Evaluation of degradation/failure mechanisms of a 10-cell PEMFC stack subjected to automotive load cycles

Fuel cells can be considered as an impending technology to substitute for internal combustion (IC) engines in transportation. In particular, the Proton Exchange Membrane Fuel Cell (PEMFC) is exceptionally suitable for the automobile sector owing to its broad power range at relatively low temperatures plus the ability to perform under discontinuous operation. However, to gain this advantage, durability of the PEMFC should be verified by achieving a minimum of 5000 hours of operating life. Particularly, durability of the stacks plays a crucial role in the process of commercialization because of the intricacies involved in its design and operation under itinerant environments. This study is an evaluation of degradation and failure mechanisms of a 10-cell 100 Watt PEMFC stack subjected to load cycles analogous to load cycles in an automotive vehicle. The durability test protocol was developed by DOE representative of transportation applications. The analysis and characterization was carried out for the stack as wells as for the individual cells using in-test and post-test diagnostic techniques including current interrupt, polarization measurements, cyclic voltammetry, post-mortem electron microscopy and X-ray diffraction.A 3% loss in stack voltage was observed from the maximum achieved performance over 480 hours of load cycling. The stack failed to perform after 480 hours of testing due to complete failure of one cell unrelated to catalyst loss and membrane damage. Post mortem analysis indicated that the major cause of failure was due to loss of both anode and cathode silicone gaskets that led to direct reaction of hydrogen and oxygen as well as short-circuiting the stack. It was also revealed that the bulk of the performance degradation was because of gradual decrease in kinetics of the cathode reaction with concomitant loss of electrochemically active surface area of the platinum nanoparticles.