质子交换膜燃料电池渗氢电流的三种测量方法的比较

Improved methods to measure hydrogen crossover current in proton exchange membrane fuel cell

Pucheng Pei

Ziyao Wu

Yuehua Li

Xiaoning Jia

Dongfang Chen

Shangwei Huang

Abstract

Hydrogen crossover current has a great influence on the performance and durability of proton exchange membrane （PEM） fuel cells． The common measuring method is linear sweep voltammetry （LSV）． But some usual approximations， such as ignoring the influence of scan rates or short－circuit resistances， can lead to greater measurement deviations． Therefore， in this study to accurately measure hydrogen crossover current， LSV is improved by building a novel charging model based on fitted zero scan rate curves and on taking effects of short circuit into consideration． On the basis of this new model， galvanostatic charging method is improved by taking short circuit of PEMs into consideration and a mass spectrometry assisted with hydrogen pump is proposed with no need of calibration with standard gas． Hydrogen crossover current and short－circuit resistance of a 34 cm2 single cell are measured by three improved methods， which are then compared with methods previously available． It is found that hydrogen crossover currents are reduced and more accurate than those obtained by previous methods， and values obtained by different improved methods are highly consistent with each other． So the proposed charging model is valid and can be used to optimize other electrochemical measurements of fuel cells．

扫描速度和充电方向对渗氢电流测量的影响，充电方向的结果的确让人感觉有些意外。作者的解释是：

Second， even if the scan rates are equal， such as 4 mV·s−1， different charging directions of fuel cell still leads to different results， as shown in Fig． 1（b）． It is speculated that different loadings of platinum catalyst on the two sides of the MEA is the main reason for these differences．

三种方法的实验参数

方法1，传统LSV法

获得两条曲线后线性外推到0mV／s时的LSV曲线，

两条外推0mV／s的LSV曲线重合度很好。

第二种方法 恒电流充电法

原理图是这样的

根据公式

可以获得不同电位条件下的漏氢电流密度，获得渗氢电流和短路电阻。

第三种方法：氢泵＋质谱法

需要注意的是在第二和第三种方法中，氢气路接的电流源的极性是不同的。

三种方法的对比

从方法的方便性上看，第一和第三更容易理解一些，但是第三种方法需要质谱设备。

Conclusions

In this paper， the LSV is modified to eliminate the negative effect of
scan rates on measurements， and a new charging model is established to differentiate four electrochemistry processes． Based on this model，
improved galvanostatic charging method has been added a measurable parameter ‘short－circuit resistance’ on the original basis， and a mass spectrometry assisted with hydrogen pump measuring hydrogen
crossover current is proposed， which does not require calibration by
standard gas． By measuring hydrogen crossover currents and shortcircuit resistances of a 34 cm2 MEA， three improved methods are
compared with previous methods to confirm their validity．

（1） The ‘hydrogen crossover current’ measured by previous LSV is actually the cross leakage current consisting of hydrogen crossover
current and short－circuit current． Hydrogen crossover current only
characterizes the permeability of the PEM， and is not related to scan
rate and charging direction． The short－circuit resistance is also independent of scan rate， but is affected by charging direction．
（2） Compared with previous methods， improved methods are more
accurate and stable． Therefore， newly－established charging model，
which is the basis for improved methods， is valid and can be used to
improve other electrochemical measurement methods of fuel cells．
（3） The improved LSV and mass spectrometry assisted with hydrogen pump are not applicable to measuring MEAs in stack． The synchronous multi parameters measurement and consistency evaluation of MEAs in stack can be conducted only by improved galvanostatic charging method．