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Flow properties of an intact MPL from nano-tomography and pore network modelling

机译：纳米断层扫描和孔网络建模的完整MPL的流动特性

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摘要

Adding a hydrophobic micro-porous layer (MPL) between a gas diffusion layer (GDL) and a catalyst layer (CL) at the cathode of a PEM fuel cell was found capable of improving cell performance. However, how an MPL does this is not well-understood because current techniques are limited in measuring, observing and simulating multiphase pore fluid flow across the full range of pores that vary to a great extent in geometry, topology, surface morphology. In this work, we focused our investigation on estimating flow properties of an MPL volume to assess the limiting effect of strongly hydrophobic sub-micron pores on water transports. We adopted a nano-tomography and pore network flow modelling approach. A pore-structure model, purposely reconstructed from an intact MPL sample using Focused Ion Beam milling and Scanning Electron Microscope (FIB/SEM) previously, was used to extract a realistic pore network. A two-phase pore network flow model, developed recently for simulating the flow of gas, liquid or their mixture in both micrometre and nanometre pores, was applied to the pore network. We firstly tested the validity of the constructed pore network, and then calculated the properties: permeability for both water and selected gases, water entry pressure, and relative permeability. Knudsen diffusion was taken into consideration in calculations when appropriate. Our calculations showed that the water permeability was three orders of magnitude smaller than experimentally measured results reported in the literature, and when the water contact angle increased from 95° to 150°, the water-entry pressure increased from 2.5 MPa to 28 MPa. Thus our results revealed that for a strongly hydrophobic MPL that contains nanometre pores only it would behave like a buffer to water, and therefore the structural preferential paths in an MPL, such as cracks, are likely to be responsible for significant liquid water transport from the CL to the GDL that has been observed experimentally recently. We highlighted the needs for multi-scale modelling of the interplays of liquid water and gas transfer in MPLs that contain variable pores.
机译：发现在PEM燃料电池的阴极处的气体扩散层（GDL）和催化剂层（CL）之间添加疏水微孔层（MPL）能够改善电池性能。然而，由于目前的技术在测量，观察和模拟跨越几何，拓扑，表面形态变化很大的整个范围的多相孔隙流体方面受到限制，因此，MPL如何做到这一点尚不为人所知。在这项工作中，我们将研究重点放在估计MPL体积的流动特性上，以评估强疏水性亚微米孔对水传输的限制作用。我们采用了纳米断层扫描和孔网络流动建模方法。以前使用聚焦离子束铣削和扫描电子显微镜（FIB / SEM）故意从完整的MPL样品重建的孔结构模型用于提取实际的孔网络。最近开发的用于模拟气体，液体或它们的混合物在微米和纳米孔中流动的两相孔网流动模型已应用于孔网。我们首先测试了构造的孔隙网络的有效性，然后计算了特性：水和选定气体的渗透率，进水压力和相对渗透率。适当时在计算中考虑了克努森扩散。我们的计算表明，水渗透率比文献中报道的实验测量结果小三个数量级，并且当水接触角从95°增大到150°时，进水压力从2.5 MPa增大到28 MPa。因此，我们的结果表明，对于仅包含纳米孔的强疏水性MPL，它的行为就像是对水的缓冲剂，因此MPL中的结构性优先路径（例如裂缝）可能是导致液态水从水中大量运出的原因。 CL到最近通过实验观察到的GDL。我们强调了对包含可变孔隙的MPL中液态水和气体传输相互作用的多尺度建模的需求。

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  • 来源
    《Fuel》 |2014年第15期|307-315|共9页
  • 作者

    Jingsheng Ma; Xiaoxian Zhang; Zeyung Jiang; Hossein Ostadi; Kyle Jiang; Rui Chen;

  • 作者单位

    Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh EH14 4AS, UK;

    School of Engineering, University of Liverpool, Brownlow Street, Liverpool L69 3GQ, UK;

    Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh EH14 4AS, UK;

    Department of Mechanical and Manufacturing Engineering, University of Birmingham, Birmingham B15 2TT, UK;

    Department of Mechanical and Manufacturing Engineering, University of Birmingham, Birmingham B15 2TT, UK;

    Department of Aeronautical and Automotive Engineering, Loughborough University, Leicestershire LE11 3TU, UK;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    PEM fuel cells; Micro-porous layer; FIB/SEM tomography; Pore network flow modelling; Liquid water flow;

    机译：PEM燃料电池;微孔层;FIB / SEM断层扫描;孔网流量建模;液态水流量;

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