The effect of metal dissolution on carbon production by high-temperature molten salt electrolysis

Abstract

High-temperature molten salt electrolysis is suitable for the production of carbon morphologies such as carbon nanotubes and nano-onions. In this study, CO2 was electrochemically reduced to solid carbon by molten lithium carbonate electrolysis in an Inconel 625 vessel at a fixed temperature of 750°C. Four different cathodes (clean nickel, used nickel, stainless steel, and galvanized steel) were used to determine the effect of the electrode material on the morphology produced. The carbonaceous products obtained were analyzed with scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), Raman microscopy, and X-ray diffraction (XRD). With nickel cathodes, the dominant forms of carbon were spherical, whereas tubular structures dominated with steel-based cathodes. Nano-onion was the structure of carbon with the least metal impurities. Iron was discovered to promote carbon nanotube growth. In the presence of iron, nanotube wool was also found. A greater number of different morphologies were observed when the amount of metal impurities increased. The correlation found between XRD results and sample masses suggests that the amount of metal impurities in the sample varied more than the carbon content. Thus, the yield of the process can be expected to be fairly similar between parallel experiments.