Insights into Electrochemical CO₂ Reduction on SnS₂: Main Product Switch from Hydrogen to Formate by Pulsed Potential Electrolysis

Tin disulfide (SnS₂ ) is a promising candidate for electrosynthesis of CO₂ -to-formate while the low activity and selectivity remain a great challenge. Herein, we report the potentiostatic and pulsed potential CO₂ RR performance of SnS₂ nanosheets (NSs) with tunable S-vacancy and exposure of Sn-atoms or S-atoms prepared controllably by calcination of SnS₂ at different temperatures under the H₂ /Ar atmosphere. The catalytic activity of S-vacancy SnS₂ (Vs -SnS₂ ) is improved 1.8 times, but it exhibits an exclusive hydrogen evolution with about 100 % FE under all potentials investigated in the static conditions. The theoretical calculations reveal that the adsorption of *H on the Vs -SnS₂ surface is energetically more favorable than the carbonaceous intermediates, resulting in active site coverage that hinders the carbon intermediates from being adsorbed. Fortunately, the main product can be switched from hydrogen to formate by applying pulsed potential electrolysis benefiting from in situ formed partially oxidized SnS2-x with the oxide phase selective to formate and the S-vacancy to hydrogen. This work highlights not only the Vs -SnS₂ NSs lead to exclusively H₂ formation, but also provides insights into the systematic design of highly selective CO₂ reduction catalysts reconstructed by pulsed potential electrolysis.