Optimizing Fermi level potential difference and reducing ineffective electron transfer to enhance the internal electric field for improving photocatalytic hydrogen evolution

Abstract

The synergistic effect of surface defect design and heterojunction engineering can significantly enhance photocatalytic hydrogen evolution. ZnIn₂S₄ nanosheets with S vacancy (V_s-ZIS) were successfully synthesized on bulk Sr₆Co₅O₁₅ (SCO) via a solvothermal method in this study. The formation of the V_s-ZISCO S-scheme heterojunction (SSH) was substantiated by DFT calculations, KPFM, EPR and in situ XPS. The incorporation of sulfur defects effectively mitigates the inefficient electron movement within the ZISCO heterojunction, thereby reducing energy loss of internal electron and concentrating electron transfer primarily at the contact interface. Furthermore, the design of sulfur vacancies facilitates an appropriate Fermi level (E_f) potential difference between V_s-ZIS and SCO. This significantly enhances carrier injection at the heterojunction interface, thereby substantially strengthening the internal electric field (IEF). In comparison with pristine ZIS, the electron transfer quantity at the interface between V_s-ZIS and SCO was elevated by 41.38 %. The design of sulfur defect and the construction of SSH effectively modulate the d-band center, shifting it downward. This adjustment facilitates the desorption of intermediate state H∗. Specifically, the V_s-ZISCO's Gibbs free energy of hydrogen adsorption (ΔG_H∗) approaches zero, thereby achieving an optimal balance between hydrogen atom desorption and adsorption.