Enhanced Photoelectrochemical Water Splitting with Doped Transition Metal Dichalcogenide Nanofilms

Cansu Ilhan^1,3,4, Ievgen Nedrygailov^1,2, Ross Smith⁴, Jun Lin³, Christopher Kent^1,5, Ian M. Povey^2,3, Colm O'Dwyer^1,2, Salvatore Lombardo⁶, Giuseppe Nicotra⁶, Paul K. Hurley^1,2,3, Mick Morris^1,4, Dara Fitzpatrick⁵, Justin D. Holmes^1,2, Scott Monaghan^1,2,3

AMBER Research Centre, Environmental Research Institute, University College Cork, Ireland¹;

Department of Chemistry, University College Cork, Ireland²;

Tyndall National Institute, University College Cork, Ireland³;

CRANN, Trinity College Dublin, Dublin, Ireland⁴;

BARDS, Cork, Ireland⁵;

CNR-IMM, Catania, Italy⁶.

Cansu Ilhan^1,3,4, Ievgen Nedrygailov^1,2, Ross Smith⁴, Jun Lin³, Christopher Kent^1,5, Ian M. Povey^2,3, Colm O'Dwyer^1,2, Salvatore Lombardo⁶, Giuseppe Nicotra⁶, Paul K. Hurley^1,2,3, Mick Morris^1,4, Dara Fitzpatrick⁵, Justin D. Holmes^1,2, Scott Monaghan^1,2,3

AMBER Research Centre, Environmental Research Institute, University College Cork, Ireland¹;

Department of Chemistry, University College Cork, Ireland²;

Tyndall National Institute, University College Cork, Ireland³;

CRANN, Trinity College Dublin, Dublin, Ireland⁴;

BARDS, Cork, Ireland⁵;

CNR-IMM, Catania, Italy⁶.

Photoelectrochemical water splitting to produce hydrogen fuel from solar energy conversion has been a hot topic for at least the past few decades. Nevertheless, Solar-to-Hydrogen efficiency levels have been severely limited due to many factors, including light absorption, charge separation and transport, surface chemical reaction rate [1]. Novel and emerging materials that may just address key bottlenecks are some of the transition metal dichalcogenides (TMDCs) due to their tuneable band gap and an ability to be doped n-type or p-type [2]. In recent times, nanometer thickness control, uniformity and large area growth of continuous films have been demonstrated by rapid deposition methods in manufacturing-compatible processes [3]. However, little is known about the effect of different impurity concentrations incorporated into TMDCs, particularly on the semiconductor transport properties; the structural, chemical, and physical stability; and their photoelectrochemical properties. In this work, we focus on the enhanced water splitting capability as photoanodes/photocathodes and tandem diode cells when combined with novel doped transition metal dichalcogenide (TMD) materials in an acidic aqueous medium. We use thermally assisted conversion (TAC) processes to form n-type and p-type TMDCs by converting transition metals to sulphide-based TMDCs with different impurity concentrations. The photoelectrochemical responses were assessed by standard potential sweep methods and electrochemical impedance spectroscopy. To determine transport properties, TMDCs were studied with 4-point resistivity measurements and AC Hall-effect measurements. Structural, chemical, optical and physical properties were characterized using Raman spectroscopy, X-Ray diffraction, UV-Vis spectroscopy, and atomic force microscopy. The performance of the cells was assessed within a purposely built PEC setup. The integrated light source was a G2V Pico Var Solar Simulator with 32 LEDs, providing an AM 1.5G 1.0 simulated Sun equal to a total irradiance of 87.2 mW cm-2 with a spectral range of 361 nm to 1556 nm. We show that the doped TMD nanofilms acting as photoelectrodes provide a significant enhancement of PEC water splitting response when compared to the underlying silicon photoelectrodes without the nanofilms. We analyze the correlation between the increased activity with and without the nanofilms, the influence of their doping density and doping type on the mechanisms and compare the different cell geometries. Finally, we assess a selection of TMDCs using photoelectrochemical methods to understand their potential contribution to solar energy conversion and hydrogen fuel generation.

[1] Eds. John A. Kilner, Stephen J. Skinner, Stuart J. C. Irvine and Peter P. Edwards, “Functional materials for sustainable energy applications”, Woodhead publishing series in energy , Oxford, 1–681 (2012);
[2] Toby Hallam et al., "Rhenium-doped MoS₂ films", Applied Physics Letters 111 (20), 203101 (2017);
[3] J. Lin et al., “Large-area growth of MoS₂ at temperatures compatible with integrating back-end-of-line functionality”, 2D Mater 8, 025008 (2021).