Poly (vinyl alcohol) hydrogel membrane as electrolyte for direct borohydride fuel cells

A direct borohydride fuel cell (DBFC) employing a poly (vinyl alcohol)hydrogel membrane electrolyte (PHME) is reported. The DBFC employs an AB(5) Misch metal alloy as anode and a goldplated stainless steel mesh as cathode in conjunction with aqueous alkaline solution of sodium borohydride as fuel and aqueous acidified solution of hydrogen peroxide as oxidant. Room temperature performances of the PHME-based DBFC in respect of peak power outputs; ex-situ cross-over of oxidant, fuel,anolyte and catholyte across the membrane electrolytes; utilization efficiencies of fuel and oxidant, as also cell performance durability are compared with a similar DBFC employing a NafionA (R)-117 membrane electrolyte (NME). Peak power densities of similar to 30 and similar to 40 mW cm(-2) are observed for the DBFCs with PHME and NME, respectively. The crossover of NaBH4 across both the membranes has been found to be very low. The utilization efficiencies of NaBH4 and H2O2 are found to be similar to 24 and similar to 59%, respectively for the PHME-based DBFC; similar to 18 and similar to 62%, respectively for the NME-based DBFC. The PHME and NME-based DBFCs exhibit operational cell potentials of similar to 1 center dot 2 and similar to 1 center dot 4 V, respectively at a load current density of 10 mA cm(-2) for similar to 100 h.

Dissolution properties of BaTiO3 nanoparticles in aqueous suspensions

Dissolution of barium ion from aqueous suspensions of commercial nano-sized barium titanate powders (BaTiO3) has been studied at various pH values, solids loading, different time intervals and different electrolyte concentrations. Zeta potential measurements at various pH values and Fourier transform infrared spectroscopy study were also carried out to know the surface behaviour. Dissolution of Ba2+ depends on the suspension pH and stirring time period. The iso-electric points were found at 3.4 and 12.2 for as-received BaTiO3 powder and 2.3 for the leached BaTiO3. The Ba2+-leached BaTiO3 suspension retards further leaching of Ba2+ ions at different pH values, which favours the achievement of stable suspension.

An improved-performance liquid-feed solid-polymer-electrolyte direct methanol fuel cell operating at near-ambient conditions

Results on the performance of a 25 cm(2) liquid-feed solid-polymer-electrolyte direct methanol fuel cell (SPE-DMFC), operating under near-ambient conditions, are reported. The SPE-DMFC can yield a maximum power density of c. 200 mW cm(-2) at 90 C while operating with 1 M aqueous methanol and oxygen under ambient pressure. While operating the SPE-DMFC under similar conditions with air, a maximum power density of ca. 100 mW cm(-2) is achieved. Analysis of the electrode reaction kinetics parameters on the methanol electrode suggests that the reaction mechanism for methanol oxidation remains invariant with temperature. Durability data on the SPE-DMFC at an operational current density of 100 mA cm(-2) have also been obtained.

Electrochemical studies of polyaniline in a gel polymer electrolyte - High energy and high power characteristics of a solid-state redox supercapacitor

Studies on redox supercapacitors employing electronically conducting polymers are of great importance for hybrid power sources and pulse power applications. In the present study, polyaniline (PANI) has been potentiodynamically deposited on stainless steel substrate and characterized in a gel polymer electrolyte (GPE). Use of the GPE facilitates a voltage limit of the capacitor to 1 V, instead of 0.75 V in aqueous electrolytes. From charge-discharge studies of the solid-state PANI capacitors, a specific capacitance of 250 F g(-1) has been obtained at a specific power of 7.5 kW kg(-1) of PANI. The values of specific capacitance and specific power are considerably higher than those reported in the literature. High energy and high power characteristics of the PANI are presented. (C) 2002 The Electrochemical Society.

The influence of corrosion on the erosion of aluminium by aqueous silica slurries

The slurry erosion-corrosion behaviour of aluminium in aqueous silica slurries containing 0.5 M NaCl, acetic acid and 0.1 M Na2CO3 at open circuit has been investigated using a modified slurry erosion rig. The erosion rates of aluminium in the NaCl and acetic acid slurries were much higher than those in an aqueous slurry without electrolyte additives even though the pure corrosion component was very small. Eroded specimens were examined by scanning electron and optical microscopy. In pure aqueous slurry erosion, the basic mechanism leading to mass loss was the ductile fracture of flakes formed on the eroded surface. In corrosive slurries, however, the mass loss was enhanced by cracking of the flakes induced by stress and corrosion. © 1995.

Interfacial behaviour of quantum well electrode/electrolyte: effect of redox species on EER spectra of a single quantum well GaAs vertical bar AlxGa1-xAs electrode

The EER spectra of a single quantum well GaAs\AlxGa1-xAs electrode were studied as a function of applied reverse bias in ferrocene, p-methyl nitrobenzene and hydroquinone+benzoquinone non-aqueous solutions. EER spectra were compared for different redox species and showed that a pronounced quantum-confined Stark effect and a Franz-Keldysh oscillation for a single quantum well electrode were obtained in the p-methyl-nitrobenzene- and hydroquinone+benzoquinone-containing solutions. A surface interaction of the single quantum well electrode with ferrocene led to fewer changes in the electric field of the space charge layer for reverse bias; this was suggested to explain the weak quantum-confined Stark effect and Franz-Keldysh oscillation effect observed for the single quantum well electrode in the ferrocene-containing solution. (C) 1997 Elsevier Science S.A.

An electrochemical study of prussian blue microcrystallines mixed in PEO400 polymer electrolyte by solid-state voltammetry

The electrochemistry of Prussian blue mixed in a polymer medium containing MClO4 (M = Li+, Na+, K+, TBA(+)) as the supporting electrolyte was studied by means of solid-state voltammetry. This approach is new in Prussian blue studies. The behavior of PB in polymer electrolytes is somewhat similar to the well-known behavior for an electrochemically synthesized PB film in aqueous media. Besides, K+, Li+ and Na+ ions can also transport through the crystal of PB because of its zeolitic nature. The transport of TBA(+) ions is possible. Kinetic control lies in the diffusion of cations in and out of the lattice of Prussian blue. Reduction waves of Prussian blue depend on both the size and type of cations. PB is very stable upon electrochemical cycling in polymer electrolytes and air. This system may be used in rechargeable batteries and electrochromic devices.

Templated electrodeposition of silver nanowires in a nanoporous polycarbonate membrane from a nonaqueous ionic liquid electrolyte

Template electrodeposition has been used to prepare a wide range of nanostructures but has generally been restricted to aqueous electrolytes. We report the deposition of silver nanowires in a commercial nuclear track-etched polycarbonate template from the nonaqueous ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) using silver electrochemically dissolved from the anode. Transmission electron microscopy (TEM) shows that the nanowires have a very high aspect ratio with an average diameter of 80 nm and length of 5 mu m. Ionic liquid electrolytes should greatly extend the range of metals that can be electrodeposited as nanowires using templates.

Surface Activity of the Triflate Ion at the Air/Water Interface and Properties of N,N,N-Trimethyl-N-Dodecylammonium Triflate Aqueous Solutions

The surface activity of salts added to water is Air orders of magnitude lower than that of surfactants. Sodium trifluoromethanesulfonate (NaTf) produced a change in surface tension. with concentration, Delta gamma/Delta c, of -13.2 mN.L/m.mol. This value is ca. 4-fold larger than those of simple salts and that of methanesulfonate. This unexpected surface effect suggested that positively charged micelles containing Tf could exhibit interesting properties. Dodecyltrimethylammonium triflate (DTATf) had a higher Kraft temperature (37 degrees C) and a lower cmc (5 x 10(-3)M) and degree of dissociation (0.11) than the chloride and bromide salts of DTA. Above the Kraft temperature, at a characteristic temperature t(1), the addition of NaTf above 0.05 M. to a DTATf solution induced phase separation. By increasing the temperature of the two-phase system to above t(1), a homogeneous, transparent solution was obtained at a characteristic temperature t(2). These results, together with well-known triflate properties, led us to suggest that the Tf ion pairs With DTA and that the -CF(3) group may be dehydrated in the interfacial region, resulting in new and interesting self-aggregated structures.

Electroanalytical determination of N-nitrosamines in aqueous solution using a boron-doped diamond electrode

The electrochemical methods cyclic and square-wave voltammetry were applied to develop an electroanalytical procedure for the determination of N-nitrosamines (N-nitrosopyrrolidine, N-nitrosopiperidine and N-nitrosodiethylamine) in aqueous solutions. Cyclic voltammetry was used to evaluate the electrochemical behaviors of N-nitrosamines on boron-doped diamond electrodes. It was observed an irreversible electrooxidation peak located in approximately 1.8 V (vs. Ag/AgCl) for both N-nitrosamines. The optimal electrochemical response was obtained using the following square-wave voltammetry parameters: f = 250 Hz, E(sw) = 50 mV and E(s) = 2 mV using a Britton-Robinson buffer solution as electrolyte (pH 2). The detection and quantification limits determined for total N-nitrosamines were 6.0 x 10(-8) and 2.0 x 10(-7) mol L(-1), respectively.

Environmental coordination chemistry: Binary systems comprising some bivalent cations and monocarboxylates in aqueous solution. Ionic medium effects on equilibrium constants

The molar single activity coefficients associated with propionate ion (Pr) have been determined at 25 degrees C and ionic strengths comprised between 0.300 and 3.00 M, adjusted with NaClO4, as background electrolyte. The investigation was carried out potentiometrically by using a second class Hg/Hg2Pr2 electrode. It was found that the dependence of propionate activity coefficients as a function of ionic strength (I) can be assessed through the following empirical equation: log y(Pr) = -0.185 I-3/2 + 0.104 I-2. Next, simple equations relating stoichiometric protonation constants of several monocarboxylates and formation constants associated with 1:1 complexes involving some bivalent cations and selected monocarboxylates, in aqueous solution, at 25 degrees C, as a function of ionic strength were derived, allowing the interconversion of parameters from one ionic strength to another, up to I = 3.00 M. In addition, thermodynamic formation constants as well as parameters associated with activity coefficients of the complex species in the equilibria are estimated. The body of results shows that the proposed calculation procedure is very consistent with critically selected experimental data.

Ionic medium effects on equilibrium constants .1. Proton, copper(II), cadmium(II), lead(II) and acetate activity coefficients in aqueous solution

The molar single ion activity coefficients associated with hydrogen, copper(II), cadmium(II) and lead(II) ions were determined at 25 degrees C and ionic strengths between 0.100 and 3.00 M (NaClO4), whereas for acetate the ionic strengths were fixed between 0.300 and 2.00 M, held with the same inert electrolyte. The investigation was carried out potentiometrically by using proton-sensitive glass, copper, cadmium and lead ion-selective electrodes and a second-class Hg\Hg-2(CH3COO)(2) electrode. It was found that the activity coefficients of these ions (y(i)) can be assessed through the following empirical equations:log y(H) = -0.542I(0.5) + 0.451I; log y(Cu) = -1.249I(0.5) + 0.912I; log y(Cd) = -0.829I(0.5) + 0.448I(1.5);log y(Pb) = -0.404I(0.5) + 0.117I(2); and log y(Ac) = 0.0370I .

The electrochemistry of ferrocene in non-aqueous solvents

the electrochemical oxidation of ferrocene on Pt in dimethylformamide, ethanol, propylene carbonate and their aqueous solutions was studied at 25°C. The concentration of the supporting electrolyte, NaClO4, was varied from 0.1 to 0.5 M. The results show that the electrode process may be described as a quasi-reversible one-electron charge transfer, followed by slow decomposition of the oxidized species. © 1987.

Formation of SnO2 gels from dispersed sols in aqueous colloidal solutions

Transparent SnO2 gels were obtained from SnCl4 aqueous solution. The sol formation from tin oxihydroxy peptization in different concentrations and by electrolyte addition in solution was measured. It was verified that the residual presence of chloride ions compromises the colloidal system stability. The sol-gel transition was investigated as a function of the quantity of solid particles in the aqueous environment and of aging time at 60°C by infrared spectroscopy and rheological measurements. The transition from plastic to pseudoplastic flow observed with the increase in loading suggests that a continuous and three-dimensional network formation is closely related to hydrogen bridges and/or hydrogen clusters, culminating in the gel formation. © 1990.

The Electrodeposition of Manganese from Certain Aqueous Solutions

Careful examination of the literature available shows that the electrodeposition of manganese from various aqueous solutions has not been attempted to any great extent. The best method for the electrodeposition of pure manganese consists in the electrolysis of a solution con­taining manganous and ammonium sulphates.