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    Öğe
    Effect of Gd-doping in Ni/NiO core/shell magnetic nanoparticles (MNPs) on structural, magnetic, and hydrogen evolution reaction
    (Aip Publishing, 2022) Adanur, Idris; Karazehir, Tolga; Dogru Mert, Basak; Akyol, Mustafa; Ekicibil, Ahmet
    In this study, Gd-x-doped Ni/NiO MNPs (x: 0.0%, 2.5%, 5.0%, and 10.0%) with a protective polyvinylpyrrolidone (PVP) layer have been synthesized via a polyol reduction process. The x-ray diffraction patterns revealed that samples have a cubic structure with Fm3m space group and no change in the crystallite structure was observed with doping Gd3+ ions. The crystallite size (D-c) decreases from 2.70 to 1.27 nm when Gd is doped into Ni/NiO MNPs. Transmission electron microscopy analysis revealed that the Ni/NiO MNPs with Gd(5%) concentration are formed as spherical multicore-like shape core/shell MNPs with a protective PVP layer. The magnetic hysteresis measurements taken at 10 and 300 K show that the saturation magnetization (M-s) decreases with increasing Gd3+ ions in the structure. The highest effective magnetic moment (mu(eff)) was obtained as 10.34 mu(B) in the NG-2 sample. We ascribe that the high mu(eff) value in this sample is due to the increase in d-f exchange interaction between Ni(3d(7)) and Gd(4f(7)) and the contribution of the dipole moment of PVP molecules. The electrochemical measurements showed that the current density values were 0.294 and 0.319 mA/cm(2) at-1.3 V in the absence of Gd (NG-0) and Gd(5%) doped (NG-2) samples, respectively. beta c was 159 and 132 mV/dec for NG-0 and NG-2 samples, respectively. The diminishing of beta c and the charge resistance (Rct) proved that the Gd doped catalyst enhanced the hydrogen evolution activity and the Gd(5%) doped sample exhibited the highest catalyst performance.
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    Öğe
    Experimental and theoretical study on hydrogen production by using Ag nanoparticle-decorated graphite/Ni cathode
    (Wiley, 2021) Yildiz, Resit; Dogru Mert, Basak; Karazehir, Tolga; Gurdal, Yeliz; Toprak Doslu, Serap
    In this study, graphite (G) electrode was coated with nickel and decorated with silver nanoparticles (G/Ni/Ag) with the help of galvanostatic method, and electrodes were used as a cathode in alkaline water electrolysis system. The characterization was achieved using X-ray diffraction and field emission scanning electron microscopy. Hydrogen evolution performance of electrodes was investigated via cyclic voltammetry, chronoamperometry, cathodic polarization curves, and electrochemical impedance measurements. Electrochemical results showed that hydrogen production efficiency significantly increased and charge transfer resistance decreased via G/Ni/Ag. The electrochemical water splitting performance of G/Ni/Ag, was established in a joint experimental and computational effort. Water and proton adsorption on Ag-decorated Ni surface were investigated using density functional theory. Electronic structure calculations identified the role of Ag adatom and Ni surface on water and proton adsorptions. From the computational studies, O in water was more reliable to adsorb at the bridge position of the Ag and Ni atoms, leading improved orbital overlap between H and Ni atoms and maximized chemical and physical interactions between the H2O molecules. Therefore, the Ag-decorated Ni(111) surface provides preferable adsorption site for the O atom in water and direct interactions between water Hs and available surface Ni atoms promote water dissociation.