Simultaneous Improvement in Hole Storage and Interfacial Catalysis over Ni-Fe Oxyhydroxide-Modified Tantalum Nitride Photoanodes

The hole-storage layer and cocatalysts have been proved to be effective for constructing highly efficient photoelectrocatalytic (PEC) systems via the rational integration of multiple interfacial layers. However, it is still a great challenge to achieve high activity with a facile individual layer modification. Herein, we report that loading an individual Ni-Fe oxyhydroxide layer on a tantalum nitride (Ta3N5) photoanode can deliver a photocurrent density of up to 9.80 mA cm-2 at 1.23 V versus RHE for the water oxidation reaction, with significant enhancement in the applied bias photon-to-current efficiency from 0.1 to 1.66%. Interestingly, it is found that the Ni-Fe oxyhydroxide plays bifunctional roles of a hole-storage layer and cocatalyst simultaneously. The hole-storage capacity mainly comes from Ni species, while the catalytic functionality is primarily contributed by Fe species coupled with Ni. Furthermore, the synergetic effects between Fe and Ni components and the existence of Fe-O-Ni bonding should be responsible for the bifunctionality of Ni-Fe oxyhydroxide. This bifunctional cognition provides insights into the charge transfer process in PEC water oxidation systems.