Mamdouh Ahmed Abdel Rahim

Electro-oxidation of methanol was studied on titanium and platinum modified titanium electrodes (Pt/Ti). Platinum was electro-deposited on Ti by potentiostatic and galvanostatic techniques. Electrodes prepared by the galvanostatic technique showed enhanced catalytic activity towards methanol oxidation in NaOH solution compared to those prepared by the potentiostatic method. Scanning electron microscopy and energy dispersive X-ray analysis were used to characterize the surface morphology and percent composition of Pt to Ti on the electrode surface. The catalytic activity of Pt/Ti electrode is much higher than that of Pt/Pt, bulk Ti and of pure Pt, in addition to minimizing the poisoning effect. In 3.0 M NaOH and in the presence of 2.0 M MeOH, the oxidation peak current density value of methanol after the 50th cycles reached 99.4% of its value at the first cycle for electrodes prepared by the galvanostatic method compared to 94.7% for electrodes prepared by the potentiostatic method. Polarizing the modified electrode at the hydrogen evolution potential region for a certain time was found to enhance the catalytic oxidation of methanol, while the presence of thick Ti-oxide as well as Ti-hydride inhibited the process.

Ni–P–TiO2 nanocomposite coatings with various contents of TiO2 nano-particulates were prepared by electroless technique from Ni–P plating bath containing TiO2 powder. X-ray diffractometer (XRD) and energy dispersive X-ray (EDX) technique have been applied in order to investigate the chemical composition and phase structure of the coatings, respectively. The incorporation of TiO2 nano-particulates was found to be improved by the addition of TiO2 powder to the plating bath. However, it has no significant effect on the wt% of P content in the deposit. Scanning electron microscope (SEM) images showed that the morphology of Ni–P–TiO2 nanocomposite coating is finer and smoother than that of Ni–P coating. The catalytic activity of the prepared electrodes toward electro-oxidation of small organic molecules was studied and their stability with time was investigated. The catalytic activity was found to vary with the amount of the TiO2 embedded into the Ni deposit.

Methanol electro-oxidation is investigated at graphite electrodes modified with various platinum and nickel nano-particle deposits using cyclic voltammetry. The modified electrodes are prepared by the simultaneous electrodeposition of metals from their salt solutions using potentiostatic and galvanostatic techniques. They show enhanced catalytic activity towards methanol oxidation in KOH solution. The catalytic activity of platinum nano-particles is found to be significantly affected by the presence of relatively small amounts of nickel deposits. A comparison is made between the electrocatalytic activity of Pt/C and (Pt-Ni)/C electrodes. The results show that the methanol electro-oxidation current increases with an increase in the nickel content. In particular, the highest catalytic activity is achieved for platinum to nickel deposits of 95%:5% (wt.-%), in other cases the catalytic activity decreases. It is found that Ni enhances the catalytic activity of Pt by increasing the number of active sites, as well as through an electron donation process from Ni to Pt. This process takes place once the nickel hydroxide (Ni(OH)2)/nickel oxy-hydroxide (NiOOH) transformation begins. The effect of the methanol concentration on the methanol oxidation reaction is investigated. The order of reaction, with respect to methanol, at the modified (Pt-Ni)/C electrode is found to be 0.5.

The effect of varying nickel ions as well as OH− ions concentration on the electrochemical oxidation of methanol on nickel impregnated silicalite-1 (Ni-S-1) electrodes was investigated. The study of nickel ions concentration effect was carried out in two different ways: by varying the soaking time in one and the same concentration of NiSO4 solution, or by fixing the soaking time in different concentrations of NiSO4 solution. The results showed that for electrodes pre-soaked in 1.0 M NiSO4 solution for 90 s, increasing the OH− ions concentration results in increasing the oxidation current density of methanol. On the basis of this result, high concentration of KOH is preferable as a medium for methanol oxidation at the Ni-S-1 electrode in presence of nickel ions. On the other hand, at a certain OH− ions concentration, the peak height of methanol oxidation increases with increasing Ni ions concentration up to a certain value after which no effect was observed. A first order reaction kinetics with respect to both nickel ions and OH− ions was estimated for the oxidation of methanol.

Nickel impregnated zeolite-modified electrodes were prepared by mixing Ni–silicalite-1 with conducting carbon black in different rations. Using the cyclic voltammetric technique the electrochemical oxidation of methanol at such electrodes was investigated. Experiments on silicalite-1 (S-1) and nickel–silicalite-1 (Ni–S-1) show that they are not electrochemically active towards methanol oxidation in KOH solution. The presence of nickel ions in the zeolite matrix, by soaking the electrode in an aqueous NiSO4 solution, markedly enhances the electro-catalytic activity which was found to depend on the nickel content. On the other hand, the presence of zeolite and/or Ni metals in the catalyst is essential, however, the electro-catalytic activity depends on the Ni–S-1:carbon black ratio. Electrodes with Ni–S-1:carbon black ratio of 1:3, show the maximum electro-catalytic activity. The importance of impregnated Ni metal in the zeolite matrix is discussed on the basis of the experimental results. A weak dependence on bulk methanol concentration was observed. SEM analysis was used to characterize the Ni–S-1 catalyst. Dependence of methanol electro-oxidation on methanol concentration was discussed.

The use of Ni as a catalyst for the electro-oxidation of methanol in alkaline medium was studied by cyclic voltammetry. It was found that only Ni dispersed on graphite shows a catalytic activity towards methanol oxidation but massive Ni does not. Ni was dispersed on graphite by the electro-deposition from acidic NiSO4 solution using potentiostatic and galvanostatic techniques. The catalytic activity of the C/Ni electrodes towards methanol oxidation was found to vary with the amount of electro-deposited Ni. The dependence of the oxidation current on methanol concentration and scan rate was discussed. It was concluded from the electro-chemical measurements and SEM analysis that methanol oxidation starts as Ni-oxide is formed on the electrode surface.

Nickel and ruthenium dispersed on graphite electrode showed a catalytic activity towards methanol oxidation in KOH solution. Various modified graphite electrodes of different Ni–Ru ratios were prepared by the electro-deposition of Ni and Ru from their salt solutions by changing the relative concentration of each metal ion in the deposition bath. Results of the electrochemical measurements revealed that simultaneous deposition of the binary metals is the best method to prepare the catalyst. The relative distribution of Ni–Ru deposits on the graphite electrode depends on the method of deposition as shown by optical microscope analysis. The catalytic activity of the bimetallic catalyst C/(Ni–Ru) towards methanol oxidation was found to vary with the amount of electrodeposited Ni and Ru. However, the catalytic activity increases with increasing the Ni content relative to Ru in the electrode. The dependence of the oxidation current on methanol concentration and the upper- and lower-potential limits was discussed. It was concluded from the electrochemical measurements that methanol oxidation begins at the potential value of NiOOH production with the formation of intermediate products. The presence of perruthenate species on the electrode surface is responsible for the complete oxidation of the intermediate species.

The new binary and ternary complexes of fluclaxocillin (HFluc) and amino acids (HAA) [glycine (HGly) and alanine (HAla)] with Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) ions were prepared and characterized using various spectroscopic methods. According to the elemental analyses, the binary complexes were found to have the general formulas [M(Fluc)(X)(H2O)x]·yH2O and [Fe(Fluc)(Cl)2(H2O)2]·4H2O while the ternary complexes had the formulas [M(Fluc)- (AA)(H2O)x]·yH2O and [Fe(Fluc)(AA)(Cl)(H2O)x]·yH2O where M=Fe(II), Co(II), Ni(II) and Cu(II), X=OAc in the case of Cu(II) and Cl in the case of Fe(II), Co(II) and Ni(II), AA=Gly− and Ala−, x=2−6 and y=1−3. IR, magnetic and solid reflectance spectral studies were utilized to infer the structure of the complexes. Thermogravimetric analysis (TGA) was utilized to differentiate between coordinated and hydrated water molecules. The Fluc−, Gly− and Ala− molecules are decomposed in a second and subsequent steps. Cyclic voltametric investigations of these complexes were also carried out.

Pt electrodes, modified by partial electrodeposited tin, were used as anodes for the catalytic electrooxidation of methanol in acid medium. Sn was electrodeposited galvanostatically and potentiostatically. Cyclic voltammetry was used to study the methanol electrooxidation. Pt modified with Sn proved superior to pure platinum as shown from the methanol peak current densities. Sn also improved the performance regarding the stability of the anode over repeated cycles. It was found that electrodeposited Sn facilitates the oxidation of intermediate poison products through a mixed homogeneous–heterogeneous catalytic mechanism.

The voltammetric behaviour of titanium electrode in 0.5 M NaOH solution was investigated. The I-E curves revealed the presence of a well-defined O2 evolution peak. The peak current density decreases to a great extent by pre-loading the metal with hydrogen by cathodic polarization, indicating that pre-loading the metal with hydrogen suppresses the O2 evolution. The oxidation of hydrogen loaded inside the metal was suggested to be responsible for reducing the O2 evolution peak current density during Ti anodization.

The charge consumed during the anodic polarization of Ti, below O2 evolution potential, was used to estimate the anodization coefficient and capacitance measurement was conducted for measuring the dielectric constant of the oxide film. Pre-loading the metal with hydrogen was found to decrease the oxide film formation rate as well as the dielectric constant.

Potentiodynamic cathodic and anodic polarization technique was used to study the effect of some common amino acids concentration on the corrosion inhibition of mild steel in H2SO4. A value of 1.0 × 10−4 M represents a critical concentration, for the aliphatic amino acids, above which the corrosion rate increases. The increase of the sulphur-containing amino acids concentration largely decreases the corrosion rate. A mono-layer adsorption of the amino acid molecules on the metal surface was proposed with the adsorption behaviour following the Temkin isotherm at 30°C.

The effect of temperature on the corrosion inhibition of amino acids was also studied over the temperature range 25 to 60°C. Values of the apparent activation energy in the range of 42 - 49 kJ mol−1 were estimated for the steel corrosion in the inhibited acid solutions.

Potentiodynamic cathodic and anodic polarization technique was used to study the effect of some common amino acids concentration on the corrosion inhibition of mild steel in H2SO4. A value of 1.0 × 10−4 M represents a critical concentration, for the aliphatic amino acids, above which the corrosion rate increases. The increase of the sulphur-containing amino acids concentration largely decreases the corrosion rate. A mono-layer adsorption of the amino acid molecules on the metal surface was proposed with the adsorption behaviour following the Temkin isotherm at 30°C.

The effect of temperature on the corrosion inhibition of amino acids was also studied over the temperature range 25 to 60°C. Values of the apparent activation energy in the range of 42 - 49 kJ mol−1 were estimated for the steel corrosion in the inhibited acid solutions.

Mechanically polished zirconium electrodes were potentiodynamically polarized in phosphate buffer solutions of various pH values and in 0.5 lvl NaOH. The results show that the shape of the I-E curves is independent of the solution pH. At relatively low scan rates, oxygen gas evolution was observed. The oxide film thickness was calculated from the values of the charge consumed in the anodic process assuming 100% current efficiency for oxide formation below oxygen evolution (lower values for the current efficiency are assumed for potentials above oxygen evolution). Capacitance measurements, together with the calculated oxide thickness, were used to estimate values for the dielectric constant of the oxide. Two different values of the dielectric constant were obtained for the oxides formed in the range of potential below and above oxygen evolution. Also, higher dielectric constant values were obtained with increasing solution pH. Anion incorporation was assumed to increase the conductivity of the oxide films and, hence, decrease the dielectric constant. A two-layer structure is proposed for the anodically formed oxide on zirconium in aqueous solutions; an anion-free layer near the metal and an outer layer containing the incorporated anions.

The electron transfer kinetics of the Fe3+/Fe2+ redox couple on the oxide covered Ti electrodes were investigated as a function of the film thickness, film stabilization, and concentration of the redox species. The oxides were formed potentiodynamically in acidic solution of pH=3 (Na2SO4+H2SO4) at a scan rate of 1 mV s−1. The cathodic and anodic Tafel lines were also measured at the same scan rate.

The logarithm of the exchange current density i0 shows an exponential decrease with the oxide film thickness. Direct tunnelling may explain the kinetics of the reaction across thin Ti02 (oxide formed at the potential region before the O2-evolution). Values of the cathodic and anodic transfer coefficients are tabulated. It was found that, the stabilization of the oxide could possibly increase its conductivity. The electron transfer reaction showed a first order dependence on the redox species concentration, independent of the conditions of oxide film formation.

Potentiodynamic measurements on mechanically polished titanium electrodes were performed in different solutions in the pH range 0.55–12. Two anodic peaks and one small cathodic peak were observed. Comparison with thermodynamic data revealed the possibility of formation of Ti2O3 or TiO2 at potentials corresponding to the first anodic peak probably directly from titanium hydride. The second anodic peak is interpreted as the oxidation of incorporated H to form H+ ions which partly remain inside the metal. The small cathodic peak represents the back reduction of the incorporated H+ to the metal hydride.

A study on the value metal character of Zr in 0.1 M solutions of H2SO4, HNO3, and H3PO4 has been performed using the anode potential as the primary variable in galvanostatic, potentiostatic, and capacity measurements. A method of surface pre-treatment, which suppresses both O2 evolution and metal dissolution, has been described. Kinetic parameters of oxide growth have been calculated. The results indicate that:

(i)
the high field approximation is applicable following an exponential law, and
(ii)
the height and activation distance of the energy barrier for ion transport through the oxide phase (Verwey model) are the same three acids.
Measurements have been also made on the dielectric breakdown of oxide, and this occurs at potentials above 200 V. Direct capacity measurements give similar results as those based on reciprocal capacity calculated from galvanostatic experiments. It is concluded that the dominant anodic oxide species is ZrO2 having a dielectric constant of 25. Open circuit potential measurements show that Zr is spontaneously oxidized in the three acids.