Sweep Rate Research Articles

Overcoming Challenges in Development of Manganese Oxide Supercapacitor Cathodes by Alkali-Free Hydrothermal Synthesis

This investigation is motivated by the need in the development of manganese oxide cathodes for supercapacitors with high capacitance at high charge–discharge rates and enhanced capacitance retention in a wide range of charge–discharge rates. It also addresses the challenge of eliminating the time-consuming activation procedure, which limits the applications of Mn3O4 cathodes. The new approach is based on the use of environmentally friendly and biocompatible pH modifiers–dispersants, such as polyethylenimine (PEI) and meglumine (MG) for hydrothermal synthesis. In this approach, the use of inorganic alkalis is avoided. We demonstrate the benefits of this approach for the fabrication of manganese oxide nanoparticles, such as Mn-PEI and Mn-MG. Electrodes with a high active mass of 40 mg cm−2 are fabricated and electrochemically tested in 0.5 M Na2SO4 electrolyte. The method of electrode material fabrication offers benefits for the accelerated electrode activation procedure, which is practically eliminated for Mn-MG electrodes. The Mn-MG electrodes showed a remarkably high capacitance of 3.68 F cm−2 (93.19 F g−1) at a sweep rate of 100 mV s−1 and a high capacitance retention of 90.6% in the CV sweep range of 1–100 mV s−1.

Facile fabrication of copper oxide modified sensor for determination of Mycophenolate mofetil in biological fluids: A cyclic voltammetric study

In the present work, the copper oxide nanoparticles (CuO Nps) was synthesized via chemical co-precipitation method for the detection of Mycophenolate mofetil (MMF). The synthesized Nps were characterised using traditional techniques namely X-ray diffraction (XRD), Scanning electron microscopy (SEM) and EDAX studies which showed better crystallinity with particle size of around 26 nm. The physiological pH of 7.4 was maintained throughout the studies. CuO Nps fabricated carbon paste electrode (CuO/FCPE) showed a considerable electroactive surface area with contrast to BCPE and showed better sensitivity and stable current responses. Further various other studies such as sweep rate, concentration, pH studies were carried out which showed lower LOQ and LOD i.e. 0.5 and 0.15 μM respectively. The developed electrode showed greater stability around 94% by retaining its activity. The fabricated electrode further studied for practical analysis of MMF in human urine trial which showed greater recovery of MMF in range of 96%–99%.

Hysteretic magnetoresistance in superconducting SrTiO3/LaAlO3/SrTiO3 trilayer interface system

We investigated the electrical transport properties of the SrTiO3/LaAlO3/SrTiO3 (STO/LAO/STO) trilayer interface system. We found that the trilayer exhibits superconductivity at temperatures below 0.2 K. In the superconducting regime, the magnetoresistance (MR) of the system shows pronounced hysteresis, possibly due to the interplay of ferromagnetism and superconductivity. The magnitude of MR hysteresis strongly depends on the magnetic field sweep rate, and we observed a threshold field-sweep rate below which no MR is detected. At high sweep rates, the MR exhibits superconducting-normal-superconducting transition behavior. To explain these observations, we propose a model based on the ohmic heating from superconducting phase slip centers beneath Bloch-type magnetic domain walls in the ferromagnetic layer. Furthermore, we observed complex features in the MR curves that are likely due to domain wall motion in the system.

The Coupling of Dihydroxybenzene Derivatives to MWCNT and Electrochemical NADH Oxidation

3,4 and 2,5- dihydroxybenzene compounds were separately and covalently coupled to the multiwalled carbon nanotube (MWCNT) deposited on the surface of glassy carbon electrode through electrochemical reduction of diazonium compound of benzylamine bearing Boc protecting group (tert-butyloxycarbonyl). Following the removal of the Boc group, an amide bond was formed between the amine-terminated surface and the acyl group of the dihydroxybenzene derivatives. The electrochemical properties of dihydroxybenzene-modified MWCNT and the influence of the sweep rate on the voltammogram were elucidated by cyclic voltammetry (CV). Electron transfer kinetics of modified MWCNT by dihydroxybenzene derivatives was also studied using Laviron’s theory. As evidenced by an improvement in the anodic peak current and a negative shift in the overpotential of NADH oxidation when compared to the bare MWCNT, 3,4 and 2,5- dihydroxybenzene modified MWCNT electrodes were shown to possess catalytic activity toward NADH oxidation.

ELECTROCHEMICAL REDUCTION OF CADMIUM IONS FROM ETHYLENE GLYCOL ELECTROLYTE

The work is devoted to the study of the process of cathodic reduction of Cd ions from anhydrous ethylene glycol electrolyte. The mechanism of the process of cadmium reduction was studied by taking linear and cyclic potentiodynamic polarization curves. The influence of cadmium chloride concentration, potential sweep rate and temperature on the process of electrochemical deposition of cadmium ions was studied. With an increase in the concentration of cadmium in the electrolyte, the rate of its release at the cathode increases. Precipitates of good quality are obtained at current densities of 25 mA/sm2. It has been established that the cadmium deposition potential almost does not change with increasing potential sweep rate. The dependence of cadmium electrodeposition from ethylene glycol electrolyte on temperature was studied, which made it possible to establish the optimal deposition temperature, which was 363–373 K, and to conclude that the deposition process is controlled by electrochemical polarization. The diffusion coefficient of cadmium ions to the cathode surface has been calculated

How do proton-transfer reactions affect current-voltage characteristics of anion-exchange membranes in salt solutions of a polybasic acid? Modeling and experiment

Insufficient understanding of transport mechanism of polybasic acid species (phosphoric, citric, malic, etc.) through anion-exchange membranes (AEMs) hinders the widespread use of electrodialysis for processing salt solutions of such acids, e.g. the recovery of phosphates from mixed solutions. In this paper, we present experimental current-voltage characteristics (CVC) and partial fluxes of H2PO4− and HPO42− across an AEM. These data are simulated using a mathematical model based on the Nernst-Planck-Poisson equations coupled with the kinetic equations for chemical reactions. The model describes the nonstationary transport of phosphate acid species through an AEM and adjacent solution diffusion boundary layers. It is shown that the proton-transfer reactions determine the occurrence of two limiting currents. The electric current sweep rate and the values of dissociation rate constants of acid anions largely affect the values of these limiting currents and generally the shape of the CVC. It is found that due to chemical reactions involving polybasic anions, the formation of their concentration profiles in the membrane occurs much slower than in the case of monobasic salts. Numerical simulation shows that a quasi-stationary CVC is possible only when the current sweep rate is such that measurements are carried out for at least 10 h.

Thermally tuned VCSEL at 850 nm as a low-cost alternative source for full-eye SS-OCT.

Swept-source optical coherence tomography (SS-OCT) demonstrates superior performance in comparison to spectral domain OCT with regard to depth ranging. The main driver of cost for SS-OCT systems is, however, the price of the source. Here we show a low-cost alternative swept source that uses a thermally tuned vertical-cavity surface-emitting laser (VCSEL) at 850 nm. Its center wavelength can be tuned by adjusting the operating temperature through modulation of the injection current. At 2 kHz sweep rate, the depth range of the system was 5 cm, with a sensitivity roll-off of under -3 dB across this range. The system achieved a sensitivity of 97 dB with a sample beam power of 0.3 mW and an axial resolution of 50 µm in air. To demonstrate the system performance in vivo, an eye of a healthy volunteer was measured, and full-eye scans were acquired at 25 and 50 kHz from the cornea to the retina. Based on our results, we believe that this technology can be used as a cost-effective alternative OCT for point-of-care diagnostics.

Enhancing asymmetric supercapacitor performance with NiCo2O4–NiO hybrid electrode fabrication

Spinel metal oxide with an extra crystalline phase is an active way to enhance the performance of the supercapacitor. Herein, a facile hydrothermal approach has been established for synthesizing nanocrystalline NiCo2O4 with an extra NiO phase material as the potential electrode for a supercapacitor. XRD analysis is executed to expose the crystalline environment and found to be dual phases ie. NiO and NiCo2O4. Further, the chemical environment of these phases is identified in FTIR, EDS, X-ray photoelectron spectroscopy, elemental mapping, and Raman analysis. The morphological analysis (SEM) of the material showed that the formation of tiny particulates aggregates become uniform in size, which consists of a nearly spherical structure. NiCo2O4–NiO showed a remarkable electrochemical performance in a 2 M potassium hydroxide. The maximum capacitance was achieved as 866 F/g at a sweep rate of 5 m V/s, which is quite higher than the normal pristine NiCo2O4. The material delivered a capacity retention of 85% over 5000 cycles. This high performance was attributed to the NiO phase in NiCo2O4 material inducing an additional charge at the boundary, prominent to synergistic effect and rapid electron and ion passage. Hence, overall, the superior performance with extra NiO phase could be beneficial for developing spinel metal oxide electrodes for battery-type supercapacitor applications.

Symmetrical Composite Supercapacitor Based on Activated Carbon and Cobalt Nanoparticles with High Cyclic Stability and Current Load

Supercapacitors play an important role in a future clean-energy landscape to meet the challenges of existing energy-storage/delivery systems. They suffer from low energy density and are mainly used for the storage/delivery of electrical energy in high power demands. However, improvement of their energy density is vital to develop energy storage systems that can respond to the energy demands of emerging technologies requiring a wider energy/power spectrum. In this article, a symmetrical capacitor is developed from a composite consisting of synthesized activated carbon and cobalt oxide to improve the energy storage performance of the supercapacitor. Uniform distribution and immobilization of cobalt nanoparticles within the composite is achieved by embedding cobalt acetate into the initial resorcinol formaldehyde polymeric aerogels, followed by the pyrolysis of the gel in Ar atmosphere and activation of the carbon in CO2 atmosphere at 800 °C. The activated carbon/cobalt composite is used as the electroactive material in electrode formulation. The electrochemical characteristics of the synthesized electrode materials demonstrates an optimized specific capacitance of 235 F g−1 at a sweep rate of 10 mV s−1 in a three-electrode system. The symmetrical capacitor has a capacitance of 66 F g−1 at 1 A g−1, a very high rate of performance in 10,000 cycle tests, and a rate capability of 24% at 30 A g−1. The capacitor shows a power density of up to 15 Wh k g−1. The presence of cobalt spices makes it possible to optimize the capacitance of a symmetrical capacitor, while the capacitance of a symmetrical activated carbon capacitor cannot be optimized.

Developing an oxygen-induced capacitive hard carbon anode for fast sodium ion storage through pore-scale engineering

Sodium-ion capacitors are highly promising for bridging the gap between high-power-density supercapacitors and high-energy-density batteries. However, developing appropriate battery-type anodes to boost Na+ transfer remains a major challenge. Herein, we manufacture a capacitive hard carbon anode with multiple pore-scale and oxygen-functionality surfaces by a sulfonation-assisted etching technique, featuring a large capacity (372.8 mAh g−1 at 0.035 A g−1), superior rate capability (129.6 mAh g−1 at 20 A g−1) and decent long-cycle stability. The synergistic effect of meso-macropores and C=O facilitates fast Na-ion migration and surface pseudocapacitive reaction, achieving 70% capacitive contribution even at a low sweep rate of 0.2 mV/s110.2 mV s-1.. These mechanisms are validated by complementary EIS, GITT, ex-situ XPS, and DFT analyses. Outstandingly, the assembled sodium-ion capacitor delivers very high energy (53.5 Wh kg−1) and power densities (17.5 kW kg−1) simultaneously. This work provides a new approach to tune the oxygen-containing functional groups in hard carbon for enhancing Na-ion storage performance toward practical applications.

Biowaste-derived oxygen-self-doped three-dimensional interconnected porous carbon for electrochemical supercapacitor applications

ABSTRACT Biowaste for producing a biomaterial is an inexpensive, profuse, widely available, and viable natural source and has been extensively investigated and applied in a wide range of research fields. In this work, jackfruit leaf waste as a biowaste source was utilized to prepare a three-dimensional (3D) interconnected porous carbon framework self-doped with oxygen by KOH impregnation, carbonization, and activation under a CO2 atmosphere. The as-prepared porous carbon has a 3D interconnected porous framework with a rich oxygen content of 36.82%, and high BET surface area of 455.687 m2 g−1 with a pore volume of 0.522 cm3 g−1. The 3D interconnected porous framework exhibits a high specific capacitance of 199 F g−1 with a maximum energy density of 27.64 Wh kg−1 at a power density of 99.60 W kg−1 at a sweep rate of 1 mV s−1 in a two-electrode setup. The correlation between structure and great performance of electrode materials is deeply studied. The great capacitive performance of porous carbon materials can be assigned to its 3D interconnected porous framework, high specific surface area, suitable pore size distributions, and advantageous heteroatom-doping, resulting in the rapid ion diffusion and sufficient charge storage along with the contributed pseudocapacitance behavior. Hence, the exciting results reveal an efficient, cost-effective, time-saving, and facile method to prepare 3D interconnected porous carbon frameworks self-doped with oxygen derived from natural biowaste sources for developing supercapacitor devices.

Hysteresis in Organic Electrochemical Transistors: Relation to the Electrochemical Properties of the Semiconductor

The ability to bridge ionic and electronic transport coupled with large volumetric capacitance renders organic electrochemical transistors (OECTs) ideal candidates for bioelectronic applications. Adopting ionic-liquid-based solid electrolytes extends their applicability and facilitates large-area printable productions. However, OETCs employing solid electrolytes tend to show a pronounced hysteresis in the transfer curve. A detailed understanding of the hysteresis is crucial for their accurate characterizations and reliable applications. Here, we demonstrated fully photopatternable poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:Tos)- based OECTs incorporating the ionic liquid [EMIM][EtSO4] in a solid electrolyte (SE). The PEDOT:Tos films deposited through vapor phase polymerization (VPP) were annealed for different durations after the polymerization step. Upon rinsing with ethanol and the deposition of the SE, the OECTs made of these films showed impressive bias stress stability under prolonged operation cycles, a high switching ratio, a low threshold voltage, and a high transconductance. Furthermore, by taking transfer measurements with different sweep rates, we revealed two distinct regimes of hysteresis: kinetic hysteresis and non-kinetic hysteresis. We observed pronounced changes in these regimes after annealing. Finally, impedance spectroscopy exhibited that the PEDOT:Tos turned from a Faradaic to a non-Faradaic response through annealing, explaining the observed hysteresis changes in both regimes.

Quantum irreversibility of quasistatic protocols for finite-size quantized systems

Quantum mechanically, a driving process is expected to be reversible in the quasistatic limit, also known as the adiabatic theorem. This statement stands in opposition to classical mechanics, where a mix of regular and chaotic dynamics implies irreversibility. A paradigm for demonstrating the signatures of chaos in quantum irreversibility is a sweep process whose objective is to transfer condensed bosons from a source orbital. We show that such a protocol is dominated by an interplay of adiabatic-shuttling and chaos-assisted depletion processes. The latter is implied by interaction terms that spoil the Bogoliubov integrability of the Hamiltonian. As the sweep rate is lowered, a crossover to a regime that is dominated by quantum fluctuations is encountered, featuring a breakdown of quantum-to-classical correspondence. The major aspects of this picture are not captured by the common two-orbital approximation, which implies failure of the familiar many-body Landau-Zener paradigm.

Statistical Analysis of Electromagnetic Ion Cyclotron Rising‐Tone Emissions Based on Deep Learning

AbstractSeveral studies have shown the importance of electromagnetic ion cyclotron (EMIC) rising‐tone emissions to the rapid precipitation of energetic radiation belt electrons. Based on a large number of Van Allen Probes observations from October 2012 to July 2019, we identify EMIC rising‐tone emissions using a convolutional neural network (CNN), a modern deep learning technique. Results of training indicate that the CNN is capable of identifying EMIC rising‐tone emissions with a recall of 99.3%. The statistical analysis of the wave events identified reveals that the average occurrence rate of the events is about 0.016%, with a high occurrence rate from the forenoon to the dusk sector at L > 5. There are also events observed at L < 5, which are scattered at almost all magnetic local times. The events in the hydrogen and helium bands have comparable wave amplitudes on average, but the larger amplitude events tend to occur around noon and in the afternoon sector in the hydrogen and helium bands, respectively. In addition, the frequency sweep rate tends to increase with the wave frequency. The frequency sweep rates of the hydrogen band EMIC rising‐tone emissions are about 6 times larger than those of the helium band events. There is also a positive correlation between the wave amplitudes and the sweep rates of the hydrogen band emissions.

Anode Process on Platinum in Low Temperature KF-AlF3-Al2O3 Based Melts: An Update

The present paper is devoted to obtaining new fundamental data on the electrochemical behavior of oxygen-evolving anodes in fluoride-oxide melts. In this work, the function of platinum and basics of its anode behavior as an ideal oxygen-releasing anode during electrolysis of the low temperature KF-AlF3-Al2O3 based melt were studied by potentiometric, cyclic voltammetric, and chronopotentiometric methods. The influence of the electrolyte composition, temperature, atmosphere, potential sweep rate, current density on the kinetics of the anode process was investigated. In order to clarify the mechanism of the process under study, electrolysis testing was carried out to inform an analysis of platinum oxidation products. Based on the experimental results, the validity of an earlier proposed scheme of the anode process on platinum when carrying out electrolysis of low temperature KF-AlF3-Al2O3 based melts was confirmed. Results will be used for theoretical modeling and studying the kinetics of the anode process on an over oxygen-evolving anodes in the fluoride-oxide melts.

Time and temperature dependent magnetic viscosity experiments on Sr/Co nanoferrite particles

Magnetic viscosity experiments have been performed in order to investigate the magnetization reversal in Sr nanoferrite particles (nanoscale SrFe12O19) and interacting Sr/Co nanoferrite particles (SrFe12O19–CoFe2O4 nanocomposites). The magnetic viscosity S = d M ( t ) / d l n ( t ), where M ( t ) is the magnetization as a function of time, has been collected. For Sr nanoferrite S shows a maximum close to the coercive field, reflecting the relation between S and the energy barrier distribution. We evidence that magnetic viscosity experiments on Sr nanoferrite and interacting Sr/Co nanoferrite particles provide reliable qualitative results for the different magnetic field sweep rate and saturating field H s a t considered. In addition, the activation volumes extracted from the magnetic viscosity experiments performed at different temperatures on Sr nanoferrite are quantitatively correlated to anisotropy changes.

Sodium Stoichiometry Tuning of the Biphasic-Nax MnO2 Cathode for High-Performance Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are promising alternatives for large-scale energy storage owing to the rich resource and cost effectiveness. However, there are limitations of suitable low-cost, high-rate cathode materials for fast charging and high-power delivery in grid systems. Herein, a biphasic tunnel/layered 0.80Na0.44 MnO2 /0.20Na0.70 MnO2 (80T/20L) cathode delivering exceptional rate performance through subtly regulating the sodium and manganese stoichiometry is reported. It delivers a reversible capacity of 87mAhg-1 at 4Ag-1 (33C), much higher than that of tunnel Na0.44 MnO2 (72mAhg-1 ) and layered Na0.70 MnO2 (36mAhg-1 ). It proves that the one-pot synthesized 80T/20L is able to suppress the deactivation of L-Na0.70 MnO2 under air-exposure, which improves the specific capacity and cycling stability. Based on electrochemical kinetics analysis, the electrochemical storage of 80T/20L is mainly based on pseudocapacitive surface-controlled process. The thick film of 80T/20L cathode (a single-side mass loading over 10mgcm-2 ) also has superior properties of pseudocapacitive response (over 83.5% at a low sweep rate of 1mVs-1 ) and excellent rate performance. In this sense, the 80T/20L cathode with outstanding comprehensive performance could meet the requirements of high-performance SIBs.

Simultaneous Heavy Metal Determination in Mussels by Anodic Stripping Voltammetry (ASV) Using Thick Film Modified Graphite Electrodes

Heavy metals are potent polluters of marine ecosystems. Consumption of contaminated seafood may lead to adverse health effects. In this work, thick film modified graphite sensors are used as working electrodes for the simultaneous determination of copper, lead, cadmium and zinc in mussel tissue from the Sea of Japan. The samples were prepared by HNO3 wet mineralization and analyzed in pH 4 acetate buffer by anodic stripping voltammetry. The analytical signal was studied as a function of accumulation potential, accumulation time, and sweep rate to determine the optimal electrolysis conditions. Standard addition method was used to evaluate the heavy metal concentrations to minimize matrix effects. The developed procedure is rapid, inexpensive, and reproducible, and has high selectivity and low limits of detection for the analytes. The relative standard deviations for the concentrations of Cu, Pb, Cd, and Zn are 13%, 21%, 7.7%, and 15%, respectively. The accuracy was confirmed by comparing the results with those obtained by inductively coupled plasma – optical emission spectrometry (ICP-OES) and inductively coupled plasma – mass spectrometry (ICP-MS).

Effect of calcium doping on the anodic behavior of E-AlMgSi (Aldrey) conducting aluminum alloy in NaCl electrolyte medium

The design of new materials intended for operation under severe conditions faces the task of rendering the materials corrosion resistant. The practical solution of this task is interrelated with the knowledge of corrosion protection of metals and alloys. The use of conducting aluminum alloys for the manufacture of thin wire may encounter specific problems. This is caused by the insufficient strength of these alloys and a small number of kinks before fracture. Aluminum alloys have been developed in recent years which even in a soft state have strength characteristics that allow them to be used as a conductive material. The E-AlMgSi (Aldrey) aluminum alloy is a well-known conducting alloy. This alloy is a heat-strengthened one, possessing good plasticity and high strength. After appropriate heat treatment this alloy acquires high electrical conductivity. Wires made from this alloy are almost exclusively used for air transmission lines. This work presents data on the corrosion behavior of calcium containing E-AlMgSi (Aldrey) aluminum conducting alloy in 0.03, 0.3 and 3.0% NaCl electrolyte medium. The anodic behavior of the alloy has been studied using a potentiostatic technique with a PI-50-1.1 potentiostat at a 2 mV/s potential sweep rate. Calcium doping of the E-AlMgSi (Aldrey) aluminum alloy increases its corrosion resistance by 15–20%. The corrosion, pitting and repassivation potentials of calcium doped alloys shift toward the positive region. An increase in the sodium chloride electrolyte concentration leads to a decrease in these potentials.

Effect of calcium doping on the anodic behavior of E-AlMgSi (Aldrey) conducting aluminum alloy in NaCl electrolyte medium

The design of new materials intended for operation under severe conditions faces the task of rendering the materials corrosion resistant. The practical solution of this task is interrelated with the knowledge of corrosion protection of metals and alloys. The use of conducting aluminum alloys for the manufacture of thin wire may encounter specific problems. This is caused by the insufficient strength of these alloys and a small number of kinks before fracture. Aluminum alloys have been developed in recent years which even in a soft state have strength characteristics that allow them to be used as a conductive material. The E-AlMgSi (Aldrey) aluminum alloy is a well-known conducting alloy. This alloy is a heat-strengthened one, possessing good plasticity and high strength. After appropriate heat treatment this alloy acquires high electrical conductivity. Wires made from this alloy are almost exclusively used for air transmission lines. This work presents data on the corrosion behavior of calcium containing E-AlMgSi (Aldrey) aluminum conducting alloy in 0.03, 0.3 and 3.0% NaCl electrolyte medium. The anodic behavior of the alloy has been studied using a potentiostatic technique with a PI-50-1.1 potentiostat at a 2 mV/s potential sweep rate. Calcium doping of the E-AlMgSi (Aldrey) aluminum alloy increases its corrosion resistance by 15–20%. The corrosion, pitting and repassivation potentials of calcium doped alloys shift toward the positive region. An increase in the sodium chloride electrolyte concentration leads to a decrease in these potentials.