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. I will present our prototype PV-PEC device, with a photo-absorbing area >100 cm², which operates with a photoanode comprising of a WO₃/BiVO₄ heterojunction on FTO. A key bottleneck in the scalability of PEC devices remains the development of scalable photocatalyst materials for the water splitting reaction. Our photoanodes are produced by conformally coating BiVO₄ onto WO₃ nanoneedles using low-cost and scalable chemical vapour deposition methods. With the band gap of BiVO₄ enabling light absorption up to 517 nm and a theoretical 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 externally connected homojunction silicon PVs this creates a cost-effective and scalable photoelectrochemical-photovoltaic (PV-PEC) device with a commercially viable fabrication method. I will discuss how the arrangement of the PVs, either behind (in tandem) or next to (side-by-side) the photoanode, affects the operation and performance of the device. 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. Without mitigation, this can lead to reductions in photocurrent of over 80%. I will present steps we have taken to mitigate this issue, with minimal performance losses between 1 cm² and 36 cm² electrodes.

Considering heat and mass transfer, as well as fluid dynamics, is not only critical when optimising the efficiency of scaled-up devices, but also to address safety challenges associated with increasingly larger systems. I will therefore discuss our work to optimise the temperature and electrolyte flowrates for long-term, stable operation. To deliver stable operating conditions, the PEC stability of materials must also be addressed. I will present work to improve the PEC stability of BiVO₄ photoanodes, through the use of co-catalysts, doping, different electrolytes and varying fabrication conditions. In preliminary results, WO₃/BiVO₄ electrodes with NiO_x co-catalyst layers have shown stability for 24 hours with an applied potential of 1.23 V_RHE in pH 9 potassium borate buffer.

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