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NI SE-HE Articles
Characterization of Mg2NiH4 type hydrides by TEM
  • Year: 2022
Characterization of Mg2NiH4 type hydrides by TEM
  • Author(s): Grigorova E., Markov P., Nihtianova D.,

Mixtures of corresponding metals with composition 95 wt% Mg2.05Ni0.7V0.3 and Mg2.1Ni0.7V0.3 and with addition of 5 wt% of activated carbon derived from apricot stones are prepared by ball milling under argon atmosphere. The received mixtures are tested for their hydrogen sorption characteristics at different temperatures. TEM characterization of these materials poses some challenges, because of their sensitivity to oxidation and the high energy of the electron beam exposure, which could cause negative impact. After hydriding at 300 °C and 1 MPa TEM results (SAED, HRTEM) showed the following phase composition: monoclinic and orthorhombic Mg2NiH4, MgO, VHx and graphite for both samples

  • Source: Materials Today: Proceedings Volume 61, 1233 - 1236
NEW EVIDENCE FOR FREQUENCY-DEPENDENT PERMITTIVITY RESPONSE OF BIOLOGICAL MATTER PART II: CARBOHYDRATE TESTING BY DIELECTRIC IMPEDANCE SPECTROSCOPY
  • Year: 2022
NEW EVIDENCE FOR FREQUENCY-DEPENDENT PERMITTIVITY RESPONSE OF BIOLOGICAL MATTER PART II: CARBOHYDRATE TESTING BY DIELECTRIC IMPEDANCE SPECTROSCOPY
  • Author(s): E. Mladenova, M. Slavova, L. Dobreva, A.-M.Mladenova, O. Kostadinova, S. Danova

Present work is a novel investigation focused on detection of some widely used monosaccharides: aldopentoses - xylose and arabinose; aldohexoses - galactose and glucose and oligosaccharaide - rafinose by measuring their dielectric response. The extension of the frequency range down to 0.1 Hz is a novel and very valuable approach. It allows examination of the whole molecules, on the one hand, and on the other, observation of induced 3D dipole structural assemblies under the external alternative electric field. This is indicated by a sharp increase in the effective capacity C′. The investigation of xylose and raffinose proved that DIS technique was able to detect concentration as low as 0.1 %. Concentration of aldohexoses galactose and glucose was studied between 2 - 20 % w/v and showed easily distinguishable concentration curves. Per contra, detection of different concentrations of arabinose was not possible, as the obtained C′ curves were overlapping.

  • Source: Journal of Chemical Technology and Metallurgy, 58, 1, 2023, 109-115
Hybrid supercapacitors with innovative binder - ex-situ structural and morphological studies
  • Year: 2022
Hybrid supercapacitors with innovative binder - ex-situ structural and morphological studies
  • Author(s): Karamanova, B., Ublekov, P., Soserov, L., Novakov, Ch., Dimitrov, I., Stoyanova, A.

In this study are presented the results from ex-situ physicochemical analyses of electrodes with synthesized poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-co-HFP) used as binder in the active electrode mass of hybrid supercapacitors. The cells based on biogenic activated carbon, αβ-Ni(OH)2 composite electrode, ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate) as electrolyte and P(VDF-co-HFP) exhibit improved capacitive characteristics. The crystal structure of the electrodes is studied using X-ray diffraction analysis. The profiles of pristine Ni(OH)2 electrode before and after the electrochemical tests are similar, however, decreases in peak intensity were observed in (001) and (110) directions. In contrast, the peak intensity of (100) and (101) increased, suggesting the formation of more perfect crystals. The electrode morphology is visualized by optical microscope and AFM techniques.

  • Source: Bulgarian Chemical Communications, 54, B2, 2022, 20-26
Accelerated Stress Tests for Solid Oxide Cells via Artificial Aging of the Fuel Electrode
  • Year: 2022
Accelerated Stress Tests for Solid Oxide Cells via Artificial Aging of the Fuel Electrode
  • Author(s): D. Vladikova, B. Burdin, Asrar Sheikh, P. Piccardo, M. Krapchanska and D.Montinaro

Solid Oxide Cells (SOCs) are under intensive development due to their great potential to meet the 2030 targets for decarbonization. One of their advantages is that they can work in reversible mode. However, in respect to durability, there are still some technical challenges. Although the quick development of experimental and modeling approaches gives insight into degradation mechanisms, an obligatory step that cannot be avoided is the performance of long-term tests. Taking into account the target for a commercial lifetime is 80,000 h, experiments lasting years are not acceptable for market needs. This work aims to develop accelerated stress tests (ASTs) for SOCs by the artificial aging of the fuel electrode via redox cycling, which follows the degradation processes of calendar aging (Ni coarsening and migration). However, it can cause irreversible damage by the formation of cracks at the interface anode/electrolyte. The advantages of the developed procedure are that it offers a mild level of oxidation, which can be governed and regulated by the direct impedance monitoring of the Ni network resistance changes during oxidation/reduction on a bare anode sample. Once the redox cycling conditions are fixed and the anode/electrolyte sample is checked for cracks, the procedure is introduced for the AST in full-cell configuration. The developed methodology is evaluated by a comparative analysis of current voltage and impedance measurements of pristine, artificially aged, and calendar-aged button cells, combined with microstructural characterization of their anodes. It can be applied in both fuel cell and electrolyzer mode. The results obtained in this study from the electrochemical tests show that the artificially aged experimental cell corresponds to at least 3500 h of nominal operation. The number of hours is much bigger in respect to the microstructural aging of the anode. Taking into consideration that the duration of the performed 20 redox cycles is about 50 to 60 working hours, the acceleration factor in respect to experimental timing is estimated to be higher than 60, without any damaging of the sample. This result shows that the selected approach is very promising for a large decrease in testing times for SOCs.

  • Source: Energies 2022, 15, 3287. https://doi.org/10.3390/en15093287
Nano-porous TiO2 electrochemically doped with Mo oxide – composition, electrochemical and photo-electrochemical properties
  • Year: 2022
Nano-porous TiO2 electrochemically doped with Mo oxide – composition, electrochemical and photo-electrochemical properties
  • Author(s): I. Betova, M. Bojinov, V. Karastoyanov, E. Slavcheva

Mixed Mo–Ti oxides are synthesized in nano-porous TiO2 templates by electrochemical deposition using cyclic voltammetry and stabilized by thermal treatment. Their thickness, phase, elemental, and chemical composition are characterized using X-ray diffraction, X-ray photoelectron spectroscopy and Glow discharge optical emission spectroscopy. Films are found to contain up to 17%Mo, mainly as Mo(VI) with some amounts of Mo(V). Electrical and electrochemical properties are assessed by current-potential measurements and electrochemical impedance spectroscopy. Photocurrent energy spectra and intensity modulated photocurrent spectroscopy (IMPS) measurements indicate that the films absorb UV and visible light in the range 365–520 nm and exhibit photo-catalytic properties. Quantitative interpretation of IMPS data using a transfer function proposed in the literature yields rate constants of charge transfer and recombination. The dependences of the kinetic parameters on potential are correlated with a mechanistic model of oxygen evolution featuring a mobile intermediate.

  • Source: Materials Chemistry and Physics Volume 285, 1 June 2022, 126139