Dual-defect engineered CuS/NiTiO3 S-scheme heterojunction with strengthened built-in electric field for boosting photocatalytic CO2 reduction

Sulfur/oxygen dual-vacancy CuS-S v /NiTiO 3 -O v S-scheme heterojunction was successfully fabricated. • Built-in electric field accelerates electron transfer in sulfur/oxygen-vacancy heterojunction. • Cu centers in CuS-S v accumulate electrons for CO 2 reduction while NiTiO 3 -O v enriches holes in CuS-S v /NiTiO 3 -O v . • Optimized 5% CuS-S v /NiTiO 3 -O v heterojunction exhibits highest CO evolution rate (490 μmol g −1  h −1 ). • Photocatalytic mechanism is proposed for CO 2 reduction. Harnessing solar energy for the photocatalytic CO 2 reduction into valuable fuels presents a sustainability strategy to simultaneously alleviate the global energy crisis and mitigate carbon emission. However, the efficiency of photocatalytic CO 2 reduction is hindered by weak adsorption and sluggish charge separation in semiconductor materials. Herein, a sulfur/oxygen dual-vacancy engineered CuS-S v /NiTiO 3 -O v S-scheme heterojunction is constructed to achieve a remarkable CO production rate of 490.0 μmol g −1  h −1 with 89.1% selectivity. Experimental results reveal that sulfur vacancies probably strengthen CO 2 adsorption and activation, while oxygen defects induced interfacial charge redistribution at the S-scheme heterojunction interface by intensifying the built-in electric field, promoting efficient separation and migration of photogenerated charge carriers. Density functional theory calculations further uncover that sulfur vacancies (S v ) are beneficial to CO 2 adsorption and activation while promoting the stabilization of the key *COOH intermediate, thereby favoring the CO 2 reduction reaction. Moreover, oxygen vacancies (O v ) promote charge redistribution and facilitate charge transfer across the heterojunction interface onto CuS-S v . In-situ diffuse reflectance infrared Fourier transform spectroscopy and Gibbs free energy (ΔG) calculations clarify the reaction pathway, showing that the synergistic interaction of sulfur and oxygen vacancies efficiently decreased the energy barrier for *CO formation by reinforcing the interaction between *COOH intermediates and the catalyst surface. This study highlights a synergistic strategy combining defect engineering and S-scheme heterojunction design to achieve highly selective and efficient photocatalytic CO 2 to CO conversion. The deliberate introduction of sulfur/oxygen dual vacancies induces electron redistribution within the CuS-S v /NiTiO 3 -O v S-scheme heterostructure, concentrating electrons Cu sites and localizing charge on Ni. The built-in electric field drives interfacial transfer, enriching Cu centers that enhance C O activation and accelerate key intermediate formation. Download: Download high-res image (152KB) Download: Download full-size image