Photoelectrochemical water splitting cells at elevated pressure using BiVO4 and platinized III-V semiconductor photoelectrodes.

Direct production of pressurized green hydrogen via photoelectrochemical water splitting reduces the need for mechanical compression and mitigates bubble-related losses. However, existing demonstrations have been limited to atmospheric pressure. Here, we bridge this gap by designing, constructing, and testing a high-pressure flow cell for photoelectrochemical water splitting using two configurations. In a back-illuminated BiVO4-based photoelectrochemical cell, increased pressure suppresses bubble evolution and alleviates photocurrent saturation under concentrated sunlight: at 10 suns, the photocurrent rises from 3× at 1 bar to ~7× at 5 bar. Direct operando imaging of the electrode surfaces confirms that this improvement comes primarily from suppressed bubble evolution. Conversely, a front-illuminated platinized triple-junction III-V-based photoelectrochemical cell shows limited pressure dependence up to 8 bar due to its dispersed catalyst and long carrier diffusion length. These findings highlight the differing response of photoelectrochemical devices to elevated pressure and demonstrate a viable pathway toward scalable, high-pressure solar-driven hydrogen production.