A carbon in molten carbonate anode model for a direct carbon fuel cell

The electrochemical oxidation of carbon at the anode of a direct carbon fuel cell (DCFC) includes charge transfer steps and chemical steps. A microstructural model of carbon particle is built, in which perfect graphene stacks are taken as the basic building blocks of carbon. A modified mechanism taking account of the irreversibility of the process and supposing that the electrochemical oxidation of carbon takes place only at the edges of the graphene sheets is proposed. A Tafel type overall rate equation is deduced along with expressions of exchange current density (j₀) and activation polarization (η_act). The performance of carbon black and graphite as the fuel of DCFC is examined. It has been found that j₀ is in the range of 0.10-6.12 mA cm⁻² at 923-1123 K and η_act is in the range of 0.024-0.28 V at 923-1123 K with current density in 10-120 mA cm⁻². Analysis of the j₀, η_act values and the product composition reveals that the charge transfer steps as well as the oxygen ion absorption steps are both important for the reaction rate. The activity of the carbon material with respect to atom location is introduced to the open circuit potential difference (OCP) calculation with Nernst equation.