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 (Cu 2 O), and it is widely assumed that the deactivation of Cu 2 O photocathodes in solar water splitting is caused by spontaneous oxidation-reduction (REDOX) reactions. However, this work shows that 〈100〉-oriented Cu 2 O photocathodes undergo a non-REDOX hydration deactivation mechanism. Briefly, water molecules are embedded in the Cu 2 O 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 Cu 2 O films with a three-dimensional skeleton structure. This study provides a new insight towards the protection and application of Cu 2 O photocathodes.