Preparation and characterization of anhydrous polymer electrolyte membranes based on poly(vinyl alcohol-<Emphasis Type="Italic">co</Emphasis>-ethylene) copolymer

Anhydrous polymer electrolyte membranes with cross-linked structure have been prepared based on poly(vinyl alcohol-co-ethylene) (PVA-co-PE) copolymer. The PVA units of copolymer served to induce thermal cross-linking with 4,5-imidazole dicarboxylic acid (IDA) via esterification while PE units controlled the membrane swelling and the mechanical properties of films. Upon doping with phosphoric acid (PA, H₃PO₄) to form imidazole-PA complexes, the proton conductivity of membranes continuously increased with increasing PA content. As a result, proton conductivity reached 0.01 S/cm at 100 °C under anhydrous conditions. X-ray diffraction analysis revealed that both the d-spacing and crystalline peak of membranes were reduced upon introduction of IDA/PA due to the cross-linking effect. The PVA-co-PE/IDA/PA membranes exhibited good mechanical properties, e.g., 150 MPa of Young’s modulus, as determined by a universal testing machine. Thermal gravimetric analysis also represented that the thermal stability of membranes was increased up to 200 °C upon introduction of IDA/PA.     

Studies on modified anode polymer hydrogen sensor

An improved polymer electrolyte membrane (PEM) fuel cell based amperometric hydrogen sensor that operates at room temperature has been developed. The electrolyte used in the sensor is PVA/H₃PO₄ blend, which is a proton conducting solid polymer electrolyte. A blend of palladium and platinum coated on the membrane is used as anode and platinum as cathode. The sensor functions as a fuel cell, H₂/Pd-Pt//PVA-H₃PO₄//Pt/O₂, and the short circuit current is found to be linearly related to the hydrogen concentration. The present study aims at investigating the dependence of sensor behaviour on the anode composition. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Dielectric and conduction mechanism studies of PVA-orthophosphoric acid polymer electrolyte

Polyvinyl alcohol (PVA)-based proton conducting polymer electrolytes have been prepared by the solution cast technique. The conductivity is observed to increase from 10⁻⁹ to 10⁻⁴ S cm⁻¹ as a result of orthophosphoric acid (H₃PO₄) addition. The plot of conductivity vs temperature shows that a phase transition occurred at 343 K in the sample PVA-33 wt% H₃PO₄. The β-relaxation peak is observed at 313 K. The glass transition temperature of PVA-33 wt% H₃PO₄ is 343 K. Orthophosphoric acid seems to play a dual role, i.e., as a proton source and as a plasticizer. The ac conductivity σ _ac = Aω ^s was also calculated in the temperature range from 303 to 353 K. The conduction mechanism was inferred by plotting the graph of s vs T from which the conduction mechanism for sample PVA-17 wt% H₃PO₄ was inferred to occur by way of the overlapping large polaron tunneling (OLPT) model and the conduction mechanism for the sample PVA-33 wt% H₃PO₄ by way of the correlated barrier height (CBH) model.     

New polymer electrolyte based on (PVA–PAN) blend for Li-ion battery applications

A polymer blend electrolyte based on polyvinyl alcohol (PVA) and polyacrylonitrile (PAN) was prepared by a simple solvent casting technique in different compositions. The ionic conductivity of polymer blend electrolytes was investigated by varying the PAN content in the PVA matrix. The ionic conductivity of polymer blend electrolyte increased with the increase of PAN content. The effect of lithium salt concentrations was also studied for the polymer blend electrolyte of high ionic conductivity system. A maximum ionic conductivity of 3.76×10⁻³ S/cm was obtained in 3 M LiClO₄ electrolyte solution. The effect of ionic conductivity of polymer blend electrolyte was measured by varying the temperature ranging from 298 to 353 K. Linear sweep voltammetry and DC polarization studies were carried out to find out the stability and lithium transference number of the polymer blend electrolyte. Finally, a prototype cell was assembled with graphite as anode, LiMn₂O₄ as cathode, and polymer blend electrolyte as the electrolyte as well as separator, which showed good compatibility and electrochemical stability up to 4.7 V.     

Experimental investigations on plasticized PMMA/PVA polymer blend electrolytes

Blend based polymer electrolytes composed of poly (methyl methacrylate) (PMMA), poly(vinylalcohol) (PVA) and LiClO₄ are prepared using solvent casting technique. The polymer films are characterized by XRD and FTIR studies to determine the molecular environment for the conducting ions. These polymer films have been investigated in terms of ionic conductivity using the results of impedance studies. The influence of the blend composition on the electrochemical behaviour is also discussed. The highest room temperature conductivity obtained for the film consisting of PMMA, PVA, LiClO₄ and DMP is 0.06×10⁻³ S/cm at 303 K. The PMMA-PVA blend based polymer electrolytes look very desirable and promising for lithium battery applications.     

Structural, vibrational, thermal, and electrical properties of PVA/PVP biodegradable polymer blend electrolyte with CH3COONH4

A biodegradable solid polymer blend electrolyte was prepared by using polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) polymers with different molecular weight percentages (wt.%) of ammonium acetate, and its structural, thermal, vibrational, and electrical properties were evaluated. The polymer blend electrolyte is prepared using solution casting technique, with water as a solvent. X-ray diffraction shows that the incorporation of ammonium acetate into the polymeric matrix causes decrease in the crystallinity degree of the samples. The Fourier transform infrared spectroscopy and laser Raman studies confirm the complex formation between the polymer and salt. Differential scanning calorimerty shows that the thermal stability of the polymer blend electrolyte and the glass transition temperature decreased as the concentration of ammonium acetate increased. The ionic conductivity of the prepared polymer electrolyte was found by AC impedance spectroscopic analysis. A maximum conductivity of 8.12?×?10^?5 Scm^?1 was observed for the composition of 50 PVA/50 PVP/30 wt.% of CH₃COONH₄.     

Characterization of blend polymer PVA-PVP complexed with ammonium thiocyanate

Thin films of blend polymer electrolytes comprising poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) complexed with ammonium thiocyanate (NH₄SCN) salt in different compositions have been prepared by solution casting technique using distilled water as solvent. The prepared films have been investigated by different experimental techniques. The complexation of these films has been studied by FTIR spectroscopy. The increase in amorphousness of the films with increase in NH₄SCN content has been confirmed by XRD analysis. The addition of ammonium thiocyanate salt to PVA-PVP polymer blend shows a shift in T_g of the blend. The effect of salt concentration and temperature on the ionic conductivity of the polymer blend films has been analyzed using AC impedance spectroscopy. The maximum conductivity of 6.85 × 10^?4 S cm^?1 at room temperature has been observed for the blend with 50 mol% PVA-50 mol% PVP complexed with 40 mol% NH₄SCN. The activation energy has been found to be minimum (0.24 eV) for this sample. Wagner’s polarization technique shows that the charge transport in these blend films is predominantly due to ions. Using the highest conductivity blend polymer electrolyte, a proton battery has been fabricated and its discharge characteristics have been studied.     

Effect of H<Subscript>3</Subscript>PO<Subscript>2</Subscript> on the mechanical,thermal, and electrical properties of polymers based on poly (vinyl alcohol) (PVA) and chitosan (CS)

A polymer based on poly (vinyl alcohol) (PVA) and chitosan (CS) with a weight ratio of 80:20 was prepared by solvent casting processes, and the effect of H₃PO₂ was investigated. Thermal analysis shows miscibility of the two polymer amorphous phases since a single T_g was located between those of the individual components and the melting point of the crystalline phase was depressed to 189 °C. It was found that the acid acts as a plasticizer for the PVA-CS blends and its T_g is depressed significantly to 23 °C as the acid concentration increases to 50%. Strain-stress tests also corroborate this effect. The DC conductivity of the blends follows an Arrhenius-type thermal activation behavior with activation energy of 0.1 eV in the 30–90 °C temperature range. Moreover, the conductivity increases with increasing acid content up to a maximum value of approximately 1.4 × 10^?2 S/cm for the blend with an acid concentration of 50%.     

Effect of temperature on the conductivity, structural, and morphology of PVA-based alkaline solid polymer electrolyte

Alkaline polymer electrolytes (ASPE) have been prepared by using poly(vinyl alcohol) (PVA) polymer and which different weight percentages of potassium hydroxide (KOH), ceramic filler (α-Al₂O₃), and propylene carbonate (PC) have been added. The pure PVA/H₂O weight ratio (1.00:1.49), the PVA/KOH/H₂O (1.00:0.67:2.22), the PVA/KOH/α-Al₂O₃/H₂O (1.00:0.67:0.09:7.56), and PVA/KOH/α-Al₂O₃/PC/H₂O (1.00:0.67:0.09:2.64:1.32) were studied. The hysteresis phenomena in the conductivity temperature of ASPE were investigated. The polymer electrolytes prepared were characterized using X-ray diffraction and scanning electron microscopy.     

Solvent-free nanocomposite proton-conducting membranes composed of cesium salt of phosphotungstic acid doped PVDF–CTFE/PEO blend

In this research, novel nanocomposite membranes were prepared using polymer blend of polyethylene oxide (PEO) and polyvinylidene fluoride–chloro tetrafluoro ethylene (PVDF–CTFE) copolymer with cesium salt of phosphotungstic acid (Cs_2.5H_0.5PWO₄₀) as proton conductor. Nanocomposite membranes were prepared by solvent-free procedure. The DSC studies show a decrease in crystalinity of polymer matrix with increasing PEO to PVDF–CTFE proportional ratio and the filler. The TGA studies show that membranes are stable up to 180 °C. The TGA also indicates that addition of cesium salt of phosphotungstic acid increases the thermal stability of membranes. The SEMs exhibit that membranes are non-porous and the additive components are homogenously dispersed. Conductivity tests for membranes were carried out in the range of 25–100 °C in dry and hydrated states. Results show that by increasing the temperature, membranes conductivities are increased. In dry state, except at the temperature of 45 °C, membranes which have the highest crystalinity, have the highest conductivity. The alteration of the conductivity in the range of temperatures in dry condition may be attributed to segmental motion of polymer which resulted in proton hopping from one site to another or increasing free volume for proton motion. In fully hydrated state, dynamic equilibrium between different proton moieties determines the mode of proton conductivity which can be described by Grothuss mechanism. In the presence of water molecule, the free proton may be formed. The conductivity for the membrane in hydrated state with the blend ratio of PVDF:PEO = 95:5 w/w and 10% addition of cesium salt of phosphotungstic acid at the temperature of 90 °C is 1.05 × 10⁻⁴ S cm⁻¹.     

An investigation of the proton conductivities of hydrated poly(vinyl alcohol)/boric acid complex electrolytes

Proton-conducting polymer complex electrolytes were prepared by incorporation of boric acid, H₃BO₃ into poly(vinylalcohol), PVA, to form hydrated PVAxH₃BO₃ where x denotes the number of moles of boric acid per polymer repeat unit. The dried materials were characterized via Fourier transform infrared spectroscopy, thermogravimetry, and X-ray diffraction. The proton conductivity of the hydrated complex electrolytes was measured by AC impedance spectroscopy. PVA2H₃BO₃ with RH ∼25% was found to be optimum composition that exhibited proton conductivity of 1.3 × 10⁻³ S/cm at 80 °C.     

Magnesium ion conducting polyvinyl alcohol–polyvinyl pyrrolidone-based blend polymer electrolyte

Structural, thermal, electrical and electrochemical behaviour of polymer blend electrolytes comprising polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) as host polymers and Mg(ClO₄)₂ as dopant salt have been investigated. The changes in the structural properties on the incorporation of dopant in the blends were investigated by XRD and FTIR analyses. Thermal properties of pure PVA–PVP blend and their complexes were examined by DSC to measure how the thermal transitions of the prepared films were affected by different concentration of Mg(ClO₄)₂. The ionic conductivity and dielectric behaviour were explored using A.C. impedance spectroscopy. The trend of ionic conductivity increases almost proportionally to the content of magnesium salt and can be related to an increase of amorphous phase at high level of dopant salt. The electrochemical stability of the optimum conducting blend polymer electrolyte is found to be ～3.5 V. The Mg²⁺ transference number for the sample with optimized conductivity was found to be 0.31.     

Preparation and Characterization of Poly(Vinyl Alcohol) (PVA)/SiO2, PVA/Sulfosuccinic Acid (SSA) and PVA/SiO2/SSA Membranes: A Comparative Study

Abstract

New organic–inorganic nanocomposites based on PVA, SiO₂ and SSA were prepared in a single step using a solution casting method, with the aim to improve the thermomechanical properties and ionic conductivity of PVA membranes. The structure, morphology, and properties of these membranes were characterized by Raman spectroscopy, small- and wide-angle X-ray scattering (SAXS/WAXS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), water uptake (Wu) measurements and ionic conductivity measurements. The SAXS/WAXS analysis showed that the silica deposited in the form of small nanoparticles (～ 10?nm) in the PVA composites and it also revealed an appreciable crystallinity of pristine PVA membrane and PVA/SiO₂ membranes (decreasing with increasing silica loading), and an amorphous structure of PVA/SSA and PVA/SSA/SiO₂ membranes with high SSA loadings. The thermal and mechanical stability of the nanocomposite membranes increased with the increasing silica loading, and silica also decreased the water uptake of membranes. As expected, the ionic conductivity increased with increasing content of the SSA crosslinker, which is a donor of the hydrophilic sulfonic groups. Some of the PVA/SSA/SiO₂ membranes had a good balance between stability in aqueous environment (water uptake), thermomechanical stability and ionic conductivity and could be potential candidates for proton exchange membranes (PEM) in fuel cells.     

LiClO4-doped plasticized chitosan and poly(ethylene glycol) blend as biodegradable polymer electrolyte for supercapacitors

Biodegradable polymer electrolyte comprising the blend of chitosan (CS) and poly(ethylene glycol) (PEG) plasticized with ethylene carbonate and propylene carbonate, as host polymer, and lithium perchlorate (LiClO₄), as a dopant, was prepared by solution casting technique. The ionic conductivity has been calculated using the bulk impedance obtained through impedance spectroscopy. The variation of conductivity and dielectric properties has been investigated as a function of polymer blend ratio, plasticizer content and LiClO₄ concentration at temperature range of 298–343 K. The DSC thermograms show two broad peaks for CS/PEG blend and increased with increase in the LiClO₄ content. The maximum conductivity has been found to be 1.1?×?10^?4 S cm^?1 at room temperature for 70:30 (CS/PEG) concentration. The electric modulus of the electrolyte film exhibits a long tail feature indicative of good capacitance. The activation energy of all samples was calculated using the Arrhenius plot, and it has been found to be 0.12 to 0.38 eV. A carbon–carbon supercapacitor has been fabricated using this electrolyte, and its electrochemical characteristics and performance have been studied. The supercapacitor showed a fairly good specific capacitance of 47 F?g^?1.     

PVdF-HFP membranes for fuel cell applications: effects of doping agents and coating on the membrane’s properties

Poly(vinylidene fluoride-co-hexafluoropropene)–hexafluoropropylene (PVdF-HFP; M _n, 130,000)-based membranes were prepared by means of phase inversion technique by coagulating with water and MeOH and then doping with H₃PO₄ and H₂SO₄. In order to improve the electrochemical properties of the PVdF-HFP membranes, coagulated membranes were also coated with polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (PSEBS) and sulfonated with chlorosulfonic acid in the second stage. The effects of the type of coagulant, coagulation time, doping agents, coating, and sulfonation on the membrane properties were investigated. Membranes were thermally stable up to 400 °C. The conductivity values were measured to be between 1.10E???01 and 6.00E???03 mS/cm for uncoated samples. The proton conductivity value of the PSEBS-coated and sulfonated membrane was increased from 6.00E???03 to 92.1 mS/cm. Water uptake values varied from 0 to 38 % for uncoated samples and from 11.5 to 65.2 % for coated samples. Chemical degradation of PVdF-HFP membranes was investigated via Fenton test. All membranes were found to be chemically stable. Morphology of the membranes was examined by scanning electron microscopy. Different membrane morphologies were observed, depending on different membrane preparation procedures.     

Proton conductivity of Al(H2PO4)3–H3PO4 composites at intermediate temperature

Composites of Al(H₂PO₄)₃ and H₃PO₄ were synthesised by soft chemical methods with different Al/P ratios. The Al(H₂PO₄)₃ obtained was found to have a hexagonal symmetry with parameter a = 13.687(3)Å, c = 9.1328(1)Å. The conductivity of this material was measured by a.c. impedance spectroscopy between 100 °C and 200 °C in different atmospheres. The conductivity of pure Al(H₂PO₄)₃ in air is in the order of 10^? 6–10^? 7 S/cm between 100 and 200 °C. For samples containing small excess of H₃PO₄, much higher conductivity was observed. The impedance responses of the composites were found to be similar with AlH₂P₃O₁₀·nH₂O under different relative humidity. The conductivity of Al(H₂PO₄)₃–H₃PO₄ composite with Al/P = 1/3.5 reached 6.6 mS/cm at 200 °C in wet 5% H₂. The extra acid is found to play a key role in enhancing the conductivity of Al(H₂PO₄)₃–H₃PO₄ composite at the surface region of the Al(H₂PO₄)₃ in a core shell type behaviour. 0.7% excess of H₃PO₄ can increase the conductivity by three orders of magnitude. These composites might be alternative electrolytes for intermediate temperature fuel cells and other electrochemical devices. Conductivity (9.5 mS/cm) changed little, when the sample was held at 175 °C for over 100 h as the conductivity stabilised.     

Proton-conducting polymer electrolyte based on PVA-PAN blend doped with ammonium thiocyanate

Blending of polymers is one of the most useful methods for modulating the conductivity of solid polymer electrolytes. Blend polymer electrolytes have been prepared with polyvinyl alcohol (PVA)-polyacrylonitrile (PAN) blend doped with ammonium thiocyanate with different concentrations by solution casting technique, using dimethyl formamide (DMF) as the solvent. The prepared electrolytes are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), nuclear magnetic resonance (NMR), ultraviolet (UV), and ac impedance measurement techniques. The increase in amorphous nature of the blend polymer electrolyte by the addition of salt is confirmed by XRD analysis. The complex formation between the polymers and the salt has been confirmed by FTIR analysis. The thermal behavior has been examined using DSC and TGA. The maximum conductivity has been found to be 2.4?×?10^?3 S cm^?1 for 92.5PVA/7.5PAN/25 % NH₄SCN sample at room temperature. The temperature dependence of conductivity has been studied with the help of Arrhenius plot, and the activation energies are calculated. The proton conductivity is confirmed by dc polarization measurement technique. ¹H NMR studies reveal the presence of protons in the sample. A proton battery is constructed with the highest conducting sample, and its open circuit voltage is measured to be 1.2 V     

Electrochemical double layer capacitor based on cellulose-PVA hybrid electrolyte

A polyvinyl alcohol (PVA) cellulose electrolyte was prepared by casting a solution of PVA and H₃PO₄ on both sides of a cellulose membrane (filter paper). The ionic species H⁺ are caused by the H₃PO₄ acid which is entrapped inside the PVA and in the pores of the filter paper. The electrolyte was sandwiched between two carbon electrodes to form an electric double layer capacitor (EDLC). The EDLC exhibits a good charge and discharge characteristics with a capacitance value of 30 Fg⁻¹. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.     

50 MeV Li3+ ion irradiation effect on structural, electrical, and dielectric properties of PVA-based nanocomposite polymer electrolytes

Nanocomposite polymer electrolyte thin films of polyvinyl alcohol (PVA)-orthophosphoric acid (H₃PO₄)-Al₂O₃ have been prepared by solution cast technique. Films are irradiated with 50 MeV Li³⁺ ions having four different fluences viz. 5?×?10¹⁰, 1?×?10¹¹, 5?×?10¹¹, and 1?×?10¹² ions/cm². The effect of irradiation on polymeric samples has been studied and characterized. X-ray diffraction spectra reveal that percent degree of crystallinity of samples decrease with ion fluences. Glass transition and melting temperatures have been also decreased as observed in differential scanning calorimetry. A possible complexation/interaction has been shown by Fourier transform infrared spectroscopy. Temperature-dependent ionic conductivity shows an Arrhenius behavior before and after glass transition temperature. It is observed that ionic conductivity increases with ion fluences and after a critical fluence, it starts to decrease. Maximum ionic conductivity of ～2.3?×?10^?5 S/cm owing to minimum activation energy of ～0.012 eV has been observed for irradiated electrolyte sample at fluence of 5?×?10¹¹ ions/cm². The dielectric constant and dielectric loss also increase with ion fluences while they decrease with frequency. Transference number of ions shows that the samples are of purely ionic in nature before and after ion irradiation.     

Electrical conductivity studies on PVA/PVP-KOH alkaline solid polymer blend electrolyte

A series of conducting thin-film solid electrolytes based on poly (vinyl alcohol)/ poly (vinyl pyrrolidone) (PVA/PVP) polymer blend was prepared by the solution casting technique. PVA and PVP were mixed in various weight percent ratios and dissolved in 20 ml of distilled water. The samples were analyzed by using impedance spectroscopy in the frequency range between 100 Hz and 1 MHz. The PVA/PVP system with a composition of 80% PVA and 20 wt.% PVP exhibits the highest conductivity of (2.2±1.4) × 10⁻⁷ Scm⁻¹. The highest conducting PVA/PVP blend was then further studied by adding different amounts of potassium hydroxide (KOH) ionic dopant. Water has been used as solvent to prepare PVA/PVP-KOH based alkaline solid polymer blend electrolyte films. The conductivity was enhanced to (1.5 ± 1.1) × 10⁻⁴ Scm⁻¹ when 40 wt.% KOH was added. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.