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Статии

НИ СЕВЕ Статии
Electrochemical Performance of Symmetric Solid-State Supercapacitors Based on Carbon Xerogel Electrodes and Solid Polymer Electrolytes
  • Година: 2023
Electrochemical Performance of Symmetric Solid-State Supercapacitors Based on Carbon Xerogel Electrodes and Solid Polymer Electrolytes
  • Автор/и: Karamanova, B., Mladenova, E., Thomas, M., Rey-Raap, N., Arenillas, A., Lufrano, F., Stoyanova, A.

For the development and optimization of solid-state symmetrical supercapacitors, herein, we propose using carbon-based electrodes and sodium- and lithium-form Aquivion electrolyte membranes, which serve as the separator and electrolyte. Carbon xerogels, synthesized using microwave-assisted sol-gel methodology, with designed and controlled properties were obtained as electrode materials. Commercial activated carbon (YP-50F, “Kuraray Europe” GmbH) was used as the active material for comparison. Notably, the developed solid-state symmetrical supercapacitors provide sufficiently high specific capacitances of 105–110 F g−1 at 0.2 A g−1, along with an energy density of 4.5 Wh kg−1 at 300 W kg−1, and a voltage window of 0–1.2 V in aqueous environments, also demonstrating an excellent cycling stability for up to 10,000 charge/discharge cycles. These results can demonstrate the potential applications of carbon xerogel as the active electrode material and cation exchange membrane as the electrolyte in the development of solid-state supercapacitor devices.

  • Списание: Gels 2023, 9(12), 983
Electrochemical testing of zeolite‑based gas‑diffusion electrodes for secondary metal air batteries—in memory of Prof. A. Milchev
  • Година: 2023
Electrochemical testing of zeolite‑based gas‑diffusion electrodes for secondary metal air batteries—in memory of Prof. A. Milchev
  • Автор/и: Miglena Slavova, Borislav Abrashev, Emiliya Mladenova, Valentin Terziev, Marin Pandev, Elena Mihaylova‑Dimitrova

The oxidation of carbon in conventional gas diffusion electrodes is a limiting factor for the life of secondary metal-air batteries. Replacement of carbon with zeolite is a possible solution to avoid its oxidation in the gas-diffusion electrodes (GDE) and thus to increase the battery lifetime. Due to the fact that the technology provides the required number of charge/discharge cycles, it is applicable for solar energy storage. Zeolites are a large group of natural or synthetic porous aluminosilicate minerals. Their porous structure provides good gas permeability. The gas diffusion layer of the electrode must also have good hydrophobicity. To prevent leakage of electrolyte from the battery, the zeolite was mixed with an appropriate amount of polytetrafluoroethylene, and the electrode was subjected to hot pressing according to a specially developed procedure. The experiments were performed in a specially designed test cell. Its construction ensures measurements of the bifunctional gas-diffusion electrode in a half-cell configuration applying a reference hydrogen electrode. The stationary volt-ampere characteristics and impedance tests were performed on the zeolite electrodes at certain operating points. The cell was subjected to cycling at charge/discharge current ± 2 mA/cm2, respectively. The obtained experimental results show that zeolite is a suitable material for carbon substitution in secondary metal air batteries. The zeolite/polytetrafluoroethylene (PTFE) ratio needs to be optimised in order to improve the gas permeability of the gas diffusion layer without compromising hydrophobicity.

  • Списание: Journal of Solid State Electrochemistry
Anodic oxidation of tungsten under illumination - multi-method characterization and modeling at the molecular level
  • Година: 2023
Anodic oxidation of tungsten under illumination - multi-method characterization and modeling at the molecular level
  • Автор/и: M. Bojinov, Y. Penkova, I. Betova, V. Karastoyanov,

Tungsten oxide has received considerable attention as photo-anode in photo-assisted water splitting due to its considerable advantages such as significant light absorption in the visible region, good catalytic properties, and stability in acidic and oxidative conditions. The present paper is a first step in a detailed study of the mechanism of porous WO3 growth via anodic oxidation. In-situ electrochemical impedance spectroscopy (EIS) and intensity modulated photocurrent spectroscopy (IMPS) during oxidation of W illuminated with UV and visible light are employed to study the ionic and electronic processes in slightly acidic sulfate-fluoride electrolytes and a range of potentials 4–10 V. The respective responses are discussed in terms of the influence of fluoride addition on ionic and electronic process rates. A kinetic model is proposed and parameterized via regression of experimental data to the EIS and IMPS transfer functions.

  • Списание: Molecules 28 (2023) 7387
In Situ Electron Paramagnetic Resonance Monitoring of Predegradation Radical Generation in a Lithium Electrolyte
  • Година: 2023
In Situ Electron Paramagnetic Resonance Monitoring of Predegradation Radical Generation in a Lithium Electrolyte
  • Автор/и: Rositsa Kukeva, Mariya Kalapsazova, Hristo Rasheev, Georgi Vassilev, Alia Tadjer, and Radostina Stoyanova*

Herein we present an innovative in situ EPR spectroscopy approach complemented with computational modeling as a methodology for assessing a nonaqueous electrolyte behavior just before its massive degradation. As a proof of concept, we use the conventional lithium electrolyte (1 M LiPF6 in EC/DMC), which is utilized in current lithium-ion batteries. Through in situ EPR, long-lived EC•– associates in amounts of 10–250 ppm were detected in a broad potential window (>2.0 V) prior to the electrolyte oxidation or reduction. The pathways of radical formation are discussed in terms of the imperfection in the electron flow across the electrolyte–electrode interface and of the strong affinity of EC to electron trapping. The radical amount could be amplified markedly (above 1000 ppm) by addition of vinylene carbonate (VC) to the electrolyte, while the added CeO2 has a moderate effect. The proposed in situ EPR methodology could be transferred to other electrolyte solutions to become a universal approach.

  • Списание: J. Phys. Chem. Lett. 2023, 14, 43, 9633–9639
Hydrogen storage properties of ball milled MgH2 with additives- Ni, V and activated carbons obtained from different by-products
  • Година: 2023
Hydrogen storage properties of ball milled MgH2 with additives- Ni, V and activated carbons obtained from different by-products
  • Автор/и: Grigorova E., Markov P., Tsyntsarski B., Tzvetkov P., Stoycheva I.

he hydrogen sorption of materials based on 80 wt.% MgH2 with the addition of 15 wt.% Ni or V and 5 wt.% activated carbons synthesized from polyolefin wax, a waste product from polyethylene production (POW), walnut shells (CAN), and peach stones (CPS) prepared by milling under an inert Ar atmosphere for a period of 1 h, is investigated. All precursors are submitted to pyrolysis followed by steam activation in order to obtain the activated carbons. The hydrogen sorption evaluations are carried out for absorption at 473 and 573 K with pressure of 1 MPa and for desorption at 623 and 573 K with pressure of 0.15 MPa. The composition of the samples after milling and hydrogenation is monitored by X-ray diffraction analyses. The 80 wt.% MgH2–15 wt. %Ni–5 wt.% POW or CAN after absorption–desorption cycling and in a hydrogenated state at 573 K and 1 MPa are analyzed by TEM.

  • Списание: Materials MDPI, 16, 2023, Article number 6823