Browsing by Author "Yilmaz, Yonca"

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3-Acrylamidopropyl Cationic Hydrogel Modified Graphite Electrode and Its Superior Sensitivity To Hydrogen Peroxide
(Taylor & Francis inc, 2019) Caglar, Aykut; Kazici, Hilal Celik; Alpaslan, Duygu; Yilmaz, Yonca; Kivrak, Hilal; Aktas, Nahit
A highly sensitive hydrogen peroxide (H2O2) sensor is fabricated by the synthesized 3-Acrylamidopropyl-trimethylammoniumchloride (p(APTMACl)) hydrogel to covered of pen- graphite (PG) electrodes. (p(APTMACl))-PG electrode is characterized using scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). The electrochemical properties of these sensors are investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The CV behavior of (p(APTMACl))-PG electrode is investigated in 0.1M PBS (pH 7, 5mm diameter of mold). The developed sensor displays significantly enhanced electrocatalytic activity through the H2O2 detection. Linear response of the sensor to H2O2 were observed in the concentration range from 0 to 130 mu M (R-2 = 0.99) with a detection limit of 1.08x10(-6) M, quantification limit of 3.62x10(-6) M (S/N=3) and sensitivity of 2375 mu A/mMcm(2). In addition, interference studies reveal that (p(APTMACl))-PG electrode is not affected by ascorbic acid (AA), uric acid (UA), and dopamine which are common interfering species. The developed sensor is also successfully applied to detect H2O2 in real commercial samples. This study describes a novel strategy to sensing characteristics to hydrogen peroxide by p(APTMACl)-PG electrode.
Development of Effective Bimetallic Electrocatalysts for Glucose Electrooxidation
(Electrochemical Soc inc, 2022) Ulas, Berdan; Yilmaz, Yonca; Kivrak, Hilal; Erunal, Ebru
Vulcan XC-72 supported PdCo and PtCo electrocatalysts were synthesized via supercritical deposition method and designed as anode catalyst for direct glucose fuel cells (DGFCs). As-prepared electrocatalysts were characterized by using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), inductively coupled plasma-mass spectrometer (ICP-MS), scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX), and transmission electron microscopy (TEM) while electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and chronoamperometry (CA) methods were used for the electrochemical characterization of PdCo/Vulcan XC-72 and PtCo/Vulcan XC-72 catalysts. PdCo/Vulcan XC-72 anode catalyst showed higher electrocatalytic activity for glucose electrooxidation than PtCo/Vulcan XC-72. In addition, chronoamperometry results showed that PdCo/Vulcan XC-72 possessed better stability within 1000 s than PtCo/Vulcan XC-72. The improvement in electrocatalytic activity and stability has been attributed to the alteration of the electronic properties of Pd with the addition of Co. The PdCo/Vulcan XC-72 catalyst is a good candidate for use as an anode catalyst in DGFCs. (C) 2022 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.
Disentangling the Enhanced Catalytic Activity on Ga Modified Ru Surfaces for Sodium Borohydride Electrooxidation
(Elsevier, 2021) Ulas, Berdan; Alpaslan, Duygu; Yilmaz, Yonca; Dudu, Tuba Ersen; Er, Omer Faruk; Kivrak, Hilal
Herein, multi walled carbon nanotube (MWCNT) supported RuGa nanocatalysts (RuGa/MWCNTs) are synthesized at varying atomic molar ratio via sodium borohydride (SBH) reduction method toward SBH electrooxidation (SBHE) and SBH hydrolysis (RSBH). From the X-ray diffraction (XRD) results, Ru and Ga metals are found to be in the alloy form and the average crystal size is determined as 2.77 nm. The distribution of RuGa particles on MWCNT is confirmed using SEM-EDX. These nanocatalysts were employed for RSBH and further measurements were performed to investigate their SBHE activity. For RSBH for RuGa/MWCNT nanocatalysts, one could note that Ga addition to Ru enhanced the initial rate, H-2 generation rate, and turnover frequency values and Ru99Ga1/MWCNT has the highest initial rate, H-2 generation rate, and turnover frequency value. According to the cyclic voltammetry (CV) results of the prepared RuGa/MWCNT nanocatalysts, Ru99Ga1/ MWCNT show the highest electrocatalytic activity for SBHE and this result is in line with the results of electrochemical impedance spectroscopy (EIS). In addition, chronoamperometric curves indicate that Ru99Ga1/MWCNT possesses long term stability compared to these of other nanocatalysts. Catalytic RSBH results of Ru99Ga1/MWCNT show that this nanocatalyst is more active than others. As a result, it is clear that RuGa/ MWCNT is a promising nanocatalyst for fuel cells.
Glucose Electrooxidation Modelling Studies on Carbon Nanotube Supported Pd Catalyst With Response Surface Methodology and Density Functional Theory
(Pergamon-elsevier Science Ltd, 2022) Kaya, Sefika; Ulas, Berdan; Duzenli, Derya; Onal, Isik; Er, Omer Faruk; Yilmaz, Yonca; Kivrak, Hilal
In this study, carbon nanotube supported Pd catalysts (Pd/CNT) are synthesized at different weight percentages by the sodium borohydride (NaBH4) reduction method to investigate catalytic performance of glucose electrooxidation reaction. 0.5% Pd/CNT, 3% Pd/CNT, and 7% Pd/CNT catalysts are characterized by using X-ray diffraction (XRD), electron microscopy with energy dispersive X-ray (SEM-EDX), and N2 adsorption-desorption measurements. The average particle size and surface area of 3% Pd/CNT catalyst are determined as 46.33 nm and 129.48 m2/g, respectively. Characterization results indicate that Pd/CNT catalysts are successfully prepared by NaBH4 reduction method. Cyclic voltammetry measurements are performed to investigate the effect of Pd loading for the glucose electrooxidation. CV results reveal that 3% Pd/CNT catalyst exhibits best glucose electrooxidation activity. Following this, experimental optimization is performed to obtain maximum glucose electrooxidation activity via response surface methodology (RSM). Estimated and experimental specific activities at optimum experimental conditions are assigned as 6.186 and 5.832 mA/cm2, respectively. To understand the glucose electrooxidation activity on the surface of Pd/CNT, surface modeling is also performed with density functional theory (DFT) method to investigate adsorption of glucose molecule on CNT supported Pd surface. The DFT results emphasize that the addition of Pd atom to the CNT structure significantly improves the catalytic performance in glucose electrooxidation.
Highly Active Polyethylene Glycol Grafted Cellulose Supported Pd Nanoparticles for Glucose Electrooxidation
(Elsevier, 2024) Ulas, Berdan; Yilmaz, Yonca; Gok, Ozgul; Kivrak, Hilal
In this study, poly(ethylene glycol) (PEG) grafted cellulose (CE) composite catalyst support material (PEG -CE) was obtained by chemically cross -linking PEG at varying molecular weight and CE with isophorone diisocyanate (IPDI) and 2,4-toluylene diisocyanate (TDI). PEG -CE supported Pd (Pd/PEG-CE) catalyst was prepared by the chemical reduction method. The crystal size of the Pd/PEG-CE catalyst is 4.79 nm and its crystal structure has been determined to be face -centered cubic Pd. Elemental mapping results indicate that Pd was reduced onto PEGCE successfully and uniformly. Pd exists in the elemental and Pd -O form in the catalyst system. The Pd loading rate of Pd/PEG-C_IPDI catalyst was determined as 18.8% by mass. Among the PEG-CEs prepared with TDI and IPDI, PEG4000-CE_TDI and PEG6000-CE_IPDI displayed the highest specific activities of 1.03 and 1.50 mA cm -2 for glucose electrooxidation. With Pd reduction on PEG4000-CE_TDI and PEG6000-CE_IPDI, the specific activities increased to 1.62 mA cm -2 and 6.97 mA cm -2. Pd/PEG6000-CE_IPDI has the highest electrocatalytic activity and stability in this study for glucose electrooxidation and is an encouraging anode catalyst for direct glucose fuel cells.
Highly Active Rupd Bimetallic Catalysts for Sodium Borohydride Electrooxidation and Hydrolysis
(Springer, 2022) Kaya, Sefika; Yilmaz, Yonca; Er, Omer Faruk; Alpaslan, Duygu; Ulas, Berdan; Dudu, Tuba Ersen; Kivrak, Hilal
In the present study, bimetallic RuPd/carbon nanotube (RuPd/CNT) electrocatalysts were synthesized at different molar ratios by sodium borohydride (NaBH4) reduction. These catalysts were characterized with advanced surface characterization techniques such as x-ray diffraction (XRD), scanning electron microscopy with energy dispersive x-ray (SEM-EDX), and x-ray photoelectron spectroscopy (XPS). The activities of these catalysts towards electrooxidation of NaBH4 and hydrogen production from hydrolysis/methanolysis of NaBH4 were investigated. According to XRD results, the particle sizes of Ru/CNT and Ru60Pd40/CNT catalysts were calculated as 3.16 and 3.05 nm, respectively. The distribution and elemental composition of Ru and Pd nanoparticles on CNT were obtained by SEM-EDX analysis. The XPS method was used to determine the oxidation states of Ru and Pd on the CNT surface. The electrochemical activities of these catalysts were determined by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. The results show that the Ru60Pd40/CNT catalyst has the highest current mass activity with 2161.94 mA/mg Ru (12.72 mA/cm(2)) current density. Consequently, the RuPd/CNT catalyst is a promising anode catalyst for direct borohydride fuel cells (DBFC) with good stability and high activity.
Highly Efficient Metal Free Aldehyde-Functionalized Indoles for Direct Glucose Fuel Cell Anode Catalyst
(Pergamon-elsevier Science Ltd, 2024) Karatekin, Hatice Calis; Ulas, Berdan; Yilmaz, Yonca; Kivrak, Hilal; Kivrak, Arif
In this study, alternative organic catalysts to metal -containing catalysts for glucose electrooxidation were prepared by the Suzuki Miyaura coupling reaction method and characterized by nuclear magnetic resonance (NMR), fourier transform infrared spectroscopy (FT-IR), and liquid chromatography with tandem mass spectrometry (LCMS -MS). InTA-1, InPA-1, InFA-1, InTA-2, InPA-2, InFA-2, InTA-3, InFA-3, and InPA-3 were obtained with the yield of 74%, 82%, 72%, 70%, 75%, 68%, 60%, 71%, and 85%. Among the synthesized catalysts, the InTA-3 catalyst possesses the highest electrocatalytic activity (3.17 mA cm -2 ) and long-term stability compared to other organic catalysts. InTA-3 catalyst has the lowest charge transfer resistance toward glucose electrooxidation. It was concluded that as a metal -free catalyst, InTA-3 is a cheap and promising electrocatalyst for direct glucose fuel cell anode.
Hydrazine Electrooxidation Performance of Cyano-Substituted Indole Derivatives as Organic Anode Catalyst
(Elsevier, 2024) Karatekin, Hatice Calis; Ulas, Berdan; Yilmaz, Yonca; Kivrak, Hilal; Kivrak, Arif
Here we present the new EWG-substituted indole derivatives, namely 2 -((5 -(1 -methyl -2 -phenyl -1 H-indol-3-yl) thiophen-2-yl)methylene) malonitrile (IPTM), 2 -((5 -(1 -methyl -2 -phenyl -1 H-indol-3-yl)furan-2yl)methyl)malonitrile(IPFM) and 2 -((4 -(1 -methyl -2 -phenyl -1 H-indol-3-yl)benzylidene) malonitrile (IPPM) was synthesized by using Sonogashira coupling, electrophilic cyclization, Suzuki-Miyaura coupling and condensation reactions. The isolated yields were obtained as 86 %, 71 %, and 69 % yields, respectively. Cyclic voltammetry(CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) were used for the electrochemical measurements to observe the electrocatalytic behavior of IPTM, IPFM and IPPM. The results exhibited that the highest -performance organic -based catalyst was 2.601 mA/cm2 (0.073 mA/mg) for IPPM which could be a good candidate as a metal -free electrocatalyst for hydrazine electrooxidation.
Hydroxyapatite Supported Pdxin100-X as a Novel Electrocatalyst for High-Efficiency Glucose Electrooxidation
(Pergamon-elsevier Science Ltd, 2023) Ulas, Berdan; Yilmaz, Yonca; Koc, Serap; Kivrak, Hilal
Fuel cells are a very good candidate to provide energy conversion with green technology. Glucose is used as a fuel in fuel cells since it is easily available and has a high energy density. Herein, hydroxyapatite (HAp) was synthesized by precipitation method, and the sodium borohydride (NaBH4) reduction method was used to fabricate HAp supported PdIn (PdIn/HAp) alloy anode catalysts at varying atomic molar ratios for glucose electro-oxidation. Structural, crystallographic, and morphological properties of the PdIn/HAps were determined with X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET) analysis, transmission electron microscopy (TEM), and inductively coupled plasma mass spec-trometry (ICP-MS). Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and chronoamperometry (CA) were employed for the electrocatalytic activity and stability of PdIn/Haps toward glucose electrooxidation. The results show that HAp has a boosting effect for PdIn alloy towards glucose electrooxidation. Pd80In20/HAp showed 2.6 times higher electrocatalytic activity than Pd/HAp, and it is the most active and stable catalyst in this study with a specific activity of 5.64 mA/cm2.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Optimization of Electrode Preperation Conditions for Enhanced Glucose Electrooxidation on Pt/Cnt by Response Surface Methodology
(Springer, 2022) Kaya, Sefika; Ulas, Berdan; Er, Omer Faruk; Kivrak, Hilal; Yilmaz, Yonca
In this study, glucose electrooxidation activities of carbon nanotube (CNT)-supported Pt catalysts synthesized at various weight percentages and optimum electrode preparation conditions are investigated. For glucose electrooxidation on Pt/CNT, electrode preparation parameters such as amount of catalyst ink (V-c), ultrasonication duration of the catalyst ink (d(u)), and drying duration of the electrode (d(d)) were optimized to obtain maximum specific activity. The catalysts (Pt/CNT) are characterized via N-2 adsorption-desorption, X-ray diffraction, and electron microscopy with energy dispersive X-ray advanced surface analysis techniques. Specific activity for glucose electrooxidation catalyst performance are determined by using cyclic voltammetry (CV) and chronoamperometry (CA) measurements. According to CV measurements, the best electrocatalytic activity obtained is 3.4352 mA/cm(2) with 7% Pt/CNT catalyst. Experimental conditions are optimized via response surface methodology (RSM) for maximizing glucose electrooxidation activity. The predicted specific activity and the actual specific activity are determined to be 5.931 mA/cm(2) and 5.421 mA/cm(2) under optimum conditions such as 7.36 mu L (V-c), 49.54 min (d(d)), and 2.45 min (d(u)).
Supported Pbhfcd Electrocatalysts Over Carbon-Hydroxyapatite Composite Fabricated by Precipitation and Nabh4 Reduction Methods for Glucose Electrooxidation
(Springer, 2023) Ulas, Berdan; Yilmaz, Yonca; Koc, Serap; Kivrak, Hilal
Fuel cells are one excellent option for converting energy through green technology. Due to its accessibility and high-energy density, glucose can be employed as a fuel in fuel cells. In this study, hydroxyapatite (HAp) was prepared by the precipitation method, and carbon-doped HAp supported PbHfCd (PbHfCd/C-HAp) composite electrocatalysts at varying metal ratios for the glucose electrooxidation were synthesized via NaBH4 reduction method. Inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM-EDX), X-ray diffraction analysis (XRD), elemental mapping, and transmission electron microscopy (TEM) were used to evaluate the chemical structure, crystallinity, and morphological characteristics of the PbHfCd/C-HAp. Chronoamperometry (CA), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were utilized to scrutinize the electrocatalytic activity and stability of PbHfCd/C-Haps for glucose electrooxidation. The findings demonstrate that HAp enhances the glucose electrooxidation of PbHfCd alloy. With a specific activity of 4.73 mA/cm(2), Pb80Hf10Cd10/C-HAp is the most stable and active anode electrocatalyst in this work, outperforming HAp by 4.9 times.
Synthesis of 3-Iodoindoles and Their Glucose Electrooxidation Performance as an Anode Catalyst
(Springer, 2023) Calis, Hatice; Ulas, Berdan; Yilmaz, Yonca; Kivrak, Hilal; Kavak, Emrah; Kivrak, Arif
Herein, indole derivatives namely 3-iodo- 1-methyl-2-phenyl-1H-indole (4A), 3-iodo-1-methyl-2-(p-tolyl)-1H- indole (4B), and 2-(2,5-dimethylphenyl)-3-iodo-1-methyl-1H-indole (4C) prepared by Sonogashira coupling and electrophilic cyclization reactions with yield of 70%, 68%, and 67%, respectively. Organic catalysts were characterized by using Liquid Chromatography with tandem mass spectrometry (LC-MS-MS), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spektrofotometre (FT-IR), and Nuclear Magnetic Resonance (NMR). Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA) were utilized to observe the electrocatalytic behavior of 4A, 4B, and 4C. Specific activity for glucose electrooxidation of 4A was determined as 3.26 mA/cm2. Compound 4A exhibits long-term stability toward glucose electrooxidation. As a metal-free catalyst, Compound 4A may be a good candidate as an electrocatalyst for glucose electrooxidation.
Towards More Active and Stable Pdagcr Electrocatalysts for Formic Acid Electrooxidation: the Role of Optimization Via Response Surface Methodology
(Wiley, 2019) Ulas, Berdan; Caglar, Aykut; Yilmaz, Sakir; Ecer, Umit; Yilmaz, Yonca; Sahan, Tekin; Kivrak, Hilal
In this study, multiwall carbon nanotube (MCNT)-supported Pd (Pd/MWCNT) catalysts are prepared by using NaBH4 reduction method. In order to maximize the oxidation and reduction of H2SO4, synthesis conditions (Pd ratio, molar ratio of NaBH4/K2PdCl4, volume of deionized water, and duration of agitation) are optimized by using response surface methodology (RSM). The optimum synthesis conditions are determined as 58.2% of Pd by weight, 154.6 molar ratio of NaBH4 to K2PdCl4, 19.48 mL of deionized water, and 186.16 min of agitation duration. The effect of electrochemical measurement conditions on the oxidation kinetics of Pd/MWCNT is also investigated by RSM. The optimum electrochemical measurement conditions are found as 10 mu L of catalyst mixture, 90 degrees C of H2SO4 solution, and 5.5 M H2SO4. The Pd/MWCNT, Pd50Ag50/MWCNT, and Pd65.6Ag33.6Cr0.80/MWCNT catalysts prepared under optimized conditions are characterized by using X-ray diffraction, transmission electron microscopy, N-2 adsorption-desorption, and inductively coupled plasma mass spectrometry. The crystallite sizes of these catalysts are found as 4.85, 5.66, and 5.26 nm for Pd/MWCNT, Pd50Ag50/MWCNT, and Pd65.6Ag33.6Cr0.80/MWCNT catalysts, respectively. Isotherms of all these catalysts are found to be similar to Type V isotherms with H3 hysteresis loop. The average particle size of Pd50Ag50/MWCNT and Pd65.6Ag33.6Cr0.80/MWCNT catalysts are determined as 5.2 and 9.2 nm, respectively. Electrochemical performance of as-prepared catalysts is evaluated by using cyclic voltammetry and chronoamperometry. The formic acid electrooxidation (FAEO) activities are found as 18.9, 27.8, and 51.6 mA/cm(2) for Pd/MWCNT, Pd50Ag50/MWCNT, and Pd65.6Ag33.6Cr0.80/MWCNT, respectively. Pd65.6Ag33.6Cr0.80/MWCNT shows the highest activity and stability. Optimization of synthesis conditions and electrochemical measurement parameters allow us to obtain very good electrochemical activity and stability for FAEO reaction compared with anode catalysts in the literature.