Copper-catalysed exclusive CO₂ to pure formic acid conversion via single-atom alloying

Converting CO₂ emissions, powered by renewable electricity, to produce fuels and chemicals provides an elegant route towards a carbon-neutral energy cycle. Progress in the understanding and synthesis of Cu catalysts has spurred the explosive development of electrochemical CO₂ reduction (CO₂RR) technology to produce hydrocarbons and oxygenates; however, Cu, as the predominant catalyst, often exhibits limited selectivity and activity towards a specific product, leading to low productivity and substantial post-reaction purification. Here, we present a single-atom Pb-alloyed Cu catalyst (Pb₁Cu) that can exclusively (~96% Faradaic efficiency) convert CO₂ into formate with high activity in excess of 1 A cm^-2. The Pb₁Cu electrocatalyst converts CO₂ into formate on the modulated Cu sites rather than on the isolated Pb. In situ spectroscopic evidence and theoretical calculations revealed that the activated Cu sites of the Pb₁Cu catalyst regulate the first protonation step of the CO₂RR and divert the CO₂RR towards a HCOO* path rather than a COOH* path, thus thwarting the possibility of other products. We further showcase the continuous production of a pure formic acid solution at 100 mA cm^-2 over 180 h using a solid electrolyte reactor and Pb₁Cu.