Low temperature durability and consistency analysis of proton exchange membrane fuel cell stack based on comprehensive characterizations

The cold start is one of the key research fields in proton exchange membrane fuel cell investigation. In this work, a low temperature durability and consistency analysis is performed on a 5-cells stack. After 20 times freezing and thaw cycles, coefficient of variation of individual cell voltage increase significantly. Through the polarization curve test, it is found that the output performance degradation of each individual cell is inconsistent. The No.1 cell which is the nearest from the gas inlets has the maximum performance degradation. Through electro-chemical impedance spectroscopy, cyclic voltammetry, scanning electron microscope, segmented current density test and synchrotron radiation X-ray scan 3D image reconstruction, the cracks on the interface of membrane and catalyst layer are observed in situ successfully for the first time. Under the condition in this work, the water content of No.1 cell is the most, and a lot amount of water is frozen at the air inlet area. Due to the frost heave stress, the structure of membrane electrode assembly is damaged. This causes the loss and the agglomeration of catalyst, and even the delamination of catalyst layer. The above structure changes cause a decrease in catalyst activity and an increase in cell resistance, and eventually lead to the inconsistent degradation in output performance. The characterization results in this work are helpful for the optimization and application of membrane electrodes assembly and stacks for vehicle fuel cells.