Selective electrocatalytic CO2 reduction to acetate on polymeric Cu–L (L = pyridinic N and carbonyl group) complex core–shell microspheres

Abstract

Low selectivity is one of the greatest challenges of an electrocatalytic CO₂ reduction reaction (CO₂RR), e.g., using copper-based catalysts in water solution. Herein, we report the production of pure acetate (aside from H₂) from a CO₂RR with a novel polymeric Cu–ligand (pyridinic N and carbonyl group) complex (p-CuL) core–shell microsphere synthesized by a facile thermal-polymerization of urea and a Cu–urea complex. The highly selective reduction of CO₂ to acetate, without any detectable gas products besides H₂, is enabled by the unique co-coordination of pyridinic N and CO with copper whose chemical state is between +1 and +2 and the porous 3D core that is kinetically favorable for the acetate product. The maximal faradaic efficiency of acetate of ∼64% is attained at −0.37 V vs. RHE in a 0.5 M KHCO₃ electrolyte, and H₂ evolution is much suppressed. In the process of the CO₂RR to acetate, the Cu(II)–carbonyl coordination remains while Cu^δ+–ligand active sites are reduced to Cu(I). In addition, the highly selective acetate production is favored by the p-CuL core–shell microsphere for the adsorption of some important intermediates of CO₂ reduction and their dimerization and further e⁻/h⁺ reduction, as seen from the distinctly increased CO and –OH groups in the O K-edge X-ray absorption spectrum (XAS) of p-CuL after the CO₂RR.