Bifunctional Film‐Like CoFeO x Overlayer on BiVO ₄ Enabled by Pulse Electrodeposition for Enhanced Photoelectrochemical Oxygen Evolution

Bismuth vanadate (BiVO 4 ) is an attractive photoanode for photoelectrochemical oxygen evolution because of its visible light absorption and favorable band energetics, but its performance is limited by short hole transport lengths, slow surface reaction kinetics, and photocorrosion. Here, CoFeO x is deposited on spin‐coated BiVO 4 by pulse electrodeposition to form a bifunctional film‐like overlayer. Among the BiVO 4 films examined, the four‐cycle film shows the best balance between light absorption and hole collection. Pulse deposition drives CoFeO x growth from dispersed nuclei to a dense nanoparticulate overlayer with film‐like coverage, producing a catalytic and protective interface on BiVO 4 . The CoFeO x overlayer accelerates interfacial hole transfer for oxygen evolution while reducing direct BiVO 4 contact with the electrolyte, thereby mitigating photocorrosion. Consequently, the photocurrent density increases from about 1.4 to 3.3 mA cm −2 at 1.23 V RHE , and stable operation is maintained for 5 h. Pulse‐grown film‐like CoFeO x overlayers improve both activity and stability in BiVO 4 photoanodes.