Dealloyed Intermetallic Cu₅Ca Fine Powders as Nanoporous Electrocatalysts for CO₂Reduction

We have prepared intermetallic Cu5Ca compound fine powders via a Na-melt synthesis method and demonstrated that Cu-based nanoporous structures exhibiting electrocatalytic CO2 reduction with higher selectivity for C2+ product formation than granular Cu particles could be facilely produced using Cu5Ca as a precursor. Depending on the nominal composition of the raw mixture (Cu, CaCl2, NaCl, and Na) and synthetic temperature, the fine powder was composed of different ratios of Cu and Cu5Ca. Among the various Cu–Ca phases, Cu5Ca was the most preferably formed phase in the current solid-state reaction, where Cu particles were attacked by Ca via a eutectic mixture melt of CaCl2 and NaCl. The Cu5Ca particles with a single phase obtained under optimal synthetic conditions had a Cu-based nanostructured surface, and the nanoporous structures (10 nm order in size) were further developed by the successive dealloying of Cu5Ca. The dealloyed products showed a high rate of formation of C2+ products [i.e., C2H4, C2H6, ethanol, and propanol with a total current efficiency (CE) of 37.9% at −2.2 V versus a reference Ag/AgCl electrode], whereas the amount of a typical C1 product, CH4, was small (CE of ∼0.4%). On the contrary, the reference granular Cu particles generated a large amount of CH4 (CE of ∼9.4%). The dealloying of Cu5Ca facilely provided nanoporous structures, and the degree of dealloying did not influence the catalytic performance, suggesting that Cu5Ca would be a useful precursor for obtaining nanoporous electrocatalysts for CO2 reduction.