Gel polymer electrolyte based on poly(acrylonitrile-co-styrene) and a novel organic iodide salt for quasi-solid state dye-sensitized solar cell

A gel polymer electrolyte based on poly(acrylonitrile-co-styrene) as polymer matrix and N-methyl pyridine iodide salt as I⁻ source was prepared. Controlling the concentration of polymer matrix of poly(acrylonitrile-co-styrene) at 17.5 wt.%, mixing the binary organic solvents mixture ethylene carbonate and propylene carbonate with 6:4 (w/w), and the concentration of N-methyl pyridine iodide and iodine with 0.5 and 0.05 M, respectively, the gel polymer electrolyte attains the maximum ionic conductivity (at 30 °C) of 4.63 mS cm⁻¹. Based on the gel polymer electrolyte, a quasi-solid state dye-sensitized solar cell was fabricated and its overall energy conversion efficiency of light-to-electricity of 3.10% was achieved under irradiation of 100 mW cm⁻².     

New highly proton-conducting membrane poly(vinylpyrrolidone)(PVP) modified poly(vinyl alcohol)/2-acrylamido-2-methyl-1-propanesulfonic acid (PVA-PAMPS) for low temperature direct methanol fuel cells (DMFCs)

A new type of chemically cross-linked polymer blend membranes consisting of poly(vinyl alcohol) (PVA), 2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPS) and poly(vinylpyrrolidone) (PVP) have been prepared and evaluated as proton conducting polymer electrolytes. The proton conductivity (σ) of the membranes was investigated as a function of cross-linking time, blending composition, water content and ion exchange capacity (IEC). Membranes were also characterized by FT-IR spectroscopy, thermogravimetric analysis (TGA), and the differential scanning calorimetry (DSC). Membrane swelling decreased with cross-linking time, accompanied by an improvement in mechanical properties and a small decrease in proton conductivity due to the reduced water absorption. The membranes attained 0.088 S cm⁻¹ of the proton conductivity and 1.63 mequiv g⁻¹ of IEC at 25±2 °C for a polymer composition PVA-PAMPS-PVP being 1:1:0.5 in mass, and a methanol permeability of 6.1×10⁻⁷ cm² s⁻¹, which showed a comparable proton conductivity to Nafion 117, but only one third of Nafion 117 methanol permeability under the same measuring conditions. The membranes displayed a relatively high oxidative durability without weight loss of the membranes (e.g. 100 h in 3% H₂O₂ solution and 20 h in 10% H₂O₂ solution at 60 °C). PVP, as a modifier, was found to play a crucial role in improving the above membrane performances.     

Novel amperometric glucose biosensor based on an ether-linked cobalt(II) phthalocyanine-cobalt(II) tetraphenylporphyrin pentamer as a redox mediator

The development of cobalt(II) phthalocyanine-cobalt(II) tetra(5-phenoxy-10,15,20-triphenylporphyrin), (CoPc-(CoTPP)₄) pentamer as a novel redox mediator for amperometric enzyme electrode sensitive to glucose is described. A glassy carbon electrode (GCE) was first modified with the pentamer, then followed by the immobilization onto the GCE-CoPc-(CoTPP)₄ with glucose oxidase (GOx) through cross-linking with glutaraldehyde in the presence of bovine serum albumin (BSA) and Nafion^® cation-exchange polymer. The proposed biosensor displayed good amperometric respose charateristics to glucose in pH 7.0 PBS solution; such as low overpotentials (+400 mV versus Ag|AgCl), very fast amperometric response time (∼5 s), linear concentration range extended up to 11 mM, with 10 μM detection limit. The biosensor exhibited electrochemical Michaelis-Menten kinetics and showed an average apparent Michaelis-Menten constant (K^′M) of 14.91 ± 0.46 mM over a storage period of 2 weeks.     

Influence of solvent on the poly (acrylic acid)-oligo-(ethylene glycol) polymer gel electrolyte and the performance of quasi-solid-state dye-sensitized solar cells

The influence of solvents on the property of poly (acrylic acid)-oligo-(ethylene glycol) polymer gel electrolyte and photovoltaic performance of quasi-solid-state dye-sensitized solar cells (DSSCs) were investigated. Solvents or mixed solvents with large donor number enhance the liquid electrolyte absorbency, which further influences the ionic conductivity of polymer gel electrolyte. A polymer gel electrolyte with ionic conductivity of 4.45 mS cm⁻¹ was obtained by using poly (acrylic acid)-oligo-(ethylene glycol) as polymer matrix, and absorbing 30 vol.% N-methyl pyrrolidone and 70 vol.% γ-butyrolactone with 0.5 M NaI and 0.05 M I₂. By using this polymer gel electrolyte coupling with 0.4 M pyridine additive, a quasi-solid-state dye-sensitized solar cell with conversion efficiency of 4.74% was obtained under irradiation of 100 mW cm⁻² (AM 1.5).     

Influence of molecular weight of PEG on the property of polymer gel electrolyte and performance of quasi-solid-state dye-sensitized solar cells

A new kind of polymer gel electrolyte based on poly(acrylic acid)-poly(ethylene glycol) (PAA-PEG) hybrid was synthesized. The factor of molecular weight of PEG in the hybrid plays an important role in determining the liquid electrolyte absorbency of the hybrid and ionic conductivity of the polymer gel electrolyte, sequentially affects the photovoltaic performance of quasi-solid-state dye-sensitized solar cells. Using the hybrid with PEG molecular weight of 20,000, a polymer gel electrolyte with liquid electrolyte absorbency of 6.9 g g⁻¹ and ionic conductivity of 5.35 mS cm⁻¹ was obtained. Based on the polymer gel electrolyte, a quasi-solid-state dye-sensitized solar cell with conversion efficiency of 5.25% was achieved under irradiation of AM 1.5, 100 mW cm⁻².     

Cross-linking polymerization of acrylic acid in supercritical carbon dioxide

Cross-linking polymerization of acrylic acid in supercritical carbon dioxide (scCO₂) was studied in a batch reactor at 50 °C and 207 bar with either triallyl pentaerythritol ether or tetraallyl pentaerythritol ether as the cross-linker and with 2,2′-azobis(2,4-dimethyl-valeronitrile) as the free radical initiator. All polymers were white, dry, fine powders. Scanning electron microscopy showed that the morphology of the polymer particles was not affected by cross-linking. As the cross-linker concentration was increased, the polymer glass transition temperature first decreased, then increased. Water-soluble and water-insoluble polymers were synthesized by adjusting the cross-linker concentration. Viscosity measurements showed that the polymer thickening effect strongly depended on the degree of cross-linking. Finally, cross-linking polymerization of acrylic acid in scCO₂ was carried out in a continuous stirred tank reactor. The use of cross-linker decreased the monomer conversion in this system.     

Radically crosslinked branched poly(N-allylethylenimine) with lithium triflate as a solid state polymer electrolyte

Branched poly(N-allylethylenimine) (BPAEI), a solid state polymer electrolyte host, was synthesized by allylation of branched poly(ethylenimine) (BPEI). Allylation was essentially complete with the 2 and 1° nitrogen atoms of BPEI being mono-allylated and di-allylated, respectively, and with little or no quaternization. BPAEI can be radically cross-linked with and without lithium trifluoromethanesulfonate (LiTf) present to form free-standing, homogeneous, minimally hygroscopic films. BPAEI has a glass transition temperature (T_g) of −65 °C, as measured by differential scanning calorimetry (DSC), which increases with the concentration of initiator upon cross-linking using V-50 (2,2-azobis(2-amidino-propane) dihydrochloride) to −15 °C at a 10:1 nitrogen to initiator molar ratio (N:initiator). BPAEI with 20:1 N:Li⁺ (molar ratio) LiTf has a T_g of −48 °C, which increases with the concentration of radical initiator upon cross-linking using V-50 to 3 °C at 10:1 N:initiator. At compositions near 60:1 N:initiator, an unusual decrease in the rate at which T_g changes with cross-linking was observed, both with and without LiTf present, indicating that some undefined morphological changes occur. The effect of this morphological change resulted in the highest Ac conductivities at 60:1 N:initiator for all LiTf concentrations studied. At 20:1 N:Li⁺ LiTf and 60:1 N:initiator, the room temperature Ac conductivity was 1×10⁻⁸ S/cm which increased to 1×10⁻⁵ S/cm at 80 °C, the highest conductivity observed in the concentration ranges studied. Infrared spectroscopy (IR) showed that the concentrations of the individual ionic species present were largely independent of either LiTf concentration or cross-linking density, suggesting that changes in ion mobility, likely resulting from morphological changes, substantially control the ionic conductivity.     

Preparation and reversible photo-crosslinking/photo-cleavage behavior of 4-methylcoumarin functionalized hyperbranched polyester

A novel hyperbranched polymer endcapped with 4-methylcoumarin group (MCTH40) was prepared via thiol-ene addition reaction of thiol-modified hyperbranched polyester (fully thioglycolic acetate of Boltorn™ H40, TAH40) with a vinyl monomer (7-(4-vinyl-benzyloxyl)-4-methylcoumarin, VBMC), and characterized with ¹H NMR and FT-IR spectroscopies. Its reversible photo-crosslinking/photo-cleavage behavior was evaluated based on the UV-vis spectroscopic analysis, and compared with the linear polymer, poly(7-(4-vinyl-benzyloxyl)-4-methylcoumarin (PVBMC)). The absorbance at 319 nm in the UV-vis spectrum gradually decreased under UVA irradiation (λ_max = 365 nm), and then rapidly recovered under UVC irradiation (λ_max = 254 nm). The fluorescence intensity of MCTH40 (λ_max = 469 nm) recovered to 85.2% of original level after photo-cleavage under UVC irradiation, higher than 83.5% of PVBMC (λ_max = 472 nm). The UV-vis analysis results indicated that MCTH40 performs more rapid photo-response than linear PVBMC under the same conditions. Furthermore, the average doses of UVA irradiation for the maximum degree of photo-crosslinking were 22.08 J cm⁻² for MCTH40 and 28.29 J cm⁻² for PVBMC. The average UVC doses of complete photo-cleavage were 9.44 J cm⁻² for MCTH40 and 9.58 J cm⁻² for PVBMC. The GPC analysis indicated that the average molecular weight and its PDI of MCTH40 showed a slight increase after three reversible cycles.     

Poly(vinyl alcohol)-based polymer electrolyte membranes for direct methanol fuel cells

We have prepared polymer electrolyte membranes (PEMs) from poly(vinyl alcohol) (PVA) and modified PVA polyanion containing 2 or 4 mol% of 2-methyl-1-propanesulfonic acid (AMPS) groups as a copolymer. The PEMs of various AMPS content and cross-linking conditions were prepared to determine the effect of AMPS content and cross-linking conditions on PEM properties. Proton conductivity and permeability of methanol through the PEMs increased with increasing AMPS content, C_AMPS, and with decreasing cross-linker concentration, C_GA, because of the increase in the water content. The permeability coefficient of methanol through the PEM prepared under the conditions of C_AMPS = 2.7 mol% and C_GA = 0.35 vol% was about 30 times lower than that of Nafion^®117 under the same measurement conditions. The proton permselectivity of the PEM, which is defined as the ratio of the proton conductivity to the permeability coefficient of methanol, gave a maximum value of 66 × 10³ S cm⁻³ s. The value is about three times higher than that of Nafion^®117.     

A laccase-glucose oxidase biofuel cell prototype operating in a physiological buffer

Here we report on the design and study of a biofuel cell consisting of a glucose oxidase-based anode (Aspergillus niger) and a laccase-based cathode (Trametes versicolor) using osmium-based redox polymers as mediators of the biocatalysts’ electron transfer at graphite electrode surfaces. The graphite electrodes of the device are modified with the deposition and immobilization of the appropriate enzyme and the osmium redox polymer mediator. A redox polymer [Os(4,4′-diamino-2,2′bipyridine)₂(poly{N-vinylimidazole})-(poly{N-vinylimidazole})₉Cl]Cl (E⁰′ = −0.110 V versus Ag/AgCl) of moderately low redox potential is used for the glucose oxidizing anode and a redox polymer [Os(phenanthroline)₂(poly{N-vinylimidazole})₂-(poly{N-vinylimidazole})₈]Cl₂ (E⁰′ = 0.49 V versus Ag/AgCl) of moderately high redox potential is used at the dioxygen reducing cathode. The enzyme and redox polymer are cross-linked with polyoxyethylene bis(glycidyl ether). The working biofuel cell was studied under air at 37 °C in a 0.1 M phosphate buffer solution of pH range 4.4-7.4, containing 0.1 M sodium chloride and 10 mM glucose. Under physiological conditions (pH 7.4) maximum power density, evaluated from the geometric area of the electrode, reached 16 μW/cm² at a cell voltage of 0.25 V. At lower pH values maximum power density was 40 μW/cm² at 0.4 V (pH 5.5) and 10 μW/cm² at 0.3 V (pH 4.4).     

The role of gel electrolyte composition in the kinetics and performance of dye-sensitized solar cells

Gel-type polymer electrolytes based on the copolymer poly(ethylene oxide-co-epichlorohydrin) and the plasticizer γ-butyrolactone (GBL) were optimized and applied in dye-sensitized solar cells. The plasticizer added to the electrolyte allowed the dissolution of a higher concentration of salt, reaching conductivity values close to 1 mS cm⁻¹ for the sample prepared with 30 wt% of LiI. Raman spectroscopy confirmed polyiodide formation in the electrolyte when the salt concentration exceeds 7.5 wt%, introducing a significant contribution of electronic conductivity in the electrolyte. The devices were characterized under AM 1.5 conditions and the I-V curves were fitted using a two diode equation. Increasing the concentration of LiI-I₂ accelerates dye cation regeneration as measured by transient absorption spectroscopy; however, it also contributes to an increase in the dark current of the cell by one order of magnitude. The best performance was achieved for the solar cell prepared with the electrolyte containing 20 wt% of LiI, with efficiencies of 3.26% and 3.49% at 100 and 10 mW cm⁻² of irradiation, respectively.     

Influence of ionic additives NaI/I2 on the properties of polymer gel electrolyte and performance of quasi-solid-state dye-sensitized solar cells

The ionic additives NaI/I₂ in polymer gel electrolyte not only provide cations, but also affect the liquid electrolyte absorbency of the poly(acrylic acid)-poly(ethylene glycol) hybrid, which results in the change of ionic conductivity of polymer gel electrolyte and the photovoltaic performance of quasi-solid-state dye-sensitized solar cell. With the optimized components of liquid electrolyte containing 0.5 M NaI, 0.05 M I₂, 0.4 M pyridine, 70 vol.% γ-butyrolactone and 30 vol.% N-methylpyrrolidone, a 4.74% power conversion efficiency of quasi-solid-state dye-sensitized solar cell was obtained under 100 mW cm⁻² (AM 1.5) irradiation.     

A polyblend electrolyte (PVP/PEG+KI+I2) for dye-sensitized nanocrystalline TiO2 solar cells

A novel polyblend electrolyte consisting of KI and I₂ dissolved in a blending polymer of polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG) was prepared. The formation of ⁻I₃ in the polymer electrolyte was confirmed by X-ray photoelectron spectroscopy (XPS) characterization. Due to the coordinating and plasticizing effect by PVP, the ionic conductivity of the polyblend electrolyte is enhanced. The highest ionic conductivity of 1.85 mS cm⁻¹ for the polyblend electrolyte was achieved by optimizing the compositions as 40 wt.% PVP + 60 wt.% PEG + 0.05 mmol g⁻¹ I₂ + 0.10 mmol g⁻¹ KI. Based on the polyblend electrolyte, a DSSC with fill factor of 0.59, short-circuit density of 9.77 mA cm⁻², open-circuit voltage of 698 mV and light-to-electricity conversion efficiency of 4.01% was obtained under AM 1.5 irradiation (100 mW cm⁻²).     

Synthesis and characterization of conducting and non-conducting polymers of sodium 2,4,6-trichlorophenolate by microwave initiation

A novel synthesis of poly(dichlorophenylene oxide) and a conducting polymer were achieved simultaneously from 2,4,6-trichlorophenol in a very short time, using microwave energy. The characterizations of poly(dichlorophenylene oxide) and the conducting polymer were performed by DSC, TGA, elemental analysis, FTIR, ¹H and ¹³C NMR, SEM, MS and X-ray diffraction spectrometer analyses. The combined molecular weight of the polymer, 1.8×10⁴, was determined by using viscometry measurement. Poly(dichlorophenylene oxide) displaces selectivity in the favor of mainly 1,2-addition structure. The optimum conditions for the polymer and the conducting polymer synthesis were 70 W for 5 min and 100 W for 1 min, respectively. The direct synthesis of highly conducting polymer, with the conductivity of 0.3 S cm⁻² were achieved in the absence of applied doping process in a very short time sequence. Conductivity-temperature relation was examined for the conducting polymer.     

Optimization of two step karanja biodiesel synthesis under microwave irradiation

The free fatty acid of crude karanja oil (Pongamia pinnata) was reduced and biodiesel was synthesized from pretreated oil under microwave irradiation. The process variables such as irradiation time, methanol-oil ratio and sulfuric acid concentration for pretreatment step; irradiation time, methanol-oil ratio and KOH concentration were optimized through the Box-Behnken experimental design. The free fatty acid of crude karanja oil was reduced to 1.11 ± 0.07% with an optimal combination of 190 s irradiation time (180 W), 33.83 (w/w)% methanol-oil ratio and 3.73 (w/w)% sulfuric acid concentration. An optimal combination of 150 s irradiation time, 33.4 (w/w)% methanol-oil ratio and 1.33 (w/w)% KOH concentration yielded 89.9 ± 0.3% biodiesel. The model was validated by conducting experiments at optimal design conditions. The present work confirmed that the microwave energy has a significant effect on esterification and transesterification reaction.     

The electrochemical redox processes in methacrylate-based polymer electrolytes II. - Study on microelectrodes

The electrochemical behaviour of ferrocene was studied in different gel polymer electrolytes based on methyl, ethyl and 2-ethoxyethyl methacrylate and compared to the liquid aprotic solution (propylene carbonate). Voltammetric and chronoamperometric measurements on microelectrodes were conducted in order to describe the qualitative as well as quantitative behaviour of ferrocene in different conditions. Heterogeneous electron-transfer rate constants and diffusion coefficients of ferrocene in polymer electrolytes were estimated to be 1.1-7.8 × 10⁻³ cm s⁻¹ and 4-13 × 10⁻⁸ cm² s⁻¹ depending on the electrolyte composition. The influence of the polymer polarity, ferrocene concentration and level of polymer cross-linkage on the kinetics of ferrocene oxidation and its transport was discussed. The electrolytes with poly(2-ethoxyethyl methacrylate) exhibit the highest ionic conductivity (2-4 × 10⁻⁴ S cm⁻¹) as well as diffusion coefficient of ferrocene (1.3 × 10⁻⁷ cm² s⁻¹) in their structure.     

Rapid formation of high-quality self-assembled monolayers of dodecanethiol on polycrystalline gold under ultrasonic irradiation

Self-assembled monolayers of dodecanethiol (C₁₂SH-SAMs) on polycrystalline gold were prepared under ultrasonic irradiation at 100 W (the actual ultrasonic power intensity is about 0.1 W cm⁻² including the heat loss) for different time and investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV experiments show that the differential capacitance C_d values of the C₁₂SH-SAM prepared under ultrasonic irradiation at 100 W (0.1 W cm⁻²) for 15 min are independent of the scan rate, the thickness d value of this monolayer is 17.5 Å, the tilt angle φ value of the molecules in this monolayer from the gold surface normal was calculated to be 30° and the difference value of the current density at −0.2 and 0.5 V (Δi_p) is only 0.69 μA cm⁻². From the EIS experiments, we find that the phase angle value at 1 Hz Φ_1 Hz of the C₁₂SH-SAM prepared under ultrasonic irradiation at 100 W (0.1 W cm⁻²) for 15 min is 89°, the charge transfer resistance R_ct value of this monolayer is 1.40 × 10⁶ Ω cm² and the surface coverage θ value of this monolayer was calculated to be 99.997% from R_ct. These results indicate that the C₁₂SH-SAM of almost defect-free structure and very low ionic permeability can be formed under ultrasonic irradiation at 100 W (0.1 W cm⁻²) in a short time (15 min).     

Delaying the onset of macrogelation for the synthesis of branched and star-like polymers via conventional free-radical polymerisation: Binary solvent effects and incorporation of surfmers

It is known that the preferential solvation and conformation of a polymer in a solvent mixture are functions of the polymer's molecular weight and the solvent qualities. This paper demonstrates that these relationships can be exploited to delay the onset of macrogelation for branched poly(methyl methacrylate/ethylene glycol dimethacrylate) (p(MMA/EGDMA)) polymers and star-like poly(methyl acrylate/ethylene glycol dimethacrylate) (p(MA/EGDMA)) polymers synthesised via conventional free-radical polymerisation (CFRP) in a binary solvent mixture (consisting of a good solvent and a precipitant for the polymer). The gelation limits of the MMA/EGDMA and MA/EGDMA polymerisations in a methyl ethyl ketone (MEK)/heptane binary solvent mixture can be extended to regions of higher monomer concentration with increases in polymer yield between 13 and 50 ± 5 w/w% for the p(MMA/EGDMA) system and between 8 and 19 ± 6 w/w% for the p(MA/EGDMA) system across the gelation boundary. Thus, a facile method of increasing the concentration of batch reaction mixtures by the simple addition of small amounts of precipitant into the reaction solutions is presented. Furthermore, the gelation limits of both polymerisation systems in the binary solvent mixtures were further extended with increases in polymer yield between 11 and 17 ± 4%w/w for the p(MMA/ODA/EGDMA) system and between 8 and 20 ± 5%w/w for the p(MA/VS/EGDMA) system by the respective incorporation of octadecyl acrylate (ODA) and vinyl stearate (VS) surfmers into the polymers, demonstrating the application of steric hinderance to shield the propagating polymers from excessive cross-linking reactions.     

A novel potentiometric sensor for promethazine based on a molecularly imprinted polymer (MIP): The role of MIP structure on the sensor performance

A novel potentiometric sensor based on a molecularly imprinted polymer (MIP) for determination of promethazine (PMZ) was prepared. Promethazine MIP particles were prepared and dispersed in 2-nitrophenyloctyl ether and then embedded in a polyvinyl chloride matrix. The effect of the monomers type on the sensor performance was investigated, and an important role for this parameter was shown. It was shown that the membrane electrode with a MIP prepared by vinylbenzene and divinylbenzene had a better performance in comparison to membrane electrodes containing MIPs prepared with methacrylic acid-ethylene glycol dimethacrylate or vinylbenzene-ethylene glycol dimethacrylate. After optimization, the membrane electrode constructed with a MIP of vinylbenzene-divinylbenzene exhibited a Nernstian response (31.2 ± 1.0 mV decade⁻¹) over a wide concentration range, from 5.0 × 10⁻⁷ to 1.0 × 10⁻¹ M, with a low detection limit of 1.0 × 10⁻⁷ M and a response time of ∼50 s. The method has the requisite accuracy, sensitivity and precision to assay PMZ in syrup samples and biological fluids.     

Synergistic gelation of solutions of isotactic polypropylene and bis-(3,4-dimethyl benzylidene) sorbitol and its use in gel-processing

We report the synergistic, rapid gelation of solutions of isotactic polypropylene (i-PP) and the nucleating agent 1,3:2,4-bis-(3,4-dimethyl benzylidene) sorbitol (DMDBS) in decalin. Cooling to room temperature of a solution comprising, for instance, 3.0 wt% of a moderately high molecular weight i-PP (M_v=1.3×10⁶ g/mol) and as little as 0.0075 wt% DMDBS (0.25 wt% based on the polymer) resulted in the fast formation of highly ductile gels. In reference experiments without DMDBS, often ‘mud-cracked’, brittle polymer films were obtained, and decaline solutions of DMDBS alone at the above concentration did not form macroscopically coherent gels. In the present work we employed this useful occurrence for gel-processing/drawing of i-PP, yielding material with Young's moduli of 35 GPa, tensile strengths of approximately 1 GPa and melting temperatures measured for constrained samples as high as 228 °C.