Copper-Nanowires Incorporated with Silver-Nanoparticles for Catalytic CO₂ Reduction in Alkaline Zero Gap Electrolyzer

Carbon capture and utilization play important roles in reducing climate change. A promising way is to directly convert CO2 to valuable fuels through electrochemical reaction using renewable energy. In the present research, a thin layer of a nanocatalyst network on a gas diffusion layer was prepared by incorporating Ag-nanoparticles into Cu-nanowires, which was used as the cathode electrode for CO2 reduction reaction (CO2RR). The catalyst was evaluated with an alkaline membrane electrolyte assembly (MEA), which is called a zero gap electrolyzer. A high-performing catalyst of Cu-Ag was identified, containing 37% Cu and 63% Ag (Cu@Ag-63). The Faradaic and energy efficiencies of CO2RR vary with operational temperature ranging from 20 to 60 degrees C at a cell voltage of 3.0 V, with the Faradaic and energy efficiencies decreasing from 89 to 52% and from 38 to 23%, respectively. The highest catalytic current density of 153 mA/cm(2) for total CO2RR products was observed at 60 degrees C. The catalytic stability of an MEA with Cu@Ag-63 as the cathode catalyst was evaluated by chronopotentiometric operation at 30 degrees C and periodically measuring the gas products with a gas chromatograph. 94% Faradaic and 38% energy efficiencies of CO2RR were obtained during continuous long-term operation at 80 mA/cm(2) and 3.0 V. Halting the CO2RR reaction for a period of time and then resuming operation of the reactor greatly enhanced C2H4 production and lowered CO production. The Faradaic efficiency of C2H4 increased from 33 to 60%; but the Faradaic efficiency of CO decreased from 60 to 22%. The internal chemical variations during resting time are unclear at the cathode surface, which is probably relevant to nanosized Cu particles' oxidation and reduction again after resuming the applied negative potential, leading to the catalyst/electrolyte interface being renewed. The fresh catalyst/electrolyte interface greatly facilitated C-C coupling.