Phase changes of newly synthesized Co-coated Ni cathode in MCFC cathodic conditions

Abstract

A molten carbonate fuel cell (MCFC) is expected to provide high efficiency generation of electricity and an environmentally clean means of power generation [1, 2]. However, the durability of the MCFC experiences difficulties at over 40 000 hr of operation. One of the lifetime limiting problems of a MCFC is the slow dissolution of the state of the art cathode material NiO into the electrolyte [3]. Two main methods have been adopted to solve this problem. One method is to use an alternative electrolyte. More basic molten carbonate melts adopting Li/Na eutectic carbonates instead of Li/K eutectic carbonates have been used to decrease the Ni dissolution rate in the electrolyte [4]. The other method is to develop alternative cathode materials. Among cathode materials, LiCoO2 seems to be one of the best candidates because of its higher stability in the molten carbonate, and the rate of dissolution is slower than that of the NiO cathode. However, application of LiCoO2 as a new cathode material has problems in scaling up the electrode area and a relatively higher manufacturing cost than that of the NiO cathode. Therefore, recently many investigators have attempted to resolve the problem by developing new cathode materials in which NiO grains have been coated with a small amount of LiCoO2 or CoO by various coating techniques to reduce their dissolution [5, 6]. In this study, we have tried to prepare a new candidate cathode material of Co3O4-coated Ni powders using the Pechini method [7] as a new coating technique. In addition, we report on the phase changes of the Co-coated Ni cathode in MCFC cathodic conditions. The Co3O4-coated Ni powders were prepared by the following method. A stoichiometric amount of cobalt acetate (Aldrich, USA, purity of 98+%) and citric acid (CA) (Aldrich., USA, purity of 99.5+%) were dissolved in distilled water and thoroughly mixed with an aqueous solution of ethylene glycol (EG) (CA:EG:cobalt ions = 2:1:1). After that, the solution was adjusted by adding NH4OH until pH 8 was achieved and Ni powder (filamentary nickel 255, Inco, USA) was immersed in the solution. The resultant solution was heated to 80 ◦C while being stirred until a gel precursor was produced. The gel precursor was calcined at 350 ◦C for 3 hr in air.