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Öğe A comparative study of electrochemical methods on Pt-Ru DMFC anode catalysts: The effect of Ru addition(PERGAMON-ELSEVIER SCIENCE LTD, 2013) Sahin, Ozlem; Kivrak, HilalIn the present study comparative electrochemical study of methanol electro-oxidation reaction, the effect of ruthenium addition and experimental parameters on methanol electro-oxidation reaction at high performance carbon supported Pt and Pt-Ru catalysts have been studied by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) in H2SO4 (0.05-2.00 M) + CH3OH (0.01-4.00 M) at 20-70 degrees C. Tafel plots for the methanol oxidation reaction on Pt and Pt-Ru catalysts show reasonably well-defined linear region with the slopes of 128-174 mV dec(-1)(alpha = 0.34-0.46). The activation energies from Arrhenius plots have been found as 39.06-50.65 kJ mol(-1). As a result, methanol oxidation is enhanced by the addition of ruthenium. Furthermore, Pt-Ru (25:1) catalyst shows best electro-catalytic activity, higher resistance to CO, and better long term stability compared to Pt-Ru (3:1), Pt-Ru (1:1), and Pt. Finally, the EIS measurements on Pt-Ru (25:1) catalyst reveals that methanol electro-oxidation reaction consists of two process: methanol dehydrogenation step at low potentials (<700 mV) and the oxidation removal of COads by OHads at higher potentials (>700 mV). Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Öğe 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.Öğe 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.Öğe 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.Öğe 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, Dilan[Abstract not Available]Öğe In Vitro Determination of 6PGD Enzyme Activity Purified from Lake Van Fish (Chalcalburnus tarichii Pallas, 1811) Liver Exposed to Pesticides(SPRINGER, 2013) Guler, Muhammet; Kivanc, M. Riza; Turkoglu, Vedat; Basi, Zehra; Kivrak, HilalIn the present study, the effect of methidathion, cypermethrin, and deltamethrin pesticides on Lake Van fish (Chalcalburnus tarichii Pallas, 1811) liver 6-phosphogluconate dehydrogenase enzyme activity was investigated due to the fact that these pesticides are extensively used to improve agricultural productivity in the Van region. 2',5'-ADP Sepharose 4B affinity chromatography was used to purify 6-phosphogluconate dehydrogenase enzyme from fish liver and SDS-PAGE technique was used to control the purity of this enzyme. The in vitro effect of methidathion, cypermethrin, and deltamethrin pesticides on the enzyme activity was investigated. The enzyme was purified 1,050-fold with specific activity of 27.04 EU/mg protein. Moreover, K-i constants of methidathion, cypermethrin, and deltamethrin were to be 3.294 +/- A 0.215, 0.718 +/- A 0.095, and 0.084 +/- A 0.009 mM respectively. The IC50 value were estimated as 9.95 x 10(-5) +/- A 0.1844 x 10(-5) mM for methidathion, 1.01 x 10(-4) +/- A 0.01413 x 10(-4) mM for cypermethrin, and 4.43 x 10(-6) +/- A 0.05653 x 10(-6) mM for deltamethrin. In conclusion, deltamethrin inhibits the enzyme activity more than methidathion and cypermethrin.Öğe 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.Öğe Synthesis and solar-cell applications of novel furanyl-substituted anthracene derivatives(ELSEVIER SCIENCE BV, 2017) Kivrak, Arif; Er, Omer Faruk; Kivrak, Hilal; Topal, Yasemin; Kus, Mahmut; Camlisoy, YesimAt present, novel furanyl-substituted anthracene derivatives; namely 9,10-di(furan-2-yl)anthracene (DFA), 5,5'-(anthracene-9,10-diyl)bis(furan-2-carbaldehyde) (DAFA) and 2,2'-((5,5'-(anthracene-9,10-diyl)bis(furan-5,2-diyl))bis(methanylylidene))dimalononitrile (DCNFA) were designed and synthesized successfully by employing Stile Cross-Coupling, Vilsmeier-Haack and Knoevenagel condensation reactions, respectively. This methodology provides a practical new route for the synthesis of furanyl-substituted anthracene derivatives bearing strong electron-withdrawing groups. The electrochemical and electro-optical properties of these novel furanyl-substituted anthracene derivatives were also examined with strong acceptor-pi-donor-pi-acceptor interactions. Furthermore, Highest occupied molecular orbital (HOMO), Lowest Unoccupied molecular orbital (LUMO), and band gap (Eg) values were investigated by using spectroscopic methods. Electrochemical and electro-optical properties were calculated and compared to DFA, DAFA and DCNFA. Eg was found as 2.85, 2.71, and 2.33 eV, respectively. Consequently, Organic Solar Cells (OSC) were fabricated to investigate their solar cell performances. The strong electron withdrawing groups did not increase the solar cell performance of furanyl-anthracenes. Surprisingly, DFA was found to exhibit the best OSCs performance (Efficiency = 3.36). As a result, one could note that these novel furanyl-substituted anthracene derivatives are good candidate for the applications of the OSCs. Our results might help in the development of new materials with important electrochemical functions by giving the advantage of designing and further derivatization of new generation small organic molecules for photovoltaic device applications. (C) 2017 Elsevier B.V. All rights reserved.Öğe Synthesis of tetracyanoethylene-substituted ferrocene and its device properties(WILEY, 2018) Kivrak, Arif; Zobi, Cengiz; Torlak, Yasemin; Camlisoy, Yesim; Kus, Mahmut; Kivrak, HilalSmall organic molecules are promising candidates for cheaper, flexible and good-performance sources for organic solar cells (OSCs) due to their easy fabrication, low cost and slightly cheaper processing. However, the lower power conversion efficiency of OSCs is the main problem for their applications. Ferrocene structures could be the best candidates for the active layers of OSCs due to their unique properties such as thermal and chemical stability. The electrochemical, electro-optical and solar cell performances of 2,5-dicyano-3-ferrocenyl-4-ferrocenylethynylhexa-2,4-dienedinitrile (DiCN-Fc) structures were investigated. First, the electrochemical and electro-optical properties were examined for finding the highest occupied and lowest unoccupied molecular orbital values and bandgap of DiCN-Fc. The best photovoltaic performance was obtained with 7 wt% of DiCN-Fc loading, with a power conversion efficiency of about 4.27%. In the light of our investigations, ferrocenyl-substituted small organic molecules could contribute to the development of organic photovoltaic devices.Öğe Synthesis of thiophenyl-substituted unsymmetrical anthracene derivatives and investigation of their electrochemical and electrooptical properties(ELSEVIER SCIENCE BV, 2017) Kivrak, Arif; Calis, Hatice; Topal, Yasemin; Kivrak, Hilal; Kus, MahmutNovel thiophenyl-substituted anthracene derivatives (D-A)bearing a variety of electron-withdrawing groups were designed and synthesized for organic solar cells (OSCs). Their electrochemical and electro-optical properties were examined with strong donor-acceptor interaction. The electrochemical properties were examined by cyclic voltammetry (CV) measurements. These estimated values from CV measurements are in good agreement with the optical band gaps. HOMO, LUMO, and Eg values of designed organic materials were estimated. Furthermore, these new generation organic materials were fabricated to find their solar cell performances.
