燃料电池热压过程中催化层的结构演变机制

Investigation on the Structure Evolution Mechanism of the Catalyst Layer During the Hot-Pressing Process

摘要:

聚合物电解质燃料电池膜电极组件的制备过程，特别是热压过程会对其发电性能产生较大的影响，但目前现有研究对热压过程中催化层内部结构演变机制的认识还不充分。为此，通过正交实验、表征和电学性能测试，探究热压温度和热压时间对催化层结构变化和电池性能的影响。基于扫描电子显微镜数据可知热压处理会压缩催化层内部孔结构且热压温度和热压时间的增加会加剧这种压缩效应，这与孔径分布分析结论保持一致；另外还发现主要是次级孔被压缩。上述现象证实了催化层内离聚物在越过玻璃化转变温度后的软化行为。此外，电学性能测试表明热压处理导致传质阻抗显著增加，其中经过热压温度为160℃，且热压时间为9 min处理的催化层具备最大传质阻抗增加量，其传质阻抗为直接喷涂法制备催化层传质阻抗的2.77倍，这主要是催化层内孔结构被压缩的结果。研究结果揭示了催化层内离聚物热响应行为对催化层结构演变的影响，并为优化热压过程的关键参数提供了理论支撑。

Abstract:

The fabricating process of polymer electrolyte fuel cell membrane electrode assembly significantly affects its power generation performance， particularly the hot-pressing process. However， the internal structure evolution mechanism of the catalyst layer （CL） during the hot-pressing period is not fully understood. Therefore， the effect of the hot-pressing temperature and the treatment time on the CL structure variations is investigated in this study， utilizing orthogonal experiments， characterization， and performance analysis. Based on the scanning electron microscope data， the compressed behavior of the pore structure in the CL can been observed after the hot-pressing treatment and increasing the hot-pressing temperature and the treatment time can deteriorate this compressed effect， which is consistent with the pore diameter analysis. In addition， the secondary pores are mainly compressed. These phenomena illustrate the soften behavior of the ionomer in the CL above the glass transition temperature. Furthermore， the electrical performance analysis demonstrates the mass transfer resistance significantly increments due to the hot-pressing treatment and the mass transfer resistance increment of the CL hot-pressed at 160 ℃ for 9min is the most significant， which is 2.77 folds more than that of the CL prepared by direct spraying method and it is the result of the compressed pore structure in the CL. This study provides more sights into comprehending the effect of the ionomer thermal response behavior in the CL on the structure evolution process of the CL， and offers theoretical support for the critical parameter optimization of the hot-pressing procedure.