Electrochemical Impedance Spectra Research Articles

Unsupervised feature extraction for lithium-ion battery electrochemical impedance spectroscopy and capacity estimation using deep learning method

In this paper, we propose an unsupervised feature extraction technique using a variational autoencoder and generative adversarial network (VAEGAN) that automatically extracts meaningful latent variables from the electrochemical impedance spectra (EIS) of lithium-ion (Li-ion) batteries. These variables accurately reflect the degree of Li-ion battery degradation and are closely related to its capacity. By analyzing the latent variables, it was found that the network can learn the effect of Li-ion battery capacity degradation on the EIS. The extracted latent variables are then used as input features for Gaussian Process Regression (GPR) to estimate the capacity of Li-ion batteries under uneven usage and with unknown historical data. The results show that the capacity prediction method proposed in this paper can significantly reduce prediction errors compared to the current state-of-the-art methods. The method not only provides a more reliable capacity estimation but is also robust to highly noisy EIS data, making it more suitable for practical application scenarios.

Battery degradation evaluation based on impedance spectra using a limited number of voltage-capacity curves

Degradation prediction is crucial for ensuring safe and reliable operation of batteries. However, relying solely on capacity to characterize aging cannot comprehensively represent the health status of the battery. This work explores the potential of using a limited number of partial voltage-capacity curves to evaluate battery degradation with the aid of deep learning approaches, which can be used for onboard applications. A sequence-to-sequence model is proposed to predict the electrochemical impedance spectra during battery degradation. It only uses capacity sequences within a specific voltage range at fixed voltage increments from a limited number of cycles, which can be flexibly adapted to different life stages in an end-to-end manner. The proposed method has been validated based on the developed degradation dataset. The root mean square errors for the prediction of impedance spectra are less than 1.48 mΩ. Capacities and resistances associated with electrochemical processes can be further extracted from the obtained impedance spectra, facilitating a comprehensive evaluation of battery degradation. As a limited number of measured data are needed, the proposed method can reduce data storage requirements and computational demands, which enables fast and comprehensive aging diagnosis.

Electrochemical applications of CdO-Co-ZnO nanocomposites, their synthesis and characterization reveal their multifunctional abilities

In this study, we investigated the electrochemical catalysis potential of hybrid nanocomposites containing CdO, Co and ZnO nanocomposites, as opposed to Zn-O doped Co nanocomposites, have weaker Coulomb interactions due their ionic bonds. Because CdO and Co form a covalent bond, Co interacts more strongly with O than Zn. In order to reduce nanoparticle crystallinity, oxygen defects improve the interaction between −O and oxygen defects in the lattice. From SEM micrographs, it appears that CdO does not completely change under the influence of dopants. It can be seen from the SEM image that both materials have very tightly packed particles. The Co and CdO dopants in ZnO nanocomposites prevent them from absorbing a large range of visible wavelengths. It is more energy-dense for nanocomposites with 5.28 eV to compare to 5.14 eV nanocomposites. The fact that CdO matrix has a tuneable bandgap is evident since different types of dopants are used in its manufacture. There are at least three distinct absorption modes in Co nanocomposites doped with CdO, around 450, 498, and 676 cm−1. In addition to its absorption from 450 cm−1 and 498 cm−1 vibrational modes, Co-O stretching absorption along the [101] plane has also been observed at 676 cm−1. As a method of studying charge carriers, photoluminescence spectroscopy is usually used. This method can be used to analyze electron-hole pairs (e−/h+) formed by semiconducting particles. It is in the blue emission range between the luminescence band of 615 nm and the valence band of 635 nm. With increasing cobalt and zinc concentrations, CdO nanomaterials lose their remanent magnetization. CdO has been demonstrated to have significant coercive effects in both pure and additively incorporated solutions regardless of their anisotropic, morphological, porosity, and particle size distribution. Electrochemical impedance spectrum measurements were conducted between 100 kHz and 0.01 Hz. According to the Nyquist plot, purity CdO, CdO doped Co, and CdO doped ZnO nanocomposites show a high frequency resistance to charge transfer. Nanocomposites that contained CdO doped Co & ZnO were exposed to UV light for 120 min to remove the solution. The degradation of MO is virtually nonexistent when no photocatalyst is present, but with a photocatalyst, degradation can reach 92.56 %.

Microstructural transformation and corrosion–cavitation behavior of ultrasonic nanocrystal surface modified nickel aluminum bronze (NAB)

In this study, nickel–aluminum bronze (NAB) is optimized by ultrasonic nanocrystal surface modification (UNSM), and its surface microstructural evolution, surface hardness, electrochemical corrosion behavior, and cavitation erosion behavior are investigated. The potentiodynamic polarization curves and electrochemical impedance spectra before and after UNSM treatment of NAB are measured using a typical three-electrode system. The cavitation erosion process is simulated through the vibration of ultrasonic waves underwater, and the cavitation erosion resistance performance of various specimens is evaluated. UNSM significantly refines the coarse and heterogeneous multi-phase structure of the cast NAB, providing a relatively uniform and dispersed structure. Simultaneously, severe plastic deformation rapidly increases micro-strains on the NAB surface, which effectively improves its surface hardness from 211 to 360 Hv. After UNSM treatment, the corrosion potential increases slightly; and the passivation potential and current decrease considerably, dropping from 207 to 103 mV and from 5.23 to 2.41 mA/cm2, respectively. This is primarily because of the slowdown of selective-phase corrosion and the uniform formation of an oxide film. Additionally, UNSM parameters affect corrosion potential by regulating surface roughness. A smoother surface corresponds to a higher corrosion potential at the same load. UNSM treatment significantly improves the cavitation corrosion resistance of NAB, primarily because an increase in hardness and uniform distribution of structure effectively slows the speed of crack formation and propagation, which is a result of the synergistic improvement of mechanical and corrosion resistance properties.

The mechanism of in-homogeneous mass transfer process of separators in lithium-ion batteries.

The liquid-phase mass transport is the key factor affecting battery stability. The influencing mechanism of liquid-phase mass transport in the separators is still not clear, the internal environment being a complex multi-field during the service life of lithium-ion batteries. The liquid-phase mass transport in the separators is related to the microstructure of the separator and the physicochemical properties of electrolytes. Here, in-situ local electrochemical impedance spectra were developed to investigate local inhomogeneities in the mass transfer process of lithium-ion batteries. The geometric microstructure of the separator affects the mass transfer process, with a reduction in porosity leading to increased overpotentials. There is a competitive relationship among porosity, tortuosity, and membrane thickness in the geometric parameters of the separator, resulting in a peak of polarization. The resistance of the liquid-phase mass transfer process is positively correlated with the viscosity of the electrolyte, making ion migration difficult due to high viscosity. Polarization is closely related to the electrochemical performance, so a phase diagram of battery performance and inhomogeneous mass transfer was developed to guide the design of the battery. This study provides a guiding basis for the development of high stability lithium-ion batteries.

Structure-electrochemical performance relationship in Sr2(Fe1-xVx)MoO6 anode

Structural property is becoming a powerful tool to manipulate oxygen vacancy concentration and electrochemical performance of electrode material. In this work, the structure-electrochemical performance relationship of Sr2(Fe1-xVx)MoO6 (x = 0, 0.1, 0.2 and 0.25) anode is investigated based on X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Energy Dispersive Spectrometer (EDS), BET surface area, DC four-point probe, I–V and electrochemical impedance spectra (EIS). XRD results show that all the compounds are of single phase, the tetragonal to cubic phase transition occurs at x = 0.1, which plays important role in its electrochemical performance. Firstly, the disappeared structural distortion in Sr2(Fe1.8V0.2)MoO6 and Sr2(Fe1.75V0.25)MoO6 anodes benefits electron hopping between Fe–O–Mo–O–Fe, so electron transfer processes (high-frequency semicircle) in their EIS are facilitated. Secondly, both XPS survey and EDS spectrum confirm the change in oxygen content with structural transition, Sr2(Fe1.9V0.1)MoO6 anode own higher concentration of oxygen vacancy, thus the oxygen surface exchange and diffusion process (low-frequency arc) of the corresponding cell is reduced significantly. Consequently, Sr2(Fe1.9V0.1)MoO6-based cell exhibits the highest power output (810 mW cm−2) at 850 °C. For Sr2(Fe1.8V0.2)MoO6 anode, BET surface area test reveals the slightly higher value, while its lower power density indicates that the influence of oxygen vacancy prevails over that of microstructure. Combining with EIS results, it can be deduced that Sr2(Fe1-xVx)MoO6 anodes with tetragonal symmetry own higher concentration of oxygen vacancy, thus the expected electrochemical performance is better than that of other cells. Understanding the critical role of structure is important for achieving highly active electrode material.

Electrochemical behaviour of redox-robust electrode in contact with protonic electrolyte: Case of double-layered Sr2Fe1.5Mo0.5O6-δ - Ce0.8Sm0.2O2-δ composite

Electrochemical devices based on proton-conducting oxides offer a significant potential for implementation in a variety of high-temperature electrochemical applications. It is a well-known fact that electrochemical devices require active electrodes to function optimally. Over the last few years, Sr2Fe1.5Mo0.5O6-δ has received much attention as an effective redox-robust electrode for oxygen conducting electrolytes. This study presents, for the first time, the results of investigations on a double-layered composite electrode based on Sr2Fe1.5Mo0.5O6-δ in contact with a barium-free proton-conducting electrolyte La0.9Sr0.1ScO3-δ. It was found that the investigated electrode exhibits low polarization resistance about 0.15 and 0.22 Ohm cm2 in wet air and wet hydrogen at 600 °C, respectively. In addition, the electrode exhibits acceptable redox stability and CO2 tolerance. Also, the results of electrochemical impedance spectra analysis and a discussion on the parallel pathways of hydrogen oxidation and oxygen reduction reactions and the nature of rate-determining steps are presented in the manuscript. The obtained results show the high prospects for a Sr2Fe1.5Mo0.5O6-δ - based composite electrode for protonic ceramic electrochemical cells.

Comparison of techniques based on frequency response analysis for state of health estimation in lithium-ion batteries

Frequency response analysis (FRA) methods are commonly used in the field of State of Health (SOH) estimation for Lithium-ion batteries (Libs). However, identifying their appropriate application scenarios can be challenging. This paper presents four FRA techniques, including electrochemical impedance spectra (EIS), mid-frequency and low-frequency domain equivalent circuit model (MLECM), distribution of relaxation time (DRT) and non-linear FRA (NFRA) technique. This paper proposes two estimation frameworks, machine learning and curve fitting, to be applied to each of the four techniques. Eight SOH estimation models are developed by linking the extracted feature parameters to the battery capacity variations. The paper compares the accuracy of estimation, estimation range, and other properties of the eight models. Application scenarios are identified for the techniques by using three classification methods: different estimation frameworks, frequency response linearity, and impedance technique. The results demonstrate that MLF is recommended for scenarios with a large amount of battery data, while CFF is recommended for scenarios with a small amount of data. NFRA could be applied to electric vehicle power batteries, while LFRA is recommended to be used for retired batteries. EIS method is recommended for complex and dynamic scenarios, while non-EIS method is recommended for scenarios that require high accuracy.

Ternary Rotational Polyanion Coupling Enables Fast Li Ion Dynamics in Tetrafluoroborate Ion Doped Antiperovskite Li2OHCl Solid Electrolyte

AbstractLi‐rich antiperovskite (LiRAP) hydroxyhalides are emerging as attractive solid electrolyte (SEs) for all‐solid‐state Li metal batteries (ASSLMBs) due to their low melting point, low cost, and ease of scaling‐up. The incorporation of rotational polyanions can reduce the activation energy and thus improve the Li ion conductivity of SEs. Herein, we propose a ternary rotational polyanion coupling strategy to fasten the Li ion conduction in tetrafluoroborate (BF4−) ion doped LiRAP Li2OHCl. Assisted by first‐principles calculation, powder X‐ray diffraction, solid‐state magnetic resonance and electrochemical impedance spectra, it is confirmed that Li ion transport in BF4− ion doped Li2OHCl is strongly associated with the rotational coupling among OH−, BF4− and Li2−O−H octahedrons, which enhances the Li ion conductivity for more than 1.8 times with the activation energy lowering 0.03 eV. This work provides a new perspective to design high‐performance superionic conductors with multi‐polyanions.

Ternary Rotational Polyanion Coupling Enables Fast Li Ion Dynamics in Tetrafluoroborate Ion Doped Antiperovskite Li2OHCl Solid Electrolyte.

Li-rich antiperovskite (LiRAP) hydroxyhalides are emerging as attractive solid electrolyte (SEs) for all-solid-state Li metal batteries (ASSLMBs) due to their low melting point, low cost, and ease of scaling-up. The incorporation of rotational polyanions can reduce the activation energy and thus improve the Li ion conductivity of SEs. Herein, we propose a ternary rotational polyanion coupling strategy to fasten the Li ion conduction in tetrafluoroborate (BF4-) ion doped LiRAP Li2OHCl. Assisted by first-principles calculation, powder X-ray diffraction, solid-state magnetic resonance and electrochemical impedance spectra, it is confirmed that Li ion transport in BF4- ion doped Li2OHCl is strongly associated with the rotational coupling among OH-, BF4- and Li2-O-H octahedrons, which enhances the Li ion conductivity for more than 1.8 times with the activation energy lowering 0.03 eV. This work provides a new perspective to design high-performance superionic conductors with multi-polyanions.

High carbon containing biomaterial offering honeycomb morphology as a charge storing electrode in aqueous alkaline electrolytes

Research on unconventional carbon structures and morphologies obtainable from renewable sources are a way forward in realizing sustainable materials for the next-generation industry. Herein, renewable porous carbon from a biomass (coconut rachis) with high carbon content (∼81 %) and honeycomb morphology (inner diameter ∼60 μm and wall thickness ∼500 nm) is developed as an electrochemical capacitor electrode. The coconut rachis upon chemical activation yield a surface area ∼1,630 m2‧g−1 and desirable pore characteristics for storing aqueous cations. The electrochemical charge storability of the porous carbon electrodes in 1 M KOH, NaOH and LiOH electrolytes showed specific capacitances ∼320, ∼140 and ∼102 F‧g−1, respectively. Electrochemical impedance spectra validated the higher capacitance in the KOH electrolyte. Besides, symmetric supercapacitor full cells were fabricated using the present electrode in 1 M KOH electrolyte with desirable charge storage properties. Given the abundance of the precursor and desirable charge storage characteristics, the present work could be useful in developing the coconut rachis-resourced honeycomb-shaped porous carbon as a charge storing electrode.

Facile synthesis of LiFePO4/Cu composite as enhanced cathode material for lithium-ion battery by a solid-state grinding method

Lithium iron phosphate (LiFePO4, LFP) is a frequently utilized cathode material for lithium-ion batteries. However, its practical applications are constrained by its relatively low ionic and electronic conductivities. To address this issue, it is possible to utilize highly conductive metallic coatings to enhance the material's electronic conductivity. Herein, LiFePO4 with Cu composites (LFP/Cu) as cathode was synthesized by a simple solid-state process via one-step grinding in the presence of CuNO3 and ascorbic acid. The discharge capacity of the LFP/Cu cathode with 0.75 wt% Cu was found to be 160.9 mA h g−1 at 0.1 C, representing a close approximation of its theoretical capacity and a notable enhancement compared to pure LFP (145.9 mA h g−1). Furthermore, it demonstrates excellent stability with a capacity retention of 136.5 mA h g−1 after 100 cycles at 2 C, as well as good rate performance. The electrochemical impedance spectra demonstrate that the incorporation of copper results in a further reduction in the resistance of LFP/Cu compared to pure LFP. The incorporation of copper particles into lithium iron phosphate has been shown to enhance its electronic conductivity, thereby further enhancing its electrochemical performance. In this study, we present a facile and cost-effective room-temperature synthesis method for the preparation of LiFePO4/Cu composites with improved electrochemical properties. This work provides a promising avenue for the design of cathode materials in lithium-ion batteries.

Effects of Deformation Microstructures on the Electrochemical Properties of Mg-Hg-Ga Alloy Anode

Mg-Hg-Ga alloy is one of the anode materials for seawater-activated batteries. Here, Mg-3.0 wt%Hg-3.0 wt%Ga alloys were prepared by extrusion and rolling and the microstructure of the Mg-3.0 wt%Hg-3.0 wt%Ga alloy after plastic deformation was studied. The effects of deformation microstructures on the discharge properties and corrosion behavior of the alloys were investigated by galvanostatic discharge, potentiodynamic polarization, electrochemical impedance spectra experiments, and Mg/AgCl battery test. The results show that the microstructure of the extruded alloy is uniform, and the corrosion activity and discharge activity of the extruded alloy are relatively weak. Hot rolling deformation refines the grains and promotes the precipitation of the Mg5Ga2 phase distribute more dispersively, which results in faster and more uniform activation of the alloy, thus improving the corrosion activity and discharge activity of the Mg-3.0 wt%Hg-3.0 wt%Ga alloy. The results of galvanostatic discharge in half battery and Mg/AgCl battery discharge tests show that rolling deformation improves the discharge properties of the alloy, and the alloy with 78% rolling reduction has the best discharge performance.

The aging pattern of lithium-ion batteries based on experiments at different temperatures

Abstract In this paper, we take an 18650-type LiFePO4 battery as the research object to investigate the aging mechanism of Li-ion batteries at different temperatures. The aging tests are conducted at 25°C, 35°C and 45°C. The results show that elevating the operating temperature can improve the cycle life of Li-ion batteries. The aging mechanism was analyzed by incremental capacity and electrochemical impedance spectrum analysis. The following conclusions were obtained: the aging mechanism of lithium-ion batteries mainly includes loss of lithium inventory, loss of active material, and conductivity loss, among which loss of lithium inventory and loss of active material are the main causes of Li-ion battery aging, and the contribution of conductivity loss is the smallest. Further analysis of the causes of battery aging by disassembling and testing the aging electrode sheet SEM and TEM shows that the aging of Li-ion battery is manifested by the rupture of graphite particles, the generation of SEI layer and lithium dendrite, and increasing the temperature can ease the rupture of graphite particles and the generation of lithium dendrite, thus improving the cycle life of the battery.

Imidazoline As a Volatile Corrosion Inhibitor for Mitigation of Top- and Bottom-of-the-Line CO2 Corrosion in Carbon Steel Pipelines.

A fatty acid imidazoline-based inhibitor was synthesized via a facile solvent-free synthesis method between tall oil fatty acid (TOFA) and diethylenetriamine (DETA) under atmospheric conditions with a short reaction time. The as-synthesized imidazoline (S-Imd) acted as an effective inhibitor for reducing or preventing corrosion of carbon steel pipelines at both bottom of the line (BOL) and top of the line (TOL) positions under simulated conditions of a gas pipeline in a CO2-saturated environment. The inhibition efficacy was examined by both weight loss and electrochemical measurements, such as the electrochemical impedance spectrum (EIS), potentiodynamic polarization (PDP), and linear polarization resistance (LPR). The results revealed that the S-Imd, 2-(8-heptadecenyl)-2-imidazoline-1-ethanamin, at 300 ppm exhibited a superior inhibition efficiency of up to 91.6 and 89.9% for BOL and TOL corrosion tests, respectively. The surface morphology of the carbon steel test specimens was also examined using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), and contact angle analysis. It was found that the as-synthesized S-Imd acted as a mixed-type inhibitor that exhibited a decreased surface roughness and oxide layer on carbon steel surfaces. However, the water contact angle was found to increase, implying enhanced hydrophobicity of the surface. Adsorption of the imidazoline molecules on carbon steel surfaces followed the Langmuir adsorption isotherm. The present work provides very promising results in the synthesis and utilization of the studied imidazoline as a volatile corrosion inhibitor (VCI), especially for carbon steel pipelines in petroleum industries.

Ti2NTx MXene/rGO nanocomposites: Optical tunning, functional bonding and electrochemical analysis for supercapacitor electrode application

Ti2NTx MXene/rGO nanocomposites were prepared via a two-step chemical etching and reduction method. TEM confirmed the stacked multilayer structure with an average interplanar spacing of 0.2 nm and the formation of Ti2NTx/rGO QDs of size from 0.14 to 0.33 nm. The absorption of Ti2NTx MXene/rGO composites decreased from 5.59 to 4.53 eV with increasing rGO concentration due to quantum confinement and microstructural rearrangement of Ti2NTx MXene within the rGO network. Cyclic voltammetry showed a specific capacitance (Cp) of 47.6–247F/g at 5 mV/s in −0.2–0.8 V. Galvanostatic charge–discharge resulted in Cp of 329.14–1203.86F/g at 1 A/g in 1 M H2SO4. The highest capacitive retention of 84.3 % was observed after 5000 cycles for Ti2NTx MXene. Electrochemical impedance spectra revealed that the charge transfer rate was maximum in (Ti2NTx)0.50/rGO0.50 due to the lowest RCT of 7.23 Ω. From the corrosion test, the Icorr ranged from 3.73 to 5.79 µA, and the Vcorr ranged from −0.008 to 0.26 V in the Ti2NTx MXene/rGO composites. Ti2NTx MXene/rGO composite showed remarkable electrochemical properties in acid electrolytes, such as high Cp and corrosion resistance, making them intriguing materials for supercapacitor electrode application.

Are Selenides the Same as Sulfides? Structure, Spectroscopy, and Properties of Narrow-Gap Rare-Earth Semiconductors RE2Sn(S1-xSex)5 (RE = La, Ce; x = 0-0.8).

The ternary rare-earth sulfides RE2SnS5 (RE = La-Nd) and the partial solid solutions RE2Sn(S1-xSex)5 (RE = La, Ce; x = 0-0.8) were prepared in the form of polycrystalline samples by reaction of the elements at 900 °C and as single crystals in the presence of KBr flux. They adopt the La2SnS5-type structure (orthorhombic, space group Pbam, Z = 2) consisting of chains of edge-sharing SnCh6 octahedra separated by RE atoms. Although the cell parameters evolve smoothly in RE2Sn(S1-xSex)5, detailed structural analysis by single-crystal X-ray diffraction revealed a pronounced preference for the Se atoms to occupy two out of the three chalcogen sites, which offers a rationalization for why the all-selenide end-members RE2SnSe5 do not form. Solid-state 119Sn NMR spectra confirmed the nonrandom distribution of SnS6-nSen local environments, which could be resolved into individual resonances. The Raman spectra of RE2SnS5 compounds show an intense peak at 307-320 cm-1 assigned to a symmetric A1g mode, which is dominated by Sn-S bonds; the Raman peak intensities varied with Se substitution in La2Sn(S1-xSex)5. Optical diffuse reflectance spectra, band structure calculations, and electrochemical impedance spectra indicated that these compounds are narrow band gap semiconductors; the optical band gaps are insensitive to RE substitution in RE2SnS5 (0.7 eV) but they gradually decrease with greater Se substitution in RE2Sn(S1-xSex)5 (0.7-0.4 eV).

Aging behavior difference between aqueous coatings and solvent coatings in sulfuric acid environment

PurposeThis paper aims to compare the aging behavior of water-based coatings and solvent-based coatings in sulfuric acid environments and to discuss the related mechanism.Design/methodology/approachA sulfuric acid solution with a concentration of 5 Wt.% was selected for immersion test at 23°C. The failure behavior of the coating was studied by combining the transformation rules of the macroscopic morphology and basic properties with the results of electrochemical impedance spectrum analysis.FindingsThe results showed that the surface smoothness of the water-based coating was lower than that of the solvent-based coating. The glossiness, thickness and hardness of the water-based coating exhibited more significant changes. The electrochemical test also indicated that the water-based coating was infiltrated by a large number of corrosive media, which may have induced corrosion under the coating. In contrast, the solvent-based coating showed good shielding properties, but the adhesion was seriously affected by the corrosive medium.Originality/valueThis work clarified the difference of failure behavior and mechanism between water-based coatings and solvent-based coatings in acidic environment and provided a theoretical basis for the selection and mechanism research of anticorrosive coatings.

Facile synthesis of Zn2V2O7/RGO nanocomposite for enhancing the electrochemical performance and evaluating the supercapacitor device

Pyrochlore-structured zinc vanadium oxide with RGO (Zn2V2O7/RGO) composite was synthesized using the simple hydrothermal process for energy storage device fabrication. The structural, vibration spectrum, surface morphology, and elemental of the Zn2V2O7/RGO composite were analyzed using different analytical methods. Then, the electrochemical performance was examined using Zn2V2O7/RGO composite modified electrode with 3-electrode and 2-electrode setup by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectrum (EIS) techniques. Consequently, the Zn2V2O7/RGO composite revealed notable pseudo-capacitive behavior which has been confirmed through CV analysis. The nano size-based Zn2V2O7/RGO composite electrode material obtained notable specific capacitance (Csp) of 1400.51F/g owing to the synergistic promotion of Zinc and vanadium oxides. Furthermore, the ASC device of Zn2V2O7/RGO ||RGO displayed the efficient power density of 1371 kW/kg at the energy density of 8Wh/kg and the device has enhanced cycling performance with 72.8 % capacitance.

Boosting the photocatalytic activity of bismuth vanadate (BiVO4) via optimization of the internal polarization

Photocatalytic performance can be improved by optimizing the morphology and surface texture of the photocatalyst or forming different p-n and/or n-n heterojunctions. Although the heterojunction system enhances photocatalytic property; however, an internal spontaneous polarization electric field may be much more effective due to the separation of electron-hole pairs when the polarization field forces them to move in different directions. The present study demonstrated this insight where the BiVO4 synthesis condition and polarization field forces were controlled via homogeneous precipitation in the presence of polyvinylpyrrolidone (PVP). The as-synthesized BiVO4 photocatalysts' structure and morphology were investigated using XRD, SEM, Raman, DRS, and PL. The result revealed that the increase of PVP concentration reformed the shaping to the truncated bipyramid-like shape and creates a spontaneous internal polarization that enhanced BiVO4 photocatalytic performance. The photocatalytic activity of BiVO4 was evaluated by monitoring the photocurrent enhancement using chronoamperometry, electrochemical impedance spectra and the photodegrading of methylene blue (MB) aqueous solution to harmless compounds in the presence of light. The spontaneous polarization between the different facets of BiVO4 crystal enhances the e−/h+ separation during internal facets homojunction and leads to four times photocurrent enhancement and the MB photocatalytic degradation rate increased from 0.43 to 1.92 min−1.