Numerical study of the effects of operating voltage on the degradation of membrane electrodes of PEMFC

doi:10.11949/0438-1157.20231344

Abstract

Abstract:

To study the effect of operating voltage on the degradation of membrane electrodes of proton exchange membrane fuel cell (PEMFC) under long-term stable operation conditions, a coupled multi-physics field PEMFC model including carbon corrosion, Pt oxidation, dissolution and ionomer degradation is established for numerical simulation. The results show that as the operating voltage increases, the Pt dissolution and carbon corrosion rates in the cathode catalytic layer accelerate. After 500 h, the oxidized area of the Pt surface increases significantly. The radius of the agglomerates in CCL and the concentration of sulfonic acid groups in the proton exchange membrane decrease drastically, and the recession area is mainly concentrated in the cathode inlet and the degree of the recession is increased drastically at a high voltage. When the cell is operated at 0.8 V for 500 h, the thickness of CCL and membrane at the cathode inlet decreased significantly by 13.62% and 35.30%, respectively. The electrochemcial active surface area of CCL and the ionic conductivity of the membrane decreased by 59.9% and 6.9%, respectively, and the equivalent weight of the membrane increased by 7.4%, and the above indexes declined drastically in the first 100 h, and then gradually stabilized. The conclusion can provide a guideline for the optimization of membrane electrode material design and control strategy.

Key words: PEMFC, membrane electrode, operating voltage, CFD, degradation, simulation

摘要：

为研究长期稳定运行条件下，工作电压对质子交换膜燃料电池膜电极衰退状况的影响，建立了包含碳腐蚀、Pt氧化与溶解以及离聚物降解的PEMFC多物理场耦合模型进行数值模拟。研究结果表明：随着工作电压增加，阴极催化层中Pt溶解与碳腐蚀速率加快，500 h后Pt表面氧化的区域大幅增加，阴极催化层中团聚体半径与质子交换膜中磺酸基团浓度剧烈减小，衰退区域主要集中在阴极入口处且高电压下衰退程度急剧增加。电池在0.8 V下运行500 h后，阴极入口处阴极催化层与膜厚度显著减小，分别降低13.62%与35.30%；阴极催化层电化学活性面积和膜的离子电导率分别减小59.9%与6.9%，膜的当量质量增加7.4%，且上述指标前100 h内衰退剧烈，随后逐渐趋于平缓。可为膜电极材料设计与控制策略的优化提供参考。

关键词: 质子交换膜燃料电池, 膜电极, 工作电压, 计算流体力学, 衰退, 模拟

CLC Number:

TM 911.4

Yaowen TAN, Panxing JIANG, Qing DU, Wanqiu YU, Xiaofei WEN, Zhigang ZHAN. Numerical study of the effects of operating voltage on the degradation of membrane electrodes of PEMFC[J]. CIESC Journal, 2024, 75(3): 974-986.

谭耀文, 姜攀星, 杜青, 余婉秋, 温小飞, 詹志刚. 工作电压对PEMFC膜电极衰退影响模拟研究[J]. 化工学报, 2024, 75(3): 974-986.

Figures/Tables 16

Fig.1 Schematic of the PEMFC model

Table 1 Structural parameters

参数	数值/ $m m$
电池总长/宽/高	60/2/2.407
流道深度	0.5
流道宽度	0.8
岸宽	0.6
阴/阳极GDL厚度	0.16
阴/阳极MPL厚度	0.03
阴/阳极CL厚度	0.009/0.006
质子交换膜厚度	0.012

Table 1 Structural parameters

参数	数值/ $m m$
电池总长/宽/高	60/2/2.407
流道深度	0.5
流道宽度	0.8
岸宽	0.6
阴/阳极GDL厚度	0.16
阴/阳极MPL厚度	0.03
阴/阳极CL厚度	0.009/0.006
质子交换膜厚度	0.012

Fig.2 Schematic diagram of ionomer degradation mechanism

Table 2 Operating conditions

参数	数值
温度/K	348.15
阴/阳极出口背压/kPa	150/150
阴/阳极进口加湿度/%	70/50
阴/阳极化学计量比	2/2

Table 3 Physical parameters［30］ and electrochemical parameters［20］

参数	数值
GDL/MPL/CL接触角/(°)	130/140/120
GDL/MPL/CL孔隙率	0.7/0.6/0.5
GDL/MPL/CL/PEM密度/(kg/m³)	2000/2000/1350/1980
GDL/MPL/CL/PEM比热容/(J/(kg·K))	1000/1000/680/1090
GDL/MPL/CL渗透率(厚度方向)/m²	6.5×10^-12/3.4×10^-12/2×10^-15
GDL/MPL/CL渗透率(平面方向)/m²	1.9×10^-12/3.4×10^-12/2×10^-15
GDL/MPL/CL/PEM电导率(厚度方向)/(S/m)	358/358/13514/0
GDL/MPL/CL/PEM电导率(平面方向)/(S/m)	27500/358/13514/0
GDL/MPL/CL/PEM热导率(厚度方向)/ (W/(m·K))	0.83/0.83/2.74/0.2
GDL/MPL/CL/PEM热导率(平面方向)/ (W/(m·K))	8.33/0.83/2.74/0.2
阴/阳极交换电流密度/(A/m³)	900/5×10⁸
阴/阳极电荷传递系数	0.65/0.5

Table 4 Grid independence test

工况	网格数量/个	电流密度/(mA/cm²)	电压/V	计算时间/h
Case1	196964	800	0.731275	5.1
Case2	261492	800	0.731949	7.3
Case3	307831	800	0.732615	8.6
Case4	363158	800	0.732826	10.4
Case5	431285	800	0.732910	12.8

Fig.3 Model validation

Fig.4 Local voltage and relative humidity of the mid-plane of CCL at the starting moment of the run

Fig.5 Carbon corrosion rate and dissolution rate of Pt in the mid-plane of CCL at the starting moment of the run

Fig.6 Ratio of oxidized to unoxidized area on Pt surface after 500 h of running

Fig.7 Variation of ECSA of CCL with operating time

Fig.8 The reduction rate of the radius of agglomerate in CLL and the thickness reduction of the catalytic layer after 500 h of running

Fig.9 Local voltage and dissolved water content of the mid-plane of ACL at the starting moment of the run

Fig.10 Gas crossover flux of O2 from CCL to ACL at the starting moment of the run

Fig. 11 Concentration of RfSO3- in mid-plane of PEM and PEM thickness reduction after 500 h of running

Fig.12 Variation in physical properties of PEM with running time

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