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Semiconductor photocorrosion is a major challenge for the stability of photoelectrochemical water‐splitting devices. Usually, photocorrosion is studied on the basis of thermodynamic aspects, by comparing the redox potentials of water to the self‐decomposition potentials of the semiconductor or analyzing the equilibrium phases at given electrolyte conditions. However, that approach does not allow for a prediction of the decomposition rate of the semiconductor or the branching ratio with the redox reaction. A kinetic model has been developed to describe detailed reaction mechanisms and investigate competition between water‐splitting and photocorrosion reactions. It is observed that some thermodynamically unstable semiconductors should photocorrode in a few minutes, whereas others are expected to operate over a period of years as a result of their extremely low photocorrosion current. The photostability of the semiconductor is mainly found to depend on surface chemical properties, catalyst activity, charge carrier density, and electrolyte acidity.

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