Understanding the degradation of Ag₂Cu₂O₃ electrocatalysts for CO₂ reduction

Recently, a mixed-metal oxide with a paramelaconite-type crystal structure (Ag₂Cu₂O₃) has been investigated as a promising catalyst for electrochemical reduction of CO₂ and CO. The catalyst operates with a reasonable overpotential and good selectivity. However, during its utilization, the catalyst experiences a degradation in conversion efficiency, thus limiting its potential in industrial application. This has so far been attributed to the unstable nature of the crystal structure, which tends to partition into metallic copper and silver. In this study, we characterized this decomposition using atom probe tomography and analytical electron microscopy. We found this decomposition to take place also under an electron beam without any ongoing reaction conditions. We also found that dissolution mechanisms must play a role in the degradation of the catalyst. This is deduced from the existence of nanostructures which only form during catalyst operation and are comprised of copper and potassium, the latter of which stems from the electrolyte. The composition of these nanostructures was confirmed using an atom probe.