Analysis of the compression characteristics of a PEM stack, development of an equivalent spring model and recommendations for compression process improvements

Optimising the compression process during assembly improves the performance of fuel cells. Sufficient and uniform compression across the x, y and z axes ensures uniform current distribution contributing to stack longevity, minimisation of mechanical stresses and optimisation of the well-recognised compromise between mass transport and ohmic losses. In addition, the sealing media experience the necessary forces required to prevent the leakage of reactant gases and thus increase the efficiency of the system. This research paper evaluates the compression characteristics of a test version of a fuel cell compression rig, designed by Horizon Fuel Cell UK, to inform future assembly line design. A MATLAB code was used to assess the compression homogeneity presented on Fuji Prescale Low pressure films. A spring equivalent model is developed to approximate required compressive force for optimal performance. Optimisation of this model is expected to facilitate the development of a compression process which lends itself to the mass production of fuel cells. Recommendations for improving the current process include the use of electronically controlled cyclic compression and an increase in the number of compression pistons. The key finding of this study is a lack of compression symmetry which is associated with the alignment of the jig or component manufacturing and assembly tolerances.