In situ depositing an ultrathin CoOxHy layer on hematite in alkaline media for photoelectrochemical water oxidation

Cocatalysts are usually deposited on semiconductors to accelerate charge transfer/separation and passivate their surface states. Although various methods have been developed to decorate cocatalysts on semiconductors, in situ depositing a transition metal oxide/oxyhydroxide catalyst in alkaline electrolyte remains a challenge. Herein, we present a facile in situ photo-assisted electrodeposition of ultrathin amorphous CoOxHy layer on hematite for efficient solar-driven water oxidation. Compared to Co(II) hydroxide, Co(III) hydroxide is much less soluble in alkaline electrolytes, thus being favorable for deposition above the anodic onset potential of Co(II)/(III). By using this metal valence dependent deposition-dissolution equilibrium, we prepared this highly efficient and adaptive CoOxHy layer on hematite for OER in 1.0 M NaOH containing 1.0 μM Co(II). This method is promising for loading cocatalysts on semiconductors for solar-driven water splitting and is general for developing in situ (photo)electrochemical deposition of nanoscale catalysts.