Molecular dynamics simulations and experimental studies of the perfluorosulfonic acid-based composite membranes containing sulfonated graphene oxide for fuel cell applications

Abstract

In this investigation, to understand the impact on glass transition temperature (Tg) and increase the mechanical properties (elastic and shear modulus), proton conductivity, and single-cell performance, sulfonic acid (-SO3H) functionalized graphene oxide (SGO) was introduced in the perfluorosulfonic acid (PFSA) membranes (Nafion). We conducted atomistic molecular dynamics simulations of fully dry and hydrated PFSA membranes at various hydration levels and SGO loading. The Tg of PFSA polymer composite membranes was increasing with the rising loading percentage of SGO because of the strong connection between the SGO and the PFSA polymer chains in the fully dry states. In addition, the strong antiplasticization effect of water resulted in a further increase of the Tg of hydrated Nafion/SGO-4 composite membranes. The elastic and shear modulus of the Nafion/SGO (Nafion is trade name PFSA membranes) composites increased significantly with SGO loading because of the strong interfacial interaction between SGO and PFSA polymer chains. PFSA membranes loaded with SGO exhibited significant improvement in proton conductivity up to 0.167 S/cm at 90% relative humidity (RH), 95˚C, 2 wt% SGO loading, which is 1.51 times of recast Nafion membrane. In addition, PFSA composite membrane showed excellent fuel cell performance in terms of maximum power density up to 0.97 W/cm2 at 100% RH, 80 ˚C, 2 wt% SGO loading, which is ∼1.3 times of recast Nafion membrane at similar test conditions because of the hygroscopic nature of SGO, the creation of interconnected proton-conducting channels, and the reduction of fuel permeability through the prepared composite membranes.