Molecular Model and Structural Stability Study of a Nafion Ionomer-Based Membrane Electrode Assembly

One of the most important parts of a polymer electrolyte membrane fuel cell (PEMFC) is the membrane electrode assembly (MEA). However, the delamination between the membrane and electrode layers, induced by uneven distribution of internal stress and stress concentration due to the inconsistent water and thermal expansion properties, greatly reduces the PEMFC durability. Based on the data from the literature or use of commercial products, this work established the molecular model of membrane and electrode layers, and aimed to find the stable structure of MEA. Nafion ionomer and its composite with graphite-supported platinum were considered as a proton exchange membrane and catalyst electrode layer materials, respectively. Molecular dynamics simulations were employed to investigate the coefficients of thermal and water expansion of membrane and electrode layers. The structural stability of a three-layer MEA model (anode-membrane-cathode) was discussed by exerting various external pressures and calculating the binding energies between layers and between graphene and platinum. The results showed that very high pressures squeeze the internal molecules excessively, resulting in the platinum particles detaching from their support material, while lower pressure weakens the binding between layers.