Polyacrylamide-lithium chloride polymer electrolyte and its applications in electrochemical capacitors

A neutral polymer electrolyte containing lithium chloride (LiCl) and polyacrylamide (PAM) was developed. The LiCl-PAM electrolyte film had an amorphous structure and an ionic conductivity > 10 mS cm^− 1. The addition of LiCl to the polyacrylamide did not alter the chemical bonding of PAM. Symmetric double layer capacitors (EDLC) were constructed using CNT-graphite electrodes. The solid EDLC retained approximately 85% of the capacitance achieved with a baseline cell in a LiCl aqueous solution. The solid EDLC devices demonstrated a wide voltage window (1.5 V), good cycle life (> 10,000 cycles), and excellent rate capability (up to 5 V s^− 1).     

An acidic cellulose–chitin hybrid gel as novel electrolyte for an electric double layer capacitor

A novel acidic cellulose–chitin hybrid gel electrolyte including binary ionic liquids (ILs) with an aqueous H₂SO₄ solution was prepared for an electric double layer capacitor (EDLC). Its electrochemical characteristics were investigated by galvanostatic charge–discharge measurements. The test cell with a hybrid gel electrolyte shows a specific capacitance of 162 F g^?1 at room temperature, which is higher than that for a cell with an H₂SO₄ electrolyte, 155 F g^?1. This hybrid gel electrolyte exhibits excellent high-rate discharge capability in a wide range of current densities as well as an aqueous H₂SO₄ solution. The discharge capacitance of the test cell can retain over 80% of its initial value in 100,000 cycles even at a high current density of 5000 mA g^?1.     

Nitrogen enriched mesoporous carbon spheres obtained by a facile method and its application for electrochemical capacitor

A kind of mesoporous carbon spheres (MCS) containing in-frame incorporated nitrogen has been prepared by a facile polymerization-induced colloid aggregation method. As the electrode material for electric double layer capacitor (EDLC) in 5 mol/L H₂SO₄, the MCS products present excellent specific capacitance as 211 F/g much larger than that of the most popularly applied activated carbon at a high discharge current density of 1 A/g. Its specific capacitance can still remain 200 F/g at 20 A/g. The superior electrochemical performance of MCS is associated with the following characteristics: high specific surface area (∼1330 m²/g) contributed mainly by the mesopores, uniform pore size as large as 29 nm and moderate content of nitrogen (10 wt%), which are the requirements for ideal supercapacitors.     

The superior electrochemical performance of oxygen-rich activated carbons prepared from bituminous coal

Oxygen-rich activated carbons (OAC) were prepared from bituminous coal through a quick KOH activation. OAC exhibited a moderately large surface area of 1950 m²/g, a relative wide pore size distribution, good conductivity and very high oxygen content (up to 12 wt.%). Compared with high surface area activated carbons prepared by the conventional KOH activation, OAC have superior capacitive behavior, power output and high energy density in electrochemical double layer capacitors (EDLC). OAC presented a high specific capacitance of 370 F/g in 3 M KOH electrolyte at a low current density of 50 mA/g and still remained 270 F/g even at a high current density of 20 A/g.     

Mean activity coefficient measurement and thermodynamic modelling of the ternary mixed electrolyte (MgCl2 + glucose + water) system at T = 298.15 K

In this work, the mean activity coefficients of MgCl₂ in pure water and (glucose + water) mixture solvent were determined using a galvanic cell without liquid junction potential of type: (Mg²⁺ + ISE)|MgCl₂ (m), glucose (wt.%), H₂O (100 wt.%)|AgCl|Ag. The measurements were performed at T = 298.15 K. Total ionic strengths were from (0.0010 to 6.0000) mol · kg⁻¹. The various (glucose + water) mixed solvents contained (0, 10, 20, 30 and 40)% mass fractions percentage of glucose respectively. The mean activity coefficients measured were correlated with Pitzer ion interaction model and the Pitzer adjustable parameters were determined. Then these parameters were used to calculate the thermodynamics properties for under investigated system. The results showed that Pitzer ion interaction model can satisfactory describe the investigated system. The modified three-characteristic-parameter correlation (TCPC) model was applied to correlate the experimental activity coefficient data for under investigation electrolyte system, too.     

Facile one-pot synthesis of fluorinated graphene oxide for electrochemical sensing of heavy metal ions

Doping and functionalization could significantly assist in the improvement of the electrochemical properties of graphene derivatives. Herein, we report a one-pot synthesis of fluorinated graphene oxide (FGO) from graphite. The surface morphology, functionalities and composition of the resulting FGO have been studied using various surface characterization techniques, revealing that layer-structured nanosheets with ~ 1.0 at.% F were formed. The carbon bound F exhibited semi-ionic bonding characteristic and significantly increased the capacitance of FGO compared to GO. Further, the FGO has been employed for the simultaneous detection of heavy metal ions Cd^2 +, Pb^2 +, Cu^2 + and Hg^2 + using square wave anodic stripping voltammetry; and a substantial improvement in the electrochemical sensing performance is achieved in comparison with GO.     

Application of Design of Experiment (DoE) for Parameters Optimization in Compression Moulding for Flax Reinforced Biocomposites

Lately, widespread research on polymer composites that consist of natural fiber as reinforcement have been widely discussed. In this work, an attempt on optimizing the hot press forming process parameters using Response Surface Methodology (RSM) have been made to improve the mechanical properties of the woven flax/PLA composites. Three independent process variables, including moulding temperature, time and pressure were studied. Through the Box Behnken approach, a set of experiment runs based on various combination of compression moulding via Minitab 16 were established. As a results the optimum value for the variables of compression moulding technique parameters were 200 °C, 3 min and 30 bar in order to yield 48.902 kJ/m^-2ofimpact strength.     

Effect of swift heavy ion irradiation on ethylene–chlorotrifluoroethylene copolymer

The swift heavy irradiation induced changes taking place in ethylene–chlorotrifluoroethylene (E–CTFE) copolymer films were investigated in correlation with the applied doses. Samples were irradiated in vacuum at room temperature by lithium (50 MeV), carbon (85 MeV), nickel (120 MeV) and silver (120 MeV) ions with the fluence in the range of 1×10¹¹–3×10¹² ions cm^?2. Structural and thermal properties of the irradiated as well as pristine E–CTFE films were studied using FTIR, UV–visible, TGA, DSC and XRD techniques. Swift heavy ion irradiation was found to induce changes in E–CTFE depending upon the applied doses.     

Reactivity of sugar cane bagasse as a natural solid phase extractor for selective removal of Fe(III) and heavy-metal ions from natural water samples

This work introduces the feasibility of using sugar cane bagasse (SCB) – a sugar cane industry waste – as a selective solid phase extractor for Fe(III). The order of metal uptake capacities in μmol g^?1 for the extraction of six tested metal ions from aqueous solution using static technique is Fe(III) > Cu(II) > Pb(II) > Zn(II) > Cd(II) > Co(II). Since SCB exhibits remarkable binding characteristics for Fe(III), special interest was devoted for optimizing its uptake and studying its selectivity properties under static and dynamic conditions. In this respect, batch experiments were carried out at the pH range 1.0–4.0, initial concentration of metal ion (10–100 μmol), weight of phase (25, 50, 75, 100, 125 and 150 mg) and shaking time (10, 30, 45, 60, 90, 120 and 150 min). FT-IR spectra of SCB before and after uptake of Fe(III) were recorded to explore the nature of the functional groups responsible for binding of Fe(III) onto the studied natural biosorbent. The equilibrium data were better fitted with Langmuir model (r² = 0.985) than Freundlich model (r² = 0.934). Moreover, Fe(III) sorption was fast and completed within 60 min. The adsorption kinetics data were best fitted with the pseudo-second-order type. As a view to find a suitable application of SCB based on its unique property as a benign sorbent, it was found that, Fe(III) spiked natural water samples such as doubly distilled water (DDW), drinking tap water (DTW), natural drinking water (NDW), ground water (GW) and Nile River water (NRW) was quantitatively recovered (>95.0%) using batch and column experiments, with no matrix interferences.     

Studies on polypyrrole modified nafion membrane for vanadium redox flow battery

In order to prevent the vanadium crossover and preferential water transfer in all-vanadium redox flow battery (VRFB), three methods – electrolyte soaking, oxidation polymerisation and Electrodeposition, were used to modify Nafion 117 membranes using pyrrole. The surface of the modified membranes was uniform and even, and the membranes were characterised in terms of morphology, membrane area resistance, vanadium permeability and water transfer property. The properties of all the modified membranes were improved greatly. The membranes modified by Electrodeposition showed a best combination of the membrane resistance, vanadium permeability and water transfer property, the experimental results showed that the V(IV) ion permeability of polypyrrole modified Nafion membranes by Electrodeposition at the conditions of 0.025 mA cm⁻² and 0 ^°C for 60 min reduced more than 5 times from 2.87 × 10⁻⁶ cm² min⁻¹ to 5.0 × 10⁻⁷cm² min⁻¹, and the water transfer property decreased more than 3 times from 0.72 ml/72 h cm² to 0.22 ml/72 h cm². All above properties made the modified Nafion membranes more applicative in the VRFB system. This paper also reported other methods for Nafion membrane modification and the influences of the deposition conditions on the properties of the membrane selectivity and water transfer.     

Thermochemistry of uracil and thymine revisited

Thermochemical properties of uracil and thymine have been evaluated using additional experiments. Standard (p⁰ = 0.1 MPa) molar enthalpies of formation in the gas phase at T = 298.15 K for uracil −(298.1 ± 0.6) and for thymine −(337.6 ± 0.9) kJ · mol⁻¹ have been derived from energies of combustion measured by static bomb combustion calorimetry and molar enthalpies of sublimation determined using the transpiration method. The G3 and G4 quantum-chemical methods were used for calculations of theoretical gaseous enthalpies of formation being in very good agreement with the re-measured experimental values.     

Novel ionic liquid electrolyte for electrochemical double layer capacitors

A novel oxygen containing spiro ammonium salt, oxazolidine-3-spiro-1’-pyrrolidinium tetrafluoroborate (OPBF₄) was synthesized using an innovative technique for use as electrolyte in electrochemical double layer capacitors (EDLC). Comparison of OPBF₄ with commercially available, tetraethyl ammonium tetrafluoroborate (TEABF₄) showed higher voltage window and higher capacitance for the OPBF₄ compound. Moreover, molarity of 3 M was produced with OPBF₄ as compared to a maximum of 1.5 M for TEABF₄ in acetonitrile (AN). This is especially important to enable the fabrication of higher energy density EDLC. This is the first report of testing OPBF₄ compound in an EDLC device, and it qualifies as a reasonable alternative to TEABF₄ for high performance ultracapacitors.     

Structural modifications of swift heavy ion irradiated PEN probed by optical and thermal measurements

The effects of swift heavy ion irradiation on the structural characteristics of Polyethylene naphthalate (PEN) were studied. Samples were irradiated in vacuum at room temperature by lithium (50 MeV), carbon (85 MeV), nickel (120 MeV) and silver (120 MeV) ions with the fluence in the range of 1×10¹¹–3×10¹²  ions cm⁻². Ion induced changes were analyzed using X-ray diffraction (XRD), Fourier transform infra red (FT-IR), UV–visible spectroscopy, thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques. Cross-linking was observed at lower doses resulting in modification of structural properties, however higher doses lead to the degradation of the investigated polymeric samples.     

Platinum nanoparticles supported on nitrobenzene-functionalised graphene nanosheets as electrocatalysts for oxygen reduction reaction in alkaline media

A systematic study on the electrocatalytic properties of Pt nanoparticles supported on nitrobenzene-modified graphene (Pt-NB/G) as catalyst for oxygen reduction reaction (ORR) in alkaline solution was performed. Graphene nanosheets were spontaneously grafted with nitrophenyl groups using 4-nitrobenzenediazonium salt. The electrocatalytic activity towards the ORR and stability of the prepared catalysts in 0.1 M KOH solution have been studied and compared with that of the commercial Pt/C catalyst. The results obtained show that the NB-modified graphene nanosheets can be good Pt catalyst support with high stability and excellent electrocatalytic properties. The specific activity of Pt-NB/G for O₂ reduction was 0.184 mA cm⁻², which is very close to that obtained for commercial 20 wt% Pt/C catalyst (0.214 mA cm⁻²) at 0.9 V vs. RHE. The Pt-NB/G hybrid material promotes a four-electron reduction of oxygen and can be used as a promising cathode catalyst in alkaline fuel cells.     

Determination of the energies of combustion and enthalpies of formation of nitrobenzenesulfonamides by rotating-bomb combustion calorimetry

The energies of combustion for 2-nitrobenzenesulfonamide (cr), 3-nitrobenzenesulfonamide (cr), and 4-nitrobenzenesulfonamide (cr) were determined using a recently described rotating-bomb combustion calorimeter. The condensed phase molar energies of combustion obtained were ?(3479.2 ± 1.0) kJ · mol^?1 for 2-nitrobenzenesulfonamide (cr), ?(3454.2 ± 1.1) kJ · mol^-1 for 3-nitrobenzenesulfonamide (cr), and ?(3450.1 ± 1.9) kJ · mol^-1 for 4-nitrobenzenesulfonamide (cr). From these combustion energy values, the standard molar enthalpies of formation in the condensed phase were obtained as: ?(341.3 ± 1.3) kJ · mol^?1, ?(366.3 ± 1.3) kJ · mol^?1, and ?(370.4 ± 2.1) kJ · mol^?1, respectively. Polyethene bags were used as an auxiliary material in the combustion experiments. The heat capacities and purities of the compounds were determined using a differential scanning calorimeter.     

Thermodynamics of the solubility of reserpine in {{2-(2-ethoxyethoxy)ethanol + water}} mixed solvent systems at different temperatures

Thermodynamics of solubility of the bioactive compound reserpine in various {2-(2-ethoxyethoxy)ethanol + water} mixed solvent systems was investigated in this study. The solubility of reserpine was determined from T = (298.15 to 338.15) K at atmospheric pressure using the reported method of Higuchi and Connors. Values of the measured solubility of reserpine were correlated with the ideal and Yalkowsky models. The root mean square deviations (RMSD) were observed to be less than 0.020 by an ideal model. However, the RMSD values were observed as less than 0.050 by the Yalkowsky model. The mole fraction solubility of reserpine was observed highest in pure 2-(2-ethoxyethoxy)ethanol (7.69 · 10⁻⁴ at T = 298.15 K) and lowest in pure water (9.71 · 10⁻⁷ at T = 298.15 K) at each temperature investigated. The results of the Van’t Hoff and Krug analysis (thermodynamic studies) indicated endothermic and spontaneous dissolution of reserpine in all {2-(2-ethoxyethoxy)ethanol + water} mixed solvent systems.     

Internal standardization in graphite furnace atomic absorption spectrometry: Comparative use of As and Ge to minimize matrix effects on Se determination in milk

Arsenic and germanium have been evaluated as internal standards to minimize matrix effects on the direct determination of selenium in milk by graphite furnace atomic absorption spectrometry (GFAAS) using tubes with integrated platform, pre-treated with W together with Pd as chemical modifier. The efficiency of As and Ge as internal standards for 25 μg L^− 1 Se plus 500 μg L^− 1 As or Ge in diluted (1 + 9 v/v) milk plus 1.0% (v/v) HNO₃ was evaluated by means of correlation graphs plotted from the normalized absorbance signals (n = 20) of internal standard (axis y) versus analyte (axis x). The equations that describe the linear regression were: A^As = − 0.004 ± 0.019 + 1.02 ± 0.019 A^Se (r = 0.9967 ± 0.005); A^Ge = − 0.017 ± 0.015 + 1.01 ± 0.015 A^Se (r = 0.9978 ± 0.004). Samples and reference solutions were automatically spiked with 500 μg L^− 1 Ge or As and 1.0% (v/v) HNO₃ by the autosampler. For 20 μL of aqueous standard solutions, analytical curves in the 5.00–40.0 μg L^− 1 Se range were established using the ratio of Se absorbance to internal standard absorbance (A^Se / A^IS) versus analyte concentration, and good linear correlations were obtained. The characteristic mass was 40 pg Se. Limits of detection were 0.55 and 0.40 μg L^− 1 with As and Ge as the internal standard, respectively. Relative standard deviations (RSD) for a sample containing 25 μg L^− 1 Se were 1.2% and 1.0% (n = 12) using As and Ge, respectively. The RSD without internal standardization was about 6%. The accuracy of the proposed method was evaluated by an addition-recovery experiment and all recovered values were in the 99–105% range with IS and in the 70–80% range without IS. Using Ge as the internal standard, results of analysis of standard reference materials were in agreement with certified values at a 95% confidence level. The selenium concentration for 10 analyzed milk samples varied from 5.0 to 20 μg L^− 1.     

Mesoporous tubular graphene electrode for high performance supercapacitor

Mesopores tubular graphene, synthesized by template method, have unique bi-directional ions transfer channel in unstack graphene layers and high mesopore ratio, exhibiting excellent capacitance performance in the EDLC using ionic liquid electrolyte at 4 V.     

Strontium(II) selective PVC membrane electrode based acetophenone semicarbazone (ACS) as an ionophore

A new PVC membrane based strontium(II) ion-selective electrode has been constructed using acetophenone semicarbazone as a neutral carrier. The sensor exhibits a Nerstian response for strontium(II) ion over a wide concentration range 1.0 × 10⁻²–1.0 × 10⁻⁷ M with the slope of 29.4 mV/per decade. The limit of detection was 2.7 × 10⁻⁸ M. It was relatively fast response time (<10 s for concentration ⩾1.0 × 10⁻³ and <15 s for concentration of ⩾1.0 × 10⁻⁶ M) and can be used for 8 months without any considerable divergence in potentials. The proposed sensor revealed relatively good selectivity and high sensitivity for strontium(II) over a mono, di, trivalent cation and can be used in a pH range of 2.5–10.5. It was also successfully used as an indicator electrode in potentiometer titration and in the analysis of concentration in various real samples.