Electrode Polarization Effects Research Articles

Numerical Analysis of Geometric Influences in Tetrapolar Electrical Impedance Spectroscopy Using Monte Carlo Simulations

Abstract Electrical impedance spectroscopy is promising for intraoperative cancer diagnosis by differentiating tissue based on its electrical properties, yet faces challenges from material nonlinearities and sensor effects. In this study, 3D finite element simulations were performed to analyze geometric dependencies. Two different tetrapolar ring electrode layouts are placed on virtual piece of normal and tumor tissue with each radius varied using Monte Carlo simulations and the resulting impedances and cell constants were evaluated statistically. Additionally, a novel sensitivity quality metric is introduced, enabling the identification of the geometry more suitable for impedance measurements. The results highlight the superior sensitivity quality of the improved geometry. Future research should integrate the geometric Monte Carlo approach with variations of dielectric properties of tissue and optimizing the quality metric taking electrode polarization effects into considerations.

(Invited) Effect of Electrode Polarization on Oxide Ion-Conducting and Proton-Conducting Electrolytes

Polarization at the electrode/electrolyte interface has been a central issue in electrochemistry, which is also true for high-temperature ion conducting devices. Charge transfer limitation does not simply apply to such interfaces where electrons make direct exchange. Thus, overpotentials have been discussed in terms of a shift of local oxygen activity from equilibrium with the gas phase [1]. This approach has been successful in explaining phenomena at high temperature electrodes, such as large chemical capacitance of mixed-conducting film electrodes and appearance of Gerischer-type impedance with porous electrodes [2,3]. As well as the effect on the electrode properties, the interface potential shift can also affect the electrolyte. The Hebb-Wagner polarization technique utilizes the polarization at ion-blocking electrode to control the chemical potential within the electrolyte. The enhanced n-type or p-type conduction of ceria-based or proton conducting oxide electrolyte under water electrolysis operations is recognized as a practical problem of reduced energy conversion efficiency. However, the effect of overpotential at practical semi-blocking electrodes (or incompletely reversible electrodes) on the electrolyte is not well understood. The aims of this study is to elucidate whether the overpotential directly defines the chemical potential shift in the electrolyte near the interface.Two kinds of approaches were taken: i.e. direct measurement of the chemical potential in the electrolyte and non-linear equivalent circuit analysis of electrochemical responses. The direct measurements were made by using embedded probes in an oxide ion conductor. Yttria stabilized zirconia powder was pressed and sintered with five platinum wires of 0.1~0.2 mm thick. Porous platinum electrodes were pasted on the both ends of the sample and direct or alternating current was applied. Electric fields between the probes/electrodes were estimated by high frequency response of ac impedance, and subtracted from the electrical potential of the probes under dc. The distribution of chemical potential of electron, and thus, of oxygen was obtained assuming constant chemical potential of oxide ion. When oxygen exchange on the cathode was blocked using a glass paste, the oxygen potential at each probe shifted to the negative direction, and the change propagated slowly from the cathode side to the anode side. The result was in close agreement with the estimation from the mobility and carrier concentration of electrons in YSZ, suggesting that the probes successfully detected the local oxygen potential. Evaluation of chemical potential shifts with half-blocking electrode is in progress.For the equivalent circuit approach, a model circuit was developed to simulate the linear and nonlinear responses of electrode/electrolyte systems. The circuit consisted of charged carrier transport lines connected by capacitors exhibiting the local defect equilibrium, as proposed by Jamnik and Maier[4]. Unlike an equivalent circuit for a regular impedance analysis, the circuit elements were defined using parameters that varied with local chemical potentials. The responses of the circuit were calculated by using a general-purpose circuit analyzer LT-SPICE that enabled analyses of transient response as well as linear impedance. It also enabled higher harmonic analyses which is useful for detecting electrolyte polarization. The developed model was tested with a simple symmetric cell with mixed conducting electrode. Qualitative correspondence was obtained regarding the oxygen potential dependence in the linear impedance and the second harmonic responses. In addition to the oxide ion conductors, proton conductor with hole and oxide ion as minor carriers were modeled. Calculations with different assumptions of the oxygen (and hydrogen) potential shift will be compared with the ongoing experiments to find the effect of polarization of a half-blocking electrode.

Influence of Hierarchical Porosity of Electrodes on the Energy and Power Densities of Electrochemical Devices

Influence of specific micropore-, mesopore and total surface areas and pore volumes and other porosity characteristics on the electrochemical parameters and power density of electrochemical devices will be discussed [1-3]. Many ionic liquids (EtMeImBF4, Et4B(CN4)4, etc.) and organic (Et3MeNBF4, Et4NBF4, Et3PrNBF4, etc.) and inorganic salts (LiBF4, NaBF4, LiClO4, NaClO4, LiPF6, NaPF6, Rb2SO4, Li2SO4, Na2SO4, LiI, NaI, NaBr, LiBr, LiCl, NaCl, CsBF4, Cs carborane, etc.) based electrolytes in various solvents (H2O, acetonitrile, ethyl methyl carbonate, propylene carbonate, diethyl carbonate, acetone) and their mixtures with specific chemical additions (fluoroethyl carbonate, propylene sulfite, diethyl sulfite) will be discussed. 1M 3-ethyl-methyl-ammonium tetrafluoroborate (Et3MeNBF4) solution in acetonitrile and on 1-ethyl-3-methylimidazolium tetrafluoroborate (Et3MeImBF4) will be analyzed for all carbon materials as reference data.The pore size distribution calculated from N2, CO2 and Ar adsorption isotherms using mainly Carbon 2D non-local density functional theory for heterogeneous surface (2D-NLDFT-HS) model will be compared with crystallographic characteristics obtained by Raman, X-ray diffraction, focused ion beam scanning electron microscopy (FIB-SEM), high-resolution transmission electron microscopy, (HR-TEM) combined with low electron energy diffraction (EELS) and selected area electron diffraction (SAED) methods. Small angle and wide-angle X-ray scattering (SAXS and WAXS), small-angel neutron diffraction (SANS), quasielastic (QENS) and inelastic neutron scattering (INES) etc. data will be analyzed. Electrochemical temperature dependent XRD will be used for analysis of influence of temperature and electrode potential on the structural parameters at various temperatures and electrode potentials.For surface analysis, electrochemical oxidation and reduction processes at electrode | vacuum and electrode | ionic liquid interfaces have been studied using synchrotron radiation photoelectron spectroscopy (Sr-XPS) and near ambient pressure dual chamber synchrotron beam XPS (Sr-NAP-DC-XPS) methods.Post–mortem analysis of electrodes applied under high temperature and high electrode overpotential conditions was conducted using FIB-TOF-SIMS (secondary ion mass spectroscopy), FIB-SEM –EDX and thermogravimetry methods to determine the effect of electrode polarization and temperature on the intercalation layer formation kinetics (mass-transfer depths) for electrodes with different micro-meso-macro porosity. For selected flatter electrodes, the in situ STM and AFM measurements combined with Raman spectroscopy surface analysis have been used. Surface structures of adsorbed and formed interfacial layers will be simulated by computation analysis using different DFT, molecular dynamic etc. methods.Based on systematic analysis on results collected, it will be demonstrated that the chemical composition and crystallographic structure of precursor material, chemical composition of activators, synthesis and activation conditions have decisive influence on the shape of the pores (spherical, cylindrical or slit-shape pores, mixed cylindrical and slit-shape, etc.) and on the hierarchically porous structure and electrical conductivity of carbon, activated carbon and complex oxide materials. For carbon materials with mixed cylindrical-slit shape hierarchical porosity, very high series and parallel capacitances from 130 to 168 F g-1 in 1M Et3MeNBF4+ acetonitrile and up to 155 F g-1 in EtMeImBF4 ionic liquid have been established. Very high gravimetric power density (up to 150kW kg- 1) has been obtained for optimized EDLCs with sol-gel method fabricated electrodes and moderate gravimetric and volumetric energy densities for d-glucose and Estonian peat derived carbons based electrodes [1-4]. The very short characteristic charging/discharging times (lower than 0.3 s for Et3MeNBF4 +AN and 1.0 s for EtMeImBF4) can be achieved for optimized EDLCs. Complicated adsorption kinetics of halide ions at micro-mesoporous carbon electrodes has been observed and explained by the strong chemical adsorption of halides. Very strong influence of hierarchical porosity and micropores inner surface roughness on the hydrogen adsorption parameters has been established by SANS/SAXS methods [5,6]. Strong influence of preparation conditions of Pt-free electro-catalysts for polymer membrane and alkaline fuel cells and electrolysis cells will be demonstrated.Acknowledgements. This work was supported by the European Regional Development Fund (TK141), Estonian Ministry of Education and Research (TK210), Personal Research Grant PRG676, by the project „Increasing the knowledge intensity of Ida-Viru entrepreneurship” co-funded by the European Union (ÕÜF12, ÕÜF1).

Crystallographically textured zinc nucleation and planar electrodeposition for zinc metal batteries via magnetoelectric and magnetization effects

The premature failure of zinc metal anodes is critically associated with the uncontrollable nucleation and random orientation of hexagonal Zn electrodeposits. Herein, we realize to control the crystallographical texture of zinc crystal nuclei and enable planar electrodeposition by simply applying a magnetic field. We unveil the novel mechanism of magnetoelectric and magnetization effects on the different deposition behavior under magnetic fields. The magnetohydrodynamic effect can flatten the uneven electrode surface during electrodeposition by deflecting the motion of Zn2+ ions. Especially, influences of the Hall effect on electrode polarization and magnetization effect on crystallographical Zn nucleation are first uncovered and validated. We demonstrate the proper use of these magnetic field-related effects is propitious to dense, homogeneous, and highly reversible deposition/dissolution of Zn metal anodes. The cycle lives of Zn anodes are extended 2–4 times at different currents and cycling capacities. Moreover, exceptional reversibility of 99.85 % is achieved. Full cells with a low N/P ratio of 5.4 and ultrahigh cathode mass loading of 19.98 mg cm−2 can release stable capacity up to 3.2 mAh cm−2. Our study provides new paradigms for magnetic field regulation of Zn metal battery electrochemistry, as well as for other external field applications in adjusting battery performance.

Simulation study of the effect of electrode polarity on microscale corona discharge characteristics

Abstract The occurrence and application scenarios of micro-scale corona discharge are diverse, and the effect of micro-scale corona discharge mechanism and needle electrode polarity on corona discharge characteristics is still unclear. This paper establishes a microscale simulation model of pin-plate DC positive and negative corona fluid chemical reactions. The phenomenon of positive and negative corona discharge is being investigated. The internal discharge mechanism is analyzed from the microscopic point of view. Results demonstrate that positive corona discharge generates space charges that reduce the electric field strength between the needle electrode and amplify it between the plate electrodes. In contrast, negative corona discharge exhibits the opposite effect. The number of charged particles produced by microscale negative corona discharge is larger than that produced by positive corona, and the discharge phenomenon is more intense than that of positive corona. Under the simulation conditions in this paper, the ionization reaction rate of micro-scale positive and negative corona rises rapidly at the initial discharge. It will gradually remain stable after experiencing an upward pulse. The pulse peak value generated by micro-scale negative corona discharge is much higher than that of positive corona, and the pulse width of negative corona discharge is about half smaller than that of positive corona, which can reach a stable corona discharge state faster.

Effect of Light and Electrode Polarization on BiVO4 and TiO2 Photoanodes for Glycerol Oxidation

In recent years, there has been a growing interest in the photoelectrochemical oxidation of glycerol to produce high-value products. Most studies have focused solely on the photocatalytic properties of the electrodes, overlooking their electrocatalytic properties and the different products obtained under dark conditions. Our work aims to address this gap by comparing the electrocatalytic activity under dark and light conditions to determine whether light influences the reactivity of the electrodes or if it just reduces the overpotential of the reaction. To achieve this, we employed two model semiconductors, TiO2 and BiVO4. We have analyzed their polarization curves under both dark and light conditions and evaluated the competence of glycerol oxidation reaction with the oxygen evolution reaction. Furthermore, we conducted long-term (photo)electrolysis revealing the beneficial role of light on the electrolytic process, as it enables the obtention of C3 products on illuminated TiO2 photoanodes at low electrode polarization, comparable to the performance of BiVO4.

Poly (aniline-co-aniline-2,5-disulfonic acid) / L-ascorbic acid / Ag@SiO2 / polysafranin nanocomposite: synthesis, characterization and anomalous electrical behaviour.

We report the synthesis of sulfonated copolyaniline/polysafranin/L-ascorbic acid/Ag@SiO2 fine powdered nanocomposites and investigate the influence of incorporating the dye on their conductivity. The composite was characterized via IR, UV, cyclic voltammetry (CV), electric, dielectric, SEM, TEM, TGA and DSC measurements. Microscopy images revealed intensified spherical particles that were dispersed across the entire surface, and the SiO2/Ag particles were distributed on the surface. The XRD results exhibited peaks at many 2q values, and their interatomic spacing (d) and crystallite (grain) sizes were calculated. The thermal degradation curves exhibited an interesting model of stability. The cyclic voltammogram exhibited redox peaks identical to those of the reported analogues. The d.c. conductivity of the oligomer varied from 0.06 - 0.016 (s/cm), and that of the composite varied from 0.008 to 0.016 (s/cm). The material changed from a semiconductor to a metallic material. The observed conductivity is mainly attributed to self-doping between the sulfonate groups and the charged nitrogen atoms in the polymer chains. The frequency dependence of the permittivity, ε', showed a marked effect on the frequency window under consideration. The permittivity, ε', is independent of the increase in the frequency of the oligomer and the composite. This behavior supports the non-Debye dependency by confirming the occurrence of electrode polarization and space charge effects. In conclusion, the incorporation of safranin dye with a thermally stable, highly sulfonated polyaniline derivative/Ag@SO2 nanocomposite achieved improved conductivity after heating. The d.c. conductivities are comparable to those of many commercial inorganic or organic composites, and because of their attractive electrical properties, we suggest that these materials are promising for electronic field applications.

Dielectric Relaxation and AC Conductivity of Fe-Doped Glassy Semiconductors: Role of Fe Doping on Relaxation Time

AC conductivity and dielectric parameters are supposed to be two noticeable parameters that ensure the applicability of present samples for electronic and other applications. Presently, Fe-doped glassy semiconductors were developed by melt-quenching route and characterized using FT-IR, SEM, EDAX and decoupling index for structural, morphological and elemental examinations. Frequency dependent dielectric constant, AC conductivity, dielectric loss at different temperatures have been explored in a wide frequency and temperatures ranges. Electric modulus formalism has been conceived asit can exclude the electrode polarization effect at low frequency regime and suggest the transition from long-range mobility to short-range mobility assembly of polarons. It is also noteworthy that relaxation times are found to decrease with temperatures, which may indicate about the faster movement of charge carriers. The variation of KWW parameters directly indicate that after doping of Fe content into the resultant materials, the relaxation process is shifted from Non-Debye to Debye type up to a limit. By crossing the limiting value of composition (x = 0.3), it becomes Non-Debye type in a very slow rate. The present system also exhibits a small relaxation time in comparison with others’ works. Lower values of dielectric constant at high frequencies are expected to be important for their applications in photonics and opto-electronics. Scaling method of electric modulus spectra indicate that the dielectric relaxation process in the present system leads to a common relaxation process at various temperatures, but it is strongly dependent on compositions.

Effect of Frequency and Temperature on Dielectric and Transport Properties of CaO stabilized ZrO2@mullite composites

AbstractThis study concerns the synthesis and structure related electrical property analysis of CaO doped ZrO2@mullite composites. Two synthesis techniques (solid state reaction route and thermal plasma sintering) are used which results the formation of a composite consisting of mixed phase of orthorhombic mullite, tetragonal and monoclinic zirconia. The lattice parameters, residual strains, average crystallite size and cell volume of these CaO‐doped ZrO2@mullite composites are obtained from XRD analysis. Stabilization of t‐ZrO2 phase at room temperature is confirmed. Porous microstructure observed in SEM images results in low dielectric constant value of these composites. At room temperature and selected frequency of 1MHz, the dielectric constant and loss factor of 4.7 and 3.826 × 10−2 is observed for conventional CaO stabilized ZrO2@mullite composite and that of 3.8 and 2.19 × 10−2 is reported for plasma sintered CaO stabilized ZrO2@mullite composite. The impedance spectroscopic analysis demonstrates the negative temperature coefficient of resistance (NTCR) behavior and non‐Debye type relaxation behavior of both the CaO stabilized ZrO2@mullite composites. A negligible effect of electrode polarization is realized in these composites. The electronic band gap of conventional and plasma sintered CaO stabilized ZrO2@mullite composites is found to be around 3eV.

Distally-referred surface electrical nerve stimulation (DR-SENS) for haptic feedback

Objective. This study’s objective is to understand distally-referred surface electrical nerve stimulation (DR-SENS) and evaluates the effects of electrode placement, polarity, and stimulation intensity on the location of elicited sensations in non-disabled individuals. Approach. A two-phased human experiment was used to characterize DR-SENS. In Experiment One, we explored 182 electrode combinations to identify a subset of electrode position combinations that would be most likely to elicit distally-referred sensations isolated to the index finger without discomfort. In Experiment Two, we further examined this subset of electrode combinations to determine the effect of stimulation intensity and electrode position on perceived sensation location. Stimulation thresholds were evaluated using parameter estimation by sequential testing and sensation locations were characterized using psychometric intensity tests. Main Results. We found that electrode positions distal to the wrist can consistently evoke distally referred sensations with no significant polarity dependency. The finger-palm combination had the most occurrences of distal sensations, and the different variations of this combination did not have a significant effect on sensation location. Increasing stimulation intensity significantly expanded the area of the sensation, moved the most distal sensation distally, and moved the vertical centroid proximally. Also, a large anodic-leading electrode at the elbow mitigated all sensation at the anodic-leading electrode site while using symmetric stimulation waveforms. Furthermore, this study showed that the most intense sensation for a given percept can be distally referred. Lastly, for each participant, at least one of the finger-palm combinations evaluated in this study worked at both perception threshold and maximum comfortable stimulation intensities. Significance. These findings show that a non-invasive surface electrical stimulation charge modulated haptic interface can be used to elicit distally-referred sensations on non-disabled users. Furthermore, these results inform the design of novel haptic interfaces and other applications of surface electrical stimulation based haptic feedback on electrodes positioned distally from the wrist.

Frequency‐Domain Dielectric Response of Insulating Paper with High Humidity

AbstractThe frequency‐domain dielectric spectroscopy (FDS) of humid insulating paper has been measured at different temperatures. The data show three independent dielectric processes: electrode polarization, hopping conductivity and interfacial polarization. The dielectric properties of humid insulating paper are composed of hopping conductivity and interfacial polarization, and its equivalent dielectric model can be represented by a Havriliak‐Negami (HN) relaxation branch parallel hopping conductivity. At high temperatures and low frequencies, the measured dielectric spectroscopy bends downward, which is caused by the electrode polarization. In this case, the equivalent dielectric model is composed of the body impedance of insulating paper and the electrode polarization in series. According to the equivalent dielectric model, the components of electrode polarization, hopping conductivity, and interface polarization can be separated, thereby eliminating the parasitic effect of electrode polarization on the dielectric properties of insulating paper. Both of hopping conductivity and interface polarization of insulating paper move toward high‐frequency direction with temperature increasing. For humid insulating paper with a moisture content of 5.9%, the activation energies of hopping conductivity and interface polarization are 1.18 and 0.99 eV, respectively. This difference in activation energies results in the inability of the spectrums of insulating paper to overlap with each other at different temperatures. Based on the insulating paper without oil immersion, the results obtained in this article are not affected by oil or oil‐immersion operations. This provides a reference for exploring the dielectric properties and physical mechanisms of oil‐paper composite insulation materials widely used in high‐voltage equipment. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Nanocomposite Solid Polymer Electrolytes with Polymer Blend (PVDF‐HFP/Pluronic) as Matrix and GO as Nanofiller: Preparation, Structural Characterization, and Lithium‐Ion Conductivity Analysis

AbstractNanocomposite solid polymer electrolytes (NSPEs) with PVDF‐HFP/Pluronic as blend polymer matrix, graphene oxide (GO) as nanofiller, and LiClO4 are reported. FTIR spectroscopy reveals the crystal phase transformation of PVDF‐HFP from nonpolar α phase to electroactive γ phase upon salt addition that suggests the ion‐dipole interaction between the salt and the matrix. Further, Pluronic not only hinders the PVDF crystallization that increases the amorphous character of the matrix but also interacts with the salt and hence assists in salt dissociation in the blend matrix. The dc conductivity of PVDF‐HFP/Pluronic/LiClO4 blend SPE improves with increasing the Pluronic content reaching 0.73 × 10−6 Scm−1 at room temperature with 60 wt.% Pluronic. The dispersion of GO in the same blend SPE leads to a significant jump in room temperature ion conductivity (≈1.2 × 10−6 Scm−1) with 0.4% GO. Temperature‐dependent ion conductivity of the NSPEs reveals an Arrhenius type thermally activated process. The dc polarization data indicates that the conductivity is predominantly due to ions. Impedance plots exhibit a distorted semicircle at higher frequency and a tilted spike at lower frequency. The spike is an indication of ion diffusion and electrode polarization effect. Further, GO also has enhanced the mechanical properties of the fabricated NSPEs.

High pressures as an effective tool to separate different contributions to the electrode polarization of polar liquids and solids

Electrode polarization effects are an important issue in electrochemistry. Here we report investigation of electrode polarization effects in ethanol (used as a model material), in solid and liquid phases at high pressures. Application of pressure has dramatic effect on electrode polarization. Firstly, it significantly reduces the fractional power exponent, which dominates the low-frequency electrode polarization impedance, from approximately 1 at ambient pressure to less than 0.1 at 1.3 GPa. At pressure we can observe transition of electrode polarization impedance from fractional frequency law to inversely proportional to frequency relationship. This transition observed for the first time solves the problem with analytical limitation of electrode polarization effects at higher frequencies. Experimental data fitting by the procedure proposed by us, enables extracting the temperature dependencies of dielectric constant and dielectric relaxation frequency in the solid phase of ethanol at high pressures.

Structural, optical and dielectric properties of nanostructured La1−xSrxMnO3 perovskites

In this study, a series of nanocrystalline perovskites, La1−xSrxMnO3 (x = 0, 0.3, 0.5, 0.7), were synthesized via the combustion method, utilizing citric acid as fuel, which is an inexpensive synthesis method compared to the vacuum methods for growth. The powder X-ray diffraction study confirms the formation of the desired compositions. The XRD pattern shows that as the Sr doping concentration increases, crystallite size decreases from 30 nm to 14 nm. SEM micrographs reveal the spongy, porous structure of the prepared samples. A good optical absorbance is present in the UV and higher wavelength regions. The optical bandgap energy was increased from 1.4 eV to 2.5 eV. The concentration of Sr2+ ions can be correlated with the differences in refractive index, high frequency dielectric constant, and static dielectric constant. The BDS scrutiny of the specimens discloses that La0.3Sr0.7MnO3 harbours a prodigious dielectric constant at ambient temperature and subsonic frequencies. The dissemination of dielectric constants within the realm of low-frequency regions is elucidated in the context of the Maxwell-Wagner model. According to the results of the dielectric analysis, the dielectric constant exhibits a decrease as frequency increases, while it shows an increase with an increase in Sr doping concentration. The conductivity scrutiny lucidly expounds Johnscher's universal power law in the realm of the high-frequency region, and from the log σ – log f plot, the discernible effects of electrode polarization become manifest. Moreover, the presence of Sr ions enhances the ac conductivity.

Feasibility study of applying a graphene oxide-alginate composite hydrogel to electrokinetic remediation of Cu(II)-contaminated loess as electrodes

Inappropriate handling of heavy metal-containing wastewater resulting from extensive mining and smelting activities causes serious threats to surrounding environments and human health. The electrokinetic (EK) technology has been extensively applied to remediate heavy metal-contaminated sites because of its great manoeuvrability. The electrochemical polarization effect, however, reduces the electron transfer rate and could badly degrade EK removal efficiency. To this end, the present work proposed a novel graphene oxide-alginate composite hydrogel and applied it to copper removal as electrodes in EK remediation. A series of laboratory tests concerning its physical, mechanical, adsorption, and electrochemical properties were conducted. The graphene oxide (GO) particles provide larger average pore size and pore volume than traditional activated carbon electrodes. The surface functional groups, including hydroxyl, carboxyl, and epoxide groups, promote hydrogen bond formation. The GO particles and the calcium alginate are crosslinked with the hydrogen bonds, improving the mechanical properties of the graphene oxide-alginate composite hydrogel. Furthermore, the functional groups also encourage copper adsorption, and a high GO proportion does not necessarily mean an improvement in copper adsorption. The dynamic mechanism of Cu(II) adsorption onto the graphene oxide-alginate composite hydrogel conforms with the pseudo-second-order kinetic model. Moreover, the absence of oxidative and reductive peaks in the cyclic voltammograms is mainly attributed to the non-faradaic nature of the graphene oxide-alginate composite hydrogel, indicating a reduced electrode polarization effect. The Nyquist plot also approves its low resistance nature. The results were then compared against other electrodes to highlight the relative merits of the proposed graphene oxide-alginate composite hydrogel electrode.

Effect of surface treatment on the dynamics of relaxation processes in confinement: ferroelectric liquid crystal in porous Anopore membrane

ABSTRACT Dielectric properties of a ferroelectric liquid crystal 2-methylbutyl 4-decyloxybenzylidene-4’-n-aminocinnamate (DOBAMBC) confined in untreated and treated porous Anopore membrane were investigated depending on the frequency and temperature. The confinement of a ferroelectric liquid crystal in an untreated Anopore membrane leads to the disappearance of the Goldstone mode. Moreover, despite the modification of the pore surface with various surfactants, no the Goldstone mode or other additional relaxation processes were observed. The relaxation rate of the molecular δ-process is slightly shifted for untreated and treated Anopore membrane in comparison to the bulk. Generally, the relaxation rate temperature dependence shows the Arrhenius-type course, while for lecithin-treated Anopore, it is similar to the Vogel–Fulcher–Tammann-type dependence. Dielectric spectra are dominated at low frequencies by conductivity and electrode polarization effects and are modified in geometric constraints.

Formation of silver particles in [PVA:CS:PEG]-AgNO3 based biopolymer electrolyte membranes: Structural and electric transport properties study

[Chitosan (CS)-poly(vinyl) alcohol (PVA)-polyethylene glycol (PEG-200)]+xwt% silver nitrate (AgNO3) (x = 0, 10, 20, 30, 40) based biopolymer blend electrolytes (BPBEs) were prepared using solution casting method. FTIR results show the interaction of Ag+/NO3− with the constituents of polymers CS/PVA. XRD results reveal that the amorphousness increases with increasing AgNO3 concentration. Optical morphological (OM) images show that the silver, Ag(o) particles are agglomerated on the surface of the membrane. Temperature dependent dc conductivity (σdc) and dielectric relaxation frequency (fr) for BPBEs follow the Arrhenius type behavior and the sample containing 30 wt% salt has optimum dc conductivity, σdc∼1.7×10−4 S/cm at 30oC with lowest activation energy∼ 0.16 eV. The ac conductivity spectra follow the Jonscher's power law (JPL) with power law exponent, s > 1. The scaling of AC conductivity and loss tangent (tanδ) spectra were performed with respect to temperatures/concentrations of salt. The dielectric permittivity study reveals that the electrode polarization effect predominates at low frequencies. The Ionic Transference Number (ITN) measurement was used to determine the nature species of charge carrier, either ionic or electronic. The linear sweep voltammetry (LSV), result shows that 30% AgNO3containing sample has the electrochemical stability window (ESW) ∼+1.5 to -1.5 V.

Unparalleled Dielectric‐Switching Effects Caused by Dual Polarization Synergy

AbstractDielectric switching materials are prospective candidates for smart electronic/electrical applications, and high dielectric switching ratios are crucial for their practical applications. However, the substantial improvement of the dielectric switching ratio is limited by the available dielectric switching mechanisms, and obtaining high dielectric switching ratios is a major challenge. Here, an unparalleled dielectric switching effect is reported in a water‐in‐oil emulsion system, caused by dual polarization synergy below the dielectric transition temperature in concert with suppression of the electrode polarization above the dielectric transition temperature. The synergistic dielectric switching effect of interfacial polarization and electrode polarization endows the emulsion with unprecedentedly high dielectric switching ratios. The highest room temperature dielectric switching ratio of this emulsion system up to 2.86 × 106 at 20 Hz, is four orders of magnitude higher than the highest switching ratio reported so far. The unparalleled high dielectric switching ratio, reliable cycle stability, good frequency adaptability, and satisfactory scalability make the inorganic salt solution/octadecane emulsions potentially excellent candidates for high‐sensitivity room‐temperature smart switching or sensing devices.

Characterizing Phase Separation of Amorphous Solid Dispersions Containing Imidacloprid.

Amorphous-Amorphous phase separation (AAPS) is an important phenomenon that can impede the performance of amorphous solid dispersions (ASDs). The purpose of this study was to develop a sensitive approach relying on dielectric spectroscopy (DS) to characterize AAPS in ASDs. This includes detecting AAPS, determining the size of the active ingredient (AI) discrete domains in the phase-separated systems, and accessing the molecular mobility in each phase. Using a model system consisting of the insecticide imidacloprid (IMI) and the polymer polystyrene (PS), the dielectric results were further confirmed by confocal fluorescence microscopy (CFM). The detection of AAPS by DS was accomplished by identifying the decoupled structural (α-)dynamics of the AI and the polymer phase. The α-relaxation times corresponding to each phase correlated reasonably well with those of the pure components, implying nearly complete macroscopic phase separation. Congruent with the DS results, the occurrence of the AAPS was detected by means of CFM, making use of the autofluorescent property of IMI. Oscillatory shear rheology and differential scanning calorimetry (DSC) detected the glass transition of the polymer phase but not that of the AI phase. Furthermore, the otherwise undesired effects of interfacial and electrode polarization, which can appear in DS, were exploited to determine the effective domain size of the discrete AI phase in this work. Here, stereological analysis of CFM images probing the mean diameter of the phase-separated IMI domains directly stayed in reasonably good agreement with the DS-based estimates. The size of phase-separated microclusters showed little variation with AI loading, implying that the ASDs have presumably undergone AAPS upon manufacturing. DSC provided further support to the immiscibility of IMI and PS, as no discernible melting point depression of the corresponding physical mixtures was detected. Moreover, no signatures of strong attractive AI-polymer interactions could be detected by mid-infrared spectroscopy within this ASD system. Finally, dielectric cold crystallization experiments of the pure AI and the 60 wt % dispersion revealed comparable crystallization onset times, hinting at a poor inhibition of the AI crystallization within the ASD. These observations are in harmony with the occurrence of AAPS. In conclusion, our multifaceted experimental approach opens new venues for rationalizing the mechanisms and kinetics of phase separation in amorphous solid dispersions.

Influence of polarization on the electrochemical activity of La2–xCaxNiO4+δ electrodes in contact with Ce0.8Sm0.2O1.9 electrolyte

The effect of electrode polarization on the electrochemical activity of La2NiO4+δ and La1.9Ca0.1NiO4+δ electrodes in contact with the Ce0.8Sm0.2O1.9 electrolyte is studied by impedance spectroscopy. It is found that anodic polarization facilitates electrode reaction for both electrodes leading to significant decrease in the polarization resistance. The effect of cathodic polarization differs between the electrodes: the polarization resistance of La2NiO4+δ electrode slightly increases, while the polarization resistance of La1.9Ca0.1NiO4+δ electrode strongly decreases with the increase in the applied potential. It is established that in all cases the polarization mostly affects the low-frequency stage of the electrode reaction, connected with oxygen surface exchange and diffusion. The surface state of the samples after exposure under polarization is studied by X-ray photoelectron spectroscopy. Correlations between electrochemical activity of the electrodes and the changes in their surface composition under polarization are discussed.