Hydration deactivation mechanism of the 〈100〉 oriented cuprous oxide photocathodes in solar water splitting and the regenerated three-dimensional structure

Photocorrosion is the most ticklish problem of cuprous oxide (Cu2O), and it is widely assumed that the deactivation of Cu2O photocathodes in solar water splitting is caused by spontaneous oxidation–reduction (REDOX) reactions. However, this work shows that 〈100〉-oriented Cu2O photocathodes undergo a non-REDOX hydration deactivation mechanism. Briefly, water molecules are embedded in the Cu2O crystals at low potential under illumination and produce amorphous CuOH, which can be dehydrated at high potential to heal the Cu–O–Cu bonds and regenerate foamed Cu2O films with a three-dimensional skeleton structure. This study provides a new insight towards the protection and application of Cu2O photocathodes.