Electrochemical oxidation of carbon in a 62/38 mol % Li/K carbonate melt

The electrochemical gasification of coal to CO in a direct carbon fuel cell (DCFC) has thermodynamical advantages, including the conversion of heat into power at a reversible efficiency of 100%. Molten carbonate fuel cell (MCFC) technology may form the basis for constructing DCFC's. Here the electrochemical oxidation of carbon in a 62/38 mol % Li/K carbonate melt is studied using impedance spectroscopy (IS) and cyclic voltammetry (CV). A set of equilibria is introduced which fully describes the electrochemical equilibrium of the system. From IS it is shown that for temperatures lower than 700 degreesC, charge transfer is the slowest step, while at higher temperatures a second unidentified step also contributes significantly to the d.c. resistance of the electrode. The d.c. resistance is 100 to 220 Ohm cm(2) at 650 degreesC and 12 to 60 Ohm cm(2) at 750 degreesC, depending on the carbon surface roughness.