Photoelectrocatalytic Water Splitting Using WO3/BiVO4-Mo/co-Catalyst Photoanodes
John Wilman Rodriguez Acosta a, George Creasey a, Tristan McCallum b, Andreas Kafizas b, Anna Hankin a
a Imperial College London, Department of Chemical Engineering, London SW7 2AZ, UK
b Department of Chemistry, Imperial College London, W12 OBZ, UK
Proceedings of Catalyst Design Strategies for Photo- and Electrochemical Fuel Synthesis (ECAT23)
Keele, United Kingdom, 2023 December 4th - 5th
Organizers: Charles Creissen, Qian Wang and Julien Warnan
Poster, John Wilman Rodriguez Acosta, 029
Publication date: 10th October 2023

Efficient photoelectrocatalytic water splitting is difficult to achieve with a single material because it requires simultaneous generation, separation, and transfer of photo-generated charge carriers. Researchers are working on developing new materials and strategies to improve this efficiency. One promising approach is to use multi-layered photocatalysts, comprising two or more different materials that are stacked together (heterojunctions). This allows for the absorption of a wider range of wavelengths of light and the separation of electrons and holes at different energy levels. Two other promising approaches are doping of the semiconducting layers and/or using a co-catalyst layer in contact with the electrolyte. The latter helps accelerate the reactions at the surface of the photocatalyst.

Bismuth vanadate (BiVO4) has attracted wide attention for water splitting because its bandgap of 2.4 - 2.5 eV enables light absorption up to 517 nm in wavelength and a theoretical solar-to-hydrogen efficiency (ɳSTH) of up to 9.2 %. Nevertheless, its performance is often strongly affected by the relatively high recombination rate of electrons and holes. The WO3/BiVO4 heterojunction system is one of the most promising solutions in terms of performance, cost and durability. WO3 improves the charge transfer between semiconductors and makes the photo-active area greater when nanostructured, but it remains necessary to improve the degree of charge transfer at the BiVO4/electrolyte interface. For this, BiVO4 doping with Mo and depositing of oxy-hydroxides of some metals, such as Fe and Ni, on the main photoactive layer (BiVO4) have shown promise.

In this research, water splitting performance of a photoanode made of BiVO4-Mo deposited on base nanostructures of WO3 and covered by different co-catalysts were investigated. Base nanostructures were synthesized on FTO by chemical vapor deposition process (CVD) and BiVO4-Mo and co-catalysts were synthesized by photo-assisted electrodeposition. In this first approach, the irradiated area for these small scale photoelectrodes was 1 cm2 as initial step for future scale up the deposition to 50 cm2.

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