While hydrogen production via photoelectrochemical (PEC) water splitting has been demonstrated on a small scale, developing an industrial scale device is a challenge that intrigues and brings together researchers from a range of disciplines. A key bottleneck in the scalability of PEC devices remains the development of scalable photocatalyst materials for the water splitting reaction. Many photoelectrodes are produced as thin films on transparent conducting oxides, such as fluorine-doped tin oxide (FTO) or indium-doped tin oxide (ITO). However, one difficulty to overcome is the resistivity of FTO glass, which can result in severe resistance losses in scale-up. I will present the initial steps we have taken to mitigate this issue.

I will present our method of photoanode fabrication by chemical vapour deposition, a prevalent and scalable method, of sequential layers of WO₃ nanorods and BiVO₄, to form a staggered heterojunction on FTO. The 2.4 - 2.5 eV bandgap of BiVO₄ enables light absorption up to 517 nm in wavelength and a theoretical solar-to-hydrogen efficiency (ɳ_STH) of up to 9.2 %. The WO₃/BiVO₄ heterojunction system is one of the most promising in terms of performance, cost and durability. Combined with a Ni mesh cathode and homojunction Si PV, and operated in a pH neutral phosphate buffer solution, this creates a cost-effective and scalable tandem photoelectrochemical-photovoltaic (PV-PEC) device with a commercially viable fabrication method.

However, another challenge to address is the PEC stability of BiVO₄-based photoanodes, which are prone to photocorrosion in aqueous solutions, particularly at non-neutral pHs, negative electrode potentials and highly positive electrode potentials. I will present our initial work to mitigate this issue, by tuning electrolyte composition, through the use of co-catalysts, doping, different electrolytes and varying fabrication[HA1] conditions to alter the structural morphology of the photoanodes. In preliminary results, BiVO₄ electrodes containing 6% Mo had a photocurrent density at 1.23 V_RHE that was five times higher than undoped BiVO₄ electrodes, while PEC degradation rates were considerably reduced.

This research seeks to elucidate challenges of developing up-scaled materials for water splitting, to facilitate the pathway to commercially viable photoelectrochemical hydrogen production.

Key words

Photoelectrochemistry, hydrogen, scale-up, electrochemical engineering, BiVO₄

and different electrolytes [HA1]