F.M. Costa

Effect of the partial replacement of Ni or Co by Cu on the electrocatalytic activity of the NiCo2O4 spinel oxide

Abstract A comparative study of Ni 1− x Cu x Co 2 O 4 and NiCo 2− y Cu y O 4 systems derived from the NiCo 2 O 4 spinel oxide by the partial replacement of Ni or Co by Cu respectively, has been performed. The two systems have been prepared by thermal decomposition of aqueous nitrate solutions, on nickel supports, at 623 K. The influence of the amount of copper on the electrode performance towards the oxygen evolution process is studied. Steady state measurements followed by Tafel analysis has been done. The electrochemical results have been correlated with the surface composition of the electrodes by means of X-ray photoelectron spectroscopy.

Effect of the partial replacement of Fe by Ni and/or Mn on the electrocatalytic activity for oxygen evolution of the CoFe2O4 spinel oxide electrode

Abstract The study of the electrochemical behaviour of mixed spinel oxide electrodes, obtained by the partial replacement of Fe by Ni and/or Mn in the cobalt ferrite CoFe 2 O 4 is presented. The electrodes were prepared by brush painting of iron substrates with a suspension of the respective oxide, prepared by solid-state reaction. The influence of the substituent on the electrodes electrocatalytic activity towards the OER is analysed in terms of the kinetic parameters obtained by steady state measurements and the cationic distribution proposed for the oxides. The data show that the introduction of Ni brings about the presence of Co 3+ tetrahedrally coordinated in addition to the Co 3+ /Co 2+ couple in octahedral sites, giving rise to a better electrocatalyst for the OER. In contrast the presence of Mn produces electrodes with lower catalytic activity.

XPS and voltammetric studies on Ni1-xCuxCo2O4 spinel oxide electrodes

Abstract Spinel oxide electrodes of Ni 1− x Cu x Co 2 O 4 (0.00≤ x ≤0.75) layers were prepared by thermal decomposition of the corresponding nitrate solutions on Ni mesh at 350°C. The surface analysis was carried out by XPS and shows that the oxides surface is rich in copper for all the studied compositions, and when x ≤0.10 an enrichment in nickel was also observed. The surface electrochemical properties were studied by cyclic voltammetry and correlated with XPS data.

Titanium dioxide anatase as matrix for matrix‐assisted laser desorption/ionization analysis of small molecules

The use of inorganic species as assisting materials in matrix-assisted laser desorption/ionization (MALDI) analysis is an alternative approach to avoid interfering matrix ions in the low-mass region of the mass spectra. Reports of the application of inorganic species as matrices in MALDI analysis of small molecules are, however, scarce. Nevertheless, titanium dioxide (TiO(2)) powder has been reported to be a promising matrix medium. In this study we further explore the use of TiO(2) as a matrix for the MALDI analysis of low molecular weight compounds. We present results showing that nanosized TiO(2) anatase and TiO(2) rutile perform better as MALDI matrices than a commercial TiO(2) anatase/rutile mixture. Moreover, when using nanosized TiO(2) anatase as a matrix, high-quality mass spectra can be obtained with strong analyte signals and weak or non-existing matrix interference ions. Furthermore, our results show that the phase type plays an important role in the application of TiO(2) as a MALDI matrix.

Preparation and characterisation of spinel oxide ferrites suitable for oxygen evolution anodes

Abstract The effect of the partial substitution of iron by Ni and also by Mn on the properties of the CoFe2O4 spinel type oxide has been studied. The oxide powders CoFe2–xMxO4 were prepared by the standard ceramic method, and the respective structural characterisation performed by X-ray powder diffraction. In particular, the electric, magnetic and electrochemical behaviour of the monophasic mixed oxides have been analysed. From the synthesised oxide samples, iron coated electrodes were fabricated and tested as anode for the oxygen evolution reaction in alkaline medium.

Electrical conductivity study of the solubility limits of tin–antimony mixed perovskites

A series of tin–antimony mixed-oxide perovskites of the ABO3 type with A = Ba and B = Sn1–xSbx was synthesized using increasing amounts of antimony. The electrical conductivity of these solids was studied to try to detect a possible solid solution phase and to determine the valence state of the cations.Antimony dissolves in the stannic sites of the stannate perovskite structure up to a mole fraction of 0.17 in a pentavalent state (Sb5+). Above this limit, the variations in electrical conductivity have been ascribed to the formation of an insulating second solid phase whose existence was confirmed by X-ray analysis (formation of the antimonate pyrochlore structure, Ba2Sb2O7).

Effect of the substrate on the electrodeposition of iron sulphides

The electrodeposition of iron sulphides films on titanium and Ebonex®, in aqueous solutions containing iron(II) ions and colloidal sulphur, has been assessed at 333 K, using periodic pulse electrolysis. Mackinawite was the only crystalline iron sulphide phase identified on the deposit. The structural and morphological characterization of the sulphide films obtained on both substrates was accomplished by X-ray powder diffraction (XRD) and scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDS). The results show that the film structure and morphology are sensitive to the substrate material.

Voltammetric study of the Fe-S-Ebonex® system

A voltammetric study of the Fe-S-Ebonex® system at pH 3 is reported. Aqueous solutions of Na2S2O3 and (NH4)2Fe(SO4)2 were used as sources of sulphur and iron, respectively. The influence of the starting potential on the electrochemical behaviour of the system is analysed. Deposits obtained at −1.1 V vs SCE, by potentiostatic methods, show X-ray diffraction peaks of the pyrite structure. Troilite and mackinawite phases are also identified.

Electrochemical characterisation of BaSn1–xSbxO3 perovskites

The electrochemical properties of the sintered pellets of the mixed oxide perovskite system BaSn1–xSbxO3 have been investigated by cyclic voltametry and a.c. impedance measurements. The solid-state properties and morphology of the materials have also been investigated and the information used to interpret the electrochemical behaviour. The conductivity of the samples increases with antimony content and for x > 0.05 the oxides behave essentially as porous metal electrodes, exhibiting a relatively wide range of electrochemical stability.

Structural singularities of superconducting Y-Ba-Cu oxides

Singular features of the orthorhombic or tetragonal array assigned to the high-T c superconducting phase YBa 2 Cu 3 O 7−δ are pointed out: order-disorder of oxygen atoms and vacancies, and subsequent formation of anti-phase and out-of-step domains; nature and reversible character of the orthorhombic/ tetragonal phase transition; distortion trends of yttrium coordination polyhedron. Sample preparation conditions - sintering temperature, annealing atmosphere, cooling regime - are commented in terms of bulk crystal chemical characteristics. Calculated bond valence summations for the orthorhombic structure are presented.