Photoelectrochemical Hydrogen Generation by Ni-Coated Gallium Arsenide Epilayers on Silicon

Green hydrogen (H2) can play a pivotal role in reducing global carbon emissions. This renewable fuel can be produced by water-splitting photoelectrochemical (PEC) devices that require a photoanode and a photocathode to serve as solar light absorbers and energy converters. So far, the use of III–V semiconductor materials as photoelectrodes has resulted in the best performance for PEC water splitting. However, the cost of these materials still prohibits their spread. Instead of employing bulk III–V wafers as photoelectrode substrates, using III–V thin film layers on inexpensive substrates to manufacture photoelectrodes appears to be, thus, a promising solution to solve this problem. Herein, we present the preparation and the study of photocathodes consisting of a thin film of GaAs grown by molecular beam epitaxy (MBE) on a p-doped Si (Si:p) substrate, which are subsequently modified by photoelectrodeposition of Ni catalyst. These Ni/GaAs/Si:p photocathodes are used for the solar-driven H2 evolution reaction (HER) in alkaline medium. We show that these photocathodes are stable in operation for several hours under illumination with a 100% Faradaic efficiency for H2. This constitutes the first example of the use of Ni as a catalyst on GaAs photocathodes. While these results support the fact that MBE-grown III–V thin films can afford HER in alkaline media when modified with an inexpensive catalyst, the effect of the GaAs thickness on incident-photon-to-electron conversion efficiency (IPCE) data shows that the III–V layer hinders the overall HER activity of the photoelectrode. Therefore, further material engineering strategies are required to improve the HER performance of these promising photocathodes.