In situ Reconstructured Alloy Nanosheets Heterojunction for Highly Selective Electrochemical CO₂ Reduction to Formate

Tin (Sn)-based materials are expected to realize efficient CO₂ electroreduction into formate. Herein, we constructed a heterojunction by depositing Cu on Cu-doped SnS₂ nanosheets. During the electrochemical reaction, this heterojunction evolves to a highly active phase of Cu₂O@Cu₆Sn₅ while maintaining its two-dimensional morphology. Specifically, a partial current density of 35 mA cm^-2 with an impressive faradaic efficiency of 93 % for formate production was achieved over the evolved heterojunction. In situ and ex situ experiments elucidated the formation mechanism of the Cu₂O@Cu₆Sn₅ heterojunction. Cu₆Sn₅ nanosheets were formed via a stepwise desulfurization process, while Cu₂O was generated through its reaction with hydroxyl radicals. This evolved heterojunction with a high electrochemically active surface area synergistically stabilized the *OCHO intermediate, thereby significantly enhancing the selectivity and activity. Our findings provide insight into the structural evolution process and guide the development of selective electrocatalysts for CO₂ reduction.