Understanding three-dimensionally interconnected porous oxide-derived copper electrocatalyst for selective carbon dioxide reduction

Abstract

In this work, we have investigated a hierarchical CuO-derived inverse opal (CuO-IO) catalyst with high CO selectivity up to 80–90% and minimal H₂ evolution at moderate potentials for CO₂ electroreduction. The three-dimensionally (3D) structured, porous catalyst was composed of small CuO nanoparticles and exhibited a peak CO faradaic efficiency (FE) of 72.5% (±1.8), complete suppression of H₂ formation, and good stability over 24 hours operation at −0.6 V versus the reversible hydrogen electrode (RHE). In situ Raman, X-ray absorption spectroscopy and X-ray diffraction measurements indicated reduction of the catalyst into metallic Cu⁰ oxidation state with dominant Cu(111) orientation under electrocatalytic conditions. We suggest that rapid depletion of CO₂ and protons at the highly roughened catalyst surface likely increased the local pH during the electrolysis. The combination of C₁ favoring Cu(111) surfaces and reduced local proton/CO₂ availability facilitated selective conversion of CO₂ into CO and reduced H₂ and C₂ products. Our work provides additional understanding of the structure–property relationships of 3D porous electrocatalysts for CO₂ reduction applications by evaluating the crystallographic orientation, oxidation state, and crystallite size of a CO-selective CuO-IO catalyst under realistic working conditions.