Kinetic competition between water splitting and photocorrosion reactions in photoelectrochemical devices

Semiconductor photocorrosion is a major challenge for the stability of photoelectrochemical water splitting devices. Usually, photocorrosion is studied on the basis of thermodynamic aspects, 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 semiconductor’s decomposition rate or the branching ratio with the redox reaction. We developed a kinetic model to describe the detailed reaction mechanisms and investigated the competition between water splitting and photocorrosion reactions. We observed that some thermodynamically unstable semiconductors should photocorrode in a few minutes while others are expected to operate over a period of years given by their extremely low photocorrosion current. The semiconductor’s photostability is found to mainly depend on surface chemical properties, catalyst activity, charge carrier density, and electrolyte acidity.