Browsing by Author "Rahul Awasthi"

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Copper-iron-molybdenum mixed oxides as efficient oxygen evolution electrocatalysts
(Royal Society of Chemistry, 2014) Venkata Kali Vara Prasad Srirapu; Chandra Shekhar Sharma; Rahul Awasthi; Ravindra Nath Singh; Akhoury Sudhir Kumar Sinha
Ternary Cu, Fe and Mo mixed oxides having a nominal compositional formula, CuxFe2-x(MoO4)3 (0 ≤ x ≤ 1.5), have been prepared by a co-precipitation method at pH ≈ 2 and characterized by FT-IR, XRD, XPS, TEM and anodic polarization techniques for use as electrocatalysts for the oxygen evolution reaction (OER) in alkaline solutions. The crystallites of oxides with x ≤ 1 have the monoclinic crystal structure. The OER study shows that replacement of Fe in the Fe2(MoO 4)3 matrix by 0.25-1.0 mol Cu increases the apparent electrocatalytic activity. However, 1.5 mol Cu-addition is detrimental to the OER activity. At E = 1.51 V (vs. RHE) in 1 M KOH, the catalytic activity of the oxide with x = 1 was approximately 50 times the activity of the base oxide (i.e. Fe2(MoO4)3). The Tafel slope of oxides with 0.25 ≤ x ≤ 1.5 ranged between 31 and 37 mV. The reaction order of OH - concentration was nearly unity for oxides with x = 0.25 and 1.5 and it was ∼2 for oxides with x = 0.5, 0.75, and 1.0. Suitable reaction mechanisms consistent with the electrode kinetic parameters have also been proposed. This journal is © the Partner Organisations 2014.
Graphene support for enhanced electrocatalytic activity of Pd for alcohol oxidation
(2011) Ravindra Nath Singh; Rahul Awasthi
Graphene nanosheets (GNS) were synthesized by the NaBH4 reduction of freshly prepared graphite oxide and utilized as a catalyst support of palladium nanoparticles for the electrooxidation of ethanol and methanol. Home-made GNS were characterized by Raman spectroscopy and XRD. The study has shown that Pd nanoparticles dispersed on GNS were highly active for the electrooxidation of ethanol and methanol in 1 M KOH. It is observed that Pd nanoparticles dispersed on GNS are more active compared to those dispersed on nanocarbon particles (NC) or multiwall carbon nanotubes (MWCNTs) for ethanol/methanol electrooxidation under similar experimental conditions. The enhanced electrochemical activity of Pd/GNS toward alcohol oxidation can be ascribed to the greatly enhanced electrochemical active surface area of Pd nanoparticles on the GNS support. © 2011 The Royal Society of Chemistry.
Graphene-cobaltite-Pd hybrid materials for use as efficient bifunctional electrocatalysts in alkaline direct methanol fuel cells
(2013) Chandra Shekhar Sharma; Rahul Awasthi; Ravindra Nath Singh; Akhoury Sudhir Kumar Sinha
Hybrid materials comprising of Pd, MCo2O4 (where M = Mn, Co or Ni) and graphene have been prepared for use as efficient bifunctional electrocatalysts in alkaline direct methanol fuel cells. Structural and electrochemical characterizations were carried out using X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, chronoamperometry and cyclic, CO stripping, and linear sweep voltammetries. The study revealed that all the three hybrid materials are active for both methanol oxidation (MOR) and oxygen reduction (ORR) reactions in 1 M KOH. However, the Pd-MnCo2O4/GNS hybrid electrode exhibited the greatest MOR and ORR activities. This active hybrid electrode has also outstanding stability under both MOR and ORR conditions, while Pt- and other Pd-based catalysts undergo degradation under similar experimental conditions. The Pd-MnCo 2O4/GNS hybrid catalyst exhibited superior ORR activity and stability compared to even Pt in alkaline solutions. © 2013 the Owner Societies.
Graphene-Manganite-Pd Hybrids as Highly Active and Stable Electrocatalysts for Methanol Oxidation and Oxygen Reduction
(Elsevier Ltd, 2014) Chandra Shekhar Sharma; Rahul Awasthi; Ravindra Nath Singh; Akhoury Sudhir Kumar Sinha
Hybrids of graphene nanosheets (GNSs) with Pd and MMn2O 4 (M = Mn & Co) have been prepared and investigated as electrocatalysts for the methanol oxidation (MOR) and oxygen reduction (ORR) reactions in 1 M KOH at 25 °C. Results show that incorporation of Mn3O4 (or CoMn2O4) into 40wt%Pd/GNS increases the electrocatalytic activity toward both the reactions (MOR and ORR) greatly; the observed enhancement in the activity being much higher with CoMn2O4 addition. It is observed that at an anodic potential, E = 0.610 V vs RHE, 8wt% CoMn2O4 addition improves the methanol oxidation current density of 40wt%Pd/GNS by more than 3 times. Similarly, at E = 0.90 V vs RHE, 5wt% CoMn2O4 addition improves the ORR activity of 40wt%Pd/GNS nearly two times. The stability of the active hybrid electrode is also found to be outstanding under both MOR and ORR conditions. Similar stabilities have not been found with other fuel cell catalysts. In a chronoamperometry experiment at E = 0.626 V vs RHE, the methanol oxidation current observed on Pd-8%CoMn2O 4/GNS at 2 min decreased by only ∼5% at 120 min. © 2014 Published by Elsevier Ltd.
Synthesis and structural characterization of a ternary palladium-ruthenium- tin nanoalloy supported on graphene nanosheets for methanol electrooxidation in alkaline medium
(2012) Rahul Awasthi; Ravindra Nath Singh
A graphene-supported ternary Pd-Ru-Sn nanoalloy with a face centered cubic structure has been synthesized by a microwave-assisted polyol reduction method and investigated for electrooxidation of methanol in 1 M KOH at 25°C. The electrocatalytic activity of the novel ternary alloy electrode is more than 2 times higher than that of the Pd/GNS (base) electrode. It is observed that the percentage increase in catalytic activity of the ternary alloy electrode in comparison with the base electrode increases with the electrolysis time during the chronoamperometry study. © 2012 The Royal Society of Chemistry.