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 CO 2 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 CO 2 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 CO 2 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 CO 2 -to-CO transformation. This work provides an effective strategy and mechanistic insights into cation-driven control of bond-length for photocatalytic CO 2 reductions.