Chemical and mechanical degradations of perfluorosulfonic-acid membranes are two factors contributing to the reduced durability of fuel cells. While the mechanisms of isolated chemical or mechanical degradation are extensively investigated, the impact of chemical degradation on mechanical degradation is not fully understood. In this paper, the fracture behavior of Nafion 212 membranes with different chemical degradation levels are investigated. To characterize the degradation level and probe the molecular origins of chemical degradation, fluoride release, Fourier-transformer infrared spectra, conductivity and swelling behavior are measured. It is found that chemical degradation causes predominant loss of side-chains. A transition from ductile to brittle fracture is observed with increasing degradation level. In addition, the cross-sections are examined to link fracture behavior with microstructure changes. While the decreased fracture toughness is attributed to reduced mechanical properties such as Young's modulus and break strain, the decreased crack propagation resistance is ascribed to reduced plastic zone size ahead of crack tip, which reduces the plastic energy dissipation. These findings not only provide new mechanical dataset of degraded membranes for performance and durability modelling to take into account of chemical degradation effect but also improve the understanding of membrane durability.

全氟磺酸膜的化学和机械降解是导致燃料电池耐久性降低的两个因素。尽管广泛研究了分离的化学或机械降解的机理，但对化学降解对机械降解的影响尚不完全了解。本文研究了不同化学降解水平的Nafion 212膜的断裂行为。为了表征降解水平并探测化学降解，氟化物释放，傅立叶变换红外光谱，电导率和溶胀行为的分子起源。发现化学降解导致侧链的主要损失。随着降解水平的提高，观察到了从韧性断裂到脆性断裂的过渡。此外，检查横截面以将断裂行为与微观结构变化联系起来。断裂韧性的降低归因于机械性能的降低，例如杨氏模量和断裂应变，而降低的裂纹扩展阻力归因于裂纹尖端之前的塑性区尺寸的减小，从而降低了塑性能量的消耗。这些发现不仅为性能和耐久性建模提供了降解膜的新机械数据集，并考虑了化学降解效应，而且还增进了对膜耐久性的理解。降低的裂纹扩展阻力归因于裂纹尖端之前的塑性区尺寸减小，从而减少了塑性能量耗散。这些发现不仅为性能和耐久性建模提供了降解膜的新机械数据集，并考虑到了化学降解作用，还提高了对膜耐久性的认识。降低的裂纹扩展阻力归因于裂纹尖端之前的塑性区尺寸减小，从而减少了塑性能量耗散。这些发现不仅为性能和耐久性建模提供了降解膜的新机械数据集，并考虑了化学降解效应，而且还增进了对膜耐久性的理解。