Research on shutdown purge characteristics of proton exchange membrane fuel cells: Purge parameters conspicuity and residual water

• Published in: Applied thermal engineering 2024-07, Vol.249, p.123437, Article 123437
• Main Authors: Zhang, Zhenya, Wei, Houyu, Xiao, Yanqiu, Cheng, Chuanxiao, Tian, Jiean, Li, Xinxin, Liu, Junrui, Liu, Zhengxuan
• Format: Article
• Language: English
• Subjects: Conspicuity analysis of purge parameters; Proton exchange membrane fuel cell; Purge strategy; Residual water; Shutdown purge characteristics
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2024.123437

•The stoichiometric ratio most significantly influences water variation.•Purge stoichiometry should exceed 9 and relative humidity should remain below 40%.•Suitable purge current density should avoid generating liquid water and high voltage.•The post-purge state is mainly determined by current density and relative humidity.•The development of a purge strategy should encompass various purge stages. This paper comprehensively investigates the purge mechanism of proton exchange membrane fuel cells during the shutdown process, which qualitatively examines the effect of purge parameters (including current density, stoichiometric ratio, and relative humidity) on water content variation, and further quantitatively investigates the remaining water content post-purge. In contrast to previous studies, this paper offers a novel perspective on analyzing the purge process and conducts a thorough examination of residual water content. This study presents a transient, isothermal, two-phase flow model for proton exchange membrane fuel cells, which is subsequently validated experimentally. Results indicate that the significance of purge parameters follows the descending order: stoichiometric ratio, relative humidity, and current density. During the purge, the stoichiometric ratio should be rapidly increased to above 9. Each incremental rise in the stoichiometric ratio from 6 to 14 leads to a respective reduction in residual membrane water content after purge of 2.19 %, 1.57 %, 1.18 %, 0.93 %, 0.76 %, 0.63 %, 0.53 %, and 0.46 %. Similarly, it is recommended to swiftly decrease relative humidity to below 40 %. Elevating the purge current density from 20 to 200 mA/cm2 decreases the time required to completely remove liquid water from 20.24 s to 6.59 s. Hence, employing a higher current density at the onset of the purge facilitates quicker removal of liquid water, albeit resulting in an increase in residual membrane water content post-purge, from 3.17 to 3.70. In summary, optimizing the purge strategy requires adjusting purge current densities according to the specific purge stage.