S. S. Sekhon

Role of plasticizer's dielectric constant on conductivity modification of PEO-NH4F polymer electrolytes

Abstract The addition of plasticizer to the polyethylene oxide (PEO)–ammonium fluoride (NH4F) polymer electrolytes has been found to result in an increase in conductivity value and the magnitude of increase has been found to depend upon the dielectric constant of the plasticizer used. The addition of dimethylacetamide as a plasticizer with dielectric constant (ϵ=37.8) higher than that of PEO (ϵ∼5) results in an increase of conductivity by more than three orders of magnitude whereas the addition of diethylcarbonate as a plasticizer with dielectric constant (ϵ=2.82) lower than that of PEO does not enhance the conductivity of PEO–NH4F polymer electrolytes. The increase in conductivity has further been found to depend upon the concentration of plasticizer, the concentration of salt in the polymer electrolyte as well as on the dielectric constant value of the plasticizer used. The conductivity modification with the addition of plasticizer has been explained on the basis of dissociation of ion aggregates formed in PEO–NH4F polymer electrolytes at higher salt concentrations.

Physicochemical properties of proton conducting membranes based on ionic liquid impregnated polymer for fuel cells

Polymer electrolyte membranes containing a room temperature ionic liquid, 2,3-dimethyl-1-octylimidazolium triflate (DMOImTf) in polyvinylidenefluoride-co-hexafluoropropylene (PVdF-HFP), show conductivity of 0.96 × 10−3 S cm−1 at 80 °C. The addition of triflic acid (HCF3SO3) increases the conductivity of the polymer electrolytes by providing free H+ ions, which is important for their potential use in proton exchange membrane fuel cells (PEMFCs) and other electrochemical devices. Line narrowing observed in the variation of 1H and 19F NMR line width with temperature shows that both protons and anions are mobile in these electrolytes. The membranes have been found to be thermally stable up to 200–300 °C. Polymer electrolyte membranes containing the ionic liquid have also been tested in a single cell fuel cell under non-humid conditions and found to be electroactive for hydrogen oxidation and oxygen reduction at platinum electrodes.

PMMA based protonic polymer gel electrolytes

The paper reports the synthesis of protonic polymer gel electrolytes containing different hydroxy benzoic acids (ortho-, meta- and para-) and aliphatic dicarboxylic acids. Gel electrolytes were prepared by adding polymethylmethacrylate (PMMA) in different weight ratios to the 1M solution of above acids in a ternary solvent mixture of propylene carbonate (PC), ethylene carbonate (EC) and dimethylformamide (DMF) in equal volume ratio. The conductivity of these gel electrolytes has been found to depend upon the amount of PMMA added to the system. A “Breathing Polymeric Chain Model” has been proposed to explain the variation of conductivity with PMMA concentration in these gel electrolytes.

Ionic conductivity of PVdF-based polymer gel electrolytes

Abstract Gel polymer electrolytes with polyvinylidenefluoride (PVdF) as the polymer, a ternary solvent mixture consisting of ethylene carbonate (EC), propylene carbonate (PC) and dimethylacetamide (DMA) as the solvent and different ( ortho -, meta - and para -) hydroxy-substituted carboxylic acids, have been studied. The conductivity value has been found to depend upon the concentration of the acid and is higher for gel electrolytes containing ortho -acid than the meta - and para -acids. The conductivity of the order of 10 −4 S/cm at 20 °C has been observed and the conductivity of gel electrolytes is found to be higher than that of the corresponding liquid electrolytes at all acid concentrations and for all the three acids studied.

Proton-conducting gel electrolyte

Abstract Proton conduction in solid state xerogels and polymeric gels are reported. Xerogels, doped with known proton conductors, were prepared by “sol–gel” method starting either from inorganic precursor sodium metasilicate (termed as hydrogel) or organic precursor tetraethyl orthosilicate (termed as silica or SiO 2 alcogel). The dopants chosen for the former were NH 4 BF 4 , NH 4 Cl, NH 4 H 2 PO 4 and N 2 H 6 SO 4 , while for the latter, the dopants used were H 3 PO 4 , NH 4 BF 4 , NH 4 H 2 PO 4 and KH 2 PO 4 . The SiO 2 :H 3 PO 4 alcogel gave the highest room temperature conductivity (∼10 −3 S cm −1 ). Some of the xerogels studied by us were stable even up to 300 °C. Another interesting group of proton-conducting materials discussed in this paper is polymeric gel which was prepared by dispersing PMMA in the liquid electrolyte obtained by dissolving o -, m -, p -hydroxybenzoic acid; o -, m -, p -nitrobenzoic acid and three dicarboxylic acids, viz., oxalic, malonic and succinic acid, in a high-dielectric constant organic solvent. The role of the dissociation constants of the dissolved acids and the interaction of the polymer were discussed. The addition of polymer, inspite of the increasing viscosity, was found to sometimes lead to an increase in the conductivity of liquid electrolyte, which was explained on the basis of a breathing polymer chain model.

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.

Micro- to Macroscopic Observations of MnAlPO-5 Nanocrystal Growth in Ionic-Liquid Media

Micro- and macroscopic studies of nucleation and growth processes of MnAlPO-5 nanosized crystals under ionothermal synthesis conditions are reported herein. The samples treated at 150 °C were extracted from the reaction mixture at various stages of crystallization, and characterized by XRD; SEM; thermogravimetric analysis (TGA); (31)P and (27)Al solid-state magic angle spinning (MAS) NMR, Raman, UV/Vis, and X-ray fluorescence spectroscopy (XRF). The starting raw materials (alumina, manganese, and phosphorous) were dissolved completely in the ionic liquid and transformed into an amorphous solid after 5 h of ionothermal treatment. This amorphous solid then undergoes structural changes over the following 5-25 h, which result in an intermediate phase that consists of octahedral Al species linked to the manganese and phosphate species. The first MnAlPO-5 nuclei on the surface of the intermediate can be observed after 50 h ionoheating. These nuclei further grow, as the surface of the intermediate is in full contact with the ionic liquid, to give crystalline MnAlPO-5 nanoparticles with a mean diameter of 80 nm. The crystals become fully detached from the intermediate and are then liberated as discrete particles after 90 h heating. The transformation process from amorphous to intermediate and then to the crystalline MnAlPO-5 nanoparticles shows that nucleation starts at the solid-liquid interface and continues through surface-to-core reversed-growth until the entire amorphous solid is transformed into discrete nanocrystals.

Ionic conductance behaviour of plasticized polymer electrolytes containing different plasticizers

The effect of different plasticizers on the properties of PEO-NH4F polymer electrolytes has been studied. Aprotic organic solvents like propylene carbonate (PC), ethylene carbonate (EC), γ-butyrolactone (γ-BL), dimethylacetamide (DMA), dimethylformamide (DMF), diethylcarbonate (DEC) and dimethylcarbonate (DMC) having different values of donor number, dielectric constant, viscosity etc. have been used as plasticizers in the present study. The addition of plasticizer has been found to modify the conductivity of polymer electrolytes by increasing the amorphous content as well as by dissociating the ion aggregates present in polymer electrolytes at higher salt concentrations. The conductivity enhancement with different plasticizers has been found to be closely related to the donor number of the plasticizer used rather than its dielectric constant. The increase in conductivity with the addition of plasticizer has further been found to be dependent upon the level of ion association present in the electrolytes. The variation of conductivity as a function of plasticizer concentration and temperature has also been studied and maximum conductivity of ∼ 10−3 S /cm at room temperature has been obtained. X-ray diffraction studies show an increase of amorphous content in polymer electrolytes with the addition of plasticizers.

Studies on poly(ethylene oxide)-CuSCN polymer electrolytes

Abstract The preparation and characterization of polymer electrolytes formed between poly(ethylene oxide) and copper (I) thiocyanate (CuSCN) for various salt concentrations are reported. Differential scanning calorimetry and X-ray diffraction studies show that complexation occurs mainly in the amorphous phase over a wide range of compositions. The a.c. impedance analysis and d.c. polarization measurements show that the polymer complexes have high ionic conductivity. The material is essentially an anionic conductor.

Efficiency Enhancement of Dye-Sensitized Solar Cells by the Addition of an Oxidizing Agent to the TiO2 Paste

The addition of various amounts of a strong oxidizing agent (3,5-dinitrosalicyclic acid, DNSA) to TiO2 paste enhances the solar-to-electrical-energy conversion efficiency of the corresponding dye-sensitized solar cells (DSSCs). Maximum performance was obtained from a device that was fabricated by using a TiO2 paste with 2 wt % DNSA, which showed a short-circuit current density of 17.88 mA cm(-2) , an open-circuit voltage of 0.78 V, and an overall conversion efficiency of 9.62 %, which was an improvement in comparison to reference cells without DNSA. This improvement was rationalized in terms of the amount of residual carbon (formed due to the oxidation of binders) remaining on the TiO2 surface. Addition of a larger amount of oxidizing agent led to a smaller amount of residual carbon on the TiO2 surface. This smaller amount of residual carbon enhanced the adsorption of a larger number of dye molecules on the TiO2 surface. The addition of an oxidizing agent facilitated the removal of more residual organic species during the high-temperature calcination process while causing no change in the surface morphology and microstructure of the TiO2 film.