Covalent Bonding Mediated Interfacial Charge Transfer Between BiVO ₄ and {Co ₄ O ₄ } Cubanes for Enhanced Photoelectrochemical Water Splitting

Abstract 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 (BiVO 4 @NM88B(Fe)/Co 4 O 4 ) is developed by immobilizing Co 4 O 4 cubanes onto NH 2 ‐MIL‐88B(Fe) (NM88B(Fe)) decorated BiVO 4 via site‐isolation strategy. The unoccupied coordination sites in NM88B(Fe) covalently bound to both Co 4 O 4 and BiVO 4 , which significantly decreases the interfacial charge transfer resistance of BiVO 4 @NM88B(Fe)/Co 4 O 4 and achieve prolonged stability. More importantly, the oxygen evolution cocatalyst (OEC) NM88B(Fe)/Co 4 O 4 remarkably lowered the energy barrier and thermodynamically favored surface water oxidation. Consequently, the photocurrent density of BiVO 4 @NM88B(Fe)/Co 4 O 4 photoanode achieved up to 5.26 mA·cm −2 at 1.23 V RHE , which is 3.73 times higher than that of bare BiVO 4 . 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.