Schiff Base Complex Cocatalyst with Coordinatively Unsaturated Cobalt Sites for Photoelectrochemical Water Oxidation

Integrating inorganic oxygen evolution cocatalysts (OECs) with photoanodes is regarded as an available strategy to increase the photogenerated charge utilization for accelerated water oxidation kinetics. Nevertheless, most widely used transition metal (oxyhydr)oxides OECs suffer from inevitable charge recombination at photoanode/OECs interfaces and underabundant catalytic active sites. Herein, a cobalt-organic complex with microflower-like features (denoted as MF) was constructed by coordination of Schiff base ligands and Co²⁺ metal ions and then decorated on porous BiVO₄ employed as photoanodes for photoelectrochemical (PEC) water oxidation. The as-synthesized BiVO₄/MF photoanode achieves a photocurrent density of 4.38 mA cm^-2 and at 1.23 V_RHE in 0.5 M Na₂SO₄ electrolyte under simulated 1 sun illumination, over approximately 5.48 times larger than that of BiVO₄ counterpart, and exhibits a 120 mV cathodic shift of onset potential with outstanding photostability. Systematic characterizations reveal that the improved PEC efficiency is mainly attributed to the well-designed coordinatively unsaturated Co²⁺ sites, which not only serve as powerful photohole extraction engines along reversed interfacial Co-O-Bi bonds to promote charge transfer across the BiVO₄/complex interface but also act as reaction active centers by accelerating surface water oxidation kinetics. This work provides new insights for designing highly effective OECs for PEC water oxidation.