photocorrosion

Photocorrosion is the chemical degradation of a material accelerated or caused by illumination, especially when the material serves as a semiconductor photoelectrode in a reactive environment. Under light, photogenerated electron-hole pairs can drive redox reactions at the surface that attack and dissolve or alter the photoactive material itself, reducing performance and lifetime.

Mechanisms of photocorrosion typically involve hole-driven oxidation of the semiconductor lattice or dopants, occurring when the valence-band edge is sufficiently positive with respect to the redox couples present in the electrolyte. This can lead to dissolution of constituent elements, surface restructuring, or the formation of nonconductive oxide or sulfide layers that hinder activity. The rate and extent of photocorrosion depend on factors such as the material’s band alignment, electrolyte composition and pH, light intensity, applied bias, and the presence or absence of protective surface states or catalysts. Materials commonly affected include metal sulfides and selenides (for example CdS, CdSe), which can undergo rapid self-oxidation, while metal oxides like TiO2 are more robust but not immune under aggressive conditions or extreme bias.

Mitigation strategies aim to separate the photoactivity from the degrading reactions. Approaches include applying protective overlayers or coatings (for example, conformal TiO2 or Al2O3 films), adding co-catalysts to drive the desired redox reactions and minimize direct oxidation of the photoelectrode, and engineering band alignments through doping or heterojunctions. Operational controls such as adjusting pH, electrolyte composition, and illumination conditions also help enhance stability.

Photocorrosion is a central challenge in the development of durable photoelectrochemical cells and solar fuel technologies, shaping material choice and device architecture.