Non-fluorinated pre-irradiation-grafted (peroxidated) LDPE-based anion-exchange membranes with high performance and stability
Non-fluorinated pre-irradiation-grafted (peroxidated) LDPE-based anion-exchange membranes with high performance and stability
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DOI：
10.1039/c7ee02053h
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发表时间：
2017-10
影响因子：
32.5
通讯作者：
Lianqin Wang;J. J. Brink-J.;Ye Liu;A. Herring;Julia Ponce-González;D. Whelligan;J. Varcoe
中科院分区：
文献类型：
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作者：
Lianqin Wang;J. J. Brink-J.;Ye Liu;A. Herring;Julia Ponce-González;D. Whelligan;J. Varcoe
辐射接枝阴离子交换膜（RG-AEM）的研究主要集中在聚合物结合的带正电荷的头基，使阴离子传导的化学稳定性。已经在较小程度上研究了前体膜的主链聚合物化学对RG-AEM稳定性的影响，并且不研究由聚合物膜在空气中的预辐照接枝（过氧化）制成的RG-AEM。聚合物薄膜的机械强度通常会因暴露于高辐射剂量（例如来自高能电子束）而减弱，这是由主链的化学降解介导的：与非氟化薄膜相比，氟化薄膜在较低的吸收剂量下机械强度减弱。本研究系统地比较了使用过氧化方法（使用电子束在空气中预辐照）由非氟化聚合物膜（低密度聚乙烯- LDPE）和部分氟化聚合物膜（聚（乙烯-共聚-四氟乙烯）- ETFE）合成的RG-AEM之间的性能差异。使用的LDPE和ETFE前体膜的厚度均为25 μm，这导致RG-AEMs的水合厚度在52-60 μm范围内。RG-AEM（分别命名为LDPE-AEM和ETFE-AEM）均含有相同的共价结合的苄基三甲基铵（BTMA）阳离子头基。LDPE-AEM在80 °C、95%相对湿度环境下实现了145 mS cm−1的OH−阴离子电导率，在80 °C完全水合时实现了76 mS cm−1的Cl−阴离子电导率。碱稳定性测试表明，与ETFE-AEM相比，当在碱性水溶液中处理时，LDPE-AEM的机械弱化程度低得多。这种LDPE-AEM在H2/O2阴离子交换膜燃料电池（AEMFC）测试中的表现优于ETFE-AEM，这是由于高阴离子电导率和增强的原位水传输（由于LDPE前体的较低密度）：在80 °C下，LDPE-AEM与Pt基阳极和阴极一起实现了1.45 W cm−2的最大功率密度（参见图1）。1.21 mW cm−2（对于基准ETFE-AEM）。机械强度更高的RG-AEM的开发首次使其能够在80 °C的燃料电池中进行常规测试（参见60 °C是可常规用于基于ETFE的RG-AEM的先前最高温度）。这一发展促进了非Pt催化剂的应用：在80 °C下使用Ag/C阴极和0.8 mg cm−2的Ag负载量获得了931 mW cm− 2（在60 °C下仅获得711 mW cm−2）。关于使用商业上可接受的过氧化型辐射接枝工艺合成大批量基于LDPE的RG-AEM的第一份报告得出结论，所得LDPE-AEM上级ETFE-AEM（对于预期应用）。
Radiation-grafted anion-exchange membrane (RG-AEM) research has predominantly focused on the chemical stability of the polymer-bound positively-charged head-groups that enable anion conduction. The effect of the backbone polymer chemistry, of the precursor film, on RG-AEM stability has been studied to a lesser extent and not for RG-AEMs made from pre-irradiation grafting of polymer films in air (peroxidation). The mechanical strength of polymer films is generally weakened by exposure to high radiation doses (e.g. from a high-energy e−-beam) and this is mediated by chemical degradation of the main chains: fluorinated films mechanically weaken at lower absorbed doses compared to non-fluorinated films. This study systematically compares the performance difference between RG-AEMs synthesised from a non-fluorinated polymer film (low-density polyethylene – LDPE) and a partially-fluorinated polymer film (poly(ethylene-co-tetrafluoroethylene) – ETFE) using the peroxidation method (pre-irradiation in air using an e−-beam). Both the LDPE and ETFE precursor films used were 25 μm in thickness, which led to RG-AEMs of hydrated thicknesses in the range 52–60 μm. The RG-AEMs (designated LDPE-AEM and ETFE-AEM, respectively) all contained identical covalently-bound benzyltrimethylammonium (BTMA) cationic head-groups. An LDPE-AEM achieved a OH− anion conductivity of 145 mS cm−1 at 80 °C in a 95% relative humidity environment and a Cl− anion conductivity of 76 mS cm−1 at 80 °C when fully hydrated. Alkali stability testing showed that the LDPE-AEM mechanically weakened to a much lower extent when treated in aqueous alkaline solution compared to the ETFE-AEM. This LDPE-AEM outperformed the ETFE-AEM in H2/O2 anion-exchange membrane fuel cell (AEMFC) tests due to high anion conductivity and enhanced in situ water transport (due to the lower density of the LDPE precursor): a maximum power density of 1.45 W cm−2 at 80 °C was achieved with an LDPE-AEM alongside a Pt-based anode and cathode (cf. 1.21 mW cm−2 for the benchmark ETFE-AEM). The development of more mechanically robust RG-AEMs has, for the first time, led to the ability to routinely test them in fuel cells at 80 °C (cf. 60 °C was the prior maximum temperature that could be routinely used with ETFE-based RG-AEMs). This development facilitates the application of non-Pt catalysts: 931 mW cm−2 was obtained with the use of a Ag/C cathode at 80 °C and a Ag loading of 0.8 mg cm−2 (only 711 mW cm−2 was obtained at 60 °C). This first report on the synthesis of large batch size LDPE-based RG-AEMs, using the commercially amenable peroxidation-type radiation-grafting process, concludes that the resulting LDPE-AEMs are superior to ETFE-AEMs (for the intended applications).