Cu/Bi metal-organic framework-based systems for an enhanced electrochemical transformation of CO2 to alcohols

This work assesses the performance of Cu(II) and Bi(III)-based metal-organic framework (HKUST-1 and CAU-17, respectively) blends into the electroreduction of CO2 to alcohols in a filter-press electrochemical cell. The bimetallic materials are supported onto porous carbon paper to form gas diffusion electrodes with a favorable continuous electrochemical conversion of CO2 to methanol and ethanol, together with formic acid and gas-phase products (i.e. hydrogen, carbon monoxide and ethylene) in a 0.5 M KHCO3 aqueous solution. The maximum reaction rates and faradaic efficiencies for CO2 conversion to methanol and ethanol are rCH3OH=29.7 μmol·m−2·s-1 (FE = 8.6%) and rC2H5OH=48.8 μmol·m−2·s-1 (FE = 28.3%), respectively, at j = 20 mA·cm−2 which enhanced the values obtained at homometallic Cu and Bi-based materials independently. This denotes a synergic effect of Cu and Bi-based MOFs, associated with a favored interplay between the actives sites and reaction intermediates, prompting methanol formation and C C coupling reaction to ethanol. The results also show that reaction selectivity to produce alcohols can be controlled by Cu/Bi loading in the electrode surface and current density applied to the system. A 12% bismuth content seems to be the optimum for the production of alcohols (FEalcohols = 36.9%, Salcohols = 0.32). Regarding the current density, CO2 reduction is more selective to methanol with a j=10 mA·cm−2 (FECH3OH = 18.2%), while at j = 20 mA·cm−2, ethanol becomes the dominant CO2 reduction alcohol (FEC2H5OH = 28.3%). The performance of the Cu/Bi-MOFs remains also pseudo-stable after 5 h of operation denoting the potential of the mixed metal-organic systems for the utilization of CO2.