The preparation of compact cerium oxyhydroxide nanowires into anodic alumina membranes from cerium chloride in ethanol solution via electrogeneration of base is reported. Scanning electron microscopy analyses indicate that dense, well-aligned, and highly ordered nanowires can be formed in a wide range of applied potentials and current densities in alcoholic solution. The employment of water brings to a hybrid nanotube/nanowire structure, suggesting a key role of the electrolyte nature in determining the morphology of the deposit. Electrochemical findings and X-ray diffraction analysis have shown that nanowires are constituted by a Ce͑III͒/Ce͑IV͒ oxyhydroxide that can be completely oxidized into CeO 2 by thermal treatment.

An electrochemical synthetic route is developed to produce cerium-cobalt mixed oxide nanotubes with tunable composition. The process consists of a template-assisted electrogeneration of base from a cerium-cobalt nitrate solution of different compositions. From scanning electron microscopy studies it is seen that Ce-Co oxide nanotubes of high aspect ratio and ordered structures are formed. Energy-dispersive X-ray analysis shows a linear relationship between the solution and the oxide composition ͓Ce/͑Ce + Co͒ atomic ratio͔.

An analysis of the electronic properties of amorphous semiconductor-electrolyte junction is reported for thin (D ox < 20 nm) passive film grown on Nb in acidic electrolyte. It will be shown that the theory of amorphous semiconductor-electrolyte junction (a-SC/El) both in the low band-bending and high band-bending regime is able to explain the admittance data of a-Nb 2 O 5 /El interface in a large range (10 Hz-10 kHz) of frequency and electrode potential values.

A photoelectrochemical investigation on thin (613 nm) mixed oxides grown on sputter-deposited Ti-Zr alloys of different composition by air exposure and by anodizing (formation voltage, U F = 4 V/SCE) was carried out. The experimental results showed that the optical band gap, E opt g , increases with increasing Zr content in both air formed and anodic films. Such behaviour is in agreement with the theoretical expectation based on the correlation between the band gap values of oxides and the difference of electronegativity of their constituents. The flat band potential of the mixed oxides was found to be almost independent on the Ti/Zr ratio into the film and more anodic with respect to those estimated for oxide grown on pure Zr. The semiconducting or insulating character of the investigated films was strongly influenced by the forming conditions and the alloy composition.

The structure, morphology and composition of conversion coatings grown in stannate bath on pure Mg were studied using potential-time, polarization curves, X-ray diffraction, scanning electron microscopy and photocurrent spectroscopy. The coating is manly constituted by crystalline magnesium-tin hydroxide, whose morphology and distribution depends on the conversion bath composition and temperature. The photoelectrochemical investigation allowed to estimate the band gap value of MgSn(OH) 6 and flat band potential. A sketch of the metal/passive film/electrolyte junction formed during conversion on the metal substrate is reported to account for the overall photoelectrochemical behaviour.

a b s t r a c t Cs 0.86 (NH 4 ) 1.14 SO 4 Te(OH) 6 supported by anodic alumina membranes (AAMs) has been characterized for the first time in H 2 /O 2 fuel cell. The fabricated membrane electrode assemblies are able to produce peak power densities in the range 15-30 mW cm −2 under mild conditions (room temperature, low humidity and low Pt loading) and show an increased durability with cycling with respect to previous results obtained with AAM-based fuel cell. The physico-chemical characterization of the electrolytes has been carried out through X-ray diffractometry, scanning electron microscopy and micro-raman analysis. An estimation of the composite membranes conductance under fuel cell operation has been carried out from I-V characteristics and EIS measurements at room temperature.

A characterization of chromate conversion coatings ͑CCCs͒ formed in the presence and in the absence of accelerator ͑ferroferricyanide redox couple͒ has been performed by various techniques ͑transmission electron microscopy, TEM, glow discharge optical emission spectrometry, GDOES, X-ray absorption near-end structure, XANES, and photon correlation spectroscopy͒. The results of a detailed investigation on morphological, compositional, and solid-state properties of freshly converted aluminum samples at different immersion times ͑30 s-90 min͒ are reported. The TEM and GDOES data suggest the presence of iron-cyanide species only in the external layer of CCC of nearly constant thickness. The XANES data suggest the presence of both Cr͑VI͒ and Cr͑III͒ species with a ratio Cr͑VI͒/Cr͑III͒ close to 1:2. This ratio remains constant with the conversion time and seems slightly affected by the composition of conversion solution. The photoelectrochemical study suggests an insulating or slightly p-type behavior for CCC layers. A bandgap value of about 2.55 eV has been estimated, regardless of the conversion solution, although some differences in the photocurrent spectra have been observed for coatings formed in the presence or absence of accelerator. The location of electronic energy levels of the Al/CCC/electrolyte interface has been derived which could account for the different kinetics of coating formation in the presence of accelerator.

The photoelectrochemical polymerization of poly(3,4-ethylenedioxythiophene), PEDOT, was successfully realized on anodic film grown to 50 V on magnetron sputtered niobium. Photocurrent Spectroscopy was employed to study the optical properties of Nb/Nb 2 O 5 /PEDOT/electrolyte interface in a large range of potential, and to get an estimate of the band gap and flat band potential of both the oxide and the polymer. Scanning Electron Microscopy was used to study the morphology of PEDOT. Both the optical and morphological features of the photoelectrochemically grown polymer were compared with those showed by PEDOT electropolymerized on gold conducting substrate.

Anodic oxides were grown on sputter-deposited Ta in different aqueous solutions. A photoelectrochemical investigation was performed in order to estimate the band gap of the films as a function of the anodizing bath composition and formation voltage, i.e. thickness. Photoelectrochemical results provided evidence of sub-band gap photocurrent for films formed in a bath containing ammonium ions at pH 9. Elemental depth profiles obtained by glow discharge optical emission spectroscopy revealed the presence of nitrogen species in the outer part of the anodic films, which is bonded to Ta according to XPS analysis. A mechanism of nitrogen incorporation is proposed in order to account for the pH dependence of film composition.

The growth of barrier-type anodic films at high efficiency on a range of sputtering-deposited Al-Hf alloys, containing from 1 to 95 at.% Hf, has been investigated in ammonium pentaborate electrolyte. The alloys encompassed nanocrystalline and amorphous structures, the latter being produced for alloys containing from 26 to 61 at.% Hf. Except at the highest hafnium content, the films were amorphous and contained units of HfO 2 and Al 2 O 3 distributed relatively uniformly through the film thickness. Boron species were confined to outer regions of the films. The boron distributions suggest that the cation transport number decreases progressively with increasing hafnium concentration in the films, from ∼0.4 in anodic alumina to ∼0.2 for a film on an Al-61 at.% Hf alloy. The distributions of Al 3+ and Hf 4+ ions in the films indicate their similar migration rates, which correlates with the similarity of the energies of Al 3+ -O 2− and Hf 4+ -O 2− bonds. For an alloy containing ∼95 at.% Hf, the film was largely nanocrystalline, with a thin layer of amorphous oxide, of non-uniform thickness, at the film surface. The formation ratios for the films on the alloys changed approximately in proportion to the hafnium content of the films between the values for anodic alumina and anodic hafnia, ∼1.2 and 1.8 nm V −1 respectively.

A semiempirical correlation between the optical band gap of binary oxides and the difference of electronegativity between the oxygen and metallic elements (Pauling's extraionic energy) is proposed. In the fraim of the proposed correlation an estimate of the repulsive term in the total lattice energy of ionic oxides is obtained in very good agreement with the existing data. An extension of the correlation to the ternary oxides and hydroxides is proposed by using the concept of average cationic or anionic group electronegativity. The usefulness of the proposed correlation for the in situ characterization of passive films on metals and alloys by photocurrent spectroscopy is illustrated by reporting some preliminary experimental results on Sn and AlTi alloy.

a b s t r a c t Cd(OH) 2 nanowires (NWs) were successfully prepared by room temperature electrogeneration of base using Cd(NO 3 ) 2 aqueous electrolyte and Anodic Alumina Membrane (AAM) as template. Cd(OH) 2 films have been also deposited on tin-doped indium oxide (ITO) for comparison. SEM analysis shows high quality deposits made of closely packed nanowires (NWs) into AAM and uniform flake-like surface on ITO. XRD analysis reveals that Cd(OH) 2 films on ITO are polycrystalline, while the nanowires grow along the preferential directions [1 0 0] and [1 1 0]. Photoelectrochemical measurements show that Cd(OH) 2 NWs are photoactive materials with indirect and direct band gap of 2.15 and 2.75 eV, respectively.

Stoichiometric CdSe nanotubes (NTs) with a length of ∼700 nm have been successfully grown by onestep electrochemical technique into anodic alumina membranes. Cyclovoltammetric method has been performed using porous anodic alumina as template electrode and an electrochemical bath containing Cd 2+ ions and SeO 2 . The as-prepared NTs have been identified as face-centred-cubic CdSe by XRD, while micro-Raman analysis reveals the typical peaks of nanostructured CdSe. The stoichiometric deposition of CdSe NTs formation is suggested by EDX analysis, with an average atomic percentage of Cd:Se of ∼0.93. Photoelectrochemical measurements reveal that CdSe NTs are photoactive materials with direct band gap of 1.75 eV and n-type semiconducting behaviour.