Development and characterization of ionic liquid doped solid polymer electrolyte membranes for better efficiency

Solid polymer electrolyte membranes based on poly(ethylene oxide) (PEO) polymer electrolyte incorporated with low viscosity ionic liquid (IL), 1-ethyl 3-methylimidazolium trifluoromethanesulfonate (EMImTFO^?) have been prepared and used in dye-sensitized solar cell (DSSC) application. Ionic conductivity (σ) measurement shows improvement in σ due to reduced crystallinity and free charge carriers provided by IL which was further affirmed by our differential scanning calorimetry (DSC) and optical microscopy (OM) measurements. Surface feature of films was characterized by scanning electron microscopy (SEM) measurement. The photovoltaic characteristics of the fabricated DSSC are compared with those without IL, in which the low viscosity IL doped solid polymer electrolyte system shows excellent improvement in efficiency.     

Ionic liquid doped poly(N-methyl 4-vinylpyridine iodide) solid polymer electrolyte for dye-sensitized solar cell

Ion conducting polymer electrolyte, poly(N-methyl 4-vinylpyridine iodide) (PVPI) is synthesized for dye-sensitized solar cell (DSSC) application. A new solid polymer electrolyte composite containing low viscosity ionic liquid (IL) 1-ethyl 3-methylimidazolium dicyanamide (EMImDCN) doped PVPI is developed and its structural, electrical and photoelectrochemical studies are presented in detail. Fourier transform infrared (FTIR) spectroscopy, proton NMR and atomic force microscopy (AFM) affirms the modified polymer and its composite nature with porous surface morphology. The developed solid polymer electrolyte shows enhancement in ionic conductivity (σ) due to IL doping. The maximum σ value of 9.12 × 10^?6 S cm^?1 was obtained at 40 wt% IL concentration. The redox behavior of the electrolyte has been verified by the cyclic voltammetry studies. For device application, we have fabricated a DSSC using this solid polymer–IL electrolyte system which shows energy conversion efficiency of the solid-state cell as 0.65% under irradiation of simulated sunlight (AM 1.5, 100 mW cm^?2).     

Ionic conductivities of polymeric solid electrolyte films containing rare earth ions

Polymeric solid electrolyte films containing rare earth metal ions (Ce³⁺, La³⁺, Yb³⁺) have been prepared, with a view to applying them to solid-state electrochemical devices. The films, composed of poly(ethylene oxide)-grafted poly(methylmethacrylate) (PEO–PMMA), were prepared by dissolving rare earth salts with appropriate amounts of poly(ethylene glycol) dimethyl ether (PEG) that have ethylene oxide units in their structure. The ionic conductance behaviour of the polymeric composite electrolyte systems was investigated by AC impedance and DC polarization methods in an ambient temperature range. The oligo(ethylene oxide) units in the polymer matrix and the PEG components ensured the dissociation of the salts and the high mobility of the resulting ionic species in the solid films. About 10⁻⁵ S cm⁻¹ or above of ionic conductivity was obtained for a PEO–PMMA/PEG/Ce(ClO₄)₃ system at room temperature. The addition of a liquid plasticizer in the composite improved the conductivity by about two orders of magnitude.     

Electrochemical synthesis of novel conducting polymer composite: Polypyrrole–pentacyanonitrosylferrate

With a view to develop conducting polymer film of high electroactivity, pentacyanonitrosylferrate (PCNFe) doped polypyrrole (PPY) composite films are prepared using cyclic voltammetry deposition method. The PPY–PCNFe composite is characterized by FTIR, TEM and TGA analysis. The electroactivity of PPY–PCNFe composite film is studied in 3 mM KCl (common electrolyte) solution. Two redox pairs at E_1/2 = ?0.59 V and 0.02 V due to redox behavior of polymer and dopant anions respectively are observed. The electroactivity study reveals the existence of two types of PCNFe dopant anions in the polymeric film: one form is loosely held and prone to easy removal from the polymer matrix whereas the other form is strongly bound to polymer backbone and prone to electrochemical redox reaction by movements of electrons. The high electroactivity of the film is attributed to the movements of ionic species into and out of the polymeric film as well as movements of electron.     

Stability of electrochemomechanical strains in polypyrrole films using ionic liquids

Electrochemomechanical strain (ECMS) of conducting polymers, polypyrrole (PPy) films was studied using several kinds of ionic liquids and the mixed solution with organic solvents from the view points of strain and stability. The PPy films, which were electrodeposited from lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), showed porous morphology. The ECMS in the films operated in ionic liquids was less than 5%, demonstrating a cation movement behavior and stable cycling. By the operation in ionic liquid/propylene carbonate (PC) mixed solution, the ECMS increased up to 24% showing the anion movement, and gradually decreased upon cycling to 16% at 10^th cycle. The strain and stability of the ECMS in mixed electrolyte solution with various ratios of the ionic liquid and PC were studied and discussed in terms of mechanisms of ECMS in mixed solutions.     

Biodegradability and anticoagulant properties of chitosan and sulfonated chitosan films coated on TiNi alloys

This study proposes a method of coating chitosan and sulfonated chitosan surface modification films on nickel–titanium shape memory alloys and investigates their biodegradability and anticoagulant properties. Sulfonated chitosan has a similar structure to chitosan, although amino groups convert during the sulfonation process. The biodegradation of chitosan by Escherichia coli DH5α does not occur when the concentration of chitosan is sufficiently high because the electrostatic interactions between the amino groups and phospholipid components damage the cell membranes of E. coli DH5α. By contrast, the biodegradation of sulfonated chitosan is independent of its concentration because the sulfonation process results in a decrease in the number of amino groups present. Bicinchoninic acid protein assay results reveal that the amount of fibrin adhered on the deposited natural chitosan surface is twice that adhered to sulfonated chitosan.     

Preparation of organo-soluble polyanilines in ionic liquid

A method for preparation of organo-soluble polyaniline (PANI) is described. Oxidative coupling polymerization of anilium chloride with ammonium persulfate in a new ionic liquid, 2-hydroxyethyl ammonium formate (HAF), gives organo-soluble polyaniline with appreciable molecular weights (M_w = 86,400). Interestingly polyaniline (PANI) prepared by this method is highly soluble in many organic solvents such as acetone, tetrahydrofurane, dioxane, dimethyformamide and N-methyl, 2-pyrrolidinone. Thin films of PANI prepared at 0 °C (by solvent casting) show reasonable conductivities (up to 37.0 S cm⁻¹) when doped with p-toluene sulfonic acid.     

Solid-state photoelectrochemical device using poly(o-methoxy aniline) as sensitizer and an ionic conductive elastomer as electrolyte

We report on a photoelectrochemical cell based on polymers (electrolyte and sensitizer) and TiO₂. Poly(epichlorohydrin-co-ethylene oxide) filled with NaI/I₂ was used as electrolyte and poly(o-methoxy aniline) doped with p-toluenesulfonic (PoAni-TSA) as dye. The short-circuit current and open-circuit voltage obtained with illumination at 120 mW cm⁻² are 12.2 μA cm⁻² and 0.048 V, respectively, indicating that the ionic conductive elastomer is appropriated for assembling a totally solid device. The monochromatic photon-to-current conversion efficiency decreases from 1.3% to 0.1%, from 410 to 600 nm, respectively, showing that the conducting polymer acts as a dye for TiO₂, injecting electrons into its conduction band.     

Nanobeads of zinc oxide with rhodamine B dye as a sensitizer for dye sensitized solar cell application

Cost effective, ruthenium metal free rhodamine B dye has been chemically adsorbed on ZnO films consisting of nanobeads to serve as a photo anode in dye sensitized solar cells. These ZnO films were chemically synthesized at room temperature (27 °C) on to fluorine doped tin oxide (FTO) coated glass substrates followed by annealing at 200 °C. These films consisting of inter connected nanobeads (20-40 nm) which are due to the agglomeration of very small size particles (3-5 nm) leading to high surface area. The film shows wurtzite structure having high crystallinity with optical direct band gap of 3.3 eV. Optical absorbance measurements for rhodamine B dye covered ZnO film revealed the good coverage in the visible region (460-590 nm) of the solar spectrum. With poly-iodide liquid as an electrolyte, device exhibits photon to electric energy conversion efficiency (η) of 1.26% under AM 1.5G illumination at 100 mW/cm².     

Doping-dependent ion selectivity of polyaniline membranes

Polyaniline (PAN) films were cast from a solution in N-methyl-2-pyrrolidone (NMP) and characterised by atomic force microscopy (AFM), FTIR, X-ray, TGA and DSC. Ion selectivity of the films as free-standing membranes in the electrolyte/membrane/electrolyte system was characterised by transmembrane electric potential. It was demonstrated that PAN membrane has completely different permeability and ion selectivity in the undoped and HCl-doped states. In the undoped state, the membrane is hardly permeable to inorganic ions, but still it is selective to H⁺. After HCl-doping transmembrane resistance decreases by a few orders of value, and the membrane becomes anion/H⁺-selective.     

Effect of various parameters on the conductivity of free standing electrosynthesized polypyrrole films

Electrical characteristics of polypyrrole films electrodeposited in different aqueous electrolyte solutions including p-toluenesulfonate, naphtalenesulfonate, nitrate, tetrafluoroborate, and perchlorate anions were investigated using the Van der Pauw procedure. The polymer films were synthesized by electrochemical oxidation at a fixed potential. Experimental parameters including the pyrrole concentration, electrolyte, applied potential and substrate were shown to affect the electrical conductivity σ of polypyrrole films. Since the substrate contributes significantly to the overall conductivity of polypyrrole-coated electrodes, the results obtained with free standing polymer films appeared more reliable. The results indicated that the p-toluenesulfonate doped PPy film showed the highest average conductivity (σ_293 K = 4.5 × 10⁵ S m^?1) whereas the perchlorate doped one produced the lowest of all the films prepared (σ_293 K = 2 × 10⁴ S m^?1).     

Fabrication of calcium phosphate/chitosan coatings on AZ91D magnesium alloy with a novel method

Four calcium phosphate/chitosan composite films were fabricated on the surface of micro-arc oxidized (MAO)-AZ91D alloy through electrophoretic deposition (EDP) followed by a conversion process of the coatings in a phosphate buffer solution (PBS). In the EPD process, nano hydroxyapatite (n-HA, Ca₁₀(PO₄) ₆(OH)₂) and Ca(OH)₂ in the layers were obtained from a n-HA/ethanol suspension and a n-HA/chitosan-acetic acid aqueous solution, respectively. After immersion into PBS, brushite (DCPD, CaHPO₄·2H₂O) and new HA were introduced into the deposited layers. The percentage of Ca(OH)₂ in the deposited layers played an important role in developing the new phase in the conversion layers. When the percentages of Ca(OH)₂ in the deposited layers were 32 wt. % and 54 wt. %, the main phase of the conversion layers was DCPD with a little HA. However, when the percentages of Ca(OH)₂ were 64 wt. % and 100 wt. %, the main phase of the conversion layers became HA with a little DCPD. The calcium phosphate/chitosan coatings with more homogeneous bioactive layers and better adhesion strength on MAO-AZ91D alloy substrate were obtained from the electrolyte whose volume percentages of the n-HA/chitosan-acetic acid aqueous solution being 60% and 80%.So, EPD combined with a conversion process into PBS could be a promising method for the preparation of new calcium phosphate/chitosan coatings.     

Transport studies of NH4NO3 doped methyl cellulose electrolyte

This work reports on the transport properties of NH₄NO₃ doped methyl cellulose (MC) polymer electrolyte. The polymer electrolyte films were prepared by the technique of solvent casting. The highest room temperature conductivity of MC doped with 25 wt.% NH₄NO₃ is 2.10 ± 0.37 × 10^?6 S cm^?1. Conductivity–temperature relationship obeys the Vogel–Tamman–Fulcher (VTF) rule from which the glass transition temperature, T_g was evaluated. The mobility, μ and number density of charge carrier, n were calculated using the Rice and Roth model.     

PEDOT/PAMPS: An electrically conductive polymer composite with electrochromic and cation exchange properties

Poly(3,4-ethylenedioxythiophene) (PEDOT)/poly(2-acrylamido-2-methyl-l-propane sulfonate) (PAMPS) composite films were electrochemically prepared from a mixture of water and N,N-dimethylformamide (DMF) containing 3,4-ethylenedioxythiophene (EDOT) and the polyelectrolyte, PAMPS. The presence of PAMPS in the PEDOT matrix was confirmed by spectroscopic and electrochemical methods. Depending on the current density, the conductivity of PEDOT/PAMPS free standing composite films reached values of 80 S/cm. Spectroelectrochemistry of neutralized PEDOT/PAMPS composite films showed a maximum absorption at 2.0 eV (615 nm) and a band gap of 1.65 eV, as calculated from the onset of the π–π* transition. Thin PEDOT/PAMPS composite films were found to switch rapidly between oxidized and reduced states in less than 0.4 s with an initial optical contrast of 76% at λ_max: 615 nm. The morphology of the polymer composites demonstrates a cauliflower structure. Despite the high molecular weight of the polyelectrolyte, the film density was found to be similar to classical PEDOT (i.e., ca. 1.4 g/cm³), while the surface roughness averaged below 5%. As expected with the use of a sulfonated polyelectrolyte as dopant, cation exchange properties were observed with hexaammineruthenium(III) chloride as an active electrolyte.     

Oxidative electropolymerization of pyrrole from neat monomer solution

Oxidative electrochemical polymerization of pyrrole at gold, indium doped tin oxide on glass, and stainless steel type 304 was accomplished from neat monomer solution containing only supporting electrolyte (0.05–0.3 M n-tetrabutyl ammonium perchlorate, n-tetrabutyl ammonium hexafluorophosphate, or n-tetrabutyl ammonium tetrafluoroborate) by multiple scan cyclic voltammetry. The results presented demonstrate that thick (>1–14 μm), stable, highly conductive (up to 0.6 S/cm) polypyrrole films can be readily prepared on a wide range of electrode substrates using this simple electrochemical method.     

Influence of doping anion on electrochemical and physical properties of polyselenienyl thiophene polymer

The effect of counter ions on electrochemical and physical properties of polyselenienyl thiophene (PSeT) films was investigated. sThe films were prepared by anodic oxidation of selenienyl thiophene in acetonitrile using PF₆, ClO₄, BF₄ and CF₃SO₃ as the doping anion. Electrochemical characterization of these films using the same electrolyte as that used for electrosynthesis shows that their electrochemical properties are mainly controlled by the anion. The influence of the electrolyte on the morphology and the conductivity of PSeT films has been analysed. We have demonstrated an anion effect that can be related to the size of the counter ion. Fourier transform infrared (FT-IR) spectra of polymer with various doping species have been obtained. The bands specific to each doping species are distinctly observable for the doped PSeT films.     

Templated polypyrrole electro-polymerization: Self-assembled bundles of bilayer membranes of amphiphiles and their actuation behavior

The electrochemical properties of conducting polymers are highly dependent on the microstructure. We report a method to produce specific microstructures of polypyrrole through electro-polymerization in the presence of the amphiphile N-{11-(2-hydroxyethyldimethylammonium)undecanoyl}-N,N′-dioctyl-l-glutamate, bromide, which forms supramolecular hydrogels with pyrrole in aqueous solution. These hydrogels were used as templates during polypyrrole electro-polymerization to give microstructures composed of the bundles of bilayer membranes. The highly porous nature of these films resulted in electrochemical properties superior to polypyrrole deposited under the same condition without use of an amphiphilic template. Analysis of the scan rate dependence on cyclic voltammogram reveals that the porous templated films facilitate fast diffusion of dopant ions. The actuation properties were also investigated in aqueous solutions containing sodium p-toluene sulfonate electrolyte. The strains displayed by the template polypyrrole films were twice those synthesized without the use of a template.     

Poly(vinyl alcohol)-colloidal silica composite membranes for fuel cells

The aim of this study is to develop an environmentally and friendly poly(vinyl alcohol) based low cost membrane with improved ionic conductivity, thermal and mechanical stability. In this work, the effect of colloidal silica content on membrane properties was investigated. Sulfosuccinic acid (SSA) was used as the sulfonating agent. In order to enhance the mechanical and ionic conduction properties, colloidal silica was used. The range of silica content in the membrane solution investigated was 5–20%. For the characterizations, the synthesized membranes were subjected to FT-IR, TGA, tensile strength analysis, water uptake, ion exchange capacity (IEC) and impedance measurements for proton conductivity. Synthesized membranes demonstrated high water uptake (up to 80%) without swelling, high ion exchange capacities was found to increase with increasing SSA content. The proton conductivity of CS doped membranes increased with increase in temperature and the temperature dependence showed significant change in the CS doped membranes. An increase in the values of the proton conductivity was driven by the mobility of free charges (free ions) as the temperature was increased. Addition of SSA and CS to the polymer matrix improved the thermal stability of the membranes. It was also discovered that membranes were in a composite structure and colloidal silica particles did not contribute to the structure of the polymer matrix at the molecular level. Mechanical durability of the membranes having SSA content above 15% decreased and these membranes showed a more fragile structure.     

Charge trapping in bilayers of conducting polymers under open circuit conditions: a protection of conducting polymer films from spontaneous charging/discharging

Spontaneous charging/discharging processes of polymers: polypyrrole and poly(N-methylpyrrole), doped with perchlorate (anion exchanging PPy and PMPy, respectively) and poly(4-styrenesulphonate) ions (cation exchanging PPy(PSS) and PMPy(PSS)) occurring in aqueous electrolyte solutions were studied using different electrochemical techniques. These reactions (oxidation of the polymer by dissolved oxygen and discharge of the polymer redox capacitance) are usually undesired processes leading to alteration of the charge accumulated in the polymer films. This paper points out that these processes can be significantly limited in polymer bilayers due to effect of charge trapping.     

Studies on the nonlinear optical properties of rf plasma polymerized aniline thin films by open aperture z-scan technique

Plasma polymerized polyaniline (PANI) thin films in their pristine and iodine doped forms were subjected to open aperture z-scan studies in order to investigate the nonlinear optical (NLO) properties of these materials. The investigations were carried out using a Q-switched resonant Nd:YAG laser at a wavelength of 532 nm for various fluences. The z-scan studies revealed that RF PANI thin films exhibit a saturable absorption (SA). Iodine doping modifies the NLO characteristics of these films substantially. These results qualify PANI thin films as potential materials for NLO materials. Investigations on the NLO properties of pristine (PANI) and iodine doped polyaniline (dPANI) thin films in its plasma polymerized form are reported for the first time.