In the present study, a physics-based procedure combining experiments and multi-physics numerical simulations is developed for overall analysis of SOFCs operational diagnostics and performance predictions. In this procedure, essential information for the fuel cell is extracted first by utilizing empirical polarization analysis in conjunction with experiments and refined by multi-physics numerical simulations via simultaneous analysis and calibration of polarization curve and impedance behavior. The performance at different utilization cases and operating currents is also predicted to confirm the accuracy of the proposed model. It is demonstrated that, with the present electrochemical model, three air/fuel flow conditions are needed to produce a set of complete data for better understanding of the processes occurring within SOFCs. After calibration against button cell experiments, the methodology can be used to assess performance of planar cell without further calibration. The proposed methodology would accelerate the calibration process and improve the efficiency of design and diagnostics.

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A mathematical model which was validated using button cells is used to predict the phosphine induced performance degradation in relatively large planar cells operating on hydrogen fuel. The empirical model parameters are calibrated using button cell experiments as guide. These parameters are then used to perform simulations to predict fuel contaminant performance degradation of planar cells. The results from the three dimensional model show that the contaminant coverage of Nickel and fuel distribution inside the anode is highly non-uniform. These non-uniform distributions are caused by the geometrical alignment of gas channels and current collectors, as well as the variation of gas concentration along the flow direction. The non uniform deactivation of anode gave raise to altering of current distribution inside the planar cell such that the cell can still produce current even when some regions of the anode are partially inactive. This is in stark contrast with what is observed in button cells where all the distributions are essentially one-dimensional. It is thus observed that the life time for planar cells could be much longer than that for similar button cells.

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The poisoning of anode materials by impurities in coal syngas is a significant problem for utilization of coal syngas in Solid Oxide Fuel Cells (SOFCs). One such impurity, phosphine is known to cause catastrophic failure of SOFC anode at ppm level concentrations. A significant phenomenon observed in SOFC anodes, made of Ni-YSZ cermets, when exposed to phosphine is migration of the nickel from porous matrix towards the surface, which is believed to be one of the reasons for performance degradation. The mechanisms responsible for the experimentally observed nickel migration are not well understood. In this study, a plausible mechanism is proposed to reveal the effect of electrical current and steam concentration on nickel migration in SOFC anodes. A physics based transport model for nickel migration is formulated based on the electro-migration, formation of the secondary phases and diffusion. This model is integrated into a readily available one dimensional in house code for predicting SOFC anode degradation due to fuel impurities. Simulations show that the proposed mechanism of Ni diffusion driven by secondary phase formation, the electrical force, and humidity can reveal the experimentally observed accumulation of Ni and secondary phases on the SOFC anode surface.

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A one-dimensional model was developed to predict the performance degradation of the SOFCs anode exposure of fuel contaminants found in typical coal syngas. This model is extended to a three-dimensional model to predict the phosphine induced performance degradation in relatively large planar cells operating on hydrogen. The model parameters are calibrated using button cell experiments conducted under accelerated tests conditions. These parameters are then used to perform simulations to predict fuel contaminant performance degradation of planar cells. The results from degradation simulations show that the contaminant coverage alter the initial current distribution, as well as the fuel and oxygen distribution inside the anode significantly. The electrochemical characteristic of the degraded cell is analyzed by performing impedance and polarization simulations at cell operating current. The polarization and impedance simulations are implemented by dividing the cell into three regions along the fuel flow direction. The results show that the degradation rates and the impedance behavior of planar cells are very different than those observed in button cells.

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