Ni/Cu/Ag: An Electrochemically Synthesised Trimetallic Stack for CO2 Reduction

Abstract

Climate change, as a result of excess atmospheric CO2 and other greenhouse gases, maintains a position, according to the United Nations as the “defining issue of our time”.1 This has led to research efforts to limit CO2 outputs as well as recycling CO2 which is already present. The electrochemical reduction of CO2 has exponentially gained interest as a possible solution since the late 1990s; if the reduction can be achieved in conjunction with a renewable energy source (e.g solar power), it could be considered carbon negative. Electrochemical CO2 reduction would remove some of the excess CO2 from the atmosphere in conjunction with providing a way for the intermittent energy generated by renewable methods to be stored as chemical bonds, both of which aid the fight against climate change.Significant focus has been placed on pure metals as electrocatalysts since Hori’s seminal discovery that Cu can uniquely reduce CO2 by more than two electrons to produce hydrocarbons.2 High overpotentials and poor selectivity remain as challenges due to the scaling relations between the simultaneous pathways of CO2 reduction.3 One approach for breaking these is alloying or the use of mixed metal phases. Bimetallic catalysts, particularly those containing Cu have gained considerable interest4, however, limited examples of trimetallic catalysts have been explored.Herein, a NiCuAg electrocatalyst has been electrochemically synthesised by copper electrodeposition on nickel, followed by galvanic replacement to produce a silver layer. The combination of Ni and Cu was proven to be promising in recent studies5,6 generating desirable non-CO and H2 products such as ethanol. Ag has been shown to promote *CO intermediate production on the Cu surface7 thus its addition to our catalyst should further promote non-CO and H2 products and increase their selectivities.Linear sweep voltammetry revealed significant activity at potentials more negative than -0.8 V vs. Ag/AgCl, thus CO2 reduction was completed in this region. Reduction products were analysed by gas chromatography and liquid products by NMR. The trimetallic stacks were characterised by XRD, and SEM/EDX before and after reduction to explore their morphology and lifetimes.