The Effect of the Distribution of Cu and Ag in Tandem Catalysts on the Production of Ethylene in the Electrocatalytic CO2 Reduction Reaction

Abstract

The increasing demand for electrical energy storage due to the energy transition has prompted research into the electrocatalytic reduction of CO2. Concentrating on the production of ethylene is a promising approach to increase the cost-efficiency and feasibility of the process. Cubased catalysts can convert CO2 into ethylene, but the poor activity of Cu alone for the first step reduction of CO2 into *CO puts limitations on the production of ethylene. Tandem catalysis divides the reaction pathway towards ethylene into two segments, with silver being an excellent metal for the first segment that reduces CO2 to CO and Cu facilitating the second segment where *CO is reduced to ethylene. Utilizing this concept, the effective transfer of CO from Ag to Cu active sites is essential to steer the CO2RR toward the production of ethylene. This study prepared and tested several Cu-Ag catalysts with different distributions of Cu and Ag, using electrodeposition, codeposition, and galvanic replacement, and evaluated their effectiveness of synergy (i.e., transfer of CO from Ag to Cu active sites based on the product ratio of ethylene and CO. The results showed that interfacial contact enhanced the effectiveness of synergy compared to separated metals. Furthermore, the homogeneous distribution of Cu and Ag resulted in the relatively high partial current densities and Faradic efficiencies for ethylene and CO. The catalyst prepared by galvanic replacement with a 1 mM AgNO3 solution for 2 minutes showed uniquely higher activity and selectivity towards ethylene than CO, resulting in the most effective synergy. Additionally, this study presents a method to synthesize uniform Cu2O nanospheres of 0.87 µm via polyol synthesis. The galvanic replacement was performed on these particles but exhibited overall very poor catalytic activity and selectivity, favoring the HER. It is suggested that this is related to the use of porous carbon paper as substrate. This is because the majority of the Cu2O nanospheres remained unaffected by galvanic replacement, exhibiting the poor activity of Cu for the reduction of CO2.