  Polymer composite electrolytes of Nafion and phosphotungstic acid (PWA) are
fabricated and analyzed using electrochemical strain microscopy (ESM) and
conductive atomic force microscopy (C-AFM) to visualize hydrophilic ion
channels near the surface, which are composed of water and sulfonic acid
groups. The results indicate that the fibrillar objects in ESM image, without
significant changes in topography, are hydrophilic ion channels and additional
ion channels formed by interaction between PWA and sulfonic groups in Nafion.
In this study, the buried ion channels lying under the surface are probed as
well as the inlet and outlet of the channels on the surface through combined
use of ESM and C-AFM. The results further enhance the understanding of ionic
conduction in composite polymer electrolytes in various fields.
