A model-based approach for current voltage analyses to quantify degradation and fuel distribution in solid oxide fuel cell stacks

Abstract

h i g h l i g h t sIdentification of fuel leakages and fuel distribution in SOFC stacks. Determination of internal resistances from (V,I)-data by eliminating fuel effects. Real-time, model-based identification of malfunctioning of SOFC stacks. Time dependent evolution of degradation phenomena from (V,I)-data. Simulated local species concentrations and current densities along fuel channels. a b s t r a c tReliable quantification and thorough interpretation of the degradation of solid oxide fuel cell (SOFC) stacks under real conditions is critical for the improvement of its long-term stability. The degradation behavior is often analyzed based on the evolution of currentevoltage (V,I) curves. However, these overall resistances often contain unavoidable fluctuations in the fuel gas amount and composition and hence are difficult to interpret. Studying the evolution of internal repeat unit (RU) resistances is a more appropriate measure to assess stack degradation. RU-resistances follow from EIS-data through subtraction of the gas concentration impedance from the overall steady-state resistance. In this work a model-based approach where a local equilibrium model is used for spatial discretization of a SOFC stack RU running on hydrocarbon mixtures such as natural gas. Since under stack operation, fuel leakages, uneven fuel distribution and varying natural gas composition can influence the performance, they are taken into account by the model. The model extracts the time-dependent internal resistance from (V,I)-data and local species concentration without any fitting parameters. RU resistances can be compared with the sum of the resistances of different components that allows one to make links between laboratory degradation experiments and the behavior of SOFC stacks during operation.

Lagrangian model using CFD flow data to predict the currentvoltage characteristics of a solid oxide fuel cell repeat unit

“…Note that ASR RU was the only fit parameter used. As shown by [Linder 2015], ASR RU values obtained by fitting their model to experimental (I-U) curves agreed well with the values extracted from electrochemical impedance spectroscopy (EIS) data. Using our model, we as well obtained a realistic ASR RU value that agreed well with corresponding EIS data.…”

“…With respect to the modelling of hydrocarbon fuels, our model perfectly reproduced that of [Linder 2015] for CPO-reformed pure methane assuming a single residence time τ ave , see Fig. 8.…”

“…Figure 8 shows a comparison between our model and that of [Linder 2015]. Here, the SOFC repeat unit operates at 900°C and is fueled by 4 g/h CPO-reformed pure methane with an airto-fuel ratio of λ = 0:27.…”

“…Figure 8: Comparison of our model as given by Eq. (32) for a single residence time of τ ave = 0.177 s with that of [Linder 2015] for a SOFC repeat unit operated at 900°C running on 4 g/h CPO-reformed pure methane with an air-to-fuel ratio of λ = 0:27.…”

“…(32) for hydrocarbon fuels up to the largest residence time _max. For this, i.e., the internal resistance ASR RU needs to be known either from electrochemical impedance spectroscopy (EIS) data or by fitting the model to experimental (I-U) data, see [Linder 2015] for details 3. For each residence time , calculate the corresponding electrical current by using Eq.…”