Polybenzimidazole-based membranes in high temperature proton exchange membrane fuel cells require doping with phosphoric acid to enable proton conductivity. The level of phosphoric acid doping is traditionally determined by titration or weighing, but these methods only provide limited information, since they do not offer spatial resolution. We show that confocal Raman microscopy can not only provide information on the level of doping, but in addition about the spatial distribution of the dopant. We prove that doping is a diffusion-limited process, leading to a spatially inhomogeneous distribution of phosphoric acid unless doping is performed to saturation. Further, evidence of a slow redistribution of the dopant within a freestanding membrane under ambient conditions is provided. Confocal Raman microscopy can be used as a non-invasive measurement tool to investigate status and progress of doping a membrane with phosphoric acid.

高温质子交换膜燃料电池中的聚苯并咪唑基膜需要掺杂磷酸以实现质子传导性。磷酸掺杂的水平传统上是通过滴定或称重来确定的，但是这些方法仅提供有限的信息，因为它们不提供空间分辨率。我们表明，共聚焦拉曼显微镜不仅可以提供有关掺杂水平的信息，而且还可以提供有关掺杂剂空间分布的信息。我们证明掺杂是一个扩散受限的过程，除非掺杂达到饱和，否则会导致磷酸在空间上的不均匀分布。此外，提供了在环境条件下掺杂剂在独立膜内缓慢重新分布的证据。