Bismuth Cathode Research Articles

Experimental and Zero-dimensional Simulation Study of an Embedded Bismuth LaB6 Hollow Cathode

Experiments and zero-dimensional simulation were conducted to evaluate the discharge performance of an embedded bismuth LaB6 hollow cathode. The experimental results demonstrate that the embedded bismuth hollow cathode can operate in diode mode without any external heating, with a mass flow rate of approximately 0.21 mg/s. In Keeper-cathode mode, the discharge voltage for bismuth was slightly lower than that of xenon and exhibited strong stability, with a maximum discharge variation of less than 0.5 V at a discharge current of 2 A. The simulation results showed that at the same mass flow rate, the electron and ion densities in the insert region of the bismuth cathode were higher than those of xenon, whereas the opposite was true for the orifice region. Notably, at discharge currents below 4 A, the power deposition of bismuth in both the insert and orifice regions was lower than that of xenon, indicating reduced orifice erosion and effective self-heating of the insert at low current levels.

Unassisted photoelectrochemical CO2-to-liquid fuel splitting over 12% solar conversion efficiency

The increasing need to control anthropogenic CO2 emissions and conversion to fuels features the necessity for innovative solutions, one of which is photoelectrochemical system. This approach, capable of yielding gaseous production progressively, is facing challenges for liquid fuels generation due to optical, electrical, and catalytic properties. This study employs a standalone photoelectrochemical setup, in which InGaP/GaAs/Ge photoanode is integrated with tin-modified bismuth oxide cathode to convert CO2 into liquid formic acid. In unassisted two-electrode assembly, setup exemplifies its operational durability for 100 h, during which it maintains an average Faradaic efficiency of 88% with 17.3 mmol L–1 h–1 of yield, thereby excelling in average solar-to-fuel conversion efficiency at 12% with 60% of electrical energy efficiency under one sun illumination. This significant performance is further associated with metal-semiconductor interface formation between tin and bismuth oxide, which bridges electronic structures and generates an electric field at their interfaces. This study outperforms conventional solar-driven systems in operational durability and liquid fuel production.

Selective extraction of Sm from LiCl-KCl molten salt into wasteforms via liquid bismuth

The electrorefining of spent nuclear fuels in a molten LiCl-KCl salt electrolyte recovers the valuable actinides but also releases radioactive fission products in the salt. To minimize the nuclear waste volume, dissolved fission products such as rare earths (REs) must be removed from the electrorefining salt and immobilized into proper wasteforms. Here we propose a two-step approach for treating the electrorefining waste salt by (i) the electrolytic recovery of REs from the salt using a liquid metal cathode; and subsequent (ii) oxidative extraction of REs from the liquid metal into durable wasteforms. Experimental demonstration using rare earth element samarium (Sm) and liquid metal (Bi) was successful. The Sm ions dissolved in the salt can be selectively recovered as dendrite Sm-Bi intermetallic products on the top of liquid bismuth cathode through electrolysis at appropriate applied currents or potentials. Then the Sm in the Sm-Bi alloy was efficiently extracted into both zinc-in-titania (ZIT) glass ceramic and lanthanide aluminoborosilicate (LABS) glass wasteforms through selective oxidation at Sm2O3 loadings of 18–25 wt% and 50 wt%, respectively. Recycling of the electrorefining salt with minimum nuclear waste generation is foreseeable with the use of this simple, efficient, and highly compatible process.

Enhanced electrochemical properties of lithium-tin liquid metal battery via the introduction of bismuth cathode material

The performance of a liquid metal battery can be significantly enhanced by lowering the cell operating temperature through alloying of the cell components. The effect of alloying pure tin metal, a cathode material for liquid metal batteries, on electrochemical properties is investigated by preparing a Li|Sn-Bi (Sn:Bi = 56:44 at%) battery cell. The Li|Sn-Bi cell achieves mean voltages of 0.856 and 0.683 V during charging and discharging, respectively, at 100 mA cm−2, which are 0.039 and 0.067 V higher than those of the Li|Sn cell. The Li|Sn-Bi cell exhibits a high rate capability owing to the low charge-transfer resistance between the liquid electrodes and liquid electrolytes. The charge and discharge capacity losses are 6.5% and 18.6%, respectively, at 1000 mA cm−2 compared with those at 100 mA cm−2. The Li|Sn-Bi cell can be discharged even at 1000 mA cm−2 owing to an increase in the mean discharge voltage by the alloying of tin with bismuth. The Li|Sn-Bi cell also exhibits improved cycle performance, with a capacity retention of 94.2% after 1000 cycles and a capacity decay of 0.0065% per cycle. This is attributed to the lack of formation of intermetallic byproducts between Bi and the stainless steel case and suppression of the side reaction between Sn and stainless steel by bismuth in the Sn-Bi lamellar microstructure. Thus, using a Sn-Bi alloy as the positive material significantly improves battery performance, making the Li|Sn-Bi cell a good candidate for stationary storage applications.

Assessment on Recovery of Cesium, Strontium, and Barium From Eutectic LiCl-KCl Salt With Liquid Bismuth System

This study provides an assessment on a proposed method for separation of cesium, strontium, and barium using electrochemical reduction at a liquid bismuth cathode in LiCl-KCl eutectic salt, investigated via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS). CV studies were performed at temperatures of 723-823 K and concentrations of the target species up to 4.0wt%. Redox reactions occurring during potential sweeps were observed. Concentration of BaCl2 in the salt did not seem to influence the diffusivity in the studied concentration range up to 4.0wt%. The presence of strontium in the system affected the redox reaction of lithium; however, there were no distinguishable redox peaks that could be measured. Impedance spectra obtained from EIS methods were used to calculate the exchange current densities of the electroactive active redox couple at the bismuth cathode. Results show the rate-controlling step in deposition to be the mass transport of Cs+ ions from the bulk salt to the cathode surface layer. Results from SEM-EDS suggest that Cs-Bi and Sr-Bi intermetallics from LiCl-KCl salt are not thermodynamically favorable.

High-Charge-State Ion Beam Generation in a High-Current Pulsed Vacuum Arc Source

We have explored the generation of high-charge-state ion beams by a vacuum arc ion source. A pulsed vacuum arc with current up to several kiloamperes and pulse duration about $1~\mu \text{s}$ was used. In a vacuum arc ion source with bismuth cathode and at a background pressure of about $40~\mu $ Pa, a bismuth ion beam was formed with a maximum charge state Bi19+. For an ion accelerating voltage of 60 kV, this corresponds to a maximum bismuth ion energy of over 1 MeV.

Directing the Outcome of CO2 Reduction at Bismuth Cathodes Using Varied Ionic Liquid Promoters.

Ionic liquids (ILs) have been established as effective promoters for the electrocatalytic upconversion of CO2 to various commodity chemicals. Imidazolium ([Im]+) cathode combinations have been reported to selectively catalyze the 2e-/2H+ reduction of CO2 to CO. Recently our laboratory has reported energy-efficient systems for CO production featuring inexpensive bismuth-based cathode materials and ILs comprised of 1,3-dialkylimidazolium cations. As part of our ongoing efforts to understand the factors that drive CO2 reduction at electrode interfaces, we sought to evaluate the catalytic performance of alternative ILs in combination with previously described Bi cathodes. In this work, we demonstrate that protic ionic liquids (PILs) derived from 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) effectively promote the electrochemical reduction of CO2 to formate (HCOO-) with high selectivity. The use of PILs comprised of the conjugate acid of DBU, [DBU-H]+, efficiently catalyzed the reduction of CO2 to HCOO- (FEFA ≈ 80%) with significant suppression of CO production (FECO ≈ 20%) in either MeCN or MeCN/H2O (95/5) solution. When they were used in combination with [DBU-H]+-based PILs, Bi-based cathodes achieved current densities for CO2 reduction (j tot ≈ 25-45 mA/cm2) that are comparable to or greater than those reported with imidazolium ILs such as [BMIM]PF6. As we demonstrate herein, the selectivity of the 2e- reduction of CO2 toward HCOO- or CO can be dictated through the choice of the IL promoter present in the electrolysis solution, even in cases in which the same electrocatalyst material is studied. These findings highlight the tunability of bismuth/IL systems for the electrochemical reduction of CO2 with high efficiency and rapid kinetics.

Capacity extended bismuth-antimony cathode for high-performance liquid metal battery

Li-Bi based liquid metal batteries (LMBs) have attracted interest due to their potential for solving grid scale energy storage problems. In this study, the feasibility of replacing the bismuth cathode with a bismuth-antimony alloy cathode in lithium based LMBs is investigated. The influence of the Bi:Sb ratio on voltage characteristics is evaluated via the constant current discharge method and electrochemical titration. On observing the cross section of the electrode at various stages of discharge, it is determined that both Sb and Bi form solid intermetallics with Li on the cathode. Additionally, the addition of Bi not only reduces the melting temperature of the Bi:Sb intermetallic but also actively contributes to the electrode capacity. Thereafter, a Li|LiCl-LiF|Sb-Bi liquid metal battery with 3 A h nameplate capacity, assembled and cycled at 1 C rate, is found to possess a stable capacity for over 160 cycles. The overall performance of this battery is discussed in the context of cost effectiveness, energy and coulombic efficiencies.

Controlling the leakage of liquid bismuth cathode elements in ceramic crucibles used for the electrowinning process in pyroprocessing

Pyroprocessing has shown promise as an alternative to wet processing for the recycling of transuranics with a high proliferation resistance. However, a critical issue for pyroprocessing is the ceramic crucibles used in the electrowinning process. These ceramic crucibles are frequently damaged by thermal stress, which results in significant volumes of crucible waste that must be properly disposed. Transuranic waste (TRU) elements intrude throughout the pores of a damaged crucible. The volume of generated radioactive waste is a concern when dealing with nuclear power plants and decontamination issues. In this study, laser treatment and sintering were performed on the crucibles to minimize the TRU elements trapped within. Secondary ion mass spectroscopy was used to measure the intrusion depth of Li in the surface-treated ceramics.

Estimation of the initial density distribution in plasma–metal liners

We describe a method for estimating the initial density profile of the liner shell from experimental current and voltage oscillograms with correction of the radius of the pinch from its optical images. It is shown that the average radial profile of the initial density distribution of plasma–metal liners can be approximated by two Gaussian curves with different dispersions. The largest contribution to the main peak of the initial density distribution comes from bismuth cathode material (bismuth) ions, while the contribution to the second Gaussian curve is due to the substance of the insulator over the surface of which the vacuum arc is initiated.

Thermo-mechano-chemical stability of ceramic materials during the electrowinning process using liquid metal electrodes in molten salts

Pyroprocessing, which results in proliferation resistance, shows promise as an alternative to wet processing in the recycling of transuranics. However, the ceramic crucible used in the electrowinning process poses an issue during pyroprocessing. The crucible is chemically unstable and prone to thermal fatigue. In this study, the thermodynamic simulation software HSC (enthalpy, entropy and heat capacity) Chemistry was employed to evaluate the chemical stabilities of different ceramic crucibles containing liquid cadmium as well as liquid bismuth cathodes, which also contained rare earth elements and lithium. The chemical stabilities were experimentally validated by measuring the contact angles between the liquid cathode (LC) materials and four ceramic materials (Al2O3, MgO, Y2O3, and BeO) in situ. The infiltration depths of the liquid bismuth cathode elements were measured using X-ray photoelectron spectroscopy. To determine the Weibull distributions of the investigated ceramics, thermal fatigue tests were performed using plates of the ceramics.

Electrochemical reduction of nitrate and nitrite in simulated liquid nuclear wastes

The electrochemical reduction of nitrate and nitrite in simulated low-level nuclear wastes containing 1.8 M NaNO 3 + 0.55 M NaNO 2 + 1.16 M NaOH was studied under galvanostatic polarization on tin and bismuth cathodes. The rate of the reduction of nitrate was about the same on both metals. The selectivity (%S) to ammonia was similar on the two metals (12% at 450 mA/cm 2) and that to nitrogen 82% on Sn and 72% on Bi. On the other hand, the %S to nitrous oxide was lower on Sn (8%) than that on Bi (18%) under the same conditions. The current efficiency (%CE) on both metals was 80% when the 99% of the initial nitrogen was removed. The %CE gradually decreases as the concentration of the nitrogen containing species in the solution decreases during the electrolysis. The energy consumption for the removal of 1 g of N was 100 W h at 450 mA/cm 2 but it can be significantly reduced by a better design of the electrolysis cell.The presence of chromate in the electrolyte, which is a known inhibitor of the cathodic reduction of nitrate, has no influence on the rate of the reduction and the distribution of the products.

Electrochemical reduction of nitrate on bismuth cathodes

The electrochemical reduction of nitrate was studied on bismuth cathodes in a 0.4 M NaHCO 3/0.4 M Na 2CO 3 solution containing 0.05 M NaNO 3. The main product of the electrolysis was nitrogen having selectivity (%S) between 58% and 65%. The other products were nitrous oxide (7–22%), ammonia (3.8–19%) and nitrite (1.8–2.6%). The total Faradaic Efficiency (%FE) was ranged from 80% at −1.8 to 20% at −2.6 V vs. Ag/AgCl. The reduction of nitrate takes place through two paths; the first is electrochemical and the second one is autocatalytic, which involves an intermediate having an oxidation number lower than +2. The rate of the autocatalytic path at −1.8 V vs. Ag/AgCl was up to 48 times higher than that of the electrochemical one. The bismuth cathode undergoes slow cathodic corrosion during the electrolysis the rate of which increases with the increase of the negative potential. Bismuth is a promising cathode for the treatment of wastewaters containing nitrate, such as the low level nuclear wastes, since both the rate of the reduction and the selectivity to nitrogen are high.

Bismuth Hollow Cathode for Hall Thrusters

B ISMUTH has several qualities that make it well suited for development as a Hall-thruster propellant. When compared with more conventional propellants such as xenon, bismuth holds significant advantages from both an energetics (lower ionization energy) [1] and cost standpoint. In addition, there are significant ground-test-facility cost savings, because bismuth does not require the use of cryogenic pumps. Unlike traditional propellants, bismuth is solid at room temperature; thus, the exhausted bismuth solidifies on the room-temperature vacuum chamber walls, and consequently the entire vacuum chamber becomes an effective pumping surface. With this in mind, operating a high-power bismuth Hall thruster would require only enough pumping speed to keep up with facility outgassing and minor vacuum leaks. However, there are some difficulties that need to be addressed when using a condensable propellant. Some of the issues include sustaining elevated temperatures for bismuth evaporation, regulating bismuth mass flow, mechanical limitations inherent with using refractory metal components, and bismuth plating of thruster and spacecraft components. Recently, there have been three new programs to develop bismuth Hall thrusters, with the first successful demonstration occurring in the spring of 2005 [2–4]. In this work, the bismuth thruster was operated using a xenonLaB6 cathode. The encouraging results of the bismuth thruster motivated a study to examine the feasibility of an all-bismuth system using a bismuth cathode. In addition to all of the physical and economical gains, it would be advantageous to incorporate a bismuth cathode to eliminate the need for multiple propellant supplies on an eventual flight unit. In 2005, a functioning prototype bismuth cathode was developed and a limited number of operating characteristics were reported [5]. The primary goals of the present research were to evaluate the operating characteristics of a bismuth LaB6 cathode at different mass flow rates, compare bismuth data with xenon and krypton performance, and to reduce the amount of power required for cathode operation.

Electron-beam enhancement of the metal vapor vacuum arc ion source

We report detailed investigations of the electron-beam metal vapor vacuum arc (E-MEVVA) ion source. The experiments were performed in Moscow and Tomsk with nearly the same design of ion sources. We recently reported the first conclusive demonstration of electron-beam enhancement of MEVVA performance using lead and bismuth cathodes, which yielded maximum ion charge states of Pb7+ and Bi8+ for E-MEVVA, as compared to Pb2+ and Bi2+ for conventional MEVVA operation. In this article we report extensive results for additional cathode materials, further details of the Moscow and Tomsk ion sources, and a discussion of electron beam effects on E-MEVVA performance. These results can be considered as a proof of the E-MEVVA principle.

Indium diffusion inside InBi during and after electrodeposition at various temperatures

The influence of temperature on indium galvanostatic electrodeposition from aqueous solutions on bismuth cathodes has been investigated, as well as the time evolution of the deposit composition. The formation of In-Bi intermetallic compounds was observed owing to indium diffusion into, and reaction inside, the bulk of the cathode. By considering the charge transfer and mass transport phenomena, we estimated the In diffusion coefficient into InBi at 30 to 70°C (from 0.79 × 10−15 to 3.77 × 10−15 m2 s−1) and from applying an Arrhenius-type relation, we estimated the activation energy (32.8 kJ mol−1) and frequency factor (3.7 × 10−10 m2 s−1).

Mechanism of indium electrodeposition on bismuth cathodes and time evolution of the deposits

The mechanism of the indium electrodeposition process from aqueous solutions on bismuth cathodes has been investigated as well as the evolution with time of the composition of the deposits after electrodeposition. The potentiometric results and the changes in composition and structure are explained by considering the transport phenomena and the reactions occurring in the solid state owing to indium diffusion into the electrode and to the formation, generally, of the multiphase layer InIn 2BiIn 5Bi 3InBi. Such analysis allows estimation of the room temperature average diffusion coefficient of indium in the three intermetallic compounds (ca. 10 −15−10 −16 m 2 s −1). Moreover, consideration of the indium chemical potentials within each compound makes it possible to account for the evolution of the system with time to InBi.

Intermetallic compounds formed by electrodeposition of indium on bismuth

Indium electrodeposition on bismuth cathodes at constant current density and room temperature gives rise to the formation of three intermetallic compounds owing to indium diffusion and reaction inside the electrode. The mechanism of this process has been investigated by scanning electron microscopy, energy-dispersive spectrometry and X-ray diffraction, analysing the morphology, composition and structure of the deposit surface and cross-section. The intermetallic compounds are In 2Bi, In 5Bi 3 and InBi, the latter being the unique compound at the end of the analysed time-scale (1500 h), while In 5Bi 3 never emerged on the electrode surface.

A hollow cathode bismuth ion laser

cw laser oscillations of Bi II at 680.9, 660.0, and 571.9 nm have been achieved for the first time by using a bismuth hollow cathode discharge. In addition, laser oscillations of Bi I at 1.1711 μm in the afterglow were observed. The ionic laser lines are excited by Penning ionization. The atomic line is produced by recombination of the bismuth ions and lowenergy electrons in the afterglow.

Fused Salt Polarography Using a Dropping Bismuth Cathode

An apparatus is described which is suitable to study fused chlorides by the polarographic technique. Dropping bismuth is used in a way analogous to dropping mercury. Polarographic waves are shown for , , and in a eutectic melt at 450°C. The method serves as an analytical tool at high temperatures, besides yielding physicochemical information such as diffusion coefficients by application of the Ilkovic equation.