Department of Physics, University of Missouri-Kansas City, Kansas City, Missouri 64110, USA.
J Phys Chem B. 2010 Nov 25;114(46):14989-94. doi: 10.1021/jp108163a. Epub 2010 Oct 28.
We have investigated changes of proton channel network in Nafion membranes annealed at elevated temperatures using current sensing atomic force microscopy aimed at understanding the aging process of the membranes. The results reveal that the changes of proton channel network undergo two steps: First, the configuration of the ionic domains on the membrane surface changes from cluster-like to chain-like structure, accompanied by an increase of the proton conductivity of the membrane. As the annealing continues, the chain-like configuration for the proton channels persists but the conductance of the membranes decreases. The time constant of the conductivity decay decreases with the annealing temperature. The observed changes can be explained in terms of reorientation of proton channels near the membrane surface from perpendicular to parallel to the surface as the annealing temperature approaches the glass transition of the membranes.
我们使用电流感应原子力显微镜研究了高温退火的 Nafion 膜中质子通道网络的变化，旨在了解膜的老化过程。结果表明，质子通道网络的变化经历了两个步骤：首先，膜表面上的离子域的构型从类簇状变为链状结构，同时膜的质子电导率增加。随着退火的继续，质子通道的链状构型保持不变，但膜的电导率降低。电导率衰减的时间常数随退火温度的升高而降低。观察到的变化可以用膜表面附近质子通道从垂直于表面到平行于表面的重新取向来解释，因为退火温度接近膜的玻璃化转变温度。
