Surface state activation driving charge separation <i>via</i> Z-scheme Fe₂O₃/CuO heterojunctions for photocatalytic H₂ evolution

Surface state modulation has emerged as a promising strategy to reduce rapid carrier recombination in photocatalytic reactions. However, surface states can paradoxically serve as indirect recombination centers due to sluggish interfacial reaction kinetics. Herein, the charge separation function of Ni-mediated surface states is reactivated <i>via</i> Z-scheme charge transfer engineering in Fe₂O₃/CuO heterojunctions, where the surface states spontaneously accumulate photoinduced electrons for efficient photocatalytic hydrogen production. Density functional theory (DFT) calculations reveal that Ni heteroatoms introduce surface states proximal to the conduction band minimum of CuO, creating electron-trapping configurations that facilitate the accumulation of photogenerated electrons. Surface photovoltage spectra demonstrate that Ni-induced surface states function as electron trapping centers, creating electron reservoirs that spatially decouple reduction sites from recombination sites. Time-resolved surface photovoltage decay kinetics quantitatively resolve the electron capture process occurring in the sub millisecond time scale, with carrier lifetimes prolonged to 4.72 ms with a 5-fold enhancement. This interfacial electron reservoir effect enhances the photocatalytic H₂ evolution rate of 1933.69 μmol g^-1 h^-1, while maintaining 98% activity over 4 cycles. This work not only elucidates the mechanism of transition metal dopants in regulating surface states but also provides a new paradigm for designing photocatalytic interfaces with dynamic electron accumulation capabilities.