Amorphous FeO_x Overlayer Coupled with Co₃O₄ Nanoparticles Passivating Hematite Photoanodes for Water Oxidation

Hematite is a significant material for photoanodes in catalytic water oxidation. Modification overlayers play an important role in improving the activity of the hematite photoanode, which suffers serious recombination by inevitable surface defects. Herein, a thin amorphous FeO x overlayer was spin-coated on Fe 2 O 3 nanorods. The photoanode reached a 1.7-fold increase in current density, and the modification improved the injection efficiency principally. A more effective functional overlayer was constructed by subsequently depositing Co 3 O 4 nanoparticles, which achieved a higher photocurrent of 1.39 mA cm –2 at 1.23 V RHE and a cathodic 80 mV shift of the onset potential. Based on electrochemical and charge kinetics characterization, the FeO x overlayer is found to passivate the surface traps, favoring charge transfer through the electrode–electrolyte interface, thus reducing the recombination. With the aid of the p–n heterojunction between Co 3 O 4 and Fe 2 O 3 and the strengthened passivation effect, the reaction kinetics was further enhanced by the deposition of Co 3 O 4 . The facile fabrication of the FeO x overlayer and the application of synergetic overlayers for hematite photoanodes consisting of passivation layers or multiple cocatalysts are inspiring and promising for future modification research.