Structure of Hydrogen-Oxygen MCFCs

The working temperature of MCFCs is around 600 to 650°C. As an electrolyte, mixed melts containing 62 to 70 mol% of Li2C03 and 30 to 38 mol% of K2CO3, with compositions close to the eutectic point, are used in MCFCs. Sometimes, Na2C03 and other salts are added to these melts. These liquid melts are immobilized in the pores of a ceramic matrix with fine pores made of sintered MgO or LiA102 powders. 

Porous metallic gas-diffusion electrodes are nsed. The anode consists of a nickel alloy with 2 to 10% chrominm. The chromium that is added prevents a recrystallization and sintering of the porous nickel while it works as an electrode. This action is based on chromium forming a thin layer of chromium oxide at the nickel grain boundaries, interfering with surface diffusion of the nickel atoms. 

The cathode consists of lithiated nickel oxide. Nickel oxide (NiO) is a p-type semiconductor that has rather low conductivity. When doped with lithium oxide, its conductivity increases tens of times, owing to a partial change of Ni to Ni3+ 

With its fine pores filled with the carbonate melt the matrix is a reliable protection against gases bubbling through and getting into the wrong electrode compartment. Therefore, there is no need to provide gas-diffusion electrodes with a special gas barrier layer. 

The MCFC components have thicknesses as follows the anode, 0.8 to 1.5 mm the cathode, 0.4 to 1.5 mm and the matrix, 0.5 to 1 mm. In a battery of the filter-press type, the individual cells are separated by bipolar plates made of nickel-plated stainless steel contacting the anode with their nickel side, and the cathode with their steel side. All structural parts are made of nickel or nickel-plated steel. In a working battery, the temperature of the outer part of the matrix electrolyte is lower than that of the inner part, so that in the outer part the electrolyte is solidified. This provides tight sealing around the periphery of the individual battery cells. 

---