Photoelectrochemical Hydrogen Generation by Ni-Coated Gallium Arsenide Epilayers on Silicon
Résumé
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 serving as solar light absorbers and energy converters. So far, the use of III-V semiconductor materials as photoelectrodes resulted in the best performance for PEC water splitting. However, the cost of these materials still prohibits their spreading. Instead of employing bulk III-V wafers as photoelectrode substrates, using III-V thin film layers on inexpensive substrates to manufacture photoelectrodes appears, 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, that 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 onto 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 show that the III-V layer hinders the overall HER activity of the photoelectrode. Therefore, further material engineering strategies are required to improve HER performance of these promising photocathodes.
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