Tailored TiO2 Protection Layer Enabled Efficient and Stable Microdome Structured p‐GaAs Photoelectrochemical Cathodes

Abstract Group III–V compound semiconductors are a promising group of materials for photoelectrochemical (PEC) applications. In this work, a metal assisted wet etching approach is adapted to acquiring a large‐area patterned microdome structure on p‐GaAs surface. In addition, atomic layer deposition is used to deposit a TiO2 protection layer with controlled thickness and crystallinity. Based on a PEC photocathode design, the optimal configuration achieves a photocurrent of −5 mA cm−2 under −0.8 V versus Ag/AgCl in a neutral pH electrolyte. The TiO2 coating with a particular degree of crystallization deposited via controlled temperature demonstrates a superior stability over amorphous coating, enabling a remarkably stable operation, for as long as 60 h. The enhanced charge separation induced by favorable band alignment between GaAs and TiO2 contributes simultaneously to the elevated solar conversion efficiency. This approach provides a promising solution to further development of group III–V compounds and other photoelectrodes with high efficiency and excellent durability for solar fuel generation.