Behavior Of Electrodes Research Articles

Processing of Aqueous Graphite–Silicon Oxide Slurries and Its Impact on Rheology, Coating Behavior, Microstructure, and Cell Performance

The mixing process is the basis of the electrode microstructure, which defines key cell performance indicators. This work investigated the effects of varying the energy input within the mixing procedure on slurry rheology, coating behavior, mechanical and electrical properties of dry electrodes and electrochemical performance of cells fabricated from these negative electrodes. Energy input differences were achieved by varying the solids content within the mixing procedure; however, the final total solids content of the slurries was always the same. The slurries, produced with graphite and silicon oxide as active materials and carboxymethylcellulose (CMC) and styrene-butadiene rubber as binders, showed large differences in flow behavior which were explained by changes in CMC adsorption and mechanical degradation because of increasing energy input. Low shear viscosity and the degree of shear thinning decreased with increasing energy input, resulting in a narrower stability window for slot-die coating. The resistance between the electrode and current collector decreased as more CMC was adsorbed on the active material. Electrode adhesion drastically dropped at the highest energy input, presumably due to a change in SBR distribution. Despite these variations, all fabricated pouch cells demonstrated excellent electrochemical performance and a slight trend of increased charge capability was observed in cells prepared with higher energy input.

A kinetic study on oxygen redox reaction of a double-perovskite reversible oxygen electrode— Part II: Modelling analysis

Mixed ionic and electronic conductor double perovskites are very promising oxygen electrode materials for solid oxide cell technology. However, understanding their specific kinetic mechanism is a fundamental preliminary step towards detecting the best reachable performance, optimising the operation conditions and the electrode architecture. Indeed, the contributions of different rate-determining steps can vary as a function of the working point. In this framework, after a detailed experimental campaign devoted to the study of SmBa0.8Ca0.2Co2O5+δ (SBCCO) oxygen electrode behaviour, the authors propose a theoretical analysis of oxygen reduction and oxygen evolution reaction paths that couples a preliminary study through equivalent circuit analysis with a physics-based model to predict the operation of SBCCO as a reversible oxygen electrode. Following a semi-empirical approach, the kinetics formulation was derived from thermodynamics and electrochemistry fundamental principles and was tuned on electrochemical impedance spectroscopy (EIS) spectra in order to retrieve the unknown kinetic parameters. The successful cross-checking of the simulated results with the experimental data obtained by direct current measurements validated the proposed model, here applicable in further works on full cells to simulate the SBCCO oxygen reversible electrode performance.

Efficiency Improvement of Photoelectrochemical Solar Cell Applications by Using Ternary Hybrid MoS2/g-C3N4/Cu2O

In this paper, molybdenum disulfide MoS2 was hybridized with graphene carbon nitrite (g-C3N4) and Cu2O in order to enhance the photoelectrochemical (PEC) activity and increase the light absorption range of Cu2O thin film. The melamine powder was poured in an empty container and then heated in a furnace to attain the powder. The ternary hetero-epitaxial growth was achieved by growing of MoS2/g-C3N4 on the Cu2O hybrid by a partial thermal oxidation process. The characteristics of MoS2/g-C3N4/Cu2O hybrid film were investigated through XRD, FT-IR and photoelectronchemistry-related measurements. The PEC behavior of the ternary hybrid electrode was investigated using current-voltage test under illumination. The efficiency calculated from current-voltage test under illumination shows that the presence of graphene carbon nitrite and molybdenum disulphide within the film networks, despite its low content, could stimulate substantial improvement in maximum photoconversion efficiency from 0.036% to 0.33%. This improvement is attributable to the enhancement of the electron-transferring proficiency upon the insertion of g-C3N4 and, MoS2 as confirmed by X-Ray Diffraction Analysis (XRD). The PEC test results signify that the photoelectrochemical activity of the MoS2/g-C3N4/Cu2O ternary hybrid is much higher than that of subtrate. The mechanisms accountable for the enhanced PEC behavior of the MoS2/g-C3N4/Cu2O ternary hybrid are discussed in detail.Keywords: Cuprous Oxide, J-V Characteristic, Hetero-structure, Photoelectrochemical, Thermal Oxidation.

Clarifying the limiting factor of material utilization in thick electrodes of lithium-ion batteries

Improving the energy density of lithium-ion batteries is a goal pursued in state-of-the-art batteries, and the use of thick electrodes with high active material loading densities is one of the most effective and direct methods. Most studies indicate that the hindrance to the practical application of thick electrodes is mainly attributed to the slow charge kinetics, resulting in very low utilization of active materials. Here, this work shows that the thermodynamic properties of the electrode material also have a significant impact on the electrode reaction behavior. When the equilibrium potential of the electrode material has a strong dependence on the state of charge, it promotes the uniform reaction of the electrode active material. By simulating the full battery under low and high load conditions, the reaction behavior of the thin electrodes is dominated by the equilibrium potential curve. However, the reaction behavior of thick electrodes is regulated by both kinetics and thermodynamics and depends on the strength of the relationship between these two properties. Meanwhile, the graphite anode limits the release of the full battery capacity to a greater extent. This work points out a new direction for the practical development and application of thick electrodes.

Morphology and Crystallinity Effects of Nanochanneled Niobium Oxide Electrodes for Na-Ion Batteries.

Niobium pentoxide (Nb2O5) is a promising negative electrode for sodium ion batteries (SIBs). By engineering the morphology and crystallinity of nanochanneled niobium oxides (NCNOs), the kinetic behavior and charge storage mechanism of Nb2O5 electrodes were investigated. Amorphous and crystalline NCNO samples were made by modulating anodization conditions (20-40 V and 140-180 °C) to synthesize nanostructures of varying pore sizes and wall thicknesses with identical chemical composition. The electrochemical energy storage properties of the NCNOs were studied, with the amorphous samples showing better overall rate performance than the crystalline samples. The enhanced rate performance of the amorphous samples is attributed to the higher capacitive contributions and Na-ion diffusivity analyzed from cyclic voltammetry (CV) and the galvanostatic intermittent titration technique (GITT). It was found that the amorphous samples with smaller wall thicknesses facilitated improved kinetics. Among samples with similar pore size and wall thickness, the difference in their power performance stems from the crystallinity effect, which plays a more significant role in the resulting kinetics of the materials for Na-ion batteries.

Impedance of porous electrodes in the presence of electroactive species and solution resistance

In a recent paper, we have presented behavior of the porous electrodes in the presence of electroactive species and the absence of the dc and ac potential gradients. This paper presents a model without dc potential gradient but including ac potential drop due to the solution resistance in pores. In this case, a high-frequency straight line at 45° characteristic of porous electrodes appears at high frequencies on the complex plane plots followed by two semicircles. This high-frequency line increases with the increase of the electrode porosity, i.e. Thiele modulus, and solution resistivity. Fitting these impedances to the classical de Levie’s model does not reproduce well the parameters of the second semicircle although the overall fit is good for moderate porosities.

Six-Electron-Redox Iodine Electrodes for High-Energy Aqueous Batteries.

Iodine (I2 ) shows great promising as the active material in aqueous batteries due to its distinctive merits of high abundance in ocean and low cost. However, in conventional aqueous I2 -based batteries, the energy storage mechanism of I- /I2 conversion is only two-electron redox reaction, limiting their energy density. Herein, six-electron redox chemistry of I2 electrodes is achieved via the synergistic effect of redox-ion charge-carriers and halide ions in electrolytes. The redox-active Cu2+ ions in electrolytes induce the conversion between Cu2+ ions and I2 to CuI at low potential. Simultaneously, the Cl- ions in electrolytes activate the I2 /ICl redox couple at high potential. As a result, in our case, I2 -based battery system with six-electron redox is developed. Such energy storage mechanism with six-electron redox leads to high discharge potential and capacity, excellent rate capability, as well as stable cycling behavior of I2 electrodes. Impressively, six-electron-redox I2 cathodes can match various aqueous metal (e.g. Zn, Mn and Fe) anodes to construct metal||I2 hybrid batteries. These hybrid batteries not only deliver enhanced capacities, but also exhibit higher operate voltages, which contributes to superior energy densities. Therefore, this work broadens the horizon for the design of high-energy aqueous I2 -based batteries.

Six‐Electron‐Redox Iodine Electrodes for High‐Energy Aqueous Batteries

AbstractIodine (I2) shows great promising as the active material in aqueous batteries due to its distinctive merits of high abundance in ocean and low cost. However, in conventional aqueous I2‐based batteries, the energy storage mechanism of I−/I2 conversion is only two‐electron redox reaction, limiting their energy density. Herein, six‐electron redox chemistry of I2 electrodes is achieved via the synergistic effect of redox‐ion charge‐carriers and halide ions in electrolytes. The redox‐active Cu2+ ions in electrolytes induce the conversion between Cu2+ ions and I2 to CuI at low potential. Simultaneously, the Cl− ions in electrolytes activate the I2/ICl redox couple at high potential. As a result, in our case, I2‐based battery system with six‐electron redox is developed. Such energy storage mechanism with six‐electron redox leads to high discharge potential and capacity, excellent rate capability, as well as stable cycling behavior of I2 electrodes. Impressively, six‐electron‐redox I2 cathodes can match various aqueous metal (e.g. Zn, Mn and Fe) anodes to construct metal||I2 hybrid batteries. These hybrid batteries not only deliver enhanced capacities, but also exhibit higher operate voltages, which contributes to superior energy densities. Therefore, this work broadens the horizon for the design of high‐energy aqueous I2‐based batteries.

Free-standing TiNb6O17/rGO composites as a superior anode host for high-performance Li-ion capacitor

Li-ion capacitors are very enticing power sources having high energy and power density as they exemplify the benefits of both Lithium-ion battery (LIB) and supercapacitors (SCs) together. However, the high performance of LIC is limited due to low specific capacity and slow reaction kinetics of electrodes. Herein, pseudo-capacitive titanium niobium oxide (TiNb6O17: TNO) and reduced graphene oxide (rGO) composite material was fabricated and investigated as a unique anode material for LIC. The application of TNO-rGO composite electrode (R-TNO) as insertion anode material in LIC has been investigated due to its excellent electrochemical performance, intrinsic fast pseudo-capacitive behavior along with good reversibility and cyclability. A novel LIC was fabricated using R-TNO electrode as an innovative insertion type anode and activated carbon (AC) as cathode for the first time. Compared to conventional method (with binder), here the electrodes are prepared using binder-free and current-collector tape casting method to further enhance the energy and power density. As a result, the flexible and free-standing electrodes were acquired and used as anode for flexible LIC application. Comprehensive electrochemical analysis elucidates the improved storage behavior of composite electrode with rapid reaction kinetics, high reversibility and excellent cyclic stability. Novel R-TNO/AC LIC exhibited maximum energy density of 142.10 Wh/kg and power density of 18.75 kW/kg. The LIC device illustrated 88% cyclic stability even after 10,000 cycles, confirming its good electrochemical stability during electrochemical process. The extraordinary performance of LIC device is ascribed to collective effect of pseudo-capacitive behavior of TiNb6O17 particles and the buffering effect provided by rGO sheets. The results obtained are encouraging and propose the utilization of fabricated intercalation anode materials for the development of safe and high performance LICs.

Synthesis and electrochemical properties of -Fe2O3 particles for energy storage devices

In this study, we fabricated α-Fe2O3 materials via a facile hydrothermal route to use as the active material for iron-based battery anode. The particle size of α-Fe2O3 is in a range of a few hundreds of nanometers to a few micrometers. The structural characteristics and particle size of the synthesized iron oxides were studied via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical behavior of iron oxide electrode was investigated by cyclic voltammetry (CV). The distribution of iron species was observed by Energy dispersive X-ray spectroscopy (EDS) measurement. Carbon was used as additive to improve the conductivity of α-Fe2O3/C composite electrode. The electrochemical measurements revealed that the prepared α-Fe2O3 particles provided the good cyclability. The EDS showed that iron species were dispersed on the carbon surface during discharge-discharge through the electrochemical dissolution-deposition process of iron.

Revealing Interfacial Reactions on Pt Electrodes in Ionic Liquids by In Situ Fourier-Transform Infrared Spectroscopy.

In situ monitoring of the electrolyte/electrode interfacial processes, such as the oxygen reduction reaction (ORR), is crucial for the design of electrolytes for fuel cells. In this study, we investigate the electrochemical behavior of platinum electrodes in protic ionic liquids (PILs) by means of in situ Fourier-transform infrared spectroscopy coupled with cyclic voltammetry. The result provides direct evidence of the change of water at the Pt electrode surface due to Pt oxide formation and reduction. A decrease in the interfacial water was observed in the spectra upon the formation of the Pt oxide. Conversely, the local water concentration at the electrode surface increases if the Pt oxide is reduced and the ORR takes place. At the same time, more cations replace anions on the electrode. The ORR kinetics in the [TFSI]-based PILs is slower than in the [TfO]-based ones, which could result from a blockage of catalytic sites by the adsorbed [TFSI] anions. It suggests that reducing the anion adsorption on the platinum surface could provide an opportunity to enhance the ORR activity.

The effects of sintering temperature and current contacting layer on the performance of lanthanum nickelate electrodes in Solid Oxide Fuel Cells

The Ruddlesden-Popper phase La2NiO4+δ (LNO214) has received a significant level of research attention with respect to its employment as a Solid Oxide Fuel Cell cathode material. However, it is known that there are many factors that are capable of influencing the performance of this phase when utilised in this role. One such factor that can impact on electrode behaviour is the choice of sintering temperature. In this paper, a study of this effect is detailed. This is achieved via the use of both symmetrical and single cell testing configurations, with additional investigation provided by ex-situ analysis. It is shown that a sizeable improvement in electrode performance can be achieved via an increase in sintering temperature. This is despite observations on the reactivity between LNO214 and the contact electrolyte material Ce0.9Gd0.1O2-δ. Further, it is also demonstrated that the addition of a noble metal contacting layer can dramatically improve the performance of an LNO214 electrode. In comparison, the impact of a contacting layer on a state-of-the-art La0.6Sr0.4Co0.2Fe0.8O3-δ composition is shown to be relatively minor. This has implications towards SOFC testing methodologies given the widespread employment of noble metal contacting pastes.

Revealing the surface modification effect on Li-ion insertion into Ni-rich NCM cathode material by cyclic voltammetry

This article presents a new approach to the determination of electrochemical parameters characterizing the degradation behavior of electrodes based on LiNi0.85Co0.10Mn0.05O2 (Ni-rich NCM) using the method of cyclic voltammetry with a linear scan of the electrode potential (CV). To establish the relationship between electrochemical, structural, and morphological characteristics, XRD, synchrotron XRD (SXRD) in the operando mode, and SEM were used. The results of the galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) were used to verify the CV data. The features of the irreversible phase transition in NCM during the first cycle of extraction-insertion of lithium ions and its influence on the further behavior of the material during cycling were studied. It was found that the nature of the slope variation of capacity and coulomb efficiency dependences on the cycle number with an increase in the electrode potential scan rate is a criterion for the ratio of reversible and irreversible components of the electrode capacity degradation. Reversible electrode capacity degradation is due to the difference between the diffusion coefficients of lithium ions in the anodic and cathodic processes, irreversible degradation is due to the structural degradation of the material. For NCM samples with different particle surface conditions (with different composition of Cathode Electrolyte Interphase (CEI)) the values of Li+ ions diffusion coefficient (D) for each stage of the intercalation process were found in the range 4.5·10−14 – 1.2·10−13 cm2·s−1 for the anodic process, 1.7·10−14 – 5.6·10−14 cm2·s−1 for the cathodic process. It has been established that the reversible and irreversible degradation components of electrodes based on Ni-rich NCM in the potential range corresponding to the H2-H3/H3-H2 interphase transition correlate with each other. Therefore, the difference in D values in the anodic and cathodic processes, which correspond to the current peaks of the cyclic voltammogram in this region, is a criterion for the irreversible degradation of the material’s capacity: the greater the difference in the D values for these peaks, the higher the irreversible degradation of the material’s capacity.

Effect of Electrode on the Dynamics of Electroactive Membrane

Abstract The dynamics of the electroactive membranes are being studied extensively due to their vast application at the current time. However, the effect of the mechanical behavior of the compliant electrode needs to be addressed. This article presents the nonlinear analysis of an electrically actuated membrane, considering the inertia of the electrode. The membrane is modeled as a hyperelastic material and is assumed to be incompressible, homogeneous, and isotropic. The proposed analysis is discussed in a generalized way for both the compression and suspension phases. Since the membrane is vulnerable to pull-in instability, the conditions to prevent electromechanical instability are defined. Further, an analytical relation is established for breakdown voltage and is validated with experimental data. The analytical solution of axial vibration is presented in the form of elliptic integrals and by the use of multiple scale method in a generalized way for both the phases. The resultant motions and their various physical aspects under suspension and compression phases for general initial conditions are described through graphical results to comprehend the proposed analysis. Also, parameter values are quantified analytically, for which the system executes reverse behavior in a given configuration.

Effect of temperature on redox active sites in sulfide based nanorods composites electrode material in a hybrid supercapacitor for energy storage and biomedical applications

Bimetallic sulfide based electrode materials have attained a lot of interest because of high chemical activity, large conductivity and porous structure. This work effectively described the impact of temperature on the specific capacity of electrode materials and is successfully used to study biomedical applications by detecting hydrogen peroxide. The high oxidation-reduction reactions and conductivity of transition metal-based electrode materials have been recognized as being advantageous for supercapacitor (SC) electrodes; however, the temperature-dependent behavior of CoMgS-based electrodes is not yet fully understood. To address this knowledge gap, CoMgS electrodes were prepared using hydrothermal process, and their electrochemical performance was characterized at various temperatures (0–55 °C). Notably, the CoMgS-based electrode materials exhibited excellent electrochemical performance at 55 °C, displaying a specific capacity (Cs) of 900.0C/g at 10 mV/s using a three-electrode system. Moreover, the CoMgS and activated carbon-based hybrid device demonstrated remarkable Cs of 293.6C/g at the temperature of 55 °C with attractive energy and power densities of 30.6 Wh/kg, and 5183 W/kg, respectively. Even after undergoing 5000 cycles, the CoMgS//AC device exhibited a capacity retention (CR) rate of 85 %, indicating its exceptional durability as an energy storage solution. Besides, the composite devices are used to detect hydrogen peroxide which exists in enough amounts in cancerous cells. Overall, the findings of this work indicate that CoMgS electrode capacitance may be increased at an optimal temperature, probably as a result of better ion diffusion and charge transfer kinetics, to improve the efficiency of the energy storage device and be utilized to identify the cancerous part in the body.

Charge Dynamics Induced by Lithiation Heterogeneity in Silicon‐Graphite Composite Anodes

AbstractThe reaction processes in Li‐ion batteries can be highly heterogeneous at the electrode scale, leading to local deviations in the lithium content or local degradation phenomena. To access the distribution of lithiated phases throughout a high energy density silicon‐graphite composite anode, correlative operando SAXS and WAXS tomography are applied. In‐plane and out‐of‐plane inhomogeneities are resolved during cycling at moderate rates, as well as during relaxation steps performed at open circuit voltage at given states of charge. Lithium concentration gradients in the silicon phase are formed during cycling, with regions close to the current collector being less lithiated when charging. In relaxing conditions, the multi‐phase and multi‐scale heterogeneities vanish to equilibrate the chemical potential. In particular, Li‐poor silicon regions pump lithium ions from both lithiated graphite and Li‐rich silicon regions. This charge redistribution between active materials is governed by distinct potential homogenization throughout the electrode and hysteretic behaviors. Such intrinsic concentration gradients and out‐of‐equilibrium charge dynamics, which depend on electrode and cell state of charge, must be considered to model the durability of high capacity Li‐ion batteries.

The effect of volume change and stack pressure on solid‐state battery cathodes

AbstractSolid‐state lithium batteries may provide increased energy density and improved safety compared with Li‐ion technology. However, in a solid‐state composite cathode, mechanical degradation due to repeated cathode volume changes during cycling may occur, which may be partially mitigated by applying a significant, but often impractical, uniaxial stack pressure. Herein, we compare the behavior of composite electrodes based on Li4Ti5O12 (LTO) (negligible volume change) and Nb2O5 (+4% expansion) cycled at different stack pressures. The initial LTO capacity and retention are not affected by pressure but for Nb2O5, they are significantly lower when a stack pressure of <2 MPa is applied, due to inter‐particle cracking and solid‐solid contact loss because of cyclic volume changes. This work confirms the importance of cathode mechanical stability and the stack pressures for long‐term cyclability for solid‐state batteries. This suggests that low volume‐change cathode materials or a proper buffer layer are required for solid‐state batteries, especially at low stack pressures.

In-Depth Investigation of Manganese Dioxide as Pseudocapacitive Electrode in Lithium- and Sodium-Doped Ionic Liquids

We investigate the contribution of pseudocapacitance to the overall capacitance of MnO2 electrodes in pure and alkaline-doped ionic liquids via two spectroscopic methods: step potential electrochemical spectroscopy (SPECS) and in situ Raman spectroscopy. For both characterization methods, thin-film electrodes of birnessite-like amorphous MnO2 were cycled in Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, pure or doped with lithium or sodium. SPECS allows determination of the influence of the electrolyte composition on the electrochemical behavior of the MnO2 electrodes. Pseudocapacitive charge storage can account for over half of the total capacitance with alkaline-doped ionic liquids. In situ Raman spectroscopy provided insight into the reversible ion intercalation in the MnO2 structure, which appears to be controlled by EMIm+ cations. These findings are supported by density functional theory (DFT) calculations, which further help unveil the charge storage mechanism in birnessite-like amorphous MnO2 thin films operated in pure and alkaline-doped ionic liquids.

Performance of Disposable Cu/CuSO4 Reference Electrode in Reinforced Concrete Corrosion Analysis

The investigation of reference electrode performance for corrosion analysis has been widely conducted over the last decade. The need for a disposable and reliable reference electrode is a specific need for corrosion investigation. This research investigated the effectiveness of liquid-based and solid-state reference electrodes, which are disposable and provide reliable performance. The electrode was prepared with low-cost material preparation (disposable usage) within a Copper-Copper Sulphate (CCS) liquid-based and solid-state electrodes. The potential stability was already tested for dependability by measuring the Open Circuit Potential (OCP) on the rebar concrete specimen. The behaviour of solid-state reference and liquid-based reference electrodes in terms of polarization was studied in a corroded environment. Real-time potential data was also obtained for the corrosion rate investigation. The result shows the consistency performance of (OCP) value during corrosion measurement. The deviation of the maximum to a minimum potential value less than 0.02 V, verifies that the liquid-based copper (Cu) electrode and solid-state copper (Cu) electrodes are reliable, adaptable, and disposable for reinforced concrete corrosion measurement. In terms of corroded rebar potential measurement, the real-time polarization measurement result shows that the high-risk corroding occurred on the embedded rebar and was validated by directly visualizing the rebar concrete specimen. Therefore, the results obtained allow us to conclude that the disposable of both reference electrodes shows their stability and significantly reduces the reinforced concrete corrosion research cost.

Analysis of the electrochemical performance of carbon felt electrodes for vanadium redox flow batteries

In the present research, the performance of three commercial graphite felts (a 6 mm thick Rayon-based Sigracell®, a 4.6 mm thick PAN-based Sigracell®, and a 6 mm thick PAN-based AvCarb®) used as electrodes in vanadium redox flow batteries (VRFBs) is analyzed before and after thermal activation. The thermal treatment of the electrodes at 500 °C for 1 h in a self-designed industrial furnace under a synthetic air atmosphere. XPS confirms that thermal activation provides with different C=O/CO and sp2/sp3 ratios to the graphite electrodes depending on their carbon precursors, providing different catalitic behavior. T-GFD4.6-EA felt electrode was also oxidized by cycling in H2SO4 and in 0.4 M VOSO4 + 2 M H2SO4 solution. In the first case, the graphite electrode increased the current density 24.27 mA cm−2 for the VO2+ electrooxidation, however the cathodic current density (VO2+ reduction reaction) was decreased 36 mA cm−2. In the second case, the increase was of 21.27 mA cm−2, whereas the current density for the VO2+ reduction hardly changed. Thermally treated GFD4.6-EA graphite felt chemical composition also changed differently when exposed to different laboratory experiments which mimic the electrode behavior in a VRFB. XPS analysis confirmed that the chemical modification of the graphite surfaces can either improve or decrease the electrocatalytic activity of the electrodes depending on their carbon precursors.