Synergistic Activation of the Inert (001) Facet in Janus ZnIn₂S₄ Through Co 3d and P 3p Orbital Hybridization for Superior Photocatalytic Hydrogen Evolution

The Janus structure of ZnIn₂S₄ (ZIS) endows it with an intrinsic built-in electric field that effectively drives photogenerated charge separation. However, this very structure also renders the predominant (001) facet (In–S termination) catalytically inert due to its low electron density and high energy barrier for the hydrogen evolution reaction (HER). This work proposes a synergistic strategy to precisely activate the inert sites on the ZIS (001) facet through atomic-level cobalt (Co) and phosphorus (P) co-doping, while fully exploiting the Janus built-in field for bulk charge separation. Theoretical calculations indicate that Co/P co-doping forms a stable active center within the In–S layer and optimizes the hydrogen adsorption free energy (ΔG_H) at the P site to a near-ideal value of −0.07 eV through P 3p and Co 3d orbital hybridization. Experimentally, Co/P co-doped ZIS nanosheets were successfully synthesized, achieving a visible-light-driven photocatalytic HER rate of 6.07 mmol g⁻¹ h⁻¹, representing a 5.62-fold enhancement over pristine ZIS. Mechanism studies confirm that the performance improvement stems from the synergy between the built-in electric field and atomic-level doping, in which the built-in field efficiently separates charges, whereas the Co-P active sites strongly trap and utilize electrons, enabling an efficient relay from charge separation to surface reactions. This work provides a new perspective for precisely regulating interfacial processes in catalytic materials through multi-strategy synergy.