Mechanical Properties Of Nafion Research Articles

Temperature‐dependent mechanical performance of Nafion® 212 proton exchange membrane under uniaxial and biaxial loading

AbstractThe degradation of proton exchange membranes (PEMs) can significantly affect the structural integrity and lifetime of fuel cells. This study investigates the effects of temperature, peak load, initial strain, and loading modes on the mechanical properties of Nafion® 212 PEM using an in‐situ biaxial testing system. The findings indicate that membrane creeping is positively correlated with temperature and peak loads. The stress relaxation rate increases with the increase of initial strain, and an increase in temperature also leads to an apparent decrease in the anti‐relaxation properties of Nafion® 212 membrane. Additionally, the mechanical properties of low‐cycle fatigue at various temperatures were explored under biaxial cyclic loading conditions. When the temperature is fixed, the membrane strain increases and gradually stabilizes with the rise of fatigue cycles. With an increase in temperature, the strain increases at a greater rate. The phase difference increases with temperature growth, and the “hysteresis” phenomenon of the strain becomes more pronounced, resulting in greater energy loss. These results provide valuable insights into the mechanical behavior of Nafion® 212 PEM under different conditions. And can inform the design and optimization of fuel cell systems and contribute to the development of more robust and durable PEM materials.

The proton conductivity and mechanical properties of Nafion®/ ZrP nanocomposite membrane

Zirconium phosphates (ZrP) were incorporated into Nafion® 117 membrane by impregnating method to obtain a reduced methanol permeation and improved proton conductivity for fuel cell application. The mechanical properties and water uptake of Nafion® membrane incorporated with zirconium phosphates nanoparticles was more improvement when compared to the commercial Nafion® 117, due to the presence of phosphoric acid within the nanoparticles. The effect of ZrP nano filler on the membrane structural morphology and thermal properties were investigated by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Thermal gravimetric analysis (TGA) and Scanning Electron Microscopy (SEM). The improved ion conductivity and decreased methanol permeability on the nanocomposite membranes showed a great potential for fuel cell applications. The nanocomposite membrane with high tensile strength was obtained due to the well dispersed zirconium phosphates within the Nafion® matrix.

Enhancing the mechanical properties of zirconia/Nafion® nanocomposite membrane through carbon nanotubes for fuel cell application

Membranes are widely used daily, such as for filtration in reverse osmosis, or in the form of electrolyte membrane fuel cells. Modified Nafion® membranes were synthesised by impregnation and their mechanical properties were observed. The effect of the incorporation of a ZrO2-CNT nano-filler within Nafion® membrane on the thermal stability and crystallinity was investigated by TGA and XRD. Tensile test results show the increases in the mechanical properties of Nafion® 117 membranes impregnated with ZrO2-CNT when compared with that of commercial Nafion® 117 membranes. The results also show that adding ZrO2-CNT in Nafion® 117 membranes improves the water contact angle and water uptake, as it enhances water retention within the membrane. The SEM results indicated that ZrO2-CNT was well distributed in the Nafion® 117 membrane pores through the impregnation method.

A new high-performance ionic polymer–metal composite based on Nafion/polyimide blends

For the first time, we report ion-exchange membranes based on Nafion and polyimide (PI, Kapton) blends to fabricate ionic polymer–metal composites (IPMCs). Polyamic acid [PAA, poly(pyromellitic dianhydride-co-4,4′-oxydianiline), as a precursor of PI] solution was blended with Nafion solution using physical blending method to provide PAA–Nafion blend membrane. This work demonstrates that, by simple physical blending method, the thermal and mechanical properties of Nafion can be improved while maintaining the excellent actuating performance. After thermal imidization, PAA converted into PI, resulting in PI–Nafion blend membrane. Optimum conditions to cast PAA–Nafion blends and thermal imidization have been established, and blend membranes with PI wt% of 6, 12, 18, and 30 were prepared. Fourier transform infrared spectroscopy confirmed the incorporation of PI in the Nafion matrix. Thermal decomposition unique to the PI became more noticeable as the content of PI increased, which was measured by thermogravimetric analysis. Dynamic mechanical analysis showed that the storage modulus (E′) increased as a function of PI content while loss modulus (E″) exhibited only a minor change, which resulted in the decrease in the damping properties (tan δ). The blend membranes were fabricated into IPMCs by deposition of platinum electrode onto the membrane surface through electroless plating process. Among tested, NPI-18 IPMC actuator, which has 18 wt% of PI in Nafion, showed comparable electromechanical performance to the commercially available Nafion 117 IPMC actuator.

Macromolecular hydration phenomena

Water plays an important role in the physicochemical and mechanical properties of Nafion (poly tetrafluorosulfonic acid) and cellulosic materials. Due to the strong influence of hydration on the properties of these materials, the mechanism and molecular-level understanding of hydration processes are the subject of ongoing interest in food, environmental and energy science. Nafion is a sulfonated tetrafluoroethylene polymer that represents a prototypical polymer electrolyte membrane (PEM) material. PEMs are often composed of a hydrophobic backbone with a strongly hydrophilic region (e.g., sulfonic acid moieties), which are directly attached to the backbone or through a pendant group. The application of Nafion in fuel cells as PEMs necessitate that the hydration properties of the membrane play an important role for maintaining high proton conductivity and mechanical properties. Cellulose on the other hand is one of the most abundant and low-cost renewable biopolymers with unique hydration properties. The hydration of cellulose impacts its biodegradability, recyclability and tunable physicochemical properties for various applications employing composite materials, pharmaceutical delivery systems, paper production, fibers and biofuel production. One of the challenges in the development and valorization of cellulose-based materials relates to its insolubility in aqueous media and conventional solvents. Therefore, evaluation of the hydration properties of Nafion and cellulose materials is required in order to characterize their physicochemical properties. Studies of the hydration properties of these materials include dielectric, spectroscopic techniques (NMR and IR), dynamic vapor sorption, differential scanning calorimetry (DSC), viscometry and computer simulations to determine the structural, kinetic and thermodynamic properties associated with such hydration processes. DSC is a sensitive and versatile thermal analysis method for the study of hydration phenomena, thermal behavior and thermodynamic state of water in hydrated macromolecular systems. The aim of this mini-review is to provide an overview of recent DSC studies relevant to aspects of hydration phenomena for Nafion and cellulose. This overview will contribute to an improved understanding of the hydration properties of Nafion and cellulose materials for applications that involve hydration phenomena.

Microscopic analysis of current and mechanical properties of nafion® studied by atomic force microscopy.

The conductivity of fuel cell membranes as well as their mechanical properties at the nanometer scale were characterized using advanced tapping mode atomic force microscopy (AFM) techniques. AFM produces high-resolution images under continuous current flow of the conductive structure at the membrane surface and provides some insight into the bulk conducting network in Nafion membranes. The correlation of conductivity with other mechanical properties, such as adhesion force, deformation and stiffness, were simultaneously measured with the current and provided an indication of subsurface phase separations and phase distribution at the surface of the membrane. The distribution of conductive pores at the surface was identified by the formation of water droplets. A comparison of nanostructure models with high-resolution current images is discussed in detail.

Deterioration of mechanical properties: A cause for fuel cell membrane failure

The mechanical properties of Nafion® membranes that were degraded after periods of open circuit voltage (OCV) conditions in a fuel cell were studied. Severe decreases in membrane modulus and ductility at 80 °C and 100% relative humidity were observed. Stress-at-break values for 45 and 72 h degraded membrane–electrode assemblies (MEAs) were 6 and 9 times lower, respectively, while strain-at-break was 24 and 28 times lower, respectively, than that of a control MEA. Contractile stresses developed in constrained hydrated membranes that were then dried were conducted as a function of drying time. A pre-OCV degraded MEA, when subjected to creep deformation at 10 MPa, showed surface cracks which were not present in the control MEA. The 72 h-degraded MEA exhibited wider cracks than those of the 45 h-degraded MEA sample. Spectroscopic analysis of degraded membranes showed various small molecule fragments associated with side chain degradation.