Electrocatalytic CO2reduction reaction (CO2RR) toward commodity chemicals and fuels presents an enticing prospect wherein the emerging metallenes as catalysts have aroused great interest. Here, we report the synthesis of a kind of tiny metallene quantum dot (QD) called the stanene QD (Sn-ene QD), which features a few atom layers and rich edge centers and provides superior CO2RR activity by delivering ampere-level current densities with near-unity selectivity for formate production. Operandoattenuated total reflection-infrared (ATR-IR) spectroscopy and theoretical calculations deciphered that the rich edge centers of Sn-ene QDs hold high reactivity, and the residual cyano ligands with electron-withdrawing nature favor the stabilization of the CO2RR intermediate. Furthermore, the Zn-CO2battery assembled with Sn-ene QDs catalyst affords a high power density of 1.25 mW cm−2and an outstanding stability of ∼100 h. This work highlights the great potential of metallene QDs as a new platform for heterogeneous catalysis and energy conversion.