Mechanical properties of Nafion and titania/Nafion composite membranes for polymer electrolyte membrane fuel cells

Abstract

Measurements of the mechanical and electrical properties of Nafion and Nafion/titania composite membranes in constrained environments are reported. The elastic and plastic deformation of Nafion-based materials decreases with both the temperature and water content. Nafion/titania composites have slightly higher elastic moduli. The composite membranes exhibit less strain hardening than Nafion. Composite membranes also show a reduction in the long-time creep of $40% in comparison with Nafion. Water uptake is faster in Nafion membranes recast from solution in comparison with extruded Nafion. The addition of 3-20 wt % titania particles has minimal effect on the rate of water uptake. Water sorption by Nafion membranes generates a swelling pressure of $0.55 MPa in 125-lm membranes. The resistivity of Nafion increases when the membrane is placed under a load. At 23 8C and 100% relative humidity, the resistivity of Nafion increases by $15% under an applied stress of 7.5 MPa. There is a substantial hysteresis in the membrane resistivity as a function of the applied stress depending on whether the pressure is increasing or decreasing. The results demonstrate how the dynamics of water uptake and loss from membranes are dependent on physical constraints, and these constraints can impact fuel cell performance.

Mechanics-based model for non-affine swelling in perfluorosulfonic acid (PFSA) membranes

“…This relationship is referred to as non-affine deformation and has been shown to occur for PFSA membranes by a number of studies in literature [11,[18][19][20][21][22]29,[33][34][35]. Despite the growing body of literature on the sorption behavior [7,8,10,24,34,35,38,40,[44][45][46][47][48][49][50] and nano-structural modeling and characterization [11,13,[17][18][19][20][21][22]28,29,31,[33][34][35][36]39,49,51,52] of PFSA ionomers, the relationship between the water uptake and nanostructure, temperature, mechanical properties and membrane pretreatment is not well established. Understanding of these issues requires a general, yet fundamental model, which is the subject of this study.…”

Degradation aspects of water formation and transport in Proton Exchange Membrane Fuel Cell: A review

“…[335] is suggesting that aging has no influence on the water transport coefficient despite other studies [220][221][222][223][224][228][229][230] where a significant change in the physical properties of aged membranes was detected. However, none of these studies have addressed the effect of water transport mechanism on membrane durability.…”

“…Statterfield et al [223] suggested the addition of Ttitanium oxide (titania) for improving the elastic and plastic deformation behaviour of Nafion under changes in temperature and water concentration. These composite membranes (e.g.…”

“…Nafion-titania) exhibited less strain hardening than Nafion and resulted in 40% reduction in the membrane's creep compared to Nafion. Similarly, the focus in [223] was to improve the elastic modulus of Nafion 115 membranes by adding titania particles. This composite membrane showed after 3000 min of operation ~40% more reduction of creeping compared to extruded and recast Nafion types under the same stress conditions.…”

Control of redundancy PEM fuel cells in UPS applications with improved performance and durability

“…For the membrane degradation, according to numerous experimental results, there are chemical degradation [8], mechanical degradation [9] and thermal degradation [10], which are strongly dependent on operating conditions such as temperature, humidity, freezethaw cycling, transient operation, and start-up/shut-down [2]. For the GDL degradation, to date, only a limited number of studies have focused on the degradation mechanisms of GDL or on the relationship between GDL properties and PEMFC performance decay, but its degradation includes the physical degradation [11], so called the mechanical and thermal degradation, and chemical and electrochemical degradation [12].…”