Selective electrochemical methanation of carbon dioxide using a sulphide derived CuZn catalyst

Efficient catalysts facilitate the electrochemical reduction of CO₂, enabling its conversion into fuels or chemical feedstocks through proton coupled electron transfer processes. Among these catalysts, Cu-based ones stand out for their unique ability to produce hydrocarbon products with high faradaic efficiencies. This study focuses on the use of sulphide-derived (SD)-Cu_xZn_y nanoparticle catalysts, which have been found to exhibit enhanced methane selectivity during CO₂ reduction in an H-Cell with 0.10 M KHCO₃ as the electrolyte. The composition of the catalysts plays a crucial role in determining their catalytic behavior. At an optimal Cu/Zn ratio of 1:1, the SD-CuZn catalyst demonstrates exceptional methane production, achieving a faradaic efficiency of 76 ± 3 % at a potential of −0.98 V vs RHE. Moreover, a partial current density of −4.5 mA cm⁻² was achieved at a more negative potential of −1.09 V vs RHE. Ex situ characterization highlighted the significance of partially reduced CuS species in influencing the selectivity of hydrogenated carbon products. When CO₂ reduction was performed in a flow cell equipped with a gas diffusion electrode with 1.0 M KHCO₃ or 1.0 M KOH electrolytes in both anodic and cathodic compartments, the current density increased due to the enhanced mass transport rate. However, the altered conditions lead to a shift in selectivity, favoring carbon monoxide over methane. It is important to note that insights garnered from H-Cell experiments may not be directly extrapolated to flow cell setups.