Maximum Cathode Research Articles

Flow field design and simulation in electrochemical machining for closed integral components

Using closed integral components (CICs) not only simplifies the structure and reduces the weight of aeroengine components but also reduces the number of parts and improves overall engine performance. However, there are currently few publicly available reports on the electrochemical machining (ECM) of CIC blades. The key factor influencing the stability of ECM is the flow-field, which is difficult to design for a CIC because its two sides are closed, thereby limiting the direction of electrolyte flow into the processing area. To achieve the ECM of CICs, flow modes involving either lateral or composite liquid supply (LLS or CLS) are proposed, followed by flow-field and cathode-deformation simulation analyses. The simulation results show that the CLS flow-field is more reasonably designed and its electrolyte distribution is more uniform. The maximum cathode deformation under CLS flow-field is only ca. 15 µm. The experiments were conducted to improve the efficiency of CIC ECM and compare the LLS and CLS flow-fields. During processing, the feed rate was increased from 0.2 min/mm to 0.45 min/mm, and the surface roughness (Ra) decreased from ca. 1.29 µm to ca. 0.37 µm. The experiments show that the CLS flow-field offers higher processing efficiency and better surface quality.

Effect of temperature on the current-voltage characteristics of PdFe/Cu and NiCo/Cu bimetallic catalysts in alkaline alcohol electrolytes

The temperature rise effect on the electrochemical activity of catalysts on a copper substrate in alkaline alcohol solutions has been studied. The object of research was bimetallic PdFe/Cu and NiCo/Cu catalysts obtained by galvanic deposition on a copper substrate. The studies were carried out in immiscible liquids EtOH + K2HPO4 + H2O. The upper phase in this system of liquids is aqueous solutions of ethanol (“alcohol layer”), the lower phase is aqueous solutions of dipotassium phosphate K2HPO4 (“salt layer”). It was found that elevate temperature from 20°C to 60°C improve the activity of all catalysts. It was found that the Ni80Co20/Cu catalyst is highly active in the oxidation and reduction of oxygen. The peak of the oxidation current increases 4 times with elevate the temperature up to 40 C, and 14 times with elevate temperature up to 60 C, compared with currents at a temperature of 20 C. The Pd90Fe10/Cu catalyst is active in relation to the oxidation of ethanol. Elevate the electrolyte temperature from 20°C to 40°C increase in the oxidation current by a factor of 1.4, and from 20°C to 60°C by a factor of 3.3. The maximum cathode current at the peak of recovery exceeds the maximum anode current at the peak of oxidation at 40°C by 1.83 times, and at 60°C by 1.15. This indicates a good regeneration of the electrode surface and the absence of oxide films and ethanol oxidation products on its surface. It was concluded that, despite the ambiguous effect of temperature on the processes occurring in the system, the improvement in the characteristics of the studied catalysts can be explained by the improvement in the processes of ethanol oxidation and improved mass transfer of the reagents.

LiNi0.5Mn1.5O4 Cathode Microstructure for All-Solid-State Batteries

Solid-state batteries (SSBs) have received attention as a next-generation energy storage technology due to their potential to superior deliver energy density and safety compared to commercial Li-ion batteries. One of the main challenges limiting their practical implementation is the rapid capacity decay caused by the loss of contact between the cathode active material and the solid electrolyte upon cycling. Here, we use the promising high-voltage, low-cost LiNi0.5Mn1.5O4 (LNMO) as a model system to demonstrate the importance of the cathode microstructure in SSBs. We design Al2O3-coated LNMO particles with a hollow microstructure aimed at suppressing electrolyte decomposition, minimizing volume change during cycling, and shortening the Li diffusion pathway to achieve maximum cathode utilization. When cycled with a Li6PS5Cl solid electrolyte, we demonstrate a capacity retention above 70% after 100 cycles, with an active material loading of 27 mg cm–2 (2.2 mAh cm–2) at a current density of 0.8 mA cm–2.

Achieving High Current Stability of Gated Carbon Nanotube Cold Cathode Electron Source Using IGBT Modulation for X-ray Source Application.

The cold cathode X-ray source has potential application in the field of radiotherapy, which requires a stable dose. In this study, a gated carbon nanotube cold cathode electron gun with high current stability was developed by using Insulated Gate Bipolar Transistor (IGBT) modulation, and its application in X-ray source was explored. Carbon nanotube (CNTs) films were prepared directly on stainless steel substrate by chemical vapor deposition and assembled with control gate and focus electrodes to form an electron gun. A maximum cathode current of 200 μA and approximately 53% transmission rate was achieved. An IGBT was used to modulate and stabilize the cathode current. High stable cathode current with fluctuation less than 0.5% has been obtained for 50 min continuous operation. The electron gun was used in a transmission target X-ray source and a stable X-ray dose rate was obtained. Our study demonstrates the feasibility of achieving high current stability from a gated carbon nanotube cold cathode electron source using IGBT modulation for X-ray source application.

Effects of cathode/anode electron accumulation on soil microbial fuel cell power generation and heavy metal removal

Microbial fuel cells (MFCs) with different electrode configurations were constructed to study the mechanism of influence of multiple current paths on their electrical performance and the removal of heavy metals in soil. Three types of MFCs were constructed, namely, double anode–single cathode (DASC), single anode–dual cathode (SADC), and single anode–single cathode (SASC). The total electricity generation of the three kinds of MFC was similar: 143.44 × 10–3 mW, 114.90 × 10–3 mW, and 132.50 × 10–3 mW, respectively. However, the maximum voltage and cathode current density produced by a single current path differed significantly. The corresponding values were 0.27, 0.23, and 0.42 V and 0.130, 0.122, and 0.096 A/m 2, respectively. The SASC had the best electricity generation performance. Based on a limited reduction rate of oxygen at the cathode, the accumulation of cathode electrons was facilitated by the construction of multiple current paths in the MFC, which significantly increased the cathode electron transfer resistance and limited the electricity generation performance of the MFC. However, at the same time, the construction of multiple current paths promoted output of more electrons in the anode, reducing the retention of anode electrons and anode electron transfer resistance. The heavy metal removal efficiencies of SASC, DASC, and SADC were 2.68, 2.18, and 1.70 times that of the open circuit group, respectively. The migration of heavy metals in the soil depended mainly on the internal electric field intensity of the MFC rather than the total electricity generation. As the internal electric field intensity increased, the removal efficiency of heavy metals in the MFC increased.

ELECTROCHEMICAL INVESTIGATIONS OF THE INTERACTION OF CAFFEINIUM COMPOUNDS WITH POLYANІОNES OF Мо AND W WITH OF 1,3,5 - TRIPHENYL VERDAZYL RADICAL

The work continues the study on the peculiarities of the interaction of 1,3,7-trimethylxanthine (caffeine) compounds with polyoxometalates of molybdenum and tungsten with the artificial radical of 1,3,5- triphenylverdazyl (TFV). Using the example of a model reaction with the TFV radical, these compounds showed a special antiradical action. Based on the research results, it was found that the nature of the destruction of the radical when interacting with (HСaf)3[PМ12O40]∙6H2O (where М = Мо, W) differs from most known systems, which are characterized by a mechanism of disproportionation. The data obtained confirmed the previously made assumption about the chemical nature of these interactions. To establish the stoichiometry of the reaction between TFV and (HСaf)3[PW12O40], electrochemical studies were conducted which showed that the activity of the radical is restored after exceeding the concentration ratio of 12 : 1, respectively. The synergism of the components of the compound (HСaf)3[PW12O40] is shown: when TFV interacts with H3[PW12O40], the maximum cathode current characteristic of TFV occurs at a concentration ratio of 4 : 1, respectively, while caffeine has no antiradical effect at all. Previously obtained data from X-ray diffraction analysis of compounds (HСaf)3[PMo12O40]∙6H2O, (HСaf)3[PW12O40]∙6H2O prove that the orientation of protonated caffeine relative to polyoxamethalate-anion is possible due to hydrogen bonds =O…H–N=. This process can result in the delocalization of the charge over the entire O-enriched surface, by all twelve groups [О–Ме–О]-, which are part of the POM, making the latter active centers capable of interacting with TFV.
 Therefore, the data presented correlate with the previously obtained results of spectrophotometric analysis and X-ray diffraction data and confirm the previously made conclusions.

Survey of Optimal Control and Model Predictive Control with State Estimation and a Real Time Application

Abstract The optimal control and its limited version namely the model predictive control represent one of the most important nonlinear control alternatives nowadays. The success of them are also proven in many practical applications. These can provide for several industrial applications the optimal trajectory calculation as well as calculation of the real-time control signal. One successful version of this is Generalized Predictive Control (GPC). A big advantage of these control algorithms is that they solutions are able to take into account the limitations of the inputs, and the states. In some cases, it is important to know the mathematical model chosen and the complete state information. Otherwise, the model can be estimated during the operation. Our study shows through the control of the cathode heating of a high-power electron beam device the self-tuning adaptive control thus constructed. Using a suitable dynamic model and an extended Kalman estimator, we determine the estimated temperature of the two cathodes during operation and the saturation electron current, which ensures the maximum cathode life. The practical application was tested on a CTW 5/60 type electron gun.

Electrodeposition by rubbing. The method of calculating the modes and the development of the high-speed copper plating process

Taking into account the processes carried out during electrodeposition by rubbing, high-speed copper electrolytes have been developed: low-acid and nitrate sulfate. There are proposed modes for anode-tools with area of 1 cm2, 3.75 cm2 and 4.43 dm2, allowing for application of matte, semi-slush and shiny copper coatings with maximum speed up to 16 µm/min. A procedure has been created for calculating the permissible cathode current density and the required rate of electrolyte supply by dipping and jet methods. The effect of the area of anodes - tools on the maximum permissible cathode current density is determined. The effect of cathodic current density in high-speed copper plating electrolytes on current output and the rate of copper coating application has been established.

Current Status and Planned Upgrades of the VEPP-5 Injection Complex

The VEPP-5 injection complex, consisting of two linacs and a damping storage ring, delivers electron and positron beams to the VEPP-4M and VEPP-2000 colliders operating at BINP. Over three years of injector operation, its efficiency has significantly increased and the maximum positron-storage rate has reached 1.2 × 1010 s–1. This progress was reached through tuning the constituent machines, upgrading the accelerator technology, and deploying a new 11-MHz station of RF cavities. By the start of the next running season, a new electron gun with a significantly increased maximum current and cathode lifetime will be installed.

Dynamic Arc Current Distribution of Parallel Vacuum Arcs Subjected to Bipolar Axial Magnetic Field

The objective of this paper is to determine dynamic anode and cathode arc current distribution of parallel vacuum arcs subjected to bipolar axial magnetic field. Drawn arc experiments were carried out in a demountable vacuum chamber. A split bipolar axial magnetic field electrode with diameter of 100 mm was specially designed. Arc current of two half split electrode discs were measured through Rogowski coils out of the vacuum chamber. Experimental current ranged from 4.5 to 45.0 kA. Vacuum arc behaviors were recorded by a high-speed camera. Unbalance phenomena of anode current and cathode current of parallel vacuum arcs were observed. The maximum average anode and cathode current density difference between parallel vacuum arcs at current of 45.0 kA were 2.57 and 2.52 A/mm 2 , respectively. Critical value of both anode and cathode current difference ratio at time instant of maximum arc current difference with different arc initial conditions was 0.60. The maximum critical value of time instant of maximum anode and cathode current differences between parallel vacuum arcs with one strong arc branch at arc initial were 3.5 and 4.0 ms, respectively. Moreover, a three-interval arc current development model was proposed to describe unbalance phenomena of parallel vacuum arcs.

Arc-cathode attachment in GMA welding

A model for arc-cathode attachment in gas metal arc welding is presented. It considers the cathodic heating in the case of a non-refractory iron cathode, with the assumption of the lowering of the local plasma temperature, due to cold metal vapor. It takes the plasma bulk temperature as well as the cathode drop voltage as free parameters and it gives a maximum of heat flux and current density for a cathode surface temperature below boiling temperature. The applicability as a heat source description in a weld pool simulation has been shown, and the temperature field of the cathode was calculated, giving rise to heat flux and current density distributions, which differ significantly from the converntionally used axisymmetric Gaussian distribution. The maximum cathode surface temperature was lower than boiling temperature, which is in agreement with the observeration.

Modeling the Effect of Electrolyte-to-Sulfur Ratio in the Cathode on the Systems-Level Performance of a Li-S Battery

Lithium-Sulfur (Li-S) batteries have received significant interest as a result of their high theoretical specific energy and non-toxic, naturally abundant and low-cost active material [1, 2]. Because of the complexity of the processes taking place in the sulfur cathode, performance of a Li-S battery is highly sensitive to the cathode design [1, 2]. Electrolyte-to-sulfur ratio (E/S) is one of the key design factors in a Li-S cathode defining both the electrochemical performance and the systems-level energy density of the battery. Increasing the E/S ratio improves the cathode kinetics and hence the discharge capacity and cyclability of the battery. On the other hand, an excess of electrolyte has an adverse impact on the energy density of the battery at the systems level. In this study, we present a systems-level analysis for a Li-S battery demonstrating the effect of E/S ratio on the energy density of the battery. The systems-level performance model for the Li-S battery has been developed based on the BatPaC model [2]. The performance model uses a 1-D electrochemical model in which the sulfur kinetics has been treated with a single kinetic parameter, cathode exchange current density (i0,PE) [1]. The model predicts the impact of the E/S ratio on the energy density firstly through this kinetic model parameter; i0,PE is defined as a linear function of the electrolyte amount in the electrochemical model. More importantly, cathode specific capacity is described with an empirical linear dependence on the E/S ratio. The dependence of the systems-level energy density on the E/S ratio has been predicted as a function of other critical design parameters such as the maximum cathode thickness, carbon-to-sulfur (C/S) ratio in the cathode and excess Li% in the anode. Figure 1 presents the effect of E/S ratio on the systems-level energy density of a Li-S battery at different C/S ratios. It can be seen in the figure that increasing the E/S ratio improves the energy density until around 9 mL/g S. Any further increase in the E/S ratio results in a significant decrease at the systems-level energy density after this point. This trend can be explained by the dependence of the specific capacity on the electrolyte amount. As mentioned earlier, cathode specific capacity or the sulfur utilization in other words, has been defined as a linear function of the E/S ratio in the model. Therefore, at low E/S ratios increasing discharge capacity with increasing E/S ratio results in higher energy densities. However, when the theoretical capacity has been reached, any further increase in the E/S ratio brings a volume penalty to the pack and thus decreases the energy density. Increasing E/S ratio also improves the cathode kinetics through increasing i0,PE; however, this influence is less significant. It can also be seen from the figure that this trend is independent of the C/S ratio. However, it is clear from the figure that energy density is more sensitive to the E/S ratio for higher C/S ratios. Figure 1.The effect of E/S ratio in the cell on the calculated energy density of a Li-S battery for different C/S ratios. In the model, specific capacity is defined as a linear function of the E/S ratio. Acknowledgment This work was partially supported by the Scientific and Technological Research Council of Turkey (TUBITAK), Grant No: 116M574.

Design of a Hollow-Beam Electron Optics System With Control Focus Electrodes

The design of a hollow electron beam (HEB) electron optics system for a 10-kW Ka-band extended interaction klystron is presented. To lower the maximum cathode current density and realize the fast switch of the current emission, an HEB with two focus electrodes (FEs) is chosen, which attains to a high area compression ratio of over 100. A 25-kV, 2.5-A beam is produced by a curved spherical segment cathode with the area of 0.321 cm2 and an average beam loading of 8 A/cm2, namely, the high area compression ratio is necessary to reduce the cathode emission current density. The HEB with an area compression ratio of 105 can propagate 40 mm long with good laminarity confined by a 0.7-T uniform magnetic field. The beam current can be quickly shut off when the voltages of the FEs are biased to −4100 V. The results were simulated with two simulation codes: EGUN and OPERA 3-D. A sensitivity analysis with respect to critical parameters such as the displacement of FE1 and FE2 in the radial direction is provided. The simulation results of OPERA 3-D/SCALA and EGUN show an excellent agreement.

Theory of cyclic voltammetry for electrochemical nucleation and growth

The theory of cyclic voltammetry for processes of 3D nucleation, diffusion-controlled growth, and dissolution is proposed. The cases of single metal cluster formation and multiple nucleation are studied. The main features of cyclic voltammograms are analyzed: current increase on forward scan during nucleation, nucleation loop, maximum cathode current on reverse scan, and anodic peak of metal stripping.

Analysis of micro-tubular SOFC stability under ambient and operating temperatures

The stability of micro-tubular solid oxide fuel cell (MT-SOFC) is predicted at ambient and operating temperatures via simulation method. The results reveal that as long as the anode failure probability satisfies the failure criterion of 1E-6 at ambient temperature, the anode will retain its structural integrity at operating temperature. For the electrolyte or cathode, the stress strength ratio at operating temperature is significantly higher than that at ambient temperature. For an inappropriate component thickness, the cathode maybe fractures at operating temperature. In order to ensure the stability of MT-SOFC, the cathode thickness must be smaller than the maximum cathode thickness (tmax–cathode), which is derived from: tmax–cathode=5.49+5.54te

Landfill leachate: A promising substrate for microbial fuel cells

Landfill leachate emerges as a promising feedstock for microbial fuel cells (MFCs). In the present investigation, direct air-breathing cathode-based MFCs are fabricated to investigate the maximum open circuit potential from landfill leachate. Three MFCs that have different cathode areas are fabricated and studied for 17 days under open circuit conditions. The maximum open circuit voltage (OCV) of the cell is observed to be as high as 1.29 V which is the highest OCV ever reported in the literature using landfill leachate. The maximum cathode area specific power density achieved in the reactor is 1513 mW m−2. Further studies are under progress to understand the origin of high OCV obtained from landfill leachate-based MFCs.

Three-dimensional graphene membrane cathode for high energy density rechargeable lithium-air batteries in ambient conditions

Lithium-air batteries have attracted significant interest for applications in high energy density mobile power supplies, yet there are considerable challenges to the development of rechargeable Li-air batteries with stable cycling performance under ambient conditions. Here we report a three-dimensional (3D) hydrophobic graphene membrane as a moisture-resistive cathode for high performance Li-air batteries. The 3D graphene membrane features a highly interconnected graphene network for efficient charge transport, a highly porous structure for efficient diffusion of oxygen and electrolyte ions, a large specific surface area for high capacity storage of the insulating discharge product, and a network of highly tortuous hydrophobic channels for O2/H2O selectivity. These channels facilitate O2 ingression while retarding moisture diffusion and ensure excellent charge/discharge cycling stability under ambient conditions. The membrane can thus enable robust Li-air batteries with exceptional performance, including a maximum cathode capacity that exceeds 5,700 mAh/g and excellent recharge cycling behavior (>2,000 cycles at 140 mAh/g, and >100 cycles at 1,400 mAh/g). The graphene membrane air cathode can deliver a lifetime capacity of 100,000–300,000 mAh/g, comparable to that of a typical lithium ion battery cathode. The stable operation of Li-air batteries with significantly improved single charge capacities and lifetime capacities comparable to those of Li-ion batteries may offer an attractive high energy density storage alternative for future mobile power supplies. These batteries may provide much longer battery lives and greatly reduced recharge frequency.

Vulcanized Polyacrylonitrile with Graphene Oxide As an Additive for High-Rate Rechargeable Lithium Sulfur Batteries

Graphene oxide (GO)-vulcanized polyacrylonitrile (SPAN) composite was developed by mixing additive GO powder with SPAN powder by ultrasound. Its performance was evaluated in Li-S battery with ether-based electrolyte. Surprisingly the pure SPAN cathode is unstable in ether-based solvent compared with in carbonated solvent, unless a certain amount of GO is added. Due to its unique layer-structure, GO could function as the barriers, which could limit the agglomeration of SPAN composite and reduce the dissolution of sulfur accompanying the electrochemical reactions. With the additive of GO, the maximum cathode capacity of 275 mA h g-1 is higher than that of either GO or SPAN alone. This composite cathode possesses high capacity even at high current density of 1.5 A g-1. More importantly, the composite cathode is stable for 500 cycles of discharge/recharge.

Effects of nanoscale vacuum gap on photon-enhanced thermionic emission devices

A new model of the photon-enhanced thermionic emission (PETE) device with a nanoscale vacuum gap is established by introducing the quantum tunneling effect and the image force correction. Analytic expressions for both the thermionic emission and tunneling currents are derived. The electron concentration and the temperature of the cathode are determined by the particle conservation and energy balance equations. The effects of the operating voltage on the maximum potential barrier, cathode temperature, electron concentration and equilibrium electron concentration of the conduction band, and efficiency of the PETE device are discussed in detail for different given values of the vacuum gap length. The influence of the band gap of the cathode and flux concentration on the efficiency is further analyzed. The maximum efficiency of the PETE and the corresponding optimum values of the band gap and the operating voltage are determined. The results obtained here show that the efficiency of the PETE device can be significantly improved by employing a nanoscale vacuum gap.

Modeling of Cathode Efficiency of Stainless Steel Under Fully Immersed Conditions

Pitting often serves as a cause of fatigue crack initiation1 resulting in failure of high-value metallic components in cyclic stress environments. In order to prevent such failure, design engineers use structural integrity analyses that can predict the maximum damage that will be suffered by a component in a given environment. From a localized corrosion standpoint, such analyses would benefit from knowing the pit sizes that can be attained on a metallic surface in a particular environment2,3. Several studies in this regard have looked at how this damage can be characterized4–9 and modeled. These studies consider the metal surface under a thin film of electrolyte, as would be expected under atmospheric conditions. Power laws are used to extrapolate long-term estimates from short-term measurements made from atmospheric exposures8. In all these studies, a limiting pit size is seen, which implies that there is an upper bound on the pit size for a particular alloy and environment. More recent work in this respect has rationalized this observation of a maximum pit size using electrochemical fundamentals based on the understanding that the galvanic couple that arises in localized corrosion can be analyzed separately for stability10,11. Following the development of expressions for anodic and cathodic current separately in terms of a length dimension, the conservation of charge was used to combine the system to obtain an estimate of the maximum pit size. Under thin film conditions, the ohmic drop along the cathode that defines the potential gradient across which the current will be supplied to the pit can be simplified to a one-dimensional distribution since the water layer thickness is small compared to the length of the cathode. This concept has been experimentally validated for stainless steel coupons under thin films of ferric chloride12 (Fig. 1). For assets that are constantly exposed to bulk corrosive solutions, such as offshore installations as well as naval vessels, modeling that considers conditions in which the metal is fully immersed in the electrolyte is more representative than thin film conditions. As a result, extending maximum pit size estimation methods to full immersion conditions would enhance predictive design of such components. Simplifications of electrolyte geometry cannot be considered in such cases, presenting new challenges which need to be addressed by numerical modeling. This study describes the computation of the maximum current that can be provided by a cathode surrounding a hemispherical pit on a metallic surface under full immersion conditions. Finite element modeling employing kinetics information from cathodic polarization was performed to calculate the potential distribution along the length of the cathode (Fig. 2). These results were used to generate the maximum cathode current delivery capacity for the system and consequently, an estimate of the maximum pit size attainable on the surface. In addition, exposure studies were conducted using stainless steel samples submerged in ferric chloride solution over different periods of time to evaluate the actual maximum pit size attainable. The results from experimental and modeling runs were compared to determine the upper bound on the pit size under full immersion conditions. The results from these tests can be compared with earlier results from thin film electrolyte experiments and modeling to evaluate the transition between bulk and thin film conditions and its effects on cathode efficiency. Furthermore, the utility of these upper pit size estimates as input data into generalized extreme value (GEV) models13–15 for very long-term pitting can also be assessed, experimentally validating such statistical models as well.