A Phase-Structure-Control Strategy Toward High-Performance Acidic CO2 Electromethanation on Cu-Based Perovskite Oxides

Abstract

Cu-based catalysts hold significant potential for acidic CO₂ 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 CO₂ electromethanation over Cu-based perovskite oxides, alongside elucidating the intrinsic correlations between phase structure and catalytic behavior. Using Sr₂CuTeO_6-δ (SCT) as a proof-of-concept system, we precisely control its phase transition from tetragonal (I4/m) to cubic (Fm-3m) structure, yielding three well-defined catalysts: SCT-(I4/m), dual-phase SCT-(I4/m+Fm-3m), and SCT-(Fm-3m). Our comprehensive investigations indicate that CH₄ selectivity increases with phase transition degree, reaching its highest value on SCT-(Fm-3m). This enhancement can be attributed to the upward-shifted Cu 3d-band center and oxygen vacancies in Fm-3m phase, which cooperatively shift the rate-determining step from *COOH formation to *CO hydrogenation by strengthening intermediate adsorption. During prolonged electrolysis, SCT-(Fm-3m) remains stable, whereas SCT-(I4/m) and SCT-(I4/m+Fm-3m) undergo thermodynamically-driven symmetry reorganization, initiated by in situ generated oxygen vacancies, to the stable Fm-3m structure. Importantly, SCT-(Fm-3m) outperforms previously reported Cu-based catalysts, achieving a high CH₄ 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.