Electrochemical conversion of CO2 into value-added carbon with desirable structures via molten carbonates electrolysis

Abstract

Direct conversion of CO₂ to high value-added carbon products based on molten salt electrochemistry has been proven to be a feasible approach to solve the climate problem and achieve carbon neutrality. In this work, carbon nanotubes (CNTs), carbon spheres (CSs) and honeycomb carbon are synthesized by electrolysis of a single or multiple alkali metal carbonate electrolyte. The elemental composition, morphology and structure, crystallinity and graphitization degree of carbon products are characterized by electron dispersive spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and Raman microspectroscopy (RAM). The results demonstrate that a high yield of CNTs is obtained in Li₂CO₃ electrolyte by regulating the electrolysis temperature and current density. Compared to pure Li₂CO₃, Li–Na carbonate electrolyte with 1 wt% stannic oxide/cerium oxide (SnO₂/GeO₂) favors CS formation rather than CNT formation. Additionally, honeycomb carbon products are generated in Li–Na–K electrolyte, when the electrolysis temperature is lower than 600 °C. Overall, this work provides a novel carbon neutral strategy where high value-added carbon products are synthesized using CO₂ as a carbon source.