Stack Compression of PEM Fuel Cells

The effect of dimensional changes of fuel cell components from temperature and hydration cycles on the stack compression is investigated in this paper. Using a simple spring model including the membrane electrode assembly (MEA), gas diffusion layers (GDL), bipolar plates, seal gaskets, current collectors, insulation plates, end plates, and side plates, we find significant compression changes from 30% over-compression to 23% compression loss from both temperature and humidity changes. The wide range of variation in stack compression is attributed to the swelling behavior of polymer electrolyte membranes, the compression behavior of gas diffusion layers, and the design of stack assembly. This paper also reports the use of finite element method to investigate the compression of MEA and GDL over the channel area where MEA buckling from membrane swelling can result in separation of MEA and GDL. It is suggested that the compression over channels can be improved with higher transverse shear modulus in the GDL in addition to the use of narrower channels. In this paper, we will also discuss the challenges facing the fuel cell manufacturers and component suppliers on the needs for new materials with improved mechanical properties and better testing/modeling techniques to help achieving stable compression and better fuel cell stack designs.