Three Dimensional Analyses of Degradation in PEMFCs
Three Dimensional Analyses of Degradation in PEMFCs
复制标题
PEMFC 降解的三维分析
DOI：
10.1017/s1431927617005475
复制
发表时间：
2017
影响因子：
2.8
通讯作者：
I. Narita
中科院分区：
文献类型：
--
作者：
T. Daio;K. Suganuma;I. Narita
质子交换膜燃料电池(PEMFC)是利用氢气而不排放温室气体的候选材料之一。然而，由于运行过程中的退化现象，质子交换膜燃料电池的寿命仍然很短。先前的研究表明，施加温度会导致负载粒子的聚集，并改变金属纳米粒子和离聚体在炭黑上的分布。近年来，这些纳米粒子和离聚体的纳米级分布引起了人们的广泛关注，以阐明PEMFC的降解机理，提高其性能。近年来，层析成像法[1]和原位观察法[2]研究了纳米粒子和离聚体在PEMFC中的分布，目前已分别采用层析成像法和原位观察法来观察其形态的动态变化。特别是，在质子交换膜燃料电池上，断层扫描(在没有加热的情况下拍摄)通过使用Z-对比度来区分图像中的纯贵金属纳米颗粒、离聚体和碳黑。并用原位模拟降解的方法对催化行为进行了可视化。然而，由于样品加热架和电热室的尺寸限制，质子交换膜燃料电池的原位层析成像还没有实现。事实上，已经提出了几种加热支架，但这些都很难应用于电子断层扫描，因为目标极片周围的空间很小，支架的厚度也很小，导致倾角很小，例如25度。另外，夹持器的加热器会使夹角丢失。此外，由于纳米粒子、离聚体和炭黑之间的反应，负载的粒子改变了粒子的大小和分布，因此加热时原位观察PEMFC是困难的。因此，需要更薄的加热单元和固定器尖端。此外，传统的加热座有一个由电线制成的加热单元。因此，尽可能地对温度进行定量识别，以避免温度超调是非常重要的。
Proton exchange membrane fuel cell (PEMFC) is one of the candidate materials which can utilize the hydrogen without emitting greenhouse effect gas. However, the lifetime of PEMFCs is still short due to the degradation phenomena during operation. Previous studies suggest that applied temperature leads aggregation of supported particles and changes the distribution of metal nanoparticles and ionomers on carbon blacks. Recently, nanoscale distribution of these nanoparticles and ionomers attracts much attention to clarify these degradation mechanisms of PEMFCs and to improve the performance. Recent studies of distribution of the nanoparticles and ionomers of PEMFCs were investigated by tomography [1] and in-situ observation [2].To date, tomography and in-situ observation have been individually conducted to observe the dynamic change of morphology. In particularly, on the PEMFCs, tomography (which was taken without heating) archived to distinguish between pure noble metal nanoparticles, ionomers and carbon blacks in an image by using the Z-contrast. And the catalytic behaviours were visualised with in-situ to simulate degradation. However, tomography with in-situ observation of PEMFCs has not been achieved because of the size limitation of the sample heating holder and the chamber. In fact, several heating holders are proposed, but these are difficult to apply for electron tomography because of tiny spaces around the objective pole piece and thickness of the holder which results in small tilt angle eg 25 degree. Also, heater of the holder makes missing angle. In addition, in-situ observation of PEMFCs with heating is difficult since the supported particles change the size and distribution due to reaction between nanoparticles, ionomers and carbon blacks. Therefore, thinner heating unit and holder tip is needed. Also, conventional heating holder has a heating unit made by wires. Therefore, it is important to quantitatively identify the temperature as much as possible to avoid over shoot of temperature.