Sharif Digital Repository

Freshwater scarcity in conjunction with population expansion puts human survival in doubt. Throughout the world, millions of people are deprived of clean and safe drinking water. The development of novel technologies to desalinate water is among the most valuable studies for humanity. Receiving benefits from low energy consumption, high environmental capability, and low-production cost, capacitive deionization (CDI) received significant attention in saline water desalination. Rational design of efficient electrode materials by tailoring their structural and compositional properties, therefore, plays a pivotal role in achieving high-performance CDI systems. Hollow carbon spheres (HCSs) with... 

This paper presents a new symmetric slew rate enhancement (SRE) circuit suitable for operational transconductance amplifiers (OTAs). The proposed SRE circuit is composed of two auxiliary circuits which are automatically activated during fast signal transitions (slewing) by comparing the input and output signals. The auxiliary circuits pump required current in/out the load capacitance. In this way, the slew rate of the amplifier is significantly improved without any extra static power dissipation. The proposed technique can be applied to a variety of operational amplifiers. However, incorporating the proposed SRE circuit into a folded-cascode amplifier (FCA) results in 7× slew rate... 

This article proposes a scheme for balancing the voltage of series-connected insulated gate bipolar transistors (IGBTs), which is also very effective under short-circuit conditions. An optimized clamp-mode snubber is proposed, including an active-driver to balance the currents of the IGBTs during short-circuit, which in turn allows for a considerable reduction of the snubber capacitance. The approach is proven to be effective under short-circuit conditions by a maximum of 55 V voltage increment and a negligible difference in the current values. The effectiveness of the proposed approach is demonstrated through simulations in PSPICE software and experimental tests performed at 2 kV. ©... 

Herein, the effect of electrodeposition time on the super-capacitive performance of three-dimensional (3D) MnO2/g-C3N4 heterostructured electrodes was investigated. MnO2 nanoparticles were electrodeposited on the g-C3N4 nanosheets drop-casted on the Ni foam substrate. The microstructural analysis, carried out by FE-SEM and TEM, confirmed the homogeneous distribution of MnO2 nanoparticles on g-C3N4 nano-sheet layers. The electrochemical capacitive performances of the MnO2/g-C3N4 electrodes were evaluated by cyclic voltammetry (CV), galvanostatic charge/discharge tests, and electrochemical impedance spectra (EIS). The obtained results suggested that the supercapacitor (SC) performance of all... 

The increasing energy demand for next-generation portable and miniaturized electronics has drawn tremendous attention to develop microscale energy storage and conversion devices with light weight and flexible characteristics. Herein, we report the preparation of flower-like cobalt vanadium selenide/nickel copper selenide (CoVSe/NiCuSe) microspheres with three-dimensional hierarchical structure of micropore growth on copper wire for a flexible fiber microsupercapacitor (microSC) and overall water splitting. The CoV-LDH microspheres are anchored on the dendrite-like NiCu nanostructured Cu wire using a hydrothermal method (CoV-LDH/NiCu@CW). The sulfidation and selenization of CoV-LDH/NiCu was... 

Capacitors are one of the most critical components in power electronic converters, yet they are notoriously susceptible to failure. Avoiding unforeseen outages caused by capacitor failures is one of the most effective approaches to increase system availability. Therefore, a variety of methods have been proposed to monitor a capacitor health condition based on different degradation indicators. This paper proposes a new approach based on the accurate measurement of an electrolytic capacitor dissipation factor to detect its end-of-life. Since the dissipation factor is affected by both the capacitor resistance and capacitance simultaneously, it can provide more information about the health... 

A capacitive voltage transformer (CVT) operating at extra high voltage (EHV) is examined for measuring power system harmonics in this paper. With the capacitor connections rearranged in the divider, the internal components can be energized with their nominal values by applying an intermediate voltage. Through this procedure, the effect of different burdens on frequency response is tested. The linearity of CVT circuits is also evaluated with respect to applied voltage level. In addition, an examination of the effects of amplitude and phase differences between harmonic components and the fundamental component is conducted. The practical test results are subsequently discussed. © 2022 IEEE  

The increasing use of power electronic equipment and the importance of their continuous and correct operation have attracted remarkable attention to the condition monitoring of power electronic converters. Since capacitors are the leading cause of power electronic converters failure, this paper attempts to attain a solution to monitor the condition of the DC-link capacitor in a three-phase back-to-back converter using the stimulated measurable transients. The proposed method works based on the temporary change of switching logic and the measurement of the DC-link voltage and converter input phase current transients. By processing the measured signals, the capacitance of the capacitor is... 

Interest in carbon nanomaterials for energy storage systems such as supercapacitors has enormously risen due to their attractive electrical conductivity, chemical inertness, and charge storage capacity. The reduction of graphitic oxide is a versatile procedure to prepare 3D graphene. Despite many green methods, the dynamics behind ultrafast thermal graphitization have remained elusive. Here, we demonstrate an effort to understand the graphitization mechanism of graphitic oxide under ultrafast thermal reduction induced by electromagnetic radiation and probably via Ar+ cation collisions. The low photon energy (10.5 μeV) locally removes oxygen functionalities and restores the π-conjugated... 

Manganese dioxide/reduced graphene oxide (MnO2/RGO) nanocomposite material was synthesized by the in-situ anodic pulse electrodeposition method to fabricate symmetric supercapacitors. The effects of the pH value of the electrodeposition bath were considered on the properties of fabricated electrodes. Three pH values of 4, 7, and 10 were evaluated, and physicochemical properties were studied using field-emission scanning and transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, nitrogen gas sorption isotherm, and thermogravimetric analysis. The electrochemical evaluation was performed by galvanostatic charge/discharge (GCD), cyclic voltammetry (CV),... 

Microscale, flexible, and lightweight electrodes are of interest for the generation of light and miniaturized energy storage systems such as microsupercapacitors. Wire or fiber-shaped electrodes can be considered as potential candidates for microsupercapacitor fabrication. Herein, a facile strategy for the preparation of high electrochemical performance fiber-shaped microsupercapacitors based on Ni(OH)2-Ni-Ti3C2 film on a copper wire (CW) electrode is presented. We employed a porous cauliflower-like Ni-Ti3C2 MXene film as the supporting scaffold to bridge a Ni(OH)2 active substance with a Cu wire current collector. This hierarchical structure supplies a high surface area, many electroactive... 

This paper presents a new symmetric slew rate enhancement (SRE) circuit suitable for operational transconductance amplifiers (OTAs). The proposed SRE circuit is composed of two auxiliary circuits which are automatically activated during fast signal transitions (slewing) by comparing the input and output signals. The auxiliary circuits pump required current in/out the load capacitance. In this way, the slew rate of the amplifier is significantly improved without any extra static power dissipation. The proposed technique can be applied to a variety of operational amplifiers. However, incorporating the proposed SRE circuit into a folded-cascode amplifier (FCA) results in 7× slew rate... 

This paper introduces a straightforward technique for parameters estimation of the RC equivalent circuit model of a battery cell with the main aim of its implementation in real-time digital simulator frameworks. The RC model parameters are precisely estimated by the analysis of the battery cell voltage curve during relaxation time using the pulse current test. In this regard, Least-squares fitting is used to mitigate the error of the battery cell voltage response, which leads to a precise estimation of the RC model parameters as a function of the state-of-charge. Exponential and Gaussian functions are utilized to define the resistances and the capacitances in the RC model respectively based... 

A pseudocapacitive electrode based on mesoporous manganese dioxide (MnO2) was fabricated via the anodic pulse electrodeposition method. Pulse current (PC) has many parameters that affect the physicochemical and electrochemical properties of the material. PC parameters are generally divided into independent and dependent types. Independent pulse parameters consist of the time of applying current (ton), interval time with zero current (toff), and peak current density (Ip). Dependent pulse parameters include duty cycle (θ), frequency (f), and average current density (Ia). In this work, the changes of two independent parameters (ton and toff) at the constant Ip = 2 mA cm-2 on the anodic pulse... 

Capacitance-Resistive Model (CRM), as a fast yet efficient proxy model, suffers from some limitations in modeling relatively complex reservoirs. Some current improvements on this proxy made it a more powerful simulator with updating parameters over time. However, the model's intrinsic uncertainty arisen from simplifying fluid-flow modeling by some limited number of constant parameters is not addressed yet. In this study, this structural limitation of CRM has been addressed by introducing a time-correlated model error, including stochastic and non-stochastic parameters, embedded into this proxy's formulation. The error term's non-stochastic parameters have been tuned to be used in forecasting... 

We present an LC circuit model that supports a tilted “Dirac cone” in its spectrum. The tilt of the Dirac cone is specified by the parameters of the model consisting of mutual inductance between the neighboring sites and a capacitance C0 at every lattice site. These parameters can be completely measured by impedance spectroscopy. Given that a tilted Dirac cone can be described by a background spacetime metric, the impedance spectroscopy can perfectly provide (local) information about the metric of the spacetime. Nonuniform spatial dependence of the mutual inductance or capacitance induces a nontrivial geometrical structure on the emergent spacetime. Our work extends the range of usefulness... 

In this study, we prepared cerium oxide (CeO2) hybridized with reduced graphene oxide (rGO) nanosheets using the hydrothermal method. CeO2 and CeO2/rGO were evaluated as electrode materials for use in supercapacitor applications. The structure and morphology of the synthesized materials were investigated. Cyclic voltammetry tests determined a high specific capacitance of 581 F g−1 for CeO2/rGO at a scan rate of 10 mV s−1 in 2 M KOH. In addition, the CeO2/rGO electrode retained 91 % of its initial capacitance after 5000 consecutive cycles, thereby indicating its excellent electrochemical stability. The excellent stability of CeO2/rGO was due to a synergistic effect between CeO2 and rGO. CeO2... 

Evolution of renewable energies in the era of the modernized world has been strongly tied up to the incessant development of high-performance energy storage systems benefiting from both high energy and power densities. In the present work, binder-free positive electrodes are fabricated via a facile electrochemical deposition route in which copper oxide nanorods (CuO NRs) directly grown onto the copper foam (CF) are decorated with bimetallic cobalt-zinc sulfide nanoarrays (Co-Zn-S NAs). The fabricated Co-Zn-S@CuO-CFs represent promising specific capacity of 317.03 C.g−1 at 1.76 A.g−1, along with superior cyclic stability (113% retention after 4500 cycles). Negative electrodes were further... 

Hereby a simple, low-cost and scalable route is being presented for preparation of binder-free electrodes of reduced graphene oxide (RGO) on Ni foam (Ni/Gr). In this regard, the Ni foams are dipped in graphene oxide (GO) slurry. Next, the GO loaded Ni foams are kept in a freeze dryer for 24 h and heated up to 800 °C in an inert atmosphere. In this approach, the amount of active materials can be easily optimized for capacitive deionization (CDI). The characterization of Ni/Gr electrodes revealed a 3D porous assembly of RGO on Ni substrate which is helpful for the fast ion diffusion and rapid electron transport. The electrochemical performance of the prepared electrodes is investigated in both... 

An efficient and commercially available method is introduced for preparation of a binder-free electrode for capacitive deionization (CDI) application. An interconnected porous composite consisting of polyphosphate (PPO), graphene (Gr) and multi-walled carbon nanotube (CNT) is fabricated and assembled on a Ni foam substrate to prepare a binder-free electrode (Ni/PPOGrCNT). The resulting electrodes were characterized using various instrumental techniques such as TEM, SEM, EDS, XRD, FT-IR, Raman, XPS and XRF. Characterization results indicated that a mesoporous PPO structure is formed on a 3D assembly of carbon backbone. Accordingly, the 3-D porous structure facilitates the ion diffusion into...