Cathode Electron Research Articles

Enhanced microbial electrosynthesis by using defined co-cultures.

Microbial uptake of free cathodic electrons presents a poorly understood aspect of microbial physiology. Uptake of cathodic electrons is particularly important in microbial electrosynthesis of sustainable fuel and chemical precursors using only CO2 and electricity as carbon, electron and energy source. Typically, large overpotentials (200 to 400 mV) were reported to be required for cathodic electron uptake during electrosynthesis of, for example, methane and acetate, or low electrosynthesis rates were observed. To address these limitations and to explore conceptual alternatives, we studied defined co-cultures metabolizing cathodic electrons. The Fe(0)-corroding strain IS4 was used to catalyze the electron uptake reaction from the cathode forming molecular hydrogen as intermediate, and Methanococcus maripaludis and Acetobacterium woodii were used as model microorganisms for hydrogenotrophic synthesis of methane and acetate, respectively. The IS4-M. maripaludis co-cultures achieved electromethanogenesis rates of 0.1-0.14 μmol cm-2 h-1 at -400 mV vs standard hydrogen electrode and 0.6-0.9 μmol cm-2 h-1 at -500 mV. Co-cultures of strain IS4 and A. woodii formed acetate at rates of 0.21-0.23 μmol cm-2 h-1 at -400 mV and 0.57-0.74 μmol cm-2 h-1 at -500 mV. These data show that defined co-cultures coupling cathodic electron uptake with synthesis reactions via interspecies hydrogen transfer may lay the foundation for an engineering strategy for microbial electrosynthesis.

Natural Hematite as a Low-Cost and Earth-Abundant Cathode Material for Performance Improvement of Microbial Fuel Cells

Developing cheap electrocatalysts for cathodic oxygen reduction in neutral medium is a key factor for practical applications of microbial fuel cells (MFCs). Natural hematite was investigated as a low-cost cathode to improve the performance of microbial fuel cells (MFCs). With hematite-coated cathode, the cell current density stabilized at 330.66 ± 3.1 mA·m−2 (with a 1000 Ω load) over 10 days under near-neutral conditions. The maximum power density of MFC with hematite cathode reached to 144.4 ± 7.5 mW·m−2, which was 2.2 times that of with graphite cathode (64.8 ± 5.2 mW·m−2). X-ray diffraction (XRD), Raman, electrode potential analysis, and cyclic voltammetry (CV) revealed that hematite maintained the electrode activities due to the stable existence of Fe(II)/Fe(III) in mineral structure. Electrochemical impedance spectroscopy (EIS) results indicated that the cathodic electron transfer dynamics was significantly improved by using hematite to lower the cathodic overpotential. Therefore, this low-cost and earth-abundant natural mineral is promised as an effective cathode material with potential large-field applications of MFCs in future.

Doping ZnO with Water/Alcohol-Soluble Small Molecules as Electron Transport Layers for Inverted Polymer Solar Cells.

By doping ZnO with porphyrin small molecules (FNEZnP-OE and FNEZnP-T) as cathode electron transport layers (ETLs), the inverted polymer solar cells (i-PSC) with PTB7:PC71BM (PTB7: polythieno[3,4-b]-thiophene-co-benzodithiophene, PC71BM:[6, 6]-phenyl-C71-butyric acid methyl ester) as the active materials exhibit enhanced device performance. While the power conversion efficiency (PCE) of the PSCs with pure ZnO ETL is 7.52%, that of the devices with FNEZnP-T-doped ZnO ETL shows a slightly improved PCE of 8.09%, and that of the PSCs with FNEZnP-OE-doped ZnO ETL is further enhanced up to 9.24% with an over 20% improvement compared to that with pure ZnO ETL. The better performance is contributed by the better interfacial contact and reduced work function induced by 9,9-bis(30-(N,N-dimethylamino)propyl)-2,7-fluorenes and 3,4-bis(2-(2-methoxy-ethoxy)-ethoxy)-phenyls in the porphyrin small molecules. More importantly, the PCE is still higher than 8% even when the thickness of FNEZnP-OE-doped ZnO ETL is up to 110 nm, which are important criteria for eventually making organic photovoltaic modules with roll-to-roll coat processing.

Impact of Fe(III) as an effective electron-shuttle mediator for enhanced Cr(VI) reduction in microbial fuel cells: Reduction of diffusional resistances and cathode overpotentials

The role of Fe(III) was investigated as an electron-shuttle mediator to enhance the reduction rate of the toxic heavy metal hexavalent chromium (Cr(VI)) in wastewaters, using microbial fuel cells (MFCs). The direct reduction of chromate (CrO4−) and dichromate (Cr2O72−) anions in MFCs was hampered by the electrical repulsion between the negatively charged cathode and Cr(VI) functional groups. In contrast, in the presence of Fe(III), the conversion of Cr(VI) and the cathodic coulombic efficiency in the MFCs were 65.6% and 81.7%, respectively, 1.6 times and 1.4 folds as those recorded in the absence of Fe(III). Multiple analytical approaches, including linear sweep voltammetry, Tafel plot, cyclic voltammetry, electrochemical impedance spectroscopy and kinetic calculations demonstrated that the complete reduction of Cr(VI) occurred through an indirect mechanism mediated by Fe(III). The direct reduction of Cr(VI) with cathode electrons in the presence of Fe(III) was insignificant. Fe(III) played a critical role in decreasing both the diffusional resistance of Cr(VI) species and the overpotential for Cr(VI) reduction. This study demonstrated that the reduction of Cr(VI) in MFCs was effective in the presence of Fe(III), providing an alternative and environmentally benign approach for efficient remediation of Cr(VI) contaminated sites with simultaneous production of renewable energy.

Petroleum refinery wastewater treatment in two-chamber microbial fuel cells (MFCS)

Petroleum refinery wastewaters (PRW) contain water-soluble hydrocarbons which can not be separated by physical methods. In recent years, there have been enormous approaches to treat PRW. The most outstanding methods involve biological, photocatalytic, electro photo-Fenton and etc. Using microbial fuel cell is a new method to treat PRW. In the present paper, treatment of petroleum wastewater of Isfahan refinery (COD= 213.9 mg/l, PH=7.1) was investigated in twochamber microbial fuel cell having 350 mL anode and cathode capacity. Anaerobic activated sludge prepared from Isfahan refinery treatment reactors was used as inoculum. Maximum power production was 0.03 W/m2 at 33 using oxygen as cathodic electron acceptor. Also COD removal efficiency was 49.27% during 44 hr. To enhance power production of the MFC, potassium permanganate was used as cathodic electron acceptor. At temperature of 33 and 0.2 g/l permanganate concentration, the maximum power density was 0.95 W/m2 and COD removal efficiency was 78% during 44hr. Then effect of temperature and external resistance on treatment of PRW was investigated. In fact the motivation of this paper is investigation of COD removal from PRW in two-chamber MFC.

(Invited) Surface Reactivity and Ionic Transport of Mixed Conductors in Wet Atmospheres

Proton ceramic fuel cells (PCFC) for electrochemical energy conversion target operation in a temperature range between 300-600 °C, reducing the degradation rates and the materials cost in comparison with high-temperature oxide ion conducting fuel cells (SOFCs). In both cases (SOFC and PCFC), one of the main limitations for cell performance is the kinetics of the cathode reaction which takes place at the cathode-electrolyte interface when the cathode materials shows only electronic conductivity (i.e. at the triple phase boundary (TPB) where cathode surface, electrolyte and gas phase are in contact). Conversely, in mixed ionic-electronic conducting cathodes (MIECs), the oxygen reduction reaction sites are extended to the whole effective surface of the air electrode, providing high electrocatalytic activity even at the intermediate and low temperature range. Recently, MIEC cathode materials used for SOFC have been proposed as promising candidates for air electrodes on proton conducting electrolytes for PCFC. Among these oxygen-conducting materials (O-MIECs), single perovskite and double perovskites have been suggested (e.g. Ba0.5Sr0.5Co0.8Fe0.2O3-δ and NdBaCo2O5+δ, respectively) (1, 2). The assumption for the use of these O-MIECs in PCFCs is that sufficient proton conductivity is present, i.e. there are three mobile carriers through the bulk of the cathode (electrons, protons and oxygen ions). Although these materials work effectively on proton conducting electrolytes, there are few direct studies on the specific ionic carriers involved in the bulk transport. On the other hand, the chemical stability of the cathode material can be compromised, especially in steam or CO2-containing atmospheres (3). Many of the suggested cathode materials are doped with aliovalent cations in order to increase their MIEC character. Nevertheless, even at the low working temperatures of PCFC devices, the segregation of the substitutional cations lead to a specific surface termination. For instance, Ba-containing double perovskites, such as GdBaCo2O5+δ, shows fast segregation of the Ba cations at 400°C, leading to a Ba-rich outer surface after annealing in an oxygen atmosphere (e.g. 15 minutes) (4, 5). The dynamics of the segregation of the divalent cations are likely to be affected by the annealing atmosphere, as well as the surface reactivity of the segregated species in the presence of CO2 and H2O. In this work, the surface composition and the ionic transport properties of MIEC air electrodes in wet atmospheres will be discussed. The relative importance of the oxygen and proton conductivities in MIEC materials is directly measured by a combination of stable isotope exchange experiments (18O and 2D2O tracers) and Time-of-Flight Secondary Ion Mass Spectrometry depth profiling (ToF-SIMS), while the surface composition of the material is studied by Low-Energy Ion Scattering (LEIS). 1. A. Grimaud, F. Mauvy, J. M. Bassat, S. Fourcade, L. Rocheron, M. Marrony and J. C. Grenier, J Electrochem Soc, 159, B683 (2012). 2. G. Goupil, T. Delahaye, G. Gauthier, B. Sala and F. L. Joud, Solid State Ionics, 209, 36 (2012). 3. S. Upasen, P. Batocchi, F. Mauvy, A. Slodczyk and P. Colomban, Ceramics International, 41, 14137 (2015). 4. H. Tellez, J. Druce, J. A. Kilner and T. Ishihara, Faraday Discuss, 182, 145 (2015). 5. H. Téllez, J. Druce, Y.-W. Ju, J. Kilner and T. Ishihara, International Journal of Hydrogen Energy, 39, 20856 (2014).

Effect of Intermetallic Particle Size and Distribution on the Corrosion of an Mg-Al Alloy

The corrosion rates for Mg alloys are dependent on their composition. In particular, the corrosion resistance is usually increased if the alloying elements remain in solid solution and decreased if the alloying elements are above the solid solution solubility limit [1, 2]. Al additions up to 4 wt. % reduce the corrosion rate [2, 3]. During heat treatment, intermetallic particle (IMP) [4, 5] sizes increase while the area fraction remains relatively constant [4]. The size and spacing of these particles impacts the corrosion behaviour and will likely alter the cathodic reaction rate and corrosion rate as observed in other alloys systems [6]. In Mg-Al alloys, IMPs are more noble than typical Mg-Al alloy solid solutions [7, 8]. The IMPs function as cathodes when coupled with the α-Mg phase [9]. These IMPs support cathodic reduction reactions at faster rates than high purity Mg [7]. The extent of attack is dependent on the composition of the IMP. For instance, the cathodic activity of Al8Mn5 is much greater than that of Mg12Al17 or Al3Mg2 [10, 11]. However, little is known about how the size and spacing of these particles alters the cathodic rates and subsequently affects the corrosion rate. Mg-Al alloy, AZ31B was heat treated at temperatures ranging from 300 to 450 °C for durations ranging from 240 to 604,800 sec to produce samples varying in particle size and spacing. The corrosion behavior was examined in terms of its instantaneous corrosion rate and cathodic kinetics as a function of IMP size and spacing for a fixed area fraction of IMPs. The corrosion resistance was determined utilizing electrochemical impedance spectroscopy (EIS) [3]. The cathodic reaction rate was determined at -1.8 VSCE after 24 hrs immersed at the open circuit potential in 0.6 M NaCl. There was a decrease in both icorr and ic (Figure 1) with increasing particle size and spacing at a fixed area fraction of IMPs. The fast reactions around IMPs were mapped using Scanning Electrochemical Microscopy [12-15]. A non-aqueous electrolyte, such as ethelyne glycol or methanol mixed with a NaCl, was found to slow the kinetics of Mg corrosion while enabling mapping of active corroding sites [16]. The solution of 50 wt% methanol and 50 wt% H2O was found to give the best results. The mediator, hexaammineruthenium(III), Ru(NH3)6Cl3, has successfully been used to map Mg corrosion and was utilized herein [12]. The reduction of Ru(NH3)6Cl3 occurred at actively corroding sites. The subsequent oxidation of Ru(NH3)6Cl3 at the tip provided an indicator of sites where significant cathodic electron transfer reactions occurred [17]. The evolution of the reactivity of an AZ31B surface with time was mapped in 0.1 M NaCl (Figure 2). The regions of high cathodic reactivity are shown to spread across the surface as a function of exposure time. Acknowledgements This work was funded by the Office of Naval Research Grant N000141210967 with Dr. David A. Shifler.

Theoretical Research on a Multibeam-Modulated Electron Gun Based on Carbon Nanotube Cold Cathodes

Multi-beam modulation in a carbon nanotube (CNT) cold cathode electron gun is herein investigated in order to develop miniaturized and fully integrated vacuum electron devices. By exposing the electron source to a millimeter-wave signal, the steady-state field emission current density is efficiently modulated by the incident high-frequency (HF) electric field. Our simulation results of this multibeam electron gun show that the field emission current density can be efficiently modulated by different incident frequency millimeter waves. We find that the modulation depth is increased by enhancing the HF input power and anode operation voltage. The modulation frequency and phase of each electron beam can be controlled using a single millimeter-wave source and by simply adjusting the lateral distance between adjacent CNT cold cathodes.

A LabView‐based hot cathode electron source simulator with no‐boundary condition computation method

SummaryFast and complex model‐based computations are often needed during the controller design process; therefore, a hot cathode electron source simulator was designed and implemented. The simulator uses the static model of electron source and is based on the LabView environment. It is developed for different materials and dimensions of filaments popular in vacuum instruments. The simulator is able to calculate the maximum temperature of the hot filament, its resistance, voltage drop and temperature and distribution of the electron emission current along the filament length in a steady state. Also, a new method was proposed and implemented for approximate calculations of distributions of the temperature and the electron emission current without measurements of the filament temperature. Copyright © 2016 John Wiley & Sons, Ltd.

Electricity Production in Microbial Fuel Cell Subjected to Different Operational Modes

The effects of inoculum species, substrate concentration, temperature, and cathodic electron acceptors on electricity production of microbial fuel cells (MFCs) were investigated in terms of start-up time and power output. When inoculated with aeration tank sludge, this MFC outperformed the cell that was inoculated with anaerobic sludge in terms of start-up time and power output. After running for a certain time period, the dominant populations of the two MFCs varied significantly. Within the tested range of substrate concentration (200–1800 mg L−1), the voltage output increased and the time span of the electricity generation lengthened with increasing substrate concentration. As the temperature declined from 35 to 10 °C, the maximum power density reduced from 2.229 to 1.620 W m−3, and anodic polarization resistance correspondingly dropped from 118 to 98 Ω. The voltage output of MFC–Cu2+ was 0.447 V, which is slightly lower than that achieved with MFC–[Fe(CN)6]3− (0.492 V), thereby indicating that MFCs could be used to treat wastewater containing Cu2+ pollutant in the cathode chamber with removal of organics in anode chamber and simultaneous electricity generation.

Impedance of an intense plasma-cathode electron source for tokamak startup

An impedance model is formulated and tested for the ∼1 kV, 1 kA/cm2, arc-plasma cathode electron source used for local helicity injection tokamak startup. A double layer sheath is established between the high-density arc plasma (narc≈1021 m−3) within the electron source, and the less dense external tokamak edge plasma (nedge≈1018 m−3) into which current is injected at the applied injector voltage, Vinj. Experiments on the Pegasus spherical tokamak show that the injected current, Iinj, increases with Vinj according to the standard double layer scaling Iinj∼Vinj3/2 at low current and transitions to Iinj∼Vinj1/2 at high currents. In this high current regime, sheath expansion and/or space charge neutralization impose limits on the beam density nb∼Iinj/Vinj1/2. For low tokamak edge density nedge and high Iinj, the inferred beam density nb is consistent with the requirement nb≤nedge imposed by space-charge neutralization of the beam in the tokamak edge plasma. At sufficient edge density, nb∼narc is observed, consistent with a limit to nb imposed by expansion of the double layer sheath. These results suggest that narc is a viable control actuator for the source impedance.

Electrons from Solid Electrode Alter Phototrophic Mat Morphology and Metabolic Activity

Phototrophic microbial mats are structured microbial communities composed of highly interactive species that have complete energy and elements within them. Aside from being an excellent ecological model that can be used to investigate how microbial populations associate and interact, microbial mats have the potential for energy capture and conversion applications. To use mats for such purpose, it is critical to understand the energy transfer and activity of microbial populations under the existence of external electron donor or acceptor sources. One method to accomplish this is by introducing a solid electrode with a controlled electrochemical potential to act as an electron donor or acceptor to the mat systems. We hypothesized that varying the electrode potential would, in turn, change the structure, activity, and community composition of the mat via regulation of electron transfer processes. In this work, the electrodes were placed under mats to establish a mat electrochemical system for testing our hypothesis. The phototrophic microbial mat was harvested from Hot Lake, a hypersaline, epsomitic lake located near Oroville (Washington, USA). The electrodes in contact with the base of the mat were polarized at -0.7 VAg/AgCl (hereafter referred to as the “cathodic mat)”. Electrodes that served as an electron sink were polarized at +0.3 VAg/AgCl (hereafter referred as the “anodic mat”). We quantified the diel variations of electron transfer rates between the electrode and the cathodic or anodic mats. We observed variations in current over a diel light cycle in which the lowest and highest magnitudes of anodic current occurred simultaneously with those of cathodic current. To understand the factors affecting these variations we examined the influences of temperature, light intensity, and substrate additions, separately, to electron transfer rate. We also used microelectrodes to measure the depth profiles of sulfide and oxygen concentrations and compared them with the variations of electron transfer rates over a diel cycle. To understand how anodic or cathodic electron transfer processes impacted mat structure and activity, we used nuclear magnetic resonance (NMR) imaging for morphology and NMR metabolite analysis to quantify the activity. The results showed that the quantitative porosity and diffusion coefficients were higher in the cathodic mat than in the anodic mat. In addition, cathodic mats produced significantly higher concentrations of osmo-protectants such as betaine and trehalose. The anodic mat had metabolic profiles similar to the control (non-polarized) mat. Finally, we employed amplicon sequencing across the V4 region of the 16S gene to determine the effect of the electrochemical regime upon mat community structure. The community structure data were consistent with variations in metabolite profiles and suggested greater changes in microbial community structure and function in the cathodic vs. the anodic and control mats. Although further work is needed to determine whether the electron transfer to and from the electrode to the mat was mediated by microbial metabolism of selectively-enriched community on the electrode or was caused by abiotic reactions on electrode, our data strongly suggest that donation of electrons via a solid electrode is capable of altering phototrophic mat morphology, community composition, and metabolic activity. It is possible that the addition of electrons from electrode to the mat alleviated the energy limitations allowing the mat to maintain large carbon pools of osmolytes. In addition, some microorganisms in the mat might use electrons from the electrode to drive carbon fixations which resulted in selectively-enriched community on the electrode and the increase of the total carbon available to the mat.

Bioelectrochemical Reduction of Fe(II)EDTA-NO in a Biofilm Electrode Reactor: Performance, Mechanism, and Kinetics.

A biofilm electrode reactor (BER) is proposed to effectively regenerate Fe(II)EDTA, a solvent for NOx removal from flue gas, from Fe(II)EDTA-NO, a spent solution. In this study, the performance, mechanism, and kinetics of the bioelectrochemical reduction of Fe(II)EDTA-NO were investigated. The pathways of Fe(II)EDTA-NO reduction were investigated via determination of nitrogen element balance in the BER and an abiotic electrode reactor. The experimental results indicate that the chelated NO (Fe(II)EDTA-NO) is reduced to N2 with N2O as an intermediate. However, the oxidation of NO occurred in the absence of Fe(II)EDTA in abiotic reactors. Furthermore, the accumulation of N2O was suppressed with the help of electricity. The preponderant electron donor for reduction of Fe(II)EDTA-NO was also confirmed via analysis of the electron conservation. About 87% of Fe(II)EDTA-NO was reduced using Fe(II)EDTA as the electron donor in the presence of both glucose and cathode electrons while the cathode electrons were utilized for the reduction of Fe(III)EDTA to Fe(II)EDTA. Michaelis-Menten kinetic constants of bioelectrochemical reduction of Fe(II)EDTA-NO were also calculated. The maximum reduction rate of Fe(II)EDTA-NO was 13.04 mol m(-3) h(-1), which is 50% higher than that in a conventional biofilter.

Potassium permanganate as an electron receiver in a microbial fuel cell

ABSTRACTMicrobial fuel cells with air as a cathode electron receiver are simple systems but they need expensive catalysts. In comparison to microbial fuel cells with oxygen as an electron receiver, microbial fuel cells with potassium permanganate produce higher voltage. In this study, electrical performance of a microbial fuel cells containing anaerobic sludge and potassium permanganate as an oxidizing agent was investigated. Glucose (1 g/l) was used as a carbon and energy source. The maximum power density and current density at the maximum power density were 93.13 mW/m2 and 0.030 mA/cm2 with respect to a potassium permanganate concentration of 400 µM. It is observed that the maximum power density increased to 114.00 mW/m2 using an acid-heat treated carbon brush anode. Also, chemical oxygen demand removal was 51% when the microbial fuel cells was operated using 400 µM of potassium permanganate.

A multiple gap plasma cathode electron gun and its electron beam analysis in self and trigger breakdown modes.

In the present paper, a pseudospark discharge based multiple gap plasma cathode electron gun is reported which has been operated separately in self and trigger breakdown modes using two different gases, namely, argon and hydrogen. The beam current and beam energy have been analyzed using a concentric ring diagnostic arrangement. Two distinct electron beams are clearly seen with hollow cathode and conductive phases. The hollow cathode phase has been observed for ∼50 ns where the obtained electron beam is having low beam current density and high energy. While in conductive phase it is high current density and low energy electron beam. It is inferred that in the hollow cathode phase the beam energy is more for the self breakdown case whereas the current density is more for the trigger breakdown case. The tailor made operation of the hollow cathode phase electron beam can play an important role in microwave generation. Up to 30% variation in the electron beam energy has been achieved keeping the same gas and by varying the breakdown mode operations. Also, up to 32% variation in the beam current density has been achieved for the trigger breakdown mode at optimized trigger position by varying the gas type.

In Russian

It is known that effect of an external constant magnetic field (CMF) on the process of electrolysis of water at a certain orientation of the vectors of the electric and magnetic fields reduces the overvoltage of hydrogen and oxygen evolution. The mechanism of this action due to the formation of magneto-hydrodynamic microvortices of electrolyte around the bubbles, facilitating their separation from the electrodes, i.e. removal electrolysis products, can take place, but it is not consistent with our results. We have found that due to the influence of CMF in the moment of separation from the electrode and within the initial section, the trajectory of the bubble is close to parabolic, which is then changed to a straight vertical motion. According to the Lorentz law, it has been found that hydrogen bubbles are negatively charged and those of oxygen - positively in the entire range of pH, including pH of 2.5, when the charge of bubbles due to adsorption of ions from the electrolyte is zero. It is known that the homogeneous CMF influence only on moving charges. It is suggested that such charges moving over the surface of the bubbles may be issued from the cathode electrons.

Simultaneous nitrification and denitrification in a novel membrane bioelectrochemical reactor with low membrane fouling tendency.

Microbial fuel cells (MFCs) can use nitrate as a cathodic electron acceptor for electrochemical denitrification, yet there is little knowledge about how to apply them into current wastewater treatment process to achieve efficient nitrogen removal. In this study, two dual-chamber MFCs were integrated with an aerobic membrane bioreactor to construct a novel membrane bioelectrochemical reactor (MBER) for simultaneous nitrification and denitrification under specific aeration. The effects of chemical oxygen demand (COD) loading rate, COD/N ratio, hydraulic retention time (HRT), and external resistance on the system performance were investigated. High effluent quality was obtained in the MBER in terms of COD and ammonium. During the operation, denitrification simultaneously occurred with nitrification at the bio-cathode of the MBER, achieving a maximal nitrogen removal efficiency of 84.3%. A maximum power density of 1.8W/m3 and a current density of 8.5A/m3 were achieved with a coulombic efficiency of 12.1%. Furthermore, compared to the control system, the MBER exhibited lower membrane fouling tendency due to mixed liquor volatile suspended solids (MLVSSs) and extracellular polymeric substance (EPS) reductions, EPSp/EPSc ratio decrease, and particle size increase of the sludge. These results suggest that the MBER holds potential for efficient nitrogen removal, electricity production, and membrane fouling mitigation.

The Use of an Electron Microchannel as a Self-Extracting and Focusing Plasma Cathode Electron Gun

A new and simple type of electron gun is presented. Unlike conventional electron guns, which require a heated filament or extractor, accelerator and focusing electrodes, this gun uses the collimated electron microchannels of an inertial electrostatic confinement (IEC) discharge to achieve the same outcome. A cylindrical cathode is placed coaxially within a cylindrical anode to create the discharge. Collimated beams of electrons and fast neutrals emerge along the axis of the cylindrical cathode. This geometry isolates one of the microchannels that emerge in a negatively biased IEC grid. The internal operating pressure range of the gun is 35-190 mTorr. A small aperture separates the gun from the main vacuum chamber in order to achieve a pressure differential. The chamber was operated at pressures of 4-12 mTorr. The measured current produced by the gun was 0.1-3 mA (0.2-14 mA corrected measurement) for discharge currents of 1-45 mA and discharge voltages of 0.5-12 kV. The collimated electron beam emerges from the aperture into the vacuum chamber. The performance of the gun is unaffected by the pressure differential between the vacuum chamber and the gun. This allows the aperture to be removed and the chamber pressure to be equal to the gun pressure if required.

High-Performance Lithium-Sulfur Batteries with a Self-Assembled Multiwall Carbon Nanotube Interlayer and a Robust Electrode-Electrolyte Interface.

Elemental sulfur electrode has a huge advantage in terms of charge-storage capacity. However, the lack of electrical conductivity results in poor electrochemical utilization of sulfur and performance. This problem has been overcome to some extent previously by using a bare multiwall carbon nanotube (MWCNT) paper interlayer between the sulfur cathode and the polymeric separator, resulting in good electron transport and adsorption of dissolved polysulfides. To advance the interlayer concept further, we present here a self-assembled MWCNT interlayer fabricated by a facile, low-cost process. The Li-S cells fabricated with the self-assembled MWCNT interlayer and a high loading of 3 mg cm(-2) sulfur exhibit a first discharge specific capacity of 1112 mAh g(-1) at 0.1 C rate and retain 95.8% of the capacity at 0.5 C rate after 100 cycles as the self-assembled MWCNT interlayer facilitates good interfacial contact between the interlayer and the sulfur cathode and fast electron and lithium-ion transport while trapping and reutilizing the migrating polysulfides. The approach presented here has the potential to advance the commercialization feasibility of the Li-S batteries.

Study on evaporation from alloys used in microwave vacuum electron devices

The development of modern satellite communication technologies is imposing higher demands on the lifetime and reliability of the microwave vacuum electronic devices, which directly depend on the evaporation properties of the extensively used Monel and stainless steel. Therefore, it is of vital importance to study the evaporation properties of these two types of metallic materials. For the first time, as far as we know, this paper proposes to study the evaporation properties of metallic materials using time-of-flight mass spectrometer (TOFMS). The components and the contents of the vacuum background, the evaporants from the Monel and from the stainless steel have been measured using the TOFMS, respectively. After the pressure of the measurement chamber is below 4.010-8 Pa, the TOFMS is used for the metallic materials working at different temperatures. They are respectively acquired when the Monel and stainless steel are at room temperature on operate between 750 to 900 ℃ under a pressure of 1.010-6 Pa. The measurements are carried out rapidly and in high sensitivity. As disclosed by the measurements, Mn and Cu began to evaporate when the Monel and the stainless steel are heated to 800 ℃, which is still far below the melting points of the two alloys (1243 ℃ and 1080 ℃). When the Monel and the stainless steel are further heated to 900 ℃, the evaporation of Mn, Cu, and Cr becomes quite considerable. Once the evaporated Mn, Cu, or Cr deposit on the ceramics for the insulation in an electron gun, its insulation will be deteriorated. Hence, the Monel and the stainless steel are not suitable to be use as the components in cathode electron guns, especially those used in the devices that are to work a long lifetime in high vacuum. Moreover, the Monel and the stainless steel are not suitable for used as the components that are often under the electron bombardment, e.g., anodes and collectors, either. The SEM images and XRD of the heat treated surface structures of the Monel and the stainless steel in ultrahigh vacuum (1.010-6 Pa) have also been studied. On heating at 900 ℃ for 30 and 120 min the surface structure and composition change remarkably and a significant reduction in Mn and Cr is visible, and also a large number of holes and crystal boundaries emerge on the surfaces of the two metallic alloys. With increasing heating time, the boundaries will grow larger and larger. As a result, the strength of the two metallic materials becomes weaker and gas permeation and leakage even occur. Therefore, it can be concluded that the components made from Monel and stainless steel, especially those with thin walls, should not be heated to high temperatures in ultrahigh vacuum for a long time. The above phenomena are analyzed in detail theoretically and the proper and feasible application methods of the metallic materials are explored in device design and technological process control. These works are expected to contribute to the prolonging of the lifetimes of the satellites, and will lead to tremendous economic benefits.