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    Ammonia decomposition on a highly-dispersed carbon-embedded iron catalyst derived from Fe-BTC: stable and high performance at relatively low temperatures
    (Elsevier, 2020) N/A; N/A; Department of Chemical and Biological Engineering; Akarçay, Özge; Öztulum, Samira Fatma Kurtoğlu; Uzun, Alper; PhD Student; PhD Student; Faculty Member; 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; College of Engineering; N/A; 384798; 59917
    Fe-BTC (iron 1,3,5-benzenetricarboxylic acid), a commercially available metal organic framework (MOF), was used as a sacrificial template to produce a series of carbon-embedded Fe catalysts upon its pyrolysis at different temperatures. The catalyst prepared by pyrolyzing Fe-BTC at 400 degrees C under flowing N-2 provided a high graphitic degree on the carbon support hosting highly dispersed Fe species at a Fe loading of 34 wt%. Performance measurements on ammonia decomposition to produce COx-free hydrogen showed that this catalyst provided an ammonia conversion of 73.8% at a space velocity of 6000 cm(3) NH3 h(-1) g(cat)(-1) and at 500 degrees C for at least 120 h. This stable performance, exceeding that of some of the best non-noble metal catalysts, was associated with the presence of highly-dispersed Fe species at a significantly high Fe loading, embedded in a carbonaceous shell. The presence of the carbonaceous shell not only protected the active species against sintering, but also made them electron rich owing to its high level of graphitization.
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    Binary CuPt alloy nanoparticles assembled on reduced graphene oxide-carbon black hybrid as efficient and cost-effective electrocatalyst for PEMFC
    (Pergamon-Elsevier Science Ltd, 2019) Yılmaz, Melike Sevim; Kaplan, Begüm Yarar; Gürsel, Selmiye Alkan; Department of Chemistry; Metin, Önder; Faculty Member; Department of Chemistry; College of Sciences; 46962
    Addressed herein is the synthesis of binary CuPt alloy nanoparticles (NPs), their assembly on reduced graphene oxide (rGO), Vulcan XC72 (VC) and their hybrid (rGO-VC) to be utilized as electrocatalysts for fuel cell reactions (HOR and ORR) in acidic medium and PEMFC tests. The synthesis of nearly-monodisperse Cu45Pt55 alloy NPs was achieved by using a chemical reduction route comprising the reduction of commercially available metal precursors in a hot surfactant solution. As-synthesized Cu45Pt55 alloy NPs were then assembled on three support materials, namely rGO, VC and rGO-VC) via liquid phase self-assembly method. After the characterization, the electrocatalysts were prepared by mixing the yielded materials with Nafion and their electrocatalysis performance was investigated by studying CV and LSV for HOR and ORR in acidic medium. Among the three electrocatalysts tested, Cu45Pt55/rGO-VC hybrid showed the highest catalytic activity with ECSA of 119 m(2) g(-1) and mass activity of 165 mA mg(pt)(-1). After the evaluation of electrochemical performance of the three prepared electrocatalysts, their performance was then evaluated in fuel cell conditions. In similar to electrochemical activities, the Cu45Pt55/rGO-VC hybrid electrocatalyst showed a superior fuel cell performance and power output by providing a maximum power of 480 mW cm(-2) with a relatively low Pt loading (0.28 mg cm(-2)). Additionally, the Cu45Pt55/rGO-VC hybrid electrocatalyst exhibited substantially better activity as compared to Pt/rGO-VC electrocatalyst. Therefore, the present study confirmed that alloying Pt with Cu enhances the catalytic activity of Pt metal along with the help of beneficial features of rGO-VC hybrid support material. It should be noted that this is the first example of studying PEMFC performance of CuPt alloy NPs supported on rGO, VC and rGO-VC hybrid.
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    Binary CuPt alloy nanoparticles assembled on reduced graphene oxide-carbon black hybrid as efficient and cost-effective electrocatalyst for PEMFC [Int J Hydrogen Energy 44 (2019) 14184–14192]
    (Pergamon-Elsevier Science Ltd, 2021) Sevim, Melike; Kaplan, Begüm Yarar; Gürsel, Selmiye Alkan; Department of Chemistry; Metin, Önder; Faculty Member; Department of Chemistry; College of Sciences; 46962
    N/A
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    Boosting electrocatalysis of oxygen reduction and evolution reactions with cost-effective cobalt and nitrogen-doped carbons prepared by simple carbonization of ionic liquids
    (Pergamon-Elsevier Science Ltd, 2022) Zdolsek, Nikola; Vujkovic, Milica; Brkovic, Snezana; Jocic, Ana; Dimitrijevic, Aleksandra; Trtic-Petrovic, Tatjana; Sljukic, Biljana; Department of Chemistry; Metin, Önder; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; 46962
    Development of cost-effective, bi-functional carbon electrocatalysts via direct carbonization of ionic liquids (bis(cholinium) tetrachlorocobaltate(II) ([Ch](2)[CoCl4]) and bis(1-butyl-3methylimidazolium) tetrachlorocobaltate(II) ([Bmim](2)[CoCl4])) is reported herein for the first time. Carbon electrocatalysts, dual-doped with cobalt and nitrogen, were tested for oxygen reduction (ORR) and oxygen evolution (OER) reactions. Both materials show high bifunctional catalytic activity and excellent stability due to synergistic effects arising from the presence of nitrogen and cobalt. Electrocatalyst prepared by carbonization of [Ch](2)[-CoCl4] show exceptional activity and selectivity toward ORR. Conversely, electrocatalyst prepared from [Bmim](2)[CoCl4] showed a slightly better OER performance indicating that different catalytic sites are responsible for O-2 reduction and H2O oxidation. Parent CoO particles with graphitic nitrogen boost activity for ORR, while elemental Co supported by nitrogen atoms is responsible for OER activity. Finally, energy consumption during electrolytic oxygen production was calculated revealing energy saving when using two materials as anode electrocatalysts.
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    PublicationOpen Access
    Effect of cerium doping on morphology and physical properties of alpha-Fe2O3 films prepared by hydrothermal electrodeposition
    (Electrochemical Society (ECS), 2014) Department of Chemistry; Akkaya, Ceren Yılmaz; Ünal, Uğur; PhD Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering
    In this study, electrochemical growth of Ce-doped alpha-Fe2O3 films is reported. Electrodeposition at 75 degrees C and also a combined hydrothermal-electrochemical method to obtain hematite are presented. Both acidic and neutral plating solutions were used for the depositions. Ferric oxyhydroxide is produced by electrodeposition at 75 degrees C and converted to hematite phase after annealing. Hydrothermal-electrodeposition at 130 degrees C results in formation of hematite phase directly. The effect of temperature, deposition solution and cerium ion amount on the morphology and physical properties of hematite films are characterized.
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    PublicationOpen Access
    Electrochemical deposition of Mn:ZnO films under hydrothermal conditions
    (Electrochemical Society (ECS), 2013) N/A; Department of Chemistry; Akkaya, Ceren Yılmaz; 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 Sciences and Engineering; College of Sciences
    This study demonstrated the electrochemical deposition of Mn-doped ZnO films under hydrothermal conditions at 130 degrees C in 50% v/v DMSO-H2O mixture. X-ray diffraction analysis showed that the deposition of the ZnO structures was along (002) direction. However, the presence of Mn2+ affected the thickness of ZnO structures and we believe that the interaction of Mn2+ with the nonpolar surface of ZnO restricts lateral growth. Mn appears in the mixed oxide state in ZnO lattice. The photoluminescence spectra of the films show only UV emission indicating high crystal quality. The blueshift of the UV emission is observed after the introduction of Mn impurity into the ZnO lattice. The surface morphology, lattice structure, Mn content, chemical binding characteristics, and optical properties of the deposits were examined by scanning electron microscopy, X-ray diffraction, X-ray photoelectron-spectroscopy and photoluminescence spectroscopy, respectively.
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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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    PublicationOpen Access
    Evaluating the manufacturing quality of lithium Ion pouch batteries
    (Institute of Physics (IOP) Publishing, 2022) Kong, Lingxi; Aalund, Ryan; Stoliarov, Stanislav, I.; Pecht, Michael; Alipour, Mohammad; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM)
    Lithium-ion batteries must undergo a series of quality control tests before being approved for sale. In this study, quality control tests were carried out on two types of lithium-ion pouch batteries, here denoted as type A (with stacked electrode configuration) and type B (with a jelly-roll arrangement) to assess the effectiveness of the tests. Electrochemical tests, which included capacity and impedance measurements, found that both types of batteries met the specifications. However, computed tomography (CT) scan, disassembly, and material characterization revealed quality concerns in battery assembly and material composition. Results showed that, for an A cell, cathode extended past anode at the top and bottom of the roll, and a CT scan revealed inhomogeneities in the electrode near the corners. Similarly, analysis of a B cell revealed gaps in the winding structure and cathode material discrepancies. More specifically, the lithium nickel manganese cobalt oxide (NMC) material specified by the battery manufacturer turned out to be lithium cobalt oxide (LCO). The findings indicate that systematic quality control tests are needed to properly identify defects in batteries before they are used in products.
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    Fabrication of 1D ZNO nanostructures on mems cantilever for VOC sensor application
    (Elsevier, 2014) Kosemen, Arif; Öztürk, Sadullah; Yerli, Yusuf; Öztürk, Zafer Ziya; Department of Electrical and Electronics Engineering; N/A; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Kılınç, Necmettin; Çakmak, Onur; Ermek, Erhan; Ürey, Hakan; Researcher; PhD Student; Other; Faculty Member; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; 59959; N/A; N/A; 8579
    This study reports the fabrication method and sensing performance for novel 1D zinc oxide (ZnO) nanorods and nanotubes grown on nickel MEMS cantilevers. The fabrication of the nanostructures and the cantilevers are simple and low-cost using standard lithography, electrodeposition, and hydrothermal etching processes. 1D ZnO nanostructures increase the total sensitive area for biological and chemical sensor applications. We performed experiments with various VOCs with a real-time sensor system developed in our laboratory. While Ni microcantilevers produced no signal, ZnO nanostructure coated microcantilevers showed good sensitivity and repeatable changes. Furthermore, the nanotube coated microcantilevers showed more than 10 fold increase in sensitivity compared to the nanorod coated microcantilevers which can be explained to the fact that ZnO nanotubes have higher surface area and subsurface oxygen vacancies and these provide a larger effective surface area with higher surface-to-volume ratio as compared to ZnO nanorods. The tests are performed using dynamic mode of operation near resonant frequency using magnetic actuation and optical sensing. The phase stability and the limit of detection of ZnO nanotube coated microcantilevers exposed to diethylamine (DEA) were 0.02 degrees and lower than 10 ppm, respectively. ZnO nanostructure coated microcantilevers have good potential for VOC sensor applications especially for amine groups.
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    PublicationOpen Access
    FR4-based electromagnetic energy harvester for wireless tyre sensor nodes
    (Elsevier, 2009) Department of Electrical and Electronics Engineering; Hatipoğlu, Gökhan; Ürey, Hakan; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; N/A; 8579
    An electromagnetic (EM) power generator having 46 Hz resonance frequency is designed to scavenge mechanical vibrations occurring in tyres due to lyre-road contact. The major innovation is the use of FR4 as a structural spring material as well as utilizing a spacer and stopper mechanism increasing the shock resistance by limiting the maximum deflection. The novel magnet assembly and spacer design provide high power density. The tangential acceleration waveforms of typical tyre rotation is used as an input in the experiments and 0.4 mW power is obtained over a 100 Omega load resistance for 15g peak-to-peak amplitude at 22,83 Hz, corresponding to about 150 kph vehicle speed. Maximum acceleration is limited with the shaker, larger power values are expected in actual operation. The performance is obtained off-resonance and superior to resonant Silicon MEMS based scavengers.