Interfacial Engineering of Gallium Indium Phosphide Photoelectrodes for Hydrogen Evolution with Precious Metal and Non-Precious Metal Based Catalysts

Gallium indium phosphide (GaInP₂) is a semiconductor with promising optical and electronic properties to serve as the large bandgap, top junction in a dual absorber tandem solar water splitting device. Poor intrinsic catalytic ability and surface corrosion in aqueous electrolyte remain key obstacles. Significant progress has been made developing thin-film protection layers and active catalysts for photoelectrochemical devices, but combining these into a catalytic protection layer that can provide long-term stability without sacrificing performance has proven difficult due, in large part, to challenges in developing active and stable interfaces. In this work, we demonstrate that a nanoscale molybdenum disulfide (MoS₂) film functions both as an effective protection layer and excellent hydrogen evolution catalyst for GaInP₂ photocathodes, with only a ∼10% loss in initial light-limited current density after 100 h, and a photocurrent onset potential better than that of the same state-of-the-art device with a platinum-ruthenium catalyst. Using transient photoreflectance spectroscopy, we probed the carrier dynamics of these photocathodes and show that the MoS₂ coated device exhibits improved electron transfer at the surface interface compared to the PtRu catalyzed device. These MoS₂ protected devices are among the most active and stable single-absorber photocathodes for solar water splitting to date and offer a promising pathway towards generating hydrogen with high efficiency and significant longevity.