ELECTROCHEMICAL OXIDATION OF CARBONACEOUS MATERIALS DISPERSED IN MOLTEN CARBONATE (COAL, FUEL CELL).

摘要

A novel approach toward electrochemical conversion of carbonaceous materials (e.g., coal) was investigated. The basic idea was to enhance the electrochemical reactivity of coal slurries by operating at high temperature. To achieve high operating temperatures, a molten carbonate electrolyte (ternary eutectic of lithum, sodium and potassium carbonate) was employed. In the experimental cell, particulated coal or carbon was dispersed by stirring of the melt. Anodic oxidation took place at an inert gold electrode, which also served as the current collector. An alumina-sheathed carbon dioxide/oxygen/gold half-cell served as the reference electrode, and a shielded graphite rod served as the counter electrode. The cell was operated at 500-900(DEGREES)C. Other parameters experimentally investigated were: type of carbonaceous material, concentration of carbonaceous material, stirring rate, anode material, and purge gas composition. The electrochemical measurements entailed generation of steady-state current-voltage curves and open circuit potential data under a wide variety of experimental conditions. Product gas measurements were also performed. The open circuit potential data agreed well with theoretical values at temperatures of 700(DEGREES)C and above. The current-voltage data at 700(DEGREES)C showed that current densities of 100 mA/cm('2) could be achieved at overpotentials of approximately 0.5 volts. Measurement of the anode off-gas at 700(DEGREES)C indicated that complete oxidation of carbon to carbon dioxide was achieved. Chemical loss of carbon by the Boudouard reaction was found to be substantial. In order for the system to be commercially attractive as a direct coal-fired fuel cell, the chemical loss of carbon would have to be reduced considerably. Passivation of the anode was sometimes encountered, and was caused by dissolved impurities originating from the coal. Fortunately, passivation was minimal in the low overpotential region (below 0.3 volts). The investigation also included a qualitative mechanistic analysis of the anode process. It was concluded that the anode process occurred by means of both direct and indirect interactions between the anode and the carbon particles.