Decoupling Interfacial Gas-Liquid Transport via Polymer Confinement on Hierarchical Copper for Highly Selective...

Toward achieving sustainable carbon neutralization, converting CO₂ via electrocatalysis into premium multicarbon (C₂₊) feedstocks represents a critical strategy. However, copper (Cu)-based catalysts frequently suffer from severe dynamic surface reconstruction and limited C₂₊ 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_xO@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_xO@PDMS/CF catalyst delivered an outstanding C₂₊ Faradaic efficiency of 55.5% (including 41.3% for ethylene) and attained a partial current density of 49 mA cm^-2 for C₂₊ 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.