膜电极参数对质子交换膜燃料电池反极的影响规律研究

随着对质子交换膜燃料电池稳定性的不断研究，结果表明燃料电池在快速启停以及快速变载工况下，燃料电池中的某些单电池会出现电极极性反转现象，导致膜电极性能衰退甚至烧毁。因此，研究燃料电池膜电极反极的现象、机理和预防对策对提高燃料电池稳定性具有重要意义。

本课题研究方向主要从调控质子交换膜燃料电池中膜电极的参数出发，通过控制在阳极通入惰性气体以模拟单电池的反极，对燃料电池反极前后的催化剂层微观形貌、理化性能进行对比分析，以及利用多种电化学诊断测试方法对燃料电池的电化学性能进行对比与分析，由此得到了膜电极抗反极时间与膜电极参数之间的规律，研究工作总结如下：

（1）在制备催化剂浆料时阳极添加不同载量的IrO₂，探究IrO₂载量对膜电极抗反极性能的影响规律。实验表明，膜电极的反极时间随着IrO₂载量的增加而增加，且两者成正比关系。这主要是IrO₂的加入，提高了阳极电解水析氧反应的发生，抑制了阳极催化层碳载体的腐蚀，从而有效提高了抗反极时间。

（2）通过改变阳极气体湿度测试膜电极在不同湿度条件下的抗反极性能，测试不同相对湿度对膜电极抗反极性能的影响规律。实验表明，在相对湿度为60 %左右时，膜电极的反极时间达到最大，在低相对湿度时，反极时间随着相对湿度的增大而增加；在高相对湿度时，反极时间随着相对湿度的增大而减少。分析表明，这主要跟催化层水含量和水的活度有关。低湿度条件下，阳极催化层由于缺水，在反极条件下容易发生碳载体腐蚀，导致阳极催化层破坏严重，膜电极很短时间就失效。相反，在高湿度条件下，阳极催化层处于水过量状态，部分水不吸附于IrO₂表面，处于失活状态，也会造成电解水析氧反应受阻，阳极催化层发生碳载体腐蚀，导致膜电极很短时间失效。

（3）将不同的分子当量值树脂溶液加入催化剂浆料制成膜电极，测试不同当量值树脂添加剂对膜电极抗反极性能的影响规律。实验表明，当树脂EW从790 g/mol增加到909 g/mol，膜电极抗反极时间逐渐减少，当树脂EW进一步增加到1100 g/mol，膜电极抗反极时间反而逐渐增加。通过后续理化表征可知，改变催化层树脂分子当量值，可以显著改变催化层三相界面的亲疏水性质，影响到反极发生时析氧反应和碳载体氧化反应两个竞争反应的速率。

With the development of critical components of proton exchange membrane fuel cells (PEMFCs), the performance has been significantly improved in the last decades. While the degradation of PEMFCs has become a significant obstacle for the further commercialization of PEMFCs. As a key component of PEMFCs, the degradation of membrane-electrode-assembly (MEA) has been considered as one of the main degradations for PEMFCs. Among various degradation ways, cell reversal happened during the start/stop and rapid load changes, has been widely studied as one of the main factors that cause the degradation of MEA. Therefore, it is of great significance to study the phenomenon, mechanism and preventive strategy to address the cell reversal issue.

The topic of this thesis mainly starts from the analysis of the key parameters of MEAs. By controlling the inert gas to be passed into the anode to simulate the voltage reversal of the single cell, the microscopic morphology, physical and chemical properties of the catalyst layer before and after the voltage reversal are comprehensively analyzed. Then, the electrochemical performance MEAs is evaluated by using a variety of electrochemical diagnosis methods. The effect of key parameters of MEAs on the cell reversal behavior is then analyzed. The research results are summarized as follows:

(1) Different loadings of IrO₂ are added to the anode catalyst layers during the preparation of the catalyst ink to explore the effect of the IrO₂ loading on the anti-reversal performance for MEAs. Experimental results show that the voltage reversal time of the MEAs almost linearly increases with the increase of IrO₂ loading. This is mainly due to the addition of IrO₂ nanoparticles improve the kinetics of the oxygen evolution reaction at the anode catalyst layers, which inhibits the corrosion of the carbon supporting materials Pt/C catalyst.

(2) The anti-reversal performance of the MEAs under different humidity conditions is tested by regulating the anode gas humidities, and the influence of different relative humidity on the anti-reversal performance of the MEAs is analyzed. Experiment results show that when the relative humidity is about 60%, the voltage reversal time of the MEAs is longest among different relative humidities. Meanwhile, the relative humidity is low, the voltage reversal time increases with an increase in the relative humidity; when the relative humidity is high, the voltage reversal time decreases with the increase of the relative humidity. After the physicochemical characterization and electrochemical diagnosis analysis, the reason for this behavior is mainly related to the water content and activity in the catalytic layer. Under low humidity conditions, the anode catalyst layer is prone to carbon corrosion due to the lack of water under the conditions of voltage reversal, thereby leading to a severe damage to the anode catalyst layer and failure of the MEAs in a short period. On the contrary, under high humidity conditions, the anode catalyst layer is in a state of excess water, and part of the water is not adsorbed on the surface of IrO₂ nanoparticles, which will also hinder the oxygen evolution reaction to continuously generate the protons and electrons, and the carbon supporting materials of anode catalyst layer will be oxidation, which will also cause the failure of MEAs in a short period.

(3) The proton resins with different equivalent weights (EW) are then used as the ionomer in the anode catalyst layer. The effect of EW values on the voltage reversal behavior is comprehensively analyzed. Experimental results show that when the EW of ionomer increases from 790 g/mol to 909 g/mol, the voltage reversal time of the MEAs gradually decreases, while when the EW of ionomer further increases to 1100 g/mol, the voltage reversal time of the membrane electrode gradually increases. Through the subsequent the physicochemical characterization and electrochemical diagnosis analysis, it can be seen that the EW can significantly influents the hydrophilic and hydrophobic properties of the three-phase interface of the anode catalyst layer and affect the rate of the two competing reactions between the oxygen evolution reaction and the carbon oxidation reaction during the course of the voltage reversal.

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