Browsing by Author "Alal, Orhan"

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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, Ozlem
At 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.
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, Ozlem
At 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.
Development of Enzymeless Hydrogen Peroxide Sensors
(2019) Alal, Orhan; Kıvrak, Hilal Demir; Şahin, Özlem
Bu tez kapsamında H2O2 tayininde kullanılmak üzere hazırlanan katalizörler, NaBH4 indirgeme yöntemiyle sentezlenen dendrimerlerim indirgenmesi ve tendrimer taslaklarının NaBH4 ile indirgeme metodu kullanılarak hazırlanmıştır. Sensörün aktivitesine ve duyarlılığa etkisi incelenmiştir. Daha sonra CNT destekli farklı atomic oranlara sahip PdxAuy bimetalik katalizörler NaBH4 indirgeme metoduyla yeni bir dendrimer taslağı sentezlenerek H2O2 indirgeme reaksiyonu için aktiviteleri incelenmiştir. Hazırlanan katalizörlerin yapısal karakterizasyonu XRD ve TEM analizleri ile gerçekleştirilmiştir. Ayrıca bu katalizörlerin elektrokimyasal karakterizasyonu dönüşümlü voltametri ve kronoamperometri yöntemleri ile yapılmıştır. CNT destekli PdxAuy bimetalik nanokatalizörlerin H2O2 için elektrokimyasal duyarlılıkları 0.1 M pH 7.4 fosfat tampon çözeltisinde incelenmiştir. PdxAuy bimetalik nanokatalizörlerin elektrokatalitik aktiviteleri yüksek olduğundan elektrokimyasal uygulamalarda yüksek uygulama potansiyeli bulunmaktadır. En yüksek katalitik aktiviteye sahip 10%Pd0.7Au0.3 /CNTdendrimer için duyarlılığın 314.25 µA cm-2 mM-1 ve tayin limitinin ise 0.2 µM olduğu bulunmuştur. 10% Pd/CNTNaBH4 ve 10% Pd/CNTdendrimer monometalik katalizör için ise duyarlılık 220.32 µA cm-2 ve tayin limiti ise 0.5 µM-1 bulunmuştur. Ayrıca girişim etkileri incelendiğinde 10% Pd0.7Au0.3 /CNTdendrimer katalizörün H2O2 tayininde herhangi bir girişime neden olmadığı gözlenmiştir.
Efficient and Rapid Microwave-Assisted Route To Synthesize Pt-Mnox Hydrogen Peroxide Sensor
(Pergamon-elsevier Science Ltd, 2015) Kivrak, Hilal; Alal, Orhan; Atbas, Dilan
A novel electrochemical sensor for the detection of hydrogen peroxide (H2O2) is proposed based on carbon supported Pt-MnOx and Pt nanoparticles, successfully synthesized via microwave irradiation polyol method. The physicochemical properties of the Pt-MnOx and Pt nanoparticles were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Transmission electron microscopy (TEM). Electrochemical properties of the nanoparticles were investigated by cyclic voltammetry (CV) and chronoamperometry (CA). Electrochemical measurements indicate that the oxidation current of H2O2 is linear (R-2=0.998) to its concentration from 2 mu M to 4.0 mM with a detection limit of 0.7 mM (signal/noise = 3). In addition, Pt-MnOx is not affected by ascorbic acid (AA) and uric acid (UA) which are common interfering species. Meanwhile, this Pt-MnOx non-enzymatic H2O2 sensor exhibits excellent selectivity, stability and reproducibility. Thus, this novel non-enzymatic sensor can be found practical applications in H2O2 detection. (C) 2015 Elsevier Ltd. All rights reserved.
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, Dilan
Carbon 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.
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
Pdau-Mnox Nanoparticles Supported on Amine-Functionalized Sio2 for the Room Temperature Dehydrogenation of Formic Acid in the Absence of Additives
(Elsevier, 2016) Karatas, Yasar; Bulut, Ahmet; Yurderi, Mehmet; Ertas, Ilknur Efecan; Alal, Orhan; Gulcan, Mehmet; Zahmakiran, Mehmet
Formic acid (HCOOH) has recently been suggested as a promising hydrogen carrier for fuel cell applications. However efficient hydrogen production through the decomposition of formic acid in the absence of additives under mild thermodynamic conditions constitutes a major challenge because of the ease poisoning of active metals with CO formed as intermediate during formic acid decomposition. Recently, we have reported (App. Catal. B: Env. 164 (2015) 324) our discovery that the separately nucleated MnOx nanoparticles act as CO-sponge around catalytically active Pd nanoparticles exist on the same support and enhances both the activity and CO-resistivity of Pd nanoparticles. Using this important finding, herein, we present a new catalyst system consists of the physical mixture of PdAu alloy and MnOx nanoparticles supported on amine-grafted silica (PdAu-MnOx/N-SiO2) for the room temperature dehydrogenation of formic acid in the absence of any additives. PdAu-MnOx/N-SiO2 catalyst was simply prepared by deposition-reduction technique in water at room temperature with high reproducibility and characterized by the combination of various spectroscopic tools including ICP-OES, P-XRD, DR/UV-vis, XPS, BFTEM, STEM-EDX, STEM-line analysis and CO-stripping voltammetry techniques. The sum of their results shows that the formation of physical mixture of PdAu alloy and MnOx (dmean=2.2 nm) nanoparticles on the surface of support material. This new catalytic material facilitates the hydrogen liberation through the additive-free formic acid dehydrogenation at room temperature with previously unprecedented activity (TOF=785 mol H-2 mol catalyst(-1) h(-1)), converging to that of the existing state of the art homogenous catalysts. This new superior catalytic system enables facile catalyst recovery and very high stability against agglomeration, leaching and CO poisoning, which make it highly reusable catalyst (retains >92% activity and 85% conversion at the 5th catalytic reuse) in the additive-free formic acid dehydrogenation at room temperature. (C) 2015 Elsevier B.V. All rights reserved.
Remarkable Activity of a Znpdpt Anode Catalyst: Synthesis, Characterization, and Formic Acid Fuel Cell Performance
(Pergamon-elsevier Science Ltd, 2021) Caglar, Aykut; Cogenli, Mehmet Selim; Yurtcan, Ayse Bayrakceken; Alal, Orhan; Kivrak, Hilal
Herein, multi-walled carbon nanotube (MWCNT) supported Zn-Pd and Zn-Pd-Pt catalysts have been prepared utilizing a sequential sodium borohydride (SBH) reduction method. The resulting Zn/MWCNT, Zn-Pd/MWCNT, and Zn-Pd-Pt/MWCNT catalysts were characterized using advanced surface analytical techniques such as X-ray diffraction (XRD), high contrast transmission electron microscopy (C-TEM), and X-ray photoelectron spectroscopy (XPS). The characterization results indicate that the Zn/MWCNT, Zn-Pd/MWCNT, and Zn-Pd-Pt/MWCNT catalysts were successfully prepared. It was observed that Pd and Pt incorporation into Zn alters the electronic structure of Zn. Cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) were used to examine the electrochemical activity of the catalysts toward the electrooxidation of formic acid (FA). The results reveal that ZnPdPt/MWCNT has a specific activity of 12.6 mA/cm(2) and an electrochemical active surface area (ECSA) of 41.1 m(2)/g. This catalyst shows high activity, stability, and resistance when compared to Pd/MWCNT and ZnPd/MWCNT. Direct FA fuel cell (DFAFC) measurements were performed at 18-60 degrees C for the ZnPd/MWCNT and ZnPdPt/MWCNT catalysts. The specific activity of ZnPdPt/MWCNT was 1.45 times greater than that measured for ZnPd/MWCNT. ZnPdPt/MWCNT is a promising catalyst according to our CV, CA, EIS, and DFAFC measurements.
Synthesis, Characterization, and Enhanced Formic Acid Electrooxidation Activity of Carbon Supported Mnox Promoted Pd Nanoparticles
(Elsevier, 2018) Bulut, Ahmet; Yurderi, Mehmet; Alal, Orhan; Kivrak, Hilal; Kaya, Murat; Zahmakiran, Mehmet
Formic acid (HCOOH) is one of the promising fuels for direct liquid fed fuel cells. However, CO poisoning is a major challenge for the development of effective catalytic system for formic acid electrooxidation (FAEO). Herein, a novel CO-resistive activated carbon supported Pd-MnOx bimetallic catalyst (Pd-MnOx/C) was presented for FAEO. Pd-MnOx/C catalyst was prepared via simple and reproducible surfactant-free deposition-reduction technique. The characterization of this novel Pd-MnOx/C catalyst was performed by inductively coupled plasma-optical emission spectroscopy (ICP-OES), powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), bright field transmission electron microscopy (BFTEM), high resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), and scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDX). The characterization results revealed that Pd and MnOx nanoparticles (NPs) were well dispersed and separately nucleated with a mean diameter of 2.9 nm on the surface of active carbon. FAEO studies were performed on both Pd-MnOx/C and Pd/C catalysts to comprehend the effect of separately formed MnOx on the electrocatalytic activity of Pd NPs. The electrochemical measurements were carried out by using Cyclic Voltammetry (CV) and Chronoamperometry (CA), CO-Strriping Voltammetry, Lineer Sweep Voltammetry (LSV), Electrochemical impedance spectroscopy (EIS) techniques. Electrochemical results revealed that FAEO was activated by the addition of MnOx. Pd-0.6-Mn-0.4 exhibited the optimum catalytic activity with 1.05 A/mg Pd current density. The sum of their results clearly points that the existence of MnOx NPs enhances the electrocatalytic activity of Pd NPs by increasing their CO-resistivity and durability throughout the FAEO. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.