Effects of applied voltage and temperature on the electrochemical production of carbon powders from CO2 in molten salt with an inert anode

• Effects of temperature and voltage on the morphology of carbon product were evaluated.
• Carbon products exhibited different forms (particles, sheets and nanostructured cages).
• Carbon powders with surface area of 868.3 m2 g−1 can be prepared.
• Optimized energy consumption for preparing the carbon products was 35.6 kW h kg−1.

With a SnO2 inert anode, amorphous carbon powders were successfully deposited on a nickel cathode by electrochemical conversion of CO2 in Li2CO3–Na2CO3–K2CO3 eutectic melt in the temperature range of 450 °C to 650 °C and under the electrolysis voltages of 3.0 V to 6.0 V. The effects of electrolysis temperature and cell voltage on the morphology and structure of the produced carbon, and on the energy consumption of the process were systematically investigated. The morphologies and particle size of the carbon products were proven to be affected by the electrolysis cell voltage and temperature. As the electrolysis condition varied, the deposited carbon exhibited different forms, including nanoparticle, nanoflake, nanosheet and heart-shape nanostructured cage, etc. The particle sizes of the obtained carbon ranged from av. 2 μm to 50 nm, and smaller particles were obtained at higher cell voltage and lower electrolysis temperature. The carbon product obtained at 450 °C under 5.5 V exhibited the highest BET surface area of 868.3 m2 g−1. FTIR analysis demonstrated that oxygen-containing functional groups presented on the surface of the carbon product, which was most likely due to the active dangling bond on the carbon materials. The optimized energy consumption for producing 1 kg of carbon is as low as 35.59 kW h with a current efficiency of 87.86% at 450 °C under a constant cell voltage of 3.5 V.