Hybrid anion exchange membrane of hydroxyl-modified polysulfone incorporating guanidinium-functionalized graphene oxide

Incorporating nanofillers is an effective method to balance conductivity and mechanical strength of anion exchange membranes (AEMs). In this work, a series of AEMs were prepared via embedding guanidinium-functionalized graphene oxide (GGO) into un-quaternized, diethanolamine-modified polysulfone (HPSf). The improved hydrophilicity of HPSf allows for better compatibility between GGO and polymer and also gives higher water uptake, which is beneficial for facilitating ion transport and alleviating hydroxide attack. AEM of HPSf embedding an optimized amount of GGO (0.88 mmol g^?1) exhibits the highest conductivity of 11 mS cm^?1 at 30 °C, which is 38% higher than that of pristine PSf-GGO membrane. It also possesses excellent anti-swelling stability (9% swelling ratio at 60 °C). When treated with 1 M NaOH at 60 °C for 120 h, HPSf-GGO-25% experienced a conductivity decay by 25%. Our work provides a route to fabrication of hybrid AEMs with improved interface properties and well-balanced conductivity and robustness.     

Bromide ion conductivities of eutectic mixtures of quaternary ammonium bromides possessing long alkyl chains

Several quaternary ammonium bromides possessing long alkyl chains and their mixtures were found to be bromide ion conductors. The ionic conductivities of quaternary ammonium bromides themselves were lower than 10^?9 S cm^?1 at a room temperature. On the other hand, the eutectic mixtures of the quaternary ammonium bromides showed large increase of ionic conductivity. The best bromide ion conductors were found for the eutectic of Q₅, Q₇, Q₈, and Q₁₂: 4×10^?8 S cm^?1 at 30°C, and 6.3×10^?6 S cm^?1 at 50°C. Addition of asymmetric quarternary ammonium bromides had a negative effect on the ionic conductivity. These results were explained by a space filling factor in the solid.     

Novel nanocomposite membranes based on polybenzimidazole and Fe<Subscript>2</Subscript>TiO<Subscript>5</Subscript> nanoparticles for proton exchange membrane fuel cells

In this work, Fe₂TiO₅ nanoparticles were used for improving the proton conductivity, and water and acid uptake of polybenzimidazole (PBI)-based proton exchange membranes. The nanocomposite membranes have been prepared using different amounts of Fe₂TiO₅ nanoparticles and dispersed into a PBI membrane with the solution-casting method. The prepared membranes were then physico-chemically and electrochemically characterized for use as electrolytes in high-temperature PEMFCs. The PBI/Fe₂TiO₅ membranes (PFT) showed a higher acid uptake and proton conductivity compared with the pure PBI membranes. The highest acid uptake (156 %) and proton conductivity (78 mS/cm at 180 °C) were observed for the PBI nanocomposite membranes containing 4 wt% of Fe₂TiO₅ nanoparticles (PFT₄). The PFT₄ composite membrane showed 380 mW/cm² power density and 760 mA/cm² current density in 0.5 V at 180 °C at dry condition. The above results indicated that the PFT₄ nanocomposite membranes could be utilized as proton exchange membranes for high-temperature fuel cells.     

Acid-base high temperature proton exchange membranes prepared from phosphonic acid functionalized siloxane

One kind of acid-base high temperature proton exchange membranes has been prepared from amino trimethylene phosphonic acid (ATMP), epoxycyclohexyethyltrimethoxysilane (EHTMS), and 3-aminopropyltriethoxysilane (APTES) by sol-gel process. The structural characteristics of these membranes with different amount of APTES were investigated by FT-IR, XRD, and SEM. These membranes showed excellent dimensional stability in water with the contribution of flexible ionic network structure and were thermally stable up to about 200 °C. In addition, the proton conductivity of the membranes increased with increasing temperature over the range of 20 to 140 °C, up to a maximum of 2.63 × 10^?2 S cm^?1 at 140 °C under anhydrous condition. The high proton conductivity was attributed to the formation of hydrogen bond network through the synergistic effect of N and P. The activation energy value of membranes became lower from 0.46 to 0.30 eV because of the acid-base pairs. The variable-temperature FT-IR further proved the formation of hydrogen bond network in the membrane.     

Preparation and characterization of proton exchange membranes with through-membrane proton conducting channels

The primary goal of this study is to develop a novel PEMs with unique surface structure utilizing the high viscosity of the impregnation solution. SiO₂ nanofiber mats were prepared via the electrospinning method and introduced into sulfonated poly(ether sulfone) (SPES) matrix to prepare hybrid membrane. The effect of concentration of impregnation solution on the morphology and properties of the proton exchange membranes (PEMs), including thermal stability, water uptake, dimensional stability, proton conductivity, and methanol permeability were investigated. SEM results showed that a unique surface structure was prepared due to the high solution concentration. Moreover, the hydrophilic nanofibers on the surface constructed continuous proton pathways, which can enhance the proton conductivity of the membranes, a maximum proton conductivity of 0.125 S/cm was obtained when the SPES concentration was 40 wt% at 80 °C, and the conductivity was improved about 1.95 times compared to that of pure SPES membrane. The SiO₂ nanofiber mat-supported hybrid membrane could be used as PEMs for fuel cell applications.     

Preparation and properties of sulfonated polybenzimidazole-polyimide block copolymers as electrolyte membranes

Sulfonated polybenzimidazole-polyimide block copolymers are synthesized through condensation polymerization at high temperature. The length of the polyimide chain is varied to give a series of block copolymers with various block lengths. The as-synthesized block polymers are used to prepare the corresponding membranes through the solvent evaporation method. The structure of the block copolymers is characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). Their mechanical strength, thermal behavior, water uptake, swelling ratio, and proton conductivity, as well as oxidative stability are also investigated. All the block copolymers exhibit good thermal stability, dimensional stability, mechanical strength, and proton conductivity. Compared to the random sulfonated polyimide-containing benzimidazole membranes with the same degree of sulfonation, the membranes prepared from the block copolymers show higher proton conductivities. The proton conductivities of the block copolymer membranes range from 6.2?×?10^?4 to 1.1?×?10^?2?S cm^?1 at 105 °C. The block copolymer membrane doped with phosphoric acid exhibits proton conductivity higher than 0.2 S cm^?1 at 160 °C, indicating its potential applications in proton exchange membrane fuel cells operated under high temperature and low humidity conditions.     

Novel cross-linked membrane for direct methanol fuel cell application: sulfonated poly(ether ether nitrile)s

In order to reduce water uptake, swelling ratio, and methanol permeability in sulfonated proton exchange membranes (PEM), novel-sulfonated aromatic poly(ether ether nitrile)s-bearing pendant propenyl groups had been synthesized by direct copolymerization method. All the results showed that the propenyl groups were suitable cross-linkable groups, and that this method was an effective way to overcome the drawbacks of sulfonated polymers at high ion exchange capacity (IEC) values. By cross-linking, the water uptake, swelling ratio, and methanol diffusion could be restricted owing to the formation of compact network structure. For example, CSPEN-60 membranes showed the proton conductivity of 0.072 S cm^?1 at 80 °C, while the swelling ratios and water uptake (17.9 and 60.7 %) were much lower than that of the SPEN-60 membrane (60.8 and 295.2 %). Meanwhile, a 1.1 × 10^?7 cm² s^?1 of methanol diffusion was obtained which was much lower than that of Nafion 117 (14.1 × 10^?7 cm² s^?1). Although the proton conductivity of the CSPEN-60 membranes is lower than that of the SPEN-60 membrane, the selectivity is much higher. The CSPEN-60 membrane exhibited the highest selectivity among the tested membranes, about 5.8 times higher compared with that of Nafion117.     

Lithium ion conductivity and dielectric properties of P(VdCl-co-AN-co-MMA)-LiCl-EC triblock co-polymer electrolytes

Lithium ion conducting polymer electrolytes based on triblock polymer P(VdCl-co-AN-co-MMA)–LiCl were prepared using a solution casting technique. XRD studies show that the amorphous nature of the polymer electrolyte has been increased due to the addition of LiCl. The maximum amorphous nature has been observed for 40 m% P(VdCl-co-AN-co-MMA)/60 m% LiCl samples. The FTIR study of the lithium ion conducting polymer membrane confirms the complex formation between the polymer P(VdCl-co-AN-co-MMA) and LiCl. The lithium ion conductivity is found to be 1.6 × 10^?5 Scm^?1 for the 40 m% P(VdCl-co-AN-co-MMA)/60 m% LiCl sample at room temperature. This value is found to be greater than that of pure polymer whose conductivity is found to be 1.5 × 10^?8 Scm^?1. To improve ionic conductivity, ethylene carbonate has been added as a plasticizer to the 40 m% P(VdCl-co-AN-co-MMA)/60 m% LiCl sample. When we add 0.6 m% of ethylene carbonate, it has been observed that the lithium ion conductivity has increased to 1.3 × 10^?3 Scm ^?1 . This value is two orders of magnitude greater than the 40 m% P(VdCl-co-AN-co-MMA)/60 m% LiCl sample. It is also observed from XRD patterns of 40 m% P(VdCl-co-AN-co-MMA)/60 m % LiCl/0.6 m % EC that the amorphous nature has been increased further. A dielectric study has been performed for the above membranes.     

Facile and green fabrication of polybenzoxazine-based composite anion-exchange membranes with a self-cross-linked structure

A new type of composite anion-exchange membrane is fabricated using benzoxazine (Bz) monomer and polytetrafluoroethylene (PTFE) via a green and facile method. Membrane fabrication is achieved via in situ ring-opening polymerization of Bz within the PTFE matrix, followed by quaternization and ion-exchange reactions. The quaternized PBz works as a self-cross-linked and anion conductive polymer. The synthesized membranes show improved conductivity (26 to 70 mS/cm) at a reasonable water uptake and a low swelling ratio; they also show improved alkaline stability for 150 h at 60 °C in 1 M KOH solution, the decrease in conductivity being only ca. 10%. Our method of AEM fabrication is advantageous over conventional ones due to facile process and the avoidance of chloro- or bromomethylation as well as the self-cross-linked structure; the resulting membranes show relatively good performance as compared with some of those obtained from conventional techniques.     

MgAl2SiO6-incorporated poly(ethylene oxide)-based electrolytes for all-solid-state lithium batteries

Poly(ethylene oxide) (PEO)-based composite polymer electrolytes (CPEs), comprising various concentrations of lithium hexafluorophosphate and magnesium aluminium silicate, were prepared by hot-press technique. The membranes were characterised by scanning electron microscopy, tensile and thermal analyses. It has been demonstrated that the incorporation of the ceramic filler in the polymeric matrix has significantly enhanced the ionic conductivity, thermal stability and mechanical integrity of the membrane. It also improved the interfacial properties with lithium electrode. Finally, an all-solid-state lithium cell composed of Li/CPE/LiFePO₄ has been assembled and its cycling performance was analysed at 70 °C. The cell delivered a discharge capacity of 115 mAh g^?1 at 1 °C rate and is found to be higher than previous reports.     

Poly(ethylene glycol)/poly(2-acrylamido-2-methyl-1-propane sulfonic acid) gel electrolytes: a detailed investigation of their conductivity and characterization

Poly(ethylene glycol)/poly(2-acrylamido-2-methyl-1-propane sulfonic acid) (PEG/PAMPS) with a transparent appearance were prepared in the presence of ammonium persulfate (APS) as an initiator at 70 °C for 24 h. PEG/PAMPS-based polymer gel electrolytes in a motionless and uniform state were obtained by adding the required amount of liquid electrolytes to a dry PEG/PAMPS polymer. Liquid electrolytes include organic solvents with high boiling points (-1-methyl-2-pyrrolidone (NMP) and γ-butyrolactone (GBL)) and a redox couple (alkali metal iodide salt/iodine). The optimized conditions for PEG/PAMPS-based gel electrolytes based on the salt type, the concentration of alkali metal iodide salt/iodine, and solvent volume ratio were determined to be NaI, 0.4 M NaI/0.04 M I₂, and NMP:GBL (7:3, v/v), respectively. The highest ionic conductivity and the liquid electrolyte absorbency were 2.58 mS cm^?1 and 3.6 g g^?1 at 25 °C, respectively. The ion transport mechanism in both the polymer gel electrolytes and liquid electrolytes is investigated extensively, and their best fits with respect to the temperature dependence of the ionic conductivity are determined with the Arrhenius equation.     

Improving the Performance of Nafion®-Based Fuel Cell Membranes by Introducing Histidine Functionalized Carbon Nanotubes

A new polymer nanocomposite membrane based on Nafion and functionalized carbon nanotubes (CNTs) was developed for proton exchange membrane fuel cell (PEMFC) applications. Histidine, an imidazole-based amino acid, was used for modifying the surface of CNTs. The modification of CNTs was characterized by means of Fourier transform infrared spectroscopy (FTIR) and their Zeta potential. The imidazole groups, due to forming and breaking of hydrogen bonding, can facilitate proton transport across the polymer matrix by the Grotthuss mechanism. The final structure of the Nafion/CNT nanocomposites was investigated by small angle X-ray scattering (SAXS). The results confirm that the transport properties of the fabricated new membranes were significantly improved in comparison with unmodified and conventional Nafion® membranes. The power density of the imidazole-CNT (Im-CNT) Nafion® composite membranes was about three times more than Nafion® membranes. Also, the experimental results showed that the proton conductivity for the conventional Nafion® membranes decreased over 100°C but the conductivity for the Nafion®/Im-CNT remained at a nearly constant value above 100°C up to 120°C. Thus, the nanocomposite based on Nafion/imidazole functionalized CNT can be considered as an anhydrous PEMFC membrane for high-temperature applications.     

Fabrication of Aquivion-type membranes and optimization of their elastic and transport characteristics

The solution casting technology was applied to manufacture thin polymer films (~?20–30 μm) from the ionomer solution of perfluorinated polymer with short side chains (an analogue of the commercial polymer Aquivion®). The influence of annealing temperature on the mechanical properties (elastic limit), proton conductivity, and heat capacity was investigated. The elastic limit, glass transition temperature, and proton conductivity of the samples were found to reach their maximum values at the annealing temperature 170?±?5 °C. Comparative studies of membrane-electrode assemblies (MEA) using the commercial (Nafion NR212) and solution-casted membranes were carried out. MEA with optimized Aquivion-type membranes showed satisfactory values of fuel crossover and maximum output power. The results of the conducted studies show that the prepared Aquivion-type membranes are very promising for practical application in MEA.     

Green electrolytes based on dextran-chitosan blend and the effect of NH<Subscript>4</Subscript>SCN as proton provider on the electrical response studies

Dextran-chitosan blend added with ammonium thiocyanate (NH₄SCN)-based solid polymer electrolytes are prepared by solution cast method. The interaction between the components of the electrolyte is verified by Fourier transform infrared (FTIR) analysis. The blend of 40 wt% dextran-60 wt% chitosan is found to be the most amorphous ratio. The room temperature conductivity of undoped 40 wt% dextran-60 wt% chitosan blend film is identified to be (3.84?±?0.97)?×?10^?10 S cm^?1. The inclusion of 40 wt.% NH₄SCN to the polymer blend has optimized the room temperature conductivity up (1.28?±?0.43)?×?10^?4 S cm^?1. Result from X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analysis shows that the electrolyte with the highest conductivity value has the lowest degree of crystallinity (χ _c) and the glass transition temperature (T _g), respectively. Temperature-dependence of conductivity follows Arrhenius theory. From transport analysis, the conductivity is noticed to be influenced by the mobility (μ) and number density (n) of ions. Conductivity trend is further verified by field emission scanning electron microscopy (FESEM) and dielectric results.     

Tamarind seed polysaccharide (TSP)-based Li-ion conducting membranes

Polysaccharide-based biopolymers have gained much attention in electrochemical devices recently. Tamarind seed polysaccharide (TSP) is a biopolymer obtained from the extract of tamarind seed. It is used as thickening and gelling agent in food and textile industries. There are no works in polymer electrolytes based on TSP in lithium-ion conducting membranes. A pure TSP membrane has been prepared by dissolving 1 g of TSP in distilled water by using solution-casting technique. The prepared biopolymer membranes are subjected to Fourier transform infrared (FTIR), X-ray diffraction (XRD), and AC-impedance techniques. FTIR analysis has been conducted to observe the possible interaction between the polymer and lithium salt based upon the changes in wave numbers of the peaks. The nature of the membrane (crystalline or amorphous) has been revealed by XRD. The electrical properties of the membranes have been analyzed by AC-impedance spectroscopy. The maximum ionic conductivity for the salt-doped membrane 1 g TSP:0.4 g lithium bromide (LiBr) has been found to be 4.83 × 10^?4 S cm^?1. The primary lithium-ion battery has been constructed using the best conductivity membrane, and the open circuit voltage (OCV) has been observed as 1.63 V.     

Effect of nano-dispersed silica on the ion-conducting behavior of PMMA-based polymer gel electrolytes containing LiPF<Subscript>6</Subscript>

Nano-sized silica poly(methylmethacrylate)-based gel electrolyte containing lithium hexafluorophosphate (LiPF₆) was synthesized by using different binary solvent mixture (propylene carbonate(PC) and dimethylformamide (DMF) in different volume ratio). Role of DMF in PC: Higher DMF content in PC-based electrolyte shows higher ionic conductivity at all polymer content and at wide temperature regions (10-70 °C). A small increment in ionic conductivity at lower content of polymer in liquid/gel electrolyte was observed and having maximum conductivity of 13.12 mS/cm at 25 °C. Stability (mechanically and electrically), viscosity and ionic conductivity of gel electrolytes were improved with the addition of nano-sized silica at ambient temperature. Ionic conductivity of nano-sized silica-based gel electrolyte does not change much over 5^o–70 °C temperature range and is factor-wise only which make indispensable in different electrochemical devices. Also polymer gel electrolyte membranes as such and with dispersed silica nano-particles were characterized through scanning electron microscope to study the morphology of gel matrix.     

Gelatin-HCl biomembranes with ionic-conducting properties

Gelatin-HCl protonic gel polymer electrolytes were obtained by crosslinking with formaldehyde in the presence of hydrochloric acid and glycerol as plasticizer and characterized in present study. The ionic conductivity measurements revealed the best value of 5.35?×?10^?5 S cm^?1 at room temperature. Factorial design analysis showed that influence of glycerol is more pronounced than influence of acid on ionic conductivity values. Moreover, the 90 % transparent membranes evidenced a linear increase of ionic conductivity values of 5.35?×?10^?5 S cm^?1 at 26.5 °C to 5.77?×?10^?4 S cm^?1 at 82.8 °C following Arrhenius type mechanism of charge mobility.     

Effect of nano-size fumed silica on ionic conductivity of PVdF-HFP-based plasticized nano-composite polymer electrolytes

Nano-composite polymer electrolytes containing poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), ammonium tetrafluoroborate (NH₄BF₄), and nano-size fumed silica (SiO₂) have been prepared and characterized by complex impedance spectroscopy. Ionic conductivity of polymer has been found to increase with the addition of NH₄BF₄, and a maximum conductivity of 3.62 × 10^?6 S/cm has been obtained at 30 wt% NH₄BF₄. The formation of ion aggregates at high concentration of salt has been explained by Bjerrum’s law and mass action considerations. The conductivity of polymer electrolytes has been increased by three orders of magnitude (10^?6 to 10^?3 S/cm) with the addition of plasticizer, and a maximum conductivity of 1.10 × 10^?3 S/cm has been observed at 80 wt% DMA. An increase in conductivity with the addition of nano-size fumed silica is attributed due to the formation of space-charge layers. A maximum conductivity of 7.20 × 10^?3 S/cm has been observed for plasticized nano-composite polymer electrolytes at 3 wt% SiO₂. X-ray diffraction analysis of polymer electrolyte system was also carried out. A small change in conductivity of nano-composite polymer electrolytes observed over the 30–130 °C temperature range and for a period of 30 days is also desirable for their use in various applications.     

Tamarind seed polysaccharide biopolymer membrane for lithium-ion conducting battery

Solid biopolymers have gained much attention in the development of polymer electrolytes due to its biocompatibility, film-forming nature, and non-toxicity. In the present work, biopolymer membrane has been prepared using tamarind seed polysaccharide (TSP) as host polymer and various concentrations of lithium chloride (LiCl) salt as dopant by solution casting technique. The prepared biopolymer electrolyte has been characterized by XRD, FTIR, differential scanning calorimetry (DSC) analysis, AC impedance spectroscopy analysis, and transference number measurement. XRD analysis has been done to investigate the amorphous/crystalline nature of the polymer membrane. The highest amorphous nature has been found for 1 g of TSP with 0.4 g LiCl. FTIR spectrum analysis confirms the complex formation between TSP biopolymer with LiCl. From AC impedance conductivity analysis, the maximum ionic conductivity is of the order of 6.7?×?10^?3 S cm^?1 at room temperature for 1 g TSP with 0.4 g LiCl, whereas for pure TSP biopolymer membrane, the ionic conductivity is of the order of 5.48?×?10^?7 S cm^?1. The glass transition temperature for the highest conducting biopolymer membrane for the composition of 1 g TSP: 0.4 g LiCl has been found to be 44.25 °C using the DSC technique. Employing the maximum conducting biopolymer membrane, a lithium-ion conducting battery has been fabricated and its discharge characteristics have been studied.     

Lithium garnet oxide dispersed polymer composite membrane for rechargeable lithium batteries

Free-standing composite polymer membranes comprising of high molecular weight poly (ethylene oxide) (PEO) complexed with lithium perchlorate (LiClO₄) and Li₆La₂BaTa₂O₁₂ (LLBTO) garnet oxide as filler were developed via standard solution-casting method. The as-synthesized composite membranes were investigated through powder x-ray diffraction (PXRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and impedance spectroscopy techniques for their phase, thermal, morphological, and electrical properties, respectively. The lithium ion conductivity of polymer composite membranes consisting of PEO₈/LiClO₄ with various weight percents (5, 10, 15, 20, 25, and 30) of LLBTO were evaluated. We demonstrated a significant enhancement in Li⁺ conductivity with the addition of LLBTO to the polymer-lithium salt complex. Among the investigated membranes, the composite containing 20 LLBTO wt% garnet oxide exhibits maximized room temperature (30 °C) Li⁺ conductivity of 2.03 × 10^?4 S cm^?1 and electrochemical stability greater than 4.5 V.