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

Abstract

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 (ZnO_x/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 (FE_CH4) of 82 % at 160 mA cm⁻² and for formic acid (FE_HCOOH) of 81.3 % at 140 mA cm⁻² using the bimetallic catalysts while maintaining H₂ evolution at < 16 %. Similarly, the bimetallic oxides exhibited slightly higher catalytic conversion of CO₂ for FE_CH4 (84.3 %) at 100 mA cm⁻², and FE_HCOOH (81.8 %) at 140 mA cm⁻², while keeping the H₂ 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.