Numerical Modeling of the Effect of Sulfur Poisoning on the Performance of the Porous Anode Solid Oxide Fuel Cell
Manafi Rasi, Negar
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A numerical model to capture the effect of H2S impurities on the Solid Oxide Fuel Cell (SOFC) performance with Ni-based porous anode is developed. H2S impurities can adversely affect the fuel cell performance, due to the sulfur poisoning of the Ni catalyst of the SOFC anode. The novelty of this work is the derivation of a Butler-Volmer type kinetic formulation that captures the effect of sulfur poisoning on the H2 electro-oxidation reaction in the Ni-YSZ anode of SOFC. The novel kinetic model is then incorporated into a 2-dimensional porous anode model with gas-phase species transport, charged species transport and anode electrochemistry. The result is a performance model that can predict the effect of H2S impurity on the polarization curves of the SOFC by taking into account the transport phenomena in addition to the electrochemistry formulations. Two types of kinetic models named as “coverage dependent kinetic model” and “coverage independent kinetic model”, differing in the coverage dependency of energy of H2 and H2S adsorption reactions are developed and incorporated in the 2D porous anode model. Loss in performance is predicted by both kinetic models and 2D performance models. Both kinetic models predictions show an increase in the current density loss with an increase in H2S concentration. 2D performance models predictions with both coverage dependent and coverage independent models show an increasing trend in both the loss in the cell voltage and increase in the cell resistance upon the increase of the inlet H2S content of the fuel. The 2D performance model with coverage-dependent kinetics predicts lower loss in the cell performance than the 2D performance model with coverage-independent kinetics. By comparing the performance model predictions with the experimental results, similar trends of increase in the sulfur poisoning effect by increase in H2S content and smaller increase in the relative cell resistance at higher current densities can be recognized in both experimental results and the 2D model predictions. Coverage-dependent 2D performance model predictions are closer to the experimental results than the coverage-independent 2D performance model predictions.