Fumihiko Yoshiba

Performance and life of 10-kW molten-carbonate fuel cell stack using Li/K and Li/Na carbonates as the electrolyte

NiO cathode dissolution is a serious problem with molten carbonate fuel cells (MCFC). The target life-time of such cells is 40,000 h, but shorting by NiO cathode dissolution markedly decreases cell performance. NiO cathode dissolution depends on the composition of the molten carbonate electrolyte. The electrolyte generally comprises a mixture of lithium carbonate and potassium carbonate. Since the solubility of NiO in a mixture of lithium carbonate and sodium carbonate is lower than in lithium and potassium carbonate, it is expected that shorting by NiO cathode dissolution will take longer in a mixture of lithium and sodium. Therefore, a mixture of lithium carbonate and sodium carbonate is a strong candidate electrolyte. A unique 10-kW class stack, which uses a mixture of lithium and potassium carbonate and mixture of lithium and sodium carbonate as the electrolyte, has been developed and tested. The basic performance and life time of both electrolyte cells of the stack are reported. In particular, the change in cathode polarization caused by NiO cathode dissolution is evaluated quantitatively.

Development of High Efficiency MCFC/GT Hybrid Power Generation System

A number of cycle simulations, which are applied by Molten Carbonate Fuel Cell (MCFC) power plants combined with gas/steam turbines, prove that it is possible to design very highly efficient power plants. However, the stack performance, the operation technology and the performance estimation technology have not yet been established during the initial development stages. The Central Research Institute of Electric Power Industry (CRIEPI) has performed many cell and stack tests and has evaluated the performance under various operating conditions. The operation, performance analysis and estimation methods have been developed for various pressure ranges. Therefore, the accuracy of the plant power estimation has been improved immensely. CRIEPI has also proposed the application of a Li/Na electrolyte instead of a Li/K to achieve higher voltages and a longer stack life. A 10 kW-class short stack consisting of ten 1-m2 cells with a Li/Na electrolyte was operated for more than 10,000 hours, and a very low voltage decay rate was measured during the governmental program. Based on these accomplishments, field tests on small MCFC/GT (gas turbine) hybrid power plants with capacities of several hundred kW will be initiated in Japan throughout the next years.Copyright

Development of Estimation of SOFC System Performance

Development of an estimation method of a SOFC system performance has been conducted in the NEDO SOFC project from 2004-2008. There are two factors that indicate SOFC system performance. One is a current versus voltage relation includes parameters of a reactive gas composition and an operating temperature of the cell; the other is a heat management method that offers thermally self sufficient condition of the SOFC stack for the purpose to decrease its fuel gas supply. Two 1kW class SOFC system operating tests were carried out and energy balances of the systems were evaluated. Based on the results of the current and voltage relation test and the evaluated energy balance of the systems, the system efficiency and a qualitative analysis of an energy recirculation of the system are discussed.

Performance of new 10 kW class MCFC using Li/K and Li/Na electrolyte

The molten carbonate fuel cell (MCFC) uses generally mixture of lithium carbonate and potassium carbonate (Li/K) as the electrolyte. NiO cathode dissolution is one of serious problems for MCFC life. The NiO cathode has been found to dissolve into the electrolyte as Ni{sup 2+} ion which is reduced to metallic Ni by H{sub 2} in the fuel gas and bridges the anode and the cathode. The bridges short circuit and degrade cell performance and shorten cell life. Since solubility of NiO in mixture of lithium carbonate and sodium carbonate (Li/Na) is lower than in Li/K, it takes longer time to take place slowing by NiO cathode dissolution in Li/Na compared with in Li/K. The ionic conductivity of Li/Na is higher than of Li/K, however, oxygen solubility in Li/Na is lower 9 than in Li/K. A new 10 kW class MCFC stack composed of Li/K cells and Li/Na cells, was tested. Basic performance of the Li/K cells and Li/Na cells of the stack was reported.