Atomic force microscopy

Abstract

In a proton exchange membrane (PEM) fuel cell the function of the dižerent components is strongly based on the nanoscale properties of the materials: • Electrodes with a complex porous mixture of ionomer, Pt nanoparticles, and graphite • Electrolyte membranes with a phase separation into hydrophilic and hydrophobic parts in the nanometer range providing an ionic conducting network for the current • Corrosion on metallic bipolar plates • Highly porous gas dižusion layers (GDLs) with functional hydrophilic/hydrophobic pores pro- viding gas-, water-, and current transport Although atomic force microscopy (AFM) is an ex situ technique, the measuring conditions can be chosen rather close to operating conditions in a PEM fuel cell. še flexibility in the analyzed areas allows an overview of the sample as well as a highly resolved measurement on the nanometer scale. še signals recorded by AFM are on the one hand based on force interaction of the AFM tip with the sample surface, thereby delivering, that is, local friction, adhesion, stižness, and energy loss. On the other hand, electrical properties such as electronic conductivity, ionic conductivity as well as surface potential, electrostatic force or reactivity can be retrieved. še AFM works in ambient air and in a humid or liquid environment, including an electrochemical cell. Hydrophilic and hydrophobic surface properties are especially important for water management in a PEM fuel cell and degradation processes can be followed by a comparison of samples in a fresh state and after operation.