Electron‐Rich Cobalt Doping Engineered Dipole Moments in Delafossite CuFeO2 Nanosheets for High‐Efficiency Solar Hydrogen Production

In recent years, p ‐type CuFeO 2 delafossite has attracted considerable interest as a cost‐effective H 2 evolution photocatalyst. However, the intrinsic alternating CuO 2 /FeO 6 layered architecture creates a high energy barrier for interlayer charge transfer, which causes rapid bulk recombination of photogenerated electron–hole pairs, severely limiting their photocatalytic reactivity. In this study, CuFeO 2 nanosheets are designed with electron‐rich Co sites, which induced enhancement of dipole moment and thereby built‐in electric field driving charge separation efficiently. X‐ray photoelectron spectroscopy analysis confirms the oxidation state of cobalt atoms is Co 2+ , which indicates the electron‐rich nature of Co sites. The photoluminescence spectra show that the fluorescence intensity of the CuFeO 2 nanosheets with electron‐rich Co sites decreases, indicating enhanced charge separation. Further time‐resolved surface photovoltage measurement reveals the separation of photoinduced electron–hole pairs within 5.26 μs, followed by surface photoinduced electron accumulation on a microsecond time scale. Density functional theory calculations demonstrate the localized electron rich around Co sites, which promotes a 1.5‐fold enhancement in dipole moment (from 2.92 × 10 −27 Cm to 4.38 × 10 −27 Cm). These electron‐rich Co serve as low‐barrier active sites (Δ G = 0.185 eV) for H 2 evolution. The optimized CuFeO 2 nanosheets achieves a H 2 evolution rate of 31.58 μmol g −1 h −1 , representing a 20.8‐fold improvement over pristine CuFeO 2 .