| Proton exchange membrane fuel cell become the the focus in the field of fuel cell research with a series of advantages such as fast start at room temperature system, simple structure, quiet, environmental protection, high energy conversion efficiency and so on. But it will meet dynamic in operation at present and it will experience degradation when it is used as a car engine especially. Take PEMFC sightseeing tour bus trial run in the Shanghai world expo for example, although the fuel cell in as a vehicle power supply as made a very great progress, but, fuel cell system service life is still a problem to be solved. Through reading and analyzing the domestic and foreign fuel cells related literature, it is known that the fuel cell of key materials within the attenuation and current density distribution have a close relationship. And the distribution and redistribution of current density is decided by the battery is constantly changing operation, which is to say that the distribution of the current density and redistribution is changing as the time changing. The cross current will form when PEMFC encountered the situation such as the start up and shut down process, mass transfer uneven, Skin Effect and so on. The generation of this current will affect catalyst layer of MEA in PEMFC. This paper is divided into three sections. The first part main tells the development course of the fuel cells, working principle and its types, and the emphasis on the proton exchange membrane fuel cells survey, and lead to the concept of Cross Current; the second part of the main tells the produce mechanism of Cross Current and the current generated conditions; The third part is the part of the experiment.As the experimental section in this paper, flowing the Dc constant current into CCM, measuring the breakdown point of the Cross Current when it in the CCM in PEMFC, effect of the Cross Current to electrochemical active area of the catalyst layer, morphological Structure of the catalyst layer.The main conclusions of experiments are as follows:(1) Through Theoretical Analysis, key materials of Fuel cell stack in dynamic operation may cause the Cross Current; Through the result of flowing the Cross Current into the single side of CCM can be proved, When the Cross Current rate of growth is fast and increases to certain current density, CCM will breakdown;(2) As the results of CV, under the strong Cross Current, the electrochemical active area of catalyst would decrease as the increasing of time under high Cross Current; Also available, the higher of the Cross Current, the more quickly decrease the electrochemical active area of catalyst;(3) By using SEM and TEM characterization methods results show that Cross Current density will aggravate the tiny cracks aperture size in CCM surface, and accelerate the catalytic platinum catalyst particle electrode layer in the condensed, which affect the fuel cell key material performance, accelerating the decay of fuel cells, affect the fuel battery life... |
