Browsing by Author "R. Awasthi"

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Alcohol Fuel Cells
(Elsevier B.V., 2013) R.N. Singh; Madhu; R. Awasthi
[No abstract available]
Application of graphene in electrochemical devices
(Nova Science Publishers, Inc., 2014) R. Awasthi; Madhu; R.N. Singh
The catenating property of carbon makes it unique to forming various architectures (e.g. diamond, fullerenes, carbon nanotubes, graphene, etc.) at nanolevel. Graphene, a 2D material, has received increasing attention since the first historical isolation of singlelayer graphene from the crystalline graphite in 2004 owing to its unique physicochemical properties and ease of functionalization. Suitable methods have been discovered to synthesize graphene and its composites with metal/oxide nanoparticles for use in electrochemical devices to improve their efficiencies. This chapter with a brief description of methods of synthesis of graphene and its structural characterization presents a detailed review of the work carried out on application of graphene to improve the performance of electrochemical devices, namely fuel cells, supercapacitors and batteries. © 2014 by Nova Science Publishers, Inc. All rights reserved.
Electro-catalytic activities of binary nano-composites of pt and nano-carbon/multiwall carbon nanotube for methanol electro-oxidation
(2010) R.N. Singh; R. Awasthi; S.K. Tiwari
Binary nano-composites of Pt and nano-carbon (NC) and Pt and multiwalled carbon nanotube (MWCNT) have been prepared with varied compositions ranging between 20 and 80wt% Pt and investigated them as electrocatalysts for methanol oxidation. The study shows that with the increase in wt% of NC, the apparent electro-catalytic activity of the composite catalyst increases initially, reaches maximum at about 40wt% NC and decreases thereafter. However, the anodic peak current value, estimated as per mg of Pt present in the composite, increases gradually with increasing wt% of NC in the composite. The electrochemical active surface area (EASA) value for Pt in the composite electrode also increases with increasing the carbon composition in the composite. Almost similar effect of the MWCNT addition on the electro-catalytic activity is also observed in the case of Pt-MWCNT composite. Results have shown that an incorporation of carbon (NC/MWCNT) improves both the geometrical as well as the electronic properties of Pt. © Singh et al.
Electrochemical characterization of a new binary oxide of Mo with Co for O2 evolution in alkaline solution
(2009) R.N. Singh; Madhu; R. Awasthi; A.S.K. Sinha
The α-CoMoO4 oxide has been obtained by a precipitation method and investigated for the first time for electrocatalysis of the oxygen evolution reaction (oer) in alkaline medium. This method produced the pure crystalline CoMoO4 monoclinic phase with crystallite size ∼46 nm and lattice constants: a = 9.666 Å, b = 8.854 Å, c = 7.755 Å and β = 113.82°. The average particle size (based on area density) and the BET surface area of powders of the oxide were 11.58 μm and 9.4 m2 g-1, respectively. Results show that the new oxide is quite active for the oer. Values of the Tafel slope and the reaction order with respect to OH- concentration are observed to be ∼60 mV and ∼1, respectively. © 2008 Elsevier Ltd. All rights reserved.
Graphene-supported Pd-Ru nanoparticles with superior methanol electrooxidation activity
(2013) R. Awasthi; R.N. Singh
Pd-Ru bimetallic nanoparticles dispersed on graphene nanosheets (GNS) have been obtained by a microwave-assisted polyol reduction method and investigated for methanol electrooxidation in 1 M KOH + 1 M CH 3OH at 25 °C. Structural and electrochemical characterizations of electrocatalysts are carried out by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, CO stripping voltammetry and chronoamperometry. The study shows that introduction of Ru (1-10 wt.%) into 40 wt.%Pd/GNS produces an alloy of Pd and Ru with the face centered cubic crystal structure. The electrocatalytic activity increased with increasing percentage of Ru in the Pd-Ru alloy showing maximum with 5 wt.%Ru. The electrocatalytic activity of the 40 wt.%Pd-5 wt.%Ru/GNS electrode at E = -0.10 V vs. Hg/HgO was ∼2.6 times greater than that of the base (40 wt.%Pd/GNS) electrode. Based on the methanol oxidation current, measured at 1 h during the chronoamperometry tests at E = -0.10 V vs. Hg/HgO, the active 40 wt.%Pd-5 wt.%Ru/GNS electrode exhibited ∼72% and ∼675% higher poisoning tolerance as compared to 40%Pd/GNS and 40%Pd/multiwalled carbon nanotube electrodes, respectively. © 2012 Published by Elsevier Ltd.
Iron molybdates as electrocatalysts for O2 evolution reaction in alkaline solutions
(2009) R.N. Singh; Madhu; R. Awasthi; S.K. Tiwari
Iron molybdates with [Mo]/[Fe] ratios 1.0, 1.5 and 3.0 have been prepared by a co-precipitation method and produced in the form of thin films on a Ni support. These oxides follow the monoclinic crystal geometry. The study shows that the new oxide is highly active towards the oxygen evolution reaction in alkaline solutions and that its activity seems to depend upon the molar ratio of Mo and Fe in the oxide. The oxide with [Mo]/[Fe] = 1.0 is observed to exhibit the greatest electrocatalytic activity. The reaction order with respect to OH- concentration has been found to be fractional (0.8-1.6). The Tafel slopes at low potentials were close to 35 mV. © 2009 International Association for Hydrogen Energy.
Manganese molybdate and its Fe-substituted products as new efficient electrocatalysts for oxygen evolution in alkaline solutions
(2013) V.K.V.P. Srirapu; M. Kumar; R. Awasthi; R.N. Singh; A.S.K. Sinha
Pure and Fe-substituted manganese molybdates with nominal compositional formula FexMn1-xMoO4 (x = 0, 0.25, 0.50 and 0.75) have been prepared by a co-precipitation method at pH ≈ 2 and characterized by FT-IR, XRD, XPS, TEM, electrochemical impedance and polarization techniques. The oxygen evolution reaction (OER) study reveals that Fe substitutions from 0.25 to 0.75 mol for Mn increase the apparent electrocatalytic activity of the base oxide showing maximum with 0.5 mol Fe. At E = 0.60 V vs. Hg/HgO in 1 M KOH at 298 K, the apparent activity of the base oxide increased ∼58 times. It is observed that on Fe addition, the Tafel slope decreases from ∼60 to ∼35 mV, however, the order of the OER with respect to OH- concentration as observed ∼2 on the base oxide (i.e. MnMoO4) does not change. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
New ternary Fe, Co, and Mo mixed oxide electrocatalysts for oxygen evolution
(2011) M. Kumar; R. Awasthi; A.S.K. Sinha; R.N. Singh
Ternary mixed oxides of Fe, Co, and Mo with composition Fe xCo1-xMoO4 (x = 0.25, 0.50 & 0.75) have been prepared by a co-precipitation method and investigated as electrocatalysts for the oxygen evolution reaction (OER) in alkaline solutions. The study indicates that partial replacement of Co by Fe in the CoMoO4 matrix increases the specific surface area as well as the apparent electrocatalytic activity of the oxide; the magnitude of increase being the greatest with x = 0.25. The order for the OER with respect to OH- concentration has been observed to be ∼2 on Fe0.75Co0.25MoO4 and ∼1 on Fe0.25Co0.75MoO4 and Fe 0.5Co0.5MoO4. The Tafel slopes at low overpotentials were close to 40 mV with each oxide catalyst. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
New ternary mixed oxides of Fe, Ni and Mo for enhanced oxygen evolution
(2011) M. Kumar; R. Awasthi; A.K. Pramanick; R.N. Singh
Ternary mixed oxides of Fe, Ni and Mo with molecular formulas Fe xNi1-xMoO4 (x = 0.25, 0.50 and 0.75) have been prepared by a co-precipitation method and investigated for their structural and electrocatalytic properties by XRD, AFM, electrochemical impedance spectroscopy and anodic Tafel polarization. Results indicate that the apparent oxygen evolution activity of the base (NiMoO4) electrode significantly increases with introduction of Fe from 0.25 to 0.75 mol. The Tafel slope for the oxygen evolution reaction at low overpotentials is found to be only ∼35 mV on Fe-substituted oxides, while it was ∼75 mV on the base oxide. The reaction follows the first order kinetics with respect to OH- concentration, regardless of Fe content in the oxide. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Optimization of the Pd-Sn-GNS nanocomposite for enhanced electrooxidation of methanol
(2012) R. Awasthi; R.N. Singh
Highly dispersed Pd nanoparticles with varying loadings (15-40 wt%) and (20 - x)%Pd-x%Sn (where x = 1, 2, 3 and 5) nanocomposites are obtained on graphene nanosheets (GNS) by a microwave-assisted ethylene glycol (EG) reduction method for methanol electrooxidation in alkaline solution. The electrocatalysts were characterized by XRD, SEM, TEM, cyclic voltammetry, and chronoamperometry. The study shows that the Pd nanoparticles on GNS are crystalline and follow the face centered cubic structure. Introduction of a small amount of Sn (1-5 wt%) shifts the characteristic diffraction peaks for Pd slightly to a lower angle. The electrocatalytic performance of the Pd/GNS electrodes has been observed to be the best with 20 wt% Pd loading; a higher or lower loading than 20 wt% Pd produces an electrode with relatively low catalytic activity. The apparent catalytic activity of this active electrode at E = -0.10 V is found to improve further by 79% and CO poisoning tolerance by 40% with introduction of 2 wt% Sn. Among the electrodes investigated, the 18%Pd-2%Sn/GNS exhibited the greatest electrocatalytic activity toward methanol electrooxidation. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Preparation and electrochemical characterization of a new NiMoO 4 catalyst for electrochemical O 2 evolution
(2009) R.N. Singh; Madhu; R. Awasthi; A.S.K. Sinha
The NiMoO 4 catalyst has been obtained by a precipitation method under a controlled pH condition and characterized ex situ by infrared, X-ray diffraction, Brunauer-Emmett-Teller (BET), and particle size, and in situ by cyclic voltammetry, impedance and steady-state anodic Tafel polarization techniques. Results show that NiMoO 4 has pure crystalline monoclinic phase with the crystallite size ~50 nm and the lattice constants, a∈=∈9.597 Å, b∈=∈8.765 Å, c∈=∈7.667 Å, and β∈=∈114.22°. Values of the average particle size and BET surface area of the oxide powders are found to be 730 nm and 11.75 m 2/g, respectively. The oxygen evolution reaction follows the first-order kinetics with respect to OH - concentration, the Tafel slope being ~70 mV. © 2008 Springer-Verlag.
Preparation of nanostructured Pd-C-Ru composite electrodes for alcohol electrooxidations. part-I: A study of ethanol oxidation by cyclic voltammetry and impedance spectroscopy
(2011) Anindita; R. Awasthi; Madhu; R.N. Singh
Ternary nanocomposite films of Pd, Ru and nanocarbon (C) are obtained on glassy carbon (GC) and studied by XRD, TEM, cyclic voltammetry (CV), impedance and chronoamperometric techniques for their use as electrocatalysts for ethanol oxidation reaction (EOR). Results show that introduction of Ru to the Pd-0.5wt%C composite electrode increases the electrocatalytic activity greatly. It is observed that with Ru addition from 1 to 50 wt%, the rate for EOR initially increases, attains a maximum (at 20wt %) and declines thereafter. Further, among the electrocatalysts investigated, the Pd- 0.5wt%C-20wt% Ru electrode has displayed the greatest electrocatalytic activity. This electrode has nearly two times higher activity than the base electrode (Pd-0.5wt%C). © Anindita et al.
Preparation of nanostructured Pd-C-ru composite electrodes for alcohol electrooxidations. Part-II: A study of methanol oxidation by cyclic voltammetry and impedance spectroscopy
(2011) Anindita; R. Awasthi; Madhu; R.N. Singh
Ternary nanocomposites of Pd, Ru and nanocarbon (NC) have been prepared by the sodium borohydride reduction method and investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry techniques for their use as electrocatalysts for the methanol oxidation reaction (MOR). The study have shown that with addition of ruthenium from 1 to 50wt %, in the Pd-0.5wt %C composite, the rate of MOR initially increases, attains maximum and declines thereafter. Among ternary composites investigated, the Pd-0.5wt % C-20wt % Ru composite exhibited the greatest electrocatalytic activity. This electrode has approximately three times higher electrocatalytic activity than the base electrode (Pd-0.5wt % C). The electrochemical active surface area (≈133 m 2/gPd) and the percentage utilization of Pd (30%) of the Pd-0.5wt % C-20wt % Ru electrode were also more than 5 times higher than that of the base electrode. © Anindita et al.
Review: An overview of recent development of platinum-based cathode materials for direct methanol fuel cells
(Electrochemical Science Group, 2014) R.N. Singh; R. Awasthi; C.S. Sharma
Among pure metals, platinum is the best electrocatalyst for the oxygen reduction reaction (ORR) in direct methanol fuel cells. Its activity is further improved when supported on a high surface area carbon support. However, platinum metal is pretty costly and highly sensitive to the presence of even small amounts of liquid fuel that permeates from anode to the cathode side through the commonly used Nafion electrolyte membrane. Concerted efforts have been made to improve its methanol tolerance and mass utilization efficiency. As a result, several novel bi- and multi-metallic Pt alloys/composites and other Pt-based electrodes with innovative designs, such as hollow Pt nano-spheres, core/shell Pt/C nanoparticles, Pt-rich (or pure) skin structure, etc. have recently been reported. This paper presents an overview of all the advances made with regard to design, synthesis and ORR activity of Pt-based cathodes during the period 2000-2013. © 2014 The Authors.
Synthesis and characterization of nano structured Pd-Ni and Pd-Ni-C composites towards electrooxidation of alcohols
(2010) R. Awasthi; Anindita; R.N. Singh
Nanostructured (100-x)% Pd -x % Ni (x = 1, 2, 5, 10, and 20) and (90 - y)%Pd-10%Ni-y%C (y = 0.5, 1, 2, 5, and 10) composite films are obtained on glassy carbon electrodes and characterized by XRD, TEM, cyclic voltammetry and chronoamperometric techniques for use as electrocatalysts towards methanol, ethanol, ethylene glycol and glycerol oxidations in 1 M KOH at 25°C. Results show that addition of Ni from 1 to 20% to the pure Pd electrode increases the electrocatalytic activity for electrooxidation of each alcohol showing maximum with 10% Ni. Further, all the Pd-Ni composite electrodes exhibit better electrocatalytic performance in the case of ethanol electrooxidation. The rate of electrooxidation of different alcohols on the active 90%Pd-10 % Ni electrode at E = -0.20 V in 1 M KOH is observed to follow the order: ethanol > methanol> ethylene glycol > glycerol. Incorporation of C from 0.5 to 10% to the active Pd- 10% Ni composite improves the electrocatalytic performance of the electrode further, the magnitude of improvement being greatest with 5%C. The apparent electrocatalytic activity of the active 90%Pd-10%Ni electrode at E = -0.20 V is enhanced ~ 1.3 to 2.1 times with introduction of 5%C. © Awasthi et al.
Ternary platinum-multiwall carbon nanotube-cobaltite composites for methanol electrooxidation
(2011) R. Awasthi; R.N. Singh
Ternary nanocomposite films of platinum, multiwall carbon nanotube (MWCNT) and cobaltite with composition 60wt%Pt-xwt%Co3O4-(40-x)wt%MWCNT (where x = 0, 5, 10, 20 and 25) are obtained on glassy carbon (GC) electrodes and investigated for electrocatalysis of the methanol oxidation reaction (MOR) in 0.5 M H2SO4. The study shows that introduction of 5 to 25wt%Co3O4 in place of MWCNT in the 60wt%Pt-40wt%MWCNT composite reduces the onset potential (Eop) and increases the rate of MOR significantly; the magnitudes of decrease in Eop and increase in the rate being the greatest with 10wt%Co3O4. The rate of MOR improved more than 50% with 10wt%Co3O4. The poisoning tolerance of the composite electrode was also observed to be better in presence of the oxide. © 2011 by ESG.
Use of Pd-MnMoO4-graphene hybrids as efficient and CO poisoning tolerant electrocatalysts for methanol oxidation
(2013) C.S. Sharma; R. Awasthi; R.N. Singh
40 wt%Pd-x wt%MnMoO4/Graphene (GNS) (0 ≤ x ≤ 20) hybrids have been synthesized for use as efficient and CO poisoning tolerant anode materials in methanol fuel cells. Investigations revealed that the addition of MnMoO4 increases the electrocatalytic activity of the base electrode (40 wt%Pd/GNS) towards the methanol oxidation reaction (MOR) in 1 M KOH significantly. The catalytic activity of the electrode is found to be the greatest with 8 wt%MnMoO4. The addition of MnMoO4 also improves CO poisoning tolerance of the base electrode by 11-73%. The MOR activity and CO poisoning tolerance of the 40 wt%Pd-8 wt%MnMoO4/GNS hybrid electrode were superior to other electrodes of the investigation. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.