Browsing by Author "S. Samuel"

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Active thin NiCo2O4 film prepared on nickel by spray pyrolysis for oxygen evolution
(1995) S.K. Tiwari; S. Samuel; R.N. Singh; G. Poillerat; J.F. Koenig; P. Chartier
Thin films of NiCo2O4 were prepared on Ni at 370 °C by the method of spray pyrolysis. The films were uniform, adherent, free from cracks and electrocatalytically much more active for oxygen evolution than other NiCo2O4 films recently reported in the literature. This film electrode showed two Tafel slopes ~40 and ~120 mV decade-1 at low and high overpotential, respectively. The second-order observed kinetics in OH- concentration at lower overpotentials changed to first-order at higher overpotentials. A suitable mechanism involving the formation of a physisorbed hydrogen peroxide intermediate in a slow electrochemical step has been suggested. © 1994.
Electrocatalytic properties of CuxCo3-xO4 (0 ≤ x ≤ 1) obtained by a new precipitation method for oxygen evolution
(1999) B. Lal; N.K. Singh; S. Samuel; R.N. Singh
Pure and copper-substituted cobaltites have been prepared by the hydroxide-carbonate-co-precipitation method and investigated in the form of films on nickel for their electrocatalytic properties towards oxygen evolution in alkaline solution. Results showed the marked improvement in the roughness as well as in the apparent electrocatalytic activity of the oxide. However, the substitution of Co by Cu in the spinel lattice did not indicate any significant electrocatalytic influence on the rate of oxygen evolution. Values of the Tafel slope and the reaction order with respect to OH- concentration have been observed to be ≅ 2.3 RT/F and one at low overpotential and 2 × 2.3 RT/F and one at high overpotential with each catalyst regardless of its nature.
Preparation of thin Co3O4 films on Ni and their electrocatalytic surface properties towards oxygen evolution
(Elsevier Ltd, 1996) S.P. Singh; S. Samuel; S.K. Tiwari; R.N. Singh
Thin films of Co3O4 of varying thicknesses have been prepared on an Ni substrate by spray pyrolysis and sequential solution coatings and investigated for their physicochemical and electrochemical properties towards O2 evolution. The study indicated that the oxide roughness factor tended to level off with increasing thickness. Further, with an increase in oxide loading, the apparent electrochemical activity enhanced considerably at low range of loadings and then became relatively constant over a range of loadings. The higher loadings were found to be harmful. The layered oxide films (2.4-4.2 mg cm-2) prepared in sequential solution coatings exhibited greatest electrocatalytic activity in 1M KOH. However, the oxide electrode (loading: 3-5.7 mg cm-2) prepared by rotating spray pyrolysis produced the lowest oxygen overpotential - 360 ± 3 mV against a current density of 1 A cm-2 in 30 w/o KOH at 70°C. The oxygen evolution reaction at these film electrodes exhibited two Tafel slopes: 51-68 mV decade-1 at low overpotentials and 120-140 mV decade-1 at high overpotentials. The reaction orders with respect to OH- concentration were found to be ∼1 for the layered and ∼2 for the sprayed films. Based on the results, a suitable mechanism is also suggested for oxygen evolution.