Subnanometer Ni@Fe Catalysts Enable High-Performance and Stable Oxygen Evolution of WO3 Photoanodes

NiFe-based catalysts are highly active for the oxygen evolution reaction, but their precise fabrication on photoanodes at subnanometer scale for accelerating charge transport and maximizing active sites remains a challenge. Herein, we report a facile approach to deposit trimesic acid (TA) coordinated subnanometer Ni@Fe hydroxides (Ni-TA-Fe) on nanoporous WO3 photoanodes. This WO3/Ni-TA-Fe photoanode exhibited a record photocurrent density of ∼2.4 mA cm–2 at 1.23 VRHE under AM 1.5 G irradiation (100 mW cm–2) with an enhanced stability, which is much higher than that of pristine WO3 photoanodes. Comparative experiments, characterizations, and density functional theory calculations revealed that the subnanometer Ni catalyst layers could effectively inhibit the dissolution of W atoms from the surface lattice and promote the structural stability of the WO3 photoanode during PEC water oxidation. Furthermore, the strong coordination and electron-trapping capability of TA could efficiently promote charge redistribution in Fe catalyst layers, resulting in the activation and transformation of surface Fe sites into high-valence Fe4+ species for significantly improving the OER activity. This work provides the viable pathway to active and durable bimetallic catalysts to achieve high-performance and stable PEC water splitting.