The electrochemical CO2 reduction reaction (CO2RR) to give C1 (formate and CO) products is one of the most techno‐economically achievable strategies for alleviating CO2 emissions. Now, it is demonstrated that the SnOx shell in Sn2.7Cu catalyst with a hierarchical Sn‐Cu core can be reconstructed in situ under cathodic potentials of CO2RR. The resulting Sn2.7Cu catalyst achieves a high current density of 406.7±14.4 mA cm−2 with C1 Faradaic efficiency of 98.0±0.9 % at −0.70 V vs. RHE, and remains stable at 243.1±19.2 mA cm−2 with a C1 Faradaic efficiency of 99.0±0.5 % for 40 h at −0.55 V vs. RHE. DFT calculations indicate that the reconstructed Sn/SnOx interface facilitates formic acid production by optimizing binding of the reaction intermediate HCOO* while promotes Faradaic efficiency of C1 products by suppressing the competitive hydrogen evolution reaction, resulting in high Faradaic efficiency, current density, and stability of CO2RR at low overpotentials.

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