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    Öğe
    Composition-dependent hydrogen evolution performance of Au-Pt nanoparticles: Correlating catalytic activity and first-principles calculations
    (Pergamon-Elsevier Science Ltd, 2026) Kaya, Dogan; Demiroglu, Ilker; Isik, Ilknur Baldan; Isik, Hasan Huseyin; Tayfun, Emre Can; Adanur, Idris; Akyol, Mustafa; Sevik, Cem; Karadag, Faruk; Ekicibil, Ahmet
    In this study, a series of Au-Pt bimetallic nanoparticles (NPs) with varying compositions (Au, Au-3-Pt-1, Au-1-Pt-1, Au-1-Pt-3) were synthesized via a modified polyol method and systematically investigated for their structural, morphological, and electrocatalytic properties toward the hydrogen evolution reaction (HER). Rietveld refinement of powder XRD data revealed a progressive lattice contraction, crystallite size reduction, and increasing microstrain with increasing Pt content, indicating partial alloying and phase segregation. High-resolution TEM and HAADF-EDS mapping confirmed the formation of core-shell, ball-cup, or Janus-type nanostructures, with Pt preferentially located at the periphery of Au-rich cores. DFT calculations corroborated the experimental findings, revealing negative excess energies for these morphologies and identifying ball-cup and Janus configurations as energetically favorable at equiatomic and Pt-rich compositions in Au-Pt nanoalloys. Electrochemical measurements in 1 M KOH showed enhanced HER activity for bimetallic systems, with Au-1-Pt-1 exhibiting the lowest overpotential (9 mV at 25 mA cm(-2)), and Au-1-Pt-3 demonstrating the highest specific (70.35 mA cm(-2)) and mass (268.56 mA mgPt(-1)) activities. Tafel slope analyses and turnover frequency calculations confirmed improved kinetics and Pt utilization efficiency. The superior stability over 500 CV cycles and favorable hydrogen adsorption energetics, as supported by DFT, highlight the potential of Au-Pt nanostructures as high-performance, durable HER electrocatalysts.
  • [ X ]
    Öğe
    Magnetically separable low Pt substituted Co nanoparticles: Investigation of structural, magnetic, and catalytic properties
    (Elsevier, 2022) Kaya, Dogan; Isik, Hasan Huseyin; Isik, Ilknur Baldan; Adanur, Idris; Wang, Yitao; Akyol, Mustafa; Karadag, Faruk
    Developing multifunctional nanoparticles (NPs) for magnetic and catalytic purposes is crucial for controlling magnetic properties and reducing production costs. We synthesized Co and low Pt loaded CoPt NPs by the modified polyol process. Co and CoPt NPs exhibited coexist fcc and hcp phases which are confirmed with x-ray diffraction and Rietveld refinement analysis. Scanning electron microscopy images revealed the average size of the NPs smaller than 9 nm with a narrow distribution. An irreversible magnetization-temperature behavior of the particles is observed in the modes of zero-field cooled and field cooled with a strong ferromagnetic signal close to 350 K. The field-dependent magnetization up to +/- 5 T was investigated to determine coercive field (H-c), exchange bias (H-E), saturation magnetization (M-s), remanent magnetization (M-r), and the ratio of remanent magnetization to saturation magnetization (M-r/M-s). There is a general decrease in magnetic values due to an increase of both the temperature and the Pt ratio in Co nanoparticles. When the Pt/Co ratio drops to 1%, the sample was measured with the highest H-c value of 648.5 Oe and M-s value of 100 emu/g at 5 K. On the contrary, increasing the concentration of Pt to 10% resulted in a reduction for the M-s value below 40 emu/g. Besides, cyclic voltammetry measurements showed apparent hydrogen reduction in the potential range of -0.91 V and -0.96 V (vs Ag/AgCl) and 10% Pt loaded CoPt NPs exhibits the highest activity after 10th cycles and increase the activity up to 15.80 mA cm(-2) at -1.2 V due to the surfactant.