Understanding the Influence of C‑Doping on CO2 Photoreduction at SnS2 Nanosheets: A First-Principles Study

In this work, the photocatalytic CO2 conversion of two-dimensional (2D) SnS2 nanosheets modified by S-defect (SnS2-VS) and carbon interstitial doping (SnS2-Cint) is investigated by first-principles calculations. From a thermodynamic point of view, SnS2-VS and SnS2-Cint show narrower band gaps, suitable band edge positions, red-shifted absorption spectrum, and stronger light absorption, suggesting a better photocatalytic activity. Importantly, Cint can not only improve the electrical conductivity of SnS2 nanosheets but also prolong the lifetime of photoexcited carriers. Furthermore, we also explain the high activity and selectivity from the reaction kinetic point of view by calculating the Gibbs free energy of different intermediates in the process of CO2 reduction. It is demonstrated that SnS2-Cint not only reduces the limiting potential (UL) of the whole reduction process to 2.77 V but also has excellent selectivity for CH3CHO and CH4 products through multielectron reduction. For SnS2-VS, CO2 can be efficiently captured and reduced into CH3CHO and CH4 with a lower Gibbs free energy barrier of 3.08 eV, which is much smaller than the 3.70 eV of SnS2. Our work provides a useful theoretical insight for VS and Cint in determining the CO2 reduction property at SnS2 nanosheets, which will help to design SnS2-related materials for photocatalysts.