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    Polyacrylonitrile nanofibers with hollow NiCu, Ni, and Cu nanospheres: Boosting electrocatalysis via enhanced interfacial charge transport and storage
    (Elsevier, 2026) Sarac, Baran; Karazehir, Tolga; Zadorozhnyy, Vladislav; Moskovskikh, Dmitry; Yermekova, Zhanna; Gumrukcu, Selin; Yuce, Eray; Sarac, A. Sezai
    Multifunctional catalytic materials combining polymers with nanoparticles (NPs) lie in advancing their long-term stability, scalability, and predictable performance under real-world operating conditions. In this study, polyacrylonitrile (PAN) nanofibers loaded with hollow nickel (Ni), copper (Cu), and nickel-copper (NiCu) nanoparticles were fabricated. X-ray diffraction confirmed crystalline metal phases in the amorphous PAN matrix while indicating that similar to 25 % of Cu as CuO. Spectroscopic analysis revealed alterations in the nitrile and aliphatic stretching bands resulting from NP incorporation. Cu/PAN exhibited a more than twofold increase in the -C-H to -CN bond area, attributed to oxygen-containing functional groups from CuO formation. UV-Vis spectra demonstrated tunable absorbance: NiCu/PAN exhibited the broadest and most intense absorption across 250-500 nm, reflecting strong plasmonic coupling between alloyed particles. Electron microscopy illustrated uniform dispersion of NPs on PAN surface, with all three nanofibers showing continuous and bead-free morphology, while NiCu composites displayed reduced NP agglomeration compared to monometallic counterparts. Electrochemical impedance spectroscopy in 0.1 M LiClO4/ACN highlighted that NiCu/PAN possessed the lowest charge transfer resistance (R-ct approximate to 9.13 x 10(2) Omega cm(2)) and highest double-layer capacitance (C-dl approximate to 43.6 mu F cm(-2)), surpassing Ni/PAN and Cu/PAN analogues. Furthermore, the smallest overpotential at 1 mA cm(-2) (-197 mV) and Tafel curve (similar to 286 mV dec(-1)) were obtained for NiCu/PAN in 1 M KOH. The main objective of this research was to demonstrate that bimetallic interactions in hollow NiCu particles synergistically enhance interfacial charge transport and storage, thereby showing how metal composition and PAN nanofiber integration can optimize polymer-based nanocomposites for energy and environmental applications.
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    Öğe
    Surface-governed electrochemical hydrogenation in FeNi-based metallic glass
    (Elsevier, 2020) Sarac, Baran; Zadorozhnyy, Vladislav; Ivanov, Yurii P.; Kvaratskheliya, Askar; Ketov, Sergey; Karazehir, Tolga; Gumrukcu, Selin
    The hydrogenation and oxide formation behavior of Fe-Ni-based metallic glasses (MGs), where measurements by the conventional gas-solid reaction method are difficult, is analyzed by a two-step approach: chronoamperometry followed by cyclic voltammetry (CA + CV). We introduce a concept of effective volume by measuring the thickness of the region where the hydrogen and hydroxyl ion interactions with Fe-based MG take place, which is characterized by high-angle annular dark-field scanning transmission electron microscopy. A very constant film thickness influenced by the OH- and H+ is confirmed by TEM, where the chemical homogeneity is maintained within this region. The weight percent of hydrogen and the corresponding hydrogen-to-metal ratio are determined as 1.16% and 0.56, respectively. When compared to previous studies conducted by the electrochemical- permeation method, the H/M ratio is found to be an order of magnitude larger. Electrochemical impedance spectroscopy (EIS) and subsequent equivalent circuit modeling (ECM) of the tested ribbons resolve the surface-diffusion processes for hydride formation and oxidation kinetics. This contribution provides a different perspective for the design and study of low-cost and high-performance amorphous nanofilms for hydrogenenergy applications, particularly when the common gas-adsorption methods are problematic.