Selective electro-reduction of CO2 into methane and formic acid using efficient bimetallic and bimetallic oxide electrocatalysts in liquid-fed electrolyzers

CO2 valorization via bicarbonate electrolysis (BCE) is a promising and emerging technology geared towards 'green' chemical synthesis. The development of active and facile electrocatalyst layers is vital for establishing efficient electrolyzers. Bimetallic (Zn-(x)/Cu(100-x)) and bimetallic oxide (ZnOx/CuO(100-x)) catalyst layers with different ratios of the respective components were electrodeposited onto pre-treated copper (Cu) mesh as active cathodic electrodes for zero-gap BCE electrolyzers. It was found that the selectivity and electrochemical performance of the as-synthesized catalysts strongly depends on the composition and nature of the formed phases of the deposited catalyst layers. This achieved a maximum Faradaic Efficiency for methane (FECH4) of 82 % at 160 mA cm(-)(2) and for formic acid (FEHCOOH) of 81.3 % at 140 mA cm(-)(2) using the bimetallic catalysts while maintaining H-2 evolution at < 16 %. Similarly, the bimetallic oxides exhibited slightly higher catalytic conversion of CO2 for FECH4 (84.3 %) at 100 mA cm(-)(2), and FEHCOOH (81.8 %) at 140 mA cm(-)(2), while keeping the H-2 evolution at <16 %. The high inter-phasal area of the materials' mixed phases promoted a high reaction rate, which translated into a maximum recorded partial current density for CH4 (j(CH4)) and HCOOH of 160 mA cm(-2) and 116.5 mA cm(-2), respectively.