Carbon formation via the electrolysis of an earth-abundant calcium-based molten salt: The effects of current density

The conversion of CO₂ to carbon via molten salt electrolysis is a promising pathway towards mitigating greenhouse gas emissions. However, costly Li-based melts have received much of the attention to date. This work details the electrochemical properties of an earth-abundant CaCl_2[sbnd]CaCO₃ melt at 700 °C. Specifically, the electrodeposited carbon yield was systematically investigated as a function of current density. Under a pure CO₂ atmosphere, a maximum Faradaic efficiency of 86 % was attained at an optimal current density 1000 mA/cm². The optimal current density is influenced by factors including, but not limited to, cell geometry and CO₂ partial pressure. At lower current densities, carbon can be attacked by O₂/CO₂. At higher current densities, cathodic CO evolution begins to compete with carbon formation. Carbon products were found to be largely amorphous with some graphitic/turbostratic characteristics. This work marks the beginning of a thorough investigation into the behaviour of the molten CaCl_2[sbnd]CaCO₃ system, with future plans to examine the effects of temperature and other parameters.