High‐rate CO₂‐to‐CH₄ Electrosynthesis by Undercoordinated Cu Sites in Alkaline‐Earth‐Metal Perovskites with Strong Basicity

Abstract The electrochemical CO₂ reduction to CH₄ has been extensively demonstrated, but still suffers from relatively poor activity and requires high overpotentials especially at large electrolysis rates. Perovskite oxides (A_xB_yO) are one type of promising electrocatalyst for the CO₂ reduction due to their tunable electronic structures. In this work, a Ca₂CuO₃ perovskite oxide catalyst is developed with alkaline‐earth A‐sites, featuring an inherently strong basic strengthand outstanding capability for CO₂ adsorption, as well as the undercoordinated Cu sites generated through partial surface Ca²⁺ cation leaching. The Ca₂CuO₃ catalyst exhibitsa high partial current density of 517 ± 23 mA cm⁻² for producing CH₄ at a low applied potential of −0.30 V versus reversible hydrogen electrode, which further reached to a peak value of 1452 ± 156 mA cm⁻². Density functional calculations show that the undercoordinated Cu sites allowed to promote the hydrogenation of ^*CO and subsequent ^*CHO intermediates, thus leading to the high CH₄ activity. This work suggests an attractive design strategy for tuning the A‐sites in perovskite oxides to realize high‐rate CO₂‐to‐CH₄ electrosynthesis with low overpotentials.