Browsing by Author "N. Lakshmi"

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A rechargeable solid-state proton battery with an intercalating cathode and an anode containing a hydrogen-storage material
(Elsevier, 1998) Kamlesh Pandey; N. Lakshmi; S. Chandra
Rechargeable proton batteries have been fabricated with the configuration Zn + ZnSO4 · 7H2O/ /solid-state proton conductor/ /C + electrolyte + intercalating PbO2 + V2O5. The solid-state proton conductor is phosphotungstic acid (H3PW12O40 · nH2O) or a H3PW12O40 · nH2O + Al2(SO4)3 · 16H2O composite. The maximum cell voltage is ∼ 1.8 V at full charge. The cell can run for more than 300 h at low current drain (2.5 μA cm-2). Further, the cell can withstand 20 to 30 cycles. The addition of a metal hydride in the anode side enhances the rechargeability and the addition of a small amount of Al2(SO4)3 · 16H2O in the H3PW12O40 · nH2O electrolyte improves the performance of the battery. © 1998 Elsevier Science S.A. All rights reserved.
Evidence of failure of hopping model of ionic conductivity in phosphomolybdic acid studied by a.c. conductivity measurements
(Kluwer Academic Publishers, 1999) Kamlesh Pandey; N. Lakshmi
The a.c. conductivity measurement has been used to probe into the possible conduction mechanisms (Vehicle or Hopping) in proton conducting acid hydrate Phosphomolybdic acid H3PO4·12MoO3·nH2O. The magnitude of hopping rate and its temperature dependence evaluated from a.c. conductivity data does not favour the hopping mechanism of conduction. The value of activation energy (Ea to approximately 0.76 eV) supports the vehicle mechanism of ion transport.
Ion transport in some solid state proton conducting composites studied from volta cell e.m.f, and complex impedance spectroscopy
(Indian Academy of Sciences, 2002) N. Lakshmi; S. Chandra
Proton conducting composites of heteropolyacid hydrates (phosphomolybdic acid H3PMo12O40·nH2O, PMA; phosphotungstic acid H3PW12O40·nH2O, PTA) and salt hydrate like NiCl2·6H2O were prepared with insulating Al2O3 as dispersoid. The ionic conductivity peaks at two concentrations of Al2O3 indicating two percolation thresholds for proton conduction. Two separate experiments were carried out to check the existence of such percolation thresholds viz. the volta battery experiment involving the measurement of e.m.f. of an electrochemical cell with composites of different compositions used as electrolyte and the composition vs conductivity measured by the complex impedance spectroscopy. The presence of two maxima has been attributed to two different percolation thresholds for the two possible mobile protonic species H+ (H3O+) and OH- arising from the hydrates.
Proton conducting composites of heteropolyacid hydrates (phosphomolybdic and phosphotungstic acids) dispersed with insulating Al2O3
(Wiley-VCH Verlag, 2001) N. Lakshmi; S. Chandra
Composites of heteropolyacid hydrates with insulating Al2O3 as the dispersoid, viz. xPMA + (1 - x)Al2O3) and xPTA + (1 - x)Al2O3, have been prepared and characterised using DTA/TGA, XRD, IR and ion transport measurements. New exothermic peaks in the DTA for the composites with more Al2O37 and the changes in XRD suggest the probable formation of a new interface compound at the Al2O3 interface. The bulk electrical conductivity has been found to depend upon the composition, temperature and relative humidity. The composition versus conductivity isotherm exhibits two maxima at x = 0.8 and 0.6 for the PTA:Al2O3 system and x = 0.7 and 0.5 for the PMA : A12O3 system. Phenomenologically, this could be either due to the two different thresholds for the two types of mobile species (H+/H3O+ and OH-) or due to the formation of a high conducting interface compound. © WILEY-VCH Verlag Berlin GmbH.
Proton conducting composites of heteropolyacid hydrates dispersed with salt hydrates
(2002) N. Lakshmi; S. Chandra
Proton conduction in the composites of heteropolyacid hydrates (Phosphotungstic acid: PTA·nH2O and Phosphomolybdic acid: PMA·nH2O) with salt hydrates like Aluminium sulphate and Ammonium paratungstate (APT) as dispersoids has been studied and compared with the composites PTA:Al2O3 and PMA:Al2O3. Thermal analysis, XRD and IR studies on acid and salt hydrates dispersed phase systems reveal the formation of composites. A significant increase in the ionic conductivity has been observed in the composites. It has been found that the conductivity of 0.5PTA + 0.5Al2(SO4)3·16H2O is ∼1.1 × 10-2 S·cm-1 and that of 0.55PMA + 0.45APT is ∼1.3 × 10-3 S·cm-1 at 65% R.H. The temperature and humidity dependence of bulk electrical conductivity of the composites is also reported.
Rechargeable solid-state battery using a proton-conducting composite as electrolyte
(2002) N. Lakshmi; S. Chandra
Proton-conducting composites of heteropolyacid hydrates (phospbotungstic acid, PTA and phosphomolybdic acid, PMA) with dispersoids such as insulating Al2O3, Al2(SO4)3·16H2O and (NH4)10W12O41·2H2O are prepared for use as possible solid-state electrolytes in batteries. Bulk electrical conductivity as a function of composition is reported. Rechargeable solid-state proton batteries are fabricated and characterized. A cell with the configuration Zn+ZnSO4·7H2O+MHx|PMA+APT|PbO2 +V2O5+C+E gives an open circuit voltage of 1.5V and can run for >850h at a current drain of 2.4μA cm-2. The cell can be recharged without much loss up to 18-20cycles. © 2002 Published by Elsevier Science B.V.
Transport and thermal behaviour of composite : xH3PMo12O40.nH2O + (1-x)Al2O3
(1999) Kamlesh Pandey; N. Lakshmi; S. Chandra
Proton conducting composite electrolyte consisting of hydrated phosphomolybdic acid and Al2O3 has been prepared. Composition dependence of conductivity has been explained on the basis of the interface created by the adsorption of water derived from the hydrated acids onto the Al2O3 particulates. Evidence of such bonding has been obtained from the resulting changes in DTA/TGA and IR spectra of the composite electrolyte.