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    Direct utilization of radioactive irradiated graphite as a high-energy supercapacitor a promising electrode material
    (Elsevier Sci Ltd, 2022) Karimi-Maleh, Hassan; Kariper, I. Afsin; Karaman, Ceren; Korkmaz, Satiye; Karaman, Onur
    Considering ever-increasing energy needs, resulting in the depletion of fossil fuels and, as a corollary, global warming, the adoption of green technologies and the development of sophisticated energy storage and conversion technologies are imperative. Although the supercapacitors have garnered a lot of attention as a highperformance energy storage solution, it is still crucial to engineer novel electrode materials via low-cost and facile, scalable methods while maintaining their enhanced power density and cycle stability. In this work, it was aimed to design and engineer graphite (GRs)-based electrode low-cost materials to be utilized as a highperformance supercapacitor. This study is of great importance in terms of it is one of the first works which offered a facile pathway to fabricate GRs-based electrode materials via the irradiation approach, as well as direct utilization of them in supercapacitor cells. In this regard, various graphite-based samples were prepared by irradiation with several point beam radiation sources, including Am-241, Sr-90, Co-60, and Na-22. The electrochemical active surface area and microcrystalline sizes of GRs were fine-tuned via the type of the radiation source. X-Ray Diffraction (XRD), Raman spectroscopy, and Scanning Electron Microscopy, Energy Dispersive X Ray (SEM-EDX) techniques were employed to assess the physicochemical features of the as-obtained GRs. The electrochemical behaviors of the samples were further tested in 3.0 M H2SO4 aqueous electrolyte via the coin-cell type supercapacitor cells based on GRs. The maximum specific capacitance was achieved for the GR-Sr90 sample, which was of the largest electrochemically active surface area (0.3087 cm(2)), as 483.20F.g(-1) at a current density of 0.2 A.g(-1), which was roughly 5 fold of the non-irradiated GR sample. At the end of the 5,000th CV cycle, the capacitance retention of GR-Sr90 was determined to be 97.40 %. The energy density and power density values of assembled supercapacitor cells based on GRs were found to be comparable to the commercial energy storage systems. All these striking results reveal that the suggested scalable fabrication method will shed an innovative light on the development and engineering of energy storage systems based on low-cost graphite-based electrode materials.
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    Engineering of GO/MWCNT/RuO2 ternary aerogel for high-performance supercapacitor
    (Elsevier Sci Ltd, 2022) Karimi, Fatemeh; Korkmaz, Satiye; Karaman, Ceren; Karaman, Onur; Kariper, I. Afsin
    It is of great importance to fabricate high-performance electrode materials via a facile fabrication pathway to be utilized in energy storage systems, specifically in supercapacitors. Herein, ruthenium(IV) oxide (RuO2) was decorated onto the nanocomposite of graphene oxide (GO) and functionalized multi-walled carbon nanotubes (MWCNT) via straight forward production pathway for the first time, and the resultant nanostructure was then characterized physicochemically via x-ray diffraction spectroscopy (XRD), Fourier transform infrared spectros-copy (FTIR), field-emission scanning electron microscope (FESEM), and energy dispersive X-ray analysis (EDX). The fabricated nanostructure was employed as the electrode material to develop a high-energy symmetrical supercapacitor cell. The electrochemical performance of the as-assembled supercapacitor was assessed by cyclic voltammetry (CV), and galvanostatic charge-discharge (GCD) techniques. The highest specific capacitance was achieved as 514.9F.g(- 1) at a current density of 0.5 A.g(- 1). Moreover, even at a high current density of 10.0 A.g(- 1), the specific capacitance value was computed still as high as 329.3F.g(- 1). The superior capacitance retention feature (94.38 % at the end of 5,000th consecutive CV cycles) revealed the outstanding electrochemical activity of the electrode material. The attained energy density of 37.96 W.h.kg(- 1) (at a power density of 8.33 kW.kg(- 1)) implied the potential application of the proposed supercapacitor cells as a high-energy system.
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    High energy supercapacitors based on functionalized carbon nanotubes: Effect of atomic oxygen doping via various radiation sources
    (Elsevier Sci Ltd, 2022) Kariper, Ishak Afsin; Korkmaz, Satiye; Karaman, Ceren; Karaman, Onur
    Herein, carbon nanotubes (CNTs) were oxygen functionalized by irradiation with diverse radiation sources including Am-241, Sr-90, Co-60, and Na-22 for the first time to be used as the electrode material in a high-energy supercapacitor. The oxygen contents of the irradiated CNTs were fine-tuned via the energy of the radiation source. The physicochemical characterization of as-obtained CNTs was conducted by X-Ray Diffraction (XRD), Raman, and Scanning Electron Microscopy, Energy Dispersive X-Ray (SEM-EDX) analysis whereas cyclic voltammetry and galvanostatic charge-discharge techniques were performed to assess the electrochemical performance of the as-assembled symmetrical supercapacitor cells. The CNT irradiated by Am-241 radiation source offered superior specific capacitance values compared to the other irradiated CNTs thanks to its higher content of oxygen functional groups. The highest specific capacitance for CNT Am-241 sample (with 7.32% oxygen) was calculated to be 489.6 F.g(-1) at a current density of 0.1 A.g(-1), which was almost 2.75 fold that of non-irradiated CNT sample. The capacitance retention of as-synthesized CNT Am-241 was determined as 98.50% for the 5,000th CV cycle. The outstanding energy density of 56.90 W.h.kg(-1) was achieved even at a high power density value of 9992.19 W.kg(-1), comparable to the commercial batteries, will pave the way for facile fabrication of high-energy electrochemical energy storage systems based on functionalized carbon nanotubes.
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    Irradiated rGO electrode-based high-performance supercapacitors: Boosting effect of GO/rGO mixed nanosheets on electrochemical performance
    (Elsevier Sci Ltd, 2022) Karaman, Onur; Kariper, I. Afsin; Korkmaz, Satiye; Karimi-Maleh, Hassan; Usta, Metin; Karaman, Ceren
    Supercapacitors are seemed to be one of the most promising choices as an energy storage system. However, there is still a gap in enhancing its energy density values and cyclic stabilities throughout a facile approach. Herein, it was aimed to propose a facile and effective way to fabricate high-energy supercapacitor electrode material based on reduced graphene oxide (rGO) nanostructure. Bearing this in mind, the bulk rGO powder was irradiated by various beam sources including Co-60, Am-241, Na-22, and Sr-90, and the resultant irradiated rGO samples were utilized as the electrode active material to fabricate symmetrical supercapacitor cells. The irradiated rGO samples were characterized both physicochemically and electrochemically. The physicochemical characterizations revealed that as a consequence of the irradiation, both GO and rGO nanosheets were formed in the resultant powder and the d-spacing of the graphene nanosheets were expanded. The highest electrochemical performance metrics were acquired for Sr-90 irradiated rGO electrode-based supercapacitor cell with the specific capacitance value of 585.44F.g ? 1 at 0.2 A.g ? 1, and outstanding capacitance retention performance of 97.14% for the 5000th CV cycles at 200 mV.s ? 1. Moreover, the energy density and power density values were comparable to other commercial energy storage systems such as lead-acid and nickel-metal hybrid batteries. Hence, it can be speculated that these pioneering breakthroughs could pave the way for cutting-edge high-energy supercapacitors based on rGO-derivatives with superior electrochemical performance metrics, as well as engineering of highperformance rGO-based materials to be employed in various energy applications.
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    MWCNT/Ruthenium hydroxide aerogel supercapacitor production and investigation of electrochemical performances
    (Nature Portfolio, 2022) Korkmaz, Satiye; Kariper, Ishak Afsin; Karaman, Ceren; Karaman, Onur
    In this study, the material obtained from the sonication of the double-walled carbon nanotube and ruthenium chloride was produced as an aerogel. Then, symmetrical supercapacitor devices were made using them, and their electrochemical properties were investigated. XRD and FTIR were used in the structural analysis of the aerogel, STEM in surface images, and elemental analyses in EDX. Electrochemical analysis was performed by galvanostat/potentiostat. From the cyclic voltammetry analysis, the highest specific capacitance for MWCNT/Ruthenium hydroxide aerogels was achieved as 423 F/g at 5 mV/s. On the other hand, the corresponding values calculated from the charge-discharge curves were found to be 420.3 F/g and 319.9 F/g at the current densities of 0.5 A/g and 10.0 A/g, respectively. The capacitance retention of as-synthesized aerogel was 96.38% at the end of the 5000 consecutive consecutive cyclic voltammetry cycles.
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    The production of rGO/RuO2 aerogel supercapacitor and analysis of its electrochemical performances
    (Elsevier Sci Ltd, 2021) Korkmaz, Satiye; Kariper, I. Afsin; Karaman, Onur; Karaman, Ceren
    In this study, ruthenium was bonded to the reduced graphene oxide in an ultrasonic bath. The aerogel of the mixture was produced at -78 degrees C. Structural characterization of aerogels was done with XRD and FTIR, surface characterization was performed with STEM, and elemental analysis was conducted by EDX analysis. The produced aerogel composites were transformed into electrodes on conductive Nickel foam. IviumStat, a potentiostat/galvanostat device, was used for the electrochemical characterization of the symmetrical supercapacitors. According to CV voltammograms, rGO/RuO2 aerogels' highest specific capacitance was calculated as 328.6 F g-1 at a potential scan rate of 5 mV s-1. The assembled rGO/RuO2 aerogel-based supercapacitor cell offered a high energy density value of 31.1 W h kg-1 even at the power density of 8.365 kW kg-1; this is comparable to that of lead-acid and nickel-metal hybrid batteries.