Ruthenium, iridium, and mixed ruthenium/iridium oxide layers on titanium substrates have been obtained by thermal decomposition of chloride solutions. The decomposition temperature of Ru02 and 1r02 was varied from 300 to 500°C and from 400 to 500°C, respectively. That on the mixed RuIr,_rO2 layer was kept constant at 400°C. For the mixed oxide electrode, the Ru content was varied over the whole compositional range. Current-potential curves and cyclic voltammetry measurements were performed in 1 M 112S04. It is shown that such oxide layers can be activated through cathodic polarization, leading to an increase of the electrocatalytic activity for hydrogen evolution. The ratio between the current density at a given electrode potential before and after completion of the activation process or the ratio between the exchange current density before and after the completion of the activation process was used to quantify this activation phenomenon. Values as high as 100 have been observed in some cases, but typical values are around ten. Through a series of specific measurements and comparison with data taken from the literature, it is shown that this activation phenomenon is not related to an increase of the electrochemically active surface area as determined through cyclic voltammetry measurements. An explanation is proposed whereby H-.chemisorption within the oxide layer is ultimately responsible for the increase of the electrocatalytic activity of the oxide layer.* Electrochemical Society Student Member. * * Electrochemical Society Active Member. looking only to pure ruthenium oxide and pure iridium

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The effect of adding oxygen on the structure of nanocrystalline Ti-Ru-Fe compounds obtained by high-energy ball-milling has been studied by X-ray and neutron diffraction using a Rietveld refinement analysis. It is shown that oxygen atoms readily oxidize Ti to form various types of titanium oxides depending on the oxygen content. In each case, a simple cubic structure (cP2-CsCl) is also formed during milling but with a concentration higher than expected on the basis of various reaction schemes. Through a detailed analysis of the neutron and X-ray diffraction peaks, it is shown that the 1a site of the CsCl-type unit cell is depleted from Ti atoms by preferential substitution with Fe. At high oxygen concentration, the alloy is a multiphase material containing Ti 2-x Ru 1+y Fe 1+z , Ti oxides, Ru, and Fe.

The high energy mechanical alloying of a Ti–Ru–Fe powder mixture (atomic ratio 2 : 1: 1) has been performed by extensive ball-milling in a steel crucible. The structural evolution of the resulting materials has been studied by x-ray powder diffraction analysis. The identification of the various phases present in the materials, as well as the crystallite size and strain, has been performed by Rietveld refinement analysis. In the first stage of the material transformation, Ru or Fe atoms dissolved into Ti to yield to the formation of β–Ti. Upon further ball-milling, almost all the original constituents of the powder mixture have disappeared and a new simple cubic Ti2RuFe phase is formed, with a crystallite size as small as 8 nm. The electrochemical properties of these materials have been tested in a typical chlorate electrolyte by cold-pressing the powders into disk electrodes. At 20 h of ball-milling, where the phase concentration of Ti2RuFe reaches 96%, a reduction of the activation overpotential at 250 mA cm−2 of nearly 250 mV is observed when compared to that of a pure iron electrode.

The structure of nanocrystalline Ti:Ru:Fe (2 -y:(1+ y)/2:(1 + y)/2) obtained by high-energy ball milling has been studied by X-ray and neutron diffraction as a function of the Ti content, for y varying from 0.00 to 1.00 by step of 0.25, using Rietveld refinement analysis. When y ) 0.00, a nanocrystalline metastable B2 cubic phase is formed, with most of the 1a site occupied by Ti atoms and the 1b site occupied by either Fe or Ru atoms. When decreasing the Ti content, the B2 structure becomes less stable. A preferential replacement of Ti by Fe on the 1a occurs and leads to the precipitation of hcp Ru. In situ X-ray diffraction measurements under hydrogen at high pressure were also made. In all cases, a shift of the diffraction peaks of the B2 structure toward the smaller 2θ values was observed. This shift is totally reversible upon removing hydrogen. It indicates that hydrogen is absorbed into the materials. The volume increase of the B2 structure varies according to the Ti content, reflecting the fact that less hydrogen is absorbed when Ti is reduced. Assuming that the volume occupied by a single hydrogen atom is ∼2.5 D 3 , the hydrogen content of the various nanocrystalline Ti:Ru:Fe (2 -y:(1 + y)/2:(1 + y)/2) is calculated from the volume increase of the unit cell of the corresponding materials.