The paper presents the results of studies of the composite LaNi0.6Fe0.4O3-delta (LNF)-Ce0.8Sm0.2O1.9 (SDC) by pulsed isotope exchange and electrochemical impedance spectroscopy. For pure SDC and LNF-SDC 1:1 and 1:9 composites, the concentration dependences of 16O2, 16O18O, 18O2 on the experimental temperature were obtained and the rates of heterogeneous oxygen exchange (rH) were calculated. The concentration dependence of heterogeneous oxygen exchange was analysed and the mechanisms of oxygen transfer in the LNF-SDC composite were proposed. The simulated polarisation resistance of electrochemical impedance spectra was calculated using the Adler-Lane-Steele analytical model. This was used to calculate the values of chemical surface exchange (k) and diffusion (D) coefficients. The paper compares and analyses k and D from two different techniques in comparison with literature values.

Hydrogen mass-transfer between molecular hydrogen and La0.8Sr0.2Ga0.8Mg0.2O3–z (LSGM) has been studied by means of hydrogen isotope exchange with gas phase equilibration. The measurements were carried out within a temperature range of 300–700 °C, with molecular hydrogen pressures of 100, 150 and 200 Pa. It was found that LSGM is capable of consuming hydrogen from the gas phase. The relative number of hydrogen atoms in the LSGM structure varied between 1 and 4 mol.%. The kinetics of hydrogen isotope redistribution revealed that the mass-transfer mechanism between molecular hydrogen in the gas phase and LSGM includes at least three steps. The first two relate to dissociative and associative/molecular adsorption of molecular hydrogen, while the third, identified as the rate-determining step in the exchange process, relates to hydrogen incorporation into LSGM structure. The kinetic and thermodynamic isotope effects of the exchange were estimated.

Studies of oxygen surface exchange kinetics for BaFeO3-delta oxide were performed using the oxygen isotope exchange method with pulsed supply of an isotopically enriched mixture (PIE) at the partial oxygen pressure 21.3 kPa in the temperature range of 350-600 degrees & Scy;. Oxygen surface exchange kinetics was considered in the framework of two-step model including two consecutive steps: dissociative adsorption of oxygen and incorporation of oxygen adatoms into the crystal lattice of the oxide. The rates of oxygen heterogeneous exchange (rH), as well as the rates of dissociative adsorption (ra) and oxygen incorporation (ri), have been calculated. The process of oxygen dissociative adsorption at the surface of BaFeO3-delta oxide was found to be the rate-determining step of the surface exchange. The appropriate models describing the oxygen exchange kinetics and possible mechanisms occurring in the system "gaseous oxygen - BaFeO3-delta oxide" were discussed.

Understanding the mechanisms of hydrogen activation and surface exchange over proton-conducting materials is of paramount importance for the advancement of solid oxide fuel cells and proton ceramic membranes for hydrogen isotope separation. In this study, we investigated the kinetics of hydrogen isotope exchange between gaseous H2 and the proton-conducting BaCe0.7Zr0.1Y0.1Yb0.1O3-alpha (BCZYYb) using hydrogen isotope exchange with gas phase equilibration (IE GPE) under two distinct initial conditions: H2pre-equilibration and D2 pre-equilibration. Experiments were conducted over a temperature range of 300-600 degrees C at a total hydrogen pressure of 200 Pa under chemical equilibrium. A theoretical framework was developed to elucidate the H/D exchange mechanisms, accounting for both the statistical nature of isotope exchange and H/D isotope effects. This theory was validated against literature data and subsequently applied to the experimental results obtained for BCZYYb. The findings indicate that the mechanism of H/D exchange between H2and BCZYYb varies with temperature and involves two parallel surface exchange pathways associated with different charge transfer processes during hydrogen oxidation. Hydrogen mass transfer isotope effects were quantified by two independent techniques: IE GPE and electrochemical impedance spectroscopy.

Hydrogen mass-transfer between molecular hydrogen and La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3-z (LSGM) has been studied by means of hydrogen isotope exchange with gas phase equilibration. The measurements were carried out within a temperature range of 300-700 degrees C, with molecular hydrogen pressures of 100, 150 and 200 Pa. It was found that LSGM is capable of consuming hydrogen from the gas phase. The relative number of hydrogen atoms in the LSGM structure varied between 1 and 4 mol.%. The kinetics of hydrogen isotope redistribution revealed that the mass- transfer mechanism between molecular hydrogen in the gas phase and LSGM includes at least three steps. The first two relate to dissociative and associative/molecular adsorption of molecular hydrogen, while the third, identified as the rate-determining step in the exchange process, relates to hydrogen incorporation into LSGM structure. The kinetic and thermodynamic isotope effects of the exchange were estimated.

Comprehensive structural studies of thin island Al films with a thickness of 20–50 nm deposited by magnetron sputtering on Si(111) substrates in an argon plasma at a pressure of 6 × 10–3 mbar and a temperature ranging from 20 to 500°C are presented. The morphology and microstructure of the films are studied using XRD, SEM, EDS, and TEM methods. It is found that most of the islands are Al 001 and Al 111 crystallites with lateral sizes of 10–100 nm, differently conjugated with the Si(111) substrate. At room temperature of the substrate, only Al 001 crystallites are epitaxially formed on it. The epitaxial growth of Al 111 crystallites is predominant as the substrate temperature increases above 400°C. The influence of the temperature of the Si(111) substrate on the process of epitaxial growth of crystallites, the dynamics of their shape, and structural perfection is shown. It is found that crystallites epitaxially connected to the substrate experience deformation at ε = 7 × 10–3 and ε = –2 × 10–3 for Al 001 and Al 111, respectively. It is shown that for thin island Al films on Si(111), the dependence of the number of crystallization centers and the particle growth rate on the supercooling temperature is consistent with the band model of crystallization. At the same time, a shift in the characteristic temperatures for the zone boundaries is observed due to the properties of the substrate. This must be taken into account when engineering the surface morphology and structural perfection of crystallites in Al island magnetron films.

In this paper we study the processes of O2 and H2O interaction with La0.9Sr0.1ScO3−δ. Using high temperature neutron powder diffraction (HT-NPD), the evolution of crystal structure and water uptake was investigated in the temperature range 25–700°C at 21.3 kPa in O2 and O2 + D2O atmospheres. The results of HT-NPD show the influence of the water uptake by La0.9Sr0.1ScO3–δ bulk on the thermal expansion of the material. The kinetics of oxygen surface exchange was studied using pulsed isotope exchange technique. The measurements were carried out in the temperature range 300−900°C at pO2 = 5.1, 12.2 and 21.3 kPa in dry and humid (pH2O = 2.6 kPa) conditions. For the first time the physical model describing the kinetics of oxygen surface exchange between the mixture of oxygen and water in the gas phase and a solid oxide has been suggested. The model includes following steps: oxygen dissociative adsorption, oxygen incorporation, hydrogen surface diffusion, water adsorption and dissociation. The rate-determining step of the exchange is considered. The influence of O2 humidification on the oxygen surface exchange is discussed.

The results of complementary studies of Al films grown by magnetron sputtering at room temperature are presented. The films were obtained on standard Si(111) substrates without and with a ∼20 nm aluminum (homobuffer) layer preliminarily grown on their surface at 400°C. The interdependence of the morphology, microstructure, and hardness of Al films on the state of the substrate surface was studied by the HRXRR, XRD, SEM, EDS, AFM, and Nano Indenter (ASTM) methods. It is shown that the formation of homobuffer layers on the substrate surface makes it possible to control the structural and mechanical properties of thin aluminum films.

In this paper we study the processes of O 2 and H 2 O interaction with La 0.9 Sr 0.1 ScO 3- delta . Using high temperature neutron powder diffraction (HT-NPD), the evolution of crystal structure and water uptake was investigated in the temperature range 25 - 700 degrees C at 21.3 kPa in O 2 and O 2 + D 2 O atmospheres. The results of HT-NPD show the influence of the water uptake by La 0.9 Sr 0.1 ScO 3 -delta bulk on the thermal expansion of the material. The kinetics of oxygen surface exchange was studied using pulsed isotope exchange technique. The measurements were carried out in the temperature range 300-900 degrees C at p O 2 = 5.1, 12.2 and 21.3 kPa in dry and humid ( p H 2 O = 2.6 kPa) conditions. For the first time the physical model describing the kinetics of oxygen surface exchange between the mixture of oxygen and water in the gas phase and a solid oxide has been suggested. The model includes following steps: oxygen dissociative adsorption, oxygen incorporation, hydrogen surface diffusion, water adsorption and dissociation. The rate-determining step of the exchange is considered. The influence of O 2 humidification on the oxygen surface exchange is discussed.

The results of complementary studies of Al films grown by magnetron sputtering at room temperature are presented. The films were obtained on standard Si(111) silicon substrates without and with a ~20 nm aluminum (homobuffer) layer preliminarily grown on their surface at 400°C. The interdependence of the morphology, microstructure, and hardness of Al films on the state of the substrate surface was studied by the HRXRR, XRD, SEM, EDS, AFM, and Nano Indenter (ASTM) methods. It is shown that the formation of homobuffer layers on the substrate surface makes it possible to control the structural and mechanical properties of thin aluminum films.

The mixed ionic and electronic oxide LaNi0.6Fe0.4O3−δ (LNF) is a promising ceramic cathode material for solid oxide fuel cells. Since the reaction rate of oxygen interaction with the cathode material is extremely important, the present work considers the oxygen exchange mechanism between O2 and LNF oxide. The kinetic dependence of the oxygen/oxide interaction has been determined by two isotopic methods using 18O-labelled oxygen. The application of the isotope exchange with the gas phase equilibrium (IE-GPE) and the pulsed isotope exchange (PIE) has provided information over a wide range of temperatures (350–800 °C) and oxygen pressures (10–200 mbar), as each method has different applicability limits. Applying mathematical models to treat the kinetic relationships, the oxygen exchange rate (rH, atom × cm−2 × s−1) and the diffusion coefficient (D, cm2/s) were calculated. The values of rH and D depend on both temperature and oxygen pressure. The activation energy of the surface exchange rate is 0.73 ± 0.05 eV for the PIE method at 200 mbar, and 0.48 ± 0.02 eV for the IE-GPE method at 10–20 mbar; for the diffusion coefficient, the activation energy equals 0.62 ± 0.01 eV at 10–20 mbar for the IE-GPE method. Differences in the mechanism of oxygen exchange and diffusion on dense and powder samples are observed due to the different microstructure and surface morphology of the samples. The influence of oxygen pressure on the ratio of contributions of different exchange types to the total oxygen exchange rate is demonstrated. For the first time, the rate-determining step in the oxygen exchange process for LNF material has been identified. This paper discusses the reasons for the difference in the mechanisms of oxygen exchange and diffusion.

Thin Co films on inclined Si(001) substrates were obtained by electron-beam evaporation. It has been established that at angles of incidence of the evaporated material on the substrate of more than 80 o (oblique angle deposition), arrays of free-standing Co nanocolumns with a cross section of 25 nm and an aspect ratio (length/transverse size) of at least 15 are formed on the substrate surface. In this case, the magnetic easy axis of the film is oriented along the axis of the nanocolumns, which leads to the appearance of a normal component of the magnetization vector to the film surface. When the substrate rotation is turned on, an array of nanospirals is formed. With a fast rotation of the substrate (30 rpm), the magnetic easy axis approaches the normal to the film surface. At a slow substrate rotation (0.6 pm), an array of nanocoils is formed, imparting pronounced chiral properties to the film. Keywords: nanostructuring, thin films, oblique angle deposition, chiral structures.

The mechanism of interaction between gaseous oxygen and the Sr1.95Fe1.4Ni0.1Mo0.5O6-delta promising material for cathodes of SOFC has been investigated by two isotopic methods: the pulse isotope exchange and the oxygen isotope exchange with the gas phase analysis, making it possible to obtain and compare the kinetic parameters under equilibrium conditions and the mixture gas carrier flow under the sample, which extends understanding of processes and makes experimental conditions of the second case closer to real operating conditions of electrode material. The time dependences of changes in O-16(2),(OO)-O-16-O-18 and O-18(2) over the sample allowed us to calculate the concentration of O-18 labeled oxygen (alpha) at the temperatures ranging from 300 to 800 degrees C. The oxygen exchange rate (r(H), atom/(cm(2) x s)), the oxygen diffusion coefficient (D, cm(2)/s), the corresponding rates of elementary processes of dissociative adsorption (r(a), atom/(cm(2) x s)) and oxygen incorporation in the lattice (r(i), atom/(cm(2) x s)) are calculated. The results of two independent isotopic methods were analyzed and revealed a good agreement of the obtained data. The effect of modifying Sr(2)Fe(1.5)Mo(0.5)O(6-delta )by introducing deficiency in the Sr-sublattice and Ni-doping in the Fe-sublattice on the kinetic parameters is discussed.

The development of technologies for the efficient conversion of methane and other light hydrocarbons is becoming vital to the chemical industry. The main technologies for methane conversion are based on solid and liquid catalysts such as metals, oxides and oxide-supported metals. Methane is a highly stable molecule, and the analysis of the catalytic activity of materials with respect to the C-H bond cleavage in methane is of paramount importance for the development of novel methane conversion catalysts. One of the most promising methods for studying methane activation over a catalyst is H/D isotope exchange between the gas and condensed phases. The method provides reliable in situ information on the cleavage of chemical bonds in molecules and allows researchers to elucidate the elementary steps of catalytic methane activation and the stable intermediates involved in the activation process. This paper focuses on the critical analysis of H/D isotope exchange studies of the methane activation mechanism over various metals, oxides, composites, and other catalysts, from the earlier studies to the recent advances in the field. The existing theoretical and experimental approaches to study the H/D exchange between methane and a catalyst are discussed in the paper. A critical analysis of the structure-composition-catalytic activity relationships of the catalysts with respect to methane activation is provided.

The complex oxide Sr1.95Fe1.4Ni0.1Mo0.5O6-x-5(Fx), where x = 0, 0.1, 0.2 and 0.3, as one of the most promising materials for electrodes of symmetrical electrochemical devices based on solid electrolytes is studied. The unit cell parameter increases monotonically with the addition of the fluorine-containing precursor in the synthesis of materials. The absence of fluorine traces in the sintered oxides was reliably confirmed by a combination of potentiometry using a fluorine-selective electrode and in situ mass spectrometry analysis of the gas media formed during heating the synthesized powders. It is suggested that the use of a fluorine-containing precursor makes it possible to increase the concentration of oxygen vacancies in the oxide, which positively affects its functional characteristics, such as the oxygen exchange rate with the gas phase and the oxygen electroreduction rate.& COPY; 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Thin Co films on inclined Si(001) substrates were obtained by electron-beam evaporation. It has been established that at angles of incidence of the evaporated material on the substrate of more than 80° (oblique angle deposition), arrays of free-standing Co nanocolumns with a cross section of 25 nm and an aspect ratio (length/transverse size) of at least 15 are formed on the substrate surface. In this case, the magnetic easy axis of the film is oriented along the axis of the nanocolumns, which leads to the appearance of a normal component of the magnetization vector to the film surface. When the substrate rotation is turned on, an array of nanospirals is formed. With a fast rotation of the substrate (30 rpm), the magnetic easy axis approaches the normal to the film surface. At a slow substrate rotation (0.6 pm), an array of nanocoils is formed, imparting pronounced chiral properties to the film.

In this study, we investigated the methane dissociation mechanism over a Ni-La0.90Sr0.10ScO2.95 (Ni-LSS) cermet using hydrogen/deuterium (H/D) exchange with the gas phase equilibration in the framework of the H/D exchange types approach. The measurements were conducted in the temperature range of 100-450 degrees C at 200 Pa methane and hydrogen mixtures (5, 10, 20 and 95 mol% methane). The hydrogen heterogeneous exchange rate between methane and Ni-LSS was found to be 2 x 10(11) atom. x cm(-2) x s(-1) at 300 degrees C and 200 Pa methane and hydrogen mixture (10 mol% methane) with activation barrier 0.03 +/- 0.09 eV. The rate-determining step of H/D exchange between the Ni-LSS and the mixtures is supposed to be associated with the exchange between methane adsorbed species (CHx)(a) and hydrogen adatoms in the adsorption layer of the cermet. The methane dissociation on the cermet can lead to the formation of dimer molecules C2H6, C2H4 and C2H2 in the gas phase from (CHx)(a) (x = 1-3). (C) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Ni-Zr0.82Y0.18O1.91 (YSZ) and Ni-La0.90Sr0.10ScO2.95 (LSS) cermets for solid oxide and protonic ceramic electrochemical cells were studied by means of H/D isotope exchange with the gas phase equilibration method for the first time. The experiments were carried out at 2 mbar of dry hydrogen in the temperature range of 400-800 degrees C. The three parallel channels of hydrogen surface exchange were found to exist in both Ni-YSZ and Ni-LSS cermets. The mechanism of hydrogen isotope exchange for Ni-YSZ was found to be temperature independent, while, in the case of Ni-LSS, the mechanism changed with temperature and was more complicated at lower temperatures (400-600 degrees C). It was revealed that hydrogen spillover was the rate-determining step for both cermets. The electrochemical kinetics of hydrogen oxidation were studied on symmetric cells with a YSZ supported electrolyte and Ni-YSZ electrodes and with an LSS supported electrolyte and Ni-LSS electrodes in a wet (3 vol % H 2O) hydrogen atmosphere at 1 atm. The mechanism of hydrogen oxidation on the Ni-LSS electrode differs from that of the Ni-YSZ electrode. It changes with temperature and is also more complicated at a lower temperature range.

Oxygen surface exchange properties of lanthanum nickelates La2NiO4+delta, La3Ni2O7-delta and La4Ni3O10-delta (LNOs) have been investigated using the Pulsed Isotope O-18/O-16 Exchange (PIE) technique in the temperature range 300-700 degrees C. The evaluation of the oxygen exchange rate from these lanthanum nickelates was conducted by measurement of isotope fractions O-18(2), (OO)-O-16-O-18, and O-16(2) in the effluent pulse at the exhaust from the reactor with a packed bed. The rates of oxygen heterogenous surface exchange (r(H)), dissociative adsorption (r(a)) and incorporation (r(i)) were calculated. The oxygen surface exchange was found to vary between the three nickelates, with r(H) decreasing between samples La3Ni2O7-delta > La4Ni3O10-delta > La2NiO4+delta, which was attributed to a decreasing presence of Ni cations on the particle surfaces. Despite possessing the lowest oxygen surface exchange, La2NiO4+delta had the best electrode electrochemical performance, which was attributed to highly mobile interstitial oxygen atoms leading to the largest r(i) (surface oxygen incorporation rate into the bulk) of the nickelates. This study reveals the key limiting factors determining lanthanum nickelate cathode performance in SOFCs, and we suggest avenues to improve these materials towards functional cathodes in devices.

The detailed investigation of the influence of strontium on the methane activation over the state-of-the-art proton-conducting oxide catalyst La1-xSrxScO3-alpha, was carried out using a combination of the novel H/D isotopic exchange method, Raman Spectroscopy, H-1 NMR and DFT studies in the temperature range 673 - 973 K, at 10 mbar of CH4 + H-2 (95%+5%) mixture. It was found that methane activation occurs via the four parallel channels of the hydrogen adsorption and incorporation mechanism, followed by the formation of methane intermediates with different hydrogen content (CHx species). The dominant type of adsorbed intermediate is governed by the temperature and the surface defect structure, which is in close correlation with the strontium content. The increase of strontium content in La1 xSrxScO3 alpha drastically increases the catalytic activity due to the surface modification with oxygen deficiencies in the ScO6 octahedron, and stabilisation of the CHx species with a low amount of hydrogen. (C) 2020 Elsevier Inc. All rights reserved.