Complex-confinement strategy to high-loading and structure-tunable indium single-atom catalysts toward efficient electrocatalytic CO2 reduction

Synthesis of high-loading single-atom catalysts (SACs) with unique coordination structures, especially those p-block main group metals (e.g., In, Sn), to realize electrocatalytic CO2 reduction reaction (CO2RR) with high performance remains a challenge. Here, we report a complex-confinement strategy to prepare In–O2N2 and In–O4 SACs on hollow mesoporous nitrogen-doped carbon, with a loading amount as high as 13.02 wt% and 9.89 wt%, respectively. In–O2N2 SACs outperform In–O4 SACs in CO2RR toward formate production, reaching a high selectivity (95.5%) and partial current density of formate (−58.2 mA cm−2). In situ Raman spectroscopy shows that In–O2N2 SACs have a sole ∗OCHO intermediate for formate product, whereas both ∗OCHO and ∗COOH intermediates are observed in In–O4 SACs. Computational calculations elucidate that coordination environment matters greatly in the electronic structure manipulation of In SACs, where a closer position of p-band center to the Fermi level enables In–O2N2 SACs to bind and activate CO2 molecules more favorably.