Boosting Photoelectrochemical Water Oxidation Performance of Nanoporous BiVO4 via Dual Cocatalysts Cobaloxime and Ni-OEC Modification

ABSTRACT: Bismuth vanadate is an excellent photoanode material for photoelectrocatalytic water oxidation due to the good light absorption and sufficiently positive valence band. However, bare BiVO4 undergoes poor charge separation and transport and slow kinetics of oxygen evolution reaction. Herein, a dual-cocatalyst-modified photoanode is prepared by depositing Ni(oxy)hydroxide/borate (Ni-OEC) and molecular cobaloxime on a nanoporous BiVO4 photoanode. The optimized BiVO4 photoanode shows an excellent photocurrent density under AM 1.5 G illumination (5.1 mA cm???2 at 1.23 V vs RHE), which is among the highest values using cocatalyst-modified BiVO4 photoanodes for PEC water oxidation. Furthermore, the maximum surface charge injection efficiency and incident photon-to-current efficiency of the ultimate composite photoanode are 85.6% (at 1.23 V vs RHE) and 83.6%, respectively. These results indicate that surface-modified Ni-OEC and molecular cobaloxime can highly improve the photoelectrocatalytic performance of bare BiVO4.