Synthesis of Ni/C nanostructured composites based on a natural raw material, i.e., wheat straw, is carried out in this work. The synthesis is performed by one- and two-stage methods using NiCl₂ as the activating agent. The X-ray diffraction and EDS analyses reveal the presence of metallic nickel in the structure of the composites, whereas magnetic measurements showed that nickel was contained in the porous carbon matrix in the nanoparticle state. For nanocomposites synthesized by the one-stage method, the largest contribution to the formation of the porous structure might be attributed to pores with radii from 5 to 30 nm; for a nanocomposite synthesized in two stages, the pore distribution function exhibits a narrow isolated peak with a maximum of around 2.6 nm. Based on the obtained magnetic data, the coercive force, specific saturation magnetization and nickel content in nanocomposites are calculated. For the measured values of the coercive force, the average size of magnetic moment carriers is determined to be ~100 nm for the two-stage synthesis nanocomposite and ~100 ÷ 110 nm for the one-stage synthesis nanocomposites. The developed Ni/C nanocomposites might be used as a cheap material for energy storage applications or as magnetically controlled adsorbents.

This article presents the technology for the preparation of a nitrogen-containing nanoporous bio-carbon and investigates its properties. It has been shown that the synthesised bio-carbon is characterised by a high degree of homogeneity, which has been confirmed by energy dispersive spectroscopy. The obtained bio-carbon has a micromesoporous structure, which has been confirmed by the results of studies using the method of low-temperature nitrogen adsorption and desorption. It was found that the specific surface area of biochar is 1247 m²/g. The data on nitrogen adsorption and desorption were compared with the data on small-angle X-ray scattering, and it was found that the micropores in the synthesised bio-carbon are open pores, while mesopores remain closed. The energy dispersion analysis showed that the structure of the bio-carbon does not contain ferromagnetic atoms, but due to the addition of nitrogen, the synthesised bio-carbon in a magnetic field has the properties of a ferromagnet with a characteristic hysteresis of the specific magnetisation. It was found that this material has a saturation magnetisation σ_s of 1.4 A∙m²∙kg⁻¹ and a coercive force H_c of 10 kA/m. Symmetric supercapacitors were fabricated from the synthesised bio-carbon material with 30% aqueous KOH and 1 M Na₂SO₄ as electrolytes. It was found that for bio-carbon synthesised at 800 °C, the specific capacitance in a 30% aqueous solution of KOH is 180 F/g, and in a 1 M aqueous solution of Na₂SO₄, it is 124 F/g. The cyclic voltammetry of the fabricated supercapacitors at different rates of potential expansion was investigated and analysed. Impedance studies on these supercapacitors were carried out. The equivalent electrical circuits describing the electrochemical processes in the studied supercapacitors were constructed and characterised.

A physical and mathematical model and a methodology for studying the mechanical properties of a nonferromagnetic conductive panel under the action of a quasi-steady electromagnetic field are proposed. A two-dimensional thermomechanics problem is formulated for the considered panel of a rectangular cross-section. The initial relations for finding the determinant functions, namely, the components of the quasi-static stress tensor, are given. The thermomechanical problem was addressed using the author’s approach, which involves approximating the defining functions by cubic polynomials along the thickness direction. This approach enabled the transformation of the initial two-dimensional boundary value problems into one-dimensional formulations based on the integral characteristics of the defining functions. Using a finite integral transformation in the transverse coordinate, the expressions of all integral characteristics and determinant functions were obtained. On the basis of the proposed mathematical model, a computer analysis of all components of the quasi-static stress tensor and stress intensity in a tungsten panel depending on the dimensionless Fourier time, the Biot criterion, and the induction heating parameters was carried out. The thermomechanical behavior of the panel was analyzed using two modes of near-surface and in-depth induction heating of the panel by a homogeneous quasi-steady electromagnetic field.

W artykule przedstawiono sposób wykorzystania akumulatorów w domu jednorodzinnym, podłączonym do systemu fotowoltaicznego. Dokonano analizy wpływu pojemności akumulatorów na współczynnik samowystarczalności oraz bilans energetyczny w okresie rocznym. Omówiono wyniki symulacji przepływu energii elektrycznej w hybrydowym systemie fotowoltaicznym przeznaczonym do domu jednorodzinnego.