M. A. Abdel Rahim

Platinum–tin alloy electrodes for direct methanol fuel cells

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.

Variation of the dielectric constant of anodic oxide films on titanium with oxygen evolution

Titanium was anodized potentiodynamically in acidic solution of pH 3 (Na2SO4 + H2SO4) in the potential region before and at oxygen evolution. The oxide film growth efficiency in the range of potential above oxygen evolution was investigated using galvanostatic charging curves. A value of 62% for the efficiency was estimated. The conductivity characteristics of the oxide film formed in the two regions were investigated on the basis of the variation of the dielectric constant. Values of 18.2 and 39.7 for the dielectric constant were obtained for oxides formed in the region before and at the oxygen evolution potential, respectively.

Anion incorporation and its effect on the dielectric constant and growth rate of zirconium oxides

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.

An approach to the effect of hydrogen loading on the anodic behaviour of Ti in NaOH solutions

The charge consumed during the anodic polarization of Ti, below O 2 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.

Carbon Supported Mono- and Bi-Metallic Dispersed Thin Film Catalysts for Oxygen Electro-Reduction Reaction in Acid Medium

The present study reports the use of monoand binary-metal thin film deposits of Pt, Cu, Ru and Pd dispersed over carbon electrode as electro-catalysts for oxygen reduction. The metals are sequentially electrodeposited on the carbon electrode from their aqueous solutions using the potentiostatic technique. The electrode surface characterization was carried out by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersed X-ray (EDX). The micrographs of SEM analyses showed that the thin films of the various deposits are located at the electrode surface in the nano-scale range. Linear sweep voltammetry was used to investigate the electrode performance towards oxygen reduction in H2SO4 solution in the absence and presence of H2O2. The results indicated that metal deposits and platinum-metal modified carbon electrodes have shown superior electro-catalytic activity toward oxygen reduction reaction (ORR) as shown by the relative increase in the peak current density values of oxygen reduction.