Abstract

 The electrochemical reduction of carbon dioxide (CO₂) to multicarbon hydrocarbons or oxygenate compounds beyond carbon monoxide is of great importance, as it offers a promising way to obtain a renewable fuel of high energy density and close the carbon cycle. Copper has been considered the predominant and effective electrocatalyst for the CO₂ reduction reaction (CO₂RR), especially when aiming for ethylene products. However, the selectivity or current density of most catalysts for ethylene production is not satisfactory at competitive prices. Here, we present a newly designed electrocatalyst comprising Al₂CuO₄ nanosheets uniformly covered with CuO nanoparticles (CuAl-1: CuO/Al₂CuO₄-23) by phase and interphase engineering, achieving an ultrahigh selectivity of 82.4% for ethylene in an H-cell system with good catalytic stability and material durability for 100 h. In a flow-cell electrolyzer, this catalyst achieves a remarkably high ethylene partial current density of 421 mA cm^-2, substantially higher than the as-synthesized bare CuO (261 mA cm^-2) counterpart. The results of time-resolved attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) suggest that compared to the CuO catalyst, CuAl-1 enabled high surface coverages of *CO intermediates and strengthened adsorption of *CO for C–C coupling toward *OCCO, which is an intermediate for the production of ethylene. X-ray absorption analysis confirms that Cu oxide species in CuAl-1 are well retained during CO₂ reduction, whereas the bare CuO catalyst is completely reduced to the metallic Cu state. Density functional theory calculations propose that a synergistic effect between CuO and Al₂CuO₄ in the CuAl-1 steers the CO₂RR pathway towards ethylene.