Browsing by Author "Ozkan, Necati"

Now showing 1 - 6 of 6

Citation - WoS: 7
Citation - Scopus: 7
Development of Non-Noble Co-N Electrocatalyst for High-Temperature Proton Exchange Membrane Fuel Cells
(Pergamon-elsevier Science Ltd, 2020) Eren, Enis Oguzhan; Ozkan, Necati; Devrim, Yilser
The development of a non-noble Co-N/MWCNT (MWCNT = multi-walled carbon nano tubes) electrocatalyst is achieved through the high-temperature pyrolysis method and successfully characterized by five-step physico-chemical analysis. By utilizing high resolution analytical surface characterization methods, the chemical states of elements are determined, and the presence of Co-N-x sites is confirmed. ORR activity of a Co-N/MWCNT is found to be auspicious. The maximum number of transferred-electron (n) and the diffusion-limiting current density (j(d)) are calculated as 3.95 and 4.53 mA.cm(-2), respectively. The catalyst is further evaluated under a single-cell test station. The test results show that the current and power density values of Co-N/MWCNT are found superior to those of the commercial Pt/C at the 150 degrees C and 160 degrees C (e.g., 57 vs. 69 mW.cm(-2) at 150 degrees C). Due to some stability issues, it is observed that the performance of the Co-N/MWCNT catalyst is slightly decreased while switching the temperature towards 180 degrees C. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Citation - WoS: 92
Citation - Scopus: 103
Fabrication and Characterization of Cross-Linked Polybenzimidazole Based Membranes for High Temperature Pem Fuel Cells
(Pergamon-elsevier Science Ltd, 2017) Ozdemir, Yagmur; Ozkan, Necati; Devrim, Yilser
In this study different types of crosslinked polybenzimidazole (PBI) membranes were compared as high temperature proton exchange membrane fuel cells (HT-PEMFC). Cross-linking of PBI was performed with different cross-linkers including bisphenol A diglycidyl ether (BADGE), ethylene glycol diglycidyl ether (EGDE), alpha-alpha'-dibromo-p-xylene (DBpX), and terephthalaldehyde (TPA). The crosslinked membranes have been characterized by thermogravimetric analysis, scanning electron microscopy, acid uptake and impedance analyses. The crosslinking of the PBI polymer matrix helps to improve the acid retention properties. PBI/BADGE presented the highest acid retention properties. Proton conductivities of the membranes were comparable to that of commercial membranes. Conductivity values up to 0.151 S.cm(-1) were obtained at 180 degrees C with PBI/DBpX membranes. Gas diffusion electrodes (GDE) were fabricated by an ultrasonic coating technique with 0.6 mg Pt.cm(-2) catalyst loading for both anode and cathode. The crosslinked membranes were tested in a single HT-PEMFC with a 5 cm(2) active area at 165 degrees C without humidification. PBI/BADGE crosslinked membranes demonstrated stability and high performance on single cell HT-PEMFC tests. The maximum power density for PBI/BADGE was determined as 0.123 W. cm(-2). As a result, the experimental results suggested that the PBI/ BADGE and PBI/DBpX cross-linked membranes are promising electrolyte options for HT-PEMFC. (C) 2017 Elsevier Ltd. All rights reserved.
Citation - WoS: 14
Citation - Scopus: 14
High-Temperature Electrochemical Hydrogen Separation From Reformate Gases Using Pbi/Mof Composite Membrane
(Pergamon-elsevier Science Ltd, 2023) Durmus, Gizem Nur Bulanik; Eren, Enis Oguzhan; Devrim, Yilser; Colpan, C. Ozgur; Ozkan, Necati
In this paper, the high-temperature electrochemical Hydrogen (H2) purification perfor-mance of a polybenzimidazole/UIO-66 metal-organic framework (PBI/UIO-66) membrane is investigated and analyzed at different values of current, temperature, and reformate feed composition. Purification measurements show that a significant reduction in gas impu-rities can be obtained. In the performance tests, three different ratios of reformate gas (RG) (H2:carbon dioxide (CO2):carbon monoxide (CO)) as RG-1= (75:25:0), RG-2= (75:22:3), and RG-3= (95:0:5) were used. The highest purification values were observed at 160 & DEG;C as 99.999%, 99.931%, and 99.708% for RG-1, RG-2, and RG-3, respectively. The obtained results show that an electrochemical H2 purification (ECHP) based on PBI/UIO-66 composite membrane is promising for H2 purification.& COPY; 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Citation - WoS: 20
Citation - Scopus: 26
Polybenzimidazole-Modified Carbon Nanotubes as a Support Material for Platinum-Based High-Temperature Proton Exchange Membrane Fuel Cell Electrocatalysts
(Pergamon-elsevier Science Ltd, 2021) Eren, Enis Oguzhan; Ozkan, Necati; Devrim, Yilser
We fabricate polybenzimidazole (PBI) wrapped carbon nanotubes (MWCNTs) as support material for platinum-based fuel cell electrocatalyst. With the aid of microwave-assisted polyol reduction, we obtain very fine platinum (Pt) nanoparticles on PBI/MWCNT support while reducing the amount of Pt waste during synthesis. Cyclic voltammetry (CV) concludes that Pt-PBI/MWCNT has 43.0 m(2) g(-1) of electrochemically active surface area (ECSA) to catalyze hydrogen oxidation. Furthermore, after the 1000th cycle, Pt-PBI/MWCNT preserves almost 80% of its maximum ECSA, meaning that Pt-PBI/MWCNT is much more durable than the Pt/MWCNT and commercial Pt/C. High-temperature proton exchange membrane fuel cell (HT-PEMFC) performance tests are conducted under H-2/Air conditions at the temperatures ranging from 150 degrees C to 180 degrees C. Nevertheless, tests conclude that the maximum power density values of the Pt-PBI/MWCNT are found inferior to the Pt/C at all temperatures (e.g., 47 vs. 62 mW cm(-2) at 180 degrees C), suggesting that some balance between durability and performance has to be taken into consideration. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Citation - WoS: 37
Citation - Scopus: 41
Preparation of Polybenzimidazole/Zif-8 and Polybenzimidazole/Uio-66 Composite Membranes With Enhanced Proton Conductivity
(Pergamon-elsevier Science Ltd, 2022) Eren, Enis Oguzhan; Ozkan, Necati; Devrim, Yilser
Metal-organic frameworks (MOFs) are considered emerging materials as they further improve the various properties of polymer membranes used in energy applications, ranging from electrochemical storage and purification of hydrogen to proton exchange membrane fuel cells. Herein, we fabricate composite membranes consisting of polybenzimidazole (PBI) polymer as a matrix and MOFs as filler. Synthesis of ZIF-8 and UiO-66 MOFs are conducted through a typical solvothermal method, and composite membranes are fabricated with different MOF compositions (e.g., 2.5, 5.0, 7.5, and 10.0 wt %). We report a significant improvement in proton conductivity compared with the pristine PBI; for example, more than a three-fold increase in conductivity is observed when the PBI-UiO66 (10.0 wt %) and PBI-ZIF8 (10.0 wt %) membranes are tested at 160 degrees C. Proton conductivities of the composite membranes vary between 0.225 and 0.316 S cm(-1) at 140 and 160 degrees C. For the comparison, pure PBI exhibits 0.060 S cm(-1) at 140 degrees C and 0.083 S cm(-1) at 160 degrees C. However, we also report a decrease in permeability and mechanical stability with the composite membranes. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Citation - WoS: 35
Citation - Scopus: 32
Preparation of Silica Coated Cobalt Ferrite Magnetic Nanoparticles for the Purification of Histidine-Tagged Proteins
(Pergamon-elsevier Science Ltd, 2015) Aygar, Gulfem; Kaya, Murat; Ozkan, Necati; Kocabiyik, Semra; Volkan, Murvet
Surface modified cobalt ferrite (CoFe2O4) nanoparticles containing Ni-NTA affinity group were synthesized and used for the separation of histidine tag proteins from the complex matrices through the use of imidazole side chains of histidine molecules. Firstly, CoFe2O4 nanoparticles with a narrow size distribution were prepared in an aqueous solution using the controlled co-precipitation method. In order to obtain small CoFe2O4 agglomerates, oleic acid and sodium chloride were used as dispersants. The CoFe2O4 particles were coated with silica and subsequently the surface of these silica coated particles (SiO2-CoFe2O4) was modified by amine (NH2) groups in order to add further functional groups on the silica shell. Then, carboxyl (-COOH) functional groups were added to the SiO2-CoFe2O4 magnetic nanoparticles through the NH2 groups. After that N alpha,N alpha-Bis(carboxymethyl)-L-lysine hydrate (NTA) was attached to carboxyl ends of the structure. Finally, the surface modified nanoparticles were labeled with nickel (Ni) (II) ions. Furthermore, the modified SiO2-CoFe2O4 magnetic nanoparticles were utilized as a new system that allows purification of the N-terminal His-tagged recombinant small heat shock protein, Tpv-sHSP 14.3. (C) 2015 Elsevier Ltd. All rights reserved.