Atomic Force Microscopy Studies of Conductive Nanostructures in Solid Polymer Electrolytes

Abstract

The morphological and conductive structure of surface and bulk of different ionomer, namely Nafion®, Aquivion®, and JST have been investigated by material-sensitive and conductive tapping mode atomic force microscopy (AFM). The thickness of the non-conducting surface skin layer could be measured directly. The ionic structure at equilibrium was found to be consistent with the 4 nm size of the "ionic peak" in SAXS. At freshly cut cross sections of Nafion® defined ionic regions with low adhesion and a high adhesion phase, interpreted as molecular back-bone, with a high density of steps were detected. A statistical analysis of the step heights delivered a most probable height, consistent with a layer of two polymer back-bones with two side-chains in between, with smaller values for Aquivion®. Platinum deposits visible inside the membrane after operation indicate the existence of two-dimensional aqueous phase and confirm the recently proposed model of flat water sheets.