A Phase‐Structure‐Control Strategy Toward High‐Performance Acidic CO ₂ Electromethanation on Cu‐Based Perovskite Oxides

ABSTRACT Cu‐based catalysts hold significant potential for acidic CO 2 electromethanation, yet suffer from insufficient selectivity and stability especially at industrial‐level current densities. Here, we report a phase‐structure‐control strategy for high‐performance acidic CO 2 electromethanation over Cu‐based perovskite oxides, alongside elucidating the intrinsic correlations between phase structure and catalytic behavior. Using Sr 2 CuTeO 6‐δ (SCT) as a proof‐of‐concept system, we precisely control its phase transition from tetragonal ( I 4/ m ) to cubic ( Fm ‐3 m ) structure, yielding three well‐defined catalysts: SCT‐( I 4/ m ), dual‐phase SCT‐( I 4/ m + Fm ‐3 m ), and SCT‐( Fm ‐3 m ). Our comprehensive investigations indicate that CH 4 selectivity increases with phase transition degree, reaching its highest value on SCT‐( Fm ‐3 m ). This enhancement can be attributed to the upward‐shifted Cu 3 d ‐band center and oxygen vacancies in Fm ‐3 m phase, which cooperatively shift the rate‐determining step from *COOH formation to *CO hydrogenation by strengthening intermediate adsorption. During prolonged electrolysis, SCT‐( Fm ‐3 m ) remains stable, whereas SCT‐( I 4/ m ) and SCT‐( I 4/ m + Fm ‐3 m ) undergo thermodynamically‐driven symmetry reorganization, initiated by in situ generated oxygen vacancies, to the stable Fm ‐3 m structure. Importantly, SCT‐( Fm ‐3 m ) outperforms previously reported Cu‐based catalysts, achieving a high CH 4 selectivity of 67.0% at 400 mA cm −2 and maintaining stable operation for over 20 h in acidic media. Furthermore, applying this strategy to two more pairs of Cu‐based perovskite oxides yields comparably successful results.