Browsing by Subject "Electrochemical impedance spectroscopy"

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    Hydrazine oxidation at gold nanoparticles and poly(bromocresol purple) carbon nanotube modified glassy carbon electrode
    (Elsevier, 2014) Koçak S.; Aslişen B.
    Bromocresol purple monomers were polymerized electrochemically at carbon nanotube modified glassy carbon electrode surface and obtained electrodes were donated as poly(BCP)/CNT/GCE. After electrochemical polymerization, Au nanoparticles were doped on the polymer film carbon nanotube modified glassy carbon electrode surface by electrochemical reduction from their acidic solutions. Modified electrodes are characterized with electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) techniques. The electrochemical behavior of hydrazine oxidation was investigated at gold nanoparticles modified poly(BCP)/CNT electrodes in pH 10.0 phosphate buffer solution. The obtained results were compared with other modified electrodes. The best catalytic activity was obtained at AuNPs/poly(BCP)/CNT/GCE due to the shift of oxidation peak to more negative values than other electrodes with a higher current value. The peak potential and current oxidation of hydrazine were obtained at AuNPs/poly(BCP)/CNT/GCE (-28 mV, 205 μA) and poly(BCP)/CNT/GCE (427 mV, 80 μA). Under optimal conditions, the calibration curves for hydrazine were obtained over the range of 5.0 × 10-7-1.0 × 10-3 M. The limit of detection for hydrazine was calculated as 1.0 × 10-7 M for AuNPs/poly(BCP)/CNT/GCE. © 2014 Elsevier B.V.
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    Electrochemical preparation, characterization of molybdenum-oxide/platinum binary catalysts and its application to oxygen reduction reaction in weakly acidic medium
    (Elsevier Ltd, 2015) Yavuz E.; Özdokur K.V.; Çakar I.; Koҫak S.; Ertaş F.N.
    This study reports a detailed analysis of an electrode material containing molybdenum oxide and platinum nanoparticles which shows superior catalytic effect towards to oxygen reduction in weakly acid medium. The material is sequentially electrodeposited on a glassy carbon electrode from aqueous solutions of MoO 4 2- and PtCl 4 2- either by cycling the potential or by applying pulsed potential technique. Chemical and morphological characterization of the electrode surface was made by X-ray photoelectron spectroscopy, scanning electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The electrode performance towards oxygen reduction reaction was investigated in pH 5.0 acetate buffer solution saturated with oxygen and parameters such as the cell content and electrodeposition conditions were optimized. The performance of the electrode was compared with Pt disk, bare glassy carbon, platinum modified glassy carbon electrodes along with the electrode modified in a single step and named as Pt-MoO x /GCE. Overall results indicated that sequentially deposited molybdenum oxide and platinum modified glassy carbon electrode designated as Pt/MoO x /GCE has shown higher catalytic activity considering the peak location and current intensities. This was consisted with the pulsed electrodeposition process and even higher catalytic activity was obtained than the electrode modified by cycling voltammetry. © 2014 Elsevier Ltd. All rights reserved.
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    Microstructure and Electrical Conductivity of ZnO Addition on the Properties of (Bi0.92Ho0.03Er0.05)2O3
    (Springer New York LLC, 2016) Ermiş I.; Çorumlu V.; Sertkol M.; Öztürk M.; Kaleli M.; Çetin A.; Turemiş M.; Arı M.
    The solid electrolyte is one of the most important components for a solid oxide fuel cell (SOFC). The various divalent or trivalent metal ion-doped bismuth-based materials exhibit good ionic conductivity. Therefore, these materials are used as electrolytes in the SOFC. In this paper, the samples of (Bi0.92−xHo0.03Er0.05)2O3 + (ZnO)x solutions with a 0 ≤ x ≤ 0.2 molar ratio are synthesized by the solid state reaction method. The detailed structural and electrical characterizations are investigated by using x-ray diffraction (XRD), alternating current electrochemical impedance spectroscopy, and scanning electron microscopy (SEM). The XRD patterns of all samples are indexed on a monoclinic symmetry with a P21/c space group. In addition, the rietveld parameters are determined by using the FullProf software program. The impedance measurements of the samples are obtained at the 1 Hz to 20 MHz frequency range. The impedance value of the pellets increases with temperature. Based on the impedance results, it is found that the contribution of grain (bulk) is more than a grain boundary in terms of conductivity, which permits the attribution of a grain boundary. The ionic conductivity decreases with an increasing amount of Zn contribution. The value of highest electrical conductivity among all samples is calculated as 0.358 S cm−1 at 800°C for undoped (Bi0.92Ho0.03Er0.05)2O3. © 2016, The Minerals, Metals & Materials Society.
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    Polymer Film Supported Bimetallic Au–Ag Catalysts for Electrocatalytic Oxidation of Ammonia Borane in Alkaline Media
    (SpringerOpen, 2016) Karabiberoğlu Ş.U.; Koçak Ç.C.; Koçak S.; Dursun Z.
    Abstract: Ammonia borane is widely used in most areas including fuel cell applications. The present paper describes electrochemical behavior of ammonia borane in alkaline media on the poly(p-aminophenol) film modified with Au and Ag bimetallic nanoparticles. The glassy carbon electrode was firstly covered with polymeric film electrochemically and then, Au, Ag, and Au–Ag nanoparticles were deposited on the polymeric film, respectively. The surface morphology and chemical composition of these electrodes were examined by scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. It was found that alloyed Au–Ag bimetallic nanoparticles are formed. Electrochemical measurements indicate that the developed electrode modified by Au–Ag bimetallic nanoparticles exhibit the highest electrocatalytic activity for ammonia borane oxidation in alkaline media. The rotating disk electrode voltammetry demonstrates that the developed electrode can catalyze almost six-electron oxidation pathway of ammonia borane. Our results may be attractive for anode materials of ammonia borane fuel cells under alkaline conditions. Graphical Abstract: [Figure not available: see fulltext.] © 2016, The Author(s).
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    Electrochemical sensing platform based on tyrosinase immobilized magnetite chitosan nanobiocomposite film and its application as catechol biosensor
    (Electrochemical Society Inc., 2019) Polatoğlu İ.
    The easy design of an enzyme electrode using tyrosinase immobilized magnetite chitosan nanobiocomposite film (TMCG) and its applicability for electrochemical sensing platform are reported in this work. The sensor components were characterized by scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Stable biomaterial was obtained by chemical immobilization of the enzyme to chitosan structure with glutaraldehyde. Magnetite nanoparticles were homogeneously distributed on the chitosan surface. Nyquist curves revealed that, chitosan and tyrosinase enzyme exhibit higher resistance to the electron transfer while magnetite nanoparticles promote the electron transfer as a result of their nanostructure behaviors. In addition to well defined oxidation peak, new reduction peak was observed from CV analysis after magnetite modification as a result of electrochemical reduction of enzymatically produced o-quinone to the catechol. The developed biosensor (TMCG*) selectively detected the catechol at a sensitivity of 0.057A/M in a linear range from 1 μM to 30 μM with a detection limit of 260 nM and Km value of 22.5 μM. These findings strongly indicate that TMCG* is applicable as an electrochemical sensing platform for detection of the sample that inhibits the tyrosinase enzyme in tap water. © 2019 The Electrochemical Society.
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    Enhanced Electrochemical Determination of Catechol and Hydroquinone Based on Pd Nanoparticles/Poly(Taurine) Modified Glassy Carbon Electrode
    (Wiley-VCH Verlag, 2020) Koçak Ç.C.; Koçak S.
    Here, Pd nanoparticles and poly(taurine) film was prepared on the glassy carbon electrode surface (Pd/Poly(TAU)/GCE) by the rapid electrochemical technique. The proposed composite surface was characterized by scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS) and electrochemical impedance spectroscopy(EIS). Enhanced electron transfer ability and higher electroactive surface area were achieved at Pd/Poly(TAU)/GCE as compared to the bare GCE and polymer film electrode. The new and highly stable Pd/Poly(TAU)/GCE was employed for the individual and simultaneous determination of hydroquinone and catechol which were environmentally toxic. Under the optimized conditions, HQ and CC were individually determined by using the differantial pulse voltammetry in the linear ranges of 0.008–100 μM and 0.001–100 μM with the detection limits of (LOD) 2.1 nM and 0.68 nM, respectively. In case of simultaneous determination, LODs were found as 10 nM and 0.88 nM for HQ and CC, respectively. The content of both analytes in the real sample analysis was evaluated in the river water and tap water successfully. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Platinum Nanoparticles/Poly(isoleucine) Modified Glassy Carbon Electrode for the Simultaneous Determination of Hydroquinone and Catechol
    (Wiley-VCH Verlag, 2021) Koçak S.
    A new electrochemical sensor based on Poly(Isoleucine) modified glassy carbon electrode decorated with platinum nanoparticles (Pt/Poly(Isoleucine)/GCE) was developed for sensitive individual and simultaneous determination of hydroquinone (HQ) and catechol (CC). Scanning electron microscopy (SEM), Electrochemical impedance spectroscopy (EIS), Cyclic voltammetry (CV) and Differential pulse voltammetry (DPV) were performed in order to characterize the Pt/Poly(Isoleucine)/GCE nanocomposite. For simultaneous determination of HQ and CC, Pt/Poly(Isoleucine)/GCE showed wide linear range between the 0.01–100.0 μM. The detection limits were 0.006 μM for HQ and 0.005 μM for CC. The Pt/Poly(Isoleucine)/GC electrode exhibited good sensitivity and reliability in the simultaneous electroanalysis of two isomers in PBS of pH 7.5. The modified electrode was used to detect the isomers in naturel samples. © 2020 Wiley-VCH GmbH
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    Charge transport kinetics in flower like α-MnO2 nano-sheet and α-MnO2 nanowire based supercapacitors
    (Elsevier B.V., 2022) Kiymaz D.; Kiymaz A.; Tekoglu S.; Mayr F.; Dincalp H.; Zafer C.
    In a supercapacitor, determining the cells’ internal dynamics and limiting factors on the efficiency is essential for device designs. In this context, electrochemical impedance spectroscopy is a powerful tool in investigating device kinetics. This study explained the performance improvement in nanostructured MnO2 electrodes from a diffusion perspective. Firstly, we reported morphological features of flower-like nanosheet MnO2 and nanowire MnO2 with identical crystal structure (α-MnO2 phase) and capacitance-voltage properties. Then, the factors limiting the bias voltage-dependent capacitance efficiency were explained via electrochemical impedance spectroscopy by setting up a three-electrode system. Both resistance and capacitance vs. frequency plots provided important information on ion diffusion and charge transfer mechanisms. © 2022 Elsevier B.V.
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    Preparation of mixed-valent manganese-vanadium oxide and Au nanoparticle modified graphene oxide nanosheets electrodes for the simultaneous determination of hydrazine and nitrite
    (Elsevier B.V., 2022) Aslışen B.; Koçak S.
    In this study, for the first time in the literature, simultaneous and individual determination of hydrazine and nitrite have performed by combining the triple electrocatalytic properties of electrochemically reduced graphene oxide (ERGO), multivalent metal oxide (MnOx-VOx) films and gold nanoparticles (AuNPs). Characterization studies of AuNP/MnOx-VOx/ERGO electrode were performed using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) methods. The determinations of hydrazine and nitrite in pH 8 BR buffer solution were studied using linear sweep voltammetry (LSV) and amperometry methods. The limit of detection (LOD) for simultaneous detection was 3.0 and 10.0 µM for hydrazine and nitrite, respectively, and the LOD for amperometric detection was 0.1 and 0.33 µM, respectively. AuNP/MnOx-VOx/ERGO electrode was tested for the determination of hydrazine and nitrite in river water and food samples, and this electrode provides a recovery of 91.0% to 113.0%. Also, the electrode has practical preparation, good repeatability, selectivity, accuracy. © 2021 Elsevier B.V.
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    Direct impedimetric detection of exosomes and practical application in urine
    (Springer Science and Business Media B.V., 2023) Sazaklıoğlu S.A.; Torul H.; Vatansever H.S.; Tamer U.; Çelikkan H.
    Abstract: Exosomes are nanoscale vesicles released from tumor-derived cells. They are very popular cancer biomarkers in non-invasive liquid biopsy diagnosis and evaluation of therapeutic response. Rapid analysis of exosomes with proteins or other biomarkers requires complex methods and has a relatively high cost. We indicate the fabrication of a biosensor for the detection of exosomes at low concentrations using immunological recognition strategies. The implementation of the biosensor consists of two steps: (i) functionalization of screen-printed electrodes (SPEs) with tetraspanin anti-CD63 antibodies and (ii) capturing exosomes by the electrode surface. Label-free detection of exosomes was successful with the Nyquist diagram, one of the main demonstrations of electrochemical impedance spectroscopy (EIS). In addition, we increased the consistency of the results by including the Bode diagrams of the measurements in our study. The proposed biosensor as a sensitive and reliable impedimetric method for detecting exosomes was established in a working range of 3.7 × 103 to 3.7 × 108 particles mL−1 with a detection limit of 2.0 × 103 particles mL−1. Graphical Abstract: [Figure not available: see fulltext.] © 2022, The Author(s), under exclusive licence to Springer Nature B.V.