Tin disulfide (SnS 2 ) is a promising candidate for electrosynthesis of CO 2 -to-formate while the low activity and selectivity remain a great challenge. Herein, we report the potentiostatic and pulsed potential CO 2 RR performance of SnS 2 nanosheets (NSs) with tunable S-vacancy and exposure of Sn-atoms or S-atoms prepared controllably by calcination of SnS 2 at different temperatures under the H 2 /Ar atmosphere. The catalytic activity of S-vacancy SnS 2 (V s -SnS 2 ) 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 V s -SnS 2 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 SnS 2À x with the oxide phase selective to formate and the S-vacancy to hydrogen. This work highlights not only the V s -SnS 2 NSs lead to exclusively H 2 formation, but also provides insights into the systematic design of highly selective CO 2 reduction catalysts reconstructed by pulsed potential electrolysis.

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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 CO2RR 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.