A Degradation Model for Solid Oxide Fuel Cell Anodes due to Impurities in Coal Syngas: Part I Theory and Validation

Abstract

A new phenomenological one‐dimensional model is formulated to simulate the typical degradation patterns observed in solid oxide fuel cell (SOFC) anodes due to coal syngas contaminants such as arsenic (As) and phosphorous (P). The model includes gas phase diffusion and surface diffusion within the anode and the adsorption reactions on the surface of the Ni‐YSZ‐based anode. Model parameters such as reaction rate constants for the adsorption reactions are obtained through indirect calibration to match the degradation rates reported in the literature for arsine (AsH3), phosphine (PH3), hydrogen sulfide (H2S), and hydrogen selenide (H2Se) under accelerated testing conditions. Results from the model demonstrate that the deposition of the impurity on the Ni catalyst starts near the fuel channel/anode interface and slowly moves toward the active anode/electrolyte interface as observed in the experiments. Parametric studies performed at different impurity concentrations and operating temperatures show that the coverage rate increases with increasing temperature and impurity concentration, as expected. The calibrated model was then used for prediction of the performance curves at different impurity concentrations and operating temperatures. Good agreement is obtained between the predicted results and the experimental data reported in the literature.

A Degradation Model for Solid Oxide Fuel Cell Anodes Due to Impurities in Coal Syngas: Part II Estimation of Tolerance Limits

“…cell performance) can be found in Part I, i.e. Cayan et al [4]. Model validation examples against experimental data can also be found in the previous work which are not presented in the current paper, Part II, for brevity.…”

“…A transport model was formulated to predict fuel impurity induced performance degradation in SOFCs anodes by Cayan et al [4], which constituted Part I of this current study. The degradation model employed in Part I of this work considers the adsorption of hydrogen and the phosphine on the nickel catalyst surface inside the anode.…”

“…Theoretical models that accurately predict the degradation behavior of SOFCs operating on syngas with very low levels of impurities could significantly reduce the time and effort involved in durability experiments. With this motivation, in Part I of this wider study by Cayan et al [4], a simple onedimensional model was developed to investigate the coal syngas impurity poisoning in the anode of SOFCs by examining the transport and reactions both in the gas phase and in the solid phase. Sezer et al [2,5,12] [4] and the experimental data reported in literature, for electrolytesupported cells at accelerated test conditions with high degradation rates.…”

“…With this motivation, in Part I of this wider study by Cayan et al [4], a simple onedimensional model was developed to investigate the coal syngas impurity poisoning in the anode of SOFCs by examining the transport and reactions both in the gas phase and in the solid phase. Sezer et al [2,5,12] [4] and the experimental data reported in literature, for electrolytesupported cells at accelerated test conditions with high degradation rates. In the present study, more case studies are performed with anode supported cells with lower impurity concentrations, which typically exhibit lower degradation rates.…”

“…One viable alternative is to use coal syngas in SOFCs to produce a pure stream of CO 2 in addition to electric power and heat and then store or sequester CO 2 [1]. However, various impurities found in coal syngas such as sulfur, phosphorus, arsenic, zinc, mercury, selenium, and vanadium affect the performance and durability of SOFCs [4,5]. It is essential that fuel cells be tolerant to these impurities up to certain levels since it is difficult and expensive to remove them completely from the fuel stream.…”