相对湿度、电流密度、装配力对燃料电池水传递（净曳力系数）的影响

Effects of clamping force on the watertransport and performance of a PEM （proton electrolyte membrane） fuel cell withrelative humidity and current density

Dowon Cha

Jae Hwan Ahn

Hyung Soon Kim

Yongchan Kim

Abstract

The clamping force should be applied to aproton electrolyte membrane （PEM） fuel cell due to its structuralcharacteristics． The clamping force affects the ohmic and mass transportresistances in the PEM fuel cell． In this study， the effects of the clampingforce on the water transport and performance characteristics of a PEM fuel cellare experimentally investigated with variations in the relative humidity andcurrent density． The water transport characteristics were analyzed bycalculating the net drag coefficient． The ohmic resistance decreased with theincrease in the clamping force due to the reduced contact resistance and moreeven membrane hydration． However， the mass transport resistance increased withthe increase in the clamping force due to the gas diffusion layer compression． The net drag coefficient decreased with theincrease in the clamping force due to high water back－diffusion．Additionally， the relationship between the total resistance and the net dragcoefficient was investigated．

以前没有考虑过装配力对燃料电池水传递（净曳力系数）还会产生一定影响。

Fig． 1． Schematic diagram of the  experimental setup．

Fig． 2． Flow channel design

Table 1 Experimental conditions．

Fig． 3． Schematic diagram of water  transport in a PEM fuel cell．

Fig． 4． Ohmic resistance according to the  clamping force at a relative humidity of 40％．

Fig． 5． Mass transport resistance  according to the clamping force at a relative humidity of 40％．

Fig． 6． Ohmic resistance according to the  clamping force at a relative humidity of 80％．

Fig． 7． Mass transport resistance  according to the clamping force at a relative humidity of 80％．

Fig． 8． Variation in the voltage  according to the clamping force at a relative humidity of 40％．

Fig． 9． Polarization curves according to  the clamping force at a relative humidity of 80％．

到这里才开始重点：

Fig． 10． Net drag coefficient according  to the clamping force at a relative humidity of 40％．

Generally， the net drag coefficient  increases with increasing the membrane thickness due to lower backdiffusion rate

Fig． 11． Net drag coefficient according  to the clamping force at a relative humidity of 80％．

as the relative humidity increased， the  reduction in the net drag coefficient became larger as the clamping force  increased．

Fig． 12． Total resistance according to  the net drag coefficient．

The total resistance represents the sum  of the ohmic and mass transport resistances

Conclusions

This study experimentally investigated  the effects of the clamping force on the water transport and performance of a  PEM fuel cell． The internal resistance was investigated using the EIS tests．  The water transport in the PEM fuel cell was analyzed by calculating the net  drag coefficient． The ohmic resistance was observed to decrease as the clamping  force increased due to the decrease in the contact resistance and more even  membrane hydration． However， the mass transport resistance increased as the clamping  force increased due to the higher water flow resistance through the membrane．  At a relative humidity of 40％， the performance of the PEM fuel cell increased  as the clamping force increased above 5．9 N－m due to the decrease in the  ohmic resistance． At a relative humidity of 80％， the increase in the clamping  force significantly degraded the performance of the PEM fuel cell due to the  higher mass transport resistance． The  net drag coefficient decreased as the clamping force increased due to the  high level of water back－diffusion． However，  for a net drag coefficient below 0．2， the total resistance significantly  increased as the clamping force increased．不知道这一条的通用性如何。

Therefore， the clamping force  has to be controlled to an optimal  level according to the water content in the PEM fuel cell． In addition， the net drag coefficient can be used  as a parameter to determine the  occurrence of water flooding．