Thin laminar CdTe nanoflake membranes grafted by oleic acid were investigated for sorption characteristics and permeation of permanent gases and hydrocarbons depending on the process temperature. A ...huge influence of temperature was revealed, enabling enhancement of the ideal selectivity for butane-methane separation from 28 to over 100 with the change of process conditions from 25 °C to 10 °C. The separation factor attains 26 in mixed-gas CH4/C4H10 separation experiments. Both sorption enthalpy and activation energy of diffusion were evaluated for penetrants, exhibiting the role of low activation barriers in fast transport of condensable hydrocarbons. The experimental results were proved by a semi-empirical calculation, illustrating swelling of grafted layer with heavy hydrocarbons. The effect was proved experimentally with in situ diffraction experiment. The low activation energy for the transport of condensable hydrocarbons, strong temperature dependence of permeance, and huge extinction coefficient of CdTe nanoflakes enable modulating the membrane permeance with laser irradiation, demonstrated with permeance photoswitching.
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•Sorption enthalpy and activation energy of diffusion were evaluated for penetrants.•Fast transport of heavy hydrocarbons governed by low activation barriers of diffusion.•Low activation energy of heavy hydrocarbons governed by swelling of the grafted layer.•Swelling of the grafted layer with heavy hydrocarbons was proved by in situ X-ray diffraction.•The permeance photoswitching was demonstrated under laser irradiation.
Kinetics of phase transitions in the surface layer of proton-exchanged planar waveguides on X-cut of lithium niobate crystal during annealing at 330, 350, and 370°C was investigated by optical ...methods (dark field microscopy, crossed-polarizers bright field microscopy, and mode spectroscopy). Nucleation and growth stages of phase transformations were identified. Based on mode spectroscopy data and analysis of previous works, we assume that transformation of κ
2
-phase into κ
1
-phase and further transformation into α-phase were observed during experiment.
Proton-selective membranes are prepared by electrochemical reduction of graphene oxide films in aqueous electrolytes. Rapid kinetics of oxygenated groups reduction was revealed by complementary FTIR- ...and XPS-spectroscopy giving rise to a partially reduced graphene oxide with C/O ratio in the range of 2–4. The reduction is accompanied by interstitial water loss and shrinkage of d-spacing from 1.15 nm, typical for graphene oxide, to graphene-like ∼0.36 nm as revealed by X-ray diffraction analysis. The presence of remaining oxygen groups in reduced graphene oxide enables fast transport of protons with Grotthuss hopping mechanism and diffusion coefficients in the range of 3–7∙10−11 m2 s−1 at 25 °C. At the same time, the reduction of GO layers hinders dramatically the transport of H2O molecules due to suppression of capillary condensation of water in the oxygen-deficient channels of the reduced graphene oxide providing the H+/H2O selectivity of up to 1400 upon electrochemical reduction. The suggested approach opens the avenue for the performance enhancement of carbon-based membranes for proton-selective transport in fuel cells and electrolyzers.
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•Proton-selective membranes are prepared by electrochemical reduction of GO films.•Reduction affects mostly carbonyls and hydroxyls, leaving epoxides mainly intact.•Shrinkage of GO interlayer spacing to 3.6–6.0 Å is induced upon reduction.•A drop in water permeance occurs combined with H+ diffusivity of 3–7∙10−11 m2·s−1•An increase in H+/H2O selectivity up to 1400 is achieved.
Composite electrode materials LiLi0.13Ni0.2Mn0.47Co0.2O2 (LNMC)–CeO2–С are obtained by the coprecipitation of Co, Ni, Mn and Ce hydroxides followed by the coating of LNMC–CeO2 composites with ...pyrolytic carbon. The introduction of 5% CeO2 promotes the reduction of LNMC grain size from 190–230 to 100–170 nm and the corresponding increase in the electrochemical capacity of LNMC-CeO2 composite. The pyrolytic coating consists of the network of 2–5 nm polymer-carbon particles at the surface of LNMC crystallites. The electrochemical impedance spectroscopy data, which was performed after the galvanostatic cycling, demonstrated considerably lower charge transfer resistance of the carbon-coated composites compared to the bare LNMC and the LNMC-CeO2 composites. The values of the discharge capacity of LNMC-CeO2-C composites are superior to the capacity of LMNC-CeO2 and LMNC-C composites at all discharge rates (C/10 – 5C). The increase of the upper boundary of potentials to 4.8 V after cycling at 5C (U – 2÷4.6 V) promotes the increase of low rate electrochemical capacity of LNMC-CeO2-C composite to 220 mAh g−1.
•CeO2 nanoparticles are formed on the surface of LNMC grains.•Deposition of CeO2 nanoparticles promotes the better rate capability of LNMC.•Coating of LNMC-CeO2 composites with carbon reduces the charge transfer resistance.•The best pyrolytic coating contains carbon and organic species.•Potential switch to 4.8 V after cycling causes the restoration of 1st cycle capacity.
Anodic oxidation of aluminum in acidic electrolytes is widely used for the formation of porous oxide films with a regular structure on the metal surface. Despite the century-old history of this ...process, the mechanism of channel ordering into a 2D hexagonal array is still not entirely clear. This work studies the modes of porous oxide film formation in 0.3 M oxalic acid at the anodizing voltages of 20 to 130 V and in 0.3 M sulfuric acid in the range of 19 to 60 V. The mass fraction of electrolyte impurities in the anodic aluminum oxide (AAO) structure, the formation efficiency, the volume expansion factor of the material in anodizing, and oxide film porosity are determined for the given conditions. The wide range of applied anodizing voltages allowed establishing a relationship between the degree of ordering of porous structures and the formation efficiency of anodic alumina and volume expansion of the material.
•PCO–GDC composites are studied as a cathode for SOFCs.•The rate-determined step of the overall electrode process vs. temperature was defined.•PCO–GDC33 composite gave the lowest area surface ...resistance of 0.41Ωcm2 at 700°C.•PCO–GDC33 is preferred to use as a cathode material for IT-SOFCs.
Pr2CuO4–Ce0.9Gd0.1O1.95 (PCO–GDC) composites screen printed on Ce0.9Gd0.1O1.95 (GDC) electrolyte were considered as a cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). Phase composition, microstructure and electrochemical properties were investigated by X-ray powder diffraction (XRD), scanning electron microscopy and AC impedance spectroscopy, respectively. The oxygen reduction on porous PCO–GDC electrode applied on CGO electrolyte was studied in a symmetrical cell configuration by AC impedance spectroscopy at OCV conditions at 670–730°C and pO2=10-2-0.21atm. The charge transfer process and the dissociation of adsorbed molecular oxygen were found to be rate-determining steps of the oxygen reduction reaction. Results reveal that both GDC addition and electrode morphology have strong influence on area specific resistance (ASR) of the electrode/electrolyte interface. The lowest ASR value of 0.41Ωcm2 was achieved for the composition containing 33wt.% GDC at 700°С in air. The data obtained allow to consider the PCO–GDC33 composite as a promising cathode material for IT-SOFCs.
LiLi0.13Ni0.2Mn0.47Co0.2O2-CeO2 composites have been obtained by coprecipitation with CeO2 and by coating with ceria followed by coating with carbon film. STEM analysis revealed the formation of 20 - ...30 nm ceria particles on the surface of LLNMC grains in all cases. Both carbon-coated LLNMC-CeO2 composites and carbon-free LLNMC coated with 1 % CeO2 demonstrated enhanced capacity values that could not be explained by the charge compensation via redox of nickel and cobalt. 5 % CeO2-coprecipitated sample demonstrated the most intense anomaly in CV at U = 4.1 - 4.5 V associated with redox processes in the anionic sublattice of LLNMC and a larger charge transfer resistance compared to other composites. The maximum values of Li+ diffusion coefficient have been observed for the samples coated with 1 % CeO2. The different electrochemical behavior of these samples could be explained by the different intensity of anionic redox processes in the samples with different amount of nanocrystalline ceria.
Abstract
The objective of this research is to develop and to study iterative methods in the Krylov subspaces for solving systems of linear algebraic equations (SLAEs) with non-symmetric sparse ...matrices of high orders arising in the approximation of multi-dimensional boundary value problems on the unstructured grids. These methods are also relevant in many applications, including diffusion-convection equations. The considered algorithms are based on constructing
A
T
A —
orthogonal direction vectors calculated using short recursions and providing global minimization of a residual at each iteration. Methods based on the Lanczos orthogonalization,
A
T
—
preconditioned conjugate residuals algorithm, as well as the left Gauss transform for the original SLAEs are implemented. In addition, the efficiency of these iterative processes is investigated when solving algebraic preconditioned systems using an approximate factorization of the original matrix in the Eisenstat modification. The results of a set of computational experiments for various grids and values of convective coefficients are presented, which demonstrate a sufficiently high efficiency of the approaches under consideration.
The results of X-ray diffraction, electron microscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy, and X-ray photoelectron spectroscopy studies of nanostructured ZnS : Cu(Mn) ...coatings obtained by ultrahigh vacuum thermal deposition onto the surface of anodic Al
2
O
3
porous matrices are presented. A comparison with data obtained for films on glass substrates is made. Deposition is carried out during the independent evaporation of ZnS powder, metallic Cu, and MnS powder at various temperatures of the evaporation of impurity-ion sources. For the first time, porous nanostructured ZnS : Cu(Mn) films are shown to be formed on the surface of a porous matrix, the structure of which depends on the parameters of the porous structure of the matrices.
A procedure for the controlled barrier layer removal is suggested in this work which provides the preparation of anodic alumina membrane with specified pore diameter and permeance. Optimal conditions ...for barrier layer removal which give membranes with high gas permeance of 400 m
3
/(m
2
atm h) by nitrogen and breaking strength of up to 440 ± 40 MPa, which is allowable for their operation in baromembrane processes, are developed.
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