Effect of purging conditions on the impedance relaxation phenomenon and low temperature start-up of PEMFC

doi:10.11949/0438-1157.20221344

Abstract

Abstract:

As a key process before starting at sub-zero temperature in a proton exchange membrane fuel cell (PEMFC), purging is effective in reducing the water content in the membrane electrode to improve the success rate of cold start. Shutdown purging, as a key process before sub-zero temperature start-up of proton exchange membrane fuel cell (PEMFC), can effectively reduce the water content of membrane electrode (MEA) before cold start, so as to improve the success rate of battery start-up. In order to investigate the impedance relaxation phenomenon of PEMFC after purging and how the purging conditions directly contribute to the low temperature start-up performance of PEMFC, an experimental study was conducted with a 25 cm² single cell as the subject. The results under experimental conditions showed that the impedance relaxation became more obvious with the increase of gas flow rate and purging temperature; the purging flow rate and purging time had significant effects on the cold start performance of PEMFC. Under experimental conditions, the test cell performed best in low temperature by purging with dry N₂ at 1500 ml/min for 15 min. The excessive or insufficient purge flow rate and purge time are not conducive to the low temperature start-up of PEMFC, and optimal purge conditions exist.

Key words: fuel cells, purge, cold start, mass transfer, porous media

摘要：

停机吹扫作为质子交换膜燃料电池(PEMFC)零下温度启动前的关键流程，能够有效降低冷启动前膜电极(MEA)的含水量，以提高电池启动的成功率。为了研究PEMFC在停机吹扫后出现的阻抗弛豫现象，以及吹扫条件如何直接作用于PEMFC低温启动性能，以25 cm²的单片电池作为对象，进行实验研究。实验条件下的结果表明，随着吹扫气体流量的增加以及吹扫温度的提高，阻抗弛豫表现更加明显；吹扫流量和吹扫时间对PEMFC冷启动性能存在显著影响。在实验条件下，以1500 ml/min的干燥N₂吹扫15 min，测试电池在低温中的表现最佳。吹扫流量过大、过小以及吹扫时间过长、过短均不利于PEMFC的低温启动，存在最佳吹扫条件。

关键词: 燃料电池, 吹扫, 冷启动, 传质, 多孔介质

CLC Number:

TK 91

Zhiguang QIAN, Yue FAN, Shixue WANG, Like YUE, Jinshan WANG, Yu ZHU. Effect of purging conditions on the impedance relaxation phenomenon and low temperature start-up of PEMFC[J]. CIESC Journal, 2023, 74(3): 1286-1293.

钱志广, 樊越, 王世学, 岳利可, 王金山, 朱禹. 吹扫条件对PEMFC阻抗弛豫现象和低温启动的影响[J]. 化工学报, 2023, 74(3): 1286-1293.

Figures/Tables 9

Fig.1 Schematic diagram of fuel cell structure

Fig.2 Schematic diagram of PEMFC purge and cold start experimental system

Table 1 Experimental conditions at each stage

运行阶段	参数	数值
稳态运行阶段	运行温度/℃	60
	氢气化学计量比	1.5
	氢气相对湿度/%	100
	空气化学计量比	2.5
	空气相对湿度/%	70
	电流密度/（A/cm²）	1.2
	运行时间/min	30
冷却阶段	冷却温度/℃	-10
冷却阶段	冷却时间/h	3
冷启动阶段	冷启动温度/℃	-10
	氢气流量/（ml/min）	95
	氢气相对湿度	0
	空气流量/（ml/min）	226
	空气相对湿度	0
	电流密度/（A/cm²）	0.04

Table 2 Purging conditions for impedance relaxation experiment

参数	数值
电池温度/℃	20/40/60
气体流量/（ml/min）	1000/1500/2000
吹扫时间/s	200
吹扫气体	干燥N₂

Fig.3 HFR variation of PEMFC under different purge flow rates

Fig.4 Schematic diagram of water removal process after purge

Fig.5 HFR variation of PEMFC with time under different purge temperatures

Fig.6 Effect of purge gas flow rate on cold start

Fig.7 Effect of purge time on cold start

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