Investigation of n‑GaAs Photoanode Corrosion in Acidic Media with Various Thin Ir Cocatalyst Layers

n-GaAs is a well-developed III–V semiconductor with excellent light absorption and charge-transport properties, making it a promising candidate for an efficient photoanode. However, strong photocorrosion under anodic bias in aqueous electrolyte prohibits this semiconductor from having durable as well as efficient photoelectrochemical performance. In this work, the photocorrosion process of n-GaAs in acidic media was monitored via in situ UV–vis spectroscopic analysis of the dissolved elements in solution, with additional insight provided by SEM imaging and XPS surface analysis. A strong dependence of the current density vs potential behavior and associated photocorrosion was correlated to the n-type doping density, with the transition into degenerate-like behavior yielding distinctly different photoelectrochemical and corrosion behavior. The photoanode behavior in acid was also investigated with thin surface layers of the acid-stable water oxidation catalyst Ir. Galvanic displacement was used to produce conformal thin films of Ir on n-GaAs, which was compared to films of Ir spin-coated from chemical precursors. In-situ UV–vis spectroscopy showed short-term decreases in the corrosion faradaic efficiency from the Ir films, but none provided sufficient protection to prevent GaAs photoetching from eventually becoming the dominant electrochemical pathway. The disparate nature of each Ir film is discussed to explain the observed differences in surface chemistry and morphology after photoanodic operation.