Oxygen reduction at the silver/hydroxide-exchange membrane interface

A solid-state cell is used to study the electrocatalysis of oxygen reduction at the silver/hydroxide-exchange membrane interface. The catalyst/membrane interface exhibits improved performance in comparison to a catalyst/aqueous sodium hydroxide interface. Surprisingly, the half-wave potential for oxygen reduction is shown to shift 185 mV higher at the silver/hydroxide-exchange membrane interface than for the silver/aqueous hydroxide solution interface, and the exchange current density is significantly higher at 1.02 × 10⁻⁶ A m⁻². On a cost per performance basis, silver electrocatalysts in a hydroxide-exchange membrane fuel cell may provide better performance than platinum in a proton-exchange membrane fuel cell.     

Application of thin film composite membranes to the membrane aromatic recovery system

The membrane aromatic recovery system (MARS) is a new membrane technology which recovers aromatic acids and bases. The first industrial installation has been operating at a Degussa site in the UK recovering cresols since 2002. The state of the art MARS technology employs a tubular silicone rubber membrane. However, this places some limitations on the process due to relatively low mass transfer rates and limited chemical resistance.In this paper, flat sheet composite membranes were investigated for application to the MARS process. In particular for recovery of compounds, such as 1,2-benzisothiazolin-3-one (BIT) which show low mass transfer rates through the current membrane. These composite membranes are comprised of a thin nonporous PDMS selective layer coated on a microporous support layer cast from polyacrylonitrile, polyvinylidene fluoride, polyetherimide or polyphenylenesulphone. The membranes have been characterised using SEM and gas permeation. The mass transfer of BIT through the composite membranes with no chemical reaction enhancement was an order of magnitude higher than through tubular silicone rubber membranes (10⁻⁷ m s⁻¹ versus 10⁻⁸ m s⁻¹). With chemical reaction enhancement, the mass transfer increased by another order of magnitude to 1.6 × 10⁻⁶ m s⁻¹ for BIT through a PVDF supported composite membrane. Mass transfer through the composite membrane was described well using analysis based on the resistance in series theory with chemical reaction. However, when a high osmotic pressure was applied across the membrane (molarity ∼ 3 M), significant water transport occurred across the membrane.     

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.     

Noise and ac impedance analysis of ion transfer kinetics at the micro liquid/liquid interface

Fluctuation analysis was utilized to determine the TEA ion transfer kinetics across the water/1,2-dichloroethane interface. The obtained data were compared with those derived from electrochemical impedance spectroscopy experiments using the same electrolytic cell. The apparent standard rate constants k_s determined by these two techniques have a similar value. The average value k_s = 0.37 cm s^− 1 is comparable with the previously reported value k_s = 0.2 cm s^− 1. The experimental approach utilizing a thick wall glass micro-capillary to fix the interface exhibits a very small stray capacitance value, proving this system to be suitable for determining the kinetics of the fast ion transfer across a liquid/liquid interface. Application of a method employing a small perturbation signal prevents polarization of the inner capillary surface by current flowing through the cell. The induced polarization of the capillary can affect ion concentration at the interface due to electroosmosis and thus make the kinetic data evaluation difficult or erroneous.     

Voltammetric study on the mechanism of ion transfer caused by weak acids in the bilayer lipid membrane

The mechanism has been investigated by cyclic voltammetry for the ion transfer from one aqueous phase (W1) to another (W2) across a bilayer lipid membrane (BLM) in the presence of a typical uncoupler, carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP). Voltammograms for the ion transfer were in steady-state and showed rotated sigmoidal and symmetrical shape about the origin (0 V, 0 A). The magnitude of the ion transfer current at a given applied potential increased linearly with the concentration of FCCP in W2 up to 10⁻⁶ M and then became saturated. The ion transfer current also showed a bell-type dependence on pH centered around pH ≅ pK_a + 1, K_a being the dissociation constant of FCCP in aqueous phase. These properties have been well explained by our proposed model that the ion transfer current is attributable to the transfers of H⁺ and Na⁺ distributed in BLM. The hydrophilic counter ions, H⁺ and Na⁺, compensate the negative charge of the dissociated FCCP in BLM. The current intensity is predominantly governed by the concentration and the ion mobility of the counter cations.     

Dehydration of tetrahydrofuran by pervaporation using a composite membrane

Tetrahydrofuran (THF) is a strong aprotic solvent, commonly used in the pharmaceuticals industry due to its broad solvency for both polar and non-polar compounds. THF and water form a homogeneous azeotrope at 5.3 wt.% water thus simple distillation is not feasible to dehydrate THF below this concentration. Pervaporation offers a solution since it is not governed by vapour–liquid equilibria. However many polymer-based pervaporation membranes are cast utilizing THF as the casting solvent and so these membranes have a tendency to swell excessively in its presence. This results in poor separation performance and poor long-term stability and thus renders these membranes unsuitable for THF dehydration.In this study, a new membrane available from CM Celfa, CMC-VP-31 has been tested for the dehydration of THF. The membrane shows excellent performance when dehydrating THF with a flux of over 4 kg m⁻² h⁻¹ when dehydrating THF containing 10 wt.% water at 55 °C dropping to 0.12 kg m⁻² h⁻¹ at a water content of 0.3 wt.%. The permeances of water and THF in the membrane were calculated to be 11.76 × 10⁻⁶ and 7.36 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹, respectively, at 25 °C and found to decrease in the membrane with increasing temperature to values of 6.71 × 10⁻⁶ and 1.63 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ at 55 °C. The flux and separation factor were both found to increase with an increase in temperature thus favouring the operation of CMC-VP-31 at high temperatures to optimize separation performance.     

Direct electrochemistry and electrocatalysis of hemoglobin in sodium alginate film on a BMIMPF6 modified carbon paste electrode

A room temperature ionic liquid (RTIL) modified carbon paste electrode was constructed based on the substitute of paraffin with 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIMPF₆) as binder for carbon paste. Direct electrochemistry and electrocatalytic behaviors of hemoglobin (Hb) entrapped in the sodium alginate (SA) hydrogel film on the surface of this carbon ionic liquid electrode (CILE) were investigated. The presence of IL in the CILE increased the electron transfer rate and provided a biocompatible interface. Hb remained its bioactivity on the surface of CILE and the SA/Hb modified electrode showed a pair of well-defined, quasi-reversible cyclic voltammetric peaks with the apparent standard potential (E^0′) at about −0.344 V (vs. SCE) in pH 7.0 Britton–Robinson (B–R) buffer solution, which was attributed to the Hb Fe(III)/Fe(II) redox couple. UV–Vis absorption spectra indicated that heme microenvironment of Hb in SA film was similar to its native status. Hb showed a thin-layer electrochemical behavior in the SA film with the direct electron transfer achieved on CILE without the help of electron mediator. Electrochemical investigation indicated that Hb took place one proton with one electron electrode process and the average surface coverage of Hb in the SA film was 3.2 × 10⁻¹⁰ mol/cm². The immobilized Hb showed excellent electrocatalytic responses to the reduction of H₂O₂ and nitrite.     

Diffusion potential is induced by coupled transport of ions through liquid membrane: nonlinear response to pH change in a reverse permeation system

In a cation exchange liquid membrane-aqueous alkali metal chloride system, diffusional flux of alkali metal ion driven by proton was observed. A supported liquid membrane formed on a Teflon filter by impregnating it with stearic acid-doped 1-octanol was used. The internal aqueous phase contained KCl and HCl, and the external aqueous phase also contained KCl. The initial concentrations of K⁺ ions of both phases were 1×10⁻¹ mol dm⁻³ for all the measurements. The concentration of HCl in the internal solution was kept at 1×10⁻² mol dm⁻³. The pH of the external solution was changed successively with HCl, appropriate buffer solution, or KOH. The pH dependence of membrane potential showed hysteresis loop in the range from neutral to alkaline pH, where reverse ion permeation was observed after the flux had been measured in the system with the external solution of an alkaline pH (pH 13). In the acidic range below neutral pH, the hysteresis of the membrane potential as well as reverse ion permeation was not observed. To elucidate the correlation between the appearance of hysteresis loop and the reverse ion permeation driven by proton across the membrane, the time course of the membrane potential in response to pH change was investigated. In the pH range where reverse permeation phenomena appeared, the time dependence of the membrane potential in nonsteady-state showed biphasic behavior. From the time course curve of the membrane potential, the total membrane potential was divided into the Donnan potential and the diffusion potential. From these findings, it was demonstrated that the diffusion potential was generated within the membrane only in the alkaline range where reverse ion permeation occurred. Analyzing the diffusional flux, the diffusion coefficient of potassium ion in the membrane was obtained taking the Donnan potential into account to be much greater than that in the membrane solvent. As a result of comparison of the diffusional fluxes measured by atomic absorption spectrometry and solution conductometry, the flux of the potassium ion was found to be significantly greater than that of the hydrogen ion in the opposite direction, especially at extremely high pH region. This implies the flows of hydroxide ions and neutralization reaction within the membrane facilitate the reverse ion permeation process of potassium ions.     

Hollow fiber supported liquid membrane: a novel technique for separation and recovery of plutonium from aqueous acidic wastes

Low plutonium content acidic waste is generated in nuclear chemical facilities. Study was initiated to develop hollow fiber supported liquid membrane (HFSLM) technique for quantitative separation and recovery of plutonium (Pu) from such wastes using tri-n-butyle phosphate (TBP) in dodecane as carrier. Hollow fiber test module was fabricated using 20 lumens of 33.91 cm² surface area and 9 cm length. After satisfactory testing of the hydrodynamic condition of the module, it was operated at a flow rate of 3 ml min⁻¹ on recycling mode with acidic waste solution containing Pu=8 mg dm⁻³, uranium=15 dm⁻³, gross β⁻=49.33 mCi dm⁻³, gross γ=15.73 mCi dm⁻³ and acidity 3 M HNO₃. In presence of various fission products, selective permeation of Pu(IV) through the bundle of hollow fiber test module was observed to be more than 90% into a stripping phase consisting 0.1 M NH₂OH·HCl in 0.3 M HNO₃. A model is presented to describe the transport mechanism and to evaluate the mass transfer coefficient. The radiation stability was also tested by exposing the membrane upto irradiation level of 1 M rad. Potentiality of the method for the selective separation of plutonium from acidic waste is, thus, clearly seen.     

Modelling of mass transfer in facilitated supported liquid membrane transport of copper(II) using MOC-55 TD in Iberfluid

The transport of copper(II) through a supported liquid membrane using MOC-55 TD (oxime derivative), dissolved in Iberfluid, as a carrier has been studied. A physico-chemical model is derived to describe the transport mechanism which consists of: diffusion process through the feed aqueous diffusion layer, fast interfacial chemical reaction and diffusion through the membrane. The experimental data can be explained by mathematical equations describing the rate of transport. The mass transfer coefficient was calculated from the described model as 2.8×10⁻³ cm s⁻¹, the thickness of the aqueous boundary layer as 2.6×10⁻³ cm⁻¹ and the membrane diffusion coefficient of the copper-containing species as 1.2×10⁻⁸ cm² s⁻¹.     

A lotus root-like porous nanocomposite polymer electrolyte

A lotus root-like porous nanocomposite polymer electrolyte (NCPE) based on poly(vinylidene difluoride-co-hexafluoropropylene) [P(VDF-HFP)] copolymer and TiO₂ nanoparticles was easily prepared by a non-solvent induced phase separation (NIPS) process. The formation mechanism of the lotus root-like porous structure is explained by a qualitative ternary phase diagram. The resulting NCPE had a high ionic conductivity up to 1.21 × 10⁻³ S cm⁻¹ at room temperature, and exhibited a high electrochemical stability potential of 5.52 V (vs. Li/Li⁺), lithium ion transference number of 0.65 and 22.89 kJ mol⁻¹ for the apparent activation energy for transportation of ions. It is of great potential application in polymer lithium ion batteries.     

Interactions of some amino acids and glycine peptides with aqueous sodium dodecyl sulfate and cetyltrimethylammonium bromide at T=298.15 K: a volumetric approach

The apparent molar volumes V_φ of glycine, alanine, valine, leucine, and lysine have been determined in aqueous solutions of 0.05, 0.5, 1.0 mol · kg⁻¹ sodium dodecyl sulfate (SDS) and 1.0 mol · kg⁻¹ cetyltrimethylammonium bromide (CTAB) by density measurements at T=298.15 K. The apparent molar volumes have also been determined for diglycine and triglycine in 1 mol · kg⁻¹ SDS and CTAB solutions. These data have been used to calculate the infinite dilution apparent molar volumes V₂⁰ for the amino acids and peptides in aqueous SDS and CTAB and the standard partial molar volumes of transfer (Δ_trV_2,m⁰) of the amino acids and peptides to these aqueous surfactant solutions. The linear correlation of V₂⁰ for a homologous series of amino acids has been utilized to calculate the contribution of the charged end groups (NH₃⁺, COO⁻), CH₂ group and other alkyl chains of the amino acids to V₂⁰. The results on the partial molar volumes of transfer from water to aqueous SDS and CTAB have been interpreted in terms of ion–ion, ion–polar and hydrophobic–hydrophobic group interactions. The volume of transfer data suggests that ion–ion or ion–hydrophilic group interactions of the amino acids and peptides are stronger with SDS compared to those with CTAB. Comparison of the hydration numbers of amino acids calculated in the present studies with those in other solvents from literature shows that these numbers are almost the same at 1 mol · kg⁻¹ level of the cosolvent/cosolute. Increasing molality of the cosolvent/cosolute beyond 1 mol · kg⁻¹ lowers the hydration number of the amino acids due to increased interactions with the solvent and reduced electrostriction.     

Investigation of immiscible alloy system of Al–Sn thin films as anodes for lithium ion batteries

The Al–Sn, which is immiscible alloy, film was prepared by e-beam deposition to explore the possibility as anode material for lithium ion batteries for the first time. The film has a complex structure with tiny Sn particles dispersed homogeneously in the Al active matrix. The diffusion coefficients of Li⁺ in these Al–Sn alloy films were determined to be 2.1–3.2 × 10⁻⁸ cm²/s by linear sweep voltammetry. The film electrode with high Al content (Al–33wt%Sn) delivered a high initial discharge capacity of 972.8 mA h g⁻¹, while the film electrode with high Sn content (Al–64wt%Sn) with an initial discharge capacity of 552 mA h g⁻¹ showed good cycle performance indicated by retaining a capacity of about 381 mA h g⁻¹ after 60 cycles. Our preliminary results demonstrate that Al–Sn immiscible alloy is a potential candidate for anodic material of lithium ion batteries.     

Room-temperature ionic liquid as a new solvent to prepare high-quality dodecanethiol self-assembled monolayers on polycrystalline gold

This paper reports a new solvent, room-temperature ionic liquid (RTIL), for the preparation of dodecanethiol self-assembled monolayers (C₁₂SH-SAMs) on polycrystalline gold. The quality of C₁₂SH-SAMs was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). From CV experiments, we find that the differential capacitance C_d values of the C₁₂SH-SAM prepared in RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆) containing 10 μL neat C₁₂SH for 24 h (C₁₂SH-SAMs_{[BMIM]PF6,10 μL,24 h}) are independent of the scan rate, the effective thickness d_eff value and the average cant angle φ value of this monolayer are 18 ± 1 Å and 27 ± 4°, respectively. The difference value of the current density at −0.2 and 0.5 V (Δi_p) is only 0.73 ± 0.18 μA cm⁻². EIS experiments show that the phase angle value at 1 Hz Φ_1 Hz, the charge transfer resistance R_ct value and surface coverage θ value of this C₁₂SH-SAM are 88.2 ± 0.7°, 3.44 ± 1.91 MΩ cm² and 99.998 ± 0.001%, respectively. These results indicate that high-quality C₁₂SH-SAMs can be formed in [BMIM]PF₆. In addition, the rate of formations of high-quality C₁₂SH-SAMs in RTIL can be substantially improved by ultrasound.     

Determination of mercury in organic solvents and gas condensates by μflow-injection — inductively coupled plasma mass spectrometry using a modified total consumption micronebulizer fitted with single pass spray chamber

A high-throughput flow-injection — inductively coupled plasma mass spectrometry (ICP MS) analytical method was developed for the determination of mercury in gas condensates and carbon-rich solvents. The sample (undiluted or diluted 10-fold) was introduced via a modified total consumption micronebulizer working at a flow rate of 30 μl min^− 1 and fitted with a singlepass spray chamber. This low flow rate and the addition of oxygen (70 ml min^− 1) assured the plasma stability and reduced the carbon build-up on the interface and on ion lenses. A limit of detection of 0.5 ng g^− 1 (2.5 μl sample) was obtained owing to the reduction of dead volume and sample dispersion (peak-width was 3 s at half-height) in the liquid pass of the nebulizer. The elimination of the memory effect reduced the washout time down to 30 s which resulted in a throughput of ca. 60 h^− 1. The method was validated by the analysis of 3 gas condensates by cold vapour atomic absorption spectrometry.     

Direct electrochemistry of hemoglobin and glucose oxidase in electrodeposited sol–gel silica thin films on glassy carbon

This work points out that electrogeneration of silica gel (SG) films on glassy carbon electrodes (GCEs) can be applied to immobilize biomolecules – hemoglobin (Hb) or glucose oxidase (GOD) or both of them in mixture – without preventing their activity. These proteins were physically entrapped in the sol–gel material in the course of the electro-assisted deposition process applied to form the thin films onto the electrode surface. SG films were prepared from a precursor solution by applying a suitable cathodic potential likely to induce a local pH increase at the electrode/solution interface, accelerating thereby polycondensation of the silica precursors with concomitant film formation. Successful immobilization of proteins was checked by various physico-chemical techniques. Both Hb and GOD were found to undergo direct electron transfer, as demonstrated by cyclic voltammetry. GCE–SG–Hb gave rise to well-defined peaks at potentials E_c = −0.29 V and E_a = −0.17 V in acetate buffer, corresponding to the Fe^III/Fe^II redox system of heme group of the protein, while GCE–SG–GOD was characterized by the typical signals of FAD group at E_c = −0.41 V and E_a = −0.33 V in phosphate buffer. These two redox processes were also evidenced on a single voltammogram when both Hb and GOD were present together in the same SG film. Hb entrapped in the silica thin film displayed an electrocatalytic behavior towards O₂ and H₂O₂ in solution, respectively in the mM and μM concentration ranges. Immobilized GOD kept its biocatalytic properties towards glucose. Combined use of these two proteins in mixture has proven to be promising for detection of glucose in solution via the electrochemical monitoring of oxygen consumption (decrease of the oxygen electrocatalytic signal).     

Fabrication of porous Co/NiO core/shell nanowire arrays for electrochemical capacitor application

We report self-supported porous Co/NiO core/shell nanowire arrays via the combination of hydrogen reduction and chemical bath deposition methods. The Co nanowire acts as the backbone for the growth of NiO nanoflake shell forming hierarchically porous Co/NiO core/shell nanowire arrays. As electrode materials for pseudo-capacitors, the Co/NiO core/shell nanowire arrays exhibit a specific capacitance of 956 F g^− 1 at 2 Å g^− 1 and 737 F g^− 1 at 40 Å g^− 1, and good cycling stability, which is mainly due to the metal nanowire based core/shell nanowire architecture which provides good conductive network as well as fast ion/electron transfer and sufficient contact between active materials and electrolyte.     

Standard Gibbs energy of formation of platinic acid H2Pt(OH) 6in the crystalline state

Heat capacity of platinic acid, hydrogen hexahydroxyplatinate(IV)H₂Pt(OH)₆ , was measured from T =  7 K toT =  310 K by means of adiabatic calorimetry. The standard entropy and the standard Gibbs energy of formation of platinic acid in the crystalline state were determined to be 176.5  ±  3.6 J · K ^− 1· mol ^− 1and  − 988.8  ±  3.8 kJ · mol ^− 1, respectively.     

Thermodynamic properties of soddyite from solubility and calorimetry measurements

The release of uranium from geologic nuclear waste repositories under oxidizing conditions can only be modeled if the thermodynamic properties of the secondary uranyl minerals that form in the repository setting are known. Toward this end, we synthesized soddyite ((UO₂)₂(SiO₄)(H₂O)₂), and performed solubility measurements from both undersaturation and supersaturation. The solubility measurements rigorously constrain the value of the solubility product of synthetic soddyite, and consequently its standard-state Gibbs free energy of formation. The log solubility product (lg K_sp) with its error (1σ) is (6.43 + 0.20/−0.37), and the standard-state Gibbs free energy of formation is (−3652.2 ± 4.2 (2σ)) kJ mol⁻¹. High-temperature drop solution calorimetry was conducted, yielding a calculated standard-state enthalpy of formation of soddyite of (−4045.4 ± 4.9 (2σ)) kJ · mol⁻¹. The standard-state Gibbs free energy and enthalpy of formation yield a calculated standard-state entropy of formation of soddyite of (−1318.7 ± 21.7 (2σ)) J · mol⁻¹ · K⁻¹. The measurements and associated thermodynamic calculations not only describe the T = 298 K stability and solubility of soddyite, but they also can be used in predictions of repository performance through extrapolation of these properties to repository temperatures.     

Cycling performance and efficiency of sulfonated poly(sulfone) membranes in vanadium redox flow batteries

As an alternative to Nafion® ion exchange membrane, an inexpensive commercially-available Radel® polymer was sulfonated, fabricated into a thin membrane, and evaluated for its performance in a vanadium redox flow battery (VRFB). The sulfonated Radel (S-Radel) membrane showed almost an order of magnitude lower permeability of VO²⁺ ions (2.07 × 10^?7 cm²/min), compared to Nafion 117 (1.29 × 10^?6 cm²/min), resulting in better coulombic efficiency (~ 98% vs. 95% at 50 mA/cm²) and lower capacity loss per cycle. Even though the S-Radel membrane had a slightly higher membrane resistance, the energy efficiency of the VRFB with the S-Radel membrane was comparable to that of Nafion because of its better coulombic efficiency resulting from the lower vanadium ion crossover. The S-Radel membrane exhibited good performance up to 40 cycles, but a decline in performance at later cycles was observed, likely as a result of membrane degradation.