Effects Of Molten Salt System On The Electrooxidation Of Carbon Anode

Direct carbon fuel cell （DCFC） is an efficient and cleaner power-generation device,which is the only fuel cell capable of converting solid carbon into electricity without areformation process. DCFC is gaining increasing attention due to its high conversionefficiency with low pollution. Solid carbon fuels used in the DCFC can be easily availablewhich include coal, petroleum, natural gas and even biomass. Further more, the productcarbon dioxide needs no further purification, and directly for commercial use。The traditional molten salt system of32%Li₂CO₃-68%K₂CO₃was respectively groundwith the metal oxide of Fe₂O₃, Co₃O₄, NiO, Ni₂O₃, MnO₂, Al₂O₃and MgO, and the ternarymolten salt system of MgCO₃-Li₂CO₃-K₂CO₃was prepared by the same treatment.Electrochemical performance of graphite anode was measured with linear potential scan testand constant potential discharge test in different molten salt system. Results indicated thatthe electrochemical performance of the graphite anode was significantly improved bymixing the catalysts of five kinds of metal oxide of the fourth period into the electrolyte.The molten salt system with Co₃O₄had the minimum effect on the increasedelectrochemical performance of graphite anode，while the molten salt system with Fe₂O₃,Ni₂O₃, MnO₂had much better performance than that with Co₃O₄. In particular, the additiveof NiO showed the best result. Also, it is found that the electrooxidation performance of thegraphite anode increased a lot mixing Al₂O₃and MgO in the electrolyte. The ternary moltensalt system of MgCO₃-Li₂CO₃-K₂CO₃was a good electrolyte for DCFC, too.When the molten salt system was added in NiO, the onset potential for electrooxidationof carbon was-0.90V in the temperature of750℃，shifted to negative value by0.32V.On the other hand, at the same applied potential, i.e., E=-0.20V, the current density of theanode increased by168.9mA·cm^-2after adding NiO in the electrolyte, and it was as highas218.0mA·cm^-2. Constant potential discharge test found that the curve of current for theanode in the electrolyte with NiO was125.0mA·cm^-2at constant potentials of-0.40V, andthe curve of current for anode was smoother than that in the blank experiment.The ICP-MS test found that the molten salt system contains all kinds of metal oxide,and it contains Al₂O₃at most, while NiO at least. The results of cyclic voltammetry for agolden three-electrode structure showed that there were redox peaks in the molten salt system with the metal oxide, and the metal oxide ion can react electrochemical reactionbetween the anode and cathode. Further more, the concentration of CO in the gas productsof carbon anode decreased with the reaction temperature rised, and the concentration ofCO in the gas products of carbon anode was more than that in the blank experiment invarious temperatures. The larger polarization potential, the less the concentration of CO inthe gas products of carbon anode was. Summing up the above data, the mechanism ofimproving the electrooxidation performance of carbon anode by the metal oxide wasanalyzed at last in the paper.