Electro-activated indigos intensify ampere-level CO reduction to CO on silver catalysts.

The electrochemical reduction of carbon dioxide (CO) to carbon monoxide (CO) is challenged by a selectivity decline at high current densities. Here we report a class of indigo-based molecular promoters with redox-active CO binding sites to enhance the high-rate conversion of CO to CO on silver (Ag) catalysts. Theoretical calculations and in situ spectroscopy analyses demonstrate that the synergistic effect at the interface of indigo-derived compounds and Ag nanoparticles could activate CO molecules and accelerate the formation of key intermediates (*CO and *COOH) in the CO pathway. Indigo derivatives with electron-withdrawing groups further reduce the overpotential for CO production upon optimizing the interfacial CO binding affinity. By integrating the molecular design of redox-active centres with the defect engineering of Ag structures, we achieve a Faradaic efficiency for CO exceeding 90% across a current density range of 0.10 - 1.20 A cm. The Ag mass activity toward CO increases to 174 A mg. This work showcases that employing redox-active CO sorbents as surface modification agents is a highly effective strategy to intensify the reactivity of electrochemical CO reduction.