Study of Morphological Evolution of Hybrid PEM by Current Sensing Atomic Force Microscopy

Abstract

The high temperature proton exchange membrane fuel cell (HT-PEMFC) is a key of solving corrosion problem in catalyst layer from CO Poisonning. The key issue of HT-PEMFC is developing novel proton exchange membrane which has good proton conductivity under dry condition and thermal properties compare with Nafion. Sulfonated graphene (S-graphene) and Nafion hybrid membrane is developed in our previous work. The proton conductivity of S-graphene and Nafion hybrid membrane is five times larger than pristine Nafion at 20 % RH. In addition, the morphological variation due to hybridization of Nafion and S-graphene is observed by using non-contact mode AFM. The morphological variation might induce the ionic channel network variation on the membrane. We measured and analyzed ionic channel network evolution in the membrane by hybridization. Nafion is perm selective membrane due to its heterogeneous structure such as hydrophobic backbone and hydrophilic side chain. The side chain can create ionic channel network which is source of proton conductivity when the membrane is hydrated and the structure of ionic channel network can vary with water faction on the membrane. Thus, in-situ and accurate observation for ionic channel network evolution is required. For in-situ and accurate measurement, we designed PEMFC mimicking method by using current sensing atomic force microscopy (CS-AFM). The pt-coated tip/membrane/catalyst layer can created nano-sized PEMFC. Extremely small tip can act as single Pt catalyst and it simultaneously can detect proton conductivity variation in the ionic channels. In this study, the proton conductivity distribution of S-graphene and Nafion hybrid membrane can measure and compared with the proton conductivity distribution of pristine Nafion. Then the result is analyzed by using statistical method.