Photocatalytic Activation and Reduction of CO₂ to CH₄ over Single Phase Nano Cu₃SnS₄: A Combined Experimental and Theoretical Study

In view of their ability to absorb visible light and their high surface catalytic activity, metal sulfides are rapidly emerging as promising candidates for CO2 photoreduction, scoring over the traditional oxide-based systems. However, their low conversion efficiencies due to serious radiative recombination issues and poor stability restrict their real-life applicability. Enhancing their performance by coupling them with other semiconductor-based photocatalysts or precious noble metals as cocatalysts makes the process cost intensive. Herein, we report the single-phase ternary sulfide Cu3SnS4 (CTS) as a robust visible-light photocatalyst for selective photoreduction of CO2 to CH4. It showed a remarkable 80% selectivity for CH4 evolution with the rate of 14 μmol/g/h, without addition of any cocatalyst or scavenger. The mechanistic pathway for catalytic activity is elucidated by first principle calculations and in situ ATR, which imply a formaldehyde pathway of hydrocarbon production. The Cu–Sn termination of the surface is shown to be the key factor for competent CO2 absorption and activation as confirmed from our X-ray spectroscopy measurements and first principle calculations. This study provides a foundation and insights for the rational design of sulfide-based photocatalysts to produce renewable fuel.