Electronic States Modulation of BiVO 4 with Transition Metal-Substituted Polyoxometalates to Activate Lattice Oxygen Mechanism for Efficient Water Oxidation

Oxygen evolution reaction (OER) is the bottleneck of photoelectrochemical (PEC) water splitting. Activating the lattice oxygen mechanism (LOM) can break the limitation of the slow O-O coupling and accelerate the water oxidation kinetics. However, the current methods for activating LOM are limited and it is crucial to develop new strategies to induce LOM. Herein, we have modified BiVO₄ with transition metal-substituted silicotungstate (X₃SiW₉, X = Co, Ni, Cu) to form X₃SiW₉-BiVO₄ photoanodes, triggering the LOM by surface modification for the first time. X₃SiW₉ can modulate the electronic structure of BiVO₄, resulting in an upward shift of the O 2p energy band position relative to the metal 3d energy band, increasing the overlap of the metal and oxygen orbital energy levels, and enhancing covalency between metal and oxygen, which facilitates the activation of the lattice oxygen, thus triggering the LOM and significantly improving the OER activity of BiVO₄. The enhancement of the OER activity depends on the influence of X₃SiW₉ on the electronic state. Among them, Co₃SiW₉ has the greatest influence on the electronic state of BiVO₄. Therefore, Co₃SiW₉-BiVO₄ exhibits the highest photocurrent density of 4.13 mA cm^-2 at 1.23 V_RHE, four times higher than that of BiVO₄ (1.02 mA cm^-2). This work modifies the photoanode with transition metal-substituted polyoxometalates to modulate the energy levels of metal and oxygen to activate LOM for significantly enhanced OER activity, which provides new strategies and perspectives on the design and application of polyoxometalates for efficient OER in PEC water splitting.