Electrochemical CO₂ reduction using alkaline membrane electrode assembly on various metal electrodes

Electrochemical CO₂ reduction reaction (CO₂RR) has received much attention as a promising technology to reduce CO₂ using renewable electricity, but it typically suffers from low CO₂ solubility in aqueous phase and a high cell resistance of a conventional liquid phase reactor. Here, we report the CO₂RR using a membrane electrode assembly that consists of gas diffusion electrode (GDE) and anion exchange membrane (AEM). The GDE enabled facile mass transfer of gaseous CO₂ directly to the catalyst and the AEM could suppress hydrogen evolution reaction (HER) by increasing local pH at the catalyst. Various metal powders of Pd, Ag, Zn, Cu, Sn, Ru, Pt, Ni were tested as cathode catalysts. Pd and Ag showed high current density of >200 mA cm^-2 at -3.0 V and faradaic efficiency >95% for CO production with a low cell resistance of <0.150 mΩ. Whereas a small amount of Pd black or Ag powder showed lower selectivity for CO production with more HER, using Pd/C or Ag/C at the same metal content could enhance the CO selectivity with better durability. The CO productivity could be maximized by changing CO₂ flow rate, and it was comparable to the values obtained from gas-phase CO₂ reduction.