E.B. Castro

Electrodeposited Ni-Co-oxide electrodes :characterization and kinetics of the oxygen evolution reaction

Abstract In this paper we present results on the characterization of Ni–Co-oxide electrodes, prepared by anodic deposition from Co(NO3)2 aqueous solutions on Ni substrates. The kinetics and mechanism of oxygen evolution was analysed. Tafel slopes close to 40 mV per decade were measured. The reaction order with respect to [OH−] was found to be approximately 2 at 25°C. A possible mechanism for oxygen evolution on these electrodes is presented, which accounts for the values of the kinetic parameters experimentally obtained.

Electrochemical characterization of porous nickel–cobalt oxide electrodes

Abstract The electrochemical characterization of mixed oxides containing cobalt and nickel prepared by cathodic electrodeposition is presented. Their catalytic properties are discussed according to the results obtained employing stationary polarization curves, voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. Impedance results were analyzed considering a porous electrode and approximated in terms of a finite transmission line model of conical pores linked in parallel. For sake of comparison, results obtained with Co–Ni cobaltites prepared by thermal decomposition are also presented.

Investigation of passive layers on iron and iron-chromium alloys by electrochemical impedance spectroscopy

The semiconductor properties of passive layers anodicaly generated on Fe and FeCr alloys in near neutral aqueous solutions, varying, at our convenience, the oxide formation potential Ef, were investigated using electrochemical impedance spectroscopy (EIS). The impedance of the system is characterized by two capacitive contributions in the 1 mHz-65 kHz frequency range. From the Mott-Schottky plots the flat band potential EFB and the donor concentration ND can be determined as a function of Ef and Cr content. A comparative study of the kinetics of the ferro-ferricyanide electron transfer reaction on passive Fe and FeCr substrates were performed to analyse the relation between the electronic properties of the anodic oxide layers and the mechanism of the redox couple electrode reaction.

The application of electrochemical impedance spectroscopy and identification procedures to the investigation of the dissolution and passivation of iron in carbonate—bicarbonate buffers at 25°C

An electrochemical impedance spectroscopy study of the dissolution and passivation of polycrystalline iron is carbonate—bicarbonate buffers at 25°C is reported. The impedance spectra analysis was performed by using an identification procedure to estimate initially the dynamic parameters from the measured impedance obtained by employing both sinusoidal and pseudo-random binary sequence perturbation, followed by a quantitative fitting on the basis of reaction schemes in terms of formal rate constants. Impedance spectra and steady-state polarization characteristics are accounted for by a reaction model involving the parallel formation of Fe(OH)2 and soluble Fe(II) species. The concentration of bicarbonate ions determines the overall current in the prepassive potential range.

An electrochemical impedance study on the kinetics and mechanism of the hydrogen evolution reaction on nickel molybdenite electrodes

Abstract Electrodeposited Ni NiMoS 2 electrodes have shown good electrocatalytic activity towards the hydrogen evolution reaction as well satisfactory long-term operational performance. The hydrogen evolution reaction on these electrodes, which in previous investigations using steady-state polarizations, cyclic voltammetry and scanning electron microscopy revealed high surface area and a very heterogeneous surface morphology, has been studied by applying electrochemical impedance spectroscopy (EIS). The kinetics and mechanism of the hydrogen evolution reaction (HER) on electrodeposited Ni NiMoS 2 electrodes have been investigated in the frequency range 5 mHz ⩽ f ⩽ 10 kHz. A detailed dynamic system analysis is presented taking into account the contributions of Tafel-Volmer-Heyrovsky reaction steps as well as the absorption and diffusion of hydrogen atoms into the electrode material. For comparison results obtained for the HER on electrodeposited Ni electrodes are also discussed.

Analysis of the impedance response of passive iron

Abstract The impedance response of passive iron is described in terms of a model that takes into account the electrochemical processes taking place at both the metal/oxide and oxide/electrolyte interfaces and the influence of the ionic transport in the passive film. The comparison of the theoretical transfer function with experimental data corresponding to iron passivated in aqueous boric acid—borate buffers leads to the conclusion that the potential perturbing signal does not interfere with the equilibrium of the layer formation reactions (deposition and removal of oxygen ions), the faradaic impedance being related to the iron dissolution through the passive film.

Parameter identification and model validation of adsorption and electron transfer processes using impedance

Abstract A procedure to identify the parameter set of electrochemical models involving adsorption–desorption of intermediates species, employing impedance measurements, is presented. Two steps are considered. First, the theoretical structural identifiability analysis of the model is carried out to know the number of parameter sets, which give the same potential/current model behavior. Second, using steady state and electrochemical impedance measurements, the parameter identification procedure based on interval analysis is carried out to identify one of the possible solutions. Accordingly, all possible parameter sets giving the same potential/current behavior are obtained . The application of structural and parametric identification procedures is discussed for the Volmer–Heyrovsky model associated with the hydrogen evolution reaction (HER).

Electrochemical performance comparison of MWCNTs/Ni (OH)2 composite materials by two preparation routes

Carbon materials are used to improve the nickel hydroxide electrode capacity in rechargeable alkaline batteries. Herein, we present the preparation of multiwall carbon nanotubes/nickel hydroxide composites (MWCNTs/Ni (OH)2) by two different routes. The first method consists of the direct incorporation of MWCNTs in the active material, and the second is based on the hydrothermal synthesis of β-nickel hydroxide, where MWCNTs are added to the precursor solutions. The electrochemical properties of the prepared positive electrodes containing MWCNTs/Ni (OH)2 composites are studied. Electrochemical results indicate that the active material with MWCNTs incorporated before the hydrothermal synthesis is capable of delivering a higher discharge capacity and exhibits a better reversibility than those composites prepared with MWCNTs after the hydrothermal route.