Electrochemical technologies are key to decarbonizing the energy sector. Electrification of the energy sector is underway with battery technologies dominating the light-duty electric vehicles market. It is more challenging to decarbonize historically difficult to decarbonize sectors, such as heavy-duty transportation, planes, ships, and the chemical manufacturing industry (ammonia, cement, steel). Green hydrogen produced via electrolysis will be used as a fuel and a feedstock in some of these processes. At the heart of the hydrogen economy are polymer electrolyte fuel cells (PEFCs), devices that convert hydrogen into electricity. Gas diffusion layers (GDLs) have an integral role in PEFCs, as they are porous carbon layers that transport reactants and products and also remove heat and conduct electricity. To improve the PEFCs’ performance and reduce degradation of materials, an understanding of coupled morphological properties and transport phenomena in the GDLs is needed. In this Account, we emphasize the integration of experimental and modeling approaches to achieve complete understanding of materials and transport properties of the GDLs. Our approach builds in complexity from simpler ex situ experiments to in situ and last to 3-D integrated modeling predictions. GDL morphology is complex, as its fabrication includes several stochastic steps (immersion of GDL in various baths to achieve the desired surface wettability) and only 3-D techniques, such as X-ray computed tomography can capture morphology correctly. Porosity, pore-size distribution, tortuosity, and formation factor are the most important morphological properties of the GDLs. For PEFC applications, water is generated in the catalyst layers and is transported through the GDLs. Therefore, GDL wettability directly impacts water permeability through the GDLs. Using in situ water injection experiments, we directly observe which pores water fill at what liquid pressure. This result provides information about the GDL’s affinity to intake water. GDLs are typically of mixed wettabilities, and internal wettability until recently has been unknown. Having images of water inside the GDL enabled us to track the triple-phase boundary at the fiber–water–air interface to obtain local contact angles in the locations where water was present. The percentage of contact angles that were hydrophilic correlated well to the percentage of surface oxides on the GDL surface using X-ray photoelectron spectroscopy (XPS). We envision many other groups using the method of XPS to determine internal surface wettability of the GDLs, as it is relatively fast. Heat transport and evaporation/condensation of water in the GDL is studied using in situ X-ray CT experiments. These provide direct insight into pore-scale water transport under thermal gradients. Three-dimensional geometries of GDLs are exported for transport simulations using the lattice Boltzmann method (LBM). Similarly, we advocate for building the LBM simulations, from water injection studies first to validate the model only to operando PEFC models later. LBM coupling with a continuum model enables a computational saving, allowing us to map local temperature, reactant, and product distributions in the GDLs.

中文翻译：

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气体扩散层：形态和传输特性的实验和建模方法

电化学技术是能源部门脱碳的关键。随着电池技术主导轻型电动汽车市场，能源行业正在电气化。历史上难以脱碳的行业脱碳更具挑战性，例如重型运输、飞机、船舶和化学制造业（氨、水泥、钢铁）。通过电解产生的绿色氢将在其中一些过程中用作燃料和原料。氢经济的核心是聚合物电解质燃料电池 (PEFC)，这是一种将氢转化为电能的装置。气体扩散层 (GDL) 在 PEFC 中起着不可或缺的作用，因为它们是多孔碳层，可以传输反应物和产物，还可以散热和导电。为了提高 PEFC 的性能并减少材料的降解，需要了解 GDL 中的耦合形态特性和传输现象。在这个帐户中，我们强调实验和建模方法的集成，以实现对 GDL 的材料和传输特性的完整理解。我们的方法构建了从更简单的异位实验到原位和持续到 3-D 集成建模预测的复杂性。GDL 形态是复杂的，因为它的制造包括几个随机步骤（将 GDL 浸入各种浴中以实现所需的表面润湿性），并且只有 3-D 技术，例如 X 射线计算机断层扫描才能正确捕获形态。孔隙度、孔径分布、曲折度和形成因子是 GDL 最重要的形态特征。对于 PEFC 应用，水在催化剂层中产生并通过 GDL 传输。因此，GDL 润湿性直接影响通过 GDL 的水渗透性。通过原位注水实验，我们直接观察到在什么液体压力下哪些孔隙水充满。该结果提供了有关 GDL 对进水的亲和力的信息。GDL 通常具有混合润湿性，直到最近才知道内部润湿性。GDL 内的水图像使我们能够跟踪纤维-水-空气界面处的三相边界，以获得存在水的位置的局部接触角。使用 X 射线光电子能谱 (XPS)，亲水性接触角的百分比与 GDL 表面上的表面氧化物百分比很好地相关。我们设想许多其他组使用 XPS 方法来确定 GDL 的内表面润湿性，因为它相对较快。使用原位 X 射线 CT 实验研究 GDL 中水的热传递和蒸发/冷凝。这些提供了对热梯度下孔隙尺度水传输的直接洞察。使用格子玻尔兹曼方法 (LBM) 导出 GDL 的 3D 几何形状以用于传输模拟。同样，我们提倡建立 LBM 模拟，从首先进行注水研究到验证模型，再到后来的操作 PEFC 模型。LBM 与连续模型的耦合可以节省计算量，使我们能够在 GDL 中绘制局部温度、反应物和产物分布。因为它比较快。使用原位 X 射线 CT 实验研究 GDL 中水的热传递和蒸发/冷凝。这些提供了对热梯度下孔隙尺度水传输的直接洞察。使用格子玻尔兹曼方法 (LBM) 导出 GDL 的 3D 几何形状以用于传输模拟。同样，我们提倡建立 LBM 模拟，从首先进行注水研究到验证模型，再到后来的操作 PEFC 模型。LBM 与连续模型的耦合可以节省计算量，使我们能够在 GDL 中绘制局部温度、反应物和产物分布。因为它比较快。使用原位 X 射线 CT 实验研究 GDL 中水的热传递和蒸发/冷凝。这些提供了对热梯度下孔隙尺度水传输的直接洞察。使用格子玻尔兹曼方法 (LBM) 导出 GDL 的 3D 几何形状以用于传输模拟。同样，我们提倡建立 LBM 模拟，从首先进行注水研究到验证模型，再到后来的操作 PEFC 模型。LBM 与连续模型的耦合可以节省计算量，使我们能够在 GDL 中绘制局部温度、反应物和产物分布。使用格子玻尔兹曼方法 (LBM) 导出 GDL 的 3D 几何形状以用于传输模拟。同样，我们提倡建立 LBM 模拟，从首先进行注水研究到验证模型，再到后来的操作 PEFC 模型。LBM 与连续模型的耦合可以节省计算量，使我们能够在 GDL 中绘制局部温度、反应物和产物分布。使用格子玻尔兹曼方法 (LBM) 导出 GDL 的 3D 几何形状以用于传输模拟。同样，我们提倡建立 LBM 模拟，从首先进行注水研究到验证模型，再到后来的操作 PEFC 模型。LBM 与连续模型的耦合可以节省计算量，使我们能够在 GDL 中绘制局部温度、反应物和产物分布。