Characterization of Trimetallic and High Entropy Alloys for Electrochemical Carbon Dioxide Reduction and Oxygen Evolution

Abstract

Bimetallic materials have exhibited synergistic catalytic activity for both electrochemical CO2 reduction and O2 evolution, improving upon limitations for single metal electrocatalysts, but few studies have explored trimetallic or high entropy alloys (HEAs) for these applications, though they have the potential to further tune the properties of their constituent metals. Working electrodes for bulk CO2 electrolysis were comprised of ternary alloy species, which were synthesized by drop-casting followed by annealing in a furnace. The mixed phase NiCo2 alloy and Ga2(SO4)3 solid catalyst exhibited higher selectivity for CO2 reduction over the H2 evolution reaction, compared to the single phase GaCo2Ni alloy. Mechanistic investigation suggests that Ga initially reduces CO2 to CO, which is then further reduced to CH3OH by NiCo2. Additionally, eight HEA candidates were characterized for their stability in chronopotentiometry experiments. Contrary to the hypothesis, only the Sc-Zr-Nb-Rh-Pd candidate fulfilled criteria for stability against oxidation. These findings present mixed phased alloys as a new avenue for CO2 reduction electrocatalyst discovery, and also indicate Sc-Zr-Nb-Rh-Pd alloys as a strong catalyst candidate for O2 evolution, although further characterization of the precise elemental ratio is needed.