Mechanical Integrity Issues of Fuel Cells

The conditions under which fuel cells are required to operate apply constraints upon the components and the entire structure of a fuel cell. These can then affect the mechanical integrity of the cells. For high and medium temperature cells such conditions might include differential expansion due to thermal property mismatch of the materials in the cell, residual stresses after manufacture and material behaviour such as creep at temperature. For lower temperature cells the effects of hydration expansion and contraction may introduce significant effects. However, to date, there has been little concentration on the mechanical integrity of fuel cells because of the paramount initial consideration of developing the technology itself, particularly from and electrical and materials standpoint. The aim of this paper is to summarise some of the factors affecting the mechanical integrity fuel cells and the work conducted to assess these at Imperial College London. Residual stresses due to thermal expansion mismatch after cooling during manufacture are evaluated; creep in high-temperature cells due to the operating temperature is measured, and thermally induced stresses due to temperature variations are predicted by a combination of thermo-mechanical computational-fluid dynamics and experimental work. The results are indicative of considerable stresses within the fuel cells and identify mechanical integrity as a significant issue.