Synergistic catalysis between In single atoms and In nanoparticles for highly selective electrocatalytic CO reduction to formate with high current densities.

The practical realization of the electrocatalytic reduction of CO to formate is limited by the lack of suitable highly active and selective electrocatalysts, particularly candidates compatible with operation at high current densities. Herein, we report a dual-active site electrocatalyst consisting of In single atoms and In nanoparticles supported on N, S-codoped porous carbon (In-NSC/NPs), which enables a remarkable formate faradaic efficiency (FE) of 92% with a large absolute partial current density for formate of up to 1.1 A cm. By using membrane electrode assembly cells, a formate FE exceeding 90% and an energy conversion efficiency of over 44% are attainable within a wide cell voltage range of 2.4-3 V. The maximum formate generation rate reaches 10.5 mmol cm h at a cell voltage of 2.9 V. By coupling with anodic glycerol oxidation, the formate yield rate in a full electrolytic cell is significantly improved to 23.2 mmol cm h while using the same reaction conditions as the standard anodic oxygen evolution reaction. A combination of control experiments and characterization methods reveals that In nanoparticles facilitate the generation of the *OCHO and the subsequent hydrogenation step to generate formate while the In single atoms boost HO dissociation. The generated *H migrates to the surface of the In nanoparticles, increasing the proton concentration and promoting the hydrogenation reaction.