Electronic States Modulation of BiVO₄ 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 VRHE, 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.