An in situ exsolved Cu-based electrocatalyst from an intermetallic Cu ₅ Si compound for efficient CH ₄ electrosynthesis

A Cu-based electrocatalyst (e-Cu₅Si) is developed by in situ exsolving ultrathin SiO_x layer-coated CuO/Cu nanoparticles (<100 nm) on the surface of a conductive intermetallic Cu₅Si parent. This specially designed e-Cu₅Si catalyst exhibits high performance for the CO₂ reduction reaction (CO₂RR), which affords an excellent CH₄ faradaic efficiency (FE) of 49.0% with partial current density of over 140.1 mA cm^-2 at -1.2 V versus reversible hydrogen electrode (RHE) in a flow cell, with outstanding stability. The strongly coupled multiphase interfaces among the SiO_x layer, CuO/Cu species, and substrate contribute to fast interfacial electron transfer for the CO₂RR. Moreover, in situ Raman analysis suggests that the ultrathin SiO_x layer simultaneously stabilizes the active Cu¹⁺ species and promotes the protonation of *CO to form *CH_xO, thereby greatly improving overall selectivity and activity of CH₄ production.