Improving the water-handling of proton exchange membrane fuel cells

氢质子交换膜燃料电池（pemfc）是实现向净零碳能源过渡的关键技术。氢燃料电池组已被证明非常适合为汽车，特别是卡车提供动力，因为大多数大型车辆都无法采用电池解决方案。氢能委员会最近的一份报告（链接如下）强调了使用电池电动汽车（bev）和燃料电池电动汽车（fcev）的协同作用，对交通运输产生的二氧化碳排放产生重大影响。由于对基础设施网络的要求较低，预计重型卡车市场将成为第一个完全商业化的燃料电池汽车应用市场。然而，严重影响pemfc性能和效率的关键问题是水驱。水淹发生在阴极侧催化剂层，由此在阴极反应中产生的水在催化剂载体的孔隙中凝结出来，从而阻止进入的氧气进入。疏水离聚体被添加到阴极催化剂层，试图减轻水淹。为了设计阴极催化剂层的最佳配方和制造工艺，有必要了解阴极催化剂层的性质，特别是孔径、孔连通性和表面润湿性/疏水性与实际PEMFC中的性能之间的关系。然而，人们发现，目前使用的表征方法无法充分区分不同层的孔隙网络和润湿性特征，从而预测其最终PEMFC性能的差异。因此，需要新的表征技术，这就是这个项目的目的。这个项目的目标是测试三种这样的候选技术的适用性。超极化（hp）氪和氙的核磁共振波谱和弛豫测量已被证明是探测网络中孔径大小和疏水/亲水表面空间分布的敏感探针。因此，我们打算测试hp Kr和hp Xe核磁共振技术，以确定离子的空间分布和阴极孔隙网络中水吸附的开始。第二个候选方法是吸附量热法。之前对页岩气吸收的重力和量热联合研究表明，该技术可以很容易地评估复杂几何结构中孔隙凝析油的空间排列和并置，以及它对质量输运的影响。这项技术也将在催化剂层上进行试验。最后，对催化剂颗粒的一系列水吸附和汞孔隙度研究表明，该方法可以表征吸附水的空间分布以及对孔隙网络内渗透途径的影响，因此将在阴极催化剂层上进行测试。我们还将致力于开发一种表征技术，可用于制造过程中的质量控制和近线测量。

Hydrogen proton exchange membrane fuel cells (PEMFCs) are a key technology in enabling the transition to net-zero carbon energy. Hydrogen powered fuel cell stacks have been demonstrated to be eminently suitable for powering cars and especially trucks, because battery solutions are not viable for most larger vehicles. A recent Hydrogen Council report (link below) emphasises the synergy in using both battery electric vehicles (BEVs) and fuel cell electric vehicles (FCEVs) to have a major impact on transport derived CO2 emissions. The heavy duty truck market is expected to be the first to become fully commercialised FCEV application due to the less-demanding infrastructure network requirements.However, a key issue severely impacting the performance and efficiency of PEMFCs is water flooding. Water flooding occurs in the cathode-side catalyst layer whereby water generated in the cathode reaction condenses out in the pores of the catalyst support thereby blocking access for in-coming oxygen. Hydrophobic ionomer is added to the cathode catalyst layer to attempt to mitigate against flooding. In order to design the optimal formulation and fabrication process for the cathode catalyst layer, it is necessary to understand the relationship between the properties of the layer, especially pore size, pore connectivity and surface wettability/hydrophobicity, and the performance in the actual PEMFC. However, it has been found that current characterisation methods used are unable to distinguish sufficiently between the pore network and wettability characteristics of different layers to predict differences in their eventual PEMFC performance. Hence, new characterisation techniques are needed, and this is the aim of this project. The objectives of this project are to test three such candidate techniques for suitability. NMR spectroscopy and relaxometry of hyperpolarised (hp) krypton and xenon have been shown to be sensitive probes of pore size and the spatial distribution of hydro-phobic/-philic surfaces within a probed network. We, thus, intend to test hp Kr and hp Xe NMR techniques for determining the spatial distribution of ionomer and inception of water adsorption within cathode pore networks. The second candidate is adsorption calorimetry. Previous combined gravimetric and calorimetric studies of gas uptake in gas shales have suggested the technique can readily assess the spatial arrangement and juxtaposition of pore condensate in complex geometries, and its impact on mass transport. This technique will also be tried on catalyst layers. Finally, serial water adsorption and mercury porosimetry studies on catalyst pellets have revealed that this method can characterise the spatial distribution of the adsorbed water and the impact on percolation pathways within the pore network, and will thus be tested on cathode catalyst layers. We will also aim to develop a characterisation technique that can be used as a quality control, near-to-line measurement during manufacturing.