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.

Hydrogel membrane electrolyte for electrochemical capacitors

Polymer electrolytes are known to possess excellent physicochemical properties that are very useful for electrochemical energy systems. The mobility in polymer electrolytes is understood to be mainly due to the segmental motion of polymer chains and the ion transport is generally restricted to the amorphous phase of the polymer. Gel polymer electrolytes (GPE) that are formed using plastizicers and polymers along with ionic salts are known to exhibit liquid-like ionic conductivity while maintaining the dimensional stability of a solid matrix. In the present study, the preparation and characterization of poly(vinyl alcohol)-based hydrogel membranes (PHMEs) as electrolyte for electrochemical capacitors have been reported. VaryingHClO4 dopant concentration leads to different characteristics of the capacitors. The EC comprising PHME doped with 2 M HClO4 and black pearl carbon (BPC) electrodes has been found to exhibit a maximum specific capacitance value of 97 F g(-1), a phase angle value of 78A degrees, and a maximum charge-discharge coulombic efficiency of 88%.

Vitrification, relaxation and free volume in glycerol-water binary liquid mixture:Spin probe ESR studies

Glass transition and relaxation of the glycerol-water (G-W) binary mixture system have been studied over the glycerol concentration range of 5-85 mol% by using the highly sensitive technique of electron spin resonance (ESR). For the water rich mixture the glass transition,sensed by the dissolved spin probe, arises from the vitrified mesoscopic portion of the binary system. The concentration dependence of the glass transition temperature manifests a closely related molecular level cooperativity in the system. A drastic change in the mesoscopic structure of the system at the critical concentration of 40 mol is confirmed by an estimation of the spin probe effective volume in a temperature range where the tracer reorientation is strongly coupled to the system dynamics.

Sinteractive anodic powders improve densification and electrochemical properties of BaZr0.8Y0.2O3-δ electrolyte films for anode-supported solid oxide fuel cells

The difficult sintering of BaZr0.8Y0.2O 3-δ (BZY20) powders makes the fabrication of anode-supported BZY20 electrolyte films complex. Dense BZY20 membranes were successfully fabricated on anode substrates made of sinteractive NiO-BZY20 powders, prepared by a combustion method. With respect to traditional anode substrates made of powders prepared by mechanical mixing, the anode substrates made of the wet-chemically synthesized composite NiO-BZY20 powders significantly promoted the densification of BZY20 membranes: dense BZY20 films were obtained after co-pressing and co-firing at 1300 °C, a much lower temperature than those usually needed for densifying BZY20 membranes. Improved electrochemical performance was also observed: the supported BZY20 films maintained a high proton conductivity, up to 5.4 × 10-3 S cm-1 at 700 °C. Moreover, an anode-supported fuel cell with a 30 m thick BZY20 electrolyte film fabricated at 1400 °C on the anode made of the wet-chemically synthesized NiO-BZY20 powder showed a peak power density of 172 mW cm-2 at 700 °C, using La0.6Sr0.4Co 0.2Fe0.8O3-δ-BaZr0.7Y 0.2Pr0.1O3-δ as the cathode material, with a remarkable performance for proton-conducting solid oxide fuel cell (SOFC) applications.

Nafion and modified-Nafion membranes for polymer electrolyte fuel cells: An overview

Polymer electrolyte fuel cells (PEFCs) employ membrane electrolytes for proton transport during the cell reaction. The membrane forms a key component of the PEFC and its performance is controlled by several physical parameters, viz. water up-take, ion-exchange capacity, proton conductivity and humidity. The article presents an overview on Nafion membranes highlighting their merits and demerits with efforts on modified-Nafion membranes.

Effect of diffusion-layer porosity on the performance of polymer electrolyte fuel cells

The gas-diffusion layer (GDL) influences the performance of electrodes employed with polymer electrolyte fuel cells (PEFCs). A simple and effective method for incorporating a porous structure in the electrode GDL using sucrose as the pore former is reported. Optimal (50 w/o) incorporation of a pore former in the electrode GDL facilitates the access of the gaseous reactants to the catalyst sites and improves the fuel cell performance. Data obtained from permeability and porosity measurements, single-cell performance, and impedance spectroscopy suggest that an optimal porosity helps mitigating mass-polarization losses in the fuel cell resulting in a substantially enhanced performance.

Ion Transport in a Polymer-Plastic Solid Soft Matter Electrolyte in the Light of Solvent Dynamics and Ion Association

Ion transport in a recently demonstrated promising soft matter solid plastic-polymer electrolyte is discussed here in the context of solvent dynamics and ion association. The plastic-polymer composite electrolytes display liquid-like ionic conductivity in the solid state,compliable mechanical strength (similar to 1 MPa), and wide electrochemical voltage stability (>= 5 V). Polyacrylonitrile (PAN) dispersed in lithium perchlorate (LiClO4)-succinonitrile (SN) was chosen as the model system for the study (abbreviated LiClO4-SN:PAN). Systematic observation of various mid-infrared isomer and ion association bands as a function of temperature and polyme concentration shows an effective increase in trans conformer concentration along with free Li+ ion concentration. This strongly supports the view that enhancement in LiClO4-SN:PAN ionic conductivity over the neat plastic electrolyte (LiClO4-SN) is due to both increase in charge mobility and concentration. The ionic conductivity and infrared spectroscopy studies are supported by Brillouin light scattering. For the LiClO4-SN:PAN composites, a peak at 17 GHz was observed in addition to the normal trans-gauche isomerism (as in neat SN) at 12 GHz. The fast process is attributed to increased dynamics of those SN molecules whose energy barrier of transition from gauche to trans has reduced under influences induced by the changes in temperature and polymer concentration. The observations from ionic conductivity, spectroscopy, and light scattering studies were further supplemented by temperature dependent nuclear magnetic resonance H-1 and Li-7 line width measurements.

Compressibilities of some electrolyte solutions in relation to their stepwise dissociation

The compressibilities of some electrolytic solutions at low concentrations have been determined by employing Carstensen's phase-comparison pulse method for measuring the ultrasonic velocity differences and by simultaneously measuring their densities with a Weld-type pyknometer. The apparent molal compressibilities φ(χ̄2) of NaHSO4, KHSO 4, NaP2PO4 and Na-HPO4 have been plotted against the square root of the molarities c. The observations are explained in terms of incomplete dissociation.

Metabolism of glycerol by an Arthrobacter species

An Arthrobacter species (tentatively identified as A. citreus), isolated by the enrichment culture method with glycerol as the sole source of carbon, was studied with a view to elucidate its pathway of glycerol breakdown. Evidence has been obtained against the functioning of the phosphorylative pathway by the study of (1) oxygen uptake with phosphorylated intermediates, (2) uptake of inorganic phosphorus by intact resting cells, (3) action of inhibitors like sodium fluoride, sodium azide, sodium arsenite, sodium iodoacetate, and parachloromercurybenzoate on oxygen uptake with resting cell suspensions and cell-free extracts in some cases. Evidence presented for the functioning of a non-phosphorylative pathway includes studies on the oxidation of glycerol, D-glyceraldehyde, glycerate, glycolic aldehyde, glycolic acid, glyoxylic acid, and formic acid to carbon dioxide and water. Further, the possibility of glyoxylate metabolism through the tricarboxylic acid cycle by its formation of malate was shown. The significance of the above pathway is that it has pointed to an alternative route of carbohydrate metabolism and entry into the tricaboxylic acid cycle without the intervention of pyruvate or the condensing enzyme.

Ambient temperature, zinc ion-conducting, binary molten electrolyte based on acetamide and zinc perchlorate: Application in rechargeable zinc batteries

Binary room temperature molten electrolytes based on acetamide and zinc perchlorate have been prepared and characterized. The electrolytes are found to be highly zinc ion-conducting with very favorable physicochemical and electrochemical characteristics. Raman and infrared spectroscopic studies reveal the presence of large free-ion concentration in the molten liquid. This is corroborated by the high conductivity observed under ambient conditions. Rechargeable zinc batteries assembled using gamma-MnO2 as the cathode and Zn as the anode with the molten electrolyte show high discharge capacities over several cycles, indicating excellent reversibility. This unique class of acetamide-based, room temperature molten liquids may become viable and green alternative electrolytes for rechargeable zinc-based secondary batteries. (C) 2009 Elsevier Inc. All rights reserved.

Effect of plasticizers on magnesium-poly(ethyleneoxide) polymer electrolyte

Solid polymer electrolytes (SPEs) of poly(ethyleneoxide) and magnesium triflate, which are plasticized with propylene carbonate (PC), ethylene carbonate (EC) and a mixture of PC and EC, are studied for their conductivity, ac impedance of the Mg I SPE interface, cyclic voltammetry, infrared spectroscopy and differential scanning calorimetry. in the presence of plasticizers, the ionic conductivity (a) increases from a value of 1 x 10(-8) S cm(-1) to about 1 x 10(-4) S cm(-1) at ambient temperature. The a is found to follow a VTF relationship with temperature. The values of the activation energy, pre-exponential factor and equilibrium glass transition temperature are shown to depend on the concentration of plasticizer. Ac impedance studies indicate lower interfacial impedance of Mg/plasticized SPE than stainless steel/plasticized SPE. The impedance spectra are analyzed using a non-linear least square curve fitting technique and the interfacial resistance of Mg/plasticized SPE is evaluated. The cyclic voltammetric results suggest a quasireversible type of Mg/Mg2+ couple in plasticized SPE. (C) 2000 Elsevier Science B.V. All rights reserved.

Novel phase-transition behavior in an aqueous electrolyte solution

We have investigated the near-critical behavior of the susceptibility of a ternary liquid mixture of 3-methylpyridine. water, and sodium bromide as a function of the salt concentration. The susceptibility was determined from light-scattering measurements performed at a scattering angle of 90 degrees in the one-phase region near the locus of lower consolute points. A sharp crossover from asymptotic Ising behavior to mean-field behavior has been observed at concentrations ranging from 8 to 16.5 mass% NaBr. The range of asymptotic Ising behavior shrinks with increasing salt concentration and vanishes at a NaBr concentration of about 17 mass%. where complete mean-field-like behavior of the susceptibility is observed. A simultaneous pronounced increase in the background scattering at concentrations above 15 mass%, as well as a dip in the critical locus at 17 mass % NaBr, suggests that this phenomenon can be interpreted as mean-field tricritical behavior associated with the formation of a microheterogeneous phase due to clustering of the molecules and ions. An analogy with tri critical behavior observed in polymer solutions as well as the possibility of a charge-density-wave phase is also discussed. In addition, we, have observed a third soap-like phase an the liquid-liquid interface in several binary and ternary liquid mixtures.

Studies on a nanocomposite solid polymer electrolyte with hydrotalcite as a filler

We have prepared a new nanocomposite polymer electrolyte using nanoparticles of hydrotalcite, an anionic clay, as the filler. Hydrotalcite has the chemical composition [M-1-x(2+) M-x(3+) (OH)(2)](x+) [A(x/n)(n-)center dot mH(2)O] where M2+ is a divalent cation (e.g. Mg2+, Ni2+, Co2+,etc.) and M3+ is a trivalent cation (e.g. Al3+, Fe3+, Cr3+, etc.). A(n-) is an anion intercalated between the positively charged double hydroxide layers. The nanoparticles of [Mg0.67Al0.33 (OH)(2)] [(CO3)(0.17)center dot mH(2)O] were prepared by the co-precipitation method (average particle size as observed by TEM similar to 50 nm) and were doped into poly(ethylene glycol) PEG (m.w.2000) complexed with LiCIO4. Samples with different wt.% of hydrotalcite were prepared and characterized using XRD, DSC, TGA, impedance spectroscopy and NMR. Ionic conductivity for the pristine sample, similar to 7.3 x 10(-7) S cm(-1), was enhanced to a maximum of = 1.1 x 10(-5) S cm(-1) for 3.6 wt.% nanoparticle doped sample. We propose that the enhancement of ionic conductivity is caused by percolation effects of the high conductivity paths provided by interfaces between the nanoparticles and the polymer electrolyte. (C) 2010 Elsevier B.V. All rights reserved.

Triacylglycerol synthesis in developing seeds of groundnut (Arachis hypogaea): Pathway and properties of enzymes of sn-Glycerol 3-phosphate formation

The enzymatic pathway for the synthesis of sn-glycerol 3-phosphate was investigated in developing groundnut seeds (Arachis hypogaea). Glycerol-3-phosphate dehydrogenase was not detected in this tissue but an active glycerokinase was demonstrated in the cytosolic fraction. It showed an optimum pH at 8.6 and positive cooperative interactions with both glycerol and ATP. Triosephosphate isomerase and glyceraldehyde-3-phosphate phosphatase were observed mainly in the cytosolic fraction while an active glyceraldehyde reductase was found mainly in the mitochondrial and microsomal fractions. The glyceraldehyde 3-phosphate phosphatase showed specificity and positive cooperativity with respect to glyceraldehyde 3-phosphate. The glyceraldehyde reductase was active toward glucose and fructose but not toward formaldehyde and showed absolute specificity toward NADPH. It is concluded that in the developing groundnut seed, sn-glycerol 3-phosphate is synthesized essentially by the pathway dihydroxyacetone phosphate ? glyceraldehyde 3-phosphate ?Pi glyceraldehyde ?NADPH glycerol ?ATP glycerol 3-phosphate. All the enyzmes of this pathway showed activity profiles commensurate with their participation in triacylglycerol synthesis which is maximal during the period 15�35 days after fertilization. Glycerokinase appears to be the rate-limiting enzyme in this pathway.