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

In recent years, p-type CuFeO₂ delafossite has attracted considerable interest as a cost-effective H₂ evolution photocatalyst. However, the intrinsic alternating CuO₂/FeO₆ 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, CuFeO₂ 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 Co²⁺, which indicates the electron-rich nature of Co sites. The photoluminescence spectra show that the fluorescence intensity of the CuFeO₂ 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 (ΔG = 0.185 eV) for H₂ evolution. The optimized CuFeO₂ nanosheets achieves a H₂ evolution rate of 31.58 μmol g^-1h^-1, representing a 20.8-fold improvement over pristine CuFeO₂.