Degradation of PEMFC catalyst under dynamic loadings

Proton Exchange Membrane Fuel Cell (PEMFC) is considered as one of the most prosperous power sources to drive vehicles, due to the high efficiency and clean exhaust. However, there are still some obstacles before their commercialization. The price of key materials and cost of the manufacture process need further reduce while the durability of the stack needs to be prolonged. Carbon supported platinum are the most widely used catalyst for PEMFCs, but many reports have demonstrated that during long time operation platinum will gradually grow in size and reduce the electrochemical active area (ECA) thus irreversibly lower the performance of PEMFCs. This phenomenon will become severer under dynamic loadings which are the case when vehicles are running. It is significant to investigate the degradation behavior and mechanism of PEMFC catalyst under dynamic loadings. In this paper, various types of dynamic loadings, such as standard square-wave pulse, non-standard square-wave pulse, standard triangle with different amplitudes, frequencies and loading speeds wave, were carried onto the PEMFCs from small single cells to a stack containing 25 sub-cells. During the hundreds of hours’ operation, on-line techniques like CV, polarization curves and AC impedance were implemented periodically to characterize the change of ECA and fuel cell performance. After tests, electrodes were taken off the cells and analyzed through TEM, XRD and other physical characterizations to further study the degradation of the catalyst materials. To exclude the influences of other fuel cell components and accelerate the degradation, catalysts were also tested under cyclic potential scan by using a rotating disk electrode system connecting to an electrochemical station. Based on all those experiments, the degradation mode of PEMFCs have been pointed out, the numerical model have been established and a preliminary degradation mechanism has been proposed