Title

Multiphysics modeling of fuel cells

Date of Completion

January 2009

Keywords

Alternative Energy|Engineering, Chemical|Engineering, Mechanical|Engineering, Materials Science

Degree

Ph.D.

Abstract

Fuel cells are expected to resist permanent changes in performance over time, to tolerate unexpected changes in the ambient conditions for a stable operation, and to sustain a structural integrity under different operating conditions. However, during the operation, both solid oxide fuel cells (SOFC) and polymer electrolyte fuel cells (PEFC) are prone to many hazards that may cause degradation of the performance even to the extent of complete failure of these devices. ^ In this study performance and degradation of SOFCs and PEFCs is studied. A computational modeling framework has been established to investigate the transport phenomena and the electrochemical performance as well as the mechanical behavior of SOFCs and PEFCs. ^ The electrochemical performance of the SOFC is investigated both in steady-state and transient operations while elucidating the transport phenomena related to the fuel cell operation. The proposed computational framework for the SOFC comprises two separate models for the test furnace and the single cell in order to more accurately model the actual test system while decreasing the computational cost. The fuel cell performance in transient operation is also studied. The performance of the SOFC is investigated in case of a failure in the fuel supply system. Mechanical behavior of the SOFC is also considered to help assessing the durability of the cells. ^ The same modeling framework is utilized for the PEFCs to investigate electrochemical and mechanical degradation during the fuel cell operation. To assess the performance degradation as a result of gas contamination, a cation transport model is presented. It is found that the effect of fuel side contamination of cationic species is much more significant than the air side contamination while there still is a significant performance degradation associated with the latter. ^ Further, the stresses induced during the PEFC operation due to the swelling and shrinkage of the membrane with hydration changes are investigated. The impact of the anisotropy in the gas diffusion layers on the mechanical stresses is investigated and found to have a significant effect on the stress distribution in the membrane.^