S.G. Real

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.

Zinc-Rich Paints on Steels in Artificial Seawater by Electrochemical Impedance Spectroscopy

Abstract Electrochemical impedance spectroscopy (EIS) was applied over a wide frequency range to characterize the corrosion protection behavior by two types of zinc-rich paints (ZRP) (zinc-rich epo...

The characteristics of the potentiodynamic potential/current profiles obtained with the Ni/0.5N H2SO4 interface. A contribution to the mechanism of the electrode process

Abstract Electrochemical data derived from different simple and complex potentiodynamic techniques for the Ni/0.5 N H 2 SO 4 interface furnish a new insight about the activation and initial stage passivation of nickel. The anodic dissolution of nickel involves a metal surface which is either partially or completely covered by species such as NiOH, [NiOH.Ni(OH) 2 ] or [Ni(OH) 2 .NiOOH]. The chemical dissolution of the various species in the acid electrolyte occurs at different rates. The relative dissolution rates can be estimated from the data derived from the complex triangular potential perturbations. The change of the E / I profile during cycling is explained through a complex reaction sequence which is in agreement with recently postulated reaction schemes and reported optical data.

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.

Study of Copper Dissolution and Passivation Processes by Electrochemical Impedance Spectroscopy

Abstract The copper electrodissolution and passivation processes in carbonate (CO32−)-bicarbonate (HCO3−) solutions at different ionic strength and hydrodynamic conditions have been studied by electrochemical impedance spectroscopy (EIS). Impedance diagrams suggest the formation of a first porous cuprous oxide (Cu2O) layer. Through this film, there is a diffusional process of Cu(II) soluble species which, together with the electrooxidation of Cu(I) to Cu(II), leads to the formation of a thicker and complex passive film. Capacitance values obtained by the application of a transfer function analysis using nonlinear fitting routines reflect the different stages during the film transformation into a stable passive one. This passive film exhibits a p-type semiconductor behavior.

An electrochemical impedance spectroscopy study of zinc rich paints on steels in artificial sea water by a transmission line model

Abstract Electrochemical impedance spectroscopy (EIS) in the 50 kHz–1 mHz frequency range was applied to characterize the corrosion protection behaviour of zinc rich ethyl silicate paints (ZRP) on steel in artificial sea water. The most accurate description of the experimental impedance spectra at the open circuit potential as a function of exposure time for different coating thicknesses, was obtained by introducing a dynamic system analysis based on the transmission line model and assuming cylindrical pores in the coating structure for the corresponding transfer function. Characteristic coating parameters of this type of ZRP during the galvanic protection period derived from nonlinear fit routines at different immersion times correlate well with the gradual coating deterioration. Results can be interpreted in terms of corrosion processes going on extensively through pores and cracks in the relatively thick ZRP coatings.

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).

The application of EIS and XPS to investigate the dissolution and passivation of Fe-Co base amorphous alloys in KHCO3-K2CO3 buffers

Abstract The corrosion behaviour of glassy Fe 80- x Co x Si 10 B 10 alloys (10 ⩽ x ⩽ 30) has been investigated and compared to that of high purity polycrystalline Fe and Co electrodes in carbonate-bicarbonate solutions. Electrochemical Impedance Spectroscopy (EIS) and X-ray Photo-electron Spectroscopy (XPS) measurements were performed under different polarization conditions. Results indicate that the dissolution and passivation reactions of Fe-Co amorphous alloys differ significantly from those of pure polycrystalline metallic components. The metal concentration ratio at the metal/solution and metal/film/solution interfaces as well as composition and morphology of the surface layers are important factors in determining the dissolution and passivation of the glassy alloys.

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.