A Vapor-Air Discharge between Electrolytic Anode and Metal Cathode at Atmospheric Pressure

An experimental investigation is performed of the structure, mechanism, and electrical and thermal characteristics of a vapor-air discharge between an electrolytic anode (EA) and a metal cathode (MC) in a wide range of parameters at pressure P = 8×10⁴ to 10⁵ Pa, current I = 0.02 to 60 A, interelectrode spacing l = 0.1 to 40 mm, and metal cathode diameter d _c = 1 to 40 mm. The main types of vapor-air discharge with EA are identified. The possibility of burning of a multichannel discharge between a metal cathode and an electrolytic anode at atmospheric pressure is demonstrated for the first time, and a vapor-air discharge with a diffuse plasma column is investigated at high currents and large interelectrode spacings. It is determined that the electrical and thermal characteristics depend significantly on current, interelectrode spacing, electrolyte composition and concentration, geometric shape, diameter, and cooling of the MC. The significant effect of the vapor-air discharge on the electrolytic anode surface is revealed. Transverse waves are observed on the electrolyte surface. Significant turbulent mixing is observed for the first time on the electrolyte-plasma interface in the case of a vapor-air discharge with electrolytic anode at atmospheric pressure and high currents.     

A Vapor-Air Discharge with a Porous Electrolytic Cathode at Atmospheric Pressure

An experimental investigation is performed for the first time of the structures and electrical and thermal characteristics of a vapor-air discharge between a porous (solid cylindrical body and hollow cylinder) electrolytic cathode and a solid anode in the range of current from 0.2 to 8 A with an interelectrode spacing of 2 to 200 mm for electrolytes of different compositions and concentrations with vertical and horizontal orientations of the plasma column in space at atmospheric pressure. An electrode of a new type is developed, namely, a porous electrolytic cathode (PEC), which makes it possible to produce cone-shaped, multichannel, and mixed discharges. The moist, boiling, and film modes of PEC operation are revealed. It is found that the heat loss on a PEC depends on the mode of its operation. The minimal heat loss is observed in the moist cathode mode, in which the electrolyte is delivered to the cathode working surface in the form of vapor only. In so doing, an almost complete regeneration occurs of heat delivered to the cathode from discharge plasma. It is found that the characteristics of a vapor-air discharge between a PEC and electrolytic anode depend significantly on the composition and concentration of the PEC electrolyte. The discharge voltage fluctuations and the nonuniform pattern of distribution of electric field intensity are revealed. The results of experimental investigation of a vapor-air discharge with a PEC are generalized in the form of an empirical formula.     

Protecting the anode foil of a high-current electron accelerator against arc-discharge damage

The mechanism of anode foil damage during the extraction of a high-power pulsed electron beam from a high-current diode has been experimentally studied on a TEU-500 electron accelerator [1]. It is established that the breakage of the anode foil is caused by the appearance of cathode spots on its surface, the intense electron emission from these spots during positive voltage pulses (postpulses following the main negative pulse of accelerating voltage), and the formation of arc discharge in the interelectrode gap. The improvement of diode matching to the pulse-forming line of the accelerator and the use of an auxiliary electrode (anode) forming additional vacuum discharge gap (crowbar) with the cathode practically excludes the anode foil breakage by arc discharge and significantly increases the working life of the foil (up to ∼10⁵ electron beam pulses).     

A two-dimensional mathematical model of a short vacuum arc in external magnetic field: results of numerical calculations

The paper deals with the investigation of the impact made by two-dimensional effects on the process of passage of current in a short vacuum arc in an axial magnetic field. A two-fluid mathematical model is used, which is based on hydrodynamic and electrodynamic equations. The axial magnetic field B _z affects significantly the magnitude of two-dimensional effects: the two-dimensional effects increase with decreasing B _z . The simulation results demonstrate that the contraction of plasma density exceeds that of current density. The distribution of anode drop of potential on the anode surface is nonuniform; in the case of certain (critical) values of current, the anode drop goes to zero on the external boundary of plasma. The dependence of the critical current on B _z is determined. The distribution of current density on the starting plane is nonuniform with a maximum on the axis, and the ion trajectories are inclined to the discharge axis. The possibility is discussed of matching the solution in the plasma region of vacuum arc with that for cathode flames.     

Fabrication of Pt, Pt–Cu, and Pt–Sn nanofibers for direct ethanol protonic ceramic fuel cell application

Poly(vinyl pyrrolidone) with a M _w of 1.3 × 10⁶ g/mol (PVP) or 4 × 10⁴ g/mol (PVP_Low) was used as a polymer to fabricate PVP–Pt, PVP–Pt–Cu, and PVP_Low–Pt–Sn composite fibers by electrospinning. The effect of varying the electrospinning conditions on the fiber morphology was investigated, and the solution composition and electrospinning parameters were optimized to obtain composite fibers with a minimal bead formation. Pt, Pt–Cu, and Pt–Sn metal nanofibers were then obtained by heat treatment of the respective PVP–metal or PVP_Low–metal composite fibers at 300, 350, and 450 °C, respectively, in air for 5 h. Single cells of a direct ethanol protonic ceramic fuel cell were subsequently fabricated by applying the metal nanofibers, or a commercial Pt paste, as the anode on the surfaces of BaY_0.2Zr_0.8O_3?δ pellets and Pt paste as the cathode. The I–V polarization results showed that the metal nanofiber-based anode single cells provided higher maximum power densities than that of the Pt paste anode, with the Pt nanofiber-based anode single cell producing the highest maximum power density of 0.58 mW/cm² at 550 °C.     

Beyond Activated Carbon: Graphite‐Cathode‐Derived Li‐Ion Pseudocapacitors with High Energy and High Power Densities

Supercapacitors have aroused considerable attention due to their high power capability, which enables charge storage/output in minutes or even seconds. However, to achieve a high energy density in a supercapacitor has been a long‐standing challenge. Here, graphite is reported as a high‐energy alternative to the frequently used activated carbon (AC) cathode for supercapacitor application due to its unique Faradaic pseudocapacitive anion intercalation behavior. The graphite cathode manifests both higher gravimetric and volumetric energy density (498 Wh kg^?1 and 431.2 Wh l^?1) than an AC cathode (234 Wh kg^?1 and 83.5 Wh l^?1) with peak power densities of 43.6 kW kg^?1 and 37.75 kW l^?1. A new type of Li‐ion pseudocapacitor (LIpC) is thus proposed and demonstrated with graphite as cathode and prelithiated graphite or Li₄Ti₅O₁₂ (LTO) as anode. The resultant graphite–graphite LIpCs deliver high energy densities of 167–233 Wh kg^?1 at power densities of 0.22–21.0 kW kg^?1 (based on active mass in both electrodes), much higher than 20–146 Wh kg^?1 of AC‐derived Li‐ion capacitors and 23–67 Wh kg^?1 of state‐of‐the‐art metal oxide pseudocapacitors. Excellent rate capability and cycling stability are further demonstrated for LTO‐graphite LIpCs.     

A High‐Energy and Long‐Life Aqueous Zn/Birnessite Battery via Reversible Water and Zn2+ Coinsertion

Aqueous rechargeable Zn/birnessite batteries have recently attracted extensive attention for energy storage system because of their low cost and high safety. However, the reaction mechanism of the birnessite cathode in aqueous electrolytes and the cathode structure degradation mechanics still remain elusive and controversial. In this work, it is found that solvation water molecules coordinated to Zn²⁺ are coinserted into birnessite lattice structure contributing to Zn²⁺ diffusion. However, the birnessite will suffer from hydroxylation and Mn dissolution with too much solvated water coinsertion. Through engineering Zn²⁺ primary solvation sheath with strong‐field ligand in aqueous electrolyte, highly reversible [Zn(H₂O)₂]²⁺ complex intercalation/extraction into/from birnessite cathode is obtained. Cathode–electrolyte interface suppressing the Mn dissolution also forms. The Zn metal anode also shows high reversibility without formation of “death‐zinc” and detrimental dendrite. A full cell coupled with birnessite cathode and Zn metal anode delivers a discharge capacity of 270 mAh g^?1, a high energy density of 280 Wh kg^?1 (based on total mass of cathode and anode active materials), and capacity retention of 90% over 5000 cycles.     

Fe and Ti cathodes sputtering by oxygen plasma in DC glow discharges

Sputtering yields of iron and titanium cathodes have been measured over wide ranges: (0.1 < p < 0.373 mbar) and (0.25 < j_d < 1 mA/cm²) of oxygen pressure (p) and current density (j_d) of the O₂/Fe discharge. The effective sputtering yields Y_efs run from 0.0017 up to 0.136 [A_Fe/A_O]. These yields are very low if compared with those characteristic of other discharge sets. The Monte-Carlo modelling of the oxygen plasma–metallic cathode interface allows the explanation of the effect of plasma characteristics on these yields and a stoichiometry of the cathode subsurface layer. High oxidation of subsurface cathode layer, redeposition of sputtered atoms and non-volatile character of metal oxides are main reasons for low values of effective sputtering yields as well as their dependence on working gas pressure.     

Vapor-air discharges between electrolytic cathode and metal anode at atmospheric pressure

Experimental investigation is performed of the structures and electrical characteristics of vapor-air discharges between a metal (solid, hollow, pointed) anode and an electrolytic cathode at atmospheric pressure. Singular features are revealed of free vapor-air discharges with an electrolytic cathode and their relative transition. Analysis and generalization of the experimental results enable one to reveal the basic physical processes which define the possible mechanism of maintaining a vapor-air discharge with an electrolytic cathode.Translated from Teplofizika Vysokikh Temperatur, Vol. 43, No. 1, 2005, pp. 005–010. Original Russian Text Copyright © 2005 by A. F. Gaisin and E. E. Son.     

A High-Energy Aqueous Manganese–Metal Hydride Hybrid Battery

Aqueous rechargeable batteries show great application prospects in large-scale energy storage because of their reliable safety and low cost. However, a key challenge in developing this battery system lies in its low energy density. Herein, a high-energy manganese–metal hydride (Mn–MH) hybrid battery is reported in which a Mn-based cathode operated by the Mn²⁺/MnO₂ deposition–dissolution reactions, a hydrogen-storage alloy anode that absorbs and desorbs hydrogen in an alkaline solution, and a proton-exchange membrane separator are employed. Given the benefit derived from the high solubility and high specific capacity of the Lewis acidic MnCl₂ in the cathode and the low electrode potential of the MH anode, this aqueous Mn–MH hybrid battery exhibits impressive electrochemical properties with admirable discharge voltage plateaus up to 2.2 V, a competitive energy density of about 240 Wh kg⁻¹ (based on the total mass of the 5.5 m MnCl₂ solution and the hydrogen storage alloy electrode system), good cycling stability over 130 cycles, and a desirable rate capability. This work demonstrates a new strategy for achieving high-performance and low-cost aqueous rechargeable batteries.     

Dynamics studies of cathode spots in a vacuum-arc discharge with ring electrodes

The effect of an external pulse magnetic field with axial and radial components on electric characteristics of the discharge and the configuration of cathode spots of a vacuum arc discharge with ring electrodes is studied experimentally. For arc currents within the range of 0.05–2 kA, shots of the cathode spots at different instants of time are obtained. The dependences of the number of the spots on the discharge current and the mean current per spot are determined. It was found that the expansion rate of the cathode spots area depends significantly on the instant value of the discharge current. It is shown that, when the pulse magnetic field is applied, the discharge voltage increases and the discharge current and number of the cathode spots decreases. It was found that the current interruption is a probability process. The probabilities of the current interruption depending on the maximal value of the external pulse magnetic field induction are determined.     

A Novel Graphite–Graphite Dual Ion Battery Using an AlCl3–[EMIm]Cl Liquid Electrolyte

Herein, a novel graphite–graphite dual ion battery (GGDIB) based on a AlCl₃/1‐ethyl‐3‐methylimidazole Cl ([EMIm]Cl) room temperature ionic liquid electrolyte, using conductive graphite paper as cathode and anode material is developed. The working principle of the GGDIB is investigated, that is, metallic aluminum is deposited/dissolved on the surface of the anode, and chloroaluminate ions are intercalated/deintercalated in the cathode material. The self‐discharge phenomenon and pseudocapacitive behavior of the GGDIB are also analyzed. The GGDIB shows excellent rate performance and cycle performance due to the high ionic conductivity of ionic liquids. The initial discharge capacity is 76.5 mA h g⁻¹ at a current density of 200 mA g⁻¹ over a voltage window of 0.1–2.3 V, and the capacity remains at 62.3 mA h g⁻¹ after 1000 cycles with a corresponding capacity retention of 98.42% at a current density of 500 mA g⁻¹. With the merits of environmental friendliness and low cost, the GGDIB has a great advantage in the future of energy storage application.     

Using open atmospheric electric discharge for water purification from surface contamination with oil products

The characteristics of open atmospheric dc discharge between a liquid nonmetal cathode (tap water layer) and a metal anode have been studied. The effect of discharge on a layer of oil products (diesel fuel, lubricant oils) contaminating the liquid cathode surface was determined. The discharge current-voltage characteristics and the dependence of the cathode current density on the discharge current I were measured in the interval 20 mA ≤ I ≤ 300 mA for the discharge gap width varied within h = 2–10 mm. For h ≥ 4 mm and I ≥ 120 mA, the cathode current density and the interelectrode voltage are independent of the discharge current, which is characteristic of the normal glow discharge. Under the action of discharge, oil products in the contamination layer on the liquid cathode surface are partly decomposed and partly converted, after which the conversion products can be readily removed from the surface by mechanical methods. The efficiency of contaminant removal can reach 98%. Analysis of the conversion products showed that they are composed of polymer chains with variable length and structure involving oxygen-containing groups.     

X-ray absorption spectroscopy studies of the Ni ion of Li(Ni0.8Co0.15Al0.05)0.8(Ni0.5Mn0.5)0.2O2 with a core–shell structure and LiNi0.8Co0.15Al0.05O2 as cathode materials

Core–shell materials have attracted a great deal of interest since core–shell particles have superior physical and chemical properties compared to their single-component counterparts. The cathode material Li(Ni_0.8Co_0.15Al_0.05)_0.8(Ni_0.5Mn_0.5)_0.2O₂ (LNCANMO) with a core–shell structure was synthesized via a co-precipitation method and investigated as the cathode material for lithium ion batteries. The core–shell particle consisted of LiNi_0.8Co_0.15Al_0.05O₂ (LNCAO) as the core and LiNi_0.5Mn_0.5O₂ as the shell. The cycling behavior between 2.8 and 4.3 V at a current of 0.1 C-rate showed a reversible capacity of ～195 mAh g^?1 with little capacity loss after 50 cycles. Extensive assessment of the electronic structures of the LNCAO and LNCANMO cathode materials was carried out using X-ray absorption spectroscopy (XAS). XAS has been used for structure refinement on the transition metal ion of the cathode. In particular, XAS studies of electrochemical reactions have been done from the viewpoint of the transition metal ion. In this study, Ni K-edge XAS spectra of the charge and discharge processes of LNCAO and LNCANMO were investigated.     

Plasma cathode for a broad-beam electron accelerator

We propose a grid-stabilized plasma cathode based on a slit-contracted low-pressure glow discharge with hollow anode. The area of the plasma cathode is one order of magnitude higher than that in systems where electrons are extracted immediately from plasma in the cathode cavity. Conditions for the discharge initiation, the current switching to the hollow anode, and the obtaining of uniform emission from the plasma cathode are determined. At an accelerating voltage of 160 kV, an electron beam with a 1000 × 180 mm cross section, a total current of several amperes, and a current pulse duration of up to 10⁻³ s was obtained. The plasma cathode operates under technical vacuum conditions (air, 0.1 Pa) and ensures high stability and reproducibility of the beam current pulses.     

Multichannel discharge between jet electrolyte cathode and jet electrolyte anode

We present the results of an experimental study of multichannel discharge between a jet electrolyte cathode and jet electrolyte anode within a wide range of parameters. We pioneer the reveal of the burning particularities and characteristics of multichannel discharge with jet electrolyte and droplet electrodes. The deviations are determined by the voltage and current probability distributions for a multichannel discharge from the normal distribution. We show the dependence of two electrolyte jets merging at the electrical parameters and the character of the jet flow.     

High-current electron beam in a hollow-cathode gas discharge at elevated pressures (∼100 Torr)

A discharge with plasma filling a flat-bottom cavity of depth δ in the cathode, partly closed by a dielectric plate with a hole (determining the aperture of the discharge between the cavity bottom and the anode), has been studied. In a discharge cell of type 1 with δ = 0.5 mm and a hole diameter of 22 mm, a pulsed electron beam was obtained with a duration of t _EB = 700 ns and a beam current j _EB approximately 10 times greater than that (j _AD) of the equivalent anomalous discharge (at fixed discharge voltage U and gas pressure p _He = 3.5 Torr). An electric field with the direction opposite to the field of applied voltage appeared at the cathode that was related to a space charge formed at the cathode plasma boundary, which could not follow a rapid drop of voltage across the discharge gap. In a discharge cell of type 2 with δ = 0.5 mm and a narrow slit (S = 0.1 × 5 cm²) in the dielectric plate, a pulsed electron beam was obtained with a duration of t _EB = 2 ns and a beam current of j _EB = 0.7 kA/cm² (j _EB/j _AD = 1.5) at U = 4.2 kV and p _He = 50 Torr.     

Dual‐Function,Tunable, Nitrogen‐Doped Carbon for High‐Performance Li Metal–Sulfur Full Cell

Lithium metal–sulfur (Li–S) batteries are attracting broad interest because of their high capacity. However, the batteries experience the polysulfide shuttle effect in cathode and dendrite growth in the Li metal anode. Herein, a bifunctional and tunable mesoporous carbon sphere (MCS) that simultaneously boosts the performance of the sulfur cathode and the Li anode is designed. The MCS homogenizes the flux of Li ions and inhibits the growth of Li dendrites due to its honeycomb structure with high surface area and abundance of nitrogen sites. The Li@MCS cell exhibits a small overpotential of 29 mV and long cycling performance of 350 h under the current density of 1 mA cm^‐2. Upon covering one layer of amorphous carbon on the MCS (CMCS), an individual carbon cage is able to encapsulate sulfur inside and reduce the polysulfide shuttle, which improves the cycling stability of the Li–S battery. As a result, the S@CMCS has a maximum capacity of 411 mAh g^‐1 for 200 cycles at a current density of 3350 mA g^‐1. Based on the excellent performance, the full Li–S cell assembled with Li@MCS anode and S@CMCS cathode shows much higher capacity than a cell assembled with Li@Cu anode and S@CMCS cathode.     

Fluorinated co-solvent promises Li-S batteries under lean-electrolyte conditions

Practical lithium-sulfur batteries stipulate the use of a lean-electrolyte and a high Coulombic efficiency of the lithium metal anode. Herein, we employ 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether as a co-solvent in the electrolyte of Li-S batteries to meet the demands. The co-solvent fosters the formation of a LiF-rich solid electrolyte interphase on lithium metal anode, as revealed by Ab initio molecular dynamics and Femtosecond Stimulated Raman spectroscopy. The co-solvent results in an average Coulombic efficiency of 99.4% for lithium plating/stripping cycles. Full cells with a capacity ratio of 2 between lithium anode and the S@PAN cathode (3 mg_s cm⁻²) exhibited a stable cycle life over 100 cycles at an electrolyte/sulfur ratio of 2 µL mg⁻¹, validating the high Coulombic efficiency of the lithium anode and demonstrating the compatibility of the electrolyte with both electrodes. To enhance the energy density, we prepared a hybrid cathode composed of 45 wt.% VS₂ mixed with ZnS-coated Li₂S@graphene as the cathode. Based on the mass of both electrodes and the electrolyte, the full cell delivers an energy density of 483 Wh kg⁻¹, which demonstrates viable Li-S batteries with the lean-electrolyte.     

Uniform Distribution of Alloying/Dealloying Stress for High Structural Stability of an Al Anode in High‐Areal‐Density Lithium‐Ion Batteries

Aluminum (Al) is one of the most attractive anode materials for lithium‐ion batteries (LIBs) due to its high theoretical specific capacity, excellent conductivity, abundance, and especially low cost. However, the large volume expansion, originating from the uneven alloying/dealloying reactions in the charge/discharge process, causes structural stress and electrode pulverization, which has long hindered its practical application, especially when assembled with a high‐areal‐density cathode. Here, an inactive (Cu) and active (Al) co‐deposition strategy is reported to homogeneously distribute the alloying sites and disperse the stress of volume expansion, which is beneficial to obtain the structural stability of the Al anode. Owing to the homogeneous reaction and uniform distribution of stress during the charge/discharge process, the assembled full battery (LiFePO₄ cathode with a high areal density of ≈7.4 mg cm^?2) with the Cu–Al@Al anode, achieves a high capacity retention of ≈88% over 200 cycles, suggesting the feasibility of the interfacial design to optimize the structural stability of alloying metal anodes for high‐performance LIBs.