Browsing by Author "P. Chartier"

Now showing 1 - 14 of 14

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.
Co3O4 and co-based spinel oxides bifunctional oxygen electrodes
(2010) M. Hamdani; R.N. Singh; P. Chartier
Many spinel cobaltite oxides meet the requirement for a wide range of electrochemical reactions. These materials have largely been investigated as electrocatalysts for the oxygen evolution reaction (OER) or oxygen reduction reaction (ORR). The objective of this article is to summarize the studies available in the literature on electrochemical and electrocatalytic properties of cobaltite spinel oxides towards the OER and ORR in alkaline media. The main focus of this review is on the recent investigations dealing with the performance of Co3O4and Cobased spinel oxides as the oxygen electrodes in the light of the earlier published work. © 2010 by ESG.
Effect of partial substitution of Cr on electrocatalytic properties of MnFe2 O4 towards O2-evolution in alkaline medium
(2006) R.N. Singh; J.P. Singh; H. Nguyen Cong; P. Chartier
Some Cr-substituted manganese ferrites have been synthesized by a precipitation method in order to reduce the oxygen overpotential on the MnFe2 O4 surface. The study showed that Cr substitution from 0.1 to 1.0 mol considerably improved the electrocatalytic activity of the oxide for the oxygen evolution reaction (OER). Values of the Tafel slope and the order for the OER with respect to OH- concentration were ∼ 2 × 2.303 RT / 3 F and ∼ 2 and ∼ 2.303 RT / F and ∼ 1.5 at low and high over potentials, respectively. © 2006 International Association for Hydrogen Energy.
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 characterization of composite films of LaNiO3 and polypyrrole for electrocatalysis of O2 reduction
(2007) R.N. Singh; M. Malviya; P. Chartier
Electronically conductive composite electrodes G/PPy/PPy(Ox)/PPy made of polypyrrole, PPy, and the perovskite oxide LaNiO} on graphite, G, have been obtained following a sequential electrodeposition method and were investigated by electrochemical impedance spectroscopy, linear and cyclic voltammetries in an aqueous solution containing 0.5 M K2SO4plus 5 mM KOH at 25°C. Results showed that the electrical conductivity of the composite electrode remained practically constant under the cathodic polarization condition. The electrocatalytic activity of LaNiO3 towards the oxygen reduction reaction (ORR) enhanced greatly when it was used in the form of the composite electrode. The incorporation of oxide particles has been observed to influence the morphology of the polymer film. © J. New Mat. Electrochem. Systems.
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.
Investigation of Oxygen Evolution on LaNi1-xMxO3 (M = Fe, Co, Cu; 0 < x < 0.5) Films of Controlled Roughness
(1999) R.N. Singh; S.K. Tiwari; T. Sharma; P. Chartier; J.-F. Koenig
Real current densities for the oxygen evolution reaction (OER) have been estimated taking into account the surface roughness in the case of films of perovskites LaNi1-xMxO3 (M = Fe, Co, Cu, 0 < x < 0.5). The oxides have been prepared in powder form via the malic acid route, involving decomposition at 650°C of an amorphous malate gel. The films were characterized ex-situ by XRD and EDAX, and in-situ by AC impedance and cyclic voltammetry (CV). Electrocatalytic properties towards the OER were investigated by ordinary stationnary voltammetry. It was found that AC impedance and CV yielded similar roughness factors. The substitution of Fe, Co and Cu had practically no effect on the roughnesses, current densities and reaction mechanism of the OER, and only marginal effect on the electrocatalytic activity.
Oxidation of methanol on perovskite-type La2-xSrxNiO4 (0 ≤ x ≤ 1) film electrodes modified by dispersed nickel in 1 M KOH
(2008) R.N. Singh; A. Singh; D. Mishra; Anindita; P. Chartier
Finely-dispersed nickel particles are electrodeposited on high surface-area perovskite-type La2-xSrxNiO4 (0 ≤ x ≤ 1) electrodes for possible use in a direct methanol fuel cell (DMFC). The study is conducted by cyclic voltammetry, chronoamperometry, impedance spectroscopy and anodic Tafel polarization techniques. The results show that the apparent electrocatalytic activities of the modified oxide electrodes are much higher than those of unmodified electrodes under similar experimental conditions; the observed activity is the greatest with the modified La1.5Sr0.5NiO4 electrode. At 0.550 V (vs. Hg|HgO) in 1 M KOH + 1 M CH3OH at 25 °C, the latter electrode delivers a current density of over 200 mA cm-2, whereas other electrodes of the series produce relatively low values (65-117 mA cm-2). To our knowledge, such high methanol oxidation current densities have not been reported on any other non-platinum electrode in alkaline solution. Further, the modified electrodes are not poisoned by methanol oxidation intermediates/products. © 2008 Elsevier B.V. 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.
Physicochemical and electrochemical characterization of active films of LaNiO3 for use as anode in alkaline water electrolysis
(1995) S.P. Singh; R.N. Singh; G. Poillearat; P. Chartier
Thin films of LaNiO3 were prepared on Ni by the sequential coating method, and the effects of film preparation variables, such as concentration of the mixed metal nitrates solution, temperature and oxide loading, were examined for the electrocatalytic activity of the film regarding oxygen evolution in concentrated KOH solution. The oxide film with a loading of ~6 mg cm-2 was found to be the best electocatalyst among the electrodes prepared in situ. The activity of this film electrode was better than those prepared by othermethods, following sequential coatings of solution or mixed oxide coatings. Electrode kinetic parameters, such as Tafel slope, reaction order and activation energy, were found to be ~65 mV decade-1, ~1.2 and 18.4 kcal, respectively. Cyclic voltammetric studies, prior to the onset of oxygen evolution, exhibited two characteristic peaks corresponding to a diffusion-controlled surface redox process: Ni2+ → Ni3+. Based on these results, a probable mechanism for oxygen evolution on the oxide film electrode is suggested. © 1995.
Polypyrrole and La1-xSrxMnO3 (0≤ x ≤0.4) composite electrodes for electroreduction of oxygen in alkaline medium
(2007) R.N. Singh; M. Malviya; Anindita; A.S.K. Sinha; P. Chartier
Composite G/PPy/PPy(La1-xSrxMnO3)/PPy electrodes made of the perovskite La1-xSrxMnO3 embedded into a polypyrrole (PPy) layer, sandwiched between two pure PPy films, electrodeposited on a graphite support were investigated for electrocatalysis of the oxygen reduction reaction (ORR). PPy and PPy(La1-xSrxMnO3) (0≤ x ≤0.4) successive layers have been obtained on polished and pretreated graphite electrodes following sequential electrodeposition technique. The electrolytes used in the electrodeposition process were Ar saturated 0.1 mol dm-3 pyrrole (Py) plus 0.05 mol dm-3 K2SO4 with and without containing a suspension of 8.33 g L-1 oxide powder. Films were characterized by XRD, SEM, linear sweep voltammetry, cyclic voltammetry (CV) and electrochemical impedance (EI) spectroscopy. Electrochemical investigations were carried out at pH 12 in a 0.5 mol dm-3 K2SO4 plus 5 mmol dm-3 KOH, under both oxygenated and deoxygenated conditions. Results indicate that the porosity of the PPy matrix is considerably enhanced in presence of oxide particles. Sr substitution is found to have little influence on the electrocatalytic activity of the composite electrode towards the ORR. However, the rate of oxygen reduction decreases with decreasing pH of the electrolyte from pH 12 to pH 6. It is noteworthy that in contrast to a non-composite electrode of the same oxide in film form, the composite electrode exhibits much better electrocatalytic activity for the ORR. © 2006 Elsevier Ltd. All rights reserved.
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.
Preparation of Perovskite-Type Oxides of Cobalt by the Malic Acid Aided Process and Their Electrocatalytic Surface Properties in Relation to Oxygen Evolution
(1995) P. Chartier; S.K. Tiwari; R.N. Singh
The electrocatalytic properties of perovskite-type cobalt oxides (La1-xSrxCoO3, where x - 0, 0.2, 0.4), in the form of thin films on conductive supports, were studied by cyclic voltammetry and Tafel polarization techniques. The films had conductive and satisfactory adherent properties. The oxides were synthesized by a low temperature malic acid aided method. The cyclic voltammetry showed a pair of redox peaks prior to the onset of oxygen evolution on the oxide film with nickel support, while similar peaks were absent in the same oxide film on Pt and Ti. The anodic polarization studies indicated two Tafel slopes: 57 to 64 mV decade-1 at low and 100 to 130 mV decade-1 at high overpotentials, and first-order kinetics with respect to OH- concentration. The electrocatalytic activity of La0.8Sr0.2CoO3 film on Ni was the highest among all the electrodes prepared. The Sr substitution enhanced the electrochemically active area greatly. Results of the present investigation have been compared to those reported for similar oxides obtained by other methods. © 1994, The Electrochemical Society, Inc. All rights reserved.
Sol-gel derived spinel MxCo3-xO4 (M = Ni, Cu; 0≤x≤1) films and oxygen evolution
(Elsevier Science Ltd, 2000) R.N. Singh; J.P. Pandey; N.K. Singh; B. Lal; P. Chartier; J.-F. Koenig
Spinel-type binary transition metal oxides of cobalt and nickel (or copper) with composition MxCo3-xO4 (where M = Ni, Cu; 0≤x≤1) were synthesized in film forms by a sol-gel route and their physicochemical and electrocatalytic properties have been investigated using SEM, XRD, cyclic and stationary voltammetries. The roughness factors, RF, of electrodes made of these films were determined by AC-impedance and cyclic voltammetry (CV). The two procedures compared well, and enabled the discrimination between apparent and true (real) electroactivity towards the oxygen evolution reaction (OER). Intermediate compositions showed a higher activity despite a lower real surface area, and laboratory tests at 70 °C in 30 wt% KOH good practical performances.