Impact of Co–Fe Overlayers on Charge Carrier Dynamics at WO3/BiVO4 Heterojunctions: A Picosecond-to-Second Spectroscopic Analysis

Surface modification with CoFe-based overlayers hasbeen widely studied to improve the performance of WO3/BiVO4photoanodes for photoelectrochemical water oxidation because suchoverlayers can increase the photocurrent and shift the onset potential tomore favorable values. Herein, we present a transient absorptionspectroscopic analysis of WO3/BiVO4 photoanodes coated with cobaltiron oxide or cobalt iron Prussian blue overlayers, designed to establishthe underlying mechanisms for these enhancements on the picosecond-to-second time scale. The data reveal that the overlayer suppressesrecombination of trapped holes in BiVO4, with free and trappedelectrons, and accepts photogenerated holes. These results show thatthe observed boost in efficiency for water oxidation can be explained by the dual role of the overlayer in inhibiting chargerecombination and enhancing charge extraction