Electrochemical Carbon Deposition from CO2 in Molten Carbonates: Substrate-Dependent Growth

Abstract

Electrochemical carbon deposition from molten carbonate salts using inert electrodes and no additional catalyst is systematically examined. At sufficiently cathodic potentials, carbon formation occurs within 30 min and transitions from a substrate-dependent nucleation to carbon-on-carbon growth. Although deposits formed on either mild steel or graphite cathodes exhibit comparable thicknesses and salt content, their macrostructures differ, reflecting differences in early-stage growth rates and surface chemistry. Characterization by ICP-OES, Raman spectroscopy, SEM/EDS, synchrotron powder X-ray diffraction, and C K-edge X-ray absorption near edge structure reveals that the as-deposited carbon is predominantly disordered sp²-bonded material; However, post-treatment reveals latent turbostratic ordering in select samples, indicating that short-range order is established during deposition but is obscured by entrained electrolyte and kinetically formed amorphous phases. No anode-derived contamination is detected and carbon grown on graphite cathodes show minimal metallic impurities. These results clarify the roles of cathode surface chemistry and provide pathways for controlling electrode-derived impurity incorporation and carbon structure in catalyst-free molten carbonate systems.