pH‐Controlled Catalyst Reconstruction Switches CO ₂ Reduction Pathways Between Methane and Ethylene

ABSTRACT Controlling product selectivity in electrochemical CO 2 reduction (CO 2 RR) on Cu‐based catalysts remains a major challenge due to the complex interplay between catalyst structure and local reaction environment. Herein, we report a pH‐controlled reconstruction strategy to regulate catalyst morphology and electronic structure, enabling selective CO 2 RR pathways toward either methane or ethylene. A maleic acid copper (MHCu) precursor is electrochemically reduced under different pH conditions, which modulates the Ostwald ripening process and results in Cu/Cu x O catalysts with distinct particle sizes and surface roughness. Under acidic conditions, accelerated ripening produces larger and smoother particles, favoring CH 4 formation with a Faradaic efficiency of up to 60.5%. In contrast, suppressed ripening under neutral and alkaline conditions generates roughened nanostructures that promote C–C coupling, delivering C 2+ products with Faradaic efficiencies exceeding 50% and a maximum C 2 H 4 selectivity of 34.0%. Notably, the product selectivity can be effectively switched between CH 4 and C 2 H 4 , with CH 4 reaching a Faradaic efficiency of 60.5% and the C 2 H 4 /CH 4 ratio increasing up to 10.0 under optimized conditions. Electrochemical and spectroscopic analyses reveal that the enhanced C 2+ production originates from the combined effects of increased surface roughness and optimized Cu valence states, which facilitate *CO accumulation and subsequent C–C coupling.