Electrodeposition of Solid Carbon from CO₂ in Molten Li₂CO₃-Na₂CO₃ as a Fuel for Direct Carbon Fuel Cells

The electrochemical conversion of CO 2 into solid carbon in high-temperature molten salts has been reported, but there is still room to develop ways of using the electrodeposited carbon. This study investigated the electrodeposition of solid carbon on Mo, Pt, and graphite electrodes in molten Li 2 CO 3 -Na 2 CO 3 at 873 K as a fuel for direct carbon fuel cells (DCFCs). The relationship between electrochemical conditions and characteristics of electrodeposited carbon suitable for DCFC fuels was revealed by electrochemical measurements, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The electrodeposited carbon on Mo electrode prepared by potentiostatic electrolysis at −1.25 V (vs Ni(II)/Ni) for 30 min had small crystallite size with 42.0 nm and was modified by oxygen functional groups, which showed the highest discharge property, with a stable output voltage and average coulombic efficiency of 90.2% for repeating galvanostatic conditions of −10 and 10 mA cm −2 for 20 cycles. In addition, the coordination structure of CO 3 2− ions in the system was also identified by high-temperature Raman spectroscopy and density functional theory simulations to discuss the mechanism of carbon electrodeposition. The reported data will contribute to tailoring and developing new utilization processes for CO 2 -derived solid carbon.