Linear Voltage Sweep Research Articles

Optimum Conditions for the Fabrication of Ordered Porous Alumina Via Anodizing in Etidronic Acid at Higher Voltages

Anodizing aluminum in an etidronic acid solution leads to the higher applied voltages of up to approximately 260 V without oxide burning and subsequent formation of porous alumina with a larger interpore distance measuring 650 nm. Typically, the interpore distance increases linearly with the applied voltage during anodizing. However, excess voltage more than 270 V during anodizing in etidronic acid causes oxide burning and the formation of non-uniform porous alumina film. In the present investigation, we describe the optimum operating conditions for the fabrication of ordered porous alumina with larger interpore distance via anodizing in etidronic acid at higher voltages more than 270 V.Commercially available 4N aluminum plates were ultrasonically degreased and electrochemically polished. The pretreated aluminum specimen was placed parallel to a platinum plate as the cathode in a 0.3 M etidronic acid solution (volume: 150-555 mL) at 293 K using an electrochemical cell (inner diameter: 55-105 mm), then anodized under a linear voltage sweep at 0.1 Vs-1and constant voltage of 260-280 V for up to 6 h. The effect of a) the surface area of the platinum cathode (6.28-624 mm2), b) distance between two electrodes (50-90 mm), and c) stirring rate (300-900 rpm) on the anodizing behavior was investigated. The anodized specimens were examined by scanning electron microscopy (SEM).The oxide burning voltages were measured by anodizing in etidronic acid under various operating conditions by the linear voltage sweep method. The burning voltage was unchanged with the surface area of the platinum cathode increased, whereas increased with the stirring rate of the etidronic acid solution due to the efficient Joule heat removal. In addition, the burning voltage increased with decreasing distance between two electrodes at the same stirring rate, because of the higher flow velocity of the solution. As a result, steady-state anodizing can be achieved in etidronic acid at the higher voltage of 270-280 V. Figure 1 shows SEM images of the dimple array formed on the aluminum surface via anodizing at 270 V and 280 V for 6 h. A larger porous alumina measuring 665-726 nm in interpore distance was successfully fabricated via anodizing under the optimum operating condition. Figure 1

Exact solution for the electrical response of a constant phase element with a series resistance to linear voltage sweep

A resistance Rs in series with a constant phase element (CPE) of frequency-dependent impedance given by the power law function Zc(s)=1/(Cαsα) is commonly used for the analysis of steady-state frequency response data exhibiting non-purely capacitive behavior. This is the case in most (bio)(electro)chemical systems including dielectrics, batteries, supercapacitors, capacitive deionization units, biological tissues and bioelectrodes. Passing to the time domain, the current, voltage and charge of the system are governed by differential equations with non-integer, fractional-order operators. The purpose of this study is to provide the exact analytical expressions for the electrical response of an Rs-CPE model under linear sweep voltammetry with the use of the Laplace transform method. The electrical variables are expressed in terms of special functions regularly encountered with fractional calculus such as the Fox’s H-function and the Mittag-Leffler function, and can be used for modeling non-ideal devices as well as extracting their characteristic parameters.

Nature of Li2O2 and its relationship to the mechanisms of discharge/charge reactions of lithium-oxygen batteries.

Lithium-air batteries (LABs) are considered one of the most promising energy storage devices because of their large theoretical energy density. However, low cyclability caused by battery degradation prevents its practical use. Thus, to realize practical LABs, it is essential to improve cyclability significantly by understanding how the degradation processes proceed. Here, we used online mass spectrometry for real-time monitoring of gaseous products generated during charging of lithium-oxygen batteries (LOBs), which was operated with pure oxygen not air, with 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) tetraethylene glycol dimethyl ether (TEGDME) electrolyte solution. Linear voltage sweep (LVS) and voltage step modes were employed for charge instead of constant current charge so that the energetics of the product formation during the charge process can be understood more quantitatively. The presence of two distinctly different types of Li2O2, one being decomposed in a wide range of relatively low cell voltages (2.8-4.16 V) (l-Li2O2) and the other being decomposed at higher cell voltages than ca. 4.16 V (h-Li2O2), was confirmed by both LVS and step experiments. H2O generation started when the O2 generation rate reached a first maximum and CO2 generation took place accompanied by the decomposition of h-Li2O2. Based on the above results and the effects of discharge time and the use of isotope oxygen during discharge on product distribution during charge, the generation mechanism of O2, H2O, and CO2 during charging is discussed in relation to the reactions during discharge.

A portable point-of-care testing device for forward blood typing with hemophilia diagnosis.

This paper presents a portable point-of-care testing (POCT) device to conduct simultaneous and on-site tests of ABO and Rh(D) forward blood typing and hemophilia diagnosis using only a small amount of human whole blood sample. The POCT device consisted of a spinning module, a measuring circuit, an interdigitated electrode (IDE) for hemophilia diagnosis, and three disposable microfluidic chips for bioassays with anti-A, anti-B, and anti-D, respectively, and measurement of the concentration of factor VIII. Agglutination will occur if red blood cells (RBCs) are exposed to the corresponding antibody. To evaluate the degree of RBC agglutination, a linear sweep voltage, ranging from - 0.5 to + 0.5V, was applied to the electrodes of the microfluidic chip and the resulting current was measured. For different levels of agglutination, the measured I-V curves were explicitly discriminated, providing five clinical levels from non-agglutination (level 0) to strong agglutination (level 4). The quantitative norm obtained from cubic fitting function of each I-V curve served as the criterion to represent this agglutination level. The ABO blood type was determined by both agglutination levels of the blood sample reacting with anti-A and anti-B. The degree of agglutination with anti-D gave the Rh(D) type. Moreover, the concentration of factor VIII was detected for the determination of hemophilia. Without requiring expensive equipment, this POCT device is especially suitable for usage in emergency or natural disasters to provide quantitative testing in rescue and relief operations.

Diagnostics of supercapacitors using cyclic voltammetry: Modeling and experimental applications

In this article, we analyzed a method of cyclic voltammetry (CV) with respect to diagnostics of supercapacitors. The main goal deals with the study of the voltage sweep rate limits allowing to reach equilibrium conditions during recording of CV curves. A mathematical model of cycling based on the De Levie model has been developed. Using this model, the CV curves of a supercapacitor with two symmetric porous electrodes and a separator have been calculated numerically for different sweep rates. These curves are in a good agreement with experimental CV curves. For the first time, an exact analytical solution is obtained for linear voltage sweep for a symmetric supercapacitor during the charge process. The concept of equilibrium CV curves is proposed and the criterium for the equilibrium conditions depending on voltage sweep rate and other parameters of the system is established. When the potential sweep rate exceeds the equilibrium conditions, the CV curves deviate from a rectangular shape and take the form of a “modified ellipses with sharp edges”. A review of publications related with experimental measurements of CV curves has been provided using the developed concept of equilibrium conditions. Application of themathematical model to experimental CV curves makes it possible to reveal the presence of Faraday reactions.

A study of electroactive polyvinyl chloride (PVC) gel actuators through the use of the electric modulus formalism and cyclic linear voltage sweeps

The conductivity and dielectric properties are integral to the function of polyvinyl chloride (PVC) gel actuators. The frequency-dependent properties of PVC gel actuators are investigated here in terms of their impedance, permittivity, and for the first time, electric modulus. The data shows that PVC gels’ conductive properties are just as, if not more, important as their dielectric properties in electromechanical transduction applications. The electrode polarization (EP) and its impact on the impedance and dielectric spectra of PVC gels, as well as the developed asymmetric space charge at the anode, are discussed. The electric modulus and tan spectra are used for the fitting of Cole-Cole (CC) and Debye relaxation models for gels of varying plasticizer content. The electrostatic adhesive force for PVC gels of varying plasticizer is also measured, indicating large electrostatic adhesion (>2 N cm−2). A cyclic linear voltage sweep is used to clarify the dynamics of space charge within the gels. The peak current (associated with space charge development) is seen to be concurrent with the onset of mechanical deformation, showing the asymmetric charge as the origin of electromechanical transduction. Additionally, the maximum charge transferred (as measured by the integration of current over time) before space charge development is found to correlate with the electrostatic adhesive force measured for the gels, pointing to a new method of characterizing PVC gels for actuation.

Enhancing the Switching Performance of CH3NH3PbI3 Memristors by the Control of Size and Characterization Parameters

AbstractThis paper analyzes the effects of scaling and measurement conditions on the performance of hybrid organic inorganic perovskite (HOIP) devices having bipolar resistive switching characteristics. Electroforming voltage, SET current, and ON/OFF ratios are found to be area dependent. Linear voltage sweep and pulse voltage characterization showed that parameters such as compliance current, voltage scan rate, pulse width, amplitude, and frequency significantly alter the device switching parameters. The CH3NH3PbI3 memristors fabricated has FORMING, SET, and RESET voltages of 1.18, 0.17, and −0.13 V, respectively, along with an ON/OFF ratio of 1.3 × 103. It has been found that, both the RESET voltage and current significantly increase with scan rate, whereas the ON/OFF ratio increases significantly with compliance current. In case of voltage pulse characterization, the ON/OFF ratio can be enhanced by increasing the pulse amplitude and width. Additionally, the experimental data fitting to a SPICE based analytical model establishes that the HOIP memristor current conduction is dominated by tunneling process in the OFF state and is ohmic in the ON state. Based on the results, the authors arrive at a general protocol that can be used to characterize memristors made of HOIPs and other related materials such that they can operate optimally.

P2- a2=3Mn2=3M1=3O2 (M = Fe, Co, Ni) cathode materials in localized high concentration electrolyte for the long-cycling performance of sodium-ion batteries

Introduction: Localized high concentration electrolytes (LHCE) have been intensively studied due to their unique properties, especially in suppressing the Na dendrite formation and long-term cycling. Therefore, the low electrochemical performance of the P2-type cathode can be overcome by using LHCE.
 Methods: P2-type sodium layered oxides Na2=3Mn2=3M1=3O2 (M = Fe, Co, Ni) cathode materials were synthesized via a simple co-precipitation following a supported solid-state reaction. XRD and Rietveld method analyzed the phase composition and lattice parameters. SEM images observed the morphology of materials. The half-cell of three cathode were performed in LHCE consisting of 2.1 M sodium bis(fluorosulfonyl)imide (NaFSI) dissolved in 1,2-dimethoxyethane (DME) and bis(2,2,2-trifluoroethyl) ether (BTFE) (solvent molar ratio 1:2). The galvanostatic charge-discharge, striping-plating, and linear sweep voltage tests were carried out to investigate the electrochemical behaviors.
 Results: As-prepared electrode materials exhibited discharge capacities of 94.5, 147.1, and 142.9 mAh/g at C/10 in the potential range of 1.5-4.2 V for Na2=3Mn2=3Fe1=3O2 (MFO), Na2=3Mn2=3Co1=3O2 (MCO) and Na2=3Mn2=3Ni1=3O2 (MNO), respectively. Interestingly, the MNO cathode material has a superior cycling performance with 86.5% capacity retention after 100 cycles than MCO and MFO.
 Conclusion: Such superior electrochemical performance of synthesized MNO could be ascribed to the combined synergistic effects between the nickel partially substituted MNO cathode structure and using LHCE 2.1 M NaFSI/DME-BTFE (1:2). Nickel substituted MNO cathode exhibited the enhancement of discharge capacity and the long cycling stability in LHCE due to the mitigation of dendrite formation on sodium metal anode.

Photoelectrochemical CO2 Reduction via Cu2O/CuFeO2 Hierarchical nanorods photocatalyst

AbstractAlthough cuprous oxide, Cu2O, has attracted attention as a promising p‐type semiconductor material for carbon dioxide reduction (CO2RR) photocatalysts, serious stability problems have always occurred due to photocorrosion. In this work, we fabricated hierarchical‐structured photocathodes with CuFeO2 on Cu2O nanorods by spray pyrolysis and oxygen‐controlled heat treatment to improve the stability of Cu2O from a thermodynamic perspective. Field‐emission scanning electron microscopy, field‐emission transmission electron microscopy and X‐ray diffraction confirmed that the Cu2O/CuFeO2 hierarchical nanorod structure was successfully fabricated. It was observed that the photocathodes show enhanced stability as the Fe content increases. Therefore, we report that the CuFeO2 layer enhances the stability of the Cu2O nanorod photocathode. A photocathode with a Cu : Fe atomic ratio of 1.52 : 1 has a current density of 1.1 mA/cm2 at 0.35 VRHE even after 10 linear voltage sweep repetitions, a decrease of only 8 % compared to the current density at the first sweep. Additionally, formate and acetate were produced during the CO2RR, exhibiting faradaic efficiencies (FEs) of 21.6 % and 68.6 %, respectively.

Cyclic voltammetry of supercapacitors with the simplest equivalent circuit

Analytical equations for the voltammetric curve at the linear voltage sweep and for cyclic voltammograms for the system of connected in series resistance and capacitance were derived. The presence of the resistance results in an substantial distortion and curvature of the voltammogram, which distinguishes this system from the system with the parallel connection of the capacitance and resistance. The character of the voltammograms is determined by the ratio of the following parameters: resistance (R), capacitance (C), voltage sweep rate (v), and voltage (U). The system is capacitive in character at RC ≪ U/v, whereas the character of the system is resistive at RC ≫ U/v.

A comparative study on the forming methods of chalcogenide memristors to optimize the resistive switching performance

Most of the memristor devices require an electroforming step to initiate resistance switching in them. Electroforming a pristine memristor could alter the material composition and/or the device structure, thereby, altering its electrical resistance. This acts as a vital step to optimize the devices for memory applications. In this work, commercially available Ge2Se3 chalcogenide memristors have been characterized electrically. In these devices, the active layer is sandwiched between a tungsten bottom electrode and a silver top layer, and their operation is based on the migration of silver ions into the active layer. Different electroforming methods, such as the use of sinusoidal signal, linear voltage sweep, linear current sweep, constant voltage bias, and fast voltage pulse have been applied to form pristine memristors and their effects on memristor performance has been studied. A current sweep signal cannot provide high enough electric field to obtain a reasonable ON/OFF ratio during forming. In fact, forming using this method is found to be redundant since the subsequent voltage sweep for device operation itself acts as a forming step. Forming with a constant bias signal provides the information regarding switching times and forming rate can be controlled. However, devices formed using this method are found to show unpredictable switching behaviour and it is challenging to choose the suitable voltage level for forming. The devices formed using positive voltage sweep method have been found to give the most repeatable switching characteristics. This method is essential to study the switching mechanism and current conduction in the device during the operation. On the other hand, ultra-fast voltage pulses form the memristor at a much faster rate in comparison to the other DC forming methods, however, at the cost of using a higher voltage level.

Influence of the rapid thermal treatment of the gate dielectric on the parameters of integrated circuits of time devices

The paper is dedicated to influence of the rapid thermal treatment of the gate dielectric at a temperature of ~1100 ° С on the electrical parameters of the programmable time device with a correction of 512PS8. As the analyzed parameters of the given integrated circuit, the authors have selected breakdown voltage, gate leakage current, charge value of the gate dielectric breakdown with its thermal field tests performed. The breakdown voltage of the p -channel of the test transistor was measured by applying the linear voltage sweep from 0 to -100 V with the step of -0,5 V with the grounded drain and source. The leakage current of the gate Ig leak was determined at the gate voltage of -20 V. For evaluation of the charge properties of the gate dielectric of devices the, the thermal field tests were performed. The quality and reliability of the gate dielectric the authors the breakdown charge control was carried out ( Q bd ). It is shown that the rapid thermal treatment of the gate dielectric at a temperature of ~1100 ° С during 7 s with its presence on the non-working side ensures the breakdown charge value of 2,040 C/cm 2 , and with its absence - 2,230 C/cm 2 , while during the standard process of creating the given integrated circuit this value constitutes 1,230 C/cm 2 . This means that the most efficient influence on the improvement of quality and reliability of the gate dielectric is ensured by its rapid thermal treatment when missing the silicon dioxide on the non-working side of the wafer. As compared with the standard process of their fabrication, carrying out such treatment allows 5,29 times reduction of the gate leakage current, 3,50 times reduction of the charge states and 1,07 times enhancement of the reliability of the p -channel transistor, and for the n -channel transistor the given values constitute 10,67, 3,50 and 1,81 times, respectively. It is established that the reliability improvement for the CMOS integrated circuits of time devices during the rapid thermal treatment of the gate dielectric is determined by a step-up of its breakdown charge owing to the more perfect microstructure of dielectric, resulting in the rebuild of the charge states both in the bulk and on the boundary with silicon.

Comparative Analysis on Dielectric Gold and Aluminium Triangular Junctions: Impact of Ionic Strength and Background Electrolyte by pH Variations

Field of generating a surface thin film is emerging broadly in sensing applications to obtain the quick and fast results by forming the high-performance sensors. Incorporation of thin film technologies in sensor development for the better sensing could be a promising way to attain the current requirements. This work predominantly delineates the fabrication of the dielectric sensor using two different sensing materials (Gold and Aluminium). Conventional photolithography was carried out using silicon as a base material and the photo mask of the dielectric sensor was designed by AutoCAD software. The physical characterization of the fabricated sensor was done by Scanning Electron Microscope, Atomic Force Microscope, High Power Microscope and 3D-nano profiler. The electrical characterization was performed using Keithley 6487 picoammeter with a linear sweep voltage of 0 to 2 V at 0.01 V step voltage. By pH scouting, I-V measurements on the bare sensor were carried out, whereby the gold electrodes conducts a least current than aluminium dielectrodes. Comparative analysis with pH scouting reveals that gold electrode is suitable under varied ionic strengths and background electrolytes, whereas aluminium electrodes were affected by the extreme acid (pH 1) and alkali (pH 12) solutions.

Gold nano-urchin integrated label-free amperometric aptasensing human blood clotting factor IX: A prognosticative approach for “Royal disease”

This article is clearly presenting the development of a biosensor for human factor IX (FIX) to diagnose the blood clotting deficiency, a so-called ‘Royal disease’ using an interdigitated electrode (IDE) with the zinc oxide surface modification. Gold nano-urchins (GNUs) with 60 nm in diameter was integrated into a streptavidin-biotinylated aptamer strategy to enhance the active surface area. Two different comparative studies have been done to validate the system to be practiced in the current work holds with a higher capability for the high-performance sense. Whereby, the presence and absence of GNUs in the aptasensing system for FIX interaction were investigated using the amperometric measurement, using a linear sweep voltage of 0–2 V at 0.01 V step voltage. The detection limit was 6 pM based on 3σ calculation when GNUs integrated aptamer assay was utilized for FIX detection, which shows 8 folds sensitivity enhancement comparing the condition in the absence of GNU and 50 folds higher than sensitive radio-isotope and surface plasmon resonance assays. Albeit, the surface and molecular characterizations were well demonstrated by scanning electron microscopy, atomic force microscopy, 3D nano-profilometry and further supports were rendered by UV–Vis spectroscopy and Enzyme-linked apta-sorbent assay (ELASA). Furthermore, the spiking experiment was done by FIX-spikes in human blood serum in order to demonstrate the stability with a higher non-fouling.

Polyaniline assisted USB based sensor for determination of benzene biomarker

Benzene is a known Hemotoxic carcinogen for humans. The carcinogenic properties justify that any exposure to Benzene in ambient air needs to be monitored. Exposure to Benzene is indicated by presence of trans-trans Muconic Acid (ttMA) in urine of human as a biomarker. Currently the levels of biomarker are measured by sophisticated and costly equipment like High Precision Liquid Chromatography (HPLC). This commercial procedure is time consuming due to rigorous sample preparation, involvement of expensive equipment and need of expertise for analysis. To remedy this, USB assisted and Polyaniline (PANI) based point of care electrochemical sensor for detection of biomarker of Benzene is developed. To operate this system, one does not require sample preparation and trained hands.The system is USB based portable potentiostat which performs Linear Sweep Voltammetry (LSV) for detection of ttMA. The design comprises of potentiostat interfaced with microcontroller FRDM-KL 25Z of NXP semiconductors. The system detects nanoampere current with linear sweep voltage resolution of 800 μV. Graphical User Interface (GUI) facilitates to set the parameters like start potential, end potential, step size and scan rate of linear sweep voltage. The real time serial plotter equips the viewing and capture of real-time sensor data from electrochemical cell. The three-electrode electrochemical cell consists of PANI coated Aluminum as working, Graphite Pencil Electrode (GPE) as counter, and Saturated Calomel Electrode (SCE) as reference which is utilized for electrochemical detection of ttMA in urine sample.This system is capable of detecting ttMA in Urine which corresponds to intermediate (1-5 ppm) and high (>5 ppm) level exposure of Benzene in ambient air.

Short-term memory in electric double-layer capacitors

Shared by various physical, chemical, and biological systems, fractional-order dynamics assert that the present state of a system is the result of not only the applied stimulus but also its past history. Consequently, in fractional-order systems, there exists a system-specific, input-dependent memory kernel. In this study, we demonstrate experimentally the existence of a memory effect in electric double-layer capacitors which are known to exhibit a fractional-order behavior through their non-single, distributed internal time constants. This is performed by showing variance in the discharge patterns of the device into a constant resistor after being charged to the same steady-state voltage and steady-state electric charge, first by using a step voltage and then using a linear voltage sweep. We observe a short-term memory effect in the transient regime which eventually fades out with time. This was attributed to the input-modulated device impedance and was confirmed mathematically.

MgTi2O5 thin films from single molecular precursor for photoelectrochemical water splitting

Magnesium dititanate MgTi2O5, thin films have been grown on fluorine doped tin oxide (FTO) substrates using a newly synthesized heterobimetallic single molecular precursor [Mg2Ti4(O)2(OH)4(TFA)8(THF)6]·THF (1) (where TFA=trifluroacetato and THF=tetrahydrofuran) using the aerosol assisted chemical vapor deposition technique (AACVD). The precursor complex (1), isolated in crystalline form by reacting magnesium (II) acetate tertahydrate with titanium (IV) isopropoxide and trifluroacetic acid in THF solution, was characterized by FTIR, single-crystal X-ray diffraction and thermogravimetric analyses. Thin films prepared at 500, 550 and 600°C were inspected by X-ray diffraction (XRD), field emission gun-scanning electron microscopic (FESEM), and energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS), which demonstrated the development of phase pure orthorhombic porous microspherical objects of MgTi2O5 with precise stoichiometry. The optical analysis showed that MgTi2O5 has a direct band gap of 3.4eV. The photoelectrochemical (PEC) experiments on MgTi2O5 electrodes showed maximum anodic photocurrent density of 400μA/cm2 at 0.7V vs. Ag/AgCl/3M KCl under simulated solar irradiation of AM 1.5G (100mW/cm2) in 1M NaOH. The improved PEC performance of MgTi2O5 electrode was attributed to the increased photo absorption ability, elevated surface area, and more efficient electron/hole transfer which were confirmed by measurements such as linear sweep voltage, transient photocurrent and electrochemical impedance spectroscopy.

MgTiO3/MgTi2O5/TiO2 heterogeneous belt-junctions with high photocatalytic hydrogen production activity

An effective photocatalytic hydrogen production catalyst comprising MgTiO3/MgTi2O5/TiO2 heterogeneous belt-junctions was prepared using magnesium ions by a thermally driven doping method. The tri-phase heterogeneous junction was confirmed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). The as-prepared MgTiO3/MgTi2O5/TiO2 heterojunctions exhibited a very high photocatalytic hydrogen production activity (356.1 mol·g0.1gcat·h-1) and an apparent quantum efficiency (50.69% at 365 nm) that is about twice of that of bare TiO2 nanobelts (189.4 mol·g0.1gcat·h-1). Linear sweep voltage and transient photocurrent characterization as well as analysis of the electrochemical impedance spectra and Mott–Schottky plots revealed that the high photocatalytic performance is caused by the one-dimensional structure, which imparts excellent charge transportation characteristic, and the MgTiO3/MgTi2O5/TiO2 tri-phase heterojunction, which effectively drives the charge separation through the inherent electric field. This titanate-based tri-phase heterogeneous junction photocatalyst further enriches the catalyst system for photocatalytic hydrogen production.

Potentiodynamic anodizing of aluminum alloys in Cr(VI)‐free electrolytes

The aerospace industry progressively develops alternatives for chromic acid anodizing, because Cr(VI) is known to be toxic and carcinogenic. In this work, potentiodynamic anodizing of AA1050 and AA2024‐T3 clad was performed in phosphoric‐sulfuric acid (PSA) and sulfuric acid (SAA). All anodizing cycles started with a linear voltage sweep, followed by a constant voltage, or a dynamic voltage. Current density responses were recorded during each anodizing cycle and comprised different stages, which could be related to growth phases of the anodic oxide film. Interesting differences were found between cycles with an intermediate increase in anodizing voltage versus cycles with an intermediate decrease in voltage. Cycles including an increase in voltage resulted in higher anodic oxide formation efficiencies because of a temporary exceedance of the steady state current (recovery period) directly after the voltage step. Also, a sudden decrease in voltage led to distinct border between a fine and coarse region in the film morphology, while a sudden increase in voltage did not. For prolonged anodizing in PSA, coarsening of the upper film part was observed because of the high solubility of Al2O3 in phosphoric acid. Pore walls close to the outer surface did not only get thinner, but completely dissolved in the electrolyte. Consequently, anodic oxide formation efficiencies were higher for SAA than for PSA. Copyright © 2016 John Wiley & Sons, Ltd.

Polysulfide transport through separators measured by a linear voltage sweep method

Shuttle of polysulfide from the sulfur cathode to lithium metal anode in rechargeable lithium–sulfur batteries is a critical issue hindering cycling efficiency and life. Several approaches have been developed to minimize it including polysulfide-blocking separators; there is a need for measuring polysulfide transport through separators. We here show a linear voltage sweep method to measure anodic (oxidization) current of polysulfide crossed separators, which can be used as a quantitative measurement of the polysulfide transport. The electrochemical oxidation of polysulfide is diffusion controlled. The electrical charge in Coulombs produced by the oxidation of polysulfide is linearly related to the concentration of polysulfide within a certain range (≤0.5 M). Separators with a high porosity (large pore size) show high anodic currents, resulting in fast capacity degradation and low Coulombic efficiencies in Li–S cells. These results demonstrate this method can be used to correlate the polysulfide transport through separators with the separator structure and battery performance, therefore provide guidance for developing new separators for lithium–sulfur batteries.