Symposium ES07 : New Carbon for Energy—Materials, Chemistry and Applications

The focus of this presentation will be on carbon-based noble metal-free or, as they are often called, platinum group metal-free (PGM-free), electrocatalysts for oxygen reduction reaction (ORR) as an alternative to the state-of-the-art low-PGM catalysts in the polymer electrolyte fuel cell (PEFC) cathode. In the past decade, PGM-free catalysts, especially those obtained by heat-treating precursors of transition metals, nitrogen and carbon, have gradually narrowed the performance gap to precious metal-based materials already used in fuel cell cars. We start by reviewing PGM-free catalyst development at Los Alamos National Laboratory (LANL), part of the DOE-EERE’s Electrocatalysis Consortium (ElectroCat), emphasizing approaches aimed at improving the ORR active-site density and electrode porosity via the use of pore-forming agents and sacrificial templates.

In the second part of this presentation, we will specifically concentrate on the sources of catalytic activity in Fe-based PGM-free catalysts and ORR active sites as a prerequisite for successful development of future noble metal-free catalysts. While of key importance to further progress in PGM-free electrocatalysis, the identification of the ORR active sites in the catalysts is highly challenging due to their embedded nature within the carbon phase and highly heterogeneous catalyst morphology resulting from the high-temperature synthesis process. They make identification and improvement of activity and durability of such sites difficult and often ambiguous. The results from both theoretical modeling and experiment will be presented. Of a number of both in situ and ex situ techniques used for gaining a better insight into the origins of ORR activity in PGM-free catalysts, we will concentrate on the microscopic and X-ray absorption spectroscopic methods, as well as on the implementation of molecular dioxygen analogues as probes for the ORR active sites on the catalyst surface, which makes otherwise bulk techniques surface-specific. This part of the presentation will include research performed in close collaboration with LANL’s ElectroCat partners.

Time permitted, we will report on the activity and durability of catalysts derived from transition metals other than Fe, specifically, Co, Mn and Ni, studied by using once again both modeling and experimental methods. Finally, we will present a few highlights from a continuing comparative study of the degradation of active sites in noble-metal-free catalysts during fuel cell testing.

In this talk, we will present our recent research on carbon-based electrode materials for oxygen electrocatalysis (related to fuel cells) and sulfur transformation (related to metal-S batteries). We investigate elemental doping (including metals, N, O, …) on carbon properties. Broadly speaking, all dopings produce structural or chemical defects in carbon. However, from practical application point of view, not all defects benefit electrochemical transformation reactions. Our research reveals that, while defects (with right composition and configuration) in general are positively related to oxygen electrocatalysis, defects (or functional groups) seem to be unfavorable for sulfur transformation in a battery under conditions relevant to real applications. We will discuss our understanding on defects vs. electrochemical transformation.

One of a grand challenge for large-scale deployment of proton exchange membrane fuel cells (PEMFCs) is to replace platinum group metal (PGM) catalysts with earth-abundant materials for the oxygen reduction reaction (ORR) in acidic media. In this presentation, we report a high-performance atomically dispersed transitiona metal sites (Fe, Co, or Mn) catalysts derived from chemically metal-doped zeolitic imidazolate frameworks (ZIFs) by directly bonding metal ions to imidazolate ligands within 3D frameworks. Although the ZIF was identified as a promising precursor, the new synthetic chemistry enables the creation of well-dispersed atomic metal sites embedded into porous carbon without the formation of aggregates. The size of catalyst particles is tunable through synthesizing metal-doped ZIF nanocrystal precursors in a wide range from 20 to 1000 nm followed by one-step thermal activation. Similar to Pt nanoparticles, the unique size control without altering chemical properties afforded by this approach is able to increase the number of PGM-free active sites. The best ORR activity is measured with the catalyst at a size of 50 nm. Further size reduction to 20 nm leads to significant particle agglomeration, thus decreasing the activity. Using the homogeneous atomic metal model catalysts, we elucidated the active site formation process through correlating measured ORR activity with the change of chemical bonds in precursors during thermal activation up to 1100 °C. In addition to traditional Fe-based catalysts, we will present our latest resrach on Fe-free catalysts through Co and Mn catalyts approaches. The general rules of catalyst design and synthesis to enhance catalyst activity and stability will be extensively discussed.^1-5

References:
1. J. Li, M. Chen, D. A. Cullen, S. Hwang, M. Wang, B. Li, K. Liu, S. Karakalos, M. Lucero, H.G. Zhang, C. Lei, H. Xu, G. E. Sterbinsky, Z. Feng, D. Su, K. L. More, G.F. Wang, Z. Wang G Wu, Atomically Dispersed Manganese Catalysts for Oxygen Reduction in Proton Exchange Membrane Fuel Cells, Nature Catalysis, doi:10.1038/s41929-018-0164-8, 2018.
2. Y. He, S. Hwang, D.A. Cullen, M.A. Uddin, L. Langhorst, B. Li, S. Karakalos, A.J. Kropf, E.C. Wegener, J. Sokolowski, M. Chen, D.J. Myers, D. Su, K.L. More, G. Wang, S. Litster, G. Wu, Highly active atomically dispersed con4 fuel cell cathode catalysts derived from surfactant-assisted MOFs: Carbon-shell confinement strategy. Energy & Environmental Science, doi:10.1039/C8EE02694G, 2018.
3. Wang, Xiao Xia; Cullen, David; Pan, Yung-Tin; Hwang, Sooyeon; Wang, Maoyu; Feng, Zhenxing; Wang, Jingyun; Engelhard, Mark; Zhang, Hanguang; Yanghua He; Shao, Yuyan; Su, Dong; More, Karren; Spendelow, Jacob; Wu, G, Nitrogen Coordinated Single Cobalt Atom Catalysts for Oxygen Reduction in Proton Exchange Membrane Fuel Cells, Advanced Materials, 30, 1706758, 2018.
4. H. Zhang, S. Hwang, M. Wang, Z. Feng, S. Karakalos, L. Luo, Z. Qiao, X. Xie, C. Wang, D. Su, Y. Shao, G. Wu, Single atomic iron catalysts for oxygen reduction in acidic media: Particle size control and thermal activation. Journal of the American Chemical Society, 139, 14143-14149, 2017.
5. G. Wu, K.L. More, C.M. Johnston, P. Zelenay, High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt. Science, 332, 443-447, 2011.

Incredible progress has been made over the past decade in increasing both the oxygen reduction reaction (ORR) activity and durability of platinum group metal-free (PGM-free) polymer electrolyte fuel cell (PEFC) cathode catalysts. For example, electrocatalytic activities approaching those of platinum have been obtained with heated-treated iron-doped zeolitic imidazolate frameworks (ZIFs). With further improvements in these materials and electrodes based on these materials, especially in hydrogen-air performance and long-term performance durability, these materials will become viable for numerous applications, including automotive propulsion power. For the pyrolyzed iron-carbon-nitrogen class of PGM-free materials, it has been determined that variables such as the metal, polymer, and carbon content, as well as the temperature and atmosphere in which the composites are pyrolyzed are important in determining the activity and activity stability of the resulting catalysts. Changing these variables and testing their effect on the resulting catalyst properties is a very time-consuming process and only a limited portion of the composite composition and temperature space have been explored for this broad class of materials. This presentation will describe the development and application of high-throughput methodology to explore the effects of these parameters on the activity and fuel cell performance of iron- zeolitic imidazolate framework-derived ORR electrocatalysts with a variety of transition metal dopants. A multi-channel flow double electrode (m-CFDE) cell was designed and constructed for the simultaneous screening the ORR activity of multiple materials using an aqueous hydrodynamic technique. The high-throughput structural characterization of the materials using techniques such as X-ray diffraction and X-ray absorption spectroscopy and correlation of the phase and atomic structure with ORR activity will be described as will the high-throughput testing and optimization of the electrode composition using a 25-electrode array fuel cell. In addition, the use of in situ multi-sample X-ray absorption spectroscopy to determine the atomic structure of the materials during pyrolysis of the precursors will be presented.

Low-dimensional (0/1/2 dimension) transition metal carbides (TMCs) possess intriguing electrical, mechanical, and electrochemical properties, and they serve as convenient supports for transition metal catalysts. Large-area single-crystalline 2D TMC sheets are generally prepared by exfoliating MXene sheets from MAX phases. Here, a versatile bottom-up method is reported for preparing ultrathin TMC sheets (≈10 nm in thickness and >100 μm in lateral size) with metal nanoparticle decoration. A gelatin hydrogel is employed as a scaffold to coordinate metal ions (Mo⁵⁺, W⁶⁺, Co²⁺), resulting in ultrathin-film morphologies of diverse TMC sheets. Carbonization of the scaffold at 600 °C presents a facile route to the corresponding MoC_x, WC_x, CoC_x, and to metal-rich hybrids (Mo_2−xW_xC and W/Mo₂C–Co). Among these materials, the Mo₂C–Co hybrid provides excellent hydrogen evolution reaction (HER) efficiency (Tafel slope of 39 mV dec⁻¹ and 48 mV_{j = 10 mA cm-2} in overpotential in 0.5 m H₂SO₄). Such performance makes Mo₂C–Co a viable noble-metal-free catalyst for the HER, and is competitive with the standard platinum on carbon support. This template-assisted, self-assembling, scalable, and low-cost manufacturing process presents a new tactic to construct low-dimensional TMCs with applications in various clean energy-related fields.

The oxygen electro-reduction reaction (ORR) is the cathode reaction in fuel cells, an electrochemical energy conversion device envisioned to replace combustion engines for transportation, and with stationary applications as well. While novel platinum nanostructures have allowed decreasing the amount of precious metal required to catalyze the ORR in proton-exchange membrane fuel cells, strong advances in the class of Earth-abundant metal-nitrogen-carbon (Me-N-C) catalysts has attracted a lot of attention. Synthesized above 700 °C, recent Me-N-C catalysts are the object of intense research regarding the nature/structure of their active site, ORR mechanism and stability in a variety of conditions. The electrolyte pH, electrochemical potential cycling, temperature, and presence of peroxide are recognized key factors that can influence the stability.
This presentation will focus on novel understanding acquired on a recent set of Fe-N-C and Co-N-C catalysts comprising, in parallel with atomically-dispersed metal cations covalently attached to the N-doped carbon matrix, a controlled amount of metal-based crystalline structures, down to their complete absence. The synthesis of model Me-N-C catalysts and the coupling of electrochemical studies with spectroscopic techniques revealed important aspects of Me-N-C catalysts regarding the origin of their ORR activity and, perhaps even more importantly, on the fate of the metal-based active sites when subjected to a broad variety of stressing conditions. It will be shown how structure-stability relationship could be established in some cases, but also how unmodified metal coordination is a necessary but non-sufficient criterion for catalyst durability. Due to the intimate integration of the metal in the nitrogen-doped carbon matrix, changes in the physico-chemical properties of the carbon surface will be shown to impact the catalytic properties (activity and selectivity) of the metal-based sites. This will highlight the importance of the properties of the hosting carbon material on metal-based sites, in strong relation with the symposium topic.

We have been studying electrode and electrolyte materials and their interface designs for Li-ion, Na-ion, and K-ion batteries [1]. Yearly paper numbers of Na and K batteries have increased drastically in recent years. Indeed, research and development of high-performance positive/negative electrode materials for Na- and K-ion are conducted actively over the world. Because of larger ionic size of potassium than lithium, much wider variety and unique feature of materials chemistry attract researchers’ interests as post Li-ion battery. New carbons are of great importance for higher energy Na-ion and K-ion batteries. In this talk, we will present our recent studies on phase transition and electrochemical properties of graphite electrode for K-ion batteries compared to some carbons for Li-ion and Na-ion batteries. [1] K. Kubota, S. Komaba et al., “Towards K-ion and Na-ion batteries as “beyond Li-ion,” Chem. Rec., 18, 459 – 479 (2018).

Electrochemical reduction of biomass-derived feedstocks is a critical need to improve conversion efficiencies without the need for generating molecular hydrogen. During an electrochemical hydrogenation (ECH) process, H^● is formed on the surface of the catalyst via reduction of protons supplied by the electrolyte, hydrogenating organic substrates. The feedstock derived from biomass are extremely complex in composition and functionality. Solvents such as water and other organic solvents add an unprecedented level of complexity to the catalyst design and synthesis. Majority of the electrocatalytic reduction studies are mostly carried on simple but versatile electrocatalyst (Pt/C or Pd/C) that have shown superior activity in PEM fuel cells. There is a critical need to understand the impact of electrocatalyst structure and composition on enhancing conversion of biogenic substrates to fuels or intermediates. Here we present our recent progress in modification of carbon felt based electrocatalysts. We have developed synthetic protocols and methods to modify these carbon felt based materials by incorporating heteroatoms such N or O containing polymeric materials. We further engineer the nanostructure by utilizing inorganic structure modifiers to enhance surface area and porosity. We have demonstrated the ability to change the surface area from 2 m2/g to 110 m2/g. The effect of these modifications on incorporation of metal nanoparticles will also be presented by XPS technique. The impact of these structural and chemical modification of the carbon felt based catalysts on electrocatalytic reduction of carbonyl compounds will be discussed.

Despite the advantageous properties, graphene has found limited use in practical applications due to the difficulty of producing appropriate graphene materials in high yield. In particular, a scalable synthesis of graphene materials would benefit electrochemical energy storage applications, i.e., batteries and supercapacitors, by virtue of graphene’s high electron mobility, allowing fast charging and discharging, and graphene’s high surface area, providing a high density of electrochemical active sites for better storage capacities. To overcome this barrier, we have developed a scalable synthesis of high quality vertical graphene nanostripes (GNSPs) via plasma enhanced chemical vapor deposition (PECVD). GNSPs are a class of vertical graphene nanostructures (VGNs), wherein multilayer graphene sheets grow vertically with respect to the growth substrate. This vertical growth allows the graphene materials to be synthesized in high density affording the possibility of scalability, as compared to horizontal sheet graphene. However, typical VGN syntheses require several hours and temperatures in excess of 700 K. In contrast, our GNSPs synthesis is fast and room temperature. In addition, typical VGN syntheses produce short graphene sheets, whereas our GNSPs synthesis produces long aspect ratio graphene materials with dimensions such as 500 nm x 70 μm; long aspect ratios are particularly desired for electrochemical energy storage due to the superior electrochemical activity of graphene edges and the percolation effect of the high aspect ratio graphene that affords greater charge transport. To achieve fast and high quality growth of GNSPs we place a copper foil in a microwave-induced hydrogen/methane plasma under medium vacuum with trace contents of substituted benzene precursors (e.g., 1,2-dichlorobenzene, toluene, etc). The substituted benzene precursor both acts as a seed that initiates growth of the sp²-hybridized graphene lattice and further propagates growth of the vertical graphene materials. In addition, methane radicals and hydrogen radicals act to enhance growth and etch/remove defects, respectively, resulting in high quality graphene materials. Various characterizations have validated the high quality of our GNSPs. The Raman spectrum contains narrow peak widths and peak height ratios that suggest high quality graphene, X-ray photoelectron spectroscopy demonstrates a chemically pure material, ultraviolet photoelectron spectroscopy reveals a work function similar to pristine graphene, and four-point probe measures reveal high electron mobility. Furthermore, the defect content, dimensions and surface areas of GNSPs can be tuned by adjusting the PECVD parameters such as the microwave power, flow rate, pressure, and gas composition. Practical application of graphene, particularly in the field of energy storage, may be achievable by this scalable growth of high quality GNSPs. Preliminary results by substituting GNSPs for a fraction of activated carbon in supercapacitor and metal air battery applications demonstrate superior performance. Further investigation of the correlation between the aspect ratios and surface areas of the GNSPs with the supercapacitor performance will be discussed.

Rational design of oxygen reduction reaction (ORR) electrocatalysts based on earth-abundant elements is critical important towards sustainable energy applications. Among various reported ORR electrocatalysts, transition metal-nitrogen doped carbon (TM-N/C) materials such as Fe-N_x/C and Co-N_x/C exhibit excellent catalytic activity. Nevertheless, comprehensive understanding of these TM-N/C electrocatalytic systems is still lacking, which demands extension of investigation to other TM-N/C systems (Cu, and Mn, etc). Herein, we developed a Cu promoted nitrogen-doped carbon (Cu-N/C) via high temperature pyrolysis of Cu-adsorbed zeolite imidazole frameworks (Cu@ZIF-8). The Cu-N/C electrocatalyst exhibited satisfactory ORR activity with half-wave potential of 0.813 V in 0.1 M KOH electrolyte. Moreover, it also showed excellent methanol tolerance and long-term stability. The enhanced ORR electrocatalytic performance is attributed to the strong synergetic effect between Cu(II)-N ligands and Cu⁰ NPs, sufficient active sites, and fast mass transfer.

To date, various approaches to synthesize zeolitic imidazole frameworks (ZIFs) have been developed, such as solvothermal, sonochemical, microfluidic, and mechanochemistry reactions. However, most of them are time-consuming and involve complex processing steps, thus they cannot rapidly screen potential candidates to obtain ZIFs on demand. Such a challenge calls for efficient synthetic approaches. Herein, we overcome this challenge by employing two nonconventional heating strategies, i.e., microwave- and Joule-heating, which are induced by laser-induced graphene (LIG) microreactors, for rapidly synthesizing ZIFs. In the first reaction, the LIG acts as a susceptor that absorbs electromagnetic energy, which is converted to heat. In the later one, LIG acts an electrical conductor that converts electrical energy to heat. Both two can rapidly heat up the reactor, accelerating the crystal growth for synthesizing ZIFs with well controlled morphology and crystallinity. To demonstrate a conceptual application, a ZIF-67/LIG composite was converted to a Co/CoNC/LIG by a CO₂ laser induction process. It shows great oxygen reduction reaction (ORR) performance with a half-wave potential (E_1/2) of 0.798 V, and superior methanol tolerance and long-term stability. These rapid and facile synthesis methodologies will enable to quickly optimize reaction conditions and fast screen compound libraries for searching new materials, paving a way to high-throughput and autonomous nanomanufacturing.

Hierarchical porous carbon (HPC) as flexible electrode attracts enormous attention due to its favorable structure, which is advantageous for the improvement of supercapacitor capacitance and rate capability. In this research, texture controllable HPC flexible electrode with high capacitive performance is successfully prepared by polymerization induced phase separation method. Solvents with various viscosities and hydroiodic acid with various amounts are used to regulate the texture. Scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), nitrogen adsorption and desorption isotherms, density functional theory (DFT) method are used to characterize or modelling the morphology, micro-pore, specific surface area and pore size distribution, respectively. The desired hierarchical porous structure endows the carbon material with a high specific surface area and ideal transportation paths. The optimized HPC flexible electrode reaches a high specific capacitance of 142.9 F g^-1 at 100 A g^-1 in a two-electrode configuration in 6 M KOH, which is 79.1% of the capacitance measured at 0.2 A g^-1. Furthermore, energy density of the supercapacitor device ranges from 6.27 Wh kg^-1 to 4.23 Wh kg^-1 with the power density ranges from 100 W kg^-1 to 46195 W kg^-1.
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In recent years, research into sustainable and renewable energy resources has attracted much attention due to the increase in concerns about the energy crisis, decreasing availability of fossil fuels and environmental issues. From these points of view, photovoltaic technologies are a highly desirable solution because clean solar energy is supplied indefinitely by the sun. Among various photovoltaic devices, dye-sensitized solar cells (DSSCs) are some of the most promising energy conversion devices because of their low fabrication cost, environmentally friendly nature and high conversion efficiency. Generally, DSSCs consist of four important components: an n-type semiconductor photoanode, a sensitizer (dye), an electrolyte with an iodine or cobalt redox couple, and a counter electrode (CE). For the high performance of a DSSC device, optimization of all components is necessary. In particular, the CE is a very important component in the DSSC device, as it behaves as a catalyst for regeneration of oxidized electrolyte, as well as an electron collector from the external circuit. However, the use of rare metals such as Pt counter electrodes (CEs) is one major drawback of DSSC devices for broad real-life applications. In this regard, alternative materials to Pt CEs have been long sought for DSSCs employing both cobalt and iodine redox couples. Therefore, in this study, soft-templated tellurium-doped mesoporous carbons (Te-SMCs) were synthesized for the first time by the simple pyrolysis of PAN-b-PBA block copolymer in the presence of a tellurium precursor for replacing the Pt CE. To confirm the chemical composition and porosity, the as-prepared Te-SMC materials were evaluated by elemental analysis (XPS, EDS), and nitrogen sorption isotherm measurements. As-prepared Te-SMC materials contained mainly mesopores and retained three-dimensionally hierarchical graphite-like structure with many defect sites. They displayed doping levels with nitrogen of 9.15 atom % and tellurium of 0.15 atom % and had specific surface area of 540 m² g^–1. Therefore, these characteristics enabled the development of a high-performance CE in DSSCs with cobalt and iodine redox couples. As a result of its catalytic performance, Te-SMC exhibited outstanding electrocatalytic activity as well as a much better electrochemical stability than the Pt CE for both redox couples even after 1000 potential cycles. The results show that a maximum conversion efficiency of 11.64 and 9.67 % could be achieved under one sun illumination (AM 1.5 G) for SGT-021/Co(bpy)₃^2+/3+- and N719/I^–/I₃^–-based devices with Te-SMC CEs, respectively and these values are superior to the corresponding device with Pt-CEs.

Recently, the fabrication of high-performance graphene films as electrode materials has become a research tendency for flexible energy-storage devices. Here, we successfully prepared iodine-doped reduced graphene oxide (I-rGO) films with excellent capacitive performance by a simple and versatile technique of iodine steam doping. The iodine as an effective p-type dopant can enhance electrical conductivity of graphene films by charge transfer process, further improving capacitive performance of the devices. The electrochemical properties of as-prepared I-rGO films with different mass loadings were systematically and comprehensively studied. With the change of mass loading (1.5~6.7 mg cm^-2), the gravimetric specific capacitance of I-rGO films remained almost invariable at the studied range of current density, and finally can reach ~150 F g^-1 at 0.2 A g^-1 with 6 M KOH electrolyte, exhibiting the high utilization of electrode materials. With the increasing mass loading, supercapacitors based on the I-rGO films show almost linear growth of areal specific capacitance at any current densities from 1 to 30 mA cm^-2 (eventually reach ~524 mF cm^-2 at 1 mA cm^-2) and nearly no decline of the rate performance. Additionally, we fabricated flexible all-solid-state supercapacitors, which also display excellent areal specific capacitance (~450 mF cm^-2), great cycling stability and favorable electrochemical stability. These results indicate that the fabricated I-rGO films have a great advantage as electrode materials for flexible energy-storage devices.

The hollow interior of CNTs provides a unique environment for the fabrication of novel morphologies by stabilizing novel phases within its cavity (1). Inorganic nanotubes are morphological counterparts of carbon nanotubes. The synthesis and structural elucidation of single walled nanotubes of inorganic compounds is still a challenge (2). In this work, we employ AC electron microscopy imaging and spectroscopy to study a novel morphology of BiI₃ and GdI₃ - SWNTs encapsulated within CNTs. Thus the single walled nanotubes of BiI₃ and GdI₃ phases in this study, are obtained by employing CNT as a nanotemplate. This method involves the capillary filling of BiI₃/GdI₃ within CNT, by annealing the BiI₃/GdI₃-CNT mixture above the melting point of BiI₃ (GdI₃). Aberration corrected electron microscopy and spectroscopy in combination with image simulations are employed to reveal the morphology, structure and composition of these nanotubes. A critical host internal diameter was estimated, for the formation of such single walled nanotubes, based on the electron microscopy images. First-principles density functional theoretical calculations were carried out to determine the stability and electronic properties of these BiI₃/GdI₃ nanotubes. The ultrathin one dimensional morphology of BiI₃/ GdI₃ presented here could lead to novel physical properties and applications (3-5).

References
1. S. Iijima<span>, </span>Nature, 1991, 354, 56-58.
2. Carbon Meta Nanotubes: Synthesis, Properties and Applications, Editors(s): Marc Monthioux, 2011, John Wiley & Sons, Ltd
3. E. A. Anumol, A. N. Enyashin, Francis Leonard Deepak, Single Walled BiI₃ Nanotubes Encapsulated within Carbon Nanotubes,
Scientific Reports 2018, 8, 10133.
4. E. A. Anumol, Franics Leonard Deepak, A. N. Enyashin, Capillary filling of carbon nanotubes by BiCl₃: TEM and MD insight,
Nanosystems: Physics, Chemistry, Mathematics, 2018, 9 (4), P. 1-11.
5. Nitin M. Batra, E. A. Anumol, J. Smajic, Andrey Enyashin, Francis Leonard Deepak and Pedro M. F. J. Costa, J. Phys. Chem C In
Press, 2018.

Among the porous materials, the hybrid porous materials metal-organic frameworks (MOF’s) have attracted attention, due to their potential applications in various fields owing to their inherent qualities like high surface area, large pore volume, active metal sites with ordered and tunable pores. But MOFs have important challenges for practical or industrial applications like moisture stability, conductivity and micro pores. However, non-porous graphene sheets are becoming an inexpensive material, have been proven an outstanding matrix to support various materials, leading to advanced materials for electro catalysis and other energy-related application. Further, hybrids of MOF and Functional Graphene materials or G/MOFs have collaborative properties like conductivity, large internal surface area with hierarchical pores and significant stabilities, which can exploit for the various energy and environmental applications. Herein, we would like to discuss, our recent research interest focused on the synthesis of various novel hybrid Graphene-MOF porous materials by different approaches. The structure and coordination environment thoroughly characterized by various microscopy and spectroscopy measurements. Depends on functional properties of these G/MOFs exploited for environmental oil spills separation from water, hydrocarbon separation and photo/electrochemical water splitting applications.^1-5

K. Jayaramulu, Adv. Mater. 2018, 30, 1705789.
K. Jayaramulu, Adv. Funct. Mater. 2017, 27, 1700451
K. Jayaramulu Adv. Mater. 2017, 29, 1605307
K. Jayaramulu, Angew. Chem. Int. Ed. 2016, 55, 1178.
K. Jayaramulu Adv. Sci. 2018 (10.1002/advs.201801029).

Enhancement in electrochemical energy storage resides in tailored nanotextures resulting from making electrode materials hierarchically nanoporous. The complex interplay of solvent and solute structure and dynamics at the charged interface, the transport of electrolyte ions into and out of the pores, the solvation/desolvation processes occurring in pores approaching bare-ion dimensions, and formation of interfaces via chemical reactions are all important parameters. Herein, several self-assembly synthesis methods for carbon composites as electrode materials for energy storage will be discussed. The objective of this talk is to demonstrate that mesoporous carbons derived from soft-template synthesis not only entail a high storage capacity but also, most importantly, can be made through self-assembly synthesis to have a significantly enhanced electronic conductivity and storage capacity. This enhanced electronic conductivity in 3D architectures is the key to providing high rate capability for the corresponding energy storage systems.

Ultrananocrystalline Diamond (UNCD) films are being investigated due to their unique combination of properties such as high wear resistance, highest hardness relative to any other film, lowest friction coefficient compared with metal and ceramic coatings, corrosion resistance, negative electron affinity, low work function, and high electrical conductivity for Boron (B) doped and nitrogen-grain boundaries incorporated UNCD films. The combination of these properties make doped UNCD films suitable for many applications like Li-ions corrosion resistant coatings for Li-ion batteries’ electrodes, corrosion resistant coatings for metal electrodes for electrolysis-based water purification, thermionic and field emission devices, and future high power electronic devices. B-UNCD films are currently marketed by Advanced Diamond Technologies, but the drawback is that B doping is produced during film growth by hot filament chemical vapor deposition (HFCVD) involving B contamination of the chamber where the film is grown, which can be used only for growing B-doped UNCD or other diamond films. This presentation will describe the results from research and development of a novel process for B doping large area UNCD films by thermal diffusion after growth, thus eliminating the problem of B contamination of the diamond film growth chamber. The research focused on understanding the chemical, structural and electrical properties of the UNCD films before and after doping with B by thermal diffusion. The UNCD films were grown by Microwave Plasma Chemical Vapor Deposition (MPCVD) and HFCVD techniques on SiO₂/ (100) Si substrates. Subsequently, 200-nm thick Spin on Dopant (SOD) coating containing B atoms was grown on the UNCD films. followed by annealing in an atmospheric oven to evaporate any excess solvent from the SOD film. Successive chamber evacuations and purges flowing N₂ were performed to minimize O₂ content in order to avoid the C-based UNCD film being etched by oxygen at the high temperatures needed for Boron diffusion. UNCD films were ultra-sonically cleaned with solvents to remove remaining SOD coating. -doped and as deposited UNCD films were characterized by Raman, XRD, SIMS, UPS, XPS and Hall effect measurements. Raman and XRD analysis confirm that there was no induced graphitization or damage in the UNCD films during the B diffusion process, while SIMS, XPS, UPS and Hall effect analysis confirmed B doping and correlation with changes in electrical properties. The B-doped UNC films exhibit 10^-1Ohm.cm resistivity.
We also explored the synthesis of UNCD films with nitrogen (N) atoms incorporation into grain boundaries,
during HFCVD growth with Ar/CH₄/N₂/H₂ gas mixture flow, and observed that N-UNCD films also exhibit 10^-1Ohm.cm resistivity. Analysis of the N-UNC films revealed that N atoms are inserted in the grain boundaries and satisfy dangling C atoms bonds, providing electrons for electrical conductions We will discuss the conductivity mechanisms in both B-UNCD and N-UNCD films and their potential applications to a new generation of energy related and high power electronic devices.

Lithium dicyanamide (LiN(CN)₂) reacts with phosphorus cyanide (P(CN)₃) in ethereal solution to form a resin, which separates into a second liquid phase, which is then redissolved in acetonitrile or other solvents. The resin can also be prepared in a single solvent in which it remains soluble for several days (pyridine), or indefinitely (propylene carbonate). The resin solution is used to coat metal coupons or disks which are then cured at temperatures of up to 300 °C, forming adherent, ion conducting films. Samples were also prepared in button cells. We characterized the ionic conductivity and chain motions of these films by dielectric relaxation spectroscopy, and the transference number by electrochemical measurements. Additionally, bulk thermoset material was analyzed by elemental analysis. We evaluated how the composition and conductivities of these materials depend on conditions of preparation.

The encapsulation of sulfur within carbon matrices is widely utilized in the cathode of a rechargeable lithium-sulfur battery, whose energy density largely depends on the design of the carbon structure. Here we report an advanced graphene nanocage structure with the capability of hosting both cyclo-S₈ and smaller sulfur molecules (S_2-4). The cage inner cavity is partially filled with S₈ to form a yolk-shell structure that enables free volumetric variation of S₈ during (de)lithiation. In the graphene shell of the cage, S₈ are downsized to S_2-4 to activate extra sulfur loading sites within graphene layers. Importantly, the graphene shell exhibits inward volumetric variation upon (de)lithiation of the loaded S_2-4, and the overall electrode strain is thus minimized. This prototyped design promises an ultimate solution to maximize sulfur loading in carbon matrices as well as to circumvent the polysulfide dissolution problem and boost the commercialization of lithium-sulfur batteries in the future.

Nowadays iodides have been extensively used in electrochemical capacitors in order to boost their energy output. Due to the presence of relatively fast reaction of 2I^-/I₂ redox couple specific capacitance recorded on the positive electrode is extremely high. However, kinetics conditions of this process limit high rate ability of the system, what is its main drawback. Furthermore, other ambiguous issues could be listed as: low energetic efficiency of charging/discharging process at higher voltage range, iodide confinement only in the positive electrode proven by Raman spectroscopy or striking increase of the specific capacitance during long-term performance. Therefore, our object of interest is to fully elucidate processes at carbon/iodide interface. Electrochemical quartz crystal microbalance (EQCM) allows detecting ions fluxes during polarization. It is possible to recognize species responsible for electric double layer (EDL) creation, their exact movement and interactions with water molecules. For detailed studies, a rubidium iodide aqueous solution has been selected using EQCM. It has been revealed that iodide anions do not participate in EDL creation. During negative polarization movement of cations with solvation shell (Rb⁺ *4H₂O) have been described simultaneously with fluxes of H⁺ and OH^-. Notwithstanding, for positive polarization mass change recorded is significantly smaller than it was expected for bare I^-. Therefore, recorded mass have been recalculated to exact species responsible for this phenomenon. It disclosures that OH^- ions are equilibrating the charge in EDL during positive polarization. In order to clarify and confirm this phenomenon rubidium hydroxide have been analysed. EQCM is capable to detect mass change resulting from OH^- movement with satisfactory quality. Moreover, it has been revealed that cations and anions affect their solvation shell. For rubidium hydroxide Rb⁺ ion is hydrated with 2 molecules of water (Rb⁺ *2H₂O). Furthermore, sodium and potassium iodides have been analysed in order to verify versatility of iodide affinity to carbon surface. In all iodide solutions, a confinement of I^- into porosity has been validated, as during positive polarization only OH^- ions were responsible for charge balance. Solvation number of alkali metals (Na⁺, K⁺, Rb⁺) have been experimentally determined by this in-situ technique. Moreover, this work proves that ions adsorption/desorption in aqueous solution reveals very complex mechanism and description of ongoing processes cannot be simplified as long as solvent interaction with ions are considered. Iodide affinity to carbon surface have been clearly demonstrated by electrochemical quartz crystal microbalance.

The electronic structure theory (e.g. density functional theory) and calculations are powerful tools to offer mechanistic insights. Here I will discuss how the electronic structure of carbon controls atoms adsorption, and use this understanding to explain a number of puzzles related with energy applications, including: (1) why structurally similar C forms have distinct binding energies with Li [1], (2) why graphite has a low Na capacity while a high capacity for other alkaline metals [2]. Finally, I will discuss the effects of varying charge and fixed potential in electrocatalysis of graphene [3], which are often neglected in modeling but are important for 2D materials due to their peculiar electronic structure, calling for re-evaluation of their electrocatalytic mechanisms by incorporating these effects into simulations.
[1] Y. Liu et al, Phys. Rev. Lett. Phys. Rev. Lett. 2014, 113, 028304
[2] Y. Liu, B. V. Merinov, W. A. Goddard, PNAS 2016, 113, 3735-3739
[3] D. Kim, J. Shi, Y. Liu, 2018, 140, 9127

Room temperature ionic liquids (ILs) represent a perspective class of electrolytes for energy storage devices, particularly electrochemical capacitors (ECs). However, the relatively high melting point of ILs limits their applicability at low temperature, which is a requirement for commercial ECs. Accordingly, lowering the melting point of ILs down to -50°C, and even beyond, is a great challenge. The first strategy to expand the liquid state of IL electrolytes to sub-zero temperatures is the formulation of binary mixtures. Besides, since ECs are primarily constructed from porous carbon electrodes, and it was already proven that the IL melting temperature maybe depressed under confinement in porous silica, it is interesting to investigate if this effect do also occur with carbons. Three aprotic ILs consisting of the same imidazolium-based cation (EMIm) and FSI, TFSI, BF₄ anions were selected for this study.
The thermal behavior and physico-chemical properties of EMImFSI, EMImTFSI, EMImBF₄ and their binary mixtures with various molar ratios were investigated. Some binary mixtures did not show any first order transition unlike the neat ILs, and remained in the liquid state down to -90°C, where only a glass transition was observed. The temperature dependence of dynamic viscosity and ionic conductivity for pure ILs and their mixtures followed the Vogel-Tamman-Fulcher equation, whilst the density showed a linear decrease. The corresponding Walden plot for pure ILs and their mixtures revealed a high degree of ionicity classifying them as “good ionic liquids”. Hence, by implementing BP2000 carbon (Cabot), carbon/carbon capacitors using binary mixtures (1:1 molar ratio) as electrolytes operated down to -40°C with good performance, contrary to the cells with the parent neat ionic liquids.
In a second part of the research, the effect of confinement in porous carbons – microporous carbon Maxsorb (Kensai), home-made mesoporous carbon and also mesoporous carbon SC2A (Cabot) with average pore sizes of 0.9 nm, 3.7 nm and 9.2 nm, respectively - on the phase transitions of neat ILs has been studied by differential scanning calorimetry. The ILs were adsorbed in preliminary degassed carbons, while varying the ratio (V_C/V_IL) of accessible pore volume of carbon (V_C) and volume of IL (V_IL) from 0.25 to 1.50. When V_C/V_IL increased up to 0.9, the intensity of the peaks corresponding to crystallization and subsequent melting decreased and the melting temperature downshifted to a value depending on the type of IL. For instance, as compared to the neat IL, the melting temperature of EMImTFSI confined in Maxsorb MSP-20X (for V_C/V_IL= 0.9) is downshifted by 6.5°C. Finally, for V_C/V_IL> 1, we did not observe any freezing/melting peak, suggesting that freezing is prevented when ILs are such dispersed within the nanopores that they cannot form an ordered crystal structure. For V_C/V_IL>1, it is also worth noting that the IL glass transition disappeared, whilst it still exists for the two mesoporous carbon matrices.

Raman spectroscopy is one of the most used characterization techniques in carbon science and technology. The measurement of the Raman spectrum of graphene triggered a huge effort to understand phonons, electron–phonon, magnetophonon and electron–electron interactions, as well as the influence of the number and orientation of layers, electric or magnetic fields, strain, doping, disorder, quality and types of edges, and functional groups. I will review the state of the art, future directions and open questions in Raman spectroscopy of graphene and carbon materials, focussing on the effect of disorder, doping, stress.

We report a directional flow-aided sonochemistry (FAS) exfoliation technique that allows for unparalleled control of graphene structural order and chemical uniformity. Depending on the orientation of the shockwave relative to the flow aligned graphite flakes, the resultant bilayer and trilayer graphene is nearly defect free (at-edge sonication graphene "AES-G") or is highly defective (in-plane sonication graphene "IPS-G"). AES-G has a Raman G/D band intensity ratio of 14.3 and an XPS derived O content of 1.3 at.%, while IPS-G has I_G/D of 1.6 and 6.2 at.% O. AES-G and IPS-G are then employed to understand the role of carbon support structure and chemistry in Na metal plating/stripping for sodium metal battery (SMB) anodes. The presence graphene defects and oxygen groups is highly deleterious: In a standard carbonate solution (1M NaClO₄, 1:1 EC:DEC, 5vol.%FEC), AES-G gives stable cycling at 2 mA/cm² with 100% CE (within instrument accuracy), and an area capacity of 1 mAh/cm². Meanwhile IPS-G performs on-par with the baseline Cu support in terms of poor CE, severe mossy metal dendrites, and periodic electrical shorts. We argue that SEI stability is the key for stable cycling, with defects IPS-G being catalytic towards SEI formation. For IPS-G, the SEI layer also shows F-rich "hot spots" due to accelerated decomposition of FEC additive in localized regions.

Lithium sulfur batteries are considered as the next generation batteries due to their high gravimetric energy density up to 350-400 Wh/kg. Highly porous carbon materials with surface areas up to 3000 m²/g play a key role for the performance of such systems. A key requirement is to achieve high sulfur loadings up to 75 wt. % in the cathode and high degree of sulfur utilization. In particular challenging is to identify new electrolytes to achieve high cycling stability. Electrolyte minimization is an often overlooked requirement to achieve high energy densities in prototype cells. The development of porous carbon materials for lithium sulfur batteries requires pore size and polarity tailoring.[1-8] Mesoporous carbon materials are ideally suited as sulfur host for the lithium sulfur batteries. Microporous carbons (d < 2 nm) show high sulfur utilization but the overall sulfur loading is limited to a maximum of about 50 wt % sulfur posing limitations to achieve a high gravimetric energy density. Hard carbons are highly promising anode materials to achieve up to 4000 cycles in a lithium sulfur battery with only minor degradation.[3] Moreover, sodium sulfur batteries can operate with this concept at room temperature.[5,7] The presentation will give examples for pouch cell production, laser cutting, silicon anode integration [9] and fundamental advances for cathode evaluation [10].

[1] J. T. Lee, Y. Zhao, S. Thieme, H. Kim, M. Oschatz, L. Borchardt, A. Magasinski, W. Cho, S. Kaskel, G. Yushin, Adv. Mater. 2013, 25, 4573–4579.
[2] I. Bauer, S. Thieme, J. Brückner, H. Althues, S. Kaskel, J. Power Sources, 2014, 251, 417–422.
[3] J. Brückner, S. Thieme, F. Böttger-Hiller, I. Bauer, H. T. Grossmann, P. Strubel, H. Althues, S. Spange, S. Kaskel, Adv. Funct. Mater. 2014, 24, 1284–1289.
[4] S. Thieme, J. Brückner, I. Bauer, M. Oschatz, L. Borchardt, H. Althues, S. Kaskel, J. Mater. Chem. A 2013, 1, 9225.
[5] M. Kohl, F. Borrmann, H. Althues, S. Kaskel, Adv. Energy Mater. 2016, 6, 1502185.
[6] P. Strubel, S. Thieme, T. Biemelt, A. Helmer, M. Oschatz, J. Brueckner, H. Althues, S. Kaskel, Adv. Funct. Mater. 2015, 25(2), 287.
[7] S. Thieme, J. Brueckner, A. Meier, I. Bauer, K. Gruber, J. Kaspar, A. Helmer, H. Althues, M. Schmuck, S. Kaskel, J. Mater. Chem. A 2015, 3(7), 3808.
[8] G.P. Hao, C. Tang, E. Zhang, P. Zhai, J. Yin, W. Zhu, Q. Zhang, S. Kaskel, Adv. Mater. 2017, 29, 37.
[9] M. Piwko, S. Thieme, C. Weller, H. Althues, S. Kaskel, J. Power Sources 2017, 362, 349-357.
[10] M. Piwko, C. Weller, F. Hippauf, S. Dörfler, H. Althues, S. Kaskel, J. Electrochem. Soc. 2018, 165 (5), A1084-A1091.

Room temperature ionic liquids (ILs) have recently emerged as highly promising electrolytes for a wide range of emerging energy technologies, including next-generation supercapacitors and ion-batteries, due to their high thermal stability, ionic conductivity and wide electrochemical windows. In this presentation, we combine first-principles simulations and synchrotron X-ray characterization experiments to unravel the key structural properties of several imidazolium-based ILs. In particular, we utilize extensive ab initio molecular dynamics simulations to probe the local density distribution and medium-range order of bulk ILs, which can be directly compared and validated by X-ray scattering measurements. Having established this cross-validation, we then compare and contrast via simulation the structural, chemical and electronic properties of the ILs in the bulk and under confinement in sub-2-nm carbon slit nanopores, which serve as as model systems for understanding confinement effects in porous carbon and eventually new carbon chemistry. Our integrated theoretical and experimental approach relates these structural and chemical signatures with the intrinsic cation-anion interactions, by considering ILs with anions having significant differences in the molecular geometry, chemical composition, and charge distribution.

This work was supported by the U.S. Department of Energy at the Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Silicon/Carbon composite anodes for LIBs have been the subject of much research over the past decade, as they are touted to be the material that will enable the arrival, and commercialization, of the 'next-generation' LIB. That being said pernicious problems, ranging from the Si volume change, continuous SEI formation, and loss of Li-inventory in a full cell setting, have hindered its growth. Moreover, characterization of these processes to enable an thorough understanding of structure-property relationships requires either destructive ex-situ methods, or labor and cost intensive in-situ, or in-operando methods that may be out of reach for academic labs or early incubation start-ups. As such, this works attempts to develop of comprehensive understanding of degradation methods of a Si/Carbon composite in a full-cell, through a simple, non-destructive, and easily applicable in-operando acoustic characterization. Through the acoustic measurements, we are able to show a two step SEI formation process, involving a gassing, and non-gassing phase, as well as the gradual time-of-flight (TOF) increase due to the passivation of the Silicon in the full cell. Coupling these results with a comprehensive dQ/dV, and half-cell analysis, we are able to show how quickly the Si passivates in a full-cell setting -- and as such develop a robust characterization methods for future Si/Carbon composite using acoustic techniques. Furthermore, such advances in acoustic in-operando measurements also set the stage for future usage in different battery chemistries, allowing for novel insights by looking at the same problem through a different lens.

Graphitic carbon nitrides have emerged as promising candidates for driving photocatalytic H₂ evolution under visible light, CO₂ reduction, and other renewable energy applications owing to their native high surface area, chemical robustness, and inexpensive synthesis routes.¹ Calcination of various N-rich precursors yields layered C_xN_yH_z compounds with interplanar spacings of ~0.32 nm. Although commonly referred to as “g-C₃N₄”, the average structure of these C_xN_yH_z’s are consistent with polymeric Melon (C₂N₃H) whose in-plane structure is composed of amine (N-H_x) bridged heptazine (C₆N₇) building blocks.² In this view, the in-plane structure is polymerized through bridging N-H units to form “zigzag” chains of heptazine molecules terminated by N-H₂ moieties. However, structural differences between different C_xN_yH_z compounds are not well understood as X-ray diffraction (XRD) and related techniques are limited to the bulk. High spatial resolution techniques, such as transmission electron microscopy (TEM), may be leveraged to investigate the in-plane structure/disorder in C_xN_yH_z compounds.

Here, aberration-corrected TEM at 300-kV under low dose rate conditions (<70 e^-/Ų/s), enabled by the use of a direct electron detector (K2-IS, Gatan), was applied to three C_xN_yH_z powders demonstrating a range in structural condensation. Prior to TEM imaging, the extent of long-range order in each sample was ranked based on the relative Bragg peak broadening observed in XRD patterns. For each sample, large field of view (~60-80 nm) images of the in-plane structure were obtained by imaging regions wherein the extended layers were perpendicular to the incident electron beam. Fourier transforms (FTs) generated from these “in-plane” images from each compound exhibit exceptional spatial resolution compared to that of XRD which is evidenced by the multiple (hk0) reflections observed up to (1 Å)^-1 in the most ordered C_xN_yH_z. When rotationally-averaged FTs are compared to the XRD patterns, a similar trend in Bragg peak broadening is observed suggesting that the low dose rates used have avoided significant structural degradation.

To investigate local variations in the in-plane structure of each C_xN_yH_z, image autocorrelations were computed over 6.5-nm windows covering the entire field of view. Each autocorrelation represents a pseudo Patterson function (PPF), revealing the heptazine-heptazine nearest neighbor (NN) distances/orientations, associated with a particular region. The PPF analysis suggests that the local structure of the most ordered C_xN_yH_z is relatively invariant and possesses a “zigzag” chain structure. In contrast, the more disordered forms exhibit considerable rotational variations in the local hexagonally-coordinated NN motif. To visualize the extent of uniformly-oriented in-plane domains for each material, virtual dark field (VDF) images were generated from the same set of TEM images. VDF images of the most ordered C_xN_yH_z show “domains” covering tens of nanometers whereas in the disordered forms, these domains are much smaller at ~2-7 nm at most.

[1] T.S. Miller et al. Phys. Chem. Chem. Phys. 2017, 19, 15613. [2] B.V. Lotsch et al. Chem. -A Eur. J. 2007, 13, 4969. [3] We gratefully acknowledge the support from the DOE (DE-SC0004954), Gatan Inc. for the use of the K2-IS detector, ASU’s John M. Cowley Center for High Resolution Electron Microscopy and ASU’s Eyring Materials Center.

Hard (non-graphitizable) carbon has emerged as a prospective low-potential electrode material for sodium-ion batteries, but electrochemical performance characteristics reported in the literature vary widely. Such inconsistencies arise due to the complexity of multi-stage sodiation reactions at carbon electrodes, whereby sodium ions can be stored in defect sites, graphitic layers, and/or micropores depending on the particular carbon structure. As an alternative, we are investigating carbon nanofoam papers that are fabricated by infiltrating the voids of carbon-fiber paper with resorcinol–formaldehyde formulations to form porous polymer nanofoam, which is then converted to the conductive carbon analog via pyrolysis [1]. When such materials are tested as free-standing electrode architectures in Na-ion cells they deliver specific capacity >300 mAh g^–1 at a 1C rate and >250 mAh g^–1 at 10C, with an initial Coulombic efficiency near 85% under galvanostatic cycling. The galvanostatic intermittent titration technique (GITT) is used to confirm the relatively high diffusion rate of Na-ions in the defect-mediated charge-storage regime. We attribute these promising characteristics to the high defect concentration of the disordered carbon domains, the 3D-interconnected open porosity of the carbon nanofoam, and the absence of otherwise-required binder and conductive additives in conventional powder-composite electrodes. Our results demonstrate the applicability of carbon nanofoam papers as device-ready, self-supported electrodes and inform the design of related carbon materials for next-generation Na-ion batteries.

[1] J.C. Lytle, J.M. Wallace, M.B. Sassin, A.J. Barrow, J.W. Long, J.L. Dysart, C.H. Renninger, M.P. Saunders, N.L. Brandell, and D.R. Rolison, Energy Environ. Sci., 4 (2011) 1913–1925.

Oxygen reduction reaction (ORR) is one of the most studied reactions for clean energy devices such as fuel cells and metal-air batteries due to its intrinsically sluggish kinetics which often limits device performance. Non-precious transmission metal oxides (TMO) such as Fe₃O₄, MnO_x and Co₃O₄[1] have been intensively probed as alternatives to platinum-based catalysts. To supplement low electronic conductivity of TMOs, they are often dispersed on a highly conductive carbon nanostructure with a large surface area, maximizing catalytically active sites per volume and mass.
We employ a hybrid structure where CeO₂ is deposited/decorated on reduced graphene oxide with extreme surface area and excellent electronic conductivity. Since only the wrinkles and edges contain active sites (binding functional groups) on graphene oxide (GO) while the basal plane is populated with rather inert epoxide groups. To functionalize the GO surface, hydrobromic and/or oxalic acids are used to create hydroxyl or carboxyl groups. The treated GO is then hydrothermally reacted (at 160 °C for 24 h) with the precursor salt of cerium (III) nitrate hexahydrate. Three different kinds of GO/CeO₂ hybrids were synthesized based upon as-synthesize, hydrobromic acid-treated, and an additional oxalic acid-treated GOs.
Results have indicated that hydroxyl groups absorb CeO₂ nanoparticles better and that CeO₂ tethered on hydroxylated GO showed the best performance in acidic media in terms of current density, electron transfer number and onset/half-wave potential, all comparable to the performance of Pt/C. Similar enhanced performance was seen for alkaline media with an exception of enhanced durability compared to Pt/C. An X-ray analysis showed a reoccurring (002) diffraction peaks among most hybrids with the exception of hydroxylated CeO₂/GO hybrids. This suggests the sample exhibit a strong binding of metal oxides to the basal planes of graphene flakes, thus prohibiting graphene restacking. From a series of experimental analyses, it is concluded that a strong tethering of metal oxide particles on the basal plane of graphene is a prerequisite of high ORR performance, and that the particle-graphene interfaces (as opposed to the particle or graphene itself) dictates the performance and reaction route.

This project was funded by NASA Advanced STEM Training and Research (ASTAR) Fellowship.

References:
[1] G. Wu and P. Zelenay, “Nanostructured nonprecious metal catalysts for oxygen reduction reaction.,” Acc. Chem. Res., vol. 46, no. 8, pp. 1878–89, Aug. 2013.
[2] Jana, S. K., Saha, B., Satpati, B. & Banerjee, S. Structural and electrochemical analysis of a novel co- electrodeposited Mn2O3-Au nanocomposite thin film. Dalt. Trans. 44, 9158–9169 (2015).

Hydrogen is considered as one of the most promising future energy carrier due to its high energy density and its production through ethanol steam reforming reaction (SRE) has the potential to be used for its on board production, in fuel cell powered motor vehicles. Nowadays, novel catalysts are investigated for the steam reforming of ethanol reactions in order to achieve high hydrogen yield with low coke formation. One of the novel catalyst is a mesoporous material templated mesoporous carbon. Mesoporous carbon materials are investigated due to their physical and chemical properties, such as electrical and thermal conductivity, mechanical and chemical stability, low density, high surface area, and large pore size. Using the mesoporous materials such as SBA-15, MCM-48 etc. as a template, having a high surface area and pore diameter carbon supports can be synthesized. Generally, hard template method is used to achieve well-defined ordered structure. Sucrose and furfuryl alcohol are used as carbon precursors and for the removal of silica materials, washing with HF or NaOH are applied. In this study, for the first time, silica aerogel was used as silica template. Moreover, sucrose was impregnated to the pores of the mesoporous materials as a carbon precursor. The effect of washing with HF or NaOH, adding silylating agent to silica aerogel in the synthesis and calcination temperature of silica aerogel on the structure of the materials were investigated. The results showed that high surface area materials with Type IV isotherm were synthesized. The carbon materials washed with HF gave higher surface areas compared to the materials washed with NaOH. It was evident that NaOH did not remove the all silica materials. This result also proved with the SEM and EDS analysis, showing the unremoved silica structures in the materials. In addition, washing with HF resulted in highly acidic carbon materials considering TPD analysis. When the silica aerogels which did not contain silylating agent as a template, the final carbon materials gave high surface area and pore diameter. Moreover, the calcination temperature of the silica aerogels did not affect the surface area and pore diameter of the carbon materials. The nickel was impregnated into these materials and they were tested in the steam reforming of ethanol reaction. The carbon material washed with HF suppressed the ethanol steam reforming reaction and favored the ethanol decomposition reaction, giving undesired products CH₄ and CO. The hydrogen yield was 3.8 using the carbon material washed with NaOH as a catalyst.

Holey graphene is a derivative of graphene that has abundant nano-holes on the basal plane of graphene sheets and has shown great potential in electrochemical and biochemical applications. Currently, the most popular synthesis method for holey graphene is the chemical etching approach, during which the mixture of graphene oxide and hydrogen peroxide are heated to generate holey graphene. However, the fundamental mechanism for the hole formation and growth during synthesis has not been fully revealed. To address this problem, this study employs density functional theory simulation to analyze and compare the various reactions between graphene and hydrogen peroxide. Molecular dynamics simulation are carried out to discuss the kinetics of the hole formation and growth. Results show that the carbon atoms around the defect areas on graphene sheets can be removed under high local temperature leaving baby holes on the basal plane. The presence of both hydrogen peroxide and high temperature ensures the cyclic insertion and removal of functional groups around those baby holes, which eventually causes the continuous growth of the in-plane holes.

Transport porosity in activated carbon microstructure plays a key role in determining the electrode performance in electrochemical capacitors. In particular, ultramicropores and mesopores can significantly contribute to the charge storage properties in ionic liquid-based EDLCs. We designed and evaluated several carbons derived from polymer precursors with distinct pore texture that exhibit bimodal porosity in order to study and correlate the effect of transport pores to the ionic liquid-based EDLC performance. This work provided insight into the synergistic influence of pore size distribution in determining the energy, power, voltage, thermal stability and lifetime of the electrochemical capacitor. The performance of the devices was evaluated using several techniques including floating voltage test, 3-electrode measurements, impedance spectroscopy, and constant current charge-discharge test. In this study, we demonstrated excellent voltage stability and good capacitance retention >90% for bimodal carbons with operating voltage up to 3.8V.
In addition, the aforementioned activated carbon materials were used as the cathode materials to fabricate Lithium-ion capacitors. In particular, bimodal activated carbon cathode in conjunction with interconnected carbon onion anode shows excellent power and energy density. Hence, we were able to fabricate a capacitor with energy and power density of 52 Wh/kg at 7.3 KW/kg, respectively. The device showed outstanding capacitance retention of 80% after 21000 cycles and remarkable energy efficiency of >90%. Additionally, the temperature stability of the device was tested ranging from room temperature to 60°C.

Li-ion batteries (LIBs) as a promising energy storage device have been widely used in portable electronics, power tools, and electric vehicles due to their high electrochemical potential, superior energy density and long cycle life. Considering the relatively high theoretical capacity (170 mAh g^-1), cost effectiveness, long cycle life, good thermal stability, and environmental friendliness, lithium iron phosphate (LiFePO₄, LFP) has been demonstrated as a suitable cathode material for LIBs. However, key limitations of LFP are its low intrinsic electronic conductivity (10^-9-10^-10 S cm^-1) and limited lithium ion diffusion channel, leading to poor rate capabilities in LFP batteries. To overcome the drawbacks of LFP, an effective way to increase conductivity is combining LFP with conductive materials. Carbon-based materials such as graphite, carbon black, graphene, and carbon nanotubes are one of the best conductive materials for LFP. Especially, carbon quantum dots (CQDs), a new type of carbon-based material, are also of high interest due to their high surface area, low toxicity, cost-effectiveness, and controllable size. However, CQDs contain a high amount of sp³ carbon, resulting in low conductivity. In this work, we investigate high-quality graphitic CQDs with diameters below 10 nm for improving the conductivity of LFP. CQDs could play a key role in energy storage for improving the electrical conductivity and charge transfer reactions in LFP batteries, since increasing the ratio of sp² to sp³ carbon exhibits better electronic conductivity, resulting in enhanced battery performance. We report the synthesis of CQDs by a hydrothermal method at different reaction temperatures (160°C to 200°C) and times (60 min to 180 min) from organic materials. High-quality graphitic CQDs are produced by using a dehydrogenation reaction. The morphology and size distribution of CQDs were characterized by transmission electron microscopy (TEM). The chemical bonding states and sp²/sp³ ratio of synthesized CQDs were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS).

Limitations of capacitive deionization (CDI) technology and future commercialization efforts are intrinsically bound to electrode stability. In this work, novel regeneration methods are explored which mitigate previously explored degradation mechanisms. Electrode-exchange studies indicate that only the anode undergoes degradation over cycling, during which both the physical and chemical properties change evidently. In particular, acidic functional groups, which are derived from the reported oxygen-containing functional groups, are formed in the anode during cycling and these account for the potential of zero charge (PZC) change of the anode, thereby degrading the overall performance of the cell. Annealing treatment of aged electrodes suggests that low temperature thermal treatments can recover the degraded properties of anode and therefore regenerate the performance of the CDI cell. Thus, the lifetime of electrode can be prolonged by applying intermittent annealing treatments once the severe degradation becomes observable. The regeneration mechanism studies also offer insights into strategies for minimizing electrode degradation or in-situ regeneration as the technology gains momentum for future commercialization.

Recycling natural carbonaceous feedstocks for alternative applications beyond burning would provide new opportunities for these materials. For example, new technologies using coal or coal-derived byproducts such as tar and pitch could be engineered to produce thin films for electronics with highly tunable electronic properties. In this work, we illustrate how laser ablation can be used to control the properties of natural carbonaceous materials (coal, tar, pitch) in order to tailor their electronic, magnetic, and optical behavior. This approach enables the use of carbonaceous feedstocks in variety of applications at extremely low cost (i.e. coal at 0.05$/kg, tar at a negative cost). We will present recent work on applications ranging from transparent heater, transistors, and flexible/stretchable electrodes. Furthermore, the laser process can also be integrated into large scale, continuous manufacturing techniques.

One of the most significant challenges in developing nanoscale carbon devices is efficiently and precisely producing the carbon. Two recent developments make this possible with carbon nanofibers. The first is a fast, low-cost method of producing catalyst for carbon deposition. A nontraditional processing route of mechanical alloying is used to produce unique catalytic materials that exhibit enhanced kinetics. The second advancement is the ability to create integrated devices in situ. This allows carbon nanofibers to be created in specifically designed geometries with controllable properties. These nonwoven structures can be made with densities as low as aerogels or much higher, allowing the fiber spacing to be varied and a high surface area to be compact and flexible. Carbon nanofibers have been proposed for applications ranging from supercapacitors to hydrogen storage to filtration. Multiscale control has been demonstrated by producing free-standing structures centimeters in scale, and carbon nanofibers have been integrated with traditional carbon materials to create unique hybrids. The methods and capabilities, as well as key device applications, are highlighted.

Carbon aqueous symmetric supercapacitors are attractive supercapacitor devices owing to the low-cost and high conductivity of porous carbons. However, the limited capacitive charge storage process in carbon symmetric capacitors in comparison to pseudocapacitors or asymmetric supercapacitors severely limit the energy density. The only effective strategy to enhance the energy density of carbon aqueous symmetric supercapacitor is to extend the cell voltage beyond the thermodynamic stability of aqueous electrolytes (1.23 V).
Also, in recent studies, researchers have focused on preparing high-performance carbon electrodes from commercial carbon fiber clothes by activating the surface usually through chemical and electrochemical routes. However, it is still a major challenge to realize a comprehensive electrochemical performance of high capacitances, excellent rate capability, stability and wide operational potential windows in the activated carbon fiber clothes.
Herein, we successfully activated the surface of commercial carbon fiber clothes using a facile-one-step air calcination at 400 ^oC for 6 hours strategy to realize a remarkable improvement in the surface area, porosity, and electrochemical performance. The successful activation of carbon fiber clothes is fully confirmed through BET tests, SEM, TEM, Raman and contact angle measurement tests. Specifically, the activated carbon exhibits a 450-fold increase in specific surface area (615 m² g^-1 for the activated carbon fiber clothes) as well as rich microporosity, excellent conductivity, and superhydrophilicity, which would be beneficial in realizing easy electrolyte penetration and excellent capacitive performance. As expected, the activated carbon fiber cloth achieves ultrahigh areal capacitances of 1553 and 1600 mF cm^-2 at 1 mA cm^-2 in wide positive and negative potential windows, good rate capability and excellent cycling stability up to 20000 cycles in 1 M Na₂SO₄ electrolyte compared to a lowly capacitance of 1.53 mF cm^-2 for the commercial carbon fiber clothes. Owing to the large overpotential for hydrogen and oxygen evolution, the activated carbon fiber cloth based symmetric supercapacitor is stable in a wide cell voltage of 2.0 V, displaying high volumetric and gravimetric energy densities of 7.62 mWh cm^-3 and 18.2 Wh kg^-1, respectively. The stability in this wide potential window is again confirmed using float voltage test method.
These results not only report one of the best electrochemical performance of activated carbon fiber clothes, but it also provides an effective and simple calcination activation method for realizing high capacitances and takes advantage of the wide operating voltage window to achieve high energy density in carbon textile supercapacitors. Importantly, our studies also showed that the electrochemical performances of metal oxides grown on carbon fiber clothes and annealed in air at 400 ^oC might be over-estimated as that temperature is sufficient to activate the surface of the carbon fibers.

References:
1. Advanced Materials, 2013, DOI: 10.1002/adma.201304756
2. Advanced Materials, 2013, DOI: 10.1002/adma.201304137
3. Advanced Materials, 2015, DOI: 10.1002/adma.201500707
4. Nature Communications, 2017 DOI: 10.1038/ncomms14264

Ultracapacitors, due to their high specific power, long cycle life, and ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells, have attracted considerable attention for commercial applications such as plug-in hybrid electrical vehicles. Functionalization of activated carbon powders with oxygen and nitrogen redox-active functional groups plays a dual role in i) incorporating pseudocapacitance along with double-layer capacitance and ii) providing anchoring points for further incorporation of stable metal/metal oxide nanoparticles to improve the energy density of the ultracapacitors of interest. We report here the sequentially doped commercial scale, microporous activated carbon (AC) with various amounts of oxygen and nitrogen moieties, and fabrication of the functionalized AC into monolayer and macroscopic (5 µm and 100 µm thick respectively) carbon powder electrodes structures. A comparison of electrochemical performance metrics in acidic and alkaline electrolyte indicates that the monolayer electrode configuration yields a significantly enhanced capacitance (250 F/g) than that of the macroscopic electrode (135 F/g), primarily due to increased accessible specific surface area, reduced diffusion length of the electrolyte molecules and reduction of contact resistance. While the behavior of pseudocapacitance and double-layer capacitance was clearly manifested in the monolayer electrode configuration, the macroscopic electrode configuration did not display these characteristics, prossibly due to a large potential gradient. We have demonstrated that the capacitance of AC based ultracapacitors can be significantly enhanced by incorporating functional groups within the interior pores of the AC powders, which can be of benefit to commercial devices.

All-solid-state batteries (ASSBs) with ceramic-based solid-state electrolytes (SSEs) and lithium metal anode enable high safety and high energy density that are inaccessible with conventional lithium-ion batteries. However, the large interfacial resistance between Li and SSEs has significantly hindered the development of ASSBs. Take Li/garnet SSE system as an example, garnet presents “lithiophobic” surface and poor contact with Li metal anode. To date, several groups have proved that coating a layer of “lithiophilic” material on garnet can improve the Li/garnet contact by the interfacial reaction. Here, we report a new strategy to solve the interface problem by adding carbonaceous materials into Li metal. The lithium-carbon (Li-C) composite shows dramatic change in wettability with garnet due the increased viscosity. The carbon can be graphite, carbon nanotube, graphene or their mixture. An intimate Li-C/garnet interface have been demonstrated and delivered a much smaller interfacial resistance compare to pure Li/garnet.

Due to the temporal, fluctuating character of sustainable energy and the increasing use of rechargeable electronic devices, there is an urgent need for the development of more efficient electrochemical energy storage technologies. Electrical double-layer capacitors (also known as supercapacitors) have become attractive due to their rapid charge-discharge rate, high power density, long lifetimes, remarkably low prize base, and potential sustainability of the involved materials. The use of ionic liquids (ILs) as electrolytes with a wide electrochemical stability window is the most promising strategy to improve the poor energy density of supercapacitors but the actual energy storage mechanism in absence of a solvent in the electrolyte remains poorly understood. Charge storage in a compression double-layer is not possible in ILs and thus new energy storage terms such as order-disorder transitions or solvation-desolvation processes likely play a rather important role. It will be shown that strong metal oxide-support interaction is crucial to activate high energy storage modes of carbon-supported hybrid electrodes in IL-based supercapacitors.
Although it is well known that conductive supports can influence the electrochemical properties of metal oxides, insights into how metal oxide-support interactions can be exploited to optimize joint energy storage properties are still lacking. We report the junction between α-Fe₂O₃ nanosplotches and phosphorus-doped mesoporous carbon (CMK-3-P) with strong covalent anchoring of the metal oxide. The enhanced oxide-carbon interaction in CMK-3-P-Fe₂O₃ is strengthening the junction and charge transfer between Fe₂O₃ and CMK-3-P. It enhances energy storage by intensifying ionic liquid coupling at the 3-phase boundary. Synergistically, density functional theory simulation reveal that strong metal oxide-support interaction increases the adsorption energy of ionic liquid to -4.77 eV as compared to -3.85 eV of physical-bonded CMK-3-Fe₂O₃ hybrid. In spite of the comparably lower specific surface area and an apparently similar energy storage mechanism, the CMK-3-P-Fe₂O₃ exhibits superior electrical double-layer capacitor performance with a specific capacitance of 179 F g^-1 at 2 mV s^-1 (0-3.5 V) in comparison to Fe₂O₃-free CMK-3 and CMK-3-P reference materials resulting from the strong junction between carbon and metal oxide. This principle for design of hybrid electrodes is applicable for future rational design of stable metal oxide-support electrodes with energy storage modes for supercapacitors which are beyond traditional double-layer compression.

Porous functional carbons stand out for their special physical and chemical properties, including high chemical stability, large surface area, high porosity and good conductivity, and have been regarded as the most promising candidates for gas separation, energy storage and electrocatalysis. Recently, one sees rising attention for the development of designer carbons with controlled structure and local material composition, due to this enormous potential in practical application. However, it is still difficult to achieve preconceived carbon structures, which is ascribed to the irregular nature of current synthetic methods. Consequently, we strongly need approaches to circumvent this limitation, in which one possible way is to use the suitable precursors with “encoded information”.
Here we present a new class of well-defined C₂(NOS)₁ carbons that have both high content of N/O/S heteroatoms and large specific surface area (up to 1704 m² g^-1), which can be efficiently synthesized by the simple condensation using gallic acid and thiourea as the bulding blocks. To be noted, as a multi-functionally inexpensive natural chemical, gallic acid is well known to decarboxylate into pyrogallol at higher temperatures, so that the carboxylic acid unit can be regarded as a “protecting/leaving group” that enables a controlled substitution chemistry to realize the high structural definition. In this synthesis, thiourea is the direct source for both nitrogen and sulphur after decomposing at 180 ^oC with abundant generation of ammonia and thiocyanic acid. The obtained 1,4-para tri-doped C₂(NOS)₁ carbon achieves not only a high CO₂ adsorption capacity (66 cm³ g^-1 at 273K), a high CO₂/N₂ selectivity (47.5 for a 0.15/0.85 CO₂/N₂ mixture at 273K), but also an excellent specific capacitances of 255 F g^-1 (0-3.5 v) as a symmetric supercapacitor electrode. The good performance could be attributed to the strong binding of CO₂ and electrolyte ions on the strongly polaring carbon surface and well- defined porosity. In virtue of the simplicity of the salt flux synthetic method and the advantage of the available sustainable starting monomers, the C₂(NOS)₁ framework has potential for use in various practical applications.

Supercapacitor, a promising energy storage solution of the future, can meet the demand for our escalating energy storage needs for electric vehicles and the implementation of renewable energy. However, high cost and low energy density are preventing its wider adoption.
Within a supercapacitor device, the carbon electrodes are the costliest material, contributing up to half of a device’s raw material cost. Efforts in finding an alternative supercapacitor electrode carbon are needed to minimize its cost.

Lignin, an underutilized renewable industrial waste and a major component in plants, can be the alternative supercapacitor electrode carbon precursor. It has been estimated that 50 million tons of lignin are produced annually in the US just from the paper and pulp industry alone. Because of lignin’s structural complexity and hyperbranching nature, researchers struggle to design lignin-derived carbon with a controllable morphology. Currently, lignin is mostly burned for heat and electricity.

In this study, we utilized the abundant thermal sensitive linkages present on lignin. By fine-tuning their crosslinking via a simple thermal stabilization step in air alone or with a 10% acrylonitrile-butadiene rubber (NBR) dope, the derived carbon’s porosity and morphology can be controlled. Because a supercapacitor’s performance directly correlates to the electrode carbon’s porosity, when made into supercapacitor electrode, the resulting lignin-derived carbon capacitance can be improved.

The increased degree of lignin and NBR-doped lignin crosslinking was first revealed from differential scanning calorimetry and thermogravimetric analysis by their thermal stability. After a one-step carbonization and chemical activation with potassium hydroxide, we found that NBR doping prior to carbonization and activation-induced macroporosity in the derived carbon. When porosity was further studied with nitrogen adsorption-desorption experiments, it was revealed that NBR doping improved lignin-derived carbon from 1750 m²/g to 2120 m²/g due to NBR templating. Thermal stabilization in air, however, reduced carbon’s surface area to 1585 m²/g. We hypothesized the drop was due to the change in lignin’s molecular weight and the shrinkage force induced from the additional crosslinking.

When the lignin-derived carbon was made into supercapacitor electrodes, as expected from the improved porosity, NBR doping improved lignin-derived carbon’s capacitance from 175 F/g to 215 F/g. On the contrary, thermally stabilized lignin displayed a reduction of capacitance to 154 F/g. The best performing NBR-doped lignin-derived carbon electrode was then further tested with its long-term capacitance cyclability by cycling for 5000 cycles and showed an impressive 100% capacitance retention, suggesting a desirable electrochemical reversibility and stability. The 22% improvement in lignin-derived carbon’s porosity and capacitance demonstrated the feasibility of using simple NBR doping of lignin for an alternative supercapacitor electrode carbon source.

Graphite dual-ion batteries represent a potential battery concept for large-scale stationary storage of electricity, especially when constructed free of lithium and other chemical elements with limited natural reserves.¹ Owing to their non-rocking-chair operation mechanism, however, the practical deployment of graphite dual-ion batteries is inherently limited by the need for large quantities of electrolyte solutions as reservoirs of all ions that are needed for complete charge and discharge of the electrodes. In this work, we will provide a balanced analysis of the overall cell-level energy density of graphite dual-ion batteries as a function of electrolyte concentration and cathodic capacity of graphite. We will discuss also other issues associated with this technology, one being the low oxidative stability of most metallic current collectors at high potentials of 4.5-5 V vs. Li⁺/Li.^2,3 Finally, we will present a novel lithium-free graphite dual-ion battery utilizing a highly concentrated electrolyte solution of 5 M potassium bis(fluorosulfonyl)imide in alkyl carbonates.¹ The resultant battery offers an energy density of 207 Wh kg⁻¹, along with a high energy efficiency of 89% and an average discharge voltage of 4.7 V.

References

[1] K.V. Kravchyk, P. Bhauriyal, L. Piveteau, C.P. Guntlin, B. Pathak, M.V. Kovalenko. Nature Communications, 2018, 9, 4469.
[2] S. Wang, K.V. Kravchyk, A.N. Filippin, U. Müller, A.N. Tiwari, S. Buecheler, M.I. Bodnarchuk, and M.V. Kovalenko. Advanced Science, 2017, 1700712.
[3] M. Walter, K.V. Kravchyk, C. Böfer, R. Widmer, and M.V. Kovalenko. Advanced Materials, 2018, 1705644.

Carbon-based catalysts play an important role in energy conversion devices such as fuel cells, metal air batteries and electrolysers. The group of Me-N-C catalysts (with molecular MeN₄ sites) is formed by a high-temperature pyrolysis of metal, nitrogen and carbon precursors. Sulfur addition can be used to increase the density of MeN₄ sites [1-3]. But sulfide species might also play an important role as active sites for some catalytic reactions, as shown for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In addition to this, in our recent work we showed that the integration of carboxylic groups in close vicinity to active sites can be used to tune the catalytic activity [4-5].
In this work, we will present different strategies of multi heteroatom doping for tuning the OER activity and stability of cobalt-based catalysts [6] as well as ORR activity and selectivity of Me-N-C catalysts. It will be shown that with the integration of dopants all three parameters, namely activity, selectivity and stability, can be tuned to optimize the catalysts for the desired applications.
References:
[1] Herrmann, I.; Kramm, U. I.et al. J. Electrochem. Soc. 156 (2009), B1283.
[2] Kramm, U. I.; Herrmann-Geppert, I.et al. J. Mater. Chem. A 2 (2014), 2663.
[3] A. Shahraei, I. Martinaiou et al., Chem. Europ. J. 24 (2018), 12480.
[4] M. Busch, N.B. Halck, , Nano Energy, 29, (2016), 126.
[5] N. Weidler, D.J. Babu et al., ECS Trans 80 (2017), 691.
[6] A. Shahraei, M. Kuebler et al., J. Mater. Chem. A. 6 (2018) 22310.

Due to the high energy density and abundance of sulfur, lithium-sulfur (Li-S) batteries are attracting broad interest. However, several hurdles need to be tackled before commercialization. For example, the batteries experience the polysulfide shuttle effect in cathode and dendrite growth in the lithium metal anode. Herein, for the first time, a mesoporous carbon sphere (MCS) that simultaneously boosts the performance of the sulfur cathode and the metallic lithium anode was designed in this work. The MCS homogenizes the flux of lithium ions and inhibits the growth of lithium dendrites, due to its high-surface-area honeycomb structure and abundance of nitrogen sites. Upon covering multiple mesoporous carbon spheres (CMCS) with a layer of amorphous carbon, individual carbon cage encapsulated sulfur inside. This reduced the polysulfide shuttle, which improved the cycle-stability of the Li-S battery. As a result, the Li@MCS cell exhibited a small overpotential of 29 mV and long lifespan of 350 h under the current density of 1 mA cm-2 for the cycling performance. Meanwhile, the S@CMCS maintained 200 cycles from the capacities of 411 mAh g-1 to 400 mAh g-1 at a current density of 2 C (3350 mA g-1). Based on the above excellent performance, the full Li-S cell assembled with Li@MCS||S@CMCS showed much higher capacity than S@CMCS1100||Li@Cu. This research developed a tunable functional material that improves the anode and cathode performance of full Li-S batteries.

The demand for high performance energy storage systems, such as electrical vehicles and electric storage stations has increased dramatically. Low temperature carbon (LTC) prepared at low temperatures (<1200 ^oC) and carbon nanotubes (CNTs) composite has attracted considerable attention due to LTC’s high reversible capacity and physical and chemical merits of CNTs, which supplement LTC’s structural instability and low electrical conductivity. Despite the recent advances in LTC-CNT electrodes, there are still remaining critical issues limiting commercialization. The most difficult one is controlling the state of CNTs in LTC since the aggregation of CNTs resulted in undesirable structure and increased electrical resistance. These aggregated CNTs also lower the surface coverage of CNTs within the LTC, interrupting the electrons on CNTs to meet ions in the LTC and consequently decreasing the accessible redox sites. Therefore it is essential to control the aggregation of CNTs in materials to fully utilize the merits of CNTs and guarantee the accessible redox sites, which is denoted as maximizing ‘triple junction’ where ions and electrons meet, suggesting that the origin of the high electrochemical performance is the perfect harmony of ion, electron, and redox sites together.

Herein, N-doped hierarchical porous carbon with highly aligned CNTs was prepared by co-polymer single nozzle electrospinning, carbonization, and KOH activation. Densely and uniaxially packed CNTs not only improve the electrical conductivity but also act as a structural scaffold, enhancing electrochemical performance of the anode. A partially graphitized N-doped LTC shell was designed to expand the redox sites from the surface of the material to the whole material by having a rapid ion accessible pore network and abundant redox sites. This material exhibited a superior reversible capacity of 1814.3 mA h g^-1 at 50 mA g^-1, and 850.1 mA h g^-1 at 1000 mA g^-1. Furthermore, comparative electrochemical analysis enabled that the use of CNTs, template polymer and KOH activation have their own effect on this material’s superior electrochemical results including rate capability, cycle stability and high reversible capacity. This study not only analyze the synergetic roles between uniaxially packed CNTs and LTC, but also suggest the rational design of the ideal structure of CNT-based carbonaceous 1D anode material to maximize triple junction.

Nowadays, lithium-ion battery is the most mature and most used technology in the market. The optimization of the storage properties of batteries requires either the search for new materials offering specific capacities which are superior to current materials either the miniaturization of electrode materials. Incorporation of nanomaterials with high specific capacities has proven to be an effective method to improve the electrochemical performance of the lithium-ion battery. The present work explores a promising and original approach for the implementation and the development of a new bottom-up technique for hierarchical hybrid nanostructured electrodes based on vertically aligned carbon nanotubes (VACNTs) decorated with nanoparticles (NPs), i.e. NPs@VACNTs.The non-metallic lithium battery is composed of Li₂S@VACNTs as positive electrode and Si@VACNTs as negative electrode. This battery provides a theoretical energy of 1500 Wh kg^-1, which is four times more than the theoretical energy of existing lithium-ion batteries based on LiCoO₂ and graphite (~ 364 Wh kg^-1). Moreover, the nanostructured design of the two electrodes overcomes the problems associated with the use of sulfur compounds and silicon in lithium-ion batteries, including poor electrical conductivity and large volumetric variations. [1-2] This hierarchical hybrid nanostructured electrodes battery with long life and low cost shows a surface capacity of 2 mAh.cm^-2 based on the mass of the active material in the electrode.
[1] S. Rehman et al, J. Mater. Chem. A, 2017, 5, 3014-3038
[2] A. Gohier et al, Advanced Materials, 2012, 84, 2592-2597

Carbon has recently been recovered from discarded tires and demonstrated a high capacity, higher rate capability and the potential to replace commercial graphite as an active anode material in lithium-ion batteries. The tailored morphology of the tire-derived carbon using a sulfonation process followed by pyrolysis yielded a high-quality carbon and the applicability of these hard carbons was demonstrated in several intercalation batteries including lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries. We will report on our recent neutron studies on the surface chemistry of the carbon material, vibrational spectroscopy of the molecular structure, chemical bonding such as C-H bonding, and intermolecular interactions of the tire-derived carbon materials. Commercial graphite and unmodified/non-functionalized tire-derived carbon are also used for comparison. A capacity of over 200 mAh/g was achieved for carbon electrodes with Na-ion intercalation batteries. It is also possible to achieve even enhanced capacities by ball milling carbon with Sb for Na-ion batteries. We will also report the current status of the tire-derived carbon composite powder scale up efforts and its use in energy storage applications.

Hollow carbon spheres (HCSs) with diverse shell structures and inner space have attracted much attention owing to their wide applications in different fields such as adsorption, catalysis, energy storage, etc. Up to now, extensive synthetic strategies have been developed to obtain HCSs. Herein, we propose a dual-template assisted route, using volatile alkane as hollow-forming soft template and organosilane as in situ hard template for the first time. The obtained HCSs possess carefully controlled characteristics, including tailed outer diameters (0.5~1 μm), controlled shell thickness (50~100 nm), specific surface area (1500~2500 m² g^-1) and pore volume (1.5~2.7 cm³ g^-1). Adjustable pore structure of HCSs can realize function-orientated applications. When used as the electrode materials for supercapacitors, hierarchically porous HCSs demonstrate an energy density of 23 Wh kg⁻¹ at a high power density of 25 kW kg⁻¹. In addition, these HCSs can served as sulfur host for Li-S battery, resulting in superior long-cycle stability and rate performance.

Lithium ion batteries (LIBs) are ubiquitous in portable electronic devices and electric vehicles. The ever-increasing material cost and uneven distribution of lithium resources limit their applications in large-scale energy storage system [1]. Sodium ion batteries (SIBs) have been considered a cost-effective alternative to LIBs because of the abundant sodium resource and similar working principle [2]. However, the sluggish kinetics arising from the slow ion and electron transport particularly at high charge/discharge rates is the main bottleneck hampering the widespread application of SIBs, requiring to enhance their reaction kinetics [3]. An effective strategy to address this challenge is to synthesize electrode materials with a desired morphology, nanoscale dimensions having a large surface area. Here, we design and fabricate a 2D MoSe₂@NPC/rGO composite consisting of few-layer MoSe₂ encapsulated by N/P co-doped carbon and reduced graphene oxide (rGO) via simple polymerization reactions followed by selenization. The 2D nanosheet structure effectively shortens the ion diffusion length, while the few-layer MoSe₂ active material exposes a large surface area to the electrolyte. The rGO sheets intercalated within the MoSe₂@NPC/rGO composite function as both channel for fast electron transfer and substrate for rapid surface reactions. Highly reversible sodiation/desodiation cycles of MoSe₂ is confirmed by ex-situ XRD, ex-situ XPS and TEM. As a result, the composite anode delivers an excellent capacity of ~400 mAh g⁻¹ at 500 mA g⁻¹ after 300 cycles. Even at a high current density of 10 A g⁻¹, it maintains a high capacity of ~250 mAh g⁻¹, demonstrating superior rate capability and long-term cyclic stability.

References
[1] J. Cui, S. Yao, J.-K. Kim, Recent progress in rational design of anode materials for high-performance Na-ion batteries, Energy Storage Mater. 7 (2017) 64–114.
[2] S. Yao, J. Cui, J.Q. Huang, Z.H. Lu, Y. Deng, W.G. Chong, J. Wu, M. Ihsan Ul Haq, F. Ciucci, J.K. Kim. Novel 2D Sb₂S₃ nanosheet/CNT coupling layer for exceptional polysulfide recycling performance. Adv. Energy Mater. 8(24) (2018) 1800710.
[3] J. Wu, Z. Lu, K. Li, et al. Hierarchical MoS₂/Carbon microspheres as long-life and high-rate anodes for sodium-ion batteries, J. Mater. Chem. A, 6 (2018) 5668-5677.