Browsing by Subject "Supercapacitor"

Now showing 1 - 10 of 10

Open Access
Broadband optical modulators based on graphene supercapacitors
(American Chemical Society, 2013) Polat, E. O.; Kocabas, C.
Optical modulators are commonly used in communication and information technology to control intensity, phase, or polarization of light. Electro-optic, electroabsorption, and acousto-optic modulators based on semiconductors and compound semiconductors have been used to control the intensity of light. Because of gate tunable optical properties, graphene introduces new potentials for optical modulators. The operation wavelength of graphene-based modulators, however, is limited to infrared wavelengths due to inefficient gating schemes. Here, we report a broadband optical modulator based on graphene supercapacitors formed by graphene electrodes and electrolyte medium. The transparent supercapacitor structure allows us to modulate optical transmission over a broad range of wavelengths from 450 nm to 2 μm under ambient conditions. We also provide various device geometries including multilayer graphene electrodes and reflection type device geometries that provide modulation of 35%. The graphene supercapacitor structure together with the high-modulation efficiency can enable various active devices ranging from plasmonics to optoelectronics. © 2013 American Chemical Society.
Open Access
Effects of carbon nanomaterials and MXene addition on the performance of nitrogen doped MnO2 based supercapacitors
(Elsevier Ltd, 2021-12-02) PeçeneK, H.; Yetiman, S.; Dokan, F. K.; Önses, Mustafa Serdar; Yılmaz, E.; Sahmetlioğlu, E.
Nitrogen-doped composites have the potential to achieve well electrochemical performance by enabling convenient contact of the electrolyte ions for carbon-based materials. A good combination of metal oxide and carbonaceous material is a critical challenge in the development of composites. Herein, we demonstrate a highly capacitive and superior cycle performance of MnO2 based supercapacitor electrodes. The addition of different forms of carbon nanomaterials (carbon nanotube and graphene) and MXene is particularly studied. MnO2 based composite materials are capable of capacitance retention over 95%, with high specific capacitance compared to pure N-doped MnO2. The highest specific capacitance was achieved with MXene based MnO2 composite, which exhibits 457 Fg-1, at a current density of 1 A g−1 with extreme cycling efficiency (102.5%, after 1000 cycles). High conductivity and large surface area are stimulated by the propitious interaction between MnO2 and nanoscale materials, resulting in superior supercapacitor efficiency. This study highlights the possible potential of carbon-based MnO2 composite electrodes which could be useful for future energy storage applications.
Open Access
The effects of stage house coupling on multipurpose auditorium acoustics
(Elsevier, 2022-03-01) Peçenek, H.; Yetiman, S.; Kılıç Dokan, F.; Onses, M. Serdar; Yılmaz, E.; Sahmetlioglu, E.
Nitrogen-doped composites have the potential to achieve well electrochemical performance by enabling convenient contact of the electrolyte ions for carbon-based materials. A good combination of metal oxide and carbonaceous material is a critical challenge in the development of composites. Herein, we demonstrate a highly capacitive and superior cycle performance of MnO2 based supercapacitor electrodes. The addition of different forms of carbon nanomaterials (carbon nanotube and graphene) and MXene is particularly studied. MnO2 based composite materials are capable of capacitance retention over 95%, with high specific capacitance compared to pure N-doped MnO2. The highest specific capacitance was achieved with MXene based MnO2 composite, which exhibits 457 Fg-1, at a current density of 1 A g−1 with extreme cycling efficiency (102.5%, after 1000 cycles). High conductivity and large surface area are stimulated by the propitious interaction between MnO2 and nanoscale materials, resulting in superior supercapacitor efficiency. This study highlights the possible potential of carbon-based MnO2 composite electrodes which could be useful for future energy storage applications.
Open Access
Femtosecond pulse generation from a Ti3+: Sapphire laser near 800 nm with voltage reconfigurable graphene saturable absorbers
(OSA - The Optical Society, 2017) Baylam, Işınsu; Özharar, Sarper; Kakenov, Nurbek; Kocabaş, Coşkun; Sennaroglu, Alphan
We experimentally show that a voltage-controlled graphene-gold supercapacitor saturable absorber (VCG-gold-SA) can be operated as a fast saturable absorber with adjustable linear absorption at wavelengths as low as 795 nm. This was made possible by the use of a novel supercapacitor architecture, consisting of a high-dielectric electrolyte sandwiched between a graphene and a gold electrode. The high-dielectric electrolyte allowed continuous, reversible adjustment of the Fermi level and, hence, the optical loss of the VCG-gold-SA up to the visible wavelengths at low bias voltages of the order of a few volts (0-2 V). The fast saturable absorber action of the VCG-gold-SA and the bias-dependent reduction of its loss were successfully demonstrated inside a femtosecond Ti3+:sapphire laser operating near 800 nm. Dispersion compensation was employed by using dispersion control mirrors and a prism pair. At a bias voltage of 1.2 V, the laser operated with improved power performance in comparison with that at zero bias, and the VCG-gold-SA initiated the generation of nearly transform-limited pulses as short as 48 fs at a pulse repetition rate of 131.7 MHz near 830 nm. To the best of our knowledge, this represents the shortest wavelength where a VCG-gold-SA has been employed as a mode locker with adjustable loss. © 2017 Optical Society of America.
Open Access
Graphene based optoelectronics in the visible spectrum
(2015) Polat, Emre Ozan
Graphene, a two dimensional crystal of carbon atoms, emerges as a viable material for optoelectronics because of its electrically-tunable broadband optical properties. Optical response of graphene at visible and near infrared frequencies is defined by inter-band electronic transitions. By electrical tuning of the Fermi energy, the inter-band transitions can be blocked due to Pauli blocking. However, controlling inter-band transitions of graphene in the visible and near infrared wavelengths, has been an outstanding challenge. We developed a new device to control optical properties of graphene in the visible spectra. Our device relies on a graphene supercapacitor which includes two parallel graphene electrodes and electrolyte between them. Mutual gating between graphene electrodes enables us to fabricate optical modulators which can operate in the visible and near-infrared. Single layer graphene, however, has performance limits due to its small optical absorption defined by fundamental constants. We extend our method and we developed a new class of electrochromic devices using multilayer graphene. Fabricated devices undergo a reversible color change with the electrically controlled intercalation process. The electrical and optical characterizations of the electrochromic devices reveal the broadband optical modulation up to 55 per cent in the visible and near-infrared. Integration of semiconducting materials on unconventional substrates enables optoelectronic devices with new mechanical functionalities that cannot be achieved with wafer-based technologies. As a novel application, we demonstrate ultra thin electronic paper displays using the multilayer graphene as a reconfigurable optical medium. We anticipate that the developed devices would find wide range of applications in optoelectronics.
Open Access
Highly stable Megalopolis lignite based N and S self-doped hierarchically porous activated carbons for high performance supercapacitors and ash content effects on performance
(Elsevier, 2022-02) Oglou, Ramadan Chalil; Gokce, Y.; Yagmur, E.; Ghobadi, T.Gamze Ulusoy; Aktas, Z.
This study proposes that high value-added activated carbon (AC) is produced from lignite (low rank coal) and used as electrode material in supercapacitors. In addition, the effects of the ash content of the activated carbon on supercapacitor performance are determined. The ACs at a temperature of 800 °C are produced in three different impregnation ratios (IR) (IR: 1, 2 and 4: KOH/precursor) using KOH as the activation agent. While the surface area of the AC produced at IR4 is 2531.4 m2 g−1, it is determined as 1321.3 (IR1) and 1989.0 (IR2) m2 g−1 for the others. The pore size analysis of the samples shows that the mesopores are dominant in the IR1 (52.73%) and IR4 (88.74%) samples, while it is observed that the micropores are dominant in the IR2 (69.03%) sample. The IR4 sample gives excellent results. The cell specific capacitances of this sample are determined as 260.47 F g−1 (at 1 A g−1) and 150.3 F g−1 (at 50 A g−1). The amount of ash in the AC samples dramatically reduces the supercapacitor performances and significantly increases the resistances.
Open Access
Impedance based modeling of battery parameters and behavior
(2017-07) Aydın, Elif
Modeling battery performance under arbitrary load has gained importance in recent years with the increasing demand on batteries in various fields from automotive industry to consumer electronic devices. Due to numerous application areas of electrochemical energy storage (EES) systems, researchers have tried to predict the battery performance and the voltage using extensive calculations. Unfortunately, in order to achieve high levels of accuracy, the model has to be algebraically and computationally complex. Models with decreased computational and algebraic complexity suffer from loss of accuracy. In this thesis, we offer a new modeling approach to predict the voltage responses of batteries and supercapacitors which is both algebraically straightforward and yielding more accurate results. Our approach is valid using any discharge profile including published by regulatory bodies such as Environmental Protection Agency (EPA). Our method is based on Electrochemical Impedance Spectroscopy (EIS) measurements done on the system to be predicted and slow DC discharge. EIS data is used directly to predict the fast moving portion of the voltage response to the profiles. The EIS data is used as is, namely, in frequency domain without any modeling. The slow DC discharge data provides DC response and is added in through a straightforward lookup table. This widely applicable approach can predict the voltage with less than 1% error, without any adjustable parameters to a large variety of discharge profiles.
Open Access
Outstanding supercapacitor performance with intertwined flower-like NiO/MnO2/CNT electrodes
(Elsevier Ltd, 2022-01-11) Peçenek, H.; Kılıç Dokan, F.; Onses, M. Serdar; Yılmaz, E.; Sahmetlioglu, E.
Binary metal oxides have been broadly investigated as a new electrode material for supercapacitor applications owing to their high reversible performance and good conductivity. When compared to a single candidate, the composite's electrochemical performance is considerably improved by the unique mix of pseudo-material and carbon material. Herein, we report a facile and rational synthesis procedure to fabricate a high performance supercapacitor electrode. The prepared NiO/MnO2/ carbon nanotube (CNT) composite has wonderfully stratified flower-like morphology. The positive synergism among components and unique structure has enabled a high specific capacitance of 1320 F/g at 1 A g−1. After 3000 cycles, the supercapacitor maintains more than 90% of its initial capacitance. Moreover, we also successfully prepared a symmetrical supercapacitor which is made up of two pieces of composite electrode separated with a membrane. The findings highlight that NiO/MnO2/CNT composite is highly desirable for future hybrid energy storage applications.
Open Access
Porous organic polymers for electrochemical and energy storage application
(2022-08) Yau, Arma Musa
The intrinsic porosity and tunable morphology of Porous Organic Polymers (POPs), materials made from organic building blocks joined by strong covalent bonds, have become appealing in the context of electrochemical applications. In the first section of this thesis, a low-cost thiophene derivative and melamine were assembled into nitrogen and sulfur-enriched microporous organic polymer (MOP) using a pyrolysis-free one-pot Schiff-base type polycondensation reaction. The synthesized polymer is characterized by FT-IR, SEM, TEM, BET, XRD, XPS, TGA and UV-VIS. With 195.731 m2 g–1 surface area and 0.047 cm3 g–1 pore volume, the as-synthesized MOP has a cotton-like morphology and a micropore-dominated pore size distribution. After encapsulating it with a nickel co-catalyst, we showed that the obtained framework (MOP) could be used as an efficient catalyst for hydrogen evolution reaction (HER) in an alkaline electrolyte with the optimum composite (Ni2@MOP) exhibiting a remarkable onset overpotential of -66 mV. Furthermore, the optimum electrocatalyst showed good stability, delivering 90.84% faradaic efficiency (FE) after a 3.5 h chronoamperometry experiment. In the second section, the synthesized porous organic polymer and CB[6]-porphyrin covalent organic framework were investigated for potential use as electrode materials for supercapacitors.
Open Access
Zero-free-parameter modeling approach to predict the voltage of batteries of different chemistries and supercapacitors under arbitrary load
(Electrochemical Society, Inc., 2017) Özdemir, E.; Uzundal, C. B.; Ulgut, B.
Performance modeling of electrochemical energy storage systems is gathering increasingly higher attention in recent years. With the ever increasing power demand of mobile applications, predicting voltage behavior under different load profiles is of utmost importance for communications, automotive and consumer electronics. The ideal modelling approach needs not only to accurately predict the response of the battery, but also be robust, easy to implement and have low computational complexity. We will present a new algorithm that is algebraically straightforward, that has no adjustable parameters and that can accurately predict the voltage response of batteries and supercapacitors. The approach works well in a variety of discharge profiles ranging from simple long DC discharge/charge profiles to pulse schemes based on drive schedules published by regulatory bodies. Our approach is based on Electrochemical Impedance Spectroscopy measurements done on the system to be predicted. The spectrum is used in the frequency domain without any further processing to predict the fast moving portion of the voltage in the frequency domain. DC response is added in through a straightforward lookup table. This widely applicable approach can predict the voltage of with less than 1% error, without any adjustable parameters to a large variety of discharge profiles.