Nanotechnologies in Russia最新文献

Abstract

The large-scale commercialization of polymer electrolyte membrane (PEM) water electrolyzers is still constrained by their high capital cost, which is largely associated with the use of noble metal-based electrocatalysts. There is an urgent need to reduce their loading in the composition of electrocatalytic layers. In the present work, an approach of the microporous sublayer made of titanium nitride (TiN_x) and formed over the anode surface by magnetron sputtering is proposed. It contributes to an increase in the anode electrocatalyst utilization, opening up wide possibilities to reduce its loading.

Abstract

In this work, a three-component system is obtained based on gellan, a graft copolymer of pullulan with side chains of poly(2-methyl-2-oxazoline), and CaCl₂, which is capable of forming gels upon contact with an aqueous solution of NaCl. Such a composition can be used for medical purposes, in particular for the treatment of ophthalmological diseases. In this work, the molecular characteristics of the initial components of the gel are obtained and its viscoelastic properties are studied. It was established that graft copolymers of pullulan with poly(2-methyl-2-oxazoline) are integrated into the gel composition, while an increase in their proportion reduces its elastic properties. The obtained gel retain elastic properties upon heating up to 70°C.

Тhe work is devoted to studying the magnetic properties of one-dimensional nanostructures: nanowires (NWs). Two types of NWs are obtained by matrix synthesis and studied by probe microscopy. The combination of probe-microscopy modes makes it possible to determine the topography of the nanocrystals and the nature of their magnetization. The change in the magnetization during the application of an external magnetic field (varying in magnitude and direction) is investigated. It is shown that magnetization reversal in an external magnetic field depends on the relative position of the nanowire. Samples of the first type are Ni/Cu layered NWs: their magnetization reversal in an external magnetic field is studied and the magnitude of this field is determined. It is shown that the latter depends on the relative position and interaction of NWs with each other. For a single NW this is 4–5 mT, and for double NWs it is noticeably higher (12–15 mT). An agglomerate consisting of several interacting NWs is undergoes magnetization reversal in stages. The second type of samples are arrays of homogeneous NWs made of FeNi alloy located directly in the growth matrix. The field of magnetization reversal of isolated NWs in all cases is 7–14 mT. On the contrary, in groups of closely located NWs, the switching of magnetization occurs in stages. In this case, the range of switching fields depends on the density of NWs in the matrix and, in general, is much broader than for isolated NWs. In general, it is shown that the magnetic properties of NWs change significantly as the distance between them decreases: their magnetization reversal becomes more difficult, and various intermediate states appear, including those with opposite (antiferromagnetic) magnetization in neighboring NWs.

А compact phenomenological model is proposed to describe the plasticity of memristive structures based on nanolayers of LiNbO₃ and (Co–Fe–B)_x(LiNbO₃)_100–x composite, taking into account the features of resistive switching of the structures and hopping electron transport in amorphous LiNbO₃. The model well describes the current–voltage characteristics of memristors in a crossbar array, and the effective microscopic parameters found in the fitting of the current—voltage characteristics make it possible to predict the result of changes in the conductivity according to spike-timing-dependent plasticity (STDP), and in addition, the dependence of the STDP window on the initial conductivity of the memristor. The results obtained can be used in the development of algorithms for training spiking neuromorphic computing systems and identifying memristive STDP, which is effective for their implementation.

Abstract—

Proton exchange membrane (PEM) water electrolysis allows the production of green hydrogen using renewable but unstable energy sources such as wind or solar power. The lifetime assessment of a PEM water electrolyzer and its components require lengthy and costly testing, so there is a need for the development and application of accelerated stress-testing methods, which allow the accelerated investigation of degradation processes occurring under realistic operating conditions. In this study, the dynamic cycling and constant operation of the membrane electrode assembly of a PEM water electrolyzer at elevated voltages are considered as two methods of accelerated stress testing. The degradation depth, its distribution, and mechanisms are studied using electrochemical impedance spectroscopy, polarization curve breakdown into voltage losses components, and scanning electron microscopy. The greatest depth of degradation (up to 133 mV) is achieved during continuous operation of the membrane electrode assembly at elevated voltage, due to the anode porous transport layer (PTL) surface passivation and slow oxygen transport in its porous structure. The degradation depth of the membrane electrode assembly after dynamic cycling is found to be significantly lower (7–20 mV), and is related to degradation of the catalyst layer, with the decrease of mass transport losses being significantly responsible for the decrease in the overall degradation rate observed at high current densities. The influence of the anode catalyst loading reducing and the Ti-hydride protective coating on the surface of the anode PTL on the degradation of the PEM water electrolyzer is also considered. The use of a protective coating on the surface of the PTL provides the formation of a compact anode catalyst layer with a developed interface between the catalyst layer and PTL even at the reduced anode catalyst loading.

The use of magnetic nanoparticles as sorbents for wastewater treatment in various industries can improve the efficiency of this process and reduce the impact of humans on the environment. Therefore, the development of a cost-effective method for the preparation of magnetic nanoparticles with optimal physical–chemical properties, especially high saturation magnetization, is a crucial task in current research. In this study, we use the sol–gel-citrate self-combustion method to synthesize a series of spinel ferrite magnetic nanoparticles with different chemical compositions. A set of cobalt-ferrite nanoparticles with the partial substitution of cobalt by zinc and manganese and iron by aluminum is obtained. Among the investigated samples, the zinc-doped cobalt-ferrite nanoparticles show the highest saturation magnetization of 88 A m²/kg at room temperature. Surface modification of the synthesized materials with polyethylene glycol and sodium dodecyl sulphate can improve their colloidal stability and as a consequence increase their sorption capacity.

Nowadays a new class of two-dimensional materials, MXenes, is attracting considerable attention as nanoadsorbents for the removal of heavy-metal ions from water. Pollutants such as copper and other heavy metals possess a negative impact on human health and the quality of natural ecosystems when their concentration exceeds an acceptable limit, which makes it urgent to develop cheap and effective methods to reduce the concentration of such pollutants. In this work we study the adsorptive properties of Ti₃C₂T_x MXenes with mixed functionalization by –O, –F, and –OH surface groups in relation to copper Cu(II) ions. Herein, multilayer MXene particles are investigated, since their yield is much greater than that of single-layer particles when using standard synthesis methods, and the experimental results are compared with previously published data for single-layer MXenes. It is established that, at low concentrations (below 50 mg/L), multilayer Ti₃C₂T_x MXenes demonstrate a comparable adsorption capacity of ~102 mg/g which makes it possible to use them for practical applications.

The synthesis of a varistor powder based on ZnO is carried out with the further fabrication of a device structure within the framework of the sol-gel method. To monitor the processes occurring in the sol, the method of Fourier-transform infrared spectroscopy is used. Studies of the surface structure of the material are carried out using scanning electron microscopy. The constructed current–voltage characteristic of the varistor structure is nonlinear with a nonlinearity coefficient of 2.36. The use of the sol-gel method for the manufacture of devices of this type makes it possible to obtain a grain size of 0.25 μm and achieve a reduction in the sintering temperature to 900°C.

The paper presents the design features and technology of the formation of a low-pressure sensor, which is a heater deposited onto the surface of a porous aluminum-oxide membrane formed on aluminum foil. The structure is fully formed using inexpensive low temperature methods. It is shown that an increase in the porosity of the membrane region separating the heating element and the substrate makes it possible to effectively measure a pressure up to 2 × 10^–2 Pa.

The mechanical behavior of porous particles of various diameters obtained by the cryolyophilization drying of frozen droplets of 1-wt % cellulose diacetate solution in 1,4-dioxane are studied. The morphology of the particles is visualized by scanning electron microscopy. It is shown that the particles have a predominantly spherical shape and a branched porous structure. The elastic and tangent moduli, Poisson’s ratio, and yield strength of the particle material are determined through mechanical tests of individual particles compressed between parallel plates. The results are then used to solve the reverse-engineering problem using the finite-element method. A bilinear stress-strain diagram taking into account the plastic properties of the particle material is obtained. Verification of the obtained model was carried out in a similar experiment upon the compression of particles of a different diameter.