Oxidation of ash-free coal in a direct carbon fuel cell

Abstract

The electro-oxidation behaviour of ash-free coal (AFC) was investigated by comparing biomass carbon and conventional hydrogen fuel. A coin-type direct carbon fuel cell (DCFC) based on molten carbonate fuel cell (MCFC) technology was employed. The investigation was carried out into active gas species in the anode, the fuel to carbonate ratio, gasification behaviour, and so on. Electrochemical methods of steady state polarization and step chronopotentiometry were used, and chemical methods, thermogravimetric analysis (TGA), and gas analysis with gas chromatography were also employed. The cells were operated at a fixed temperature of 850 °C, and their conditions were initially checked by hydrogen fuel. The cell performance of AFC was similar to carbon fuel but inferior to H2 fuel at 150 mA cm−2. The oxidation of AFC was progressed via the gasification of coal by heat, similar to carbon fuel. But the AFC showed H2 and CO as major gas species in the anode, a different gas species than carbon fuel which had only CO as a main gas species. In addition, the gasification temperature of AFC was much lower than that of carbon fuel, indicating that the AFC fuel can reduce the operational temperature below that of the carbon fuel, down to at least 700 °C.