Bias-Adaptable CO2-to-CO Conversion via Tuning the Binding of Competing Intermediates.

CO2 electroreduction powered by renewable electricity represents a promising method to enclose anthropogenic carbon cycle. Current catalysts display high selectivity toward the desired product only over a narrow potential window due primarily to unoptimized intermediate binding. Here, we report a functional ligand modification strategy in which palladium nanoparticles are encapsulated inside metal-organic frameworks with 2,2'-bipyridine organic linkers to tune intermediate binding and thus to sustain a highly selective CO2-to-CO conversion over widened potential window. The catalyst exhibits CO faradaic efficiency in excess of 80% over a potential window from -0.3 to -1.2 V and reaches the maxima of 98.2% at -0.8 V. Mechanistic studies show that the 2,2'-bipyridine on Pd surface reduces the binding strength of both *H and *CO, a too strong binding of which leads to competing formate production and CO poison, respectively, and thus enhances the selectivity and stability of CO product.