Hierarchical Copper with Inherent Hydrophobicity Mitigates Electrode Flooding for High-Rate CO₂ Electroreduction to Multicarbon Products

Copper is currently the material with the most promise as catalyst to drive carbon dioxide (CO₂) electroreduction to produce value-added multicarbon (C₂₊) compounds. However, a copper catalyst on a carbon-based gas diffusion layer electrode often has poor stability-especially when performing at high current densities-owing to electrolyte flooding caused by the hydrophobicity decrease of the gas diffusion layer during operation. Here, we report a bioinspired copper catalyst on a gas diffusion layer that mimics the unique hierarchical structuring of Setaria's hydrophobic leaves. This hierarchical copper structure endows the CO₂ reduction electrode with sufficient hydrophobicity to build a robust gas-liquid-solid triple-phase boundary, which can not only trap more CO₂ close to the active copper surface but also effectively resist electrolyte flooding even under high-rate operation. We consequently achieved a high C₂₊ production rate of 255 ± 5.7 mA cm^-2 with a 64 ± 1.4% faradaic efficiency, as well as outstanding operational stability at 300 mA cm^-2 over 45 h in a flow reactor, largely outperforming its wettable copper counterparts.