Electrochemical Conversion of (Bi)carbonate-based CO2 Capture Solutions to Ethylene on PorousCopper-based Nanowire Electrodes

Rising atmospheric CO2 concentrations threaten global climate stability and ecosystem health. One promising approach to tackling this challenge is the development of novel technologies capable of capturing CO2 and converting it into valuable chemicals such as ethylene (C2H4). Alkali hydroxide scrubbing captures CO2 as carbonate/bicarbonate-rich solutions; however, regenerating pure CO2 for vapour-fed CO2 electrolyzers is energy- and cost-intensive. (Bi)carbonate-fed electrolyzers circumvent these steps by directly converting the capture solution into valuable chemicals. Nevertheless, the activity and stability of state-of-the-art (bi)carbonate-fed electrolysis systems remain inferior to vapour-fed CO2 electrolyzers, necessitating the development of improved electrocatalysts, electrodes, and device designs. This research systematically explores nanostructured copper-based porous electrodes to improve the electrocatalytic conversion of (bi)carbonate to ethylene (C2H4), a compound of significant industrial importance. Specifically, we examine uniformly distributed polycrystalline copper nanowires grown on copper substrates, with nanowire size, density, and spatial distribution tuned via varied electrochemical oxidation protocols. Comprehensive morphological and structural characterization was conducted via scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD). The best-performing electrodes demonstrated Faradaic efficiencies toward ethylene of ~37% at a current density of 150 mA cm−2 and a cell voltage of 3.3 V, and remained stable for at least 100 hours. Compared to previous state-of-the-art (bi)carbonate-fed electrolyzers with comparable stability, this system nearly doubles the energy efficiency toward ethylene production, reaching ~13%. To elucidate the mechanisms behind this performance boost, we employed operando high-speed optical microscopy combined with mass-transport numerical modeling, which revealed two complementary phenomena at play: (1) localized increase in pH within the nanowire array suppresses the competing hydrogen evolution reaction (HER); and (2) promotion of rapid bubble growth and detachment, due to the high aerophobicity of the electrode induced by Wenzel-state wettability, increases convective CO2 transport to the electrode surface and mitigates local CO2 depletion. Finally, our techno-economic analysis indicates that the (bi)carbonate-fed electrolyzer system becomes more cost-effective than vapour-fed CO2 electrolyzers when electricity prices exceed 2.6 ¢/kWh—a threshold commonly surpassed in most regions worldwide.