Enhancing Photoelectrochemical Performance of the Printed Nanoporous FeVO₄ Photoanode by Dual-Layer CoO_x-CoPi Catalysts

Photoelectrochemical solar water splitting has become a potential approach for producing clean hydrogen fuels by utilizing semiconductor photoelectrodes and solar energy. Among emerging metal oxide photoelectrodes, iron vanadate (FeVO₄) with its unique electronic band structure and suitable bandgap energies for absorbing visible light from the solar spectrum has become a promising photoanode. However, the reported photocurrent density of this material is still low because of the poor water oxidation kinetics and the slow separation of carriers, leading to recombination at the surface. In this study, we attempted to solve these limitations by nanostructuring the FeVO₄ photoanode and modifying its surface with cocatalysts (CoO_x, CoPi, and CoO_x-CoPi). Both photocurrent and onset potential are significantly improved, resulting from the enhancement of charge injection and separation efficiencies. For the first time, the dual layer of oxygen evolution CoO_x-CoPi catalysts is found more effective than single-layer CoO_x or CoPi catalysts for the nanoporous FeVO₄ photoanode with the increased photocurrent density at 1.23 V vs RHE of a 5-fold improvement compared to the pristine FeVO₄. This result offers a strategy to further improve FeVO₄ photoanode performance for efficient solar water splitting toward practical applications.