Bio-inspired hydrophobicity promotes CO₂ reduction on a Cu surface

The aqueous electrocatalytic reduction of CO₂ into alcohol and hydrocarbon fuels presents a sustainable route towards energy-rich chemical feedstocks. Cu is the only material able to catalyse the substantial formation of multicarbon products (C₂/C₃), but competing proton reduction to hydrogen is an ever-present drain on selectivity. Here, a superhydrophobic surface was generated by 1-octadecanethiol treatment of hierarchically structured Cu dendrites, inspired by the structure of gas-trapping cuticles on subaquatic spiders. The hydrophobic electrode attained a 56% Faradaic efficiency for ethylene and 17% for ethanol production at neutral pH, compared to 9% and 4% on a hydrophilic, wettable equivalent. These observations are assigned to trapped gases at the hydrophobic Cu surface, which increase the concentration of CO₂ at the electrode-solution interface and consequently increase CO₂ reduction selectivity. Hydrophobicity is thus proposed as a governing factor in CO₂ reduction selectivity and can help explain trends seen on previously reported electrocatalysts.