A Host–Guest Strategy to Achieve Selective and Robust CO2-to-CO Electrocatalysis in Aqueous Media

Heterogeneous materials incorporating molecular catalysts hold strong promise for efficient electrocatalytic CO2 reduction to value-added products. While activity and selectivity are traditionally tuned through ligand design, increasing attention is being paid to the second-coordination sphere, which modulates reactivity beyond the metal center. Inspired by enzymatic systems, this outer-sphere environment enhances catalysis through spatial confinement and noncovalent interactions. Here, we report a host–guest strategy to control CO2 reduction using the [bpyMn(CO)3MeCN]+ catalyst encapsulated in an anionic cage. When immobilized on an electrode surface, the assembly selectively produces CO. Mechanistic studies indicate that the cage promotes proton-coupled CO2 binding while preventing catalyst deactivation. This demonstrates that supramolecular second-sphere engineering is a powerful strategy for enhancing electrocatalytic performance and provides a basis for future developments in molecular electrocatalysts.