<p>Electrocatalytic conversion of carbon dioxide (CO₂) into formate offers a sustainable pathway to mitigate environmental degradation and the energy crisis. Tin (Sn)-based materials are promising electrocatalysts for CO₂ reduction to formate; however, their efficiency is limited by weak CO₂ adsorption and activation, as well as sluggish reaction kinetics. In this work, we designed an intercrossing nanoporous Cu₆Sn₅/Sn intermetallic heterojunction via a scalable alloying-etching protocol. The resulting Cu₆Sn₅/Sn catalyst with abundant interfacial sites exhibited enhanced formate selectivity (60.79%) at − 0.93 V versus the reversible hydrogen electrode (RHE), together with a high partial current density of 12.56 mA/cm² and stable operation for 16 h. The modulated electronic structure of Cu₆Sn₅ coupled with the robust interfacial interaction between Sn and Cu₆Sn₅ synergistically promoted CO₂ adsorption and activation, thereby improving CO₂ reduction reaction (CO₂RR) performance. Electrochemical measurements and in situ infrared spectroscopy confirmed that the dual-phase interfaces facilitate H₂O decomposition and the generation of abundant *H intermediates, which in turn accelerate the protonation of CO₂ to formate. This work highlights a scalable strategy for constructing intermetallic heterojunction catalysts that combine facile synthesis, reproducibility, and superior catalytic activity for CO₂RR.</p>