A stabilized NiO cathode was proposed and evaluated for the reduction of NiO dissolution in molten carbonate fuel cells. The NiO cathode was stabilized by the addition of alkaline earth oxide(MgO) to the cathode. The solubilities of NiO and stabilized NiO in alkali metal carbonate($62Li_2CO_3-38K_2CO_3$) were measured as a function of temperature, $CO_2$ and $O_2$ partial pressures. The MgO content in the stabilized NiO cathode was optimized with respect to its solubility. Conductivity of stabilized NiO cathode was measured to confirm whether stabilized NiO was electrically conductive or not. Half cell and single cell tests were also performed to evaluate the electrochemical performance of stabilized NiO cathode. From the linear sweep voltammetry and impedance test, it was confirmed that the catalytic activity of the stabilized NiO cathode for oxygen reduction should be comparable to that of the NiO cathode. In a long run operation of single cell test with a 10% MgO-stabilized cathode, a significant reduction of Ni precipitation was obtained. However, 10% addition of MgO to the NiO cathode resulted in poor mechanical strength of sintered cathode.
A mathematical model was proposed to describe the NiO cathode dissolution in molten carbonate fuel cell. The Ni precipitation reaction, intra pore diffusion, migration, convection and variation of pore geometry and Ni deposition amount were considered in the model. Simulated Ni deposition amount and the position of deposition zone were in good agreement with the experimental results. Simulated deposition profiles were given to examine the effects of operating time, reaction rate and diffusion rate, initial condition of $H_2$ and $Ni^{2+}$ and tortuosity of matrix. Using the proposed model, the circuit-shorting phenomenon was explained by the composition variation of reactant between the inlet and the outlet of the gas.
