Decoupling Interfacial Gas–Liquid Transport via Polymer Confinement on Hierarchical Copper for Highly Selective Ethylene Electrosynthesis

Toward achieving sustainable carbon neutralization, converting CO 2 via electrocatalysis into premium multicarbon (C 2+ ) feedstocks represents a critical strategy. However, copper (Cu)-based catalysts frequently suffer from severe dynamic surface reconstruction and limited C 2+ selectivity under highly negative operational potentials. Herein, we report an interfacial covalent confinement strategy by designing a poly(dimethylsiloxane) (PDMS)-encapsulated cauliflower-like catalyst on a copper foam (CF) skeleton (Cu x O@PDMS/CF). The conformal PDMS overlayer physically constructs a “carbon-rich, water-poor” hydrophobic microenvironment that kinetically impedes proton and water diffusion, thereby heavily curbing the competitive hydrogen evolution. Chemically, the establishment of robust interfacial Cu–O–Si covalent bonds induces local lattice tensile strain and generates electron-deficient Cu sites (Cu δ+ ). Mechanistic analyses reveal that this tailored electronic structure strengthens the electrostatic binding affinity toward the crucial negatively charged dimer intermediate (*OCCO δ− ), substantially lowering the activation energy barrier for the pivotal C–C coupling step. Consequently, evaluated in an H-type cell, the optimized Cu x O@PDMS/CF catalyst delivered an outstanding C 2+ Faradaic efficiency of 55.5% (including 41.3% for ethylene) and attained a partial current density of 49 mA cm –2 for C 2+ species at −1.4 V vs RHE. Additionally, outstanding long-term stability was achieved, with the system preserving 92.3% of the original current response following a 120 h uninterrupted constant-potential operation.