Nanophase-Segregated Structures and Transport Properties in Polysuflonated (190-PSU-Sn) based Ionomers for Proton Exchange Membrane Fuel Cell

摘要

Nafion is commonly used in polymer electrolyte membrane fuel cells (PEMFC) due to its high proton conductivity and thermal, chemical, and mechanical stability. However due to several limitations it has, such as high methanol crossover and poor performance under low humidity and at high temperature condition, polysulfonated monomers have been considered as alternatives with the specifications that is essential for the fuel cell membranes. This specification includes high proton conductivity, reduction-oxidation stability, and excellent mechanical, thermal, and chemical stability with its ‘aryl-SO2-aryl' backbone. In this study, mechanical properties of polysulfonated ionomers are investigated using full-atomistic MD simulation methods. In order to determine how the structure of sulfonate groups affects the mechanical properties, we considered three different functional groups (-SCF2CF2SO3H, -OCF2 SO3H and –CF3 2(C4H4CF2 SO3H) attached to polysulfone. Various water contents were implemented to achieve effective results on the relationship between structure and transport of hydrated polysulfonated membranes. Each of PSU-S4, PSU-S5 and PSU-S6 membranes are equilibrated with two different water contents (10 wt. % and 20 wt. %) through an annealing procedure. The equilibrated states were assumed to be reached with the generally standardized density and potential energy distribution curves. The pair correlation function was examined in order to analyze the local structure of various atoms in the membrane, which determines the solvation. The diffusion coefficient of water and hydronium were determined to calculate the position probability diffusing over time with the mean squared displacement equation.