Catalytic effects of ruthenium and osmium spontaneous deposition on platinum surfaces toward methanol oxidation.

The influence of ruthenium and osmium spontaneous deposition on polycrystalline platinum in sulfuric acid was studied by conventional electrochemical techniques. The inhibition of the hydrogen adatom voltammetric profile by the foreign adatoms was used to calculate the degree of surface coverage of ruthenium, osmium, and a mixture of both metal ions from solutions of different composition. Methanol adsorption and oxidation were compared on bare platinum, platinum/ruthenium, platinum/osmium, and ternary compounds, considering the efficiency of methanol oxidation per hydrogen adatom displaced by the foreign metal on platinum.

Inhibition of steel corrosion by calcium benzoate adsorption in nitrate solutions: theoretical and experimental approaches.

The inhibitive effects of calcium benzoate on steel corrosion were studied in sodium nitrate solutions at room temperature. Corrosion parameters of the steel/nitrate and steel/benzoate + nitrate interfaces were obtained from polarization curves. Adsorption parameters of benzoate on steel in sodium nitrate solutions were determined through changes in the degree of surface coverage by the inhibitor, as a function of concentration, time, and adsorption potential. The most likely adsorption configuration of benzoate on iron was envisaged with the help of semiempirical calculations such as extended Hückel calculations. A two-dimensional flat configuration was involving at least two metal atoms, one interacting with the phenolic group and the other with the carboxylate moiety. The effect of chloride on the corrosion inhibition of benzoate was analyzed by exposing the metal to different chloride solution concentrations, from which corrosion parameters were calculated and compared with those in nitrate solutions.

Crystallographic rearrangement of platinum induced by square wave potentials.

This paper provides experimental evidences of crystalline rearrangements on platinum surfaces by applying square wave potential perturbations. The phenomenon was followed by differential ex situ X-ray diffraction patterns and in situ cyclic voltammetry in sulfuric acid solutions. Various upper and lower potential limits were employed covering anion, hydrogen, and/or oxygen adsorption ranges. When the -0.05 to 1.50 V (vs. reversible hydrogen) potential region is covered an increase in the distribution of (200) planes is observed. However, when the 0.65 to 1.50 V region is used, (220), (311), and (420) planes developed. The development of a longitudinal propagation mode is responsible for this rearrangement. The new equilibrium position of the platinum surface atoms in the lattice was calculated from the minimization of the potential energy expression.