A Computer Simulation of the Oxygen Reduction Reaction in Carbonate Melts

A computer simulation of the oxygen reduction reaction in various carbonate melts has been carried out under steady-state conditions on the basis of a proposed kinetic model which takes into consideration the autocatalytic reaction involving oxygen and other reducible oxygen species in the melt, and the neutralization of oxide ions by dissolved carbon dioxide. A simulation of the presence of (physically) dissolved oxygen, in the diffusion layer region of the melt, corresponding to the possible situation in porous electrodes, causes a significant enhancement in the polarization curves, particularly in the mass-transfer control region. On the other hand, high levels of dissolved CO2 in the melt reduce the current density in the mass-transfer control region by reducing the concentration of active dioxygen ions, but enhance it considerably in the kinetic limiting (CO2 neutralization) region. High rates of the autocatalytic and neutralization reactions display the same effects on the polarization curves as dissolved O2 and CO2, respectively, but to a lesser degree. Comparison of the simulated polarization curves in various carbonate melts indicates that Li-rich melts show the best kinetic performance. On the contrary, the highest limiting currents are observed in K- or Na-rich melts. Variation of the cation composition in Li/K carbonate melts indicates that melts of high Li-content should give better kinetic performance.