Yin Chongshan, Wang Lingtao, Li Jingjing, Zhou Yawei, Zhang Haining, Fang Pengfei, He Chunqing
Key Laboratory of Nuclear Solid State Physics Hubei Province, School of Physics and Technology, Wuhan University, Wuhan 430072, China.
Phys Chem Chem Phys. 2017 Jun 21;19(24):15953-15961. doi: 10.1039/c7cp03052e.
The free volumes and proton conductivities of Nafion membranes were investigated at different humidities by positron annihilation lifetime spectroscopy (PALS) and using an electrochemical workstation, respectively. The results showed that the variation in o-Ps lifetime τ was closely associated with the microstructure evolution and the development of hydrophilic ion clusters in Nafion membranes as a function of water uptake, regardless of metal oxide additives. In particular, with increasing relative humidity, the maximum value of τ in the Nafion membranes corresponded to the formation of numerous water channels for proton transportation. Numerous well-connected water channels in Nafion-TiO hybrid membranes could be formed at a much lower relative humidity (∼40% RH) than in the pristine one (∼75% RH), due to the better water retention ability of the Nafion-TiO membranes. Further, a percolation behavior of proton conductivity at high water uptake in Nafion membranes was observed, which showed that the percolation of ionic-water clusters occurred at the water uptake of ∼4.5 wt%, and ∼6 wt% was basically enough for the formation of a well-connected water channel network.
分别通过正电子湮没寿命谱（PALS）和使用电化学工作站，研究了不同湿度下Nafion膜的自由体积和质子传导率。结果表明，无论金属氧化物添加剂如何，o-Ps寿命τ的变化都与Nafion膜中微观结构的演变以及亲水性离子簇随吸水率的发展密切相关。特别是，随着相对湿度的增加，Nafion膜中τ的最大值对应于形成众多用于质子传输的水通道。由于Nafion-TiO膜具有更好的保水能力，在比原始膜（约75%RH）低得多的相对湿度（约40%RH）下，Nafion-TiO混合膜中可以形成许多连接良好的水通道。此外，观察到Nafion膜在高吸水率下质子传导率的渗流行为，这表明离子-水簇的渗流发生在吸水率约为4.5 wt%时，约6 wt%基本上足以形成连接良好的水通道网络。
