氢氮气氛阴阳极平衡稳态下温度、压力、湿度条件对燃料电池入口、中心和出口不同位置氢渗透速率的影响

Local resolved investigation of hydrogencrossover in polymer electrolyte fuel cell

Jing Shan

Pawel Gazdzicki

Rui Lin

Mathias Schulze

K． Andreas Friedrich

Abstract

In this study， the effects of temperature， pressure and relative humidity （RH） onhydrogen crossover rate from anode to cathode of a PEMFC is investigated．Segmented cells are used to measure the local hydrogen crossover currentdensity （jcross H2） distribution． The results present approximate linear increase of the hydrogen crossover rate withincreasing temperature and hydrogen back pressure with rates of 0．038 mA cm−2K−1 and 3．33 mA cm−2 bar−1， respectively． Generally， slightly increased H2 crossover is observed in gas inlet areas thancell average． Unlike the approximate linear relationship betweentemperature or pressure with hydrogen crossover， the effect of relative humidification on hydrogen crossover is morecomplex with different increasing rate before fully humidification and dramaticdecline at excessive humidification． It is demonstrated that segmentedcells can be advantageously applied to study local H2 crossover of intact MEAs．

Fig． 1． H2 crossover current density at  different cell temperature of MEA1． （H2 flow： 380 ml min1， N2 flow： 120 ml  min1， 100％ RH， back pressure： 1．5 bars absolute pressure for both

electrodes）． In （A） the average current  density of the entire cell is plotted along with a linear fit （included in  other panels for comparison这句话的意思是说后面的图中的虚线是平均值，用于对比）． In （B） the gas inlet area corresponds to segments in lines 1  and 2 according to the images in Fig． 2． Center area is defined as segments  of lines 3， 4， and 5 （C）． Gas outlet area corresponds to segments of lines 6  and 7．

气体出口的波动最大

The relatively low H2 crossover at the  outlets with very high fluctuations is likely due to periodic accumulation  and blowing out of condensed water．

Fig． 2． The evolution of jcross H2  distributions （mA／cm2） of MEA1 fed with fully humidified H2／N2 （H2：380 ml min1，  N2： 120 ml min1） with the increase of cell temperature at 100％

RH for both electrodes． In （b） the  definition of the different flow field areas is illustrated． （Segment A1 and  G7 are inlet and outlet of hydrogen． G1 and A7 are inlet and outlet of air．）

Generally， with increasing cell  temperature the crossover rate increases but the H2 crossover distribution  remains largely unchanged．

Fig． 3． H2 crossover current density at  different anode back pressures of MEA1． （H2 flow： 380 ml min1， N2 flow： 120  ml min1， 100％ RH， Tcell＝80C）． In （A） the average current density of the  entire cell is plotted along with a linear fit （included in other panels for  comparison）． In （B） the gas inlet area corresponds to segments in lines 1 and  2 according to the images in Fig． 4． Center area is defined as segments of  lines 3， 4， and 5 （C）． Gas outlet area corresponds to segments of lines 6 and  7．

Fig． 4． The evolution of jcross H2  distributions （mA／cm2） of MEA1 fed with fully humidified H2／N2 （H2：380 ml min1，  N2： 120 ml min1） with the increase of back pressure at both electrodes at  steady state． （Segment A1 and G7 are inlet and outlet of hydrogen． G1 and A7  are inlet and outlet of air．）

Fig． 5． The jcross H2 distributions （mA／cm2）  at the initial stage （when voltage applied at cathode was 150 mV） of MEA1 fed  with fully humidified H2／N2 （H2：380 ml min1， N2： 120 ml min1） at different  back pressures． （Segment A1 and G7 are inlet and outlet of hydrogen． G1 and  A7 are inlet and outlet of air．）

Fig． 6． Polarization curves of MEA2 at  different humidification． （Tcell＝80 C， back pressure： 1．5 absolute bars for  both electrodes， stoichiometry H2／Air：1．5／2．0）．

Fig． 7． The influence of relative  humidity on hydrogen crossover of MEA2． （Tcell＝80 C， 1．5 bars absolute back  pressure for both electrodes， H2 flow： 60 ml min1， N2 flow：190 ml min1） In （A）  the average current density of the entire cell is plotted along with a linear  fit （included in other panels for comparison）． In （B） the gas inlet area  corresponds to segments in lines 1 and 2 according to the images in Fig． 8．  Center area is defined as segments of lines 3， 4， and 5 （C）． Gas outlet area  corresponds to segments of lines 6 and 7． Pay attention to different Y axis scale in （A）．

应该把前端40％－100％的趋势线总结出来做对比

Fig． 8． The evolution of hydrogen  crossover current density distribution of MEA2 at different reactant gases  humidification． （Tcell＝80 C， 1．5 bars absolute back pressure for both electrodes，  H2 flow： 60 ml min1， N2 flow： 190 ml min1， segment A1 and G7 are inlet and  outlet of hydrogen． G1 and A7 are inlet and outlet of air．）

A relative high hydrogen crossover could  be observed in hydrogen outlet area．

这个结论不太明显

This could be attributed to the better  humidification state of the membrane in this area．

Conclusions

In this study， the segmented cell  technology was applied for the first time to study local H2 crossover of  intact MEAs versus cell temperature， gas pressure and humidity． From the  measurements following conclusions have been drawn：

e A linear increase of H2 crossover with  increasing temperature and hydrogen back pressure was observed． Thereby， H2 crossover was higher in the gas inlet  area than cell average．

－ RH has a smaller effect on H2 crossover  than that of temperature or pressure． The dependence of H2 crossover rate is  non－linear increasing for RH increasing up to 100％ and decreasing at excessive  humidification： The measured H2  current density distribution is homogeneous at all studied RH values．

－ The effect of RH on H2 crossover is  explained by taking into account the H2 partial pressure， H2 solubility and  diffusion coefficients in the membrane as well as microscopic structure of the  membrane at different humidification levels．

不对称的压力、不对称的湿度对氢渗透速率的影响

一定工况运行后一直到有膜穿孔时不同位置氢渗透速率随时间的变化规律更令人感兴趣

从事燃料电池注定了你不一定出类拔萃，但必定与众不同。