Current-time Response Research Articles

Understanding the influence of cation and anion migration on perovskite light-emitting diodes via transient response

Despite the rapid progress demonstrated in the efficiency of Perovskite light-emitting diodes (PeLEDs) in the past few years, ion migration has challenged the practical applications of these devices with undesirable hysteresis and degradation effect. Mobile ions in PeLEDs induced many unique and fast transient phenomena occurring on the time scale of microseconds to seconds and it is still far from clear how the underlying physical mechanism of ion motion-induced variation relates to the device performance. Therefore, in this work, we employ an ionic Drift–Diffusion Model (DDM) to evaluate measuring transient current response in a time scale of sub-seconds. The results show that spatial redistribution of ions within the perovskite results in dynamic electric field variation, which in turn, affects charge carrier injection and distribution. Moreover, the time delay between anion and cation migration leads to an unequal rate of charge carrier injection, hence the multi-stage behavior of the current–time response. It is also realized that the potential barrier of charge injection due to cation and anion accumulation at perovskite interfaces with electron and hole transporting layers reduces. Therefore, the facilitation of charge injection favors radiative recombination, and improved IQEs are expected at higher ion densities. It is found that the current–time response of the device gives beneficial information on cation and anion migration time scales. Choosing an appropriate scan rate in accordance with cation-related slow migration time is the first step to achieving reliable measurement procedures and hysteresis-free PeLED.

A voltage waveform design method for shortening current response time of a coil

SummaryCoils are widely used in magnetorheological dampers, solenoid valves, and electron guns, where a quick response of the magnetic induction to the excitation voltage is needed. To achieve a quick response, the response time of the magnetic induction relative to the current and that of the current relative to the voltage should be shortened as much as possible. The latter is dominant in the total response time and can be shortened by using voltage control with an increased resistance or current control. The current time responses of the Helmholtz coils based on voltage control with an increased resistance and current control are measured. The results indicate that the current response times of the coils based on voltage control with resistances of 23.7 and 162 Ω and current control with a resistance of 23.7 Ω are 235.3, 42.3, and 62.1 μs, respectively. The current time responses of the voltage control are smooth, while those of the current control have large oscillations. Based on Kirchhoff's equilibrium equation, an overshoot voltage waveform design method is proposed to shorten the current response time and eliminate the current oscillations. The experimental results show that the current time response is smooth, and the current response time can be shortened by 91.8%, 54.4%, and 68.9% in comparison with those of the former three control cases. The demonstration experiments of the effect of the different control methods on the electron‐beam scanning path and hot spot distribution show that the scanning path and dwell duration are closer to the expected ones with the proposed method. The proposed method is of great value for improving the damping performance of a magnetorheological damper, the accuracy of the fluid injection of a solenoid valve, and the accuracy of the electron‐beam thermal assessment.

Oxide Film Formation on Stainless Steel 304L by Anodizing Method with Different Power Sources

In order to generate a nanoporous oxide film, stainless steel 304L is anodized using an alternating current (AC) and direct current (DC) source in an ethylene glycol solution containing ammonium fluoride, NH4F, and water, H2O. This study focuses on the differences between AC and DC anodizing in terms of current density versus time response, thickness, and depth of the oxide film formed on the anodized specimens, surface roughness, and element composition of the specimens because there is limited study on AC anodizing of stainless steel. In 0.5% 0.3M NH4F and 3% H2O in a glycol solution, the AC and DC anodizing is conducted for 30 minutes at voltages ranging from 30 V to 50 V and 21.2 V to 35.4 V, respectively. The current density versus time response revealed that AC anodizing produced more current density than DC anodizing. As for the thickness and depth of the generated oxide films, only the specimens that had been anodized in AC indicated an increase in these films, whereas specimens that had been anodized in DC showed the metal dissolving as the specimens degraded. The surface roughness of AC anodized specimens reduced with increasing anodizing voltage, whereas DC anodized specimens increased with increasing anodizing voltage. The element composition of the anodized specimens revealed that the mass percentage of oxygen, O element is higher for AC anodized specimens compared to DC specimens. This suggests that AC anodizing on stainless steel might offer important advantages and should be further researched.

Model of Chronoamperometric Response towards Glucose Sensing by Arrays of Gold Nanostructures Obtained by Laser, Thermal and Wet Processes.

Non-enzymatic electrochemical glucose sensors are of great importance in biomedical applications, for the realization of portable diabetic testing kits and continuous glucose monitoring systems. Nanostructured materials show a number of advantages in the applications of analytical electrochemistry, compared to macroscopic electrodes, such as great sensitivity and little dependence on analyte diffusion close to the electrode-solution interface. Obtaining electrodes based on nanomaterials without using expensive lithographic techniques represents a great added value. In this paper, we modeled the chronoamperometric response towards glucose determination by four electrodes consisting of nanostructured gold onto graphene paper (GP). The nanostructures were obtained by electrochemical etch, thermal and laser processes of thin gold layer. We addressed experiments obtaining different size and shape of gold nanostructures. Electrodes have been characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry, and chronoamperometry. We modeled the current-time response at the potential corresponding to two-electrons oxidation process of glucose by the different nanostructured gold systems. The finest nanostructures of 10-200 nm were obtained by laser dewetting of 17 nm thin and 300 °C thermal dewetting of 8 nm thin gold layers, and they show that semi-infinite linear diffusion mechanism predominates over radial diffusion. Electrochemical etching and 17 nm thin gold layer dewetted at 400 °C consist of larger gold islands up to 1 μm. In the latter case, the current-time curves can be fitted by a two-phase exponential decay function that relies on the mixed second-order formation of adsorbed glucose intermediate followed by its first-order decay to gluconolactone.

The Enzymatic Doped/Undoped Poly-Silicon Nanowire Sensor for Glucose Concentration Measurement.

In this work, enzymatic doped/undoped poly-silicon nanowire sensors with different lengths were fabricated using a top-down technique to measure glucose concentration. The sensitivity and resolution of these sensors correlate well with the dopant property and length of nanowire. Experimental results indicate that the resolution is proportional to the nanowire length and dopant concentration. However, the sensitivity is inversely proportional to the nanowire length. The optimum resolution can be better than 0.02 mg/dL for a doped type sensor with length of 3.5 μm. Furthermore, the proposed sensor was demonstrated for 30 applications with similar current-time response and showed good repeatability.

Preparation, characterization, and electrochemical sensing performance of a novel pristine Cd-MOF and its composite with carbon nanotubes.

A novel Cd(II)-organic framework (Cd-MOF) {[Cd(isba)(bbtz)2(H2O)]·H2O}n (1) and its composite with CNTs (Cd-MOF@CNTs), [H2isba = 2-iodo-4-sulfobenzoicacid; bbtz = 1, 4-bis(1,2,4-triazolyl-1-methyl)benzene], were synthesized successfully under ambient conditions. The Cd-MOF is a 2D (4, 4) topological framework, further extending into a two-fold interpenetrated 3D supramolecular network via hydrogen bonding. The activation energy for proton transfer in the composite Cd-MOF@CNT/Nafion membrane is lower than that in pristine Cd-MOF/Nafion, leading to its more temperature-insensitive proton conductivity. Hence, the proton conduction of the composite Cd-MOF@CNT/Nafion membrane was greatly improved. Cyclic voltammograms indicate that the Cd-MOF/GCE only has an oxidation peak with the peak potential suitable for the oxidation of glucose in 0.1 M NaOH. The i-t current response demonstrates that the Cd-MOF/GCE exhibits sensitive and selective oxidative sensing of glucose in the linear range of 0-5 mM with a limit of detection (LOD) of 9.64 μM. Different from the pristine Cd-MOF, Cd-MOF@CNTs shows a pair of irreversible redox peaks with an anodic peak potential appropriate for the glucose oxidation and a cathodic peak potential suitable for the hydrogen peroxide reduction in 0.1 M NaOH. So, the Cd-MOF@CNTs/GCE can be used not only for the electrocatalytic oxidation of glucose, but also for the electrocatalytic reduction of H2O2. The current-time response curve demonstrates that the Cd-MOF@CNTs/GCE exhibits more sensitive and selective oxidative sensing for glucose exponentially in the 0-18.5 mM range with a lower LOD down to 2.63 μM. The reductive sensing of H2O2 increases linearly in the range of 0-14.0 mM (LOD = 33.70 μM). Moreover, the Cd-MOF@CNTs/GCE can detect glucose and H2O2 efficiently in real-world samples. Cd-MOF@CNTs may act as a dual non-enzymatic electrochemical sensory material for glucose and H2O2.

Proton conduction and electrochemical glucose sensing property of a newly constructed Cu(II) coordination polymer

The assembly between 5-sulfo-1, 2, 4-benzoic acid (H4SBTB) and Cu2+ in the presence of 4, 4´-bipyridine (Bipy) results in a novel ionic coordination polymer with two crystallographically independent hexa-coordinated Cu1 and Cu2 ions, namely, [Cu3(HSBTB)2(Bipy)3(H2O)8]n (1), which consists of an anionic Cu12(C1O1O2)2-Bipy-bridged double-chain and a cationic Cu2-Bipy-bridged mono-chain. With the aid of H-bonds, the anionic Cu12(C1O1O2)2-Bipy-bridged double-chains extend into a 2D supramolecular anionic double-layer, which is further linked by the cationic Cu2-Bipy-bridged mono-chain, resulting in a 3D supramolecular network. The H4SBTB acid exhibits a new coordination mode, i.e. one carboxyl group still remains protonated in 1. The analysis of the solid-state diffuse reflectance UV-Vis-NIR spectrum reveals that the indirect bandgap exists in 1, which was further illustrated by the theoretical calculation on the basis of Density Functional Theory (DFT) using the CASTEP program. The electrochemical studies indicate that the composite membrane of 1 with nafion shows interesting temperature-insensitive proton conduction behavior at pH = 3. Cyclic voltammograms indicate that 1 exhibits electrocatalysis to glucose oxidation in 0.1 M NaOH. The current-time (i-t) response curves reveal that 1 demonstrates sensitive and selective electrochemical oxidation sensing of glucose with an exponential detection range of 0-30 mM. The limit of detection (LOD) was calculated to be 38.74 μM.

Straw-sheaf-like Co3O4 for preparation ofanelectrochemical non-enzymatic glucose sensor.

3D straw-sheaf-like cobalt oxide (SS-Co3O4) was prepared via the hydrothermal method and inert gas calcination of precursors without the assistance of any template or surfactant. It was composed of numerous nanoneedles with a length of ~ 8µm and a diameter of ~ 30nm strongly tied in the center. The SS-Co3O4 exhibited high crystallinity, a large surface area (39.01 m2.g-1), a smaller pore size (6nm), and lower charge transfer resistance (Rct = 9.35 Ω) at the electrode/electrolyte interface. A non-enzymatic glucose oxidizing electrode fabricated with SS-Co3O4 showed a high sensitivity (669 µA.mM-1.cm-2), wide linear range (0.04-4.85mM), low limit of detection (0.31µM), good selectivity, fast response time (5s), and high reproducibility with a relative standard deviation of 2.25%. In addition, its robust structure demonstrated excellent electrochemical stability by retaining 83.8% of the initial sensitivity when its current density vs. time response was measured for 75min in bare electrolytes prior to the glucose-sensing test. Furthermore, it demonstrated excellent repeatability performance by retaining 87.0% of the initial sensitivity when a single electrode was tested for 4 cycles. The proposed robust structured 3D SS-Co3O4 electrode successfully responds to the content of glucose in human saliva, which substantially proves its suitability in practical application. The synthesis technique is advantageous to prepare other metal oxides with interesting morphology and robust structure for the development of more reliable non-enzymatic glucometers and other electrochemical devices.

Electrochemical Studies on Interactions of Cu<sup>2+</sup>, Zn<sup>2+</sup> and Cd<sup>2+</sup> with Leucine and Isoleucine

The interaction of some divalent metal ions with leucine (leu) and isoleucine (ile) was studied in aqueous solution. Electrochemical techniques like cyclic voltammetry, chronoamperometry and chronocoulometry were used for this study. The electrochemical study demonstrates that the maximum interaction of each metal ion occurs with two deprotonated ligand. The metal ions exchange electrons quasi-reversibly in presence of the ligands and some sort of chemical reaction may be competing with diffusion process at the electrode surface. The current-time and charge-time response accounts for the adsorption of reactant or product or both at the electrode surface. Dhaka Univ. J. Sci. 69(3): 230-237, 2022 (June)

Small signal analysis of an infrared imaging device based on equivalent circuit model

This paper presents an analytical model of an infrared thermal imaging device. This device is composed of a Quantum Well Infrared Photodetector (QWIP), a Heterojunction Bipolar transistor (HBT) and a Light Emitting Diode (LED). It is called as QWIP-HBT-LED Optoelectronic Integrated Device. The device is modeled based on its equivalent circuit by considering a nonlinear gain HBT, early effect. Analytical expressions describing the current time response, rise time, and output derivative as a measure of device speed have been derived. The numerical results show that the transient performance of this device version is enhanced by the injected current from QWIP to the base of HBT, also the output current is increased with the increase of the gain and early coefficient of HBT, on the other hand, it degrades when the base recombination factor of HBT or the load resistance is increased. Also, the rise time increases when the current gain or the early coefficient is increased. This type of models can be exploited as a pixel in thermal image processing applications.

Anodizing of Hydrogenated Titanium and Zirconium Films.

Magnetron-sputtered thin films of titanium and zirconium, with a thickness of 150 nm, were hydrogenated at atmospheric pressure and a temperature of 703 K, then anodized in boric, oxalic, and tartaric acid aqueous solutions, in potentiostatic, galvanostatic, potentiodynamic, and combined modes. A study of the thickness distribution of the elements in fully anodized hydrogenated zirconium samples, using Auger electron spectroscopy, indicates the formation of zirconia. The voltage- and current-time responses of hydrogenated titanium anodizing were investigated. In this work, fundamental possibility and some process features of anodizing hydrogenated metals were demonstrated. In the case of potentiodynamic anodizing at 0.6 M tartaric acid, the increase in titanium hydrogenation time, from 30 to 90 min, leads to a decrease in the charge of the oxidizing hydrogenated metal at an anodic voltage sweep rate of 0.2 V·s−1. An anodic voltage sweep rate in the range of 0.05–0.5 V·s−1, with a hydrogenation time of 60 min, increases the anodizing efficiency (charge reduction for the complete oxidation of the hydrogenated metal). The detected radical differences in the time responses and decreased efficiency of the anodic process during the anodizing of the hydrogenated thin films, compared to pure metals, are explained by the presence of hydrogen in the composition of the samples and the increased contribution of side processes, due to the possible features of the formed oxide morphologies.

Electrochemistry Under Microscope: Measuring the Thickness of Diffusion Layer in Thin Layer Electrochemical Cells with Optical Microscope

Electrochemical reactions are heterogeneous in nature, and an electrochemical reaction involves mass transfer from the bulk solution to the electrode surface, heterogeneous electron transfer at the electrode surface, and mass transfer back to the bulk solution. There are three modes of mass transport to the working electrode surface: diffusion, migration, and convection. Among these modes, diffusion is the one that involved in all electrochemical processes and sometimes is the sole mode of mass transfer. Thus, the key concept underpinning electrochemical science are that of the diffusion and diffusing layer, the region in the vicinity of an electrode layer that affected by electrode reaction. The thickness of diffusion layer is an important parameter in understanding chronoamperometry, cyclic and hydrodynamic voltammetry. The thickness of this zone can be measured either by simulation or analysis of the electrochemical responses. But interpretation of the concentration profiles and related current time responses require understanding the Fick’s law and its related mathematical representations. Although these basic are crucial in understanding electrochemistry but their mathematical representation is challenging specially for the students or scientists who are new to the field. The thickness of diffusion layer for a typical electroanalytical experiment varies between 20 to 200 micrometers, depends on the time of experiment. The size is not visible to the human eye easily but doesn’t required expensive research-grade microscopes and can be seen using even kids grade microscopes with 100 times magnification. Here we have developed a thin-layer electrochemical cell compatible with low-cost microscopes to demonstrate a microscopy activity in which students measure the thickness of micrometer-sized diffusion layer. The electrode processes involve the reactions of redox indicators with sharp color changes or acid base indicators with sharp color change in response to electrochemically generated proton or hydroxide, from water electrolysis. This Imaging tools advance electrochemistry education by enabling students to see the electrode processes that are not visible to the human eye without any research grade instrumentation. This device also aids in the explicit visualization and interpretation of a typical concentration profiles near the working electrode surface for chronoamperometry, cyclic and hydrodynamic (e.g., rotated disk) voltammetry experiments.

A facile hydrothermal reduction synthesis of multilayer flake Ag/Ni(OH)2 nanostructures and their electrocatalytic activity toward the oxidation of glucose

Multilayer flake Ag/Ni(OH)2 nanostructures are synthesized with a facile hydrothermal reduction method. In the preparation process, N, N-dimethylformamide (DMF) is used as a reducing agent, and polyvinylpyrrolidone (PVP) is used as a surfactant. The effects of several influencing factors such as the concentration of silver nitrate, reaction temperature and reaction time on the crystal phase of the products are characterized by X-ray diffraction (XRD) analysis. The morphology and chemical composition are characterized by Scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), Energy dispersive spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS). In a three-electrode system, the electrocatalytic oxidation activity of Ag/Ni(OH)2 nanostructures for glucose was tested by cyclic voltammetry (CV) curve, current-time (i-t) responses and electrochemical impedance spectroscopy (EIS). The results show that Ag/Ni(OH)2 modified glassy carbon electrode (GCE) has better catalytic activity for glucose than the Ni(OH)2 modified electrode.

Electrochemical quantification of accelerated FADGDH rates in aqueous nanodroplets

Enzymes are molecules that catalyze reactions critical to life. These catalysts are often studied in bulk water, where the influence of water volume on reactivity is neglected. Here, we demonstrate rate enhancement of up to two orders of magnitude for enzymes trapped in submicrometer water nanodroplets suspended in 1,2-dichloroethane. When single nanodroplets irreversibly adsorb onto an ultramicroelectrode surface, enzymatic activity is apparent in the amperometric current-time trace if the ultramicroelectrode generates the enzyme cofactor. Nanodroplet volume is easily accessible by integrating the current-time response and using Faraday's Law. The single nanodroplet technique allows us to plot the enzyme's activity as a function of nanodroplet size, revealing a strong inverse relationship. Finite element simulations confirm our experimental results and offer insights into parameters influencing single nanodroplet enzymology. These results provide a framework to profoundly influence the understanding of chemical reactivity at the nanoscale.

Effects of surface nanocrystallization on the anodic oxidation behavior of Aluminum

Gradient microstructures on the surface of metals induced by severe shot peening (SSP) is relatively a new research topic in the field of severe plastic deformation processing. The treated surface is known to show three distinct features: a spectrum of grain size from nanometer to sub-micron to micron regime, a work-hardened surface layer, and a compressive residual stress profile near the surface. The current study is defined to investigate the effects of SSP pre-preprocessing on the anodization behavior of Aluminum. Gradient microstructures were obtained on AA1050 Al substrate using SSP with different coverage levels. SSP was performed with ceramic media to prevent contamination of the treated surface. Then the treated surface was anodized at a constant voltage in a sulfuric acid solution. The current-time responses were recorded to study the reaction kinetics. The average grain size on the surface treated by SSP was evaluated to be 255.6 nm and 181.5 nm for 1000% and 2000% coverage levels, respectively, using X-ray diffraction; while the Vickers microhardness was increased from 10.8 HV for the untreated sample to 19.8 HV and 25.8 HV by SSP with 1000% and 2000% coverage levels, respectively. It was found that the nanocrystalline microstructure of Al substrate enhances the growth rate of anodic oxide. A variable growth rate is detected within the treated layer. The nucleation of anodic oxide nanopores is discussed in terms of underlying oxide formation mechanisms and the extent of surface grain refinement.

Enhanced electrocatalytic water oxidation using cobalt-based polyaniline hybrid assembly

This study investigates the performances of cobalt-based polyaniline hybrid electrocatalyst towards oxygen evolution reaction. The hybrid materials were prepared electrochemically using different deposition protocols. The prepared electrocatalyst proved to have low overpotential, high current density, high electrochemical surface area, and enhanced oxygen evolution performance. Current-time chronoamperometric response was used to study the stability of the electrode materials toward oxygen evolution. Scanning electron microscopy shows that the deposition protocols were associated with significant changes in the electrode materials' morphology. Energy-dispersive X-ray spectroscopy verifies the incorporation of metal ions and illustrates that different deposition protocols significantly alter the film composition. X-ray diffraction patterns indicate the preservation of the crystal structure of Co3O4 after deposition on ITO and Pan.

Revealing Dynamic Rotation of Single Graphene Nanoplatelets on Electrified Microinterfaces.

Nanoparticles interact with a variety of interfaces, from cell walls for medicinal applications to conductive interfaces for energy storage and conversion applications. Unfortunately, quantifying dynamic changes of nanoparticles near interfaces is difficult. While optical techniques exist to study nanoparticle dynamics, motions smaller than the diffraction limit are difficult to quantify. Single-entity electrochemistry has high sensitivity, but the technique suffers from ambiguity in the entity's size, morphology, and collision location. Here, we combine optical microscopy, single-entity electrochemistry, and numerical simulations to elucidate the dynamic motion of graphene nanoplatelets at a gold ultramicroelectrode (radius ∼5 μm). The approach of conductive graphene nanoplatelets, suspended in 10 μM NaOH, to an ultramicroelectrode surface was tracked optically during the continuous oxidation of ferrocenemethanol. Optical microscopy confirmed the nanoplatelet size, morphology, and collision location on the ultramicroelectrode. Nanoplatelets collided on the ultramicroelectrode at an angle, θ, enhancing the electroactive area, resulting in a sharp increase in current. After the collision, the nanoplatelets reoriented to lay flat on the electrode surface, which manifested as a return to the baseline current in the amperometric current-time response. Through correlated finite element simulations, we extracted single nanoplatelet angular velocities on the order of 0.5-2°/ms. These results are a necessary step forward in understanding nanoparticle dynamics at the nanoscale.

Measurement of Dissolved Oxygen Concentrations of Chloroaluminate Ionic Liquids in Dry Air

The electrodeposition of Al has been studied in various ionic liquids represented by the 1-ethyl-3-methylimidazolium chloride-AlCl3 system. However, AlCl3-based (chloroaluminate) ionic liquids are generally handled in an inert atmosphere of nitrogen or argon because they are highly hygroscopic and susceptible to hydrolysis through the reaction with moisture in the air. To maintain an inert atmosphere, a closed system that typically uses a glove box is required, but operation in a closed system leads to low productivity and high cost. Therefore, electrodeposition in an inert atmosphere is unsuitable for mass production on an industrial scale. To alleviate this problem, we have previously studied the feasibility of Al electrodeposition in dry air using chloroaluminate ionic liquids. Because the electrodeposition process in dry air does not require a glove box, it is considered to be more productive than the electrodeposition process under an inert atmosphere.In our previous study, four different chloroaluminate ionic liquids consisting of different organic cations ([cation]Cl-AlCl3) with a molar ratio of [cation]Cl : AlCl3 = 1 : 2 were used as Al electrodeposition baths to study Al electrodeposition behavior in dry air. The cations used were 1-ethyl-3-methylimidazolium (EMI+), 1-butylpyridinium (BP+), 1-butyl-1-methylpyrrolidinium (BMP+), and trimethylphenylammonium (TMPA+). We found that electrodeposition in dry air using the bath composed of EMI+ or BP+ could not produce an Al film covering the entire surface of the substrate, whereas electrodeposition using the bath composed of BMP+ or TMPA+ could produce an Al film covering the entire surface of the substrate in dry air as well as in an inert atmosphere.The reason for the difference in the results of Al electrodeposition in dry air according to cationic species has not yet been ascertained, but it is speculated that dissolved oxygen has some influence on the Al electrodeposition. In the present study, we measured the concentration of oxygen dissolved in four types of ionic liquids in dry air.For measuring the dissolved oxygen concentration, ionic liquids with a composition of [cation] Cl: AlCl3 = 1: 0.9 were used. This composition was chosen because only AlCl4 −, which is an ionic species that is difficult to be reduced to Al metal, is present in the bath when the AlCl3 mole fraction is less than 50 mol% (Lewis base)in chloroaluminate ionic liquids. Consequently, Al electrodeposition does not occur, and low extent of electrochemical reaction other than Al electrodeposition at a potential of 0 V vs. Al / Al (III) or less can be investigated. The concentration of dissolved oxygen was measured by chronoamperometry using two types of electrodes, a macroelectrode and a microelectrode, both of which have a circular active area with a diameter in the order of millimeter and micrometer, respectively. In the case of chronoamperometric measurement with a macroelectrode, the reduction current of oxygen follows the equation in the upper row in Table 1, assuming that the reaction rate is controlled by the planar diffusion of oxygen from the bulk electrolyte to the surface of the electrode. Upon measuring the current–time response, two unknowns remain, namely, the concentration and the diffusion coefficient of dissolved oxygen; and it is not possible to determine the dissolved oxygen concentration through the chronoamperometric measurement using the macroelectrode alone. In the case of chronoamperometric measurement with a microelectrode, the geometry of the diffusion of the reactant to the electrode surface changes to semi-spherical, and the reduction current of oxygen thus follows the equation in the lower row in Table 1. The concentration and diffusion coefficient of dissolved oxygen can thus be determined through the two chronoamperometric measurements.The chronoamperometric measurements revealed that there was no significant difference in the oxygen concentrations of the ionic liquids with different cationic species. The results that we have obtained so far are as follows: 1) In an inert atmosphere, an Al film covering the entire surface of the substrate can be electrodeposited from a bath containing any cation species. 2) In dry air, an Al film covering the entire surface of the substrate can only be electrodeposited from some baths composed of specific cation species. 3) There is no significant difference in the dissolved oxygen concentrations of the baths in dry air, even though the cation species in the baths are different. In consideration of these results, the reason for the different results of Al electrodeposition in dry air according to the cationic species is neither dissolved oxygen alone nor cationic species alone but the combined action of both dissolved oxygen and the cation. Figure 1

A hybrid of ultrathin metal-organic framework sheet and ultrasmall copper nanoparticles for detection of hydrogen peroxide with enhanced activity.

Here, we design and synthesize a novel 2D Cu-tetrakis(4-carboxyphenyl)porphyrin (TCPP) metal-organic framework (MOF) sheet and ultrasmall Cu5.4O nanoparticle (Cu5.4O USNP) hybrid (Cu-TCPP MOF/Cu5.4O nanocomposite). The graphene-like ultrathin Cu-TCPP MOF sheets offer high surface-to-volume atom ratios and many active sites, which is beneficial for loading more Cu5.4O USNPs. The Cu5.4O USNPs with ultrasmall size (<5nm) have promising conductivity and excellent enzymatic ability for H2O2. The successfully prepared nanocomposites are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) techniques. The 2D graphene-like ultrathin Cu-TCPP MOF sheets show no H2O2-sensing signals, whereas Cu5.4O USNPs exhibit a clear reduction peak for detection of H2O2. Interestingly, the combination of two kinds of nanomaterials improved the H2O2 sensing ability due to their synergistic effect. The properties of the unmodified electrodes and the Cu-TCPP MOF/Cu5.4O nanocomposite-modified electrodes were systemically studied by cyclic voltammetry (CV), current-time (i-t) response, and square-wave voltammetry (SWV) techniques. The electrochemical sensor for the detection of H2O2 based on the Cu-TCPP MOF/Cu5.4O nanocomposite has a lower detection limit of 0.13μmol·L-1 and wider linear range of 0.1 × 10-6 ~ 0.59 × 10-3mol·L-1 and 1.59 × 10-3 ~ 20.59 × 10-3mol·L-1 when compared with the Cu5.4O USNPs-modified electrode. The electrochemical sensor can be further used to detect H2O2 produced by cells. Graphical abstract The mechanism for sensing H2O2 produced from cells based on a Cu-TCPP MOF/Cu5.4O USNPs nanocomposite-modified electrode.

Fast terminal sliding mode control-based direct power control for single-stage single-phase PV system

Today, grid-connected photovoltaic systems have gained widespread penetration among renewable energy systems. For low power applications, a single-phase inverter with less power converter is a good compromise for high efficiency. The control must make it possible to extract the maximum power from the photovoltaic modules, ensure good dynamic performance for active and reactive power injection, ensure power quality, and reject disturbances and parameter mismatch. Besides, the controllers of the grid and PV sides should be coordinated. In this study, a fast terminal sliding mode control combined with Direct Power Control is proposed. Thanks to the two-cascaded control loops, simulations and experimental results with a 1 kW test bench have proven the proposal’s effectiveness in terms of dynamic performances and robustness to irradiance variations. Comparison with deadbeat-Direct Power Control, predictive control, and power hysteresis control shows that our proposal leads to lower Total Harmonic Distortion (3,5%) for the electrical grid’s current and lower time response (one-tenth of half the grid cycle).