Browsing by Author "Sahin, Ozlem"
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Article Coccoidea (Hemiptera) Species of Taurus Cedar (Cedrus Libani) in Turkey(Entomological Soc Turkey, Ege Univ, 2012) Ulgenturk, Selma; Sahin, Ozlem; Ayhan, Bikem; Saribasak, Halil; Kaydan, M. BoraCoccoidea species on Taurus cedar (Cedrus libani A. Richard) was collected natural cedar forests, reforestations and urban green areas in mainly Aegean, Marmara, Mediterranean and some neighboring regions. Totally 11 species were determined from Diaspididae (8), Coccidae (2), Pseudococcidae (1), four of them (Chionaspis kabyliensis Balachowsky, Dynaspidotus jaapi (Leonardi), Gomezmenoraspis nr. pinicola (Leonardi) and Phenacoccus arambourgi (Balachowsky) are new records for Turkish fauna. Ceroplastes floridensis Comstock and Dynaspidiotus britannicus (Newstead) are new records on C. libani in the world.Article 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, HilalAt 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.Article A Complementary Study on Novel Pdauco Catalysts: Synthesis, Characterization, Direct Formic Acid Fuel Cell Application, and Exergy Analysis(Pergamon-elsevier Science Ltd, 2018) Kivrak, Hilal; Atbas, Dilan; Alal, Orhan; Cogenli, M. Selim; Bayrakceken, Ayse; Mert, Suha Orcun; Sahin, OzlemAt present, Pd containing (10-40 wt%) multiwall carbon nanotube (MWCNT) supported Pd monometallic, Pd:Au bimetallic, and PdAuCo trimetallic catalysts are prepared via NaBH4 reduction method to examine their formic acid electrooxidation activities and direct formic acid fuel cell performances (DFAFCs) when used as anode catalysts. These catalysts are characterized by advanced analytical techniques as N-2 adsorption and desorption, XRD, SAXS, SEM-EDX, and TEM. Electronic state of Pd changes by the addition of Au and Co. Moreover, formic acid electrooxidation activities of these catalysts measured by CV indicates that particle size changes in wide range play a major role in the formic acid electrochemical oxidation activity, ascribed the strong structure sensitivity of formic acid electrooxidation reaction. PdAuCo (80:10:10)/MWCNT catalyst displays the most significant current density increase. On the other hand, lower CO stripping peak potential obtained for PdAuCo (80:10:10)/MWCNT catalyst, attributed to the awakening of the Pd-adsorbate bond strength down to its optimum value, which favors higher electrochemical activity. DFAFCs performance tests and exergy analysis reveal that fuel cell performances increase with the addition of Au and Co which can be attributed to synergetic effect. Furthermore, temperature strongly influences the performance of formic acid fuel cell. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Article Composition Dependent Activity of Pdagni Alloy Catalysts for Formic Acid Electrooxidation(Academic Press inc Elsevier Science, 2018) Ulas, Berdan; Caglar, Aykut; Sahin, Ozlem; Kivrak, HilalIn the present study, the carbon supported Pd, PdAg and PdAgNi (Pd/C, PdAg/C and PdAgNi/C) electrocatalysts are prepared via NaBH4 reduction method at varying molar atomic ratio for formic acid electrooxidation. These as-prepared electrocatalysts are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma mass spectrometry (ICP-MS), N-2 adsorption desorption, and X-ray electron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), and lineer sweep voltammetry (LSV). While Pd-50,Ag-50/C exhibits the highest catalytic activity among the bimetallic electrocatalyst, it is observed that Pd70Ag20Ni10/C electrocatalysts have the best performance among the all electrocatalysts. Its maximum current density is about 1.92 times higher than that of Pd/C (0.675 mA cm(-2)). Also, electrochemical impedance spectroscopy (EIS), chronoamperometry (CA) and lineer sweep voltammetry (LSV) results are in a good agreement with CV results in terms of stability and electrocatalytic activity of Pd50Ag50/C and Pd70Ag20Ni10/C. The Pd70Ag20Ni10/C catalyst is believed to be a promising anode catalyst for the direct formic acid fuel cell. (C) 2018 Elsevier Inc. All rights reserved.Article Dendrimer Templated Synthesis of Carbon Nanotube Supported Pdau Catalyst and Its Application as Hydrogen Peroxide Sensor(Wiley-v C H verlag Gmbh, 2019) Alal, Orhan; Caglar, Aykut; Kivrak, Hilal; Sahin, OzlemAt present, CNT supported catalysts were prepared by two different methods as NaBH4 reduction and dendrimer templated NaBH4 reduction method to observe the effect of preparation method on the sensitivity and activity of H2O2 reduction. Then, CNT supported PdxAuy bimetallic nanocatalysts having various atomic ratio were synthesized via novel dendrimer templated NaBH4 reduction method. The resulting materials were characterized employing XRD and TEM. Crystallite size of 10 %Pd0.7Au0.3/CNTdendrimer was obtained from XRD 17.1 nm and mean particle size obtained from TEM is about 15 nm. Moreover, the electrochemical behavior of these catalysts was characterized by cyclic voltammetry (CV) and chronoamperometry (CA) techniques. PdxAuy bimetallic nanocatalysts have excellent electrocatalytic properties and great potential for applications in electrochemical detection. The sensitivity and the limit of detection values for the prepared sensor with monometallic 10 % Pd/CNTdendrimer catalysts are 219.78 mu A mM(-1)cm(-2) and 2.6 mu M, respectively. However, the sensor constructed with 10 %Pd0.7Au0.3/CNTdendrimer modified electrode has a very high sensitivity of 316.89 mu A mM(-1) cm(-2) with a quick response time of 2 s and a wide linear range of 0.001-19.0 mM. In addition, the interference experiment indicated that the 10 % Pd0.7Au0.3/CNTdendrimer nanoparticles have good selectivity toward H2O2.Article An Ethanol Electrooxidation Study on Carbon-Supported Pt-Ru Nanoparticles for Direct Ethanol Fuel Cells(Taylor & Francis inc, 2016) Sahin, Ozlem; Duzenli, Derya; Kivrak, HilalCarbon 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.Article Fabrication of Novel Palladium-Platinum Based Graphene/Ito Electrodes and Third Metal Addition Effect Through the Glucose Electrooxidation(Elsevier Science Sa, 2022) Caglar, Aykut; Hansu, Tulin Avci; Sahin, Ozlem; Kivrak, HilalGraphene was coated on Cu foil by chemical vapor deposition (CVD) method. The graphene on the Cu foil was modified by doping N. Then, N-doped graphene (G) was coated on several layers of indium tin oxide (ITO) electrodes. In addition, Pd, Pt, and M (Ag, V, Ni, Zn) metals were electroprecipitated on the graphene/indium tin oxide electrode by electrochemical technique. In this way, the glucose (C6H12O6) electrooxidation activities of these electrodes obtained from PdMPt-N doped graphane/indium tin oxide were investigated by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. The obtained materials were characterized by SEM-EDX. Results revealed that the network of Pd, Pt, Ag, V, Ni, Zn and graphene was clearly visible from the SEM results. As a consequence, PdZnPt-N doped G/ITO showed the most effective C6H12O6 electrooxidation activity with a specific activity of 14.5 mA cm(-2), considerably above the literature's published values. In all electrochemical measurements, PdZnPt-N doped G/ITO exhibited the best electrocatalytic activity, stability, and resistance. PdZnPt-N doped G/ITO electrode is promising electrode for glucose electrooxidation.Article Facile and Rapid Synthesis of Microwave Assisted Pd Nanoparticles as Non-Enzymatic Hydrogen Peroxide Sensor(Esg, 2017) Sahin, Ozlem; Kivrak, Hilal; Kivrak, Arif; Kazici, Hilal Celik; Alal, Orhan; Atbas, DilanCarbon supported Pd catalyst was prepared with microwave-assisted polyol method (M-Pd@C) and investigated sensing activity for non-enzymatic hydrogen peroxide (H2O2). Moreover, M-Pd@C and Pd@C catalyst which synthesized via polyol method (P-Pd@C) were compared to each other in terms of electrocatalytic activity. X-ray diffraction (XRD), X-ray photo electron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate structural and morphological properties of these catalysts. Furthermore, electrochemical measurements were performed via cyclic voltammetry (CV), chronoamperometry (CA) techniques. CV results exhibited that M-Pd/C catalyst showed perfect electrocatalytic activity in terms of reduction of H2O2. M-Pd/C catalyst showed a fast response of less than 7 s with a linear range of 5.0x10(-3)-11.0 mM and a relatively low detection limit of 1.2 mu M amperometric response. M-Pd/C catalyst exhibited great selectivity for detecting H2O2 in the existence of several hindering species such as uric acid and ascorbic acid.Correction Facile and Rapid Synthesis of Microwave Assisted Pd Nanoparticles as Non-Enzymatic Hydrogen Peroxide Sensor (Vol 12, Pg 762, 2017)(Esg, 2018) Sahin, Ozlem; Kivrak, Hilal; Kivrak, Arif; Kazici, Hilal Celik; Alal, Orhan; Atbas, DilanArticle Few-Layer Graphene Coated on Indium Tin Oxide Electrodes Prepared by Chemical Vapor Deposition and Their Enhanced Glucose Electrooxidation Activity(Wiley, 2019) Caglar, Aykut; Ulas, Berdan; Sahin, Ozlem; Kivrak, Hilal DemirAt present, few-layer graphene is deposited on copper (Cu) foil by chemical vapor deposition (CVD) method. Then, the few-layer graphenes produced on the Cu foil are coated onto the indium tin oxide (ITO) electrode to investigate their glucose electrooxidation activities. Hexane and hydrogen flow rate and deposition time parameters with CVD method are examined on different Cu foils. These electrodes are characterized by scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Furthermore, glucose electrooxidation is examined with cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. One could note that the graphene network is clearly visible from SEM images. The deconvoluted XPS spectrum indicates that carbon appeared in the form of non-oxygenated ring C atoms for few-layer graphene. The few-layer graphene structure is confirmed by Raman analysis. Few-layer graphene/ITO produced at 5 sccm Hexane and 50 sccm hydrogen flow rate and 20minutes deposition time (G7/ITO) reveals the best electrode activity. The specific activity of G7/ITO electrode is obtained as 6.58mAcm(-2). According to CV, CA, and EIS results, G7/ITO electrode has high electrocatalytic activity, stability, and resistance in comparison with other electrodes.Article Methanol Electrooxidation Study on Mesoporous Silica Supported Pt-Co Direct Methanol Fuel Cell Anode(Walter de Gruyter Gmbh, 2014) Kivrak, Hilal; Can, Mukaddes; Duru, Hatice; Sahin, OzlemAt present, Pt was impregnated by incipient wetness impregnation method on Co-doped SBA-15 catalysts prepared by sol-gel method at different weight percentages of Co to investigate the effect of Pt: Co ratio on methanol electrooxidation reaction (MOR). Cyclic voltammetry (CV), chronoamperometry (CA), and linear sweep voltammetry (LSV) techniques were employed to examine the MOR activities, poisoning capacity, and stability of these Pt/SBA-15 and Pt-Co/SBA-15 catalysts. Co presence in the platinum structure enhances the electrocatalytic activity of MOR, due to oxidation of Co at relatively low positive potentials. CV and CA measurements indicated that the most active catalyst was Pt-Co (86:14)/SBA-15 catalyst for MOR. Stability and poisoning measurements revealed that Co presence in the catalyst increases CO poisoning resistance and its stability, in agreement with CV and CA measurements.Article 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, HilalAt 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.Article 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, HilalA 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.Article Synthesis of in Situ N-, S-, and B-Doped Few-Layer Graphene by Chemical Vapor Deposition Technique and Their Superior Glucose Electrooxidation Activity(Wiley, 2019) Caglar, Aykut; Ulas, Berdan; Sahin, Ozlem; Kivrak, HilalAt present, N-, S-, and B-doped grapheme-modified indium tin oxide (ITO) electrodes are produced and doping method effect on the glucose electrooxidation is investigated. Firstly, few-layer graphene is produced by chemical vapor deposition (CVD) method. Then, N, S, and B doping is carried out after graphene produced by CVD to prepare N-doped, B-doped, and S-doped few-layer graphene. N, S, and B doping is carried out by two different ways as (a) doping after synthesis of few-layer graphene and (b) in situ doping during few-layer graphene production. These materials are characterized by X-ray diffraction, scanning electron microscopy-energy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). One could note that graphene and nitrogen networks are clearly visible from SEM images. Raman spectra show that B, N, and S are doped on few-layer graphene/ITO successfully. XPS results of graphene, N-doped graphene, and in situ N-doped graphene reveal that graphene and nitrogen atoms used in the preparation of the electrodes obtain mainly in their elemental state. Then, these N-, S-, B-doped and in situ N-, S-, B-doped few-layer graphene materials are coated onto indium tin oxide (ITO) to obtain N-, S-, B-doped and in situ N-, S-, B-doped ITO electrodes for glucose (C6H12O6) electrooxidation. C6H12O6 electrooxidation measurements are investigated with cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy measurements. As a result, in situ N-doped few-layer graphene/ITO electrode displays the best C6H12O6 electrooxidation activity with 9.12 mA.cm(-2) current density compared with other N-, S-, B-doped graphene and in situ doped S and B grapheme-modified ITO electrodes. Furthermore, this current density value for in situ N-doped few-layer graphene/ITO is highly above the values reported in the literature. In situ N-doped few-layer graphene/ITO electrode is a promising electrode for C6H12O6 electrooxidation because it exhibits the best electrocatalytic activity, stability, and resistance compared with other electrodes.