Grain-Boundary-Enriched Cocatalyst Coupled With CuSCN Hole Transport Layer for Efficient Solar Water Oxidation in BiVO₄ Photoanode

Solar-driven photoelectrochemical (PEC) water splitting represents a promising pathway toward carbon neutrality, yet the practical conversion efficiency remains severely constrained by the substantial charge recombination losses. Herein, CuSCN as hole transport layer (HTL) coupled with a grain-boundary-enriched NiFe cocatalyst (NiFe-GB) was integrated with BiVO₄ photoanodes to improve hole extraction/transport and interfacial oxygen evolution reaction (OER) kinetics. The optimized NiFe-GB/CuSCN/BVO photoanode delivered a photocurrent density of 6.54 mA cm⁻² at 1.23 V versus RHE. Through a multi-technique approach encompassing intensity-modulated photocurrent spectroscopy (IMPS), Kelvin probe force microscopy (KPFM), scanning photoelectrochemical microscopy (SPECM), we demonstrate markedly improved charge separation, interfacial hole transfer, and surface charge utilization in the integrated architecture. Comparative experiments with NiFe LDH/CuSCN/BVO and trend-level density functional theory calculations suggest that the grain-boundary-enriched NiFe structure modulates electronic states and lowers the energy barrier for OER intermediate transformation. This work highlights cocatalyst microstructure regulation as a complementary strategy to hole transport layer engineering for designing efficient BiVO₄-based photoanodes.