Search Results (8)

This work looks at the effects of a varying concentration, soak time, pH and temperature on the sorption of tetraammineplatinum(II) chloride (Pt-Ammine) in Nafion-117 films in the context of the electroless plating of ionic polymer–metal composites (IPMCs). Sorption is characterised by atomic absorption spectroscopy. A definitive screening design carried out determined all four factors to be significant for further analysis using response surface modelling. A duplicated central composite design (CCD) was utilised to characterise how the four factors affect the sorption amount and efficiency. Regression models for both responses were of poor fit. Nevertheless, key insights were obtained on the effects of the process parameters on sorption behaviour. The results indicate that above 0.5 g/L Pt-Ammine sorption, the platinisation of 10 × 50 mm IPMC samples through sodium borohydride reduction becomes redundant by the surface resistance metric. IPMCs with surface resistance values of approximately 2.5 Ω/square were obtained through only one round of chemical reduction. Varying surface morphologies and electrode thicknesses were analysed under a scanning electron microscope. The CCD parameter settings were validated. Recommended settings for optimised Pt-Ammine sorption in 10 × 50 mm Nafion-117 films were identified as follows: 1.0 g/L Pt-Ammine concentration, 24 h soak time, pH of 3 and temperature of 20 °C. Full article

Membrane technologies and materials development appear crucial for the hydrogen/natural gas separation in the impending transition to the hydrogen economy. Transporting hydrogen through the existing natural gas network could result less expensive than a brand-new pipe system. Currently, many studies are focused on the development of novel structured materials for gas separation applications, including the combination of various kind of additives in polymeric matrix. Numerous gas pairs have been investigated and the gas transport mechanism in those membranes has been elucidated. However, the selective separation of high purity hydrogen from hydrogen/methane mixtures is still a big challenge and nowadays needs a great improvement to promote the transition towards more sustainable energy source. In this context, because of their remarkable properties, fluoro-based polymers, such as PVDF-HFP and Nafion^TM, are among the most popular membrane materials, even if a further optimization is needed. In this study, hybrid polymer-based membranes were deposited as thin films on large graphite surfaces. Different weight ratios of PVDF-HFP and Nafion^TM polymers supported over 200 μm thick graphite foils were tested toward hydrogen/methane gas mixture separation. Small punch tests were carried out to study the membrane mechanical behaviour, reproducing the testing conditions. Finally, the permeability and the gas separation activity of hydrogen/methane over membranes were investigated at room temperature (25 °C) and near atmospheric pressure (using a pressure difference of 1.5 bar). The best performance of the developed membranes was registered when the 4:1 polymer PVDF-HFP/Nafion^TM weight ratio was used. In particular, starting from the 1:1 hydrogen/methane gas mixture, a 32.6% (v%) H₂ enrichment was measured. Furthermore, there was a good agreement between the experimental and theoretical selectivity values. Full article

Proton-exchange membrane fuel cells (PEMFCs) are the heart of promising hydrogen-fueled electric vehicles, and should lower their price and further improve durability. Therefore, it is necessary to enhance the performances of the proton-exchange membrane (PEM), which is a key component of a PEMFC. In this study, novel pore-filled proton-exchange membranes (PFPEMs) were developed, in which a partially fluorinated ionomer with high cross-linking density is combined with a porous polytetrafluoroethylene (PTFE) substrate. By using a thin and tough porous PTFE substrate film, it was possible to easily fabricate a composite membrane possessing sufficient physical strength and low mass transfer resistance. Therefore, it was expected that the manufacturing method would be simple and suitable for a continuous process, thereby significantly reducing the membrane price. In addition, by using a tri-functional cross-linker, the cross-linking density was increased. The oxidation stability was greatly enhanced by introducing a fluorine moiety into the polymer backbone, and the compatibility with the perfluorinated ionomer binder was also improved. The prepared PFPEMs showed stable PEMFC performance (as maximum power density) equivalent to 72% of Nafion 212. It is noted that the conductivity of the PFPEMs corresponds to 58–63% of that of Nafion 212. Thus, it is expected that a higher fuel cell performance could be achieved when the membrane resistance is further lowered. Full article

Over recent years, investigations of coordination polymer thin films have been initiated due to their unique properties, which are expected to be strongly enhanced in the thin film form. In this work, a crystalline [Fe^II(H₂O)₂]₂[Nb^IV(CN)₈]∙4H₂O (1) film on a transparent Nafion membrane was obtained, for the first time, via ion-exchange synthesis. The proper film formation and its composition was confirmed with the use of energy dispersive X-ray spectroscopy and infrared spectroscopy, as well as in situ Ultraviolet-Visible (UV-Vis) spectroscopy. The obtained film were also characterized by scanning electron microscopy, X-ray diffraction, and magnetic measurements. The [Fe^II(H₂O)₂]₂[Nb^IV(CN)₈]∙4H₂O film shows a sharp phase transition to a long-range magnetically ordered state at T_c = 40 K. The 1 film is a soft ferromagnet with the coercive field H_c = 1.2 kOe. Compared to the bulk counterpart, a decrease in critical temperature and a significant increase in the coercive field were observed in the films indicating a distinct size effect. The decrease in T_c could also have been related to the possible partial oxidation of Fe^II ions to Fe^III, which could be efficient, due to the large surface of the thin film sample. Full article

Previous experiments of water vapor penetration into polyelectrolyte membrane (PEM) thin films have indicated the influence of the water concentration gradient and polymer chemistry on the interface evolution, which will eventually affect the efficiency of the fuel cell operation. Moreover, PEMs of different side chains have shown differences in water cluster structure and diffusion. The evolution of the interface between water and polyelectrolyte membranes (PEMs), which are used in fuel cells and flow batteries, of three different side-chain lengths has been studied using dissipative particle dynamics (DPD) simulations. Higher and faster water uptake is usually beneficial in the operation of fuel cells and flow batteries. The simulated water uptake increased with the increasing side chain length. In addition, the water uptake was rapid initially and slowed down afterwards, which is in agreement with the experimental observations. The water cluster formation rate was also found to increase with the increasing side-chain length, whereas the water cluster shapes were unaffected. Water diffusion in the membranes, which affects proton mobility in the PEMs, increased with the side-chain length at all distances from the interface. In conclusion, side-chain length was found to have a strong influence on the interface water structure and water penetration rates, which can be harnessed for the better design of PEMs. Since the PEM can undergo cycles of dehydration and rehydration, faster water uptake increases the efficiency of these devices. We show that the longer side chains with backbone structure similar to Nafion should be more suitable for fuel cell/flow battery usage. Full article

Herein, we report the production of ionic polymer-metal composites (IPMCs) hybridized with cellulose nanofibrils (CNF) as a partial substitute for Nafion^®. The aim is not only to reduce the production cost and enhance respective mechanical/thermal properties but also to bestow a considerable degree of biodegradability to such products. Formulations with different CNF/Nafion^® ratios were produced in a thin-film casting process. Crack-free films were air-dried and plated by platinum (Pt) through an oxidation-reduction reaction. The produced hybrids were analyzed in terms of thermal stability, mechanical and morphological aspects to examine their performance compared to the Nafion-based IPMC prior to plating process. Results indicated that films with higher CNF loadings had improved tensile strengths and elastic moduli but reduced ductility. Thermogravimetric analysis (TGA) showed that the incorporation of CNF to the matrix reduced its thermal stability almost linearly, however, the onset of decomposition point remained above 120 °C, which was far above the temperature the composite membrane is expected to be exposed to. The addition of a cross-linking agent to the formulations helped with maintaining the integrity of the membranes during the plating process, thereby improving surface conductivity. The focus of the current study was on the physical and morphological properties of the films, and the presented data advocate the potential utilization of CNF as a nontoxic and sustainable bio-polymer for blending with perfluorosulfonic acid-based co-polymers, such as Nafion^®, to be used in electroactive membranes. Full article

The main aim of this work was the design and development simple fiber optic Fabry-Perot interferometer (FPI) sensor devices for relative humidity (RH) sensing with emphasis on high sensitivity and good stability. The RH fiber FPI sensor is fabricated by coating the end of a cleaved standard multi-mode (MM) fiber with hydrophilic Nafion^® sensing film. The Nafion^® thin film acts as an active resonance cavity of the low-coherence interferometric sensing structure. The fringe pattern, which is caused by interfering light beam in the Nafion^® thin film will shift as the RH changes because the water molecules will swell the Nafion^® film and thus change optical pathlength of the sensing structure. The operating principle of a FPI sensor based on the adsorption and desorption of water vapour in the Nafion^® and the limitations of this sensor type are discussed in this work. The fiber optic hygrometer was tested in the visible (400–900 nm) region of spectra for measurement of relative humidity (RH) in the range of 5.5–80% at room temperature (RT) in air. The fiber optic humidity sensor has a very short response time (t₉₀ = 5–80 s) and a fast regeneration time (t₁₀ = 5–12 s) as good as commercial sensors. Full article

An MgO-templated mesoporous carbon, CNovel^®, was employed as a catalyst support for the cathode of polymer electrolyte fuel cells (PEFCs) after modifying its dimensional, crystalline, surface and porous structures and the electrochemical oxygen reduction reaction (ORR) activities were examined by the thin-film rotating disk electrode (RDE) method and as well as the membrane electrode assembly (MEA) method. Although the catalytic activity of Pt on CNovel^® was comparable with that on a non-porous carbon, Vulcan^®, in the RDE configuration without Nafion^®, Pt/CNovel showed a considerably higher activity than Pt/Vulcan in the MEA condition with Nafion^®. The mechanism inducing this difference was discussed from the results of electrochemical surface area and sulfonic coverage measurements which suggested that Pt particles on inside pores of CNovel^® are not covered with Nafion^® ionomer while protons can still reach those Pt particles through water network. The MEA performance in the middle and high current-density regions was drastically improved by heat-treatment in air, which modified the pore structure to through-pored ones. Full article