Marina Makarova

Influence of Oxygen on Reactivity of Ru1 − x Fe x O2 − y -Doped Materials

Single-phase iron-substituted nanocrystalline ruthenium dioxide with composition Ru 0.98 Fe 0.02 O 2-ν and Ru 0.70 Fe 0.30 O 2-ν of rutile structure was prepared. The electrocatalytic behavior of the prepared materials was tested with respect to oxygen evolution reaction and chlorine evolution reaction (CER) The substitution with iron leads to a slight increase of the materials activity toward oxygen evolution. The selectivity of iron-doped materials in parallel oxygen and chlorine evolution is affected by oxygen content in the electrolyte solution. The CER is preferred in oxygen-free solutions; in oxygen-saturated solutions oxygen evolution is enhanced.

The Effect of Coherent Domain Size on the Insertion Activity of Nanocrystalline RuO2

The size dependence of the electrochemical activity of nanocrystalline ruthenium dioxide samples was studied using the lithium insertion reaction. The samples were prepared by a sol-gel reaction followed by annealing of initially amorphous precursor at various temperatures to obtain samples with average particle size ranging between 14 and 25 nm. According to analysis of X-ray diffraction patterns, the RuO 2 samples prepared at temperatures below 600°C show internal organization into smaller coherent domains separated by planar defect walls. With increasing annealing temperature the coherent domain sizes grow; this process is accompanied by an increase of the particle internal stress. All prepared samples are active toward lithium insertion. The insertion activity of samples improves with increase of the coherent domain size. The coherent domain size affects the mechanism of the Li insertion process. The samples with large coherent domains show typical sequence tetragonal → tetragonal expanded → orthorhombic of phase transitions accompanying the Li insertion process with coexistence of all phases in partially reduced material. The material with small coherent domains shows behavior characterized by a single tetragonal → orthorhombic phase transition.

Electrochemical Behavior of Nanocrystalline Ru0.8Me0.2O2 − x ( Me = Fe , Co , Ni ) Oxide Electrodes in Double-Layer Region

Nanocrystalline oxides with average chemical composition corresponding to Ru 0.8 Me o.2 O 2-x (Me = Fe, Co, Ni) were prepared by the sol-gel approach. All prepared materials were of single-phase character with rutile-type structure. The effect of nanocrystal size and nature of doping cation on electrochemical supercapacitor behavior was studied by means of cyclic voltammetry and electrochemical impedance. The specific capacitance of the Ru-based oxides increases by doping with lower-valence cation from ca. 22 μF cm -2 of actual electrode surface area observed for pure RUO 2 to 230 μF cm -2 in the case of Ni doped material. The improved capacitance behavior of the doped materials is ascribed to improvement of transport properties of the oxide structure enabling easier diffusion of compensating protons.

Optical Spectra and Direct Optical Transitions in Amorphous and Crystalline ZnO Thin Films and Powders

Comparative studies of ZnO crystalline and amorphous thin films and nanocrystalline powders are reported. The UV-visible optical spectra were analyzed with special attention paid to the direct optical bandgap. Atmospheric radio-frequency barrier torch discharge and pulsed hollow cathode sputtering techniques for the film fabrication were used. For the crystalline films, similar values of the direct optical bandgap were found independent of the growth method used. The analysis of the amorphous films and powders revealed a pronounced Urbach-like exponential absorption tail approaching the bandedge. For the powders, the bandgap energies were larger than those for the crystalline and amorphous films. A decrease in the powder particle size in the powders leads to an increased direct optical bandgap.