Grain boundary-abundant copper nanoribbons on balanced gas-liquid diffusion electrodes for efficient CO2 electroreduction to C2H4

The electrocatalytic CO2 reduction reaction (CO2RR) is a promising technology to produce value-added hydrocarbon chemicals, however, achieving a high selectivity to C2+ products at the industrial current density remains a great challenge. Herein, we demonstrate grain boundary-abundant copper (Cu) nanoribbons on balanced gas-liquid diffusion electrodes for efficient CO2RR to ethylene (C2H4). The Cu(II) carbonate basic (Cu2CO3(OH)2) nanoribbon is used as a precursor to convert into metal Cu under in situ electrochemical reduction. Unexpectedly, the generated Cu nanoribbon is formed by stacking tiny nanoparticles with exposure of Cu(111), Cu(200) and Cu(220) facets, which creates abundant grain boundaries (GBs). During CO2RR test, the thickness of the catalyst layer is identified as a crucial factor for the mass transfer of CO2 and electrolyte. By tailoring the thickness of catalytic layer, CO2 and electrolyte can simultaneously reach the surface of catalyst and participate in CO2RR. Under the synergetic effects of GBs and balanced gas-liquid diffusion, the optimized electrode delivers the Faradaic efficiencies toward C2H4 and C2+ products as high as 67.2% and 82.1% at the current density of 700 mA cm−2, respectively. Moreover, the partial current density of C2H4 can reach up to 505 mA cm−2, which is significantly higher than most reported results. The in situ Raman and attenuated total reflection surface-enhanced infrared absorption spectra show that abundant GBs enhance the activation of CO2 and significantly promote the formation and adsorption of *CO intermediates, which accelerate C-C coupling to form *OCCO and *OCCOH intermediates and improve the production of C2H4 and other C2+ products.