G.E. Shahnazaryan

Investigation of ceramic Fe2O3〈Ta〉 photoelectrodes for solar energy photoelectrochemical converters

Abstract Photocurrent and electrochemical impedance spectroscopy of a polycrystalline semiconductor photoelectrode, Fe 2 O 3 〈Ta〉, was carried out. The analysis of the frequency dispersion of the real and imaginary parts of the complex impedance allowed us to obtain an equivalent circuit for the electrochemical cell. The capacitance of the space-charge layer in the semiconductor electrode was isolated, and the limiting step of the electrode process was determined. Measurements of the temperature dependencies of the electroconductivity were used to determine the activation energy for the mobility of the charge carriers. A pair of simultaneously illuminated n-Fe 2 O 3 〈Ta〉 and p-Cu 2 O photoelectrodes were shown to split water spontaneously.

Investigations of the Fe1.99Ti0.01O3-electrolyte interface

The Fe1.99Ti0.01O3–electrolyte interface is investigated using electrochemical impedance spectroscopy. The analysis of the frequency dispersion of the real and imaginary parts of the complex impedance at various electrode potentials allows us to define the equivalent circuit for the electrochemical cell and calculate its associated parameters. The capacitance of the space-charge layer in the semiconductor electrode is isolated, and the limiting step of the electrode process is determined.

Gas sensor based on nanosize In2O3:Ga2O3 film

Nanosize films of In2O3:Ga2O3 (96:4 weight %) have been deposited on a glassceramic substrate by the method of rf magnetron sputtering. The surfaces of fabricated films were studied with use of a scanning electron microscope; sizes of grains were determined and the thicknesses of films were measured. In order to prepare a gas-sensitive structure, a thin catalytic palladium layer and ohmic comb contacts were deposited on the In2O3:Ga2O3 film surface by the method of ion-plasma sputtering. The sensitivity of sensors based on the glassceramic/In2O3:Ga2O3 (96:4 weight %)/Pd structure to different concentrations of propane and butane gas mixture, as well as to methane was investigated at temperatures of working substance from 250 to 300°C.

Gas sensors made of multiwall carbon nanotubes modified by tin dioxide

Thin film gas sensors made of nanocomposite MWCNT·SnO2(1:66), semiconductor compound WO3·SnO2(1:9), and also multicomponent structure MWCNT·SnO2(1:66)/WO3·SnO2(1:9) have been fabricated by high-frequency magnetron sputtering and electron-beam deposition methods. Sensitivity of the prepared sensors to influence of gases, such as hydrogen, methane, butane, and also ethanol vapors, was investigated. Sensors made of MWCNT·SnO2(1:66) and WO3·SnO2(1:9) show appreciable sensitivity to hydrogen and alcohol vapors already at working body temperature 100–150°C. Sensors made of MWCNT·SnO2(1:66)·WO3·SnO2(1:9) can be used for detection of low concentrations of hydrogen and ethanol vapors; besides, monotonous increase in the structure sensitivity with increase in content of the alcohol vapors allows one to apply these sensors also for fast detection of concentration of these vapors in air.

Investigation of gas sensor based on In2O3:Ga2O3 film

We have fabricated a LPG and butane sensor whose sensitive element is a nanosize In2O3:Ga2O3 (96:4 weight %) film covered with a thin palladium catalytic layer. Technology of deposition of these films on a glassceramic substrate by the method of rf magnetron sputtering was elaborated. The surfaces of fabricated films were studied with use of a scanning electron microscope and the thickness of films was measured. The sensitivity of sensors based on the glassceramic/In2O3:Ga2O3 (96:4 weight %)/Pd structure depending on the thickness and sizes of film grains was studied. We revealed technological regimes of sputtering providing fabrication of films with the best parameters.

Semiconductor photoanodes in the system Fe2O3-Nb2O5 for photoelectrochemical water splitting

Ceramic semiconductor photoelectrodes made of the Fe2O3-Nb2O5 solid solutions were synthesized. The spectral and capacitance-voltage characteristics of the photoelectrodes were determined, and the dynamic polarization with chopped light was investigated. The anodic photocurrent onset potential, the flat band potential and the shallow and deep donor density of these materials were determined. The threshold photon energies corresponding to the inter-band optical transitions near the edge of the fundamental absorption of the semiconductor photoelectrode were calculated. Analysis of the frequency dispersion of the real and imaginary parts of the complex impedance of photoelectrochemical cell was carried out. On the basis of this analysis, equivalent circuits describing the structure of the double electrical layer of the semiconductor - electrolyte interface were proposed and their parameters were calculated. The main limiting steps of the electrode processes, which determine the electrode polarization and current, are determined.