prepare thin, transparent and homogeneous films of advanced and multi-component materials, based on immiscible liquid/liquid interfaces (for example, Zarbin et al., Adv. Funct. Mater. 2013; Electrochim. Acta 2016; Sci. Reports 2016; Sci. Reports 2017; J. Power Sources 2017; Electrochim. Acta 2018). Due to the specific preparation route (unique for some classes of materials as the ones discussed here), the films can be deposited over any kind of substrates, plastics included, allowing the preparation of flexible devices. Also, evident material economy is observed in the final process.
We will demonstrate the application of some of those films in green energy. First, carbon nanotubes/Prussian blue analogues developed according a methodology developed by us (Zarbin et al. J. Mater. Chem. 2012; J. Phys. Chem. C 2014; Chem. Eur. J. 2016), were applied as cathodes in ion-based batteries totally operating in aqueous electrolytes. Aqueous electrolytes are safer, cheaper, environmentally friendly and more conductive than organic ones. Results showed huge performances in K- and Na-ions batteries (cheaper than Li-ions ones), achieving impressive high discharge rates (up to 44.4 A g^-1), capacities up to 150 mAh g^-1 at 0.67 A g^-1 rate, and retention of 90% after 2000 cycles. A transparent and flexible device was built using those thin films deposited over plastics as cathode, a C/Co₃O₄ nanocomposite as anode and an aqueous NaCl solution as electrolyte, showing capacity of 85 mA h.g^-1, energy density of 53.3 Wh kg^-1 and retention higher than 90% after 2000 cycles. Flexible and transparent batteries correspond to emerging technology with direct impact on modern flexible and transparent devices. The device operation will be demonstrated showing four charged 1x1 cm devices connected in series and lightening a white LED. Also, flexible and transparent alkaline-batteries based on carbon nanotubes/nickel hydroxide thin films, as well as symmetric supercapacitors based on carbon nanostructures/polyaniline thin films will be demonstrated.
Prussian blue was also utilized as an innovative sensitizer in a photoanode for dye-sensitized solar cells – DSSC. An innovative tri-component nanocomposite thin films of carbon nanotubes/TiO₂/Prussian blue was prepared through the liquid/liquid route. In this configuration in a single film we have the sensitizer (Prussian blue, used by the first time for this application), the semiconductor (TiO₂ nanoparticles) and the carbon nanotubes as the anchoring point for both the sensitizer and the semiconductor, as well as an efficient charge-transport material. The photoresponse evaluated in a total aqueous electrolyte was of impressive 600 µA cm².
Summarizing, this work presents the preparation of complexes and multi-component materials, their innovative deposition as thin films using an unique metodology and their application as active components in environmentally friendly batteries and photovoltaics, fully operating in water. Materials and processes for green energy.
Authors acknowledge CNPq, CAPES/PRINT, INCT-Nanocarbon and COPEL (PD 2866-0470/2017) by the financial support.

Conductive polymers have been extensively investigated as part of next-generation green electrochemical energy storage solutions. Organic electrochemical capacitors/supercapacitors are great candidates for flexible, portable power supply due to quick charge delivery and environmentally friendly materials and production. The combination of conductive polymer Poly (3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) and bio-sourced cellulose nanofibrils (CNF) provides a mechanically robust, ionically and electronically conductive nanonetwork for high energy and power density paper electrodes that can be solution-processed into supercapacitor systems.
Spray coating allows large area, roll-to-roll compatible fabrication of nanometer thin up to, macroscopically thick, free-standing electrodes from functional inks. In this work, up to 30 µm thick conductive nanocomposite electrodes made from CNF and PEDOT: PSS were achieved by industrial spray deposition and then combined into supercapacitors. The crystalline structure of these spray coated nanocomposite films with certain additives and different thicknesses was evaluated by grazing incidence wide-angle x-ray scattering (GIWAXS).
The manufacturing strategies introduced in this study are to realize customized supercapacitor architectures for portable printed electronics by combining spray-coated electroactive paper electrodes with stencil printing of gel electrolyte and screen-printed cell components. Excellent electrochemical performance with 1.2 µWh/cm² energy and 20 mW/cm² power densities at 0.1 mA/cm² was demonstrated, and all-printed devices survived extreme bending tests and cycle life up to 3000 charge-discharge cycles. The proposed fabrication methods and architectures enable the integration of thin and flexible energy storage devices with printed solar cells, exemplified in a wristband for applications in low power wearable electronics.

The rapid development of Internet-of-Things (IoT) requires the use of embedded electronics into physical components and daily objects which stimulates a tremendous and rapidly grown interest for electronic devices and energy storage systems that are flexible, wearable and conformal. Typical fabrication methods, such as photolithography and winding or stacking, that are commonly used in conventional electronics and energy storage systems respectively, are difficult to be applied as fabrication strategies towards devices with advanced form factors (e.g. three-dimensional (3D), stretchable, conformal). In this study, we demonstrate the fabrication of supercapacitors on 3D objects through inkjet and water-transfer printing. To the best of our knowledge, this is the first reported study on water-transfer printing of an active functional device such as energy storage. Planar supercapacitors constituted from nanoparticle-based silver current collector, nanoparticle-based nickel (II) oxide (NiO) active electrode material and an ionic liquid or surfactant-based saturated magnesium perchlorate /ultraviolet-cured triacrylate polymer-based solid-state electrolyte, were chosen as model materials to explore the feasibility of the proposed concept. To further explore the practical potential of the inkjet-printed supercapacitors with a particular focus on wearable applications, we fabricated an epidermal (or tattoo) printable supercapacitor, that was water-transferred on the skin of a human subject, to potentially serve as the power source for wearable health systems. The 3D and epidermal devices showed areal specific capacitances of up to 52 mF cm^-2 and 27 mF cm^-2 respectively. This new class of water transferable, inkjet-printed, all-solid-state supercapacitors with advanced conformality, offer new alternative approach towards monolithically-integrated/object-tailored power sources that are needed for complex-shaped devices for IoT and flexible/wearable electronic applications.

The redox chemistry of organic molecules is increasingly attracting interest as it has the potential to provide battery electrode material candidates combining high capacities, practical redox potentials and allow for transition metal-free chemistries. While many redox chemistries have been extensively explored, achieving high redox potentials has long remained a challenge. What is more important, lithiated organic redox chemistries (akin Li-ion inorganic cathodes) are severely lacking which makes difficult thus far practical implementation of an organic Li-ion battery technology.
This contribution aims at reporting some of our recent advances for the development of true organic Li-ion cathode materials. Design principles for new organic redox chemistries with limited solubility [1], high voltage via structural electrostatic interactions [2], as well as a new organic redox chemistry with intrinsic high voltage and ambient air stability will be detailed [3]. We hope that such findings can pave the way for designing high voltage organic Li-ion batteries in a near future.
[1] L. Sieuw, (...), A. Vlad, 2019, Chemical Science.
[2] L. Sieuw, (...), A. Vlad, 2019, submitted.
[3] J. Wang, (...), A. Vlad, 2019, submitted.

Clean and renewable energy has become a focal point due to its multiple impacts on our global sustainability. Lithium-ion batteries (LIBs), owing to its unique properties, have dominated the consumer electronics, automotive, medical, and industrial markets since the 1990s. Recently, the rapid development of portable electronic devices and electric vehicles (EVs) has led to an unprecedented demand for LIBs. Therefore, lithium, “the new gold,” become a strategically important commodity and is one of the most valuable resources in the foreseeable future. However, the current lithium production can’t satisfy the spiking demand for lithium and has been reported to cause negative impacts on the environment. Therefore, seeking new lithium sources and developing new lithium mining methods are the overarching issues to reach a sustainable future.
To address this challenge, we proposed to use an electrochemical method to extract lithium from the ocean. Inspired by lithium-ion rechargeable batteries, we applied lithium iron phosphate (LFP) to extract lithium from seawater due to its innate properties of lithium-ion selectivity, appropriate working potential, and fast cycling life.
The ocean has been reported as the most potential source of lithium. While lithium is abundant in seawater, its low concentration hinders its practical application. Furthermore, the high concentration of sodium-ions that coexist in the seawater further increase the difficulty of the extracting process. From our experimental result, it showed that the lithium-recover ability, the number of lithium-ions that can be released back into recovery solution, of LFP decrease 54% after one cycle in artificial seawater (0.1M LiCl + 0.5M NaCl) comparing to pure lithium solution (0.1M LiCl). Consequently, designing an electrode that can selectively extract lithium-ions, meanwhile, hinder the negative impacts causing by sodium-ions is the main challenge when developing electrochemical mining of oceanic lithium.
From the electrochemical performance (galvanostatic charge-discharge measurement) of LFP in artificial seawater, we, the first, observed the second platform occurring in the discharge curve, corresponding to sodium-ion co-intercalation. The sodium-ion co-intercalation have been reported to cause phase transformation from LFP (olivine structure) to sodium iron phosphate (maricite structure), which not only cause capacity decay but also lower the reversibility. Surface modification has been used in our work to alleviate the co-intercalation reaction. We design a polymer, containing lithium ionophore, acting as a customized tunnel for lithium-ion to diffuse, but block sodium-ion, to enhance the selectivity. The second platform occurring in the discharge curve can be inhibited by applying our method; besides enhancing the concentration by a factor of 10.77 (Li/Na molar ratio of initial solution = 0.2 and Li/Na molar ratio of recovery solution = 2.15), we improve the selectivity of the LFP electrode by a factor of 3.15, and increase 19% of the “recovery efficiency” (amount of lithium-ions that can be released back into recovery solution/ amount of lithium-ions that have been extracted from the artificial seawater) after 25 cycles.
By utilizing the surface modification, we can greatly block the co-intercalation of sodium-ions, prevent the phase transformation of LFP, and enhance the cycling ability. By applying the electrochemical lithium mining method, we can shorten the manufacturing cycle from years to days and provide new opportunities to harvest the ocean’s resources, and accelerate progress toward a sustainable future.

We report two different strategies to achieves nanocomposites with very high precision at the nanoscale:
i) Layer-y-Layer (LbL) self-assembly of a small molecule, tris(2-aminoethyl) amine (TAEA), in combination with a colloidal dispersion of the 2D material, Ti3C2Tx MXene, to form self-assembled multilayers. This LbL assembly of MXenes with small molecules is fundamentally different from assembly with polymers and results in highly ordered pillared (MXene/TAEA)n multilayer where the TAEA expands the interlayer spacing of MXene layers by only around 1 Å and reinforces the interconnection between MXene flakes. The TAEA-pillared MXene multilayers show higher electronic conductivity of 7.3 × 104 S m-1 to other MXene multilayers fabricated by LbL self-assembly. These multilayers are also resistant to mechanical deformation. Importantly, the MXene/TAEA multilayers could be used as electrodes for flexible all-solid-state supercapacitors delivering a high volumetric capacitance of 583 F cm-3 and an integrated high energy density of 3.0 Wh L-1 corresponding to a power density of 4400 W L-1. This strategy enables large-scale fabrication of highly conductive pillared MXene multilayers, and potentially fabrication of other types of 2D heterostructures on various substrates.

ii) Aqueous self-assembly of a multifunctional nanocomposite using the combination of a one-dimensional (1D) abundant biomaterial (cellulose nanofibrils, CNFs) with Ti₃C₂T_xMXene. This nanocomposite has one of the best multifunctional integration of strength (341 MPa), conductance (295 S cm^-1), and capacitance (298 F g^-1) than any previously reported composite. We rigorously studied and optimized these nanocomposites and concluded that the geometrical match between the 1D and 2D particles are crucial as they define the strength as well as the conductivity of the composite, and that the 1D and 2D phase must have a strong interaction at short range to overcome the colloidal repulsion and lock into a strong composite

References:
i) Weiqian Tian, et al“Layer-by-layer self-assembly of pillared two-dimensional multilayers”, Nature Communications, 10: 2558, 2019
ii) Weiqian Tian, et al. “Multifunctional Nanocomposites with High Strength and Capacitance Using 2D MXene and 1D Nanocellulose”, Advanced Materials, 1902977, 2019.

Routine access to power sources is an essential factor towards the continuing progress of our technology-oriented society, and toward ensuring a better quality of life. In this context, due to the ever-increasing implementation of renewable energy sources, electrical energy storage systems are set to play a central and potentially critical role in the next-generation energy infrastructure. The use of rechargeable (or secondary) batteries, which are already widely used for powering electric vehicles and electronic devices of all kinds, also seems to be particularly relevant with respect to this future scenario [1]. However, being faced with such a high global battery demand, issues concerning the resource availability or the recyclability also have to be further addressed together with the technical requirements in terms of capacity, energy density, cyclability, safety or cost. In this regard, and in parallel to research activities on regular inorganic-based electrode materials, the past decade has seen significant progress with respect to redox-active organic compounds, attracting much interest from the energy storage community. This is evidenced by the rapid increase in the number of studies and recent reviews on the topic [2], although this approach is still in its infancy. Based on the tailoring of naturally abundant chemical elements (C, H, N, O, and S in particular), organic chemistry also provides great opportunities for the discovery of innovative electrode materials able to operate both in aqueous and non-aqueous electrolytes. Additionally, it must be pointed out that two types of electrochemical mechanisms can be used in practice: n-type structures involving a charge transfer between the negatively charged state and the neutral state of the organic moieties (with cation release/uptake) and p-type structures involving a charge transfer between the neutral state and the positively charged state of the organic moieties (with anion uptake/release). In this communication, we will present our past and recent advances for developing efficient and sustainable organic electrode materials. In particular, we will report on several types of terephthalate derivatives [3] able to reversibly host both cations or anions by electrochemical reactions making different cell configurations possible including anionic “rocking-chair” batteries for which few examples are reported in the literature.

References:
[1] P. Poizot and F. Dolhem, Energy Environ. Sci., 2011, 4, 2003–2019.
[2] Y. Liang et al., Adv. Energy Mater., 2012, 2, 742–769; Q. Zhao et al., Ind. Eng. Chem. Res., 2016, 55, 5795−5804; P. Poizot et al., Curr. Opin. Electrochem., 2018, 9, 70–80.
[3] E. Deunf et al., J. Mater. Chem. A, 2016, 4, 6131–6139; E. Deunf et al., CrystEngComm, 2016, 18, 6076–6082; A. E. Lakraychi et al., J. Mater. Chem. A, 2018, 6, 19182–19189; A. Jouhara et al., Nat. Commun., 2018, 9, 4401.

The rapid expansion of electrochemical energy storage markets has imposed an impending need for low-cost, sustainable materials for high-performance electrodes, separators, and electrolytes. A rational strategy is to derive the electrochemical materials from renewable biomass. Here, we report a feasible approach to fabricate flexible, all-solid supercapacitors from eggs. Egg white/yolk and eggshell acted as the carbon source and sacrificial templates for porous activated carbon, respectively. The egg-derived 2D graphene-like carbon sheets with a thickness of 1.25 nm exhibited an outstanding combination of energy density and power density when being used in supercapacitor electrodes due to their high specific surface area (1527.2 m²/g) and naturally doped functional groups. Egg white/yolk also reacted with KOH, forming gel-like solid electrolyte with competitive ionic conductivity and water preservation. With eggshell membrane as a superb separator, flexible, all-solid supercapacitors were assembled which exhibited superlative electrochemical performance and mechanical flexibility. The proof-of-concept study provides inspirations of comprehensive utilization of biomass materials for energy storage. The egg-derived 2D graphene-like carbon and solid-state electrolytes should find more applications in different fields.

We explored the possibility to integrate the conversion and storage functions within the same multi-functional bio-sourced material. We identified the redox-active, quinone-based, melanin pigment, featuring a broad band absorption in the UV-Vis region, as the ideal candidate for such an exploration. Electrodes of melanin on carbon paper were investigated for their morphological, optical and voltammetric characteristics prior being assembled into symmetric supercapacitors operating in aqueous electrolytes. We observed that, under solar light, the capacity and the capacitance of the melanin electrodes significantly increase with respect to the dark conditions (by 22% and 39%, respectively). Once in supercapacitor configuration, besides featuring a Coulombic efficiency close to 100% after 5,000 cycles, the capacitance and capacity of the electrodes, rated by the initial values, improve after prolonged illumination, as it is the case for the energy and power density.

Electrochemical or chemical relithiation of end-of-life cathodes has been used to compensate the loss of lithium ion in the lithium-ion battery cathodes and recover their electrochemical reversibility. This method opens a new venue to directly recycle the spent cathode materials in a fast, energy-efficient and nondestructive way, without destroying the original structures happened in the traditional pyrometallurgy and hydrometallurgy processes. However, the direct relithitation method can effectively restore the electrochemical properties of the spent materials, only if the loss of lithium ion is the primary aging mechanism for the cathodes. The lack of efficiently identifying the degradation mechanism and determination of lithium ion content in the spent cathode materials makes it difficult to sort spent cathode materials suitable for direct relithiation in the battery recycling process. The determination of lithium ion content in the cathode materials, which is currently performed by coupled plasma-mass spectrometry (ICP-MS), involves tedious procedure and error-prone preparation. In this work, a new method has been developed to quickly sort the spent cathode materials—herein, Li(Mn0.35Ni0.4Co0.23)O2—for relithiation recycling. Furthermore, we introduce a new methodology to fast determine the lithium content in spent cathode materials without using ICP-MS. Finally, we have applied these methods developed in this work, to investigate the effectiveness of direct electrochemical-relithiation on recycling the spent cathodes and provide the insights in the future development of direct battery materials recycling.

With the development of flexible wearable electronics, fiber-shaped energy storage devices (FSESs) have attracted considerable interest in recent years. Owing to their large geometric dimension and solid inner structure, the specific surface area and the utilization of the electrodes are limited, which results in low capacities and energy densities of FSESs. To further improve the energy densities of the FSCs, the nanostructure of the one-dimensional electrodes should be designed to promote the utilization and increase the accessible area for electrolyte and thus improving their specific capacities and energy density.
In this study, polymer or carbon-based fiber electrodes with hierarchical porous structures have been fabricated as electrodes of FSESs. As electrodes of the all solid-state or quasi-solid-state FSESs, the fiber electrodes exhibit high flexibility and remarkable electrochemical performances with a high energy density.

Nickel-rich layered oxide materials (LiNi_xMn_yCo_1-x-yO₂, NMC), such as NMC622 and NMC811, have attracted great interest for application as high energy-density cathode materials in lithium-ion batteries (LIBs) because of their high specific capacities at high voltages compared with other commercial cathodes. Pushing cathode materials towards high-voltage operation is an effective way to further increase the energy density of the batteries. However, it is still a big challenge to operate Ni-rich NMC in LIBs under high voltage conditions (e.g. 4.4 V and above) due to the severe capacity fading. This fading is directly related to the instability of the cathode/electrolyte interface, induced by the ongoing chemical and electrochemical decompositions of electrolyte, the structural degradation of the cathode material and the dissolution of transition metals from the cathode; therefore, the commercial application of the Ni-rich NMC is limited so far. Besides the approaches of doping and coating the Ni-rich NMC materials to improve the long-term cycling stability of the batteries, developing new electrolytes is also an effective way to improve the practical application of Ni-rich NMC materials in LIBs. Here, we report new localized high-concentration electrolytes (LHCEs) that can greatly enhance the stability of Ni-rich NMC cathode and full cells with graphite (Gr) anode under 4.4 V comparing to the conventional carbonate electrolyte. This effect, in combination with the superior stability of Gr in these LHCEs, achieves dramatically improved long-term cycling performances of Gr||NMC cells in a wide temperature range from -30 to 60 °C. The findings in this work shed light a very promising strategy to develop new electrolytes for practical high-energy LIBs with Ni-rich NMC cathodes.

Porous carbon fibers with a high surface area and rich functionality are attracted as electrode materials for electrochemical energy storage devices (for example, supercapacitors and rechargeable batteries). Their widespread use is limited by their low porosity and ion-accessible surface area, and relatively sluggish electron/ion transport. Here, we present a new strategy of utilizing the microphase separation of block copolymers associated with electrospinning, pyrolysis and chemical activation to synthesize a porous carbon fiber with a well-controlled improved porosity, a highly effective ion-accessible surface area, and a fast electron/ion transport. Two-electrode supercapacitors fabricated from the prepared porous carbon fibers yielded high capacitance values in ionic liquid electrolyte. In addition, this approach is readily scalable to produce porous carbon fibers on industrial levels.

The MnO₂/nitrogen-containing graphene (x-NGM) composites with various Mn contents hydrothermally fabricated were used as electrode active materials for flexible asymmetric solid-state supercapacitors (ASSCs). By SEM, TEM, EDS mappings, XPS, and Raman spectra, the presence of nitrogen-containing graphene (NG) and MnO₂ was confirmed. TEM results manifested that the MnO₂ in the composites was a two-phase mixture of γ- and α-MnO₂. The co-existence of NG and MnO₂ enhanced not only the reversible Faraday reactions on the surface but also the charge transfer capability. However, excess MnO₂ caused reduced conductivity and a smaller slope of Nyquist plot in the low-frequency region unfavorable for ion diffusion and charge transfer. Better charge transfer efficiency was achieved only when the optimum MnO₂ content was contained. Overloaded mass of active materials on the flexible electrode was detrimental to improved conductivity. Thus, both the mass loading of active materials and the MnO₂ content were crucial to capacitor performance. The x-NGM composites and graphene (G) were used as the active materials for cathodes and anode, respectively, so the ASSCs were operated simultaneously by two charge storage mechanisms. The synergistic effect enabled better charge storage purposes. Among the supercapacitors, the 3-NGM1//G1 capacitor showed the highest conductivity, more efficient charge transfer, and thereby best capacitive properties. It exhibited a high specific capacitance of 579 F/g, giving rise to the high energy density and power density of 1223.3 Wh/kg and 73153.6 W/kg, respectively. The high retention rate (86.7 %) of specific capacitance after 2000 bending cycles demonstrated good cycle stability of the flexible ASSCs using the x-NGM composites. The best capacitor performance achieved in this work was superior to most literature results, implying that x-NGM composites are indeed promising electrode active materials for flexible ASSCs.

Emerging energy technologies rely on materials, at the same time that the production of these materials relies on an energy supply. To keep a balance between the production of new materials we need to minimise the energy we employ to produce them, starting from which precursors we chose for their synthesis. In this context, we want to unlock part of the technological challenge of upgrading compounds generated from anthropogenic pollution, biomass and industrial by-products. We propose to produce highly efficient and low-cost energy components through the catalytic conversion of waste into non-geopolitically compromised rechargeable Na-ion battery electrodes as a sustainable solution to keep such energy/materials balance.


We present preliminary data on the hydrothermal carbonisation and microwave treatment of different biomass/plastic waste precursors in the presence of environmentally friendly catalysts. We study the relationship of carbonisation treatment with the final microstructure and relate this to the Na-ion absorption mechanism during electrochemical charge-discharge cycles between 2.5 and 0 V.

Hydrogen peroxide (H₂O₂) synthesis generally requires substantial post-reaction purification. Here I will introduce a direct electrosynthesis strategy that delivers separate H₂ and O₂ streams to an anode and cathode separated by a porous solid electrolyte, wherein the electrochemically generated H⁺ and HO₂^- recombine to form pure aqueous H₂O₂ solutions. By optimizing a functionalized carbon black catalyst for 2-electron oxygen reduction, we achieved > 90% selectivity for pure H₂O₂ at current densities up to 200 mA cm^-2, which represents a H₂O₂ productivity of 3.4 mmol cm^-2 h^-1 (3660 mol kg^-1_cat h^-1). A wide range concentrations of pure H₂O₂ solutions up to 20 wt.% could be obtained by tuning the water flow through the solid electrolyte, and the catalyst retained activity and selectivity for 100 hours. As one representative practice, our device demonstrated a continues treatment of total organic carbon in Houston rainwater with a processing rate up to 2180 L m^-2_electrode h^-1 to meet drinking water standards.