Atomic Force Microscopy Detection of Electronic Short-Circuits in Solid Polymer Electrolytes Fuel Cell Membranes after Accelerated Degradation

Abstract

In this work we investigated Nafion® 211 polymer electrolyte membranes after 1600 h operation at open circuit voltage. With scanning electron microscopy (SEM) platinum deposition was identified inside the membrane. By investigation of cross sections with Atomic Force Microscopy (AFM) numerous platinum particles and micrometer large two-dimensional sheets of platinum particles were found across the membrane. Conductive AFM was performed to measure the electronic current across the membrane. To avoid additional ionic current contributions the measurements were performed at dry membranes in argon atmosphere with a noncatalytic gold coated AFM tip. At a few sites a steady state electronic current measured through the half cell membranes was detected that had an ohmic current-voltage polarization curve. These electric short-circuit connections, formed by platinum deposition inside the membrane, can be considered as a failure mechanisms for the fuel cell and by enhancement of radical formation may lead to formation of pin-holes.