Due to the same mechanism as descri

Due to the same mechanism as described above, in the presence of electro-osmotic drag that transports water in the opposite direction, the water accumulated at the cathode region cannot be effectively transported through membrane by back-diffusion and pressure-driven permeation towards anode for subsequent removal. Therefore, this water should be mainly removed by transportation through cathode GDL in the form of water vapor or liquid water, and the effectiveness of this method relies critically on the humidification conditionin cathode GDL and GC, hence the inlet cathode humidification condition. By means of this reasoning, it can be argued that the removal of the accumulated water will become moreimpeded as the inlet relative humidity at cathode is increased. The excessive accumulation of water then leads to the formation of liquid water that occupies the GDL pores andpartially blocks the transportation of oxygen to CL; these effects of increased inlet cathode humidification are reflected by the plots of liquid water saturation and the corresponding concentration overpotential in Fig.7. It can be seen from Figs.5 and 6 that although inlet cathode humidification does affect membrane’s resistivity, the effect is less significant compared to its effect on concentration overpotential and hence thelimiting current density. In summary, the influence of inlet cathode humidification on the performance of PEM fuel cell is more pronounced in respect of its contribution to the control of liquid water saturation at the cathode region.