Unravelling electrolyte dynamics in reversible molten carbonate fuel cells through distribution of relaxation times

The identification of the different processes occurring during the operation of a molten carbonate fuel cell is presented using the distribution of relaxation times in a button cell and the electrodes operating in reversible mode. Five main peaks are identified, related to electric charge transfer, ionic charge transfer, gas diffusion, electrolyte distribution, and electrolyte segregation. The identification is based on the time constant and is contrasted with experimental data of the different processes, showing good agreement. An accurate separation of the charge transfer and diffusion resistances is presented. The filling degree of electrolyte is accounted for using the charge transfer, and the contact angle of the electrolyte is predicted based on the time constant of the peak related to the electrolyte distribution. An average filling degree of 24.4 % is calculated in the Ni electrode and 13.3 % in the NiO electrode. This work offers an alternative approach to study the electrolyte dynamics in molten carbonate fuel cells under operation.