Capture and electrochemical conversion of CO2 to ultrathin graphite sheets in CaCl2-based melts

Abstract

Molten CaCl₂ is reported to be a potential dopant for reactivation of CaO and enhancement of the cyclic capture ability of CaO. The present work showed that O²⁻ in molten CaCl₂–CaO has a strong affinity for CO₂ at 850 °C, with resulting formation of carbonates. Using a RuO₂·TiO₂ inert anode, the formed carbonates were successfully electrochemically split into value-added ultrathin graphite sheets, which look like a kind of graphene, accompanied by evolution of carbon monoxide at the cathode and environmentally friendly by-product oxygen at the anode. The reduction mechanism of CO₃²⁻ was investigated by cyclic voltammetry and square wave voltammetry. Results demonstrated that there are two steps in electrochemical reduction of CO₃²⁻, and the transferred electron numbers calculated for each step are 1.76 and 1.99, respectively. The kind of graphene generated at the cathode may have applications in fields such as energy storage and electronic devices. The molten CaCl₂–CaO has potential applications and prospects in large-scale capture of CO₂, and electrochemical conversion of CO₂ into high value added carbon material such as ultrathin graphite sheets with renewable energy sources.