Self-supported copper-based gas diffusion electrodes for CO2 electrochemical reduction

Abstract

Nanostructured copper materials are catalytically active for the electrochemical reduction of CO₂ (CO₂RR) to produce hydrocarbons. However, most of these catalysts were investigated in conventional batch reactors at low current densities (<50 mA cm⁻²) due to the limitation of mass transport. Herein, a nondestructive strategy is proposed to transform nanostructured Cu catalysts into self-supported gas diffusion electrodes (GDEs), which enables the evaluation of the CO₂ reduction performance in a flow cell at high current densities (up to 300 mA cm⁻²). Two typical self-supported GDEs were prepared through simply coating a hydrophobic microporous layer onto Cu_xO nanowires grown on Cu gauze. Both GDEs show high selectivity (>40%) for converting CO₂ to multi-carbon products, e.g. C₂H₄ and ethanol, at commercially relevant current densities (>100 mA cm⁻²) and low overpotentials (η < 0.65 V). The GDEs are stable for more than 6 hours at current densities higher than 100 mA cm⁻². Moreover, the nondestructive method allows us to directly compare the product distributions of the nanostructured Cu catalysts in a batch reactor and flow reactor and to demonstrate the influence of the reaction environment and mass transport on the CO₂RR. While the CO₂RR in the H-cell shows high selectivity towards CO and formate, the reaction in the flow cell produces a greater amount of multi-carbon products due to the fast CO₂ diffusion and high pH. Combined, the electrode design strategies and the experimental findings presented in this work are valuable for the development of other self-supported electrodes for practical applications.