Proton Conducting Polymer Gel Electrolytes Research Articles

Electrical Characterization of PVdF based Proton Conducting Polymer Gel Electrolytes

Background: Polymer gel electrolytes have attracted much intention due to their high ionic conductivity (10-2 - 10-3 S/cm) along with other suitable properties like good thermal stability, compatibility with electrode materials, easy workability, wider control of properties etc. These materials are also called smart materials due to their practical applications in various devices like high energy power devices, electrochromic devices, supercapacitors, devices for Infra-red systems etc. This paper mainly discusses the enhancement of an ionic conductivity with the addition of polymer. No appreciable change in conductivity of gel electrolytes has been observed with temperature, which makes them suitable for device applications. Methods: Liquid electrolytes were prepared by dissolving orto-nitro benzoic acid (o- NBA) in the ternary mixture of ethylene carbonate (EC), propylene carbonate (PC), and dimethylacetamide (DMA) (in 2:2:1 volume ratio). The homogeneous polymer solution of PVdF in acetone is prepared and then added to the liquid electrolyte along with continuous stirring. Polymer gel electrolytes are obtained after the evaporation of acetone. Ionic conductivity of liquid and polymer gel electrolytes is measured by HP4284A precision LCR meter (having frequency range from 20Hz-1MHz) using complex impedance spectroscopy. Results: The conductivity of liquid electrolytes increases by two orders of magnitude with an addition of ortho-nitro benzoic acid (10-6 to 10-4 S/cm) and maximum room temperature conductivity of 1.46 x 10-4 S/cm has been obtained at 2M concentration of o-NBA in ternary mixture of EC, PC and DMA. The conductivity of electrolytes increases with the addition of polymer and maximum conductivity of 5.91 x 10-4 S/cm has been obtained at room temperature. The increase in conductivity has been explained by using “Breathing Polymer Chain Model”. Ionic transference number was calculated and it was found out to be nearly 1, which suggests that gel electrolyte is principally ionic conductor. Conclusion: Maximum conductivity of 5.91 x 10-4 S/cm at room temperature has been observed for gel electrolyte containing 2M ortho-nitrobenzoic acid in EC:PC:DMA (2:2:1) with 8 wt% PVdF. The conductivity of polymer gel electrolytes has been found to increase with the addition of PVdF concentration. The conductivity of gel electrolytes is found to be higher than that of liquid electrolytes at all PVdF concentrations i.e. σ(gel) > σ(liquid). The increase in conductivity has been found to depend upon the concentration of acid, dissociation constant of acid and concentration of PVdF used. No appreciable change in conductivity of gel electrolytes has been observed with temperature, which make them suitable for device applications. Ionic transference number measurements suggest that these electrolytes are principally ionic conductors. Keywords: Conductivity, dimethylacetamide, ethylene carbonate, gel, transference number.

Role of Polymer in Enhancement of Conductivity of Proton and Lithium Conducting Polymer Gel Electrolytes

Role of Polymer in Enhancement of Conductivity of Proton and Lithium Conducting Polymer Gel Electrolytes

Conductivity, FTIR studies, and thermal behavior of PMMA-based proton conducting polymer gel electrolytes containing triflic acid

The addition of polymer to liquid electrolytes containing trifluoromethanesulfonic acid (HCF3SO3) in propylene carbonate (PC) has been found to result in an increase in conductivity of gel electrolytes. The increase in conductivity has been observed to be due to the dissociation of ion aggregates present in the electrolytes which has also been supported by Fourier transform infrared studies. The maximum ionic conductivity (at 25 °C) of 7.55 × 10−3 S/cm has been observed for polymer gel electrolytes containing 1.5 wt% polymethylmethacrylate in 0.5 M solution of HCF3SO3 in PC. Polymer gel electrolytes have been found to be thermally stable up to a temperature of 125 °C by simultaneous differential scanning calorimetry/thermogravimetric analysis studies. The conductivity of polymer gel electrolytes does not show any appreciable change over a limited period of time.

Conductivity modification of proton conducting polymer gel electrolytes containing a weak acid (ortho-hydroxy benzoic acid) with the addition of PMMA and fumed silica

Polymer gel electrolytes synthesized by dispersing nano size fumed silica in polymer gel electrolytes containing polymethylmethacrylate (PMMA), ortho-hydroxy benzoic acid (o-OHBA) and dimethylacetamide (DMA) have been studied by complex impedance spectroscopy, viscosity and pH measurements. The addition of acid, polymer and fumed silica has been found to result in an increase in conductivity and viscosity of gel electrolytes and gels with conductivity higher than the corresponding liquid electrolytes have been obtained. Nano dispersed polymer gel electrolytes show conductivity 2.95 × 10−4 S cm−1 and viscosity 1.74 × 104 cP at 25 °C. Two maxima observed in the variation of conductivity of nano dispersed gels with fumed silica concentration have been assigned to the enhanced dissociation of weak acid and the formation of a high conducting interfacial region between fumed silica and gel electrolyte, respectively, which has also been supported by pH and viscosity studies. The small increase in conductivity of nano dispersed gels over the 20–100 °C temperature range and its constant value with time is suitable for devices.

Conductivity modification of proton conducting polymer gel electrolytes with the addition of fumed silica

AbstractThe addition of nano size fumed silica to non aqueous proton conducting polymer gel electrolytes containing ammonium hexafluorophosphate (NH4PF6) has been found to modify the conductivity and viscosity behavior. Two maxima observed in the conductivity vs. fumed silica plot at very low concentrations have been explained to be due to an increase in free ion concentration with the dissociation of ion aggregates, and the formation of a high conducting interfacial layer between the particles of fumed silica and polymer gel electrolytes respectively. The change in free ion concentration has been monitored by pH measurements whereas change in mobility has been checked from viscosity measurements. The dissociation of ion aggregates with the addition of fumed silica has also been supported by FTIR results. The variation of conductivity and viscosity with temperature has also been studied and conductivity of nano dispersed gels does not show any change with time. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

PMMA-based polymer gel electrolytes containing NH 4PF 6: Role of molecular weight of polymer

The effect of the molecular weight of polymethylmethacrylate (PMMA) on the conductivity and viscosity behavior of proton conducting polymer gel electrolytes containing ammonium hexafluorophosphate (NH 4PF 6) in propylene carbonate (PC) has been studied. The addition of PMMA having molecular weights: 15,000; 120,000; 350,000; 996,000 results in an increase in conductivity and gels with conductivity higher than the corresponding liquid electrolytes have been obtained. The maxima observed in the variation of conductivity with PMMA concentration shifts towards higher concentrations of PMMA with an increase in the molecular weight of PMMA. The increase in conductivity with PMMA addition also depends upon the molecular weight of PMMA and has been found to be more for gels containing PMMA with lowest molecular weight (15,000). The increase in conductivity at low concentrations of PMMA is due to an increase in free ion concentration with the dissociation of ion aggregates, whereas the decrease in conductivity at higher concentrations of PMMA, is due to the exponential increase in viscosity, which lowers mobility and as a result conductivity decreases. These gels show high value of conductivity (∼10 −2 S/cm at 25 °C) which does not vary with time and shows only a small increase over the 20–100 °C temperature range and is desirable for their potential use in applications.

Effect of dielectric constant of solvent on the conductivity behavior of polymer gel electrolytes

Non aqueous polymer gel electrolytes are currently attracting considerable attention due to their use as electrolytes in solid state batteries, fuel cells, supercapacitors, etc. [1–3]. Polymer gel electrolytes belong to a salt–solvent-polymer hybrid system in which the salt solution is immobilized with the addition of a suitable polymer matrix [4, 5]. The solvent helps in the dissociation of the salt and also provides a conducting medium and should generally have high dielectric constant— which ensures the dissociation of salt, low viscosity— which shall result in higher mobility and low melting point and high boiling point—so that the electrolyte could be used over a wide range of temperature [6]. If a single solvent with suitable properties is not available, then a binary/ternary solvent mixture can also be used [7]. The addition of polymer to salt solution increases the viscosity of the electrolytes accompanied by a small decrease in conductivity, which suggests that the polymer generally plays the role of a stiffener only [8–10]. However recent results on proton conducting polymer gel electrolytes containing weak acids indicate that the addition of polymer can also lead to an increase in the conductivity and gel electrolytes with conductivity higher than the corresponding liquid electrolytes have been reported [11, 12]. This increase in conductivity with polymer addition has been found to depend upon the dissociation constant of acid, dielectric constant of solvent and molecular weight of the polymer used [6, 13, 14]. The present study has been undertaken to investigate the role of the dielectric constant of the solvent on the conductivity behavior of polymer gel electrolytes. Lithium ion conducting polymer gel electrolytes containing lithium trifluoromethanesulphonate (LiCF3SO3), different single/binary solvents based on dimethylacetamide (DMA) and diethylcarbonate (DEC) with polymethylmethacrylate (PMMA) as the gelling polymer have been synthesized and the variation of conductivity and viscosity with the concentration of salt, polymer and the dielectric constant (e) of the solvent has been studied. Liquid electrolytes were prepared by dissolving LiCF3SO3 in different concentrations (expressed as molarity values) in DMA, DEC and in binary mixtures of DMA and DEC taken in different volume ratios. Polymer gel electrolytes were then obtained by adding PMMA in different ratios (expressed as wt.% of liquid

Non-aqueous proton conducting polymer gel electrolytes

A new family of non-aqueous proton conducting polymer gel electrolytes containing different weak acids namely aromatic carboxylic acids have been prepared by using polyvinylidenefluoride (PVdF) and polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) as the gelling polymers. These gel electrolytes possess high value of conductivity in the range of 10 −3 to 10 −4 S/cm at room temperature, which has been found to depend upon the dissociation constant of the acid used. PVdF and PVdF-HFP provide good dimensional stability to these gel electrolytes and the addition of polymer has also been found to result in an increase in conductivity, i.e. σ (gel) > σ (liquid) which suggests that the polymer does not play a passive role but also affects the conduction process. From FTIR studies it has been observed that the polymer enhances the dissociation of acid in these gel electrolytes resulting in an increase in carrier concentration.

Effect of donor number of solvent on the conductivity behaviour of nonaqueous proton-conducting polymer gel electrolytes

The effect of donor number of solvent on the conductivity behaviour of gel electrolytes has been studied. Liquid electrolytes were prepared by dissolving salicylic acid in solvents based on ethylene carbonate (EC), propylene carbonate (PC) and dimethylformamide (DMF) with different donor number and dielectric constant values. Three different polymers, polymethylmethacrylate (PMMA), polyacrylonitrile (PAN) and polyethylene oxide (PEO), were used as the gelling polymer. The conductivity of polymer gel electrolytes has been found to be higher than the corresponding liquid electrolytes, i.e. σ (gel)> σ (liquid). This has been explained to be due to an increase in carrier concentration by the dissociation of undissociated salicylic acid/ion aggregates present in the electrolytes with the addition of polymer. However, the relative increase in conductivity observed with the addition of different gelling polymers has been found to depend upon the donor number of the solvent used.

Conductivity behaviour of polymer gel electrolytes: Role of polymer

Polymer is an important constituent of polymer gel electrolytes along with salt and solvent. The salt provides ions for conduction and the solvent helps in the dissolution of the salt and also provides the medium for ion conduction. Although the polymer added provides mechanical stability to the electrolytes yet its effect on the conductivity behaviour of gel electrolytes as well as the interaction of polymer with salt and solvent has not been conclusively established. The conductivity of lithium ion conducting polymer gel electrolytes decreases with the addition of polymer whereas in the case of proton conducting polymer gel electrolytes an increase in conductivity has been observed with polymer addition. This has been explained to be due to the role of polymer in increasing viscosity and carrier concentration in these gel electrolytes.

Proton conducting polymer gel electrolytes with NO 2 substituted carboxylic acids

Proton conducting polymer gel electrolytes based on different nitro substituted aromatic carboxylic acids have been studied. The conductivity of solution and gel electrolytes containing these acids has been found to depend upon the dissociation/acidity constant value of the acid and varies as σ (ortho -) > σ ( meta-). The addition of polymethylmethacrylate (PMMA) modifies the conductivity of these gel electrolytes which depends upon the dissociation constant and concentration of the acid present. The rate of change of conductivity of gel electrolytes with gelling polymer (PMMA) has been found to be different in the low and high PMMA regions which has been explained to be due to different mechanisms being responsible for the modification of conductivity in the low and high PMMA regions.

Conductivity behaviour of proton conducting polymer gel electrolytes with PVdF-HFP

Electrical conductivity of polymer gel electrolytes containing different hydroxy substituted benzoic acids and polyvinylidenefluoride-hexafluoropropylene (PVdF-HFP) has been studied. The conductivity of solution and gel electrolytes shows ortho effect and has been found to depend upon the acidity constant of the acid used and varies as σ ( ortho-) > σ ( meta-) > σ ( para-). The addition of PVdF-HFP to solution electrolytes results in an increase in conductivity and the conductivity of gel electrolytes has been found to be higher than that of the corresponding liquid electrolytes for all the three acids studied i.e. σ (gel) > σ (liquid). The increase in conductivity with polymer addition has also been found to depend upon the acid concentration.

Ambient and subambient temperature proton-conducting polymer gel electrolytes

Nonaqueous proton-conducting polymer gels have been synthesized and characterized by impedance spectroscopy and cyclic voltammetry. Special emphasis has been put to the subambient temperature characteristics of the samples studied with respect to their possible application in electrochromic devices. The gels studied exhibit ambient temperature conductivities exceeding 10 −3 S/cm, which remains higher than 10 −4 S/cm even at −50 °C. The electrochemical stability of the studied protonic gels depends mainly on the type of solvent used and is the highest for samples plasticized with propylene carbonate.

Effect of Gel Composition on the Conductivity of Proton-Conducting Gel Polymeric Electrolytes Doped with H3PO4

It is shown that the conductivity, mechanical properties, and chemical stability of proton-conducting polymer gel electrolytes based on polymethacrylate matrixes can be modified by changing the polymer matrix composition and accordingly the type and concentration of organic solvent used as plasticizer. The use of the glycidyl methacrylate-methyl methacrylate copolymers enhances ionic conductivity, improves mechanical stability and adhesion to the glass substrate compared to the system based on poly(methyl methacrylate) matrixes, and extends chemical stability compared to the system based on pure poly(glycidyl methacrylate). These copolymers also enable the use of N,N-dimethyl formamide-propylene carbonate mixtures as plasticizers, which leads to conductivity enhancement relative to pure propylene carbonate.

Proton conducting polymer gel electrolytes

Novel proton conducting gel electrolytes from poly(vinylidene fluoride)-dimethylformamide-H3PO4 system are synthesized and characterized by impedance spectroscopy, infra-red spectroscopy and differential scanning calorimetry. Highly conducting (5×10−4 S/cm at 20°C) colorless polymeric membranes are obtained in a relatively narrow component concentration range. The gel electrolytes studied are thermally stable up to 70–120°C as shown by the DSC experiments.