M.I. Rojas

The oxygen and chlorine evolution reactions at titanium oxide electrodes modified with platinum

Abstract The oxygen (OER) and chlorine (CLER) evolution reactions were used as probes to test the electronic properties of modified electrodes (Ti/TiO 2 -Pt). Both reactions were studied in acidic solutions by means of current-potential (j-E) and impedance measurements under steady state conditions. The effect of dopant concentration, TiO 2 thickness, and the concentration of the electroactive species in the solution was analyzed. A diminution of the electron transfer current with titanium oxide thickness was obtained whereas an increase of the current was found on augmenting Pt amount. At low titanium oxide thickness both inner-sphere reactions behave in the same way as in the case of pure Pt, indicating that platinum sites are the active ones. However, at higher titanium oxide thickness, the platinum sites become less active and the valve metal oxide (TiO 2 ) begins to block OER and CLER reactions. The electrochemical impedance spectroscopy results are compared with those of the current-potential measurements and a good correlation is found between them.

Curvature effect in the longitudinal unzipping carbon nanotubes

Density functional theory (DFT) calculations are performed to analyze curvature effects in the oxidative longitudinal unzipping of carbon nanotubes (CNTs) of different diameters. The reactions considered involve the adsorption of permanganate, followed by the oxidation of the nanotube, which results in dione and hole formation. The study was performed with armchair CNTs of different diameters and with corrugated graphene layers, which emulate the curvature of CNT of larger radii, with the finding that the curvature and the pyramidalization angle of the these structures strongly affects the stability of the intermediate dione structure formed during the unzipping process. Permanganate adsorption energies increase for more curved surfaces promoting the oxidation reaction in surfaces of small radius, making this reaction spontaneous for small radius. The second permanganate adsorbs on the parallel carbon–carbon bond to first diona formation resulting the longitudinal unzipping of the CNT.

An extended Hückel/point dipole model for the calculation of dipole potentials for sp metals

Abstract A semiempirical model of the metal/electrolyte interphase is presented, in which the metal is represented by a three-dimensional cluster emulating a single crystalline electrode and the solvent by a hexagonal point dipole lattice. The dipole potential for the electrochemical double layer is calculated for various sp metals and the results are compared with experimental data.