Capture and electrochemical conversion of CO2 to value-added carbon and oxygen by molten salt electrolysis

Abstract

A molten salt electrochemical system comprising a eutectic mixture of Li–Na–K carbonates, a Ni cathode, and a SnO₂ inert anode is proposed for the capture and electrochemical conversion of CO_2. It is demonstrated that CO₂ can be effectively captured by molten carbonates, and subsequently electrochemically split into amorphous carbon on the cathode, and oxygen gas at the anode. The carbon materials generated at the cathode exhibit high BET surface areas of more than 400 m² g⁻¹ and as such, represent value-added products for a variety of applications such as energy storage and pollutant adsorption. In the carbonate eutectic (500 °C), the presence of Li₂CO₃ is shown to be required for the deposition of carbon from the melt, wherein O²⁻ or Li₂O serves as the intermediate for CO₂ capture and electrochemical conversion. SnO₂ proved to be an effective anode for the electrochemical evolution of oxygen. Electrochemical reactions were found to proceed at relatively high current efficiencies, even though the current densities exceed 50 mA cm⁻². The intrinsic nature of alkaline oxides for CO₂ capture, the conversion of CO₂ to value-added products, and the ability to drive the process with renewable energy sources such as solar power, enables the technology to be engineered for high flux capture and utilization of CO₂.