Enhanced CO₂ photoreduction to CH₄ via *COOH and *CHO intermediates stabilization by synergistic effect of implanted P and S vacancy in thin-film SnS₂

Reduction of CO₂ to value-added hydrocarbons through artificial photosynthesis is one of the way to address the energy crisis and climate change issues. It is known that lowering the activation energy of CO₂ molecules on the photocatalyst surface and key intermediates is crucial in photocatalytic CO₂ reduction. Herein, we present phosphorus-implanted 20-nm SnS₂ continuous thin film with sulfur vacancies (i.e., S_V-SnS₂:P where P substitutes on S sites). The fabrication process involves thermal evaporation, post-sulfurization, and ion implantation. Our gas-phase photocatalytic experiments show an enhanced and selective CO₂ photoreduction to CH₄ with a yield of 0.13 µmol cm⁻² and selectivity of 92 % under solar-light irradiation for 4 h over an optimal ∼4.5 % P and ∼16 % S_V. Experimental observations, conducted through X-ray absorption near edge, in situ near ambient pressure X-ray photoelectron, and in situ Fourier transform infrared spectroscopies, along with first-principle density functional theory calculations. Results reveal that P dopant is significantly affected by nearby S_V via local charge density transfer from P to the nearest Sn and next-nearest S neighbor atoms, consequently, leads to the stabilization of *COOH and *CHO intermediates, where asterisks stand for P as the active site. Our results demonstrate how active site modulation, without using precious co-catalysts, plays a crucial role in intermediate stabilization in a wireless photocatalysis process.