Modulating CO₂/H₂O Ratio at Hydrophobic Catalytic Interface Promotes C-C Coupling in Acidic CO₂ Electroreduction

Optimizing the electrocatalytic interface for the electroreduction of carbon dioxide (CO₂) in acid through the usage of cations in the electrolyte has shown its effectiveness in enhancing CO₂ conversion efficiency. However, such a positive impact in promoting CO₂ activation is limited by the solubility of salt, hence alternative ways to optimize the interface shall be sought for. Here, the hydrophobicity of the catalytic interface is tuned through the judicious design of a sandwich-like structure by covering the catalytic copper layer with polytetrafluoroethylene (PTFE) particles. After optimizing the thickness of the PTFE layer on a commercial CuO_X nanoparticle catalyst, an improved FE for multi-carbon products from 35.0% to 59.3% in 0.05 m H₂SO₄ electrolyte with the addition of 0.8 m K⁺ (pH = 1.6) is achieved. Moreover, in situ Raman spectroscopy proves that the hydrophobic layer facilitates the formation of ^*CO intermediates and promotes the transition of bridge-bonded ^*CO to atop-bonded ^*CO. The reduction of carbon monoxide (CO) is further performed at different partial pressures to reveal the critical role of ^*CO coverage for the formation of multi-carbon products. Collectively, it is proposed that the optimized hydrophobic modification of the catalyst effectively tunes the coverage of ^*CO intermediate as well as reduces the available water molecules at the interface, thereby promoting the formation of multi-carbon products and simultaneously suppressing hydrogen evolution reaction. The study illustrates a new venue toward improving the efficiency of CO₂ conversion in acid.