Secondary Coordination Sphere Engineering of Single‐Sn‐Atom catalyst via P Doping for Efficient CO2 Electroreduction

The regulation of the local microenvironment in the single‐atom catalysts affords a scheme for accelerating the overall reaction kinetics of electrochemical CO2 reduction reaction (CO2RR), which is of vital importance but remains challenging. Herein, a carbon nanotube‐supported single‐Sn‐atom catalyst (P‐SnN4‐CNT) is developed by a modified pyrolysis procedure with P‐doping into the second coordination shell of SnN4 moiety to modulate the electron structure of metal Sn center. The resulting P‐SnN4‐CNT delivered a high CO partial current density of −380 mA cm−2 with Faradaic efficiency (FE) of CO above 90% across a wide range of −0.5 to −0.8 V versus reversible hydrogen electrode (vs RHE), along with optimal FE (CO) of ≈98.5% at −0.6 V versus RHE in a flow cell. Moreover, P‐SnN4‐CNT achieved an extremely high turnover frequency of 126 471 h−1 with an applied potential of −0.8 V versus RHE, which ranks the best among the reported M─N─C catalysts for electrocatalytic CO2 reduction. The combination of in situ characterization techniques and density functional theory calculation revealed that the doping of P atoms benefited the activation and hydrogenation steps of CO2 and promoted the Sn4+ reduction to Sn2+ during the reaction process, where Sn2+ is identified as the active site for the CO generation. The work provides a clear mechanistic insight for both electron structure optimization and identification of active sites by local microenvironment regulation of single‐Sn‐atom, which shall pave a way for the exploitation of other M─N─C catalysts with high CO2RR performance. A remarkably enhanced CO2RR performance is achieved by engineering the secondary coordination sphere of a single‐Sn‐atom catalyst via P doping. The promoted reduction of Sn4+ to Sn2+, with in situ generated Sn2+ as the true active site, reduces the energy barrier for the hydrogenation steps of CO2, thus boosting its electroreduction to CO.