Electrochemical deposition of carbon nanotubes from CO2 in CaCl2–NaCl-based melts

Abstract

As part of the efforts to address global climate change, the identification of methods for the capture of carbon dioxide and its selective electrochemical conversion into value-added carbonaceous materials in molten salt electrolytes is a research topic of scientific and technological significance. In most cases, metal electrodes such as nickel and stainless steel are used as the cathode to investigate the nucleation and growth of a variety of carbon nanostructures. In this study, the electrochemical deposition of carbon nanotubes (CNTs) and carbon microstructures was performed in molten CaCl₂–NaCl–CaO using glassy carbon and graphite rod as the cathode and RuO₂–TiO₂ as the anode. The capture formula was established and the capture coefficient was defined and calculated to be 1.8 s⁻¹. Cyclic voltammetry, constant voltage electrolysis, as well as on-line outlet gas analysis were conducted to investigate the electrode reactions, and the results indicated that the captured CO₂ can be electrochemically converted to carbon and environmentally-friendly oxygen as the only by-product. SEM and TEM images showed that quasi-spherical and nanotubular carbon were deposited on the graphite and glassy carbon cathodes at 750 °C. However, by regulating the temperature, quasi-spheres and nanosheets were observed at the glassy carbon cathode.