Covalent Bonding Mediated Interfacial Charge Transfer Between BiVO4 and {Co4O4} Cubanes for Enhanced Photoelectrochemical Water Splitting

Although molecular cocatalysts (MCs) have demonstrated significant application potential for photoelectrochemical (PEC) water splitting, the immobilization and stabilization of them for long-term application remains challenging. Herein, an integrated photoanode (BiVO₄@NM88B(Fe)/Co₄O₄) is developed by immobilizing Co₄O₄ cubanes onto NH₂-MIL-88B(Fe) (NM88B(Fe)) decorated BiVO₄ via site-isolation strategy. The unoccupied coordination sites in NM88B(Fe) covalently bound to both Co₄O₄ and BiVO₄, which significantly decreases the interfacial charge transfer resistance of BiVO₄@NM88B(Fe)/Co₄O₄ and achieve prolonged stability. More importantly, the oxygen evolution cocatalyst (OEC) NM88B(Fe)/Co₄O₄ remarkably lowered the energy barrier and thermodynamically favored surface water oxidation. Consequently, the photocurrent density of BiVO₄@NM88B(Fe)/Co₄O₄ photoanode achieved up to 5.26 mA·cm⁻² at 1.23 V_RHE, which is 3.73 times higher than that of bare BiVO₄. This work presents a site-isolation strategy to overcome molecular catalyst stabilization challenges in PEC systems while offering crucial insights into designing efficient charge transfer channels between OECs and semiconductors for enhanced water splitting performance.