Browsing by Author "Demir Kivrak, Hilal"

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The Effect of Temperature and Concentration for Methanol Electrooxidation on Pt-Ru Catalyst Synthesized by Microwave Assisted Route
(Tubitak Scientific & Technological Research Council Turkey, 2015) Demir Kivrak, Hilal
At present, the methanol electrooxidation reaction (MOR) activities of carbon supported bimetallic Pt-Ru (M-PtRu@C) catalyst and monometallic Pt (M-Pt@C) catalysts prepared via microwave assisted polyol method and carbon supported Pt-Ru (P-PtRu@C) catalysts prepared by conventional polyol were examined to investigate the effect of the preparation method. These catalysts were characterized by X-ray diffraction, X-ray photo electron spectroscopy, and transmission electron microscopy (TEM). From TEM, the particle size of the M-PtRu@C catalyst was estimated as 3.54 nm. The MOR activities of these catalysts were examined at room temperature by cyclic voltammetry and chronoamperometry. Furthermore, stability measurements were performed on these catalysts to examine their long term stability. As a result, M-PtRu@C catalyst exhibited the best electrocatalytic activity and long term stability. Furthermore, MOR measurements at varying temperatures on M-PtRu@C catalyst showed turnover number reached its optimum value at 60 degrees C. At this temperature, M-PtRu@C catalyst could catalyze more methanol in the same period using the same number of sites compared to other applied temperatures.
Remarkable Bismuth-Gold Alloy Decorated on Mwcnt for Glucose Electrooxidation: the Effect of Bismuth Promotion and Optimization Via Response Surface Methodology
(Tubitak Scientific & Technological Research Council Turkey, 2021) Er, Omer Faruk; Ulas, Berdan; Demir Kivrak, Hilal
In this study, the carbon nanotube supported gold, bismuth, and gold-bismuth (Au/MWCNT, Bi/MWCNT, and Au-Bi/ MWCNT) nanocatalysts were prepared with NaBH4 reduction method at varying molar atomic ratio for glucose electrooxidation (GAEO). The synthesized nanocatalysts at different Au: Bi atomic ratios are characterized via x-ray diffraction (XRD), transmission electron microscopy (TEM), and N-2 adsorption-desorption. For the performance of AuBi/MWCNT for GAEO, electrochemical measurements are performed by using different electrochemical techniques namely cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). Monometallic Au/MWCNT exhibits higher activity than Bi/MWCNT with 256.57 mA/mg (0.936 mA/cm(2)) current density. According to CV results, Au80Bi20/MWCNT nanocatalyst has the highest GAEO activity with the mass activity of 320.15 mA/mg (1.133 mA/cm(2)). For Au80Bi (20)/MWCNT, central composite design (CCD) is utilized for optimum conditions of the electrode preparation. Au80Bi20/MWCNT nanocatalysts are promising anode nanocatalysts for direct glucose fuel cells (DGFCs).
Structure of Ruthenium Nanocatalysts of Bismuth, Investigation of Its Effect on Hydrolysis Performance and Kinetic Studies
(Wiley, 2021) Avci Hansu, Tulin; Caglar, Aykut; Demir Kivrak, Hilal; Sahin, Omer
In this study, a new nanocatalyst, RuBi/carbon nanotube, was synthesized to be used in the hydrolysis reaction of sodium boron hydride. The sodium boron hydride hydrolysis performance was investigated by adding bismuth to the structure of ruthenium nanocatalysts. Hydrolysis experiments were carried out by adding bismuth at different atomic proportions to ruthenium. The best atomic ratio was determined to be 90:10. These catalysts are characterized by scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy. The parameters affecting hydrolysis such as temperature, catalyst amount, sodium hydroxide concentration, and sodium borohydride concentration were examined. The reusability of the catalyst was tested five times. In the calculations, the reaction order was calculated as n, 0.73, and activation energy E-a, 49657 kJ/mol.
Untangling the Cobalt Promotion Role for Ruthenium in Sodium Borohydride Dehydrogenation With Multiwalled Carbon Nanotube-Supported Binary Ruthenium Cobalt Catalyst
(Wiley-hindawi, 2021) Avci Hansu, Tulin; Sahin, Omer; caglar, Aykut; Demir Kivrak, Hilal
In the present study, multiwalled carbon nanotube-supported Ru (Ru/MWCNT) and RuCo (RuCo/MWCNT) nanocatalysts with 3 wt% Ru loading were synthesized via sodium borohydride (SBH) reduction method for the dehydrogenation of SBH (R-SBH)(.) These nanocatalysts were characterized with XRD, XPS, SEM-EDX, and TEM. Ru/MWCNT and Ru:Co/MWCNT catalysts with varying Ru:Co atomic ratios were prepared successfully, and electronic state of Ru:Co altered compared to Ru. R-SBH activities of these Ru/MWCNT and RuCo/MWCNT were examined in alkaline environment. RuCo/MWCNT at 80:20 atomic ratio exhibits superior H-2 evolution. Further experiments were performed with RuCo/MWCNT at 80:20 atomic ratio to determine how NaOH concentration (C-NaOH), reaction temperature (T-rxn), SBH concentration (C-SBH), and amount of nanocatalyst (M-c) affect R-SBH activities. Activation energy (Ea) was calculated using the Arrhenius equation. RuCo/MWCNT at 80:20 atomic ratio exhibits superior H-2 evolution activities compared to the literature values. Initial rate (IR) for this nanocatalyst was found as 123.9385 mL H-2 g(cat)(-1) min(-1). As a result of these kinetic calculations, the Ea of the nanocatalysts was calculated as 35.978 kJ/mol. The degree of reaction (n) was found to be 0.53 by trial and error. RuCo/MWCNT at 80:20 atomic ratio is a promising nanocatalyst for R-SBH.