Interfacial Cation-Driven Bond-Length Engineering for Selective CO ₂ Photoreduction to Syngas

Bond-length of semiconductors critically influence charge distribution and orbital hybridization, potentially offering an effective route to optimize photocatalytic CO2 reduction. Conventional doping and heterostructure formation strategies frequently induce defects or band-edge shifts, thereby constraining performance and rendering direct bond-length regulation rarely concerned in semiconductor photocatalysis. In this work, we propose an in situ strategy to modulate Zn–S bond-length in hexagonal ZnS via interfacial cation engineering with Li+, Na+, K+, and Cs+ ions to fine-tune photocatalytic performance. Density functional theory (DFT) calculations predict a cation-dependent Zn–S bond contraction trend, which is experimentally verified by extended X-ray absorption fine structure spectroscopy. Photocatalytic CO2 reduction in both organic and inorganic media shows that CO evolution correlates with bond contraction, with ZnS–K+ yielding the highest CO rate (79.3 μmol·h–1·g–1) and selectivity (77.2%), outperforming most sulfide photocatalysts. In situ Fourier transform infrared spectroscopy and thermogravimetric analysis confirm that progressive Zn–S bond shortening enhances CO2 adsorption and stabilizes some key intermediates (*COOH and *CO). DFT analysis further reveals that bond contraction induces an upward shift of Zn d-band center, reducing energy barriers for intermediates conversion and promoting selective CO2-to-CO transformation. This work provides an effective strategy and mechanistic insights into cation-driven control of bond-length for photocatalytic CO2 reductions.