Ivo Paseka

Evolution of hydrogen and its sorption on remarkable active amorphous smooth NiP(x) electrodes

Abstract Hydrogen evolution reaction was studied on electrolytically prepared amorphous smooth NiP(x) layers with a phosphorus content of 3 to 14 wt%. NiP(x) electrodes with a low P content about 3 wt% are very active. At the potential E = − 0.2 V [ rhe ] in 1 N KOH at 23 °C the current density of the hydrogen evolution is ≈0.2 A cm −2 , which is approximately 10 times higher than on platinum and 300 times higher than on nickel. The polarization curve NiP(3%) has a low slope b ≈ 0.058 V dec −1 in the range of current densities 0.001–1 A cm −2 . This low slope is caused probably by a barrierless electron transfer reaction mechanism. High activity of amorphous NiP(3) electrodes is caused by the ability of these electrodes to adsorb and absorb great amounts of hydrogen, which changes the electron structure of the basic metal. The thermal treatment of layers at approximately 150 °C causes the crystallisation of layers and the loss both of the activity and the ability to sorb hydrogen.

Ruthenium-modified MCM-41 mesoporous molecular sieve and Y zeolite catalysts for selective hydrogenation of cinnamaldehyde

Abstract Ru-modified MCM-41 mesoporous molecular sieve and Y zeolite catalysts were synthesised and characterised using XRD, electrochemical voltammetry, ESCA (XPS), nitrogen adsorption and H2-TPD. Selective liquid-phase hydrogenation of cinnamaldehyde to cinnamyl alcohol was investigated over these catalysts and compared to hydrogenation on a commercial Ru/C catalyst. The effect of support (MCM-41, Y and C), solvent (cyclohexane, hexane and 2-propanol) and catalyst pre-treatment (calcination) on the conversion of cinnamaldehyde and selectivity to cinnamyl alcohol was studied. The zeolite structure, pore size, acidity, catalyst pre-treatment as well as the solvent influenced the activity and selectivity. Non-calcined Ru/Y exhibited the highest selectivity to cinnamyl alcohol. The activity of Ru/Y was highest with 2-propanol as a solvent.

Hydrogen evolution and hydrogen sorption on amorphous smooth MeP(x) (MeNi, Co and FeNi) electrodes

Abstract Hydrogen evolution reaction (HER) was studied on amorphous CoP( x ), NiP( x ) and FeNiP( x ) electrodes, prepared by an electrolytic deposition. The activities of Ni and CoP( x ) electrodes prepared at room temperature are nearly equivalent, those of FeNiP( x ) are somewhat lower. Alloys prepared by the electrodeposition at room temperature are very active for the HER, while those prepared at elevated temperatures 80–90 °C are less active. It has been proved that the high activity of MeP( x ) electrodes is caused by dissolved hydrogen in the amorphous layer in the course of the electrodeposition.

Sorption of hydrogen and kinetics of hydrogen evolution on amorphous Ni-Sx electrodes

Abstract Electrolytically prepared Ni-S x layers with a sulphur content ranging between 10 and 20 wt% have a higher activity for the hydrogen evolution reaction (HER) ( j 0 ≌ 2.5–35 × 10 −5 A cm −2 ) in comparison with nickel electrodes ( j 0 ≅ 1.5 × 10 −5 A cm −2 ). Ni-S x electrodes sorb high amounts of hydrogen. The greater part of this hydrogen is present in the absorbed hydride form. The thermal treatment of electrodeposited layers (1–4 h at 150°C) causes the decrease in the rate of HER by approximately one order of magnitude and, simultaneously, the decrease in hydrogen sorption. X-ray diffraction analysis showed that Ni-S x layers are originally amorphous but become crystalline after a thermal treatment.

Characterisation of ruthenium catalysts and determination of their surfaces by electrochemical oxidation and reduction

Methods of electrochemical voltammetry and potential step method were tested both for a characterisation and the surface determination of ruthenium black, ruthenium and bi-metallic Ru–Sn catalysts on Al2O3 and sol–gel SiO2 supports. It was demonstrated that transforming ruthenium to its oxide is necessary for acquiring reproducible and correct results. It was found that compared to the BET determination, the above mentioned electrochemical methods also produce exact results when RuO2 black is used. Voltammetric curves of ruthenium dioxide deposited on supports showed that these oxides have rather different redox properties in comparison with RuO2 black. Consequently, this phenomenon brought about a decrease in the absolute accuracy of the electrochemical methods used for the determination of ruthenium surface on carriers, since it was not possible to exactly verify the value of the specific redox charge using any other independent method. Nevertheless, the tested electrochemical methods are possible to be utilised at least for the determination of relative surface area values of a supported ruthenium.

Structure and magnetic properties of ball-milled iron nitride powders

Abstract In the present work we studied the influence of ball milling of iron nitrides–α′ martensite+γ austenite in the NH 3 atmosphere on the content of nitrogen, the phase composition, and the magnetic moment of nitrides. Only a small increase in the nitrogen content (from 6.5 to 7.0 at.% N) was found after milling. XRD and Mossbauer spectroscopy analyses of milled samples showed that at first austenite was transformed into nanocrystalline α-Fe and amorphous γ′-Fe 4 N and FeN x during milling. The decrease in the austenite content was gradually accompanied also by the change of martensite into the above mentioned compounds. The structure of the samples milled for the longest time (8 h) was so destroyed that these samples were not able to be transformed into α″-Fe 16 N 2 by subsequent annealing. The magnetic moment of milled samples firstly slightly increased and then decreased with increasing milling time.