摘要/Abstract

为了制备出兼具高电导率和优异力学性能的高温质子交换膜，本工作采用化学自交联的方法将含氮功能基团聚乙烯亚胺（PEI，平均分子量200）接枝到氯甲基化聚砜（CMPSF）高分子链上制备磷酸掺杂型高温质子交换膜的基膜（PEI-PSF）.其中，PEI上的含氮功能基团既作为磷酸吸附位点，使高温质子交换膜获得高的质子传导率，同时又作为交联位点与CMPSF高分子链上的苄氯基团发生自交联反应，使聚合物膜具有优良的力学性能.傅里叶变换红外光谱和X-射线光电子能谱测试结果表明，CMPSF高分子链上的苄氯基团与PEI上的含氮功能基团发生完全反应，且随着聚砜氯甲基化程度的增加，膜中引入的PEI含量相应增加，进而提升了PEI-PSF膜的磷酸掺杂水平.氯甲基化程度为58%的PEI-PSF膜（PEI-PSF-58）磷酸吸附量达到122 wt%，在180℃无水条件下质子电导率达到3.4×10^-2 S·cm^-1，同时该复合膜拉伸强度达到30 MPa.基于磷酸掺杂的PEI-PSF-58复合膜的高温质子交换膜燃料电池在150℃干气条件下的输出峰功率达到200 mW·cm^-2，并且在78 h的测试时间内展示出了良好的稳定性.
关键词: 燃料电池, 磷酸掺杂高温质子交换膜, 自交联, 质子电导率, 力学性能
High temperature proton exchange membrane fuel cells (HT-PEMFC) operated at a temperature range from 120℃ to 200℃ show high reaction kinetics, high tolerance of the Pt catalyst for impurities such as carbon monoxide and simplified water and heat management. HT-PEMFC has attracted great attentions in many applications including portable devices, unmanned vehicles and fuel cell cars. One of the essential components of the HT-PEMFC is high temperature proton exchange membrane (HT-PEM). The state-of-the-art HT-PEM is phosphoric acid (PA) doped polybenzimidazole (PBI) composite membrane. Phosphoric acid acts as the proton conductor while the PBI plays as a skeleton to hold the PA molecules and provides mechanical strength for the composite membrane. Nevertheless, the complex fabrication procedures and expensive cost hinder wide application of PBI in HT-PEMFC. Alternative polymer skeletons including polyvinylpyrrolidone and amino-functionalized proton exchange membrane have been developed for the HT-PEM. Generally, the high proton conductivity of the HT-PEMs results from high doping level of PA. However, the plasticizer effect of PA molecules reduces the Van der Waals force among the polymer macromolecules. That leads to the low mechanical strength of the HT-PEMs. Cross-linking method significantly increases the mechanical strength of the HT-PEMs. On the other hand, the cross-linking reaction consumes the PA doping site of the HT-PEMs, leading to the low proton conductivity of these HT-PEMs. In this research, a novel self-crosslinked polyethyleneimine-polysulfone (PEI-PSF) HT-PEM with both high mechanical strength and high proton conductivity has been designed. The PEI molecules are anchored to the PSF backbones by chloromethylation and tertiary aminating reactions. That is prone to enhance the mechanical strength of the membrane. In addition, the PEI also acts as PA adsorption sites, which improves the PA doping level and proton conductivity of the HT-PEM. The degree of crosslinking is controlled by the degree of chloromethylation. The ¹H nuclear magnetic resonance characterization shows successfully graft of benzyl chloride onto the PSF backbone to form chloromethylated polysulfone (CMPSF). In addition, the X-ray photoelectron spectra confirm the reaction of PEI with CMPSF to form a self-crosslinked PEI-PSF membrane. With the increase of crosslinking degree, the PA doping level of the PEI-PSF membrane increases whereas its tensile strength decreases. A proton conductivity of 3.4×10^-2 S·cm^-1 is obtained for a PEI-PSF membrane with a chloromethylation degree of 58%, denoted as PEI-PSF-58, and PA doping level of 122 wt% at 150℃ under anhydrous conditions. Meanwhile, the PEI-PSF-58 membrane remains excellent mechanical property with tensile strength of 30 MPa at room temperature. Moreover, HT-PEMFC based on the PEI-PSF-58 membrane exhibits a high peak power density of 200 mW·cm^-2 and outstanding stability under 150℃ with a constant cell voltage of 0.4 V. In summary, a series of self-crosslinked PEI-PSF HT-PEMs with both high proton conductivity and excellent mechanical properties have been synthesized. The self-crosslinking is a promising strategy to cope with trade-off between high proton conductivity and mechanical strength for the conventional PA doped HT-PEMs.
Key words: fuel cell, phosphoric acid doped high temperature proton exchange membrane, self-crosslinked, proton conductivity, mechanical property


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