Nonequilibrium Electrochemical Synthesis of Cu-In Intermetallic Compound Nanoparticles for Selective CO₂ Reduction

An In-rich Cu-In intermetallic compound (IMC), CuIn₂, was accessed through an electrochemical nonequilibrium pathway and obtained as bulk Cu₂In core/CuIn₂ shell nanoparticles. CuIn₂ is thermodynamically metastable in the Cu-In binary phase diagram and has previously been observed only at Cu/In interfaces in sputtered thin films. Here, electrochemical reduction of a mixed metal oxide precursor (Cu₂In₂O₅) under aqueous CO₂ reduction conditions enables the formation of a metastable CuIn₂ shell encapsulating a Cu₂In core. The resulting biphasic IMC particles exhibit characteristic CO₂ reduction selectivity with strongly suppressed competing H₂ evolution. Density functional theory calculations suggested that CO adsorption at Cu bridge sites on the In-rich CuIn₂(121) surface competitively inhibits H adsorption, which may contribute to the suppressed H₂ evolution. This work demonstrates a nonequilibrium electrochemical route for accessing metastable IMC phase through oxygen-elimination-induced restructuring of a mixed metal oxide precursor.