Solid Electrolyte Tubes Research Articles

Sensor for operational control of oxygen and combustible gases concentration in waste gases of thermal units

A new sensor has been developed for continuous monitoring of oxygen and combustible gases content in the waste gases of thermal units. The target application of the sensor is its installation in shunt pipes of thermal units, directly into the waste gas flow. The sensor is characterized by one reference gas electrode and three measuring electrodes applied on the surface of a solid electrolyte tube made of a zirconia electrolyte (e.g., 8YSZ). The reference gas electrode and one of the measuring electrodes were made of silver, the second measuring electrode was made of platinum, the third measuring electrode was made of a mixture of zinc oxide (95 wt %) and lanthanum-strontium manganite (5 wt %). The oxygen content in the gas mixture was determined by the well-known potentiometric method in accordance with the Nernst equation, i.e. an Ag|8YSZ|Ag electrochemical cell was used. To determine the products of incomplete combustion of fuel, the method of mixed potential between Pt- and Zn-based electrodes was used; the obtained potential value was determined by the difference in the oxidation rate of carbon monoxide as the main component of unburned fuels, on different materials of measuring electrodes. The experimental results of the sensor for the determination of carbon monoxide, hydrogen, and methane in a gas mixture are presented.

Yttria-Stabilized Zirconia Assisted Green Electrochemical Preparation of Silicon from Solid Silica in Calcium Chloride Melt

A novel integrated cell with O2-|YSZ|Pt|O2(air) reference and counter electrodes was constructed using a short yttria-stabilized zirconia solid electrolyte (YSZ) tube. Combining with cyclic voltammetry and potentiostatic electrolysis methods, green electrochemical preparation of Si from solid SiO2 in CaCl2 melt at 1173 K was studied via an experimental apparatus containing the novel integrated cell under completely carbon-free conditions; the effect of electrolysis time on the morphology of the Si product was also investigated by scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDS). The results show that the morphology of the product obtained from potentiostatic electrolysis at a low overpotential (− 1.6 V) undergoes an evolution from SiO2 raw powder with different sizes to aggregates of spherical particles and small particles with partial reduction, and then to Si nuclei, and finally to Si wires or flakes. The morphology of electrolytic products has little relation with that of SiO2 raw powder and may be controlled by applying different potentials. Furthermore, the longer the electrolysis time, the more the Si wires grow, and the higher the Si purity overall. It is feasible that the experimental apparatus without the sealed stainless steel reactor and any carbonaceous materials can be used to prepare Si from solid SiO2 in CaCl2 melt and release O2 gas at the same time.

The Renaissance of Liquid Metal Batteries

Next-generation batteries with long life, high-energy capacity, and high round-trip energy efficiency are essential for future smart grid operation. Recently, Cui et al. demonstrated a battery design meeting all these requirements—a solid electrolyte-based liquid lithium-brass/zinc chloride (SELL-brass/ZnCl2) battery. Such a battery design overcomes some inherent problems of conventional ZEBRA batteries and lithium ion batteries.

Molten Lithium-Brass/Zinc Chloride System as High-Performance and Low-Cost Battery

Summary Batteries with high safety, low cost, and reasonable energy density are essential for grid-scale energy storage and still remain elusive. Here, we report a solid electrolyte-based liquid lithium-brass/zinc chloride (SELL-brass/ZnCl2) battery using garnet-type lithium-ion solid electrolyte, lithium anode, and brass/ZnCl2 cathode. The chemistry of the cell reaction and the ability of being assembled in discharged state ensures a high safety. The use of low-cost ZnCl2 cathode can realize a low cell material cost of $16 kWh−1. The adoption of lithium anode guarantees a high theoretical energy density of 750 Wh kg−1 and 2,250 Wh L−1. Moreover, by using brass powder as a Zn source in the cathode, the Zn particle growth issue is successfully solved, and a good cycling stability of the battery can be obtained. As full cell performance and scalability are also verified, our SELL-brass/ZnCl2 battery shows a high potential for practical use in grid energy storage.

An intermediate temperature garnet-type solid electrolyte-based molten lithium battery for grid energy storage

Batteries are an attractive grid energy storage technology, but a reliable battery system with the functionalities required for a grid such as high power capability, high safety and low cost remains elusive. Here, we report a solid electrolyte-based molten lithium battery constructed with a molten lithium anode, a molten Sn–Pb or Bi–Pb alloy cathode and a garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZTO) solid electrolyte tube. We show that the assembled Li||LLZTO||Sn–Pb and Li||LLZTO||Bi–Pb cells can stably cycle at an intermediate temperature of 240 °C for about one month at current densities of 50 mA cm−2 and 100 mA cm−2 respectively, with almost no capacity decay and an average Coulombic efficiency of 99.98%. Furthermore, the cells demonstrate high power capability with current densities up to 300 mA cm−2 (90 mW cm−2) for Li||LLZTO||Sn–Pb and 500 mA cm−2 (175 mW cm−2) for Li||LLZTO||Bi–Pb. Our design offers prospects for grid energy storage with intermediate temperature operations, high safety margin and low capital and maintenance costs.

Thermal behavior of heat-pipe-assisted alkali-metal thermoelectric converters

The alkali-metal thermal-to-electric converter (AMTEC) changes thermal energy directly into electrical energy using alkali metals, such as sodium and potassium, as the working fluid. The AMTEC system primarily consists of beta-alumina solid electrolyte (BASE) tubes, low and high-pressure chambers, an evaporator, and a condenser and work through continuous sodium circulation, similar to conventional heat pipes. When the sodium ions pass through the BASE tubes with ion conductivity, this ion transfer generates electricity. The efficiency of the AMTEC directly depends on the temperature difference between the top and bottom of the system. The optimum design of components of the AMTEC, including the condenser, evaporator, BASE tubes, and artery wick, can improve power output and efficiency. Here, a radiation shield was installed in the low-pressure chamber of the AMTEC and was investigated experimentally and numerically to determine an optimum design for preventing radiation heat loss through the condenser and the wall of AMTEC container. A computational fluid dynamics (CFD) simulation was carried out to decide the optimum size of the low-pressure chamber. The most suitable height and diameter of the chamber were 270 mm and 180 mm, respectively, with eight BASE tubes, which were 150 mm high, 25 mm in diameter, and 105 mm in concentric diameter. Increasing the temperature ratio (T Cond /T B ) led to high power output. The minimum dimensionless value (0.4611) for temperature (T Cond /T B ) appeared when the radiation shield was made of 500-mesh nickel. Simulation results for the best position and shape for the radiation shield, revealed that maximum power was generated when a stainless steel shield was installed in between the BASE tubes and condenser.

Magnesia-stabilised zirconia solid electrolyte assisted electrochemical investigation of iron ions in a SiO2-CaO-MgO-Al2O3 molten slag at 1723 K.

Production of metallic iron through molten oxide electrolysis using inert electrodes is an alternative route for fast ironmaking without CO2 emissions. The fact that many inorganic oxides melt at ultrahigh temperatures (>1500 K) challenges conventional electro-analytical techniques used in aqueous, organic and molten salt electrolytes. However, in order to design a feasible and effective electrolytic process, it is necessary to best understand the electrochemical properties of iron ions in molten oxide electrolytes. In this work, a magnesia-stabilised zirconia (MSZ) tube with a closed end was used to construct an integrated three-electrode cell with a "MSZ|Pt|O2 (air)" assembly functioning as the solid electrolyte, the reference electrode and also the counter electrode. Electrochemical reduction of iron ions was systematically investigated on an iridium (Ir) wire working electrode in a SiO2-CaO-MgO-Al2O3 molten slag at 1723 K by cyclic voltammetry (CV), square wave voltammetry (SWV), chronopotentiometry (CP) and potentiostatic electrolysis (PE). The results show that the electroreduction of the Fe2+ ion to Fe on the Ir electrode in the molten slag follows a single two-electron transfer step, and the rate of the process is diffusion controlled. The peak current on the obtained CVs is proportional to the concentration of the Fe2+ ion in the molten slag and the square root of scan rate. The diffusion coefficient of Fe2+ ions in the molten slag containing 5 wt% FeO at 1723 K was derived to be (3.43 ± 0.06) × 10-6 cm2 s-1 from CP analysis. However, a couple of subsequent processes, i.e. alloy formation on the Ir electrode surface and interdiffusion, were found to affect the kinetics of iron deposition. An ECC mechanism is proposed to account for the CV observations. The findings from this work confirm that zirconia-based solid electrolytes can play an important role in electrochemical fundamental research in high temperature molten slag electrolytes.

Preparation of an electrochemical sensor for measuring the silicon content in molten iron

A silicon sensor for measuring the silicon content in molten iron that included a new membrane electrode was synthesized by coating a slurry of CaF2, SiO2 and 5% Polyvinyl alcohol (PVA) onto the surface of a ZrO2 (MgO) solid electrolyte tube, followed by sintering in a high purity Ar atmosphere. The influences of the preparation conditions, such as the chemical composition, solid (CaF2+SiO2 powder) to liquid (5% PVA solution) ratio and sintering temperature, on the coating layer adhesive properties, active ingredients and detection performance of the formed auxiliary electrode layer were systematically investigated. It is indicated that the synthesized coating layer showed strong adhesive properties and the main active ingredients were SiO2 (ZrSiO4) solid particles-CaO·MgO·2SiO2 solid solution under the optimum preparation conditions. The as-prepared silicon sensor, which was used to detect the silicon content in molten iron at 1450°C, exhibited superior performance. When the silicon content ranged from 0.5 to 1.5% in liquid iron, the testing result from the silicon sensor with a response time of 15s and steady time greater than 30s agreed well with the values from the chemical analysis method.

Effect of Basicity on Electroreduction with Controlled Oxygen Flow of Molten Slag Containing FeO

This paper reports on electroreduction with controlled oxygen flow (COF) for extraction of iron along with oxygen by-product from molten slags containing iron oxide at 1723 K. An electrolytic cell with COF was constructed by an iridium wire cathode and a porous platinum anode sintered on a one-end-closed magnesia-stabilized zirconia-based solid electrolyte tube. Effect of basicity of SiO2–CaO–Al2O3–MgO–FeO slag on electroreduction behavior of FeO was investigated by means of the linear sweep and the potentiostatic electrolysis. The possibility of the zirconia membrane as conductive noncorrosive anode material was also discussed. The results indicate that both cathode alloying and increasing slag basicity are helpful to the FeO electrolytic reduction in the molten slag. With the iridium wire as a cathode and an applied voltage at 2.5 V, higher slag basicity results in higher electrolysis rate and higher reduction ratio of the FeO; however, silicon is also precipitated during electrolysis. The applied voltage can cause the increased porosity in the zirconia membrane. The corrosion of the molten slag to the zirconia membrane during electrolysis is evidently aggravated when the slag basicity reaches 0.8. In order to minimize the corrosion of the molten slag to the zirconia membrane during electrolysis, the slag basicity of 0.6 is relatively advisable for extraction of iron under conditions of experimentation.

ELECTROCHEMICAL BEHAVIOR OF Ni2+ IN SiO2-CaO-MgO-Al2O3 MOLTEN SLAG AT 1673 K

The modern iron and steel industry produces large emissions of CO2 annually. Electrolytic reduction of molten slag containing iron oxide at high temperature using an inert oxygen evolving anode is an alternative process to reduce or eliminate the formation of CO2. In order to establish reasonable process parameters of electrolytic method for steel containing Ni, it is necessary to master the electrochemical behavior of Ni + in molten slag. However, investigations on the electrochemical behavior of Ni in molten slag at higher temperatures were very limited, which can probably be attributed to the experimental difficulties associated with the operation of high-temperature electrochemical cells. An electrolytic cell with a controlled oxygen flow and Pt, O2(air)|ZrO2 used as reference electrode was constructed integrally through a one-end-closed magnesia partially stabilized ZrO2 solid electrolyte tube. Electrochemical behavior of Ni + on Ir electrode was investigated in SiO2-CaO-MgO-Al2O3 molten slag at 1673 K by means of electrochemical techniques such as cyclic voltammetry (CV), square wave voltammetry (SWV), chronopotentiometry (CP) and potentiostatic electrolysis. The results show that both diffusion in the molten slag and electromigration in the ZrO2 solid electrolyte for the O are not rate-determining steps of electrochemi*国家自然科学基金项目51174148和武汉科技大学大学生科技创新基金研究项目14ZRA004资助 收到初稿日期: 2015-01-22,收到修改稿日期: 2015-04-27 作者简介:洪川,男, 1990年生,硕士生 DOI: 10.11900/0412.1961.2015.00065 第1001-1009页 pp.1001-1009

Study on the Characteristics of an Alkali-Metal Thermoelectric Power Generation System

In the present study, a numerical simulation and experimental studies of an alkali-metal thermoelectric energy converter (AMTEC) system were carried out. The present, unique AMTEC model consists of an evaporator, a β-alumina solid electrolyte (BASE) tube, a condenser, and an artery cable wick. The key points for operation of the present AMTEC were 1100 K in the evaporator and 600 K in the condenser. A numerical model based on sodium-saturated porous wicks was developed and shown to be able to simulate the AMTEC system. The simulation results show that the AMTEC system can generate up to 100 W with a given design. The AMTEC system developed in the present work and used in the practical investigations could generate an electromotive force of 7 V. Artery wick and evaporator wick structures were simulated for the optimum design. Both sodium-saturated wicks were affected by numerous variables, such as the input heat power, cooling temperature, sodium mass flow rate, and capillary-driven fluid flow. Based on an effective thermal conductivity model, the presented simulation could successfully predict the system performance. Based on the numerical simulation, the AMTEC system operates with efficiency near 10% to 15%. In the case of an improved BASE design, the system could reach efficiency of over 30%. The system was designed for 0.6 V power, 25 A current, and 100 W power input. In addition, in this study, the temperature effects in each part of the AMTEC system were analyzed using a heat transfer model in porous media to apply to the computational fluid dynamics at a predetermined temperature condition for the design of a 100-W AMTEC prototype. It was found that a current density of 0.5 A/cm2 to 0.9 A/cm2 for the BASE is suitable when the temperatures of the evaporator section and condenser section are 1100 K and 600 K, respectively.

Fluoride Based Solid Electrolyte Tubes for Electrochemical Sensing

Under reducing conditions fluoride based solid electrolyte sensors with sulphur-sensitive auxiliary electrodes are able to measure the sulphur content in liquid metals and gases at elevated temperatures. In this work CaF2 doped with YF3 and SrF2 doped with LaF3 were selected as solid electrolyte material, because of their high ionic conductivity. Solid electrolyte tubes were prepared from these materials by slip casting to apply them as electrochemical sensors e.g. in the float glass industry.

Electrochemical Behavior of Ni Ion in SiO2-CaO-MgO-Al2O3 Molten Slag

A novel electrolytic cell with Pt,O2(air)|ZrO2 used as reference electrode was constructed integrally by using a one-end-closed magnesia partially stabilized zirconia solid electrolyte tube. Various electrochemical measurement techniques such as cyclic voltammetry (CV), chronopotentiometry (CP) and chronoamperometry (CA) were applied, and thermodynamic software Factsage was combined to study the effects of NiO concentration and temperature on electrochemical behavior of Ni ion in SiO2-CaO-MgO-Al2O3 molten slag at temperatures not less than 1673 K. The results indicate that Ni in molten slag is in stable form of Ni2+ instead of Ni3+; reduction of Ni2+ in molten slag is a diffusion control reaction process with a single step; smaller concentration of NiO and higher temperature lead to better reversibility of Ni2+ reduction reaction; with CV, CP and CA electrochemical measurement techniques, diffusion coefficients of Ni2+ at 1723 K are derived, respectively. Further, diffusion activation energy of Ni2+ from data corresponding to CV and CA techniques is derived from Arrhenius equation factored in diffusion coefficient and temperature.

Evaluation of CaO–Al2O3 adhesive bonding properties for β″-Al2O3 solid electrolyte sealing for alkali metal thermal electric converter

The β″-Al 2 O 3 solid electrolyte (BASE) tube is an essential component of the alkali metal thermal electric converter (AMTEC) system for inducing the conduction of Na ions and generating electricity. Maintaining gas-tightness to produce Na vapor pressure deference and providing insulation to prevent the loss of generated current from BASE are important factors for the AMTEC system. The Na–sulfur (NAS) battery has a similar driving system and uses glass adhesives, which are not adequate for operation temperatures higher than 800 °C or in a Na atmosphere. In this study, CaO–Al 2 O 3 was used as the adhesive to resolve such bonding issues. The bonding strength changes were evaluated as the adhesive bonding process temperature varied and also the results showed that CaO–Al 2 O 3 maintained bonding shear strength of 400 MPa for more than 1000 h in a molten Na environment. This study also proposes an experimental technique based on tube-type impedance measurement to assess the bonding between the BASE and the α-Al 2 O 3 insulator and to detect Na leakage. After conducting the experiment for 500 h, CaO–Al 2 O 3 adhesive can offer higher reliability than glass adhesives.

MgO-PSZ Solid State Electrolyte Tubes for Metallurgical Oxygen Sensors Made by Powder Injection Moulding

MgO-PSZ tubes used in metallurgical oxygen sensors were prepared by powder injection molding process. The microstructure was characterized by SEM, XRD and Thermomechanical Analyzer. The sintered tubes were assembled into oxygen sensors and tested in RH vessel. SEM images demonstrated that there were few pores in the tubes. The optimum injection pressure for the present organic binder is 20~30 MPa. XRD demonstrated that cubic, tetragonal, and monoclinic phase coexisted in the tube and the main phase is monoclinic phase. The results show a few monoclinic phase should be helpful for the thermal shock resistance. The thermal shock resistance of MgO-PSZ tubes was enough to determinate the active oxygen concentration in the steel melt.

Thermodynamic studies on LnCoO 3(s) (Ln = Dy, Ho) by solid-state electrochemical cells

Ternary oxides, DyCoO 3(s) and HoCoO 3(s) have been synthesized by citrate–nitrate gel combustion method and characterized by X-ray powder diffraction method. The standard molar Gibbs energies of formation of DyCoO 3(s) and HoCoO 3(s) have been measured using solid oxide galvanic cell technique employing yttria-stabilized zirconia (YSZ) and calcia-stabilized zirconia (CSZ) as solid electrolyte tubes, respectively. The standard molar Gibbs energies of formation of DyCoO 3(s) and HoCoO 3(s) were calculated from the measured e.m.f. data and are given as: Δ f G m ° ( DyCo O 3 , s , T ) kJ mo l − 1 ( ± 4 ) = − 1211.3 + 0.2449 ∗ ( T K ) , ( 1013 K ≤ T ≥ 1167 K ) , Δ f G m ° ( HCo O 3 , s , T ) kJ mo l − 1 ( ± 4 ) = − 1237.8 + 0.2590 ∗ ( T K ) . ( 964 K ≤ T ≥ 1102 K ) , A set of self consistent thermodynamic functions for LnCoO 3(s) (Ln = La, Nd, Sm, Eu, Gd, Dy, Ho) has been computed from available experimental data in the literature.

Investigation on pumping oxygen characteristics of (Bi 2O 3) 0.73(Y 2O 3) 0.27 solid electrolyte

(Bi 2O 3) 0.73(Y 2O 3) 0.27 fine powders prepared by wet chemical precipitation method were cold isostatically pressed to form solid electrolyte tubes, and sintered at 900 °C for 10 h in the air. Their pumping oxygen characteristics in non-dehydrated Ar gas were investigated, where a ZrO 2 (Y 2O 3 stabilized) oxygen sensor was used to measure the oxygen partial pressure Po 2. The results showed that the Po 2 value reached magnitudes of 1 × 10 −20–1 × 10 −10 Pa at the applied pumping oxygen voltage of 0.5 V, 1 × 10 −37–1 × 10 −27 Pa at 1.0 V and 1 × 10 −53–1 × 10 −47 Pa at 2.0 V within the temperature range from 550 to 650 °C. Moreover, no cracks were found in the tested solid electrolyte tubes. Thus, the Bi 2O 3-Y 2O 3 system might be used in solid electrolyte oxygen pump for purifying gases.

Capillary Limit of Evaporator Wick in Alkali Metal Thermal-to-Electric Converters

Vapor anode, multitube alkali metal thermal-to-electric converters are being developed for potential use in space and terrestrial electric power generation. In these converters, the capillary pressure head produced in the evaporator wick circulates the sodium working fluid. A two-dimensional, thermal-hydraulic model of the porous evaporator wick and of the liquid sodium return artery is developed and thermally coupled to an integrated model of a five-beta-alumina solid electrolyte (BASE) tube, stainless-steel sodium converter (PX-3A), and an eight-tube, Mo-41% Resodium converter. Results showed that the capillary limit in the evaporator wick of the PX-3A converter is reached at zero electrical current, when the thermal input power to the converter exceeds 16 W, or the hot-side temperature exceeds 1136 K. For the Mo-41%Re converter, these values are 22 W and 1150 K, respectively. Before reaching the capillary limit, however, two or more of the following temperature limits occurred in both converters: 1) the TiNi metal-ceramic braze joints' temperature exceeded 1123 K, 2) the evaporator wick surface temperature exceeded 1023 K, or 3) the temperature difference between the cold end of the BASE tubes and the evaporator wick surface was less than +20 K.

Fabrication of a Lithium Sensor Based on LiYO 2 by Liquid Phase Processing

A galvanic cell was constructed to measure the activity of lithium in liquid alloys. LiYO2 solid electrolyte tubes were made by slip casting. Y2O3-12.5% MgO was selected as the lid composition due to its inertness to molten lithium and optimum strength. The tube and lid were joined by reaction bonding in which Li2CO3 acts as the bonding agent and also plays an important role as sintering additive. The tube-lid assembly was used in a galvanic cell to measure the emf of Li in Li-Sn and Li-Zn alloys at temperatures of 240–720°C. The emf results demonstrated the reproducible functioning of the sensor.

Performance analyses of an Nb–1Zr/C-103 vapor anode multi-tube alkali-metal thermal-to-electric conversion cell

The results of performance analyses of a refractory Nb–1Zr/C-103 vapor anode multi-tube alkali-metal thermal-to-electric conversion (AMTEC) cell are presented and discussed. This cell could be used with a radioisotope heater unit to provide electric power from tens to a few hundreds of watts. In the tens of kilowatts electric range, the AMTEC cells could be used with a parabolic solar concentrator or a nuclear reactor heat source. The present cell measures 41.27 mm in diameter and is 125.3 mm high and has eight sodium beta ′′-alumina solid electrolyte (BASE) tubes, which are connected electrically in series to provide a load voltage in excess of 3 V. The hot structure of the cell, including the hot plate, the BASE tube support plate, the hot plenum wall and conduction stud, the evaporator standoff and porous wick and the side wall facing the BASE tubes, is made of Nb–1Zr. The cell's colder structure, which includes the condenser structure, the interior thermal radiation shield, the casing and wick of the liquid sodium return artery and the side wall above the BASE tubes, is made of C-103. This niobium alloy is stronger and has a lower thermal conductivity than Nb–1Zr, reducing the parasitic heat conduction losses in the cell wall, hence enhancing the cell's performance. The base cell weighs 163.4 g and delivers 7 W e at 17% conversion efficiency and load voltage of 3.3 V (cell specific mass of 23.4 g/W e). These performance parameters were for TiN BASE electrodes characterized by B=75 A K 1/2/m 2 Pa and G=50, assuming a BASE/electrode contact resistance of 0.06 Ω cm 2 and a BASE braze structure leakage resistance of 3 Ω. Also, the inner surfaces of the thermal radiation shield and the cell wall above the BASE tubes were covered with low emissivity rhodium. The temperatures of the BASE brazes and the evaporator were below the recommended design limits (1123 and 1023 K, respectively), and the temperature margin was ⩾+20 K to avoid sodium condensation inside the BASE tube, shorting the cell. When high performance electrodes, characterized by B=120 A K 1/2/m 2 Pa and G=10, were used, the cell's electric power increased to 8.38 W e at 3.5 V, and the efficiency increased to 18.8%, decreasing the specific mass of the cell to 19.7 g/W e without exceeding any of the design temperature limits.