A New Low Temperature Catalytic Molten Electrolyte For Carbon Electrooxidation

The direct carbon fuel cell （DCFC） is a special type of fuel cell that directly uses solidcarbon as fuel and anode by which the chemical energy stored in solid carbon can beconverted into electricity at high efficiency and low emission. The theoreticalelectrochemical conversion efficiency of DCFC is100%, and the practical is more than80%. DCFC has less emissions and the relased CO2has high purity, which can be easilyrecovered. Solid carbon fuels can be easily produced from many low-priced resourceswhich include coal, petroleum, natural gas, biomass and even organic garbage. Therefore,DCFC is a very promising power generation device.The eutectic CsVO₃-MoO₃salt mixture is used as catalyst which is added to the moltensalt electrolyte of32%Li₂CO₃-68%K₂CO₃. Electrooxidation performance of graphite in thismolten salt system was measured by linear potential scan and constant potential dischargetest. Results indicated that the electrooxidation performance of graphite was significantlyimproved by the addition of CsVO₃-MoO₃to Li₂CO₃-K₂CO₃. At750℃, the onset potentialfor electrooxidation of graphite shifted to negative value by0.36V reaching-0.94V, andthe oxidation current density at-0.4V increased by73.7mA·cm^-2reaching105.2mA·cm^-2.after adding the catalyst in the electrolyte.The results of cyclic voltammetry using gold working electrode showed that there wereredox peaks in the molten salt electrolyte with the catalyst of CsVO₃-MoO₃, indicating theoccurance of redox reaction of the catalyst. The concentration of CO in the gas products ofgraphite oxidation was analysed. It is shown that the concentration of CO decreased byadding the catalyst of CsVO₃-MoO₃. So the columbic efficiency of graphite oxidation isenhanced, and the highest columbic efficiency is98.8%. based on the the above data, themechanism for the improvement of graphite electrooxidation performance by the catalyst ofCsVO₃-MoO₃was discussed.A new low temperature molten salt （CsVO₃-MoO₃-Li₂CO₃-Na₂CO₃-K₂CO₃） wasprepared. The effect of its composition and reaction temperature on graphiteelectrooxidation performance was investigated. The conductivity of the new molten saltelectrolyte was measure. It was found that the conductivity of the new molten saltelectrolyte is1.155S·cm^-1when the mass ratio of CsVO₃-MoO₃and Li₂CO₃-Na₂CO₃-K₂CO₃is1:5at550℃, which is0.43S·cm^-1larger thanLi₂CO₃-Na₂CO₃-K₂CO₃. With the increase of the content of CsVO₃-MoO₃and reactiontemperature, graphite electrooxidation performance was significantly enhanced. The newmolten salt electrolyte with the mass ratio of CsVO₃-MoO₃to Li₂CO₃-Na₂CO₃-K₂CO₃to be1:5exhibited a superior catalytic performance for the graphite electrooxidation at the lowtemperatures. At550℃, the onset potential for graphite oxidation is significantly shifted tonegative value by0.3V, and the current density at-0.4V and0.2V increased by6times.The onset potential for graphite oxidation is-0.98V at650℃, shifted to negative value by0.39V, and the current density （at-0.4V） is71.5mA·cm^-2and increase by11times.