N. V. Alexeev

Bio: N. V. Alexeev is an academic researcher from Russian Academy of Sciences. The author has contributed to research in topics: Nanoparticle & Plasma. The author has an hindex of 5, co-authored 10 publications receiving 108 citations.

Metal Oxide Nanopowder Production by Evaporation–Condensation Using a Focused Microwave Radiation at a Frequency of 24 GHz

Abstract: The new method for metal oxide nanopowder production is proposed. It is the evaporation–condensation using a focused microwave radiation. The source of microwaves is technological gyrotron with frequency of 24 GHz and power up to 7 kW with the energy density flux of 13 kW/cm2. Radiation was focused on the layer of powder of the treated material to ensure its evaporation, subsequent condensation of vapor in the gas stream, and deposition of particles on the water-cooled surface. Deposited powders consist of particles whose sizes are in the range of 20 nm to 1 μm. The powder consists of particles having different shapes—close to spherical shape as well as octahedral, which indicates that the mechanism of particles formation is “vapor–liquid–crystal” as well as “vapor–crystal.” The maximum evaporation rate was 100 g/hr. The proposed approach is original and extends the possible methods of producing nanoparticles.

Synthesis of nanoscale zirconium dioxide powders and composites on their basis in thermal DC Plasma

Abstract: ZrO2, ZrO2–MgO, and ZrO2–Al2O3 nanopowders are obtained via oxidation of disperse ZrCl4 and its blends with (Mg, Al) metals by oxygen in a plasma reactor with confined plasma jet flow on the basis of an dc arc plasma generator. The change in the ZrCl4 rate and plasma jet enthalpy allows one to synthesize nanopowders with the specific surface area of 18–32 m2/g (Dav = 33–58 nm). The obtained nanopowders are polydisperse, consist of uniaxial spherical particles, and contain 0.25–0.75 wt % of chlorine. The dependence of the chlorine content in powders on the zirconium chloride output exhibits an extreme behavior. The ZrO2 nanopowders represent a mixture of monoclinic and tetragonal zirconium dioxide modifications with approximately equal contents. The ZrO2–MgO nanopowders (10 mol %) with the cubic structure identified as Zr0.875Mg0.125O1.875 are obtained in oxidation of the ZrCl4–Mg mixture in an oxygen–argon plasma stream. The ZrO2–Al2O3 nanopowders (30 wt %) are synthesized by oxidation of the ZrCl4–Al blend, whose phase composition is represented by tetragonal ZrO2 structure with monoclinic phase impurity in the absence of any Al2O3 phases, which can be explained by the formation of nonequilibrium Zr–Al–O solid solution with tetragonal structure as a result of the size effect.

Noble metal-free hydrogen evolution catalysts for water splitting

Abstract: Sustainable hydrogen production is an essential prerequisite of a future hydrogen economy. Water electrolysis driven by renewable resource-derived electricity and direct solar-to-hydrogen conversion based on photochemical and photoelectrochemical water splitting are promising pathways for sustainable hydrogen production. All these techniques require, among many things, highly active noble metal-free hydrogen evolution catalysts to make the water splitting process more energy-efficient and economical. In this review, we highlight the recent research efforts toward the synthesis of noble metal-free electrocatalysts, especially at the nanoscale, and their catalytic properties for the hydrogen evolution reaction (HER). We review several important kinds of heterogeneous non-precious metal electrocatalysts, including metal sulfides, metal selenides, metal carbides, metal nitrides, metal phosphides, and heteroatom-doped nanocarbons. In the discussion, emphasis is given to the synthetic methods of these HER electrocatalysts, the strategies of performance improvement, and the structure/composition-catalytic activity relationship. We also summarize some important examples showing that non-Pt HER electrocatalysts could serve as efficient cocatalysts for promoting direct solar-to-hydrogen conversion in both photochemical and photoelectrochemical water splitting systems, when combined with suitable semiconductor photocatalysts.

Nitrogen-doped tungsten carbide nanoarray as an efficient bifunctional electrocatalyst for water splitting in acid.

Abstract: Tungsten carbide is one of the most promising electrocatalysts for the hydrogen evolution reaction, although it exhibits sluggish kinetics due to a strong tungsten-hydrogen bond. In addition, tungsten carbide’s catalytic activity toward the oxygen evolution reaction has yet to be reported. Here, we introduce a superaerophobic nitrogen-doped tungsten carbide nanoarray electrode exhibiting high stability and activity toward hydrogen evolution reaction as well as driving oxygen evolution efficiently in acid. Nitrogen-doping and nanoarray structure accelerate hydrogen gas release from the electrode, realizing a current density of −200 mA cm−2 at the potential of −190 mV vs. reversible hydrogen electrode, which manifest one of the best non-noble metal catalysts for hydrogen evolution reaction. Under acidic conditions (0.5 M sulfuric acid), water splitting catalyzed by nitrogen-doped tungsten carbide nanoarray starts from about 1.4 V, and outperforms most other water splitting catalysts. Water electrolysis can generate carbon-neutral hydrogen gas from water, yet the required catalysts are often expensive, scarce, and poor at gas release. Here, the authors prepared nitrogen-doped carbon tungstide nanoarrays with high water-splitting activities and bubble-releasing surfaces.