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