While hydrogen production via photoelectrochemical water splitting has been demonstrated on a small scale, developing an industrial scale device is a challenge that brings together researchers from a range of disciplines, including engineers, material scientists and chemists. Development of photoelectrochemical water splitting devices requires an understanding of semiconductor physics, optics, (photo)electrochemistry (including catalysis and corrosion) and chemical engineering (e.g. fluid mechanics, heat and mass transport). These are all critical to the development of efficient and robust devices.

I will discuss our in-house developed photoelectrochemical (PEC) device, with a total photo-absorbing area in excess of 100 cm². The device operates with photoanodes fabricated 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 to 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 an externally mounted homojunction Si PV, and operated in a pH neutral phosphate buffer solution, this creates a cost-effective and scalable photoelectrochemical-photovoltaic (PV-PEC) device with a commercially viable fabrication method. In initial experiments, we have achieved a spontaneous solar-to-hydrogen efficiency (ɳ_STH) of 4.0 %.

Scale-up of PEC devices comes with numerous challenges which must be addressed by both computational and experimental approaches. I will discuss the ways in which we have combined these approaches in our research and initial progress to-date. I will also show strategies we have been developing towards mitigating performance losses within our device, including reducing severe potential and current gradients across poorly conducting photoelectrodes. I will discuss other aspects critical to the scale-up of photoelectrochemical devices, including heat and mass transfer, fluid dynamics and safety challenges associated with increasing product and precursor volumes.

Despite the urgent need for engineering progress in this area to accelerate this type of solar hydrogen technology, there are relatively few academic publications that address this topic. With a lack of demonstration prototypes, it remains difficult to envisage what an industrial-scale installation for clean hydrogen production might look like. Ultimately, availability of green hydrogen is expected to result in the hydrogen market expansion. This research seeks to elucidate engineering challenges of developing large-scale water splitting devices, to facilitate the pathway to commercially viable photoelectrochemical hydrogen production.

Key words

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