Researcher:
Öztuna, Feriha Eylül Saraç

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Feriha Eylül Saraç

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Öztuna

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Öztuna, Feriha Eylül Saraç

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2012 - 2019112020 - 20223

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Now showing 1 - 10 of 14
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    Graphene aerogel-supported ruthenium nanoparticles for COx-free hydrogen production from ammonia
    (Elsevier, 2021) N/A; N/A; N/A; Department of Chemical and Biological Engineering; Department of Chemistry; Department of Chemistry; Koçer, Tolga; Öztulum, Samira Fatma Kurtoğlu; Uzun, Alper; Ünal, Uğur; Öztuna, Feriha Eylül Saraç; Researcher; PhD Student; Faculty Member; Faculty Member; Researcher; Department of Chemical and Biological Engineering; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; College of Sciences; N/A; 384798; 59917; 42079; N/A
    Ruthenium was highly dispersed on graphene aerogel (GA) at high loadings to achieve high performance in COx-free hydrogen production from ammonia. Catalytic performance measurements on ammonia decomposition showed that the GA-supported catalyst with a Ru loading of 13.6 wt% provides an ammonia conversion of 71.5 % at a space-velocity of 30,000 ml NH3 g(cat)(-1)h(-1) and at 450 degrees C, corresponding to a hydrogen production rate of 21.9 mmol H-2 g(cat)(-1)min(-1). The addition of K increased the ammonia conversion to a record high value of 97.6 % under identical conditions, reaching a hydrogen generation rate of 30.0 mmol H-2 g(cat)(-1) min(-1), demonstrated to be stable for at least 80 h. A comparison of the turnover frequencies of catalysts indicated that this increase in performance upon the addition of K originated from an increase in the number of the active Ru sites and the corresponding electron density available for reaction.
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    Free-standing N-doped reduced graphene oxide papers decorated with iron oxide nanoparticles: stable supercapacitor electrodes
    (Wiley-V C H Verlag Gmbh, 2019) N/A; Department of Chemistry; N/A; Department of Chemistry; Department of Chemistry; Beyazay, Tuğçe; Öztuna, Feriha Eylül Saraç; Ünal, Özlem; Acar, Havva Funda Yağcı; Ünal, Uğur; Researcher; Researcher; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; College of Sciences; College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; N/A; 178902; 42079
    In this study, graphene oxide paper is obtained via vacuum-assisted filtration of graphene oxide solution to prepare self-standing electrodes for supercapacitors. Simultaneous reduction and N-doping of graphene oxide paper are performed by chemical reduction followed by thermal annealing. Influence of different reduction techniques on the electrochemical properties of the self-standing papers is investigated. N-doped reduced graphene oxide papers are decorated with iron oxide nanoparticles to increase the energy density of the material. Increasing the amount of iron oxide nanoparticles in the composite paper results in enhanced capacitance. In the galvanostatic charge-discharge measurements, iron oxide/N-doped reduced graphene oxide electrode exhibits specific capacitance of 203 F g(-1) at 0.5 mA cm(-2). This value is remarkable since the electrode has a high mass loading of 2 mg cm(-2), which shows that the electrode can be used for practical purposes. Moreover, these electrodes operate in a wide potential window (1.6 V) and exhibit 79 % capacitance retention at 10000 cycles.
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    Layer-by-layer grown electrodes composed of cationic Fe 3 O 4 nanoparticles and graphene oxide nanosheets for electrochemical energy storage devices
    (Amer Chemical Soc, 2019) Erdem, Emre; Department of Chemistry; N/A; Department of Chemistry; Department of Chemistry; Öztuna, Feriha Eylül Saraç; Ünal, Özlem; Acar, Havva Funda Yağcı; Ünal, Uğur; Researcher; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; 178902; 42079
    Ultrathin electrodes composed of layer-by-layer assembled (3-aminopropyl)trimethoxysilane functionalized iron oxide nanoparticles and graphene oxide nanosheets were prepared by a simple and low-cost dip coating method without using any binders or conductive additives. The thickness of the Fe3O4/GO films was simply altered with the number of dip coating cycles. Multilayered films were chemically reduced with hydrazine vapor in order to increase the electrical conductivity. Characterization of multilayer films was performed with scanning transmission electron microscopy, UV-vis spectroscopy, atomic force microscopy, quartz crystal microbalance, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy. We have performed cyclic voltammetry and electrochemical impedance spectroscopy for the evaluation of Fe3O4/GO multilayers as possible electrochemical capacitor electrodes. Reduced Fe3O4/GO films exhibit high specific capacitances (varying between 200 and 350 F g(-1) at 5 mV s(-1)), Outperforming the layer-by-layer assembled iron oxides/carbon derivatives (carbon nanotube, graphene).
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    Graphene aerogel supported pt electrocatalysts for oxygen reduction reaction by supercritical deposition
    (Elsevier, 2017) Yu, Haibo; Aindow, Mark; N/A; N/A; N/A; Department of Chemistry; Department of Chemical and Biological Engineering; Öztuna, Feriha Eylül Saraç; Barım, Şansım Bengisu; Bozbağ, Selmi Erim; Ünal, Uğur; Erkey, Can; PhD Student; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; Department of Chemical and Biological Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; N/A; N/A; 42079; 29633
    Mesoporous graphene aerogel (GA) supported Pt nanoparticles with narrow size distribution were prepared via supercritical deposition (SCD) using supercritical CO2 (scCO(2)). Pt(cod)me(2) precursor was dissolved in scCO(2) and adsorbed onto GA at 35 degrees C and 10.7 MPa. The Pt precursor was converted to its metal form under atmospheric pressure at various temperatures. The effects of precursor conversion temperature (400, 600, and 800 degrees C) on the structural properties of the composites were investigated using Raman Spectroscopy, XRD, XPS, and TEM. The average particle size increased from 1.2 to 2.9 nm when the conversion temperature was increased from 400 to 800 degrees C. The electrocatalytic activity of the samples towards the Oxygen Reduction Reaction were evaluated using cyclic voltammetry (CV) and rotating disc electrode (RDE) measurements. SCD helped to preserve the textural properties of the GA after the Pt nanoparticle deposition, and thus Pt/GA converted at 600 degrees C exhibited an enhanced mass activity of 30.6 mA mg(Pt)(-1), outperforming the mass activities reported in the literature for Pt/GA electrocatalysts prepared using conventional routes. (C) 2017 Elsevier Ltd. All rights reserved.
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    Effect of nickel precursor on the catalytic performance of graphene aerogel-supported nickel nanoparticles for the production of cox-free hydrogen by ammonia decomposition
    (Wiley-V C H Verlag Gmbh, 2022) N/A; N/A; N/A; Department of Chemical and Biological Engineering; Department of Chemistry; Department of Chemistry; Koçer, Tolga; Öztulum, Samira Fatma Kurtoğlu; Uzun, Alper; Ünal, Uğur; Öztuna, Feriha Eylül Saraç; Researcher; PhD Student; Faculty Member; Faculty Member; Researcher; Department of Chemical and Biological Engineering; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; College of Sciences; N/A; 384798; 59917; 42079; N/A
    Graphene aerogel (GA), a promising porous material with high specific surface area and electrical conductivity, is utilized to disperse nickel nanoparticles to reach high catalytic activity in COx-free hydrogen production from ammonia. Ni(NO3)(2)center dot 6H(2)O and Ni (II) acetylacetonate (Ni(acac)(2)) were considered as metal precursors and the pH of the impregnation solution was varied to investigate the effects on the catalytic properties of the GA-supported nickel catalysts. Data showed that the best dispersion and homogeneity, as well as the catalytic performance, is achieved with Ni(acac)(2). An average Ni nanoparticle size of 13.6 +/- 4.3 nm was obtained on the GA-supported catalyst prepared by using Ni(acac)(2) dissolved in an impregnation solution with a pH of 10.2. This catalyst with a Ni loading of 11.1 wt% provided an ammonia conversion of 70.2% at a space velocity of 30 000 mL NH3 g(cat)(-1) h(-1) and 600 degrees C corresponding to a hydrogen production rate of 21.5 mmol H-2 g(cat)(-1) min(-1). Data illustrated that the difference between the point of zero charge of the support and the pH of the impregnation solution set by the type of the Ni precursor is a major parameter controlling the metal dispersion and the consequent catalytic activity.
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    Atomically dispersed reduced graphene aerogel-supported iridium catalyst with an iridium loading of 14.8 wt %
    (American Chemical Society (ACS), 2019) Debefve, Louise M.; Boubnov, Alexey; Bare, Simon R.; Gates, Bruce C.; N/A; Department of Chemical and Biological Engineering; Department of Chemistry; Department of Chemistry; Babucci, Melike; Uzun, Alper; Öztuna, Feriha Eylül Saraç; Ünal, Uğur; PhD Student; Faculty Member; Researcher; Faculty Member; Department of Chemical and Biological Engineering; Department of Chemistry; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; College of Sciences; N/A; 59917; N/A; 42079
    Atomically dispersed iridium complexes were anchored on a reduced graphene aerogel (rGA) by the reaction of Ir(CO)(2)(acac) [acac = acetonylacetonato] with oxygen-containing groups on the rGA. Characterization by X-ray absorption, infrared, and X-ray photoelectron spectroscopies and atomic resolution aberration-corrected scanning transmission electron microscopy demonstrates atomically dispersed iridium, at the remarkably high loading of 14.8 wt %. The rGA support offers sites for metal bonding comparable to those of metal oxides, but with the advantages of high density and a relatively high degree of uniformity, as indicated by the same turnover frequencies for catalytic hydrogenation of ethylene at low and high iridium loadings. The atomic dispersion at a high metal loading- and the high density of catalytic sites per unit of reactor volume, a key criterion for practical catalysts-set this catalyst apart from those reported.
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    Electrochemical-hydrothermal synthesis of manganese oxide films as electrodes for electrochemical capacitors
    (Elsevier, 2015) N/A; Department of Chemistry; Öztuna, Feriha Eylül Saraç; Ünal, Uğur; PHD Student; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Science and Engineering; College of Sciences; N/A; 42079
    Electrochemical capacitors have attracted great interest because they can maintain high power density along with high energy density. In this study, manganese oxides were electrodeposited onto nickel mesh substrate under hydrothermal conditions to be used as electrodes for electrochemical capacitors. Obtained Mn3O4 (hausmannite) phase was electrochemically oxidized to mixed-valent MnO2 during potential cycling. MnO2 electrodes showed excellent pseudocapacitative behaviour in cyclic voltammetry (CV) and charge-discharge (CD) measurements. Produced electrodes had specific capacitance of 518.8 F g(-1) at 0.1 mA cm(-2). Also, the electrodes maintained their capacitative properties at high scan rates/current densities and after 10,000 cycles of CV measurement. (C) 2015 Elsevier Ltd. All rights reserved.
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    First-row transition-metal cations (Co2+, Ni2+, Mn2+, Fe2+) and graphene (Oxide) Composites: From structural properties to electrochemical applications
    (Wiley-V C H Verlag Gmbh, 2019) N/A; Department of Chemistry; N/A; Department of Chemistry; Öztuna, Feriha Eylül Saraç; Yağcı, Mustafa Barış; Ünal, Uğur; Researcher; Researcher; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; N/A; College of Sciences; N/A; N/A; 42079
    Composites of graphene (oxide) (GO) and first-row transition-metal cations (Co2+, Ni2+, Mn2+, Fe2+) are prepared by mixing GO and aqueous metal salt solutions. The amount of metal cation bound to GO nanosheets is calculated by using inductively coupled plasma mass spectrometry (ICP-MS) and the possible binding sites of the metals are investigated by means of attenuated total reflectance infrared (ATR-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements. Electrodes loaded with the metal/GO composites are prepared by a simple drop-casting technique without any binders or conductive additives. The effect of electrochemical reduction on the structure of the composite electrodes is investigated by Raman spectroscopy, XPS, X-ray diffraction (XRD) analysis, and field emission scanning electron microscopy (FESEM). A detailed electrochemical characterization is performed for the utilization of the composite electrodes for electrochemical capacitors and possible oxygen reduction reaction electrocatalysts by cyclic voltammetry (CV) and rotating disk electrode measurements. The highest areal capacitance is achieved with the as-deposited Fe/GO composite (38.7mFcm(-2) at 20mVs(-1)). In the cyclic stability measurements, rCo/GO, rNi/GO, rMn/GO, and rFe/GO exhibit a capacitance retention of 44, 1.1, 73, and 87% after 3000 cycles of CV at 100mVs(-1), respectively.
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    Ultrasound-assisted hexamethylenetetramine decomposition for the synthesis of alpha nickel hydroxide intercalated with different anions
    (Springer, 2015) N/A; N/A; N/A; (TBD); N/A; Ertaş, Fatma Sinem; Öztuna, Feriha Eylül Saraç; Ünal, Uğur; Birer, Özgür; Master Student; Researcher; Faculty Member; Researcher; (TBD); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 42079; N/A
    Alpha nickel hydroxide was prepared by the sonochemical degradation of hexamethylenetetramine at elevated temperatures using chloride, acetate, nitrate, and sulfate nickel salts. This method yielded dense layered structures with two different interlayer spacing of 11 and 8 . The specific capacitance of these samples was further improved by the addition of extra anions to the reaction mixtures in the form of sodium salts. This approach yielded structures in flowerlike morphology with a single interlayer spacing of 8 . The sulfate-intercalated sample, however, formed the flowerlike morphology even without the addition of extra anions. The highest specific capacitance value of 543 F g(-1), at a scan rate of 50 mV s(-1), was obtained for sulfate-intercalated sample with extra anions. The differences due to different anions likely arise from size of their solvation shells and the distance between the anions and hydroxide layer. Anions surrounded tightly by water molecules are located farther from the hydroxide layers, interact less strongly and therefore are more labile and lead to higher specific capacitance values.
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    Charge storage characteristics of layer-by-layer assembled nickel hydroxide and graphene oxide nanosheets
    (Springer, 2019) N/A; Department of Chemistry; Department of Chemistry; Öztuna, Feriha Eylül Saraç; Ünal, Uğur; Researcher; Faculty Member; Department of Chemistry; College of Sciences; College of Sciences; N/A; 42079
    In this study, layer-by-layer assembled thin films composed of nickel hydroxide and graphene oxide nanosheets were produced via simple dip coating process. The surface topography of the thin films was investigated by atomic force microscopy measurements. Electrical conductivity of the thin films was enhanced by chemical reduction with hydrazine vapor. The effect of chemical reduction on the surface chemical structure was analyzed by X-ray photoelectron spectroscopy. To utilize the produced thin films as possible electrodes for electrochemical energy storage devices, cyclic voltammetric measurements were performed. The areal capacitance of a reduced 9-bilayer [Ni(OH)(2)/graphene oxide] thin film reached 5.2mFcm(-2) at a scan rate of 2mVs(-1), outperforming similar layer-by-layer assembled metal hydroxide/graphene thin films. Lastly, charge storage characteristics of as-deposited and reduced films were investigated by performing cyclic voltammetry at different scan rates and electrochemical impedance spectroscopy.