Analysis by electrochemical impedance spectroscopy of new MCFC cathode materials

The corrosion and electrochemical behaviours of Li1−xNi1+xO2 and Li1−x(NiyCo1−y)1+xO2 oxides were investigated in a molten carbonate electrolyte at 650°C and compared with a NiO reference cathode material. These oxides are future candidate cathode materials for molten carbonate fuel cell (MCFC) and are divided in two families: monophasic oxides and biphasic oxides. The monophasic oxides show an important dissolution or a lower catalytic activity and are not good candidates for future use in MCFC. The biphasic oxides show a low dissolution and a good catalytic efficiency close to the NiO value. In this first study of new cathode materials by electrochemical impedance spectroscopy (EIS), it appears that the biphasic Li–Ni–Co–O oxides are the best candidates for MCFC. The MCFC electrochemical cathodic mechanism, taking into account the peroxide and the superoxide pathways and the O2−, CO2 and H2O diffusion proposed in the bibliography [I. Uchida, T. Nishina, Y. Mugikura, K. Itaya, J. Electroanal. Chem., 206 (1986) 229; C. Yuh, J.R. Selman, AIChE J., 34(12) (1988) 1949; T. Nishina, I. Uchida, Proc. Symp. Molten Carbonate Fuel Cell Technol., The Electrochem. Soc., PV90-16 (1990) 438; T. Nishina, G. Lindbergh, T. Kudo, I. Uchida, The International Fuel Cell Conference Proceedings, NEDO (1992) 189–192], is used to discuss the EIS results. The limiting rate of the peroxide or/and superoxide reactions of the new oxides was compared with the NiO reference oxide.