The effect of electrolyte additives on the rate performance of hard carbon anode at low temperature for lithium-ion capacitor

Lithium-ion capacitor (LIC), which combines the advantages of lithium-ion battery (LIB) and electrical double layer capacitor (EDLC), has a rapid development during last decade, however, the poor low temperature performance still limits its application. In this paper, three electrolyte additives including vinylene carbonate (VC), fluoroethylene carbonate (FEC) and 1,3,2-dioxathiolane 2,2-dioxide (DTD) have been utilized and their effects on the rate performance of hard carbon (HC) anode of LIC at various temperatures ranging from 25 °C to ?40 °C have been well evaluated. The cell containing FEC shows the best rate performance at various temperatures and has the charge and discharge capability even at ?40 °C. For HC anode, the charge transfer impedance (R_CT) increases exponentially at low temperature, while the equivalent series resistance (Rs) and the impedance of solid electrolyte interface (SEI) increase relatively few. At low temperatures, the effect of FEC may be mainly reflected in its effect on the charge transfer process.     

Configurational stereoselectivity in the nucleophilic substitution of poly(vinyl chloride) with sodium thiophenate: NMR study and Monte-Carlo simulation of the reaction

The nucleophilic substitution of the chlorine atoms of poly(vinyl chloride) with sodium thiophenate is assumed to obey an SN2 mechanism with inversion of configuration and a steric control according to which reactivities R of the triads follow the order R_mm > R_mr ? R_rr. Such a reaction cannot be described by simple differential equations, but a Monte Carlo simulation, first generating a random Bernouillian chain and then simulating random attack of the chain by the reactant according to the triad reactivities, allows a good agreement with the experimental results of both the kinetics of a reaction carried out in cyclohexanone solution at 40°C and the evolution of the ¹³C and ¹H NMR spectra of the tertiary carbon atoms, assuming the following parameters: Bernouillian probability for a meso placement in the initial chain: 0.431; relative reactivities of the mm, mr and rm, rr triads: 1, 0.5, and 0., respectively. The agreement is excellent until the reaction is about three-quarters complete; this shows a limiting level of about 60% substitution. Better agreement can be obtained up to the limit, if a secondary process of steric control by the substituant in a partially substituted mr triad is assumed. Other possibilities for that secondary process are discussed.     

Photoinitiated homopolymerization and copolymerization of furfuryl methacrylate and N-vinylpyrrolidone

The study of the homo- and copolymerization of furfuryl methacrylate ( F ) and vinylpyrrolidone ( P ) in bulk, initiated by the photoactivation of AIBN at low temperatures (0 and 40°C), is described. The kinetic diagrams for the homopolymerization of F and P were obtained following the evolution of the heat of reaction by DSC, and revealed the autoacceleration and the vitrification effects on the polymerization rate. The influence of oxygen in the photoinitiated polymerization was analyzed by determining the steady-state concentration of oxygen from the kinetic data obtained for polymerizations performed out in the presence and absence of oxygen. The results obtained indicate that P is more sensitive than F to the presence of oxygen in free radical polymerization. The photoinitiated copolymerization process is little affected by the concentration of monomers, giving similar R_p and θ_m values for both systems. However, at low polymerization temperature 0°C non-crosslinked copolymers are obtained, whereas at a temperature of 40°C, the copolymers prepared at conversion higher than 20 mol % become crosslinked as a result of the active participation of the furfuryl ring in the polymerization process at this temperature. © 1996 John Wiley & Sons, Inc.     

Acceleration of the cationic polymerization of an epoxy with hexanediol

Thin films of 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexane carboxylate were UV irradiated (1.1 J cm^-2) under isothermal conditions ranging from 0 to 50°C. Under these conditions the polymerization advanced quickly but only to a conversion level of less than 10% before the reaction rate slowed by more than an order of magnitude. This drop off in rate was not caused by the glass transition temperature, T _g, reaching or exceeding the reaction temperature, T _rxn, since the epoxide's T _g remained at least 40°C below T _rxn. Raising the sample temperature above 60°C caused a sharp increase in the conversion level. At 100°C conversion exceeds 80% and the ultimate T _g approaches 190°C. The addition of 10 mass% 1,6-hexanediol, HD, to the epoxy caused the conversion at room temperature to quintuple over the level obtained without the alcohol present. The heat liberated from this alcohol epoxy blend during cure on a UV conveyor belt system caused the sample's temperature to increase by about 100°C above ambient whereas the epoxy alone under these conditions only experienced a modest temperature rise of about 26°C. If the amount of HD in the blend is increased above 10% the heat of reaction at 23°C decreases due to HD being trapped in a nonreactive crystalline phase. Boosting reaction temperatures above 50°C melts the HD crystals and yields significantly improved conversion ratios. As the level of alcohol blended with the epoxy is raised its ultimate T _g is lowered and when the concentration of alcohol in the blend nears 30 mass%T _g drops below room temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Desorption behavior of a surfactant in a linear low‐density polyethylene blend at elevated temperatures

The desorption behavior of a surfactant in a linear low‐density polyethylene (LLDPE) blend at elevated temperatures of 50, 70, and 80 °C was studied with Fourier transform infrared spectroscopy. The composition of the LLDPE blend was 70:30 LLDPE/low‐density polyethylene. Three different specimens (II, III, and IV) were prepared with various compositions of a small molecular penetrant, sorbitan palmitate (SPAN‐40), and a migration controller, poly(ethylene acrylic acid) (EAA), in the LLDPE blend. The calculated diffusion coefficient (D) of SPAN‐40 in specimens II, III, and IV, between 50 and 80 °C, varied from 1.74 × 10^?11 to 6.79 × 10^?11 cm²/s, from 1.10 × 10^?11 to 5.75 × 10^?11 cm²/s, and from 0.58 × 10^?11 to 4.75 × 10^?11 cm²/s, respectively. In addition, the calculated activation energies (E_D) of specimens II, III, and IV, from the plotting of ln D versus 1/T between 50 and 80 °C, were 42.9, 52.7, and 65.6 kJ/mol, respectively. These values were different from those obtained between 25 and 50 °C and were believed to have been influenced by the interference of Tinuvin (a UV stabilizer) at elevated temperatures higher than 50 °C. Although the desorption rate of SPAN‐40 increased with the temperature and decreased with the EAA content, the observed spectral behavior did not depend on the temperature and time. For all specimens stored over 50 °C, the peak at 1739 cm^?1 decreased in a few days and subsequently increased with a peak shift toward 1730 cm^?1. This arose from the carbonyl stretching vibration of Tinuvin, possibly because of oxidation or degradation at elevated temperatures. In addition, the incorporation of EAA into the LLDPE blend suppressed the desorption rate of SPAN‐40 and retarded the appearance of the 1730 cm^?1 peak. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1114–1126, 2004     

Ultra‐high molecular weight poly(ε‐caprolactone) by means of diphenyl bismuth bromide

Diphenyl bismuth bromide (Ph₂BiBr) allows for polymerizations of ε‐caprolactone in bulk at temperatures as low as 40 °C. Time conversion curves indicate a lower reactivity than tin(II) 2‐ethyl hexanoate (SnOct₂) plus alcohol at 120 °C and also at 60 °C. Ph₂BiBr also proved to be less reactive than Ph₂BiOEt, but more reactive than BiBr₃ and Bi(III)n‐hexanoate. Small amounts (≤1 wt %) of cyclic oligoester were detectable by MALDI‐TOF mass spectrometry even at a polymerization temperature of 40 °C. The molar masses depend on the monomer–initiator ratio (M/I) but not in a simple parallel manner. With M/I = 600/1 number average molecular weights (M_ns, corrected values) around 500 kDa were obtained. Even at low M/Is high molar mass polylactones were found and CH₂Br endgroups were not detectable. However, upon addition of tetra(ethylene glycol) the coinitiator was completely incorporated yielding telechelic polylactones and the molar mass increased with the monomer–coinitiator ratio. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 851–859, 2008     

Ignition limits of hydrogen–methane–air mixtures over metallic Rh at a pressure of 1–2 atm

The ignition temperatures and effective activation energies of the ignition limits of mixtures (40–70% H₂ + 60–30% CH₄)_stoich + air over Rh were experimentally determined at a pressure of 1 atm in the temperature range 20–300 °C. Over an ignition-treated Rh surface, the ignition temperature of a mixture of 70% H₂ + 30% methane + air is 62 °C. This indicates the potential of using Rh to markedly lower the ignition temperature of fuels based on hydrogen–methane mixtures.     

Heterobimetallic complexes containing iron (II) and hexa-coordinated organosilicon

Heterobimetallic complexes of the type R₂Si(HL)Cl₂ and R₂SiL₂ (where R = Me, Et, Ph; L = ferrocenyl aroylhydrazone) have been synthesized at 40 °C to 50 °C and at room temperature (25 °C), respectively, and characterized by elemental analysis, molar conductance, infrared and NMR (¹H, ¹³C and ²⁹Si) spectral data. The ligands behave as bidentate, coordinating through the azomethine nitrogen and the oxygen in the amidic and the imidic acid forms of the ligand at low temperature and at room temperature, respectively. The ligands and their organosilicon complexes have been evaluated for the antifungal activity against Alternaria alternata, Fusarium oxysporum and Rhizoctonia solani, as well as antibacterial activity against gram negative, Escherichia coli and gram positive, Bacillus subtilis, at 28 °C. Organosilicon complexes of ferrocenyl aroylhydrazone were found to be more potent than the parent ligands.      

Synthesis of ultrahigh molecular weight poly(N‐vinylcarbazole) with a high yield using low‐temperature heterogeneous‐solution polymerization

To prepare ultrahigh molecular weight (UHMW) poly(N‐vinylcarbazole) (PVCZ) with a high conversion, I heterogeneous‐solution‐polymerized N‐vinylcarbazole (VCZ) in methanol/tertiary butyl alcohol (TBA) at 25, 35, and 45 °C with a low‐temperature initiator, 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN), and I investigated the effects of the polymerization conditions on the polymerization behavior and molecular parameters of PVCZ. A low‐polymerization temperature with ADMVN, a heterogeneous system with methanol, and a low chain transfer with TBA proved to be successful in obtaining PVCZ of UHMW [weight‐average molecular weight (M_w) > 3,000,000] and high conversion (>80%) with a smaller temperature rise during polymerization but still of free‐radical polymerization by an azoinitiator. The polymerization rate of VCZ in methanol/TBA at 25 °C was proportional to the 0.97 power of the ADMVN concentration, indicating a heterogeneous nature for the polymerization. The molecular weight was higher and the molecular weight distribution was narrower with PVCZ polymerized at lower temperatures. For PVCZ produced in methanol/TBA at 25 °C with an ADMVN concentration of 0.0001 mol/mol of VCZ, an M_w of 3,230,000 was obtained, with a polydispersity index of 2.4. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 539–545, 2001     

Alkoxyamine‐mediated “living” radical polymerization: MS investigation of the early stages of styrene polymerization initiated by cumyl‐TEISO

A new series of 1,1,3,3‐tetraethylisoindoline‐2‐oxyl (TEISO)‐based alkoxyamines was prepared. The half‐lives for thermal dissociation indicated that the most sterically congested cumyl‐TEISO alkoxymine had the greatest potential as an initiator for the polymerization of monomers at lower temperatures. The polymerization of styrene at 110 °C gave a linear evolution of M_n with conversion in the early stages. Further evidence for the “living” nature was given by the polydispersities of the polymers that remained low (M_w/M_n = 1.13–1.27) throughout the polymerization (up to 80% conversion). No polymer was formed for the styrene system in a reasonable time below 100 °C. High‐performance liquid chromatographic/mass spectrometric investigations of the distribution of trapped oligomers containing one to nine monomer units formed at 60 °C revealed that the trapping of oligomeric cumyl–styryl radicals by TEISO is irreversible at this temperature. Methyl methacrylate polymerized with cumyl‐TEISO at 60–70 °C, although the initial high rates of polymerization soon decreased to zero at low conversions (10–15%), and the high polydispersities (M_w/M_n = 1.42–1.73) indicated significant side reactions. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1232–1241, 2001     

Influence of the mobility of oxygen on the reactivity of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> perovskites in methane oxidation

Radically different dependences of the activity of La_{1 − x} Sr _x MnO₃ (x = 0−0.5) perovskites in methane oxidation on the degree of substitution of strontium for lanthanum are observed for low and high temperatures. Unsubstituted LaMnO₃ exhibits the highest activity in the temperature range from 300 to 500°C, while the sample with the maximum degree of substitution (La_0.5Sr_0.5MnO₃) shows the highest activity at higher temperatures of 700–900°C. In the low temperature region, the activity of La_{1t - x} Sr _x MnO₃ is determined by the amount of weakly bound (overstoichiometric) oxygen, which is formed in cation-deficient lattices and is characterized by a thermal desorption peak with T _max = 705°C. At higher temperatures (800–900°C), the strongly bound oxygen of the catalyst lattice is involved in the formation of the reaction products under both unsteady- and steady-state conditions. As a consequence, the catalytic activity in methane oxidation correlates with the apparent rate constant of oxygen diffusion in the oxide bulk.     

Effects of humidity and temperature on the electrochemical activities of H2/O2 PEMFCs using hybrid membrane electrolytes

Electrochemical characteristics of single cell performances at various humidity conditions and constant temperatures of 40?100 °C using membrane electrode assemblies (MEAs) were studied. The MEAs consist of alternative proton-conducting hybrid membrane electrolyte and noble Pt/C catalyst for the H₂/O₂ proton exchange membrane fuel cells (PEMFCs). The function of humidity on the cell performances was investigated at larger current density values of 501 mA cm^?2 and constant cell temperatures of 80 and 90 °C and the relative humidity of 100 %. The power density value of 400 mW cm^?2 was obtained when the same MEA at similar operating conditions was used. The effects of temperature on the single cell performances were investigated at various temperature ranges of 40–100 °C and constant relative humidity of 50, 70, and 100 %. The maximum current density and power density values of about 600 mA cm^?2 and 160 mW cm^?2, respectively, were obtained at 90 °C with 100 % RH. The results were compared with the reported results of Nafion membrane and similar hybrid membranes operating at low temperatures for H₂/O₂ fuel cells. Finally, the results provided an alternative proton-conducting electrolyte as promising candidate for low/intermediate temperature operating H₂/O₂ fuel cells.     

Morphology of polylactic acid crystallized during annealing after uniaxial deformation

Uniaxial deformation of amorphous L -polylactic acid films was performed at two different temperatures at which thermal degradation was minimal, 70 °C or T_g + 10 and 90 °C or T_g + 30. Samples were annealed postdeformation for long times (either 15 or 45 min) to approach equilibrium conditions. Samples deformed and annealed at 70 °C showed low crystallinity and poor crystalline order or crystal size, as determined by wide-angle X-ray diffraction. At 90 °C, high crystallinity and order parameters were observed. In addition, once the oriented chains had crystallized at this temperature, nonoriented chains also underwent crystallization, and a small fraction of nonordered crystal phase was therefore observed after long annealing times. These observations are explained on the basis of different morphologies in samples drawn at the two temperatures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Copolymerization of styrene with maleic anhydride initiated by thiol compounds

Copolymerization of styrene (ST) with maleic anhydride (MAH) initiated by thiol compound was investigated under various conditions. The kinetics of copolymerization of ST with MAH initiated by p-toluenethiol (pTT) was studied in dioxane in the temperature range of 25–60°C, and the rates (R_p) of copolymerization and activation energy were determined. R_p was found to depend on [pTT],^0.6 ([ST] + [MAH])^2.7. The overall energy of activation was 10.8 kcal/mol in the temperature range of 25–60°C. A mechanism involving the formation of a complex between MAH and pTT the decomposition of which yields the initial radical is suggested.     

Temperature‐dependent desorption of surfactants in LLDPE blend films

The temperature‐dependent desorption behavior of surfactants in linear low‐density polyethylene (LLDPE) blend films was studied with Fourier transform infrared spectroscopy at 25, 40, and 50 °C. The LLDPE/low‐density polyethylene blend was 70/30. Three different specimens (labeled II, III, and IV) were prepared with various compositions of the surfactant, sorbitan palmitate (SPAN‐40), and the migration controller, poly(ethylene acrylic acid) (EAA). The calculated diffusion coefficients of SPAN‐40 in specimens II, III, and IV at 25, 40, and 50 °C varied from 9.6 × 10⁻¹² to 17.4 × 10⁻¹² cm²/s, from 5.5 × 10⁻¹² to 11.0 × 10⁻¹² cm²/s, and from 3.1 × 10⁻¹² to 5.8 × 10⁻¹² cm²/s, respectively. In addition, the activation energies of specimens II, III, and IV measured between 25 and 50 °C were 18.74, 19.42, and 20.14, respectively. Hence, the desorption rate of the surfactant increased with the temperature and decreased with an addition of EAA, but the activation energy increased with EAA. The diffusion kinetics, analyzed with a plot of the integrated intensity ratio as a function of time, log(I_t/I_∞) versus log t, at 25, 40, and 50 °C obeyed Fickian diffusion behavior. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 218–227, 2001     

Chemo-bio catalyzed synthesis of <Emphasis Type="Italic">R</Emphasis>-1-phenylethyl acetate over bimetallic PdZn catalysts,lipase, and Ru/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>. part I

One-pot synthesis of R-1-phenyethylacetate at 70°C was investigated using three different catalysts simultaneously, namely a bimetallic PdZn/Al₂O₃ as a hydrogenation catalyst, an immobilized lipase as an acylation catalyst and Ru/Al₂O₃ as a racemization catalyst. The most active bimetallic catalyst was PdZn/Al₂O₃ calcined at 300°C and reduced at 400°C, whereas the most selective although less active catalyst was the one being calcined and reduced at 500°C. The highest selectivity to R-1-phenylethyl acetate over this catalyst was 32 at 48% conversion. Ru/Al₂O₃ was confirmed to have a positive effect on the formation of the desired product, although it was not very active in the racemization during one-pot synthesis.     

Modeling cellobiose hydrolysis with integrated kinetic models

The enzyme cellobiase Novozym 188, which is used for improving hydrolysis of bagasse with cellulase, was characterized in its commercial available form and integrated kinetic models were applied to the hydrolysis of cellobiose. The specific activity of this enzyme was determined for pH values from 3.0–7.0, and temperatures from 40–75°C, with cellobiose at 2 g/L. Thermal stability was measured at pH 4.8 and temperatures from 40–70°C. Substrate inhibition was studied at the same pH, 50°C, and cellobiose concentrations from 0.4–20 g/L. Product inhibition was determined at 50°C, pH 4.8, cellobiose concentrations of 2 and 20 g/L, and initial glucose concentration nearly zero or 1.8 g/L. The enzyme has shown the greatest specific activity, 17.8 U/mg, at pH 4.5 and 65°C. Thermal activation of the enzyme followed Arrhenius equation with the Energy of Activation being equal to 11 kcal/mol for pH values 4 and 5. Thermal deactivation was adequately modeled by the exponential decay model with Energy of Deactivation giving 81.6 kcal/mol. Kinetics parameters for substrate uncompetitive inhibition were: Km=2.42 mM, V _max=16.31 U/mg, Ks=54.2 mM. Substrate inhibition was clearly observed above 10 mM cellobiose. Product inhibition at the concentration studied has usually doubled the time necessary to reach the same conversion at the lower temperature tested.     

Optic and catalytic properties of gold nanoparticles tuned by homopolymers

Gold nanoparticles (GNs) are prepared through in situ reduction using NaBH₄ in the presence of homopolymer PDMAEMA. The sizes of the GNs can be adjusted by alternating the molar ratio of gold to DMAEMA. Pure PDMAEMA aqueous solution shows a phase-transition at 50°C at pH 10 and 25°C at pH 14, while PDMAEMA-supported GNs aqueous solution shows a phase-transition at 47°C at pH 10 because of the increasing hydrophobic property resulting from GNs. Due to the pH and temperature-responsible characteristics of PDMAEMA, the resulting PDMAEMA-supported GNs exhibit pH adjustable temperature-responsive characteristics in optic and catalytic aspects. Under an acidic condition (pH 2), the GNs show unchanged surface Plasmon absorbance with a peak of 518 nm in a temperature range from 20 to 65°C. Under a basic condition (pH 10), the GNs first show the same absorbance with a peak at 518 nm in a temperature range from 20 to 40°C, and then the absorbance red shifts from 518 to 545 nm as temperature increases from 40 to 65°C. When the GNs are used as catalysts to catalyze the reduction of p-nitrophenol, the catalytic activity can be adjusted by changing the permeation of reactants in the PDMAEMA layer at low and high temperatures, respectively.     

Applying thermodynamics to digestion/gasification processes: the Attainable Region approach

The research shows theoretical calculations on the thermodynamics of digestion/gasification processes where glucose is used as a surrogate for biomass. The change in Enthalpy (?H) and Gibbs Free Energy (?G) is used to obtain the Attainable Region (AR) that shows the overall thermodynamic limits for digestion/gasification from 1 mol of glucose. Gibbs Free Energy and Enthalpy (G–H) plots were calculated for the temperature range 25–1500 °C. The results show the effect of temperature on the AR for the processes when water is in both liquid and gas states using 25 °C, 1 bar as the reference state. The AR results show that the production of CO, H₂, CH₄ and CO₂ are feasible at all temperatures studied. The minimum Gibbs Free Energy becomes more negative from ?418.68 kJ mol^?1 at 25 °C to ?3024.34 kJ mol^?1 at 1500 °C while the process shifts from exothermic (?141.90 kJ mol^?1) to endothermic (1161.80 kJ mol^?1) for the respective temperatures. Methane and carbon dioxide are favoured products (minimum Gibbs Free Energy) for temperatures up to about 600 °C, and this therefore includes Anaerobic Digestion. The process is exothermic below 500 °C, and thus Anaerobic Digestion requires heat removal. As the temperature continues to increase, hydrogen production becomes more favourable than methane production. The production of gas is endothermic above 500 °C, and it needs a supply of heat that could be done, either by combustion or by electricity (plasma gasification). The calculations show that glucose conversion at temperatures around 700 °C favours the production of carbon dioxide and hydrogen at minimum G. Generally, the results show that the gas from high-temperature gasification (>~800 °C) typically carries the energy mainly in syngas components CO and H₂, whereas at low-temperature gasification (<500 °C) the energy is carried in CH₄. The overall analysis for the temperature range (25–1500 °C) also suggests a close relationship between biogas production/digestion and gasification as biogas production can be referred to as a form of low-temperature gasification.     

Influence of storage time and temperature of air-dried soils on pH and extractable nutrients using 0.01 mol/L CaCl2

The stability of pH and certified amounts of nitrate, ammonia, total soluble nitrogen, total soluble organic carbon, magnesium, sodium, potassium and phosphorus obtained by extraction from air-dried (40 °C) soil samples by 0.01 mol/L CaCl₂ solution during storage at –18 °C, 4 °C, ambient temperature, 40 °C and 70 °C was investigated in one calcareous soil and one acid sandy soil. Even at storage times of 45 and 90 days, extractable amounts changed. Extractable amounts of P, NH₄-N, total soluble N and soluble organic C increased even at a storage temperature of 40 °C. The pH was lower for samples stored at a temperature of 70 °C and also the Mg concentration became lower at elevated storage temperatures after 45 days in both soils. It is suggested that reference materials certified for values using unbuffered extractants should be stored at a temperature not higher than 4 °C. Received: 13 May 1997 / Revised: 16 July 1997 / Accepted: 18 July 1997