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Boron-doped porous carbon material derived from ZIF-11: Investigation of cotton fabric supercapacitor and Li-ion battery performances
(Wiley, 2022) Bugday, Nesrin; Altin, Serdar; Bulut, Fatih; Altin, Emine; Yasar, Sedat
Nitrogen-doped porous carbon (NPC@ZIF-11) and boron-NPC (BNPC@ZIF-11) materials were synthesized by pyrolysis methods, and structural characterization of the compounds was carried out by scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, Brunauer-Elmet-Teller technique, Raman spectroscopy, and inductively coupled plasma-mass spectrometry techniques. The ZIF-11 was converted to the NPC@ZIF11 by pyrolysis. BNPC@ZIF-11 was fabricated from NPC@ZIF-11 by pyrolysis in the presence of phenylboronic acid. The fabric supercapacitor, sandwich-type supercapacitor, and Li-ion battery performances of NPC@ZIF-11 and BNPC@ZIF-11 were investigated. The capacity of the Li-ion cell was found as 720 mAh g(-1) for the first cycle, and it was decreased to 250 mAh g(-1) after 100 cycles. The capacitance values of the cylindrical devices were 92 F g(-1) and 115.6 F g(-1), for C1 and C4000 in KOH electrolytes. The BNPC@ZIF-11 was used as an electrode material on cotton fabric, and the highest obtained capacitance was 72.8 mF for 0.1 mA, which is a promising result for wearable energy storage materials.
Cationic versus anionic Pt complex: The performance analysis of a hybrid-capacitor, DFT calculation and electrochemical properties
(Pergamon-Elsevier Science Ltd, 2019) Akkoc, Mitat; Demirel, Serkan; Oz, Erdinc; Altin, Serdar; Bayri, Ali; Dorcet, Vincent; Roisnel, Thierry
The synthesis and characterization of cationic versus anionic platinum(II) complex of the type [PtCl3(DMSO)](-)[NHC](+) (NHC: N-heterocyclic carbene) is reported for the first time. The complex 3 was synthesized from silver(I)-NHC2, and K-2[PtCl4] in DMSO at 80 degrees C under exclusion of light. The ionic platinum(II) complex was obtained in high yield and fully characterized by H-1, C-13, Pt-195 NMR and HRMS spectroscopy, X-ray diffraction and elemental analysis. The structural properties of the complex were investigated by using Gaussian suit and the obtained parameters were crosschecked with the X-ray data. The HOMO-LUMO energies and electrostatic surface mapping of the complex were calculated and the results were discussed with the capacitive properties of the complex. Electrochemical analysis by cyclic voltammetry (CV) of the complex shows reversible redox peaks about platinum center. The complex was used as an electrode material for the capacitor device and result is promising that the highest performance of complex 3 was found as 10.22 F/g. (C) 2018 Elsevier Ltd. All rights reserved.
Current-Voltage Measurements and Vortex Dynamics in a Bi2Sr2CaCu2O x Whisker: Observation of the Peak Effect and Calculation of the Critical Current in the Flux Flow Regime with and Without Applied Field
(Springer, 2013) Altin, Serdar; Bernstein, Pierre
In this article, we report current-voltage measurements carried out on a Bi2Sr2CaCu2O (x) whisker in a large temperature range below the critical temperature with and without applied magnetic field. We examine the critical current peak effect and the vortex dynamics at low field. The critical current peak effect consists of the initial increase of the critical current that subsequently decreases as the applied field is increased. For current-voltage measurements, this effect is associated with a change in the current-voltage curves that are typical of the flux flow regime at low fields and resemble flux creep characteristics for higher fields. As a general rule, our observations are consistent with the models that link the peak effect to vortex phase transitions. We calculate the critical current in self-field in the flux flow regime taking into account intervortex forces. We suppose that most vortices are pinned by defects while mobile vortices move through plastic channels between the strongly pinned vortex regions. When an external field is applied, we suggest that the increase in the critical current that is observed is linked to oscillations of the pinned vortices.
Effect of carbon nanotubes/graphene nanoplates hybrid to ZnO matrix: production, electrical and optical properties of nanocomposite
(Springer, 2020) Guler, Omer; Yavuz, Cagdas; Basgoz, Oykum; Altin, Serdar; Yahia, Ibrahim S.
Electrical and optical properties of pure andcarbon nanotube (CNT)/graphene nanoplate (GNP) mixture-reinforced zinc oxide (ZnO)matrix at different temperatures were investigated. UV-Vis absorption andelectrical conductivity measurements were used in order to determine theproperties were mentioned above. Samples were divided two main groups based ontheir matrix: one of them commercially acquired ZnO and the other one wasproduced via sol-gel method. Both groups have the same four sub-groupsaccording to the percentage of the weight of the reinforcing. SEM imagesindicated that commercially obtained ZnO matrix has hexagonal structure whileZnO manufactured by sol-gel was mainly in sphere form. Raman spectroscopy and TEM analyses proved that graphene nanoplate structure was producedsuccessfully, and XRD characterization shows that ZnO was produced in asuitable way by sol-gel method. The results indicated that electricalconductivity of the samples which from pure to 0.4% reinforced was decreasedwith increasing in reinforcing percentage. However, samples with 0.8% CNT/GNPmixture reinforcing showed greatest electrical conductivity. The highest reflectionpercentages of the samples were obtained from the pure specimens while thelowest ratios were observed in the highest reinforced samples. Activationenergy and optical band gap values were calculated according to electrical andoptical graphs.
Effect of Vanadium-Titanium Co-doping on the BPSCCO Superconductor
(Springer, 2011) Yazici, Duygu; Ozcelik, Bekir; Altin, Serdar; Yakinci, M. Eyyuphan
We have produced the (BiPb)(2)V (x) Sr2Ca3Cu4-y Ti (y) O12+delta compounds for x=0.05 and y=0, 0.05, 0.10 and 0.20 by glass-ceramic method. The effects of vanadium adding and Ti doping on the structure have been investigated by electrical resistance, scanning electron micrographs (SEM), XRD patterns and magnetic hysteresis loop measurements. It has been found that the high-T (c) superconducting phase, (2223), is formed in the samples annealed at 845 degrees C for 185, with concentration x=y=0.05. However, with increasing Ti doping the (2223) phase transforms into the (2212) phase. We have observed no superconducting properties for x=0.05 and y=0.20 compound. It has completely transformed to semiconductor. In addition, the critical current densities (J (c)), calculated from the hysteresis loop measurements by using Bean's critical state model are obtained for the samples in the same doping range. Our data have indicated that J (c) decreases with increasing temperature and Ti concentration.
Electrical Properites of Superconducting Cross - (nano) Whiskers Junction
(Tubitak Scientific & Technological Research Council Turkey, 2005) Altin, Serdar; Yakinci, Eyuphan; Balci, Yakup; Aksan, M. Ali
Bi-2212 superconducting single crystal (nano) whiskers have been fabricated by annealing a melt-quenched (glass) Bi3Sr2Ca2Cu3Ox precursor. A couple of (nano) Whiskers obtained were placed crosswise on a YSZ single crystal substrate and then heat treated at 830 C for 25 minute to form nano-scale junction. The T-c of each nano-whisker was found to be 85 K and the critical current density, J(c), of the whiskers was calculated to be 1177 Acm(-2) at zero field. The I - V characteristics of the nano-junction at 30 K were found to show a multiple-branch structure, which is the main behavior of the Josephson junction.
Fabrication and electrochemical performance of Ho-substituted C/LiFePO4: Improved battery performance
(Springer, 2021) Altin, Serdar; Yolun, Abdurrahman
Ho-substituted C/LiFePO4 samples were successfully fabricated, and their structural properties were examined by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) measurements. The magnetic structure of LiFePO4 correspondence to the high spin configuration of Fe2+ ions and Ho3+ causes the increase of the mu(eff) values and suppressed the antiferromagnetic transition. The XRD analysis showed an amorphous structure due to carbon, and peaks were matched by olivine-type LiFePO4. Furthermore, the lattice volume was increased with the addition of Ho. The Ho-substituted cells show similar cycling voltammetry (CV) graphs with the CV of the undoped LiFePO4 cells. According to charge/discharge cycling measurements for constant current at room temperature, the highest capacity was obtained for LiFe0.99Ho0.01PO4. The Ho-substituted LiFePO4 has a higher C-rate when compared with the undoped LiFePO4 and so it is found that a low concentration of Ho in LiFePO4 has better battery performance and may be used in commercial batteries.
Fabrication, electrochemical performance, and in situ infrared thermal imaging of Na0.67(Mn0.5Fe0.5)1-xCuxO2 battery cells
(Wiley, 2021) Altin, Serdar; Korkusuz, Keziban
Na-0.67(Mn0.5Fe0.5)(1-x)CuxO2 powders (where x = 0, 0.05, 0.1, 0.2, and 0.3) were produced by quenching at 900 degrees C, and the structural features of the powders were studied in detail. It was found that the undoped and Cu-substituted for (x <= 0.2) powders had no impurity phases in the structure. Furthermore, the lattice volume calculated by the GSAS-II open-source program decreased with increasing Cu content, and it is suggested that Cu ions have a 3+ valence state in the samples. The cycling voltammetry of the cells is very similar to each other. The constant current charge/discharge cycling measurements were performed for up to 100 cycles, and the best performance was observed for x = 0.2 Cu substitution in Na-0.67(Mn0.5Fe0.5)(1-x)CuxO2. The best capacity value was obtained as 182.3 mAh/g at the C/10 rate for x = 0.2 Cu substitution. The cycling measurements at 50 degrees C exhibit worse capacity fade when compared to the measurements performed under ambient conditions. The in situ infrared thermal imaging measurements for the cell that had the highest performance in this study were performed for a constant voltage of 4.3 V for charging and 1.5 V for discharging of the cell. The ohmic heat was calculated from chronoamperometry measurements, and the heat generation was fitted with the quadratic term in the system.
High-performance electrodes for Li-ion cell: Heteroatom-doped porous carbon/CoS structure and investigation of their structural and electrochemical properties
(Wiley, 2022) Bugday, Nesrin; Altin, Emine; Altin, Serdar; Yasar, Sedat
As an essential class of anode materials, the synthesis and characterization of CoS@ZIF-12-C composite anode materials are reported. The two-step synthesis of CoS nanoparticles embedded in N-doped porous carbon by using a metal-organic framework (MOF) as the template. After structural characterization of CoS@ZIF-12-C composite materials, the main phase was found as CoS with symmetry of P63mmc. Benefiting from the CoS embedded in porous carbon structure, the half Li-ion battery cell tests of CoS@ZIF-12-C composite materials were performed by a 2-electrode method using CR2032 cells, and the capacities of the cells were measured for 200 cycles using 300 mAg(-1) and 500 cycles using 1000 mAg(-1). The first discharge capacities of the cells for 1000 mAg(-1) were found as 458, 1178, and 815 mAhg(-1) for CoS@ZIF-12-C-T, T = 700, 800, and 900 degrees C, respectively. An unexpected capacity increase was observed for the CoS@ZIF-12-C-700 and CoS@ZIF-12-C-900 half cells during the cycling. Ex-situ x-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and cyclic voltammetry (CV) analysis were performed after cycling of the cells for explanations of the capacity increase. Ex-situ XRD analysis of these cells showed phase transitions from crystalline to amorphous type structure, and ex-situ FTIR proves the preservation of the CoS phase during the cycling. A redox reaction mechanism was suggested to explain the cells' battery performance by ex-situ XRD analysis.
High-performance Na-ion full-cells with P2-type Na0.67Mn0.5-xNixFe0.43Al0.07O2 cathodes: Cost analysis for stationary battery storage systems
(Elsevier, 2024) Kalyoncuoglu, Burcu; Ozgul, Metin; Altundag, Sebahat; Bulut, Fatih; Oz, Erdinc; Sahinbay, Sevda; Altin, Serdar
Na -ion batteries are viable alternatives to Li-ion batteries especially for stationary applications. Developing suitable electrode materials, half-cell and full-cell studies and cost analysis are major steps and challenges for their commercialization. In this study, we report the synthesis of a promising cathode material, Na0.67Mn0.5- xNixFe0.43Al0.07O2 (x = 0.02-0.10 with Delta x = 0.02), using a modified solid-state synthesis technique. The materials were heated at high temperature for 6 h in air and quenched in liquid N-2. We determined the solubility limit of Ni in Na0.67Mn0.5Fe0.43Al0.07O2 as x <= 0.06. The interlayer separation increases with increasing Ni content due to the ionic radii difference between Mn and Ni. X-ray photoelectron spectroscopy (XPS) measurements evidence the valance state of Ni in the x = 0.06 sample as 2+ and 3+. Cyclic voltammetry (CV) analysis of the half-cells were performed at 10 C-degrees, room temperature, and 50 degrees C to observe the effect of environmental temperature on redox mechanism. The highest half-cell capacity of the cells was determined as 181 mAh/g for x = 0.06 at C/3-rate. Artificial solid electrolyte interface (SEI) formation was performed on the hard carbon anode by presodiation technique and the full-cells of Na0.67Mn0.44Ni0.06- Fe0.43Al0.07O2/hard carbon were assembled in CR2032 coin cells. The capacity values of the cells at C/2, C, and 2C-rate were determined as 131.4 mAh/g, 116 mAh/g and 100.8 mAh/g for the 1 cycle and 33 mAh/g, 40.6 mAh/g and 49.9 mAh/g for the 500th cycle, respectively. The cost analysis for the commercial package for stationary energy storage system was performed by BatPac program and results are discussed.
High-performance P2-Na0.67Mn0.85Cu0.15O2/Hard carbon full cell Na-ion battery: Pre-Sodiation of anode, p/n ratio optimizations, and Operando XAS studies
(Pergamon-Elsevier Science Ltd, 2023) Altundag, Sebahat; Altin, Emine; Altin, Serdar; Ates, Mehmet Nurullah; Ji, Xiaobo; Sahinbay, Sevda
Na-ion batteries have gained significant attention as a cost-effective and efficient energy storage option for large scale applications, serving as an alternative to the Li-ion batteries. However, commercialization of these batteries is still many steps away since most cathode materials suffer from significant capacity loss and more full-cell studies are required. In this work, we report the electrochemical properties of half-and full-cells of P2-type Na0.67Mn0.85Cu0.15O2 synthesized by solid state technique. X-ray diffraction, FT-IR, and Raman spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy techniques are used to determine the structural properties. Surface properties are studied by X-ray photoelectron spectroscopy and Bru-nauer-Emmett-Teller techniques. Half cells and full cells were constructed with Na-metal and hard carbon, respectively. Na-ion diffusion kinetics at 10 degrees C, room temperature, and 50 degrees C were determined experimentally. Galvanostatic cycling tests on half-cells show capacity values of 165/124 mAh/g for the 1./100. cycles with 24.8 % capacity fade. Operando x-ray absorption spectroscopy measurements were utilized to study local structural modification around transition metal ions during charge/discharge. In the full-cell studies, electrode mass ratio (p/n) and parameters for presodiation of hard carbon were optimized. Using 30 mA/g current density, the un-processed and the pre-sodiated full-cells reach capacity values of 48 mAh/g (p/n = 2.5) and 150 mAh/g (p/n = 0.75 and 1.15), respectively.
Highly Active Fe3O4@SBA-15@NHC-Pd Catalyst for Suzuki-Miyaura Cross-Coupling Reaction
(Springer, 2022) Akkoc, Mitat; Bugday, Nesrin; Altin, Serdar; ozdemir, Ismail; Yasar, Sedat
A novel Pd-NHC functionalized magnetic Fe3O4@SBA-15@NHC-Pd was synthesized and used as an efficient heterogeneous catalyst in the Suzuki-Miyaura C-C bond formation reactions. The Fe3O4@SBA-15@NHC-Pd characterized by X-Ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray analysis (EDX), Thermogravimetric Analysis (TGA), Differential Thermal Analysis (DTA). The Inductively Coupled Plasma-Optical emission spectroscopy (ICP-OES) analysis was used to determine the exact amount of Pd (0.33 wt%) in Fe3O4@SBA-15@NHC-Pd. The TEM images of the catalyst showed the existence of palladium nanoparticles immobilized in the catalyst's structure, while no reducing agent was used. The NHC moieties in the catalyst structure could be stabilize Pd(0) nanoparticles prevents agglomeration. The magnetic catalyst was effectively used in the Suzuki-Miyaura cross-coupling reaction of substituted phenylboronic acid derivatives with (hetero)aryl bromides in the presence of a K2CO3 at room temperature in aqueous media and magnetic catalyst could be simply extracted from the reaction mixture by an external magnet. Different aryl bromides were converted to coupled-products in excellent yields with spectacular TOFs values (up to 1,960,339 h(-1)); in the presence of 1 mg of Fe3O4@SBA-15@NHC-Pd catalyst (contains 3.1 x 10(-6) mol% Pd) at room temperature in aqueous media. After reusability experiments, it is found that this catalyst was effectively used up to ten times in the reaction with almost consistent catalytic efficiency. A decrease in the activity of the 10th reused catalyst was found as 9%. Graphic Abstract
In vitro comparison of physical, chemical, and mechanical properties of graphene nanoplatelet added Angelus mineral trioxide aggregate to pure Angelus mineral trioxide aggregate and calcium hydroxide
(Wiley, 2021) Kucukyildiz, Elif Nihan; Dayi, Burak; Altin, Serdar; Yigit, Oktay
It is important to cover the pulp surface with a biocompatible material that is physically, mechanically, and chemically adequate. Graphene has the potential to form hard tissue, but at high doses, it shows toxic effects. It can be added to biocompatible materials at low doses to enhance their hard tissue forming potential. The aim of this study was to compare the physical, chemical, and mechanical properties of graphene nanoplatelet (GNP) added Angelus mineral trioxide aggregate (A-MTA) to pure A-MTA and calcium hydroxide. Homogeneous mixtures (created by adding +0.1 weight[wt]% and 0.3 wt% GNP to A-MTA), pure A-MTA, and Dycal were used. Three disc-shaped samples of each material were prepared using Teflon mold. Scanning electron microscope-energy dispersive X-ray (SEM-EDX), particle size, microhardness, and Fourier transform infrared spectroscopy (FTIR) analysis of the materials were performed in vitro. Data were analyzed using Kruskal-Wallis test followed by Conover test (p < .001). A-MTA and GNP added samples showed similar peaks in FTIR analysis. In the EDX analysis, the amount of carbon was observed with a higher increase at A-MTA + 0.3 wt% GNP than A-MTA + 0.1 wt% GNP. In the SEM image, hollow structure and particle size decreased as the amount of GNP increased; particle size was smaller at A-MTA + 0.3 wt% GNP than A-MTA + 0.1 wt% GNP (p < .001). A-MTA + 0.3 wt% GNP showed the highest microhardness while Dycal showed the lowest microhardness. The addition of GNP, a material with high potential for forming hard tissue, to the structure of capping materials can also positively contribute to the microhardness of the capping materials.
Investigation of electrochemical performance of Na-ion batteries by hard carbon anodes produced by biomass of Prunusarmeniaca seeds
(Springer, 2023) Oktay, Zeynep Melek; Onal, Yunus; Depci, Tolga; Altundag, Sebahat; Altin, Serdar; Yasar, Sedat; Altin, Emine
Hard carbon is successfully fabricated using biomass of Prunusarmeniaca seed shells, and its structural properties are examined by different spectroscopic techniques. For using as an anode electrode in Na-ion batteries, the material is subjected to further pyrolysis at varying temperatures for achieving the necessary levels of conductivity and surface area which are important features for electrode materials. Distinguish properties of the hard carbon in the XRD study appeared as broad peaks at 2 & theta; = 23 & DEG; and 43 & DEG;. The purity of produced hard carbons was approved by EDX to analyze that the purity of hard carbon is greater than 99.9%, making it suitable for industrial use. It was found that the CV curves of the cells created in this work utilizing hard carbon were quite comparable to the CV curves of commercially produced hard carbon cells. According to charge/discharge cycling measurements for constant current at rt, the highest capacity of 210.2 mAh/g using 0.1 A/g is obtained for the material pyrolyzed at 1200 & DEG;C and the capacity fade was found as 0.11. From these promising results, it is thought that the produced hard carbon can be easily used in the production of anode electrodes in commercial Na-ion batteries and technological applications. So it is summarized that P. armeniaca seed shells is one of the main sources for the production of the hard carbon and it can be used as an anode materials in battery cells.
Investigation of hybrid-capacitor properties of ruthenium complexes
(Wiley-Hindawi, 2019) Altin, Serdar; Oz, Erdinc; Altundag, Sebahat; Bayri, Ali; Roisnel, Thierty; Dorcet, Vincent; Bruneau, Christian
Ru complexes were successfully produced, and their structural properties were investigated using FTIR, Raman, and single crystal XRD patterns. The HOMO, LUMO, Eg, and electronic surface potential (ESP) values of the molecules were calculated by a Gaussian program. The complexes were used for producing hybrid capacitor cells as electrode materials. According to electrochemical analysis, complex 2 showed the best CV graph between -1 V and +1 V and had the highest current value and hysteresis area when compared with the other complexes. The performance analysis and the capacity fade of the cells were investigated. The first capacity values of the complexes were 57.5, 22.1, 16.9, and 0.0021 F/g for complexes 1, 2, 3, and 4, respectively. The capacitive mechanism of the cells as relates to molecular interactions was also investigated. We suggested that the ESP values of the molecules were directly related to the capacitive performance of the cells. In addition to this, the best cycling performance was obtained for complex 2, which has the lowest Eg value among the complexes. We speculate that the charged regions on the complex materials have a crucial role in the increasing the capacitance of the cells.
Investigation of physical and electrochemical properties of Ni-doped Tunnel/P2 hybrid Na0.44MnO2 cathode material for sodium-ion batteries
(Academic Press Inc Elsevier Science, 2023) Oz, Erdinc; Altin, Serdar; Avci, Sevda
The increasing demand for energy in recent years has accelerated the efforts to increase the efficiency of energy storage systems. Although lithium-ion batteries are very popular in energy storage systems, the dramatic increase in costs due to the decrease in lithium resources has greatly increased the interest in sodium-ion batteries. Na0.44MnO2 has recently received increasing attention due to the fact that the tunnel structures in the crystal structure are suitable for the diffusion of Na ions. However, rapid structural degradation is an important problem that must be overcome to move into practical applications. In this study, the tunnel/P2 hybrid type Na0.44MnO2 was synthesized by a one-step heat treatment with the Ni substitution to Mn sites for improving cyclic perfor-mance. It was demonstrated by various physical analyses, that biphasic hybrid material starts forming with Ni substitution, and Ni occupied the Mn sites in the P2 phase. Electrochemical measurements provide that after 100 cycles at 0.3C, while Na0.44MnO2 has 77% capacity retention, 1% and 5% Ni substituted samples have 86.4% and 77.3%, respectively. The results show that tunnel-P2 hybrid cathode materials can be developed for practical applications in sodium-ion batteries.
Investigation of structural and electrochemical performance of Ru-substituted LiFePO4 cathode material: an improvement of the capacity and rate performance
(Springer, 2022) Yolun, Abdurrahman; Altin, Emine; Altundag, Sebahat; Arshad, Muhammad; Abbas, Syed Mustansar; Altin, Serdar
LiRuxFe1-xPO4 (where x = 0.01-0.12) samples are successfully fabricated by conventional solid-state reaction technique and the structural properties are analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and fourier transform infrared spectroscopy (FTIR) measurements. The XRD analysis shows that the minor impurity phases of RuO2 and LiRuO2 are observed for x >= 0.05 samples. Furthermore, the lattice volume is decreased with increasing Ru-content in the structure. The Ru-substituted battery cells exhibit similar cycling voltammetry (CV) data with the unsubstituted LiFePO4 battery cells. According to the charging/discharging cycles measurements for C/3-rate, the best capacity (147.58 mAh g(-1)) is obtained for LiFe0.93Ru0.07PO4 with a capacity fade of 0.0084 per cycle. It is found that Ru-substituted LiFePO4 has maximum C-rate when we analogize with the pristine LiFePO4 and the battery cycling performance is investigated for 4 C-rate up to 100 cycles and 3 and 4 C-rate up to 1000 cycles and it is found that Ru-substituted LiFePO4 exhibits excellent electrochemical performance such as 122, 84.5, and 53.1 mAh g(-1) for 1st, 500th, and 1000th cycles at 4 C-rate.
Investigation of Ti-substitution effects on structural and electrochemical properties of Na0.67Mn0.5Fe0.5O2batterycells
(Wiley-Hindawi, 2020) Altin, Serdar; Altundag, Sebahat; Altin, Emine; Oz, Erdinc; Harfouche, Messaoud; Bayri, Ali
Ti-substituted Na(0.67)Mn(0.5)Fe(0.5)O(2)powders were fabricated by quenching at high temperatures, and the structural properties were investigated by Fourier transform infrared (FTIR), Scanning Electron Microscope (SEM), X-ray powder diffraction (XRD), and X-ray absorption spectroscopy (XAS) measurements. According to XRD analysis, it was not observed any impurity phases and it was found that the lattice constants of the powders were slightly increased by Ti content. The change in the valence state of both Mn and Fe ions was investigated by X-ray absorption near edge structure (XANES), and it was found that Ti-substitution caused a decrease in the valance state of Fe in Na0.67Mn0.5Fe0.5O2. Fourier transform (FT) of XANES showed that the local structure around the metal ions changed with the addition of Ti ions. The cycling voltammetry (CV) graphs of Ti-substituted cells were almost the same as the pure sample, which may not change the cycling mechanism in the cells. According to galvanostatic cycling measurements at room temperature, the best performance was obtained with Ti-substitution of 0.06 to 0.09 in the structure. The effect of environmental temperature in the battery cells was investigated at 10 degrees C to 50 degrees C, and it was found that the battery performance depends on the environmental temperatures.
Investigations of the capacity fading mechanism of Na0.44MnO2via ex situ XAS and magnetization measurements
(Royal Soc Chemistry, 2018) Altin, Serdar; Oz, Erdinc; Altin, Emine; Demirel, Serkan; Bayri, Ali; Avci, Sevda
Na-ion batteries represent a promising complementary alternative to Li-ion batteries due to their high energy density and natural abundancy of Na. However, these batteries have short cycle life and extensive research activities on these batteries are required to understand the mechanism of such drawbacks. In this report, we investigate the capacity fading mechanism of Na(0.44)MnO(2)via ex situ X-ray diffraction, X-ray absorption spectroscopy, Fourier transform infrared spectroscopy and magnetization measurements. Our results show that the unit cell volume, the effective mass of Mn-O bonds, the number of Mn4+ ions and the effective magnetic moment decrease upon repeated cycling. We propose that some Mn4+ ions in the octahedral environment become Mn3+ ions in a square pyramidal environment, causing oxygen release upon cycling. Any free oxygen in the battery is expected to react with the electrolyte and cause capacity fade.
The leakage study between restorative and pulp capping materials and diffusion analysis by Fick laws
(Biointerface Research Applied Chemistry, 2016) Kamalak, Hakan; Demirel, Serkan; Oz, Erdinc; Altin, Serdar
The investigation of adhesion behaviour of restorative and pulp Capping Materials in dental treatment is an important subject for the development of new maerials and prevent unwanted conditions such as secondary carriers prevelance and pain due to the leakage. The aim of the study is the development of new methods for leakage studies between the restorative and pulp capping materials. The micro-CT experiment was supported by the obtained mechanism by using Fick diffusion laws for leakage. It is found that the X-ray micro tomography analysis should be supported by the other techniques like electron microscopy and energy dispersive X-ray spectroscopy. Diffusion mechanism calculations have been identified by EDX analysis and it is found that there are two different diffusion mechanisms in the interface region between the pulp capping and the restorative materials. So the suffer duration after dental treatment is strongly dependent on the strong of inner part of the interface region.

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