Cobalt oxide nanopowders are synthesized by the pyrolysis of aerosol particles of water solution of cobalt acetate. Cobalt nanopowder is obtained by subsequent reduction of obtained cobalt oxide by annealing under a hydrogen atmosphere. The average crystallite size of the synthesized porous particles ranged from 7 to 30 nm, depending on the synthesis temperature. The electrochemical characteristics of electrodes based on synthesized cobalt oxide and reduced cobalt oxide are investigated in an electrochemical cell using a 3.5 M KOH solution as the electrolyte. The results of electrochemical measurements show that the electrode based on reduced cobalt oxide (Re-Co₃O₄) exhibits significantly higher capacity, and lower Faradaic charge–transfer and ion diffusion resistances when compared to the electrodes based on the initial cobalt oxide Co₃O₄. This observed effect is mainly due to a wide range of reversible redox transitions such as Co(II) ↔ Co(III) and Co(III) ↔ Co(IV) associated with different cobalt oxide/hydroxide species formed on the surface of metal particles during the cell operation; the small thickness of the oxide/hydroxide layer providing a high reaction rate, and also the presence of a metal skeleton leading to a low series resistance of the electrode.

This work presents a one-step controlled method for the synthesis of copper oxide nanoparticles using an arc discharge in deionized water without subsequent thermal annealing. The synthesis conditions were varied by changing the arc discharge current from 2 to 4 A. Scanning electron microscopy images of samples synthesized at discharge current of 2 A revealed the formation of tenorite (CuO) nanopetals with an average length of 550 nm and a width of 100 nm, which had a large surface area. Arc discharge synthesis at 3 and 4 A current modes provides the formation of a combination of CuO nanopetals with spherical cuprite (Cu₂O) nanoparticles with sizes ranging from 30 to 80 nm. The crystalline phase and elemental composition of the synthesized particles were identified by X-ray diffraction analysis, Raman spectroscopy and Energy dispersive analysis. As the arc discharge current was raised from 2 to 4 A, two notable changes occurred in the synthesized particles: the Cu/O ratio increased, and the particle sizes decreased. At 4 A, the synthesized particles were from 30 to 80 nm in size and had a spherical shape, indicating an increase in the amount of cuprite (Cu₂O) phase. The optical band gap of the aqueous solutions of copper oxide particles also increased from 2 to 2.34 eV with increasing synthesis current from 2 to 4 A, respectively. This suggests that the proposed synthesis method can be used to tune the band gap of the final material by controlling the Cu/O ratio through the current of arc discharge. Overall, this work demonstrates a novel approach to the synthesis of copper oxide nanoparticles with controllable CuO/Cu₂O/Cu ratios, which has the potential to be useful in a variety of applications, particularly due to the significant enhancement of photocatalytic abilities and widen the working spectral range.

Zinc oxide is a promising multifunctional material. The practical use of nano- and polycrystalline ZnO devices faces a serious problem of instability of electrical and luminescent characteristics, due to the adsorption of oxygen by the surface during aging. In this paper, the aging effect in ZnO films and nanorod arrays was studied. It was found that ZnO samples demonstrate different behavior of the degradation process, which corresponds to at least two different types of adsorbing surface sites for O₂, where O₂ adsorption is of a different nature. The first type of surface sites is rapidly depassivated after hydrogen passivation and the aging effect takes place due to these centers. The second type of surface sites has a stable structure after hydrogen passivation and corresponds to HO–ZnO sites. The XPS components of these sites include the Zn2p_3/2 peak at 1022.2 ± 0.2 eV and Zn2p_1/2 peak at 1045.2 ± 0.2 eV, with a part of the XPS O1s peak at 531.5 ± 0.3 eV. The annealing transforms the first type of site into the second one, and the subsequent short-term plasma treatment in hydrogen results in steady passivation, where the degradation of characteristics is practically reduced to zero.

Widespread use of Mg-Zn-Ca alloys in clinical orthopedic practice requires improvement of their mechanical properties—in particular, ductility—and enhancement of their bioactivity for accelerated osteoreconstruction. The alloy was studied in two structural states: after homogenization and after equal-channel angular pressing. Immersion and potentiodynamic polarization tests showed that the corrosion rate of the alloy was not increased by deformation. The mass loss in vivo was also statistically insignificant. Furthermore, it was found that deformation did not compromise the biocompatibility of the alloy and did not have any significant effect on cell adhesion and proliferation. However, an extract of the alloy promoted the alkaline phosphatase activity of human mesenchymal stromal cells, which indicates osteogenic stimulation of cells. The osteoinduction of the deformed alloy significantly exceeded that of the homogenized one. Based on the results of this work, it can be concluded that the alloy Mg-1%Zn-0.3%Ca modified by equal-channel angular pressing is a promising candidate for the manufacture of biodegradable orthopedic implants since it stimulates osteogenic differentiation and has greater ductility, which provides it with a competitive advantage in comparison with the homogenized state.

Electrochemical pseudocapacitors, along with batteries, are the essential components of today’s highly efficient energy storage systems. Cobalt oxide is widely developing for hybrid supercapacitor pseudocapacitance electrode applications due to its wide range of redox reactions, high theoretical capacitance, low cost, and presence of electrical conductivity. In this work, a recovery annealing approach is proposed to modify the electrochemical properties of Co₃O₄ pseudocapacitive electrodes. Cyclic voltammetry measurements indicate a predominance of surface-controlled redox reactions as a result of recovery annealing. X-ray diffraction, Raman spectra, and XPES results showed that due to the small size of cobalt oxide particles, low-temperature recovery causes the transformation of the Co₃O₄ nanocrystalline phase into the CoO phase. For the same reason, a rapid reverse transformation of CoO into Co₃O₄ occurs during in situ oxidation. This recrystallization enhances the electrochemical activity of the surface of nanoparticles, where a high concentration of oxygen vacancies is observed in the resulting Co₃O₄ phase. Thus, a simple method of modifying nanocrystalline Co₃O₄ electrodes provides much-improved pseudocapacitance characteristics.