A numerical and experimental comparison of a single reversible molten carbonate cell operating in fuel cell mode and electrolysis mode

Abstract

This work summarizes the experimental and numerical activities done in a molten carbonate cell operated in reversible mode using a single cell with an electrodes-electrolyte interface area of 80 cm2. The experimental activity is divided into two sets. Firstly, running the cell only in fuel cell mode in order to compare five electrochemical zero-dimensional models available in literature and choose the one with the smallest deviation with respect to the experimental data, which is applied later in electrolysis mode. The second experimental set is focused on studying the cell working in reversible mode by varying the gas composition entering the fuel electrode and oxygen electrode, the ratio of the flow rate of the oxygen electrode to the fuel electrode and the cell temperature. The results indicate that molten carbonate cells present lower polarization losses in electrolysis mode than in fuel cell mode. According to the parameter variations, a lower cell temperature decreases the performance in both modes; besides, in the fuel electrode the results indicate carbon dioxide reduction apart from the reduction of water; moreover, the oxygen electrode is strongly sensible to the high presence of carbon dioxide that could cause a faster nickel oxide dissolution accelerating the degradation. Throughout the experimental campaign the molten carbonate cell presents a quite high degradation, contrary to previous results of reversible molten carbonate cells carried out using button cells where an improvement was found instead of a degradation. Electrolyte refilling was tried at the end of the second experimental campaign obtaining a significant decrease of internal resistance with a difference of only 20.6% with respect to the initial condition. According to the experimental activity, the fitted model gives a good prediction of the performance in fuel cell mode; however, in electrolysis mode the prediction is weak mainly attributed to the differences in the diffusive phenomena between both operative modes.