Browsing by Author "G. Poillerat"

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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.
Electrocatalysis of oxygen evolution/reduction on LaNiO3 prepared by a novel malic acid-aided method
(Springer Netherlands, 1998) S.K. Tiwari; J.F. Koenig; G. Poillerat; P. Chartier; R.N. Singh
A kinetic study of the electroformation and electroreduction of oxygen in KOH solutions has been carried out on a LaNiO3 electrode obtained through a malic acid precursor route. The new electrocatalyst was found to show greatly enhanced activity for both oxygen evolution and reduction. The apparent electrocatalytic activity of this electrode for oxygen reduction was more than 10 times higher than those reported for similar electrodes obtained by other methods. It was, however, observed to be less active electrocatalytically for oxygen evolution as compared to the active LaNiO3 electrode obtained by the Bockris-Otagawa coprecipitation method. The electrochemical reaction order with respect to OH- concentration was found to be approximately 1 in the case of oxygen evolution while that for oxygen reduction, was approximately -1. The Tafel slope values for the reactions were ∼2.3 RT/F and ∼2 × 2.3 RT/3F, respectively.
Electrochemical Studies on Protective Thin Co3O4 and NiCo2O4 Films Prepared on Titanium by Spray Pyrolysis for Oxygen Evolution
(1990) Ravindra N. Singh; J.-F. Koenig; G. Poillerat; P. Chartier
Electrochemical studies were done on thin Co3O4 and NiCo2O4 films on Ti by cyclic voltammetric and potentiostatic polarization techniques. The films were quite conductive and prevented the underlying surface from playing a harmful role during measurements. The results indicated the formation of a surface quasi-reversible redox couple, CoIV/CoIII, in KOH solution. The reaction order with respect to OH− ion concentration was found to be nearly 2. The Tafel slopes decreased with increasing KOH concentrations. NiCo2O4 was observed to evolve oxygen gas at a lower overpotential as compared to that of Co3O4. Electrode kinetic parameters suggest similar mechanisms for the oxygen evolution for both the oxides. © 1990, The Electrochemical Society, Inc. All rights reserved.
Physicochemical and electrocatalytic properties of LaNiO3 prepared by a low-temperature route for anode application in alkaline water electrolysis
(Kluwer Academic Publishers, 1995) R.N. Singh; A.N. Jain; S.K. Tiwari; G. Poillerat; P. Chartier
LaNi1-xFexO3 (x = 0, 0.25, 0.5) has been synthesized by the hydroxide solid solution precursor method for electrochemical characterization as oxygen anode in strongly alkaline medium. Studies were made at the oxide film, which was obtained by the oxide-slurry painting technique. The cyclic voltammetric study showed the formation of a diffusion-controlled quasireversible redox couple, Ni(ii)/Ni(iii), (E0 ∼- 430 ± 10 mV) at the oxide surface in 1 m KOH. The reaction was observed to follow approximately first-order kinetics in OH- concentration. Values of the Tafel slope ranged between 59 and 86 mV decade-1 with all the oxide film electrodes. The electrocatalytic activity was found to be greatest with the Ni/LaNi0.75Fe0.25O3 electrode. A comparison was made between the electrocatalytic activities of LaNiO3 prepared by the hydroxide solid solution precursor and by the hydroxide coprecipitation technique. © 1995 Chapman & Hall.
Preparation and characterization of thin films of LaNiO3 for anode application in alkaline water electrolysis
(Kluwer Academic Publishers, 1994) R.N. Singh; L. Bahadur; J.P. Pandey; S.P. Singh; P. Chartier; G. Poillerat
LaNiO3 electrodes were prepared, in the form of thin films on platinum by the methods of spray pyrolysis and sequential coating of mixed metal nitrate solutions followed by thermal decomposition. The films were adherent and of p-type semiconducting. Cyclic voltammetric studies indicated the formation of a quasireversible surface redox couple, Ni(iii)/Ni(ii), on these films before the onset of oxygen evolution in 1 m KOH. The anodic Tafel slopes were ∼40 and ∼65 mV decade-1, on the sprayed LaNiO3 film and on the film obtained by a layer method, respectively. The reaction order with respect to OH- was found to be 2.2 on the sprayed oxide film and 1.2 on the layer film. The sprayed oxide film was found to be electrocatalytically more active. It is suggested that the oxygen evolution reaction proceeds on both the film electrodes via the formation of the physisorbed H2O2 as an intermediate in the rate determining step. © 1994 Chapman & Hall.