A comparative study of electrochemical CO ₂ reduction on hydrothermally synthesized carbon nanosphere-supported Ni-, Cu-, and NiCu-hydroxide catalysts

The electrochemical reduction of CO₂ (CO₂RR) offers a promising route for sustainable fuel and chemical production. This study compares the CO₂RR performance of hydrothermally synthesized carbon nanosphere-supported nickel hydroxide (Ni-C), copper hydroxide (Cu-C), and bimetallic nickel-copper hydroxide (NiCu-C) catalysts, investigating the influence of metal composition. Significant differences in product selectivity were observed: Cu-C primarily yielded C₂ products, whereas Ni-C and NiCu-C generated mixtures of H₂, CO, formate, and acetate, with minimal C₃ products. Faradaic efficiencies (FEs) for C₃ products (including propylene, propane, and <i>n</i>-propanol) were very low for Ni-C and NiCu-C (<0.3% combined). In comparison, Cu-C showed modest FEs (∼3-5%) primarily for <i>n</i>-propanol. X-ray photoelectron spectroscopy revealed partially oxidized nickel species (Ni ^<i>δ</i>+) in Ni-C and NiCu-C and predominantly Cu(i) species post-reaction, while scanning electron microscopy confirmed a distinct fibrous morphology for the Ni-containing catalysts. Control experiments with CO and acetate, and <i>in situ</i> Raman spectroscopy, suggest reaction pathways that differ from the typical Cu-catalyzed routes, potentially involving hydrogenated intermediates such as *CHO. This work provides a comparative analysis, highlighting how catalyst composition and associated electronic/structural properties influence the overall CO₂RR activity and selectivity pathways in Ni, Cu, and NiCu hydroxide systems, rather than achieving significant C₃ production.