Constant Charge Research Articles

Electropolymerized porphyrin films as active materials in organic supercapacitors. A study of the effect of different central metals

Four metallized (Zn, Co, Cu) and non-metallized AA-BB substituted porphyrins were used in the electrochemical synthesis of redox-conjugated polymers, formed as electroactive organic conducting films over solid substrate. Electrochemical and spectroelectrochemical characterization shows that these materials can undergo several (thousands) oxidation–reduction cycles without degradation or desorption from the electrode surface. Also, the electrochemical response and the spectral changes demonstrate that all the electroactive species present in the materials (tetrapirrolic ring, tetraphenylbenzidine and dicarbazole) are involved in fully reversible redox processes. Because of this, the supercapacitive capacity of these polymeric materials was analyzed. Constant current charge–discharge cycles and electrochemical impedance spectroscopy showed that the copper porphyrin-based polymer exhibited the highest gravimetric capacitance (332 F g−1), being also the material with the largest superficial roughness parameters, analyzed by atomic force microscopy. Using Cu(II) porphyrin dendrimeric polymer as active material, an electrochemically generated organic polymer-based supercapacitive device was assembled with a gelled-composited electrolyte.

Electronic properties of diamond semiconductor materials: based on response surface model

Abstract Diamond, a wide bandgap semiconductor material, has excellent physicochemical properties. It has great potential for application in high temperature, high frequency, high power electronic devices and other high technology fields. In order to study the electronic properties of diamond more precisely, an AM-response surface model is developed in this paper to investigate the electronic structures of diamond, P-doped diamond and N-doped diamond surfaces in depth. It is shown that there are three forms of charge states in the single vacancy on the diamond surface. When E=0 V, the negative charge energy level is -0.5 mV, the positive charge is 1 mV, and the zero level remains 0. And its energy level is unstable. In contrast, the double vacancy charge on the diamond surface varies depending on the valence band taken by E, and only one charge state exists. When E<0, the diamond surface vacant electron nature is negative charge state. When E>0, it is positive charge energy level. The electronic properties of the P-doped diamond semiconductor material are calculated to have a constant positive charge (1 mV). The electronic property of N-doped diamond semiconductor material is constant negative charge (-1mV).

Approximating constant potential DFT with canonical DFT and electrostatic corrections.

The complexity of electrochemical interfaces has led to the development of several approximate density functional theory (DFT)-based schemes to study reaction thermodynamics and kinetics as a function of electrode potential. While fixed electrode potential conditions can be simulated with grand canonical ensemble DFT (GCE-DFT), various electrostatic corrections on canonical, constant charge DFT are often applied instead. In this work, we present a systematic derivation and analysis of the different electrostatic corrections on canonical DFT to understand their physical validity, implicit assumptions, and scope of applicability. Our work highlights the need to carefully address the suitability of a given model for the problem under study, especially if physical or chemical insight in addition to reaction energetics is sought. In particular, we analytically show that the different corrections cannot differentiate between electrostatic interactions and covalent or charge-transfer interactions. By numerically testing different models for CO2 adsorption on a single-atom catalyst as a function of the electrode potential, we further show that computed capacitances, dipole moments, and the obtained physical insight depend sensitively on the chosen approximation. These features limit the scope, generality, and physical insight of these corrective schemes despite their proven practicality for specific systems and energetics. Finally, we suggest guidelines for choosing different electrostatic corrections and propose the use of conceptual DFT to develop more general approximations for electrochemical interfaces and reactions using canonical DFT.

Broad Electronic Modulation of Two-Dimensional Metal-Organic Frameworks over Four Distinct Redox States.

Two-dimensional (2D) inorganic materials have emerged as exciting platforms for (opto)electronic, thermoelectric, magnetic, and energy storage applications. However, electronic redox tuning of these materials can be difficult. Instead, 2D metal-organic frameworks (MOFs) offer the possibility of electronic tuning through stoichiometric redox changes, with several examples featuring one to two redox events per formula unit. Here, we demonstrate that this principle can be extended over a far greater span with the isolation of four discrete redox states in the 2D MOFs LixFe3(THT)2 (x = 0-3, THT = triphenylenehexathiol). This redox modulation results in 10,000-fold greater conductivity, p- to n-type carrier switching, and modulation of antiferromagnetic coupling. Physical characterization suggests that changes in carrier density drive these trends with relatively constant charge transport activation energies and mobilities. This series illustrates that 2D MOFs are uniquely redox flexible, making them an ideal materials platform for tunable and switchable applications.

Ensemble Learning and Voltage Reconstruction Based State of Health Estimation for Lithium-Ion Batteries With Twenty Random Samplings

Accurate estimation of state of health (SOH) is critical for the safe and efficient operation of lithium-ion batteries in electric transport tools. However, the random charge/discharge behaviors complicate online SOH estimation and discount estimation accuracy. To overcome this difficulty, this study presents an ensemble learning and voltage reconstruction-based SOH estimation framework through the incorporation of individual estimators and with the consideration of limited charging data. First, by analyzing more than 100 000 charging behaviors, the difficulty of feature extraction is addressed based on voltage distribution. Then, a voltage shape fitting method combing mechanistic and prognostic model is developed to reconstruct the constant current charge voltage, and the model parameters are identified by the moth-flame optimization algorithm. Next, the extreme learning machine and random forest are leveraged to estimate SOH preliminarily from the random discontinuous charging points with preferable diversity and high efficiency. On this basis, an induced ordered weighted averaging operator is exploited to efficiently integrate the individual learners and adaptively update the weight of each learner, thereby achieving better estimation than individual ones. The experimental results manifest that the SOH can be reliably estimated within an error of 3.42% using only 20 random samplings.

Effect of nano-enhanced phase change material on the thermal management of a 18650 NMC battery pack

Thermal control employing phase change material (PCM) for battery cooling application is quite well recognized throughout recent years. However, due to its limitations of poor thermophysical property, it is a less favoured thermal design for high voltage battery packs. Advanced nano-enhanced PCM appears to be particularly promising in PCM aided passive thermal design since it has greater higher thermal conductivity with acceptable latent heat. In present study, the CFD numerical analysis is developed considering battery pack operating at varying ambient temperature for 4S4P configured high voltage cathodic chemistry NMC 8:1:1 lithium-ion cell with 12Ah capacity and 14.2 network voltage. The objective of current study is to numerically investigate passive thermal performance of a battery pack, in which PCM is modeled based on enthalpy-porosity phase-change computational framework. A comparative thermal performance is investigated between conventional paraffin wax PCM and nano-enhanced Al2O3 PCM. The battery pack is considered operating at 1C and 2C constant charge rate with mimicked ambient temperature of 25°C and 35°C. Concluding results show, conventional paraffin wax PCM is incapable of providing better battery maximum temperature delay performance as compared to nano-enhanced PCM, this happens due to the poor heat transfer rate of conventional paraffin wax PCM which causes it to become liquidous state prematurely as compared to nano-enhanced PCM. Overall battery thermal effectiveness is found to be increased with nano-enhanced PCM as compared to conventional paraffin wax PCM.

Triboelectric polymer with excellent enhanced electrical output performance over a wide temperature range

Due to thermionic emission of triboelectric charge and degradation of mechanical stability of polymer tribomaterials (PTMs), PTMs based TENG (PTM-TENG) cannot maintain efficient electrical output and operate stably at high temperatures. Herein, a series of fatty acid doped PVDF-HFP (PH-FA) PTMs are fabricated. The introduction of FA lubricants dramatically increases the β-phase relative fraction, dielectric constant and surface charge potential of PTMs. Therefore, the PH-SA (stearic acid) based TENG shows improved electrical output over a wide temperature range, extraordinary stability, and durability. Particularly, the VT/VRoom, IT/IRoom and QT/QRoom of PH-SA at 100 °C are separately up to 231.10%, 251.46% and 234.01%, the output efficiency of PH-SA is still higher than 100% at 120 °C. This study not only provides pioneering reference for the development of advanced PTM-TENG with enhanced output performance over a wide temperature range, but also greatly promotes the application of PTM-TENG devices in harsh environments.

Strong ions and charge-balance

It has been shown that the ability to predict the pH in any chemically characterized fluid, together with its buffer-capacity and acid content can be based on the requirement of electroneutrality, conservation of mass, and rules of dissociation as provided by physical chemistry. More is not required, and less is not enough. The charge in most biological fluids is dominated by the constant charge on the completely dissociated strong ions but, nonetheless, a persistent narrative in physiology has problematized the notion that these have any role at all in acid-base homeostasis. While skepticism is always to be welcomed, some common arguments against the importance of strong ions are examined and refuted here. We find that the rejection of the importance of strong ions comes with the prize that even very simple systems such as fluids containing nothing else, or solutions of sodium bicarbonate in equilibrium with known tensions of CO2 become incomprehensible. Importantly, there is nothing fundamentally wrong with the Henderson–Hasselbalch equation but the idea that it is sufficient to understand even simple systems is unfounded. What it lacks for a complete description is a statement of charge-balance including strong ions, total buffer concentrations, and water dissociation.

Tracking surface ionic movement of Ni3S2@CuS electrode materials with high electrochemical performance

Supercapacitors have overwhelming advantages in cycle life, charging time and power density. Metal sulfides involve reversible Faraday redox reactions, and chemical reactions occur during charge and discharge, resulting in high specific capacity of the electrode. Different from the traditional nickel foam as a current collector, in this work, vulcanized nickel foam (Ni3S2) is used to further grow CuS nanosheets by hydrothermal reaction to produce new cathode material. The results show that the electrochemical properties of the electrode material Ni3S2@CuS obtained at 190 °C for 4 h reach a mass specific capacity of 967.7F/g. When assembled as a supercapacitor device, it has an energy density of 103.7 Wh/kg and a power density of 15050.3 W/kg. The coulomb efficiency of the device remains 97.4 % after 10,000 cycles of constant current charge and discharge. To deeply understand the mechanism of the capacitance increase, we carry out a molecular dynamics (MD) simulation on pure Ni3S2 electrode and Ni3S2@CuS to investigate the influence of this unique structure on capacitance for the first time. We discover that the CuS tunnel on the Ni3S2 electrode surface will restrict the deintercalation of K+ ions and promote the intercalation of OH–, and this phenomenon will promote the reversible redox reaction on the surface of the metal sulfides and enhance the capacitance of this pseudocapacitor.

Design and Implementation of a Digital Control System for Lead Acid Battery Charging

Ensuring a long battery life and satisfactory performance requires accurate charging cycles. There are three phases to the charge cycle - Constant Current Charge, Constant Voltage Charge, and Float Charge. It is usual that lead acid battery users complain about fast degrading performance because most the low cost commercially available lead Acid Battery chargers provides only single-stage charging phase which is that of constant-voltage charging phase. To ensure long service life and good performance, it is of paramount importance that all charging modes are respected. This said it is clear that the battery charger should have a certain degree of controllability over voltage and current quantities through-out the charging process. In this paper, we designed and built a lead acid battery charger to use in conjunction with a synchronous buck converter topology. After implementing and testing the system, we obtained good results in both the quantitative and qualitative analysis of the implemented system tested, a 12 V- 7000mAh battery. With the help of a MCU-based digital control system containing two different control transfer functions - constant current Feedback Control and Constant Voltage Feedback Control monitoring the charging process proved possible without any overshoot. The prototype showed us an efficiency rating of 86.60%, the maximum error level was recorded at 0.05V, and there were no problems related to overshoot or transient response when testing our prototype which worked flawlessly.

Nano-Silicon@Exfoliated Graphite/Pyrolytic Polyaniline Composite of a High-Performance Cathode for Lithium Storage

In this paper, a Si@EG composite was prepared by liquid phase mixing and the elevated temperature solid phase method, while polyaniline was synthesized by the in situ chemical polymerization of aniline monomer to coat the surface of nano-silicon and exfoliated graphite composites (Si@EG). Pyrolytic polyaniline (p-PANI) coating prevents the agglomeration of silicon nanoparticles, forming a good conductive network that effectively alleviates the volume expansion effect of silicon electrodes. SEM, TEM, XRD, Raman, TGA and BET were used to observe the morphology and analyze the structure of the samples. The electrochemical properties of the materials were tested by the constant current charge discharge and cyclic voltammetry (CV) methods. The results show that Si@EG@p-PANI not only inhibits the agglomeration between silicon nanoparticles and forms a good conductive network but also uses the outermost layer of p-PANI carbon coating to effectively alleviate the volume expansion of silicon nanoparticles during cycling. Si@EG@p-PANI had a high initial specific capacity of 1491 mAh g-1 and still maintains 752 mAh g-1 after 100 cycles at 100 mA g-1, which shows that it possesses excellent electrochemical stability and reversibility.

Research on the Performance of Cobalt Oxide Decorated Graphite Felt as Electrode of Iron‐Chromium Flow Battery

AbstractIn this paper, cobalt oxide‐modified graphite felt electrodes were prepared by electrodepositing cobalt nitrate on graphite felt and calcined. The surface morphology of graphite felt modified by cobalt oxide was characterized in detail by scanning electron microscope X‐ray diffraction and X‐ray photoelectron spectroscopy. Shape, microstructure, etc. And using the three‐electrode system to conduct cyclic voltammetry, electrochemical impedance spectroscopy, and single‐cell constant current charge and discharge detection on the graphite felt electrodes modified with different concentrations of cobalt oxide, and study its use as an electrode for iron‐chromium redox flow battery performance. The results show that the method of calcination after electrodeposition successfully attaches cobalt oxide to the graphite felt fiber uniformly in granular form, increases a large number of oxygen‐containing functional groups, and has the highest coulombic efficiency for the first charge‐discharge cycle at a current density of 142mAcm−2 It can reach 82 %, and the charging capacity is also increased by 1.59 times compared with the original graphite felt.

Influence of Charge Regulation on the Performance of Shock Electrodialysis.

In order to understand the ion transport in a continuous cross-flow shock electrodialysis process better, numerous theoretical studies have been carried out. One major assumption involved in these models has been that of a constant surface charge. In this work, we considered the influence of charge regulation, caused by changes in salt concentration, on the performance of a shock electrodialysis cell. Our results show that, by including charge regulation, much higher potentials need to be applied to reach the same degree of desalination, compared to the constant surface charge model. Furthermore, we found that operating at higher potentials could lead to substantial Joule heating and therefore temperature increases. Although somewhat lower potentials were required in the nonisothermal case versus the isothermal case with charge regulation, the required energy input for desalination is still much higher than the thermodynamic minimum. This works highlights the important role charge regulation can play in a shock electrodialysis process.

Qualitative Assessment of the Contribution of Various Components to Cu(II) Adsorption by Alluvial Soddy-Gley Soil

Using the method of sequential removal of various types of sorption surfaces, a qualitative assessment of the contribution of organic matter, non-silicate iron compounds, and clay minerals to the adsorption of Cu(II) by alluvial soddy-gley soil was carried out under the conditions of laboratory equilibrium experiments. It has been established that the contribution of each of the components is determined both by the ability to form surface inner-sphere complexes at pH-dependent positions, and by the availability of sorption centers in the places of localization of a constant charge of clay minerals. In the AY horizon, the main components sorbing Cu(II) are organic matter and nonsilicate iron compounds, while in the ABg and BDg horizons, clay minerals make the main contribution to Cu(II) adsorption under the experimental conditions. The main mechanism of Cu(II) adsorption in the AY horizon is ion exchange with H+ on functional groups of organic matter and surface hydroxyls of nonsilicate iron compounds. In the underlying horizons, Cu(II) is mainly sorbed as a result of ion exchange with cations that compensate for the constant charge of the crystal lattices of clay minerals. Soil treatment with 10% H2O2 and the Mehra-Jackson reagent leads to a change in the surface area, quality and quantity of sorption centers, and to the transformation of the crystal lattices of clay minerals. These changes should be taken into account when assessing the contribution of soil components to the sorption of metal ions.

Controllable Preparation of Ge/Cu Composite Porous Microspheres as High‐Performance Anode Materials for Lithium‐Ion Batteries

Germanium (Ge) has great advantages as a cathode material for lithium‐ion batteries, but its application in the anode of lithium‐ion batteries is limited by its volume expansion and poor electrical conductivity. Currently, nano‐Ge and composite Ge are the main research directions. Using Ge/copper (Cu) alloy as raw material, herein, pulse discharge and chemical etching method are adopted to prepare a kind of Ge/Cu composite porous microsphere (Ge/Cu@PMS). A 3D conductive network structure is obtained to increase the conductivity of Ge and alleviate the volume expansion of lithium‐ion battery during charge and discharge. As an anode material for Li‐ion batteries, Ge/Cu@PMS has a capacity retention rate reaching 590 mAh g−1 after 200 constant current charge–discharge cycles at a current density of 800 mA g−1, with a capacity retention rate of 79.1%. Therefore, Ge/Cu@PMS has great potential application in lithium energy storage‐related technologies due to its excellent energy‐storage performance and ease of preparation.

Direct Current Piezoelectric Energy Harvesting Based on Plasmon‐Enhanced Solar Radiation Pressure

AbstractA piezoelectric energy generating device that produces electricity using plasmon‐enhanced solar radiation pressure (SRP) is developed. The SRP is greatly enhanced on the operational region of the device with a unique crater‐like structure, and direct current is generated successfully on the device. By optimizing the material and thickness of top electrode, a maximum power density of 396 µW cm−2 is obtained. In addition, by using Raman measurements, finite‐difference time‐domain simulation, and COMSOL Multiphysics analysis, it is confirmed that the SRP is greatly amplified on the operational region with the nanoscale surface roughness due to resonance between the incident light and surface plasmons. By increasing the rotational speed of an optical chopper used to measure the change in the output characteristics of the device, and comparing this with the simulated result, it is found that the constant charge produced by the piezoelectric effect arose due to the superposition of charge phases in the device.

Energy deposition and formation of nanostructures in the interaction of highly charged xenon ions with gold nanolayers

The effect of the deposition of kinetic energy and neutralization energy of slow highly charged xenon ions on the process of the nanostructures creation at the surface of gold nanolayers is investigated. The nanolayers of thickness of 100 nm were prepared by e-beam evaporation of gold on crystalline silicon Si(100) substrate. The samples were irradiated at the Kielce EBIS facility of the Jan Kochanowski University (Kielce, Poland), under high vacuum conditions. The irradiations were performed for constant kinetic energy 280 keV and different ions charge states (Xeq+, q = 25, 30, 35, 36 and 40) and for constant charge state Xe35+ and different kinetic energies: 280 keV, 360 keV, 420 keV and 480 keV. The fluence of the ions was on the level of 1010 ions/cm2. Before and after irradiation the nanolayer surfaces were investigated using the atomic force microscope.As the result, well pronounced modifications of the nanolayer surfaces in the form of craters have been observed. A systematic analysis of the crater sizes (diameter on the surface and depth) allowed us to determine the influence of the deposited kinetic and the neutralization energy on the size of the obtained nanostructures. The results are theoretically interpreted within the micro-staircase model based on the quantum two-state vector model of the ionic Rydberg states population. The charge dependent ion–atom interaction potential inside the solid is used for the calculation of the nuclear stopping power. According to the model the formation of the nanostructures is governed by the processes of the ionic neutralization in front of the surface and the kinetic energy loss inside the solid. The interplay of these two types of processes in the surface structure creation is described by the critical velocity. Using the proposed theoretical model, the neutralization energy, deposited kinetic energy and critical velocities were calculated and compared qualitatively with the experimental results. The results are consistent (after normalization) with previous experimental data and molecular dynamics simulations for single ionized Xe and crystalline gold surface.

Designing porous photonic crystals for MIR spectral region—a deeper insight into the anodic alumina layer thickness versus charge density relation

The mid-infrared region (MIR) is crucial for many applications in security and industry, in chemical and biomolecular sensing, since it contains strong characteristic vibrational transitions of many important molecules and gases (e.g. CO2, CH4, CO). Despite its great potential, the optical systems operating in this spectral domain are still under development. The situation is caused mainly by the lack of inexpensive and adequate optical materials which show no absorption in the MIR. In this work, we present an easy and affordable way to develop 1D photonic crystals (PCs) based on porous anodic alumina for MIR region. The porous PCs were produced by the pulse anodization of aluminum using charge-controlled mode. The first order photonic stopbands (λ 1) were located within ca. 3.5–6.5 μm. Annealing of the material at 1100 °C for an hour has allowed to recover the wavelength range from around 5.8 to 7.5 μm owing to the decomposition of the absorption centers (oxalate anions) present in the anodic oxide framework while maintaining the PC structural stability. The spectral position and the shape of the resonances were regulated by the charge passing under high (U H) and low (U L) voltage pulses, porosity of the corresponding d H and d L segments, and dura tion of the process (t tot). The thickness of the d H and d L layers was proportional to the charge passing under respective pulses, with the proportionality coefficient increasing with the applied voltage. Despite the constant charge (2500 mC cm−2) applied during the anodization, the thickness of anodic alumina (d) increased with applied voltage (10–60 V) and anodizing temperature (5 °C–30 °C). This behavior was ascribed to the different kinetics of the anodic alumina formation prompted by the variable electrochemical conditions. The photonic material can be used in portable nondispersive gas sensors as an enhancement layer operating up to around 9 μm.

Adaptive Electric Fields Embedded Electrochemical Barrier Calculations.

Electrochemical interfaces are grand canonical ensembles of varying electrons. Simulating them by standard first-principles methods is a challenging task, since the number of electrons (or charge) is fixed in the calculation. Under the constant charge framework, we developed a constant potential simulation method realized by adding an adaptive electric field to a charge neutral system. Electric field is the controlling variable. In addition, we defined an internal reversible hydrogen electrode potential (ϕIRHE), which can ensure the model independence of our method. To validate our method, the reaction energies of some electrochemical reactions are calculated, the results are comparable with the computational hydrogen electrode model and experiments. At last, the evolution of transition state structures and charge transfer coefficients of some electrochemical reactions on Ag(111) surface were discussed by our method.

Design and Performance Assessment of Split Gate Dielectric Modulated Junction less TFET Variation of Hfo2 by the Divided Gate Insulator for High Sensitivity Using Tcad Simulation

A number of more recent discoveries in microbiology have made reliable identification of nano-biomolecules and extensive analyses of them necessary. A variety of proteins, including DNA, biotin-streptavidin, amino acids, as well as many types of bacteria and viruses, must be found and analyzed in order to fully comprehend any odd behavior occurring inside of live cells. Rapid testing and detection are essential steps in preventing undiscovered biohazards from eradicating the human race and other terrestrial living things. Since many decades ago, developing an accurate, affordable biosensor has been a struggle for scientists [1]. When compared to pricey laboratory-based sensors and detection methods, FET-based lab-on-chip nano biosensors appear to be a promising substitute. It is significantly more dependable than conventional bulk sensors because of its size, affordability, low power consumption, resilience, faster response time, and better sensitivity [1]. Due to their precision, adaptability, and compatibility with embedded systems, dielectrically modulated FET biosensors with Nano cavities are emerging as a promising research area that can yield useful data on bio-analyses. As an alternative to conventionally doped TFET devices, using a charge plasma SiGe-heterojunction double gate TFET, a label-free biosensor can be produced, bypassing the need for conventional semiconductors, which require a large thermal budget and are susceptible to random dopant fluctuations (RDFs). The effect of changing the dielectric constant (k), the positive and negative charge density, the gate work function, and the cavity size has been investigated to better understand how these factors affect the performance of the proposed biosensor. These parameters modify the biosensor's electric characteristics, improving detection [2]. There is also discussion of how these factors influence the device's drain current, electric field, surface potential, sub-threshold swing (SS), insulator-to-metal film (ION/IOFF) ratio, and electron tunneling rate (ETR). The sensitivity of the drain current in the proposed biosensor is also investigated. There is no restriction on whether or whether the proposed structure is used for charged or neutral molecules.Under lower supply voltages, it is discovered that the SG-DM current JLFET's sensitivity is high, measuring 1.2 *10^3, with a potential sensitivity of 1.4 V. A result, the SG-DM [2] JLFET exhibits good application potential while consuming little power and having ahigh sensitivity.