Browsing by Author "Duzenli, Derya"

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A Comparative Experimental and Density Functional Study of Glucose Adsorption and Electrooxidation on the Au-Graphene and Pt-Graphene Electrodes
(Pergamon-elsevier Science Ltd, 2020) Caglar, Aykut; Duzenli, Derya; Onal, Isik; Tersevin, Ilker; Sahin, Ozlem; Kivrak, Hilal
At present, the graphene is covered on Cu foil with the 5 sccm hexane (C6H14) flow rate, 50 sccm hydrogen (H-2) flow rate, and 20 min deposition time parameters by the CVD method. The graphene on the Cu foil is then covered onto few-layer ITO electrode. Furthermore, the Pt and Au metals are electrodeposited on graphene/ITO electrode with electrochemical method. These electrodes are characterized by Raman spectroscopy and Scanning Electron Microscopy-Energy Dispersive X-Ray analysis (SEM-EDX). The graphene structure is approved via Raman analysis. Au, Pt, and graphene network are openly visible from SEM results. In addition, glucose (C6H12O6) electrooxidation is investigated with cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. As a result, Pt-graphene/ITO indicates the best C6H12O6 electrooxidation activity with 9.21 mA cm(-2) specific activity (highly above the values reported in the literature). In all electrochemical measurements, Pt-graphene/ITO exhibits best electrocatalytic activity, stability, and resistance compared to the other electrodes. The adsorption of the C6H12O6 molecule is examined theoretically over metal atom (gold and platinum)-doped graphene surfaces using the density functional theory (DFT) method. The interaction between C6H12O6 molecule and OH adsorbed Pt-doped surface is stronger than that of OH adsorbed Au-doped graphene surface thermodynamically according to the reaction energy values. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
An Ethanol Electrooxidation Study on Carbon-Supported Pt-Ru Nanoparticles for Direct Ethanol Fuel Cells
(Taylor & Francis inc, 2016) Sahin, Ozlem; Duzenli, Derya; Kivrak, Hilal
Carbon supported Pt-Ru catalysts were prepared at varying Pt:Ru ratios by polyol method. The crystallite sizes of these catalysts were determined by X-ray diffraction technique. The specific surface areas of these catalysts were also defined by Brunauer-Emmett-Teller technique. Cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy measurements were conducted on these carbon supported Pt-Ru catalysts to investigate the effect of ruthenium on the ethanol electrooxidation kinetics. Results indicated that Pt-Ru (25:1) catalyst showed the best ethanol electrooxidation activity. In conclusion, ethanol electrooxidation mechanism was proposed.
Glucose Electrooxidation Modelling Studies on Carbon Nanotube Supported Pd Catalyst With Response Surface Methodology and Density Functional Theory
(Pergamon-elsevier Science Ltd, 2022) Kaya, Sefika; Ulas, Berdan; Duzenli, Derya; Onal, Isik; Er, Omer Faruk; Yilmaz, Yonca; Kivrak, Hilal
In this study, carbon nanotube supported Pd catalysts (Pd/CNT) are synthesized at different weight percentages by the sodium borohydride (NaBH4) reduction method to investigate catalytic performance of glucose electrooxidation reaction. 0.5% Pd/CNT, 3% Pd/CNT, and 7% Pd/CNT catalysts are characterized by using X-ray diffraction (XRD), electron microscopy with energy dispersive X-ray (SEM-EDX), and N2 adsorption-desorption measurements. The average particle size and surface area of 3% Pd/CNT catalyst are determined as 46.33 nm and 129.48 m2/g, respectively. Characterization results indicate that Pd/CNT catalysts are successfully prepared by NaBH4 reduction method. Cyclic voltammetry measurements are performed to investigate the effect of Pd loading for the glucose electrooxidation. CV results reveal that 3% Pd/CNT catalyst exhibits best glucose electrooxidation activity. Following this, experimental optimization is performed to obtain maximum glucose electrooxidation activity via response surface methodology (RSM). Estimated and experimental specific activities at optimum experimental conditions are assigned as 6.186 and 5.832 mA/cm2, respectively. To understand the glucose electrooxidation activity on the surface of Pd/CNT, surface modeling is also performed with density functional theory (DFT) method to investigate adsorption of glucose molecule on CNT supported Pd surface. The DFT results emphasize that the addition of Pd atom to the CNT structure significantly improves the catalytic performance in glucose electrooxidation.
A Novel Experimental and Density Functional Theory Study on Palladium and Nitrogen Doped Few Layer Graphene Surface Towards Glucose Adsorption and Electrooxidation
(Pergamon-elsevier Science Ltd, 2021) Caglar, Aykut; Duzenli, Derya; Onal, Isik; Tezsevin, Ilker; Sahin, Ozlem; Kivrak, Hilal
At present, few layer graphene (G) and nitrogen doped few layer graphene (N doped-G) are firstly coated on Cu foil via chemical vapor deposition (CVD) method and G and N doped-G coated Cu foil is transferred to the indium tin oxide (ITO) substrate surface to obtain electrodes. Pd metal is electrodeposited onto the N doped-G/ITO electrode (Pd-N doped-G/ITO). Pd-N doped-G/ITO electrode are characterized with advanced surface characterization methods such as Raman spectroscopy and SEM-EDX. Characterization results reveal that G and N structures are succesfully obtained and the presence of Pd on Pd-N doped-G/ITO is confirmed with SEM-EDX mapping. The cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) are employed to examine glucose electrooxidation of G/ITO, N-doped G/ITO, and Pd-N-doped G/ITO electrodes. P-N-dopedG/ITO electrode exhibits the best glucose electrooxidation activity with 2 mA/cm(2) specific activity. Density functional theory (DFT) calculations are also carried out to better understand the interaction of the molecules on Pd modified G (Pd-G) and Pd modified N-doped G (Pd-3NG) surfaces.
Synthesis and Characterization of Novel Ti Doped Hexagonal Mesoporous Silica Catalyst for Nonenzymatic Hydrogen Peroxide Oxidation
(Elsevier Science Bv, 2018) Duzenli, Derya; Sahin, Ozlem; Kazici, Hilal Celik; Aktas, Nahit; Kivrak, Hilal
A new electrocatalyst, Ti-HMS was successfully synthesized by sol-gel method employing Ti source tetrabutyl orthotitanate (TBOT) and silica source tetraethyl orthosilicate (TEOS, 99% purity). Ti-HMS catalysts were prepared at varying Ti:Si ratios by employing sol-gel method. Physicochemical properties of these nanoparticles were characterized and confirmed by BET, TG-DTA, XPS, and XRD. Electrochemical properties of Ti-HMS catalysts prepared at varying Ti:Si ratios were examined by cyclic voltammetry (CV) and chronoamperometry (CA) for determination of the oxidation and reduction activity of H2O2. It was observed that the Ti-HMS (Ti:Si = 0.02) electrode exhibits significant oxidation and reduction of H2O2 at applied potentials of 0.65 V and -0.30 V with the addition of H2O2, respectively. The excellent electrocatalytic response to H2O2 is mainly attributed to varying electronic properties with the incorporation of Ti to HMS. (C) 2017 Elsevier Inc. All rights reserved.