Abstract We present a coupled simulation method for evaluating oxygen diffusivity in cathode catalyst layers of polymer electrolyte membrane fuel cells under capillary condensation of water partially filling the pore network. The voxel data of a catalyst layer formed with platinum-supported carbon and Nafion ionomer are prepared from sequential cross-sectional images taken by a cryo-focused ion beam scanning electron microscope. Capillary condensation of water, which effectively alters the pore network, is simulated using the lattice density functional theory. Then, the effective porosity eeff, chord length distribution, and characteristic length of the partially wet catalyst layer are evaluated. The effective diffusion coefficients of oxygen in the Knudsen regime are evaluated using the mean-square displacement method. The ratio eeff/τ, with τ being the tortuosity factor, roughly exhibits intermediate behavior between the Bruggeman correlations of sphere- and cylinder-filling for eeff ≳ 0.2, while eeff/τ drastically deviates from the Bruggeman correlation for eeff ≲ 0.2. The effective oxygen diffusion coefficients at 350 K are predicted as a function of relative humidity and total pressure based on the kinetic theory of gases. The proposed method gives deeper insights into oxygen diffusivity under capillary condensation, contributing to more efficient material design.

中文翻译：

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聚合物电解质膜燃料电池阴极催化剂层水毛细冷凝作用下氧气扩散率与多孔特性的关系

摘要 我们提出了一种耦合模拟方法，用于评估在部分填充孔隙网络的水的毛细冷凝下聚合物电解质膜燃料电池阴极催化剂层中的氧扩散率。由载有铂的碳和 Nafion 离聚物形成的催化剂层的体素数据是从低温聚焦离子束扫描电子显微镜拍摄的连续横截面图像中制备的。使用晶格密度泛函理论模拟了水的毛细管冷凝，它有效地改变了孔隙网络。然后，评估部分湿润催化剂层的有效孔隙率 eeff、弦长分布和特征长度。使用均方位移法评估 Knudsen 状态下氧气的有效扩散系数。比率eeff/τ，τ 是曲折系数，大致表现出 eeff ≳ 0.2 的球体和圆柱体填充的布鲁格曼相关性之间的中间行为，而 eeff / τ 大大偏离 eeff ≲ 0.2 的布鲁格曼相关性。根据气体动力学理论，将 350 K 下的有效氧扩散系数预测为相对湿度和总压力的函数。所提出的方法可以更深入地了解毛细管冷凝下的氧气扩散率，有助于更有效的材料设计。根据气体动力学理论，将 350 K 下的有效氧扩散系数预测为相对湿度和总压力的函数。所提出的方法可以更深入地了解毛细管冷凝下的氧气扩散率，有助于更有效的材料设计。根据气体动力学理论，将 350 K 下的有效氧扩散系数预测为相对湿度和总压力的函数。所提出的方法可以更深入地了解毛细管冷凝下的氧气扩散率，有助于更有效的材料设计。