Covalent bonding mediated interfacial charge transfer between BiVO₄ and {Co₄O₄} 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 (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 VRHE, 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.