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1.
Self-organized porous titanium oxide prepared in Na2SO4/NaF electrolytes   总被引:1,自引:0,他引:1  
The anodic formation of nanoporous TiO2 on titanium was investigated in Na2SO4 electrolytes containing low concentrations of NaF (0.1-1 wt.%). It was found that under optimized electrolyte conditions and extended polarization, a self-organized nanostructure consisting of porous TiO2 is obtained. The porous structure is arranged in sections of arrays with single pore diameters of typically 100 nm and an average spacing of 150 nm. The pores are open at the top and covered by oxide at the bottom. Compared with earlier work, we show that using a neutral NaF electrolyte significantly thicker porous layers can be obtained than in acidic solutions.  相似文献   

2.
The oxygen reduction reaction (ORR) was studied on carbon dispersed Pt and Pt-Co alloyed nanocatalysts with high contents of Co in H2SO4 and H2SO4/CH3OH solutions. The characterization techniques considered were transmission electron microscopy (TEM), X-ray diffraction (XRD) and in situ X-ray absorption near edge structure (XANES). The electrochemical activity for the ORR was evaluated from steady state polarization measurements, which were carried out in an ultra thin layer rotating disk electrode. The results showed that with the increase of Co content, the nanoparticle size distributions become sharper and the mean particle diameters become smaller. XRD indicated low degree of alloy formation but significant phase segregation of Co was observed only for Pt-Co/C 1:3 and 1:5 (Pt:Co atomic ratios). The electrochemical measurements indicated that the four-electrons mechanism is mainly followed for the ORR on all materials and the electrocatalytic activities per gram of Pt is higher for the catalysts with higher Co contents. This was explained based on the XANES results which evidenced a decrease of the coverage of oxygenated Pt adsorbates due to the presence of Co. In the methanol-containing electrolyte, the Pt-Co/C 1:5 catalyst showed the highest performance. This was attributed to its low activity for the methanol oxidation due to the smaller probability for presenting three Pt neighboring Pt active sites.  相似文献   

3.
To investigate the role of polyaniline (PANI) in the corrosion protection of stainless steel (SS) in oxygen-deficient acidic solution, a separate doped PANI film electrode on a glass substrate was prepared and the test solution (1 M H2SO4) was purged with high-purity N2 until dissolved oxygen level decreased more than two orders of magnitude. In this deaerated 1 M H2SO4 solution, the galvanic coupling interaction between the separate PANI film electrode and 410 SS was studied. Results reveal that the separate PANI film can passivate the 410 SS steadily for a long period of time. A variety of experimental methods including potentiodynamic measurement, potentiostatic (current-time) examination and X-ray photoelectron spectroscopy (XPS) are used to explore the mechanism by which the separate PANI film passivated the galvanic coupling SS in the deaerated sulfuric solution. These studies show that passivation is achieved because PANI film provides a large critical current at the early stage of coupling and a persistent passive current by its electrochemical dedoping/re-doping equilibrium activity with the acidic environment at the subsequent stage of coupling.  相似文献   

4.
Titanium is a valve metal able to withstand corrosion, due to the presence of a passivating layer of titanium oxide on its surface. But, due to that more or less insulating layer, titanium cannot be used directly as an anodic material. However, modification of the surface of a Ti/TiO2 substrate may lead to the formation of new structures: Ti/TiO2/M or Ti/TiO2/OX, in which M is a metal such as platinum and OX a conducting oxide exhibiting electrocatalytic properties. These structures have interesting electrochemical properties and may be used as efficient electrode materials.In this paper, after a review of the electrochemical behaviour of these structures, we give new results concerning the selective electrodeposition of lead dioxide on Ti/TiO2 substrates and we propose an interpretation of the results taking into account the dielectric properties of the underlying TiO2. It is shown that there is a dramatic decrease of the resistance of the electrode when a PbO2 layer is electrodeposited onto a Ti/TiO2 structure. That effect allows the preparation of electrodes (low-cost DSAs) that may be used as anodes in spite of the presence of the underlying TiO2 layer, that layer being useful to avoid corrosion of the titanium substrate. At last, the effect of stabilization of the underlying TiO2 layer is discussed.  相似文献   

5.
Anodic charging curves have been measured on polycrystalline Bi in H2SO4 solutions (0·01–6·0 N) at 30°C. The effect of various experimental procedures, eg electrode treatment and stirring, has been established. The anodic behaviour of Bi depends markedly on the acid concentration. In the high range, the results indicate dissolution which follows a Tafel relation. However, in dilute solutions, growth of oxide film occurs, and the potential rises rapidly with time, reaching over 100 V at high cds. Sparking and oxide breakdown start at about 150 V. Oxide growth follows the high field ionic conduction. The reciprocal capacitance is linearly related to the logarithm of cd. The constants of the exponential law, the half-barrier width, and the field strength have been calculated The last lies between 1 and 3 × 106 V/cm at 1 mA/cm2. The effect of F and Cl ions on oxide growth in H2SO4 has been also investigated.  相似文献   

6.
Open circuit dependence of potential on oxygen partial pressure as well as potentiostatic behavior in O2- and He-saturated solution were determined. Stable hydrogen-oxygen species were formed, but potential-determining reversbility was found only in the potential range from 0·64–0·70 V (nhe). This equilibrium could be reasonably explained by an O2/H2O2 exchange. Oxygen, H2O2, or other hydrogen-oxygen species may affect open circuit potentials and potentiostatic behavior, but analysis of data assuming reversibility or quasi-equilibrium kinetic theory may be justified only between 0·64 and 0·70 V.  相似文献   

7.
The localised corrosion resistance of 316L SS metallic implant due to H2SO4 treatment is being studied through electrochemical studies involving cyclic polarisation experiments and impedance studies. The efficiency of hydroxyapatite (HAP) coatings on H2SO4 treated 316L SS is also been investigated through electrochemical studies and the dissolution characteristics of the coatings. The study reveal that 15% H2SO4 treatment was found to be efficient in the corrosion resistance of 316L SS and dissolution of alloy is considerably reduced in the hydroxyapatite coatings on 15% H2SO4 treated 316L SS.  相似文献   

8.
In this paper, we investigate the electrochemical formation of layers of self-organized high aspect ratio TiO2 nanotubes, grown by anodization of Ti in viscous electrolytes at different temperatures. In electrolytes consisting of glycerol or ethylene glycol with small additions of fluorides, the nanotube morphology can be strongly influenced by the viscosity, the electrolyte temperature and the applied potential. Compared with water-based electrolytes, in viscous electrolytes much longer and smoother tubes can be grown. Depending on experimental conditions, the nanotubes have an aspect ratio reaching up to about 150 for glycerol and 32 for ethylene glycol. The results further show that in glycerol electrolytes the current efficiency for nanotube formation is close to 100% (this is significantly higher than for comparable water-based electrolytes).  相似文献   

9.
The electrochemical behavior of the annealed Cu-5wt.%Ni alloy in 0.5 M H2SO4 was studied by means of open-circuit potential (EOCP) measurements, cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and quasi-stationary linear potential sweep. The hydrodynamics of the system was also studied. This material is constituted by a single α1 phase. The anodic behavior of a Cu-Ni alloy in H2SO4 consists fundamentally on the electrodissolution of Cu, its main component, and the formation of a sulfur-containing passive layer. The presence of Ni decreases the rate of Cu oxidation, mostly at high positive potentials. The impedance spectra, obtained for the unrotating electrode, can be interpreted in terms of a simple charge-transfer reaction across a surface layer. When the electrode is rotated, the occurrence of an inductive loop evidenced the existence of an adsorbed layer. All the resistance estimated from the proposed equivalent circuits diminished with the electrode rotation rate, emphasizing the influence of ion transport in the overall electrode process. The system presented two anodic Tafel slopes: 40 mV dec−1 for E<255 mV and 67 mV dec−1 for E>275 mV. A Tafel slope of 40 mV dec−1 evidences that copper dissolution can be interpreted in terms of the mechanism proposed by Mattsson and Bockris. The second Tafel suggests that at potentials more positive than 275 mV, copper dissolves according to a mechanism that considers the disproportionation of adsorbed Cu(I) species.  相似文献   

10.
Electropolishing of NiTi shape memory alloys in methanolic H2SO4   总被引:2,自引:0,他引:2  
The electropolishing of NiTi shape memory alloys was surveyed electrochemically. Anodic polarization of NiTi up to 8 V was performed in various aqueous and methanolic H2SO4 solutions. The passivity could be overcome in methanolic solutions with 0.1moldm−3≤CH2SO4≤7moldm−3. The dissolution kinetics was studied in dependence of the polarization potential, the H2SO4-concentration, the water concentration and the temperature. For lower concentrations of sulfuric acids (CH2SO4≤0.3moldm−3) electropolishing conditions were not observed for potentials up to 8 V. The dissolution remained under Ohmic control. In the concentration range from 1 to 7 mol dm−3 a potential independent limiting current was registered depending linearly on the logarithm of concentration. The best results were obtained with a 3 mol dm−3 methanolic sulfuric acid at 263 K which yielded an electropolishing current of 500 A m−2 at a potential of 8 V. Surface roughness as well as current efficiency showed an optimum under these conditions.  相似文献   

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