Promoting electrocatalytic CO2 reduction to formate via sulfur-boosting water activation on indium surfaces

Electrocatalytic reduction of CO₂ to fuels and chemicals is one of the most attractive routes for CO₂ utilization. Current catalysts suffer from low faradaic efficiency of a CO₂-reduction product at high current density (or reaction rate). Here, we report that a sulfur-doped indium catalyst exhibits high faradaic efficiency of formate (>85%) in a broad range of current density (25-100 mA cm^-2) for electrocatalytic CO₂ reduction in aqueous media. The formation rate of formate reaches 1449 μmol h^-1 cm^-2 with 93% faradaic efficiency, the highest value reported to date. Our studies suggest that sulfur accelerates CO₂ reduction by a unique mechanism. Sulfur enhances the activation of water, forming hydrogen species that can readily react with CO₂ to produce formate. The promoting effect of chalcogen modifiers can be extended to other metal catalysts. This work offers a simple and useful strategy for designing both active and selective electrocatalysts for CO₂ reduction.