Electrochemical characterization of thin passive films on Nb electrodes in H3PO4 solutions

The electrical and semiconducting properties of thin anodic passive films potentiostatically formed (1 V £ Ef £ 5 V vs. sce) on polycrystalline niobium electrodes in aqueous 0.5 mol/L H3PO4 solutions (pH 1.3) were studied, at room temperature, using electrochemical impedance spectroscopy. The data were analysed with a transfer function using a non-linear fitting routine, assuming that the resistance of the film is coupled in series with the faradaic impedance of the Nb(0) Nb(V) reaction, and these in parallel with the capacitance of the passive film/electrolyte interface. The relative permittivity of the films was estimated as about 44. The number concentration of donors (N D) in the films was found to decrease with Ef (i.e., with increasing film thickness). A flat band potential value of -0.72 V was also obtained from Mott-Schottky plots

Electrochemical Characterization of Thin Passive Films on Nb Electrodes in H3PO4 Solutions

The electrical and semiconducting properties of thin anodic passive films potentiostatically formed (1 V ≤ Ef ≤ 5 V vs. sce) on polycrystalline niobium electrodes in aqueous 0.5 mol/L H3PO4 solutions (pH 1.3) were studied, at room temperature, using electrochemical impedance spectroscopy. The data were analysed with a transfer function using a non-linear fitting routine, assuming that the resistance of the film is coupled in series with the faradaic impedance of the Nb(0) → Nb(V) reaction, and these in parallel with the capacitance of the passive film/electrolyte interface. The relative permittivity of the films was estimated as about 44. The number concentration of donors (ND) in the films was found to decrease with Ef (i.e., with increasing film thickness). A flat band potential value of -0.72 V was also obtained from Mott-Schottky plots.Utilizando-se a espectroscopia de impedância eletroquímica, foram estudadas as propriedades elétricas e semicondutoras de filmes anódicos passivos formados potenciostaticamente (1 V ≤ Ef ≤ 5 V vs. ecs) sobre eletrodos de nióbio policristalino em soluções aquosas de H3PO4 0,5 mol/L (pH 1,3), a temperatura ambiente. Os dados foram analisados com uma função de transferência usando uma rotina de ajuste não-linear, supondo que a resistência do filme está acoplada em série com a impedância faradaica da reação Nb(0) → Nb(V) e estas em paralelo com a capacitância da interface filme/eletrólito. A permissividade relativa dos filmes foi estimada como cerca de 44. Encontrou-se que a concentração em número de doadores (ND) nos filmes decresce com Ef (isto é, à medida que a espessura do filme aumenta). A partir de gráficos de Mott-Schottky, também obteve-se um valor de -0,72 V para o potencial de banda plana.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Microwave-Assisted Synthesis of Pt-Au Nanoparticles with Enhanced Electrocatalytic Activity for the Oxidation of Formic Acid

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) is gratefully acknowledged for financial support under Research Project BJT-2014/400117/2014-2 and for the research support (HV: grant #306151/2010-3). Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) is also acknowledged for financial support (grants #2013/07296-2 and #2013/16930-7), and scholarship (FWH: grant #2014/08030-9). GC gratefully acknowledges R. Camargo for his collaboration in the acquisition of the HR-TEM images and for useful discussion and suggestions.Peer reviewedPostprin

Influence of the preparation procedure on the electrochemical properties of Pani(DMcT-Cu ion)/carbon fiber composites

The electrochemical properties of Pani(DMcT-Cu ion)/carbon fiber composites, obtained by electrochemical means, are analysed as a function of the preparation procedure and the different copper salts (CuCl2.2H2O or CuSO4) used as source of Cu2+ ions to be incorporated into the Pani(DMcT)/carbon fiber composite. The composites were prepared according to two procedures: by adding the copper salt directly to the electrolyte during the polyaniline electrosynthesis (procedure A), or by allowing the copper ion to be physically adsorbed onto the carbon fiber prior to the polymer electroformation (procedure B). The electrochemical stability, electrical properties and morphology of the composites were analysed by cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy, respectively