This paper presents a multi‐scale model of a solid oxide fuel cell (SOFC) stack consisting of five anode‐supported cells. A two‐dimensional isothermal elementary kinetic model is used to calculate the performance of single cells. Several of these models are thermally coupled to form the stack model. Simulations can be carried out at steady‐state as well as dynamic operation. The model is validated over a wide range of operating conditions including variation of temperature, gas composition (both on anode and cathode side), and pressure. Validation is carried out using polarization curves and impedance spectra. The model is then used to explain the pressure‐induced performance increase measured at constant fuel utilization of 40%. Results show that activation and concentration overpotentials are reduced with increasing pressure.

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The influence of pressure on an SOFC was studied with steam-reformed methane as a fuel. Experiments were performed with a reformate containing 58.4% H 2 , 20% H 2 O, 12.2% CO, 5.5% CO 2 and 3.9% CH 4 and another mixture containing 18% H 2 , 34% H 2 O, 2% CO, 27% CO 2 and 19% CH 4 as well as a hydrogen/nitrogen mixture. The influence of pressure on OCV, power density at constant voltage and constant current as well as on gas composition was examined for the different fuels. Pressure dependency of OCV was found to be different for the reformate gases than for hydrogen. The pressure increase of OCV through pressurization for reformates showed a strong dependency on temperature due to changes in the equilibrium gas compositions of the fuel. Under load pressurization showed a positive effect on performance for all fuels. Power density increases of up to 70% were found with reformate as fuel.The demand for electrical energy increases and will continue to increase. Therefore new power plants with high efficiencies and low emissions have to be developed. A hybrid power plant consisting of a pressurized solid oxide fuel cell (SOFC) system coupled with a gas turbine is seen to fulfill both requirements because such a power plant may reach electrical efficiencies of above 60% with low emissions. 1 This kind of hybrid power plant also has the advantage of being suitable for a wide range of applications ranging from several 10 kW to the MW class. It can also be operated on a wide range of fuels. Highest efficiencies and power are to be expected when the SOFC is operated at elevated pressures. 2 During operation of the hybrid power plant air is compressed in the compressor of the gas turbine. It is then preheated and fed to the SOFC system. The off-gases of the SOFC system are used in the combustion chamber of the gas turbine where additional fuel may be added for example for starting the system. After expansion of the gas in the gas turbine the off-gas is used to preheat the air for the fuel cell system. In the context of the planned hybrid power plant the fuel cell will be operated at elevated pressures between 3 and 5 bar. 3 For the realization of the power plant it is necessary to understand the behavior of each subsystem as well as their interactions. The pressurized solid oxide fuel cell is an essential part of the system but there is still little data available from literature concerning the behavior of SOFC at elevated pressures although several institutes and companies have performed experimental and modeling work in the area of pressurized SOFC and hybrid power plants. [2][3][4][5][6][7][8][9][10][11][12][13]16 Since the pressuredependant behavior cannot quantitatively be derived from measurements at ambient pressure because of complex and interdependent mechanisms taking place at the cell, a test rig for the characterization of SOFC stacks exposed to pressures up to 8 bar has been built at DLR. 13 The hybrid power plant planned by DLR will eventually run on natural gas, therefore the SOFC stack will be operated with...

In this contribution the influence of pressure on an SOFC is studied with steam-reformed methane as a fuel. Experiments were performed with a reformate containing 58.4% H 2 , 20% H 2 O, 12.2% CO, 5.5% CO 2 and 3.9% CH 4 and another mixture containing 18% H 2 , 34% H 2 O, 2% CO, 27% CO 2 and 19% CH 4 as well as a hydrogen/nitrogen mixture. The influence of pressure on OCV, power density at constant voltage and constant current as well as on gas composition was examined for the different fuels. Power density increases of up to 70% were found.