Experimental And Modeling Research Of GDL Of PEMFC

As an important component of proton exchange membrane fuel cell (PEMFC), gas diffusion layer(GDL) has the important influence on the water equilibrium. In high current density, electrochemistry reaction will produce abundant water, which could lead to jam for reactant gas and the flooding of catalyst layer, decrease the performance of the fuel cell consequently.Because the heat and mass transfer are complicated in the working PEM fuel cell, this paper proposed an ex-situ experiment to investigate liquid water transport through the gas diffusion layer(GDL) . A transparent bipolar plate was made to observe the process of water droplet formation and detachment on the surface of a GDL through a CCD camera. The breakthrough pressure, at which the liquid water penetrates the GDL and starts to form a droplet, was measured. The breakthrough pressure was found to be different for the GDLs with different porosities. The maintain pressure was also measured, which is considered as the minimum pressure needed to maintain the liquid water flowing. For the same GDL, the maintain pressure was found to be much lower than the breakthrough pressure. The difference between these two pressures might be due to the surface tension between the liquid water and the GDL. The results of this paper will be useful in re-examining the mathematical models to describe the liquid water transport in the porous GDL. According to the result of experiment, it was found that distribution of pore diameter of GDL determined the penetration pressure.To research the impact of the liquid water drainage on the performanceof cell, a capability test of PEM single cell was processed at the same time. The results showed that, the cell which used the GDL which has the MPL on it had the best performance. In the low electrical current, the cell which used the GDL which was harder for liquid water transport had the better capability, but in the high electrical current, the performance of it was worse oppositely.Network model was discussed in the end of this paper. Using this model and the parameter of the experiment, the breakthrough pressure was calculated in Matlab. It was found that the distribution of pore diameters, the thickness of the carbon paper and the distance between the screens were functioned on water break through synthetically. And in the range of computation, the liquid flow in in-plane direction has no relation with the breakthrough pressure.