Moisture and thermal expansion properties and mechanism of interaction between ions of a Nafion-based membrane electrode assembly

Abstract

A membrane electrode assembly (MEA) is a multi-layer composite material. The different water and thermal expansion properties in MEA layers easily lead to delamination and electrode cracks, greatly decreasing the cell performance. Based on commonly used materials, we establish molecular models, investigate the coefficients of moisture and thermal expansion, and explore the diffusion mechanism and interaction behaviors of various particles. The effects of system size, oligomer chain length, and catalyst size and content are discussed. The moisture expansion properties of the membrane are verified by experimental results obtained with Nafion® 117. The differences in moisture and thermal expansion between layers can be reduced by decreasing the chain length of the oligomer and the size and content of Pt in the catalyst layer; increasing the chain length of the oligomer in the membrane; and controlling the working temperature at approximately 320 or 358 K. The introduction of Pt and graphene is also found to prevent the diffusion of water molecules and decrease water connectivity.