Liquid Metal Anode Research Articles

Discharge between the jet and dropping liquid cathode and metal anode

Low-temperature gas-discharge plasma is investigated that is generated within the electrode space between the jet and dropping liquid cathode and metal anode at ambient pressure. The results of plasma composition, electrophysical parameters, electron concentration are presented, the discharge types are specified.

Thermal Rayleigh-Marangoni convection in a three-layer liquid-metal-battery model.

The combined effects of buoyancy-driven Rayleigh-Bénard convection (RC) and surface tension-driven Marangoni convection (MC) are studied in a triple-layer configuration which serves as a simplified model for a liquid metal battery (LMB). The three-layer model consists of a liquid metal alloy cathode, a molten salt separation layer, and a liquid metal anode at the top. Convection is triggered by the temperature gradient between the hot electrolyte and the colder electrodes, which is a consequence of the release of resistive heat during operation. We present a linear stability analysis of the state of pure thermal conduction in combination with three-dimensional direct numerical simulations of the nonlinear turbulent evolution on the basis of a pseudospectral method. Five different modes of convection are identified in the configuration, which are partly coupled to each other: RC in the upper electrode, RC with internal heating in the molten salt layer, and MC at both interfaces between molten salt and electrode as well as anticonvection in the middle layer and lower electrode. The linear stability analysis confirms that the additional Marangoni effect in the present setup increases the growth rates of the linearly unstable modes, i.e., Marangoni and Rayleigh-Bénard instability act together in the molten salt layer. The critical Grashof and Marangoni numbers decrease with increasing middle layer thickness. The calculated thresholds for the onset of convection are found for realistic current densities of laboratory-sized LMBs. The global turbulent heat transfer follows scaling predictions for internally heated RC. The global turbulent momentum transfer is comparable with turbulent convection in the classical Rayleigh-Bénard case. In summary, our studies show that incorporating Marangoni effects generates smaller flow structures, alters the velocity magnitudes, and enhances the turbulent heat transfer across the triple-layer configuration.

Transient modeling of spent nuclear fuel electrorefining with liquid metal electrode

During the molten salt electrorefining of spent nuclear fuel, multiple phases such as oxide, solid metal, liquid metal, and molten salt often co-exist. Computational modeling can be a useful tool for understanding the reaction mechanism across the multiple phases. The new model has been developed and applied to a lab-scale electrorefining with liquid metal anode and solid cathode LiCl-KCl molten salt. The benchmark study predicts anodic dissolution and cathodic deposition of U and Pu with minor disagreements. In particular, the on-set of Pu deposition on the surface of the solid cathode is well estimated, which is important for the quality of U ingot and the safeguards of process. The underestimation of U deposition (∼6%) and the overestimation of Pu dissolution (∼7%) at the end of simulation are explained by unconsidered reaction species such as Np and Am from the liquid Cd anode, which overestimates the dissolution of Pu from the anode compared to the measured data. The sensitivity study also reveals the transition behaviors of electrochemical reactions for U and Pu on the solid cathode are changed by diffusion boundary layer thickness, transfer coefficients, and the difference of electrochemical potentials more sensitively than those of the liquid metal anode. For this specific experiment case, the thinner diffusion boundary layer improves the prediction of cathodic reactions particularly at the end of electrorefining.

Mechanistic Studies of Liquid Metal Anode SOFCs II: Development of a Coulometric Titration Technique to Aid Reactor Design

Improved understanding of the operation of liquid metal anode solid oxide fuel cells (LMA-SOFCs) is required to progress this promising energy conversion technology. In order to facilitate analysis and interpretation, initial studies have been carried out with a simple system in which hydrogen is used as the fuel and the liquid metal electrode is operated in a potential region where it effectively behaves as an ‘inert’ solvent for dissolved gases. A model for the processes taking place in a liquid tin anode (LTA) supplied with hydrogen has previously been reported which identified a key parameter, the Dynamic Oxygen Utilisation Coefficient, z̅, important for understanding the operation and design of these systems. This parameter serves a similar role to the Damköhler number, widely applied in chemical reaction engineering to relate the chemical reaction rate to the transport phenomena rate. This paper describes the development of a method, named Anodic Injection Coulometry (AIC), to determine z̅, together with an example of its application.

Mechanistic Considerations of Liquid Metal Anode SOFCs Fueled with Hydrogen

Much interest is currently being devoted to solid oxide fuel cells (SOFCs) with liquid metal anodes.1–3 Technological developments of SOFCs operating with various molten anodes have been reviewed recently.4 Novel approaches to understanding this molten electrode system include the development of the Rotating Electrolyte Disc (RED)5. This technique offers the prospect of allowing the determination of parameters controlling mass transport of dissolved species in the melt. Development of the RED technique and of molten anode SOFCs requires careful probing of the fundamentals of operation. As such, a stepping stone to operation on direct solid fuel is the use of a simpler system such as the anodic oxidation of hydrogen at a liquid tin anode / YSZ interface. This paper discusses the dissolution of hydrogen and its electrochemical oxidation at a liquid tin anode / YSZ interface. The approach is also suitable for use with other gaseous reactants (e.g. CO). An electrochemical model is developed, used for analysis and validated against experimental data. An important factor, w ’ , is proposed, which is a measure of the balance between the rate of dissolution of hydrogen in liquid tin and its rate of removal via anodic oxidation to water, which is of technological significance when designing such reactors. To avoid any complexity associated with formation of metal oxide, including blockage of the electrolyte (a typical adverse effect) during operation of liquid tin anode SOFCs6, the cell was operated in a narrow potential window in which tin electrode was effectively “inert” and could not interfere in any electrochemical reactions (Figure 1). The lower limit of operating potential was set by the Sn-SnO2 couple and the upper limit by generation of electronic carriers in YSZ. Hydrogen with partial pressures ranging from 8 to 26 kPa was supplied to the liquid tin anode and anodically oxidised at the liquid tin / YSZ interface on the inner surface of a 8YSZ tube by application of a potential of -0.90 V vs. air electrode (RE) at 780 °C. Platinum counter and reference electrodes were coated on the outer side of YSZ tube. Electrical connection to the working electrode was achieved using a glassy carbon rod immersed within the liquid tin inside the YSZ tube. The anodic current was monitored with time while p(H2) was increased step-wise from zero to 8, 15 and 26 kPa (Figure 2a) and reduced back from 26 kPa to zero (Figure 2b). The observed direct proportionality between steady currents and p(H2) was evident (for the range of flow rates studied) and served as an indicative effect that was considered in the modelling. Experimental investigations were first performed to assess the effect of hydrogen partial pressure in terms of current generation and dynamics associated with changes in hydrogen concentration in the melt. These results were then used in support of an analytical modelling analysis. Determination of the w ’ parameter, as well as solubility limits of hydrogen in liquid tin during the operation, are also considered.

Mechanistic Considerations of Liquid Metal Anode SOFCs Fueled with Hydrogen

Liquid metal anode (LMA) solid oxide fuel cells (SOFCs) are a promising type of high temperature fuel cell suitable for the direct oxidation of gaseous or solid fuels in the bulk of liquid metal. Depending upon the operating conditions, they can be run in four different modes. In the present study, concerning the mechanism of reaction and species transport in LMA SOFCs, the oxidation of fuel (H2) in the bulk of a liquid tin anode has been investigated via operation in so-called Chemical - Electrochemical mode (CE mode) and Electrochemical - Chemical (EC) modes. Theoretical considerations to be applied in the modelling of the obtained experimental data regarding the dissolution of hydrogen in a molten tin anode and its oxidation with oxygen dissolved in liquid tin followed by anodic oxygen injection in mode CE are also discussed.

Influence of the electrolyte composition on the current distribution in an electrolytic cell with liquid-metal electrodes

The article discusses the influence of the molten electrolyte composition on the direct current distribution in a cylindrical electrolytic cell over the surface of a liquid-metal anode and in the volume of a KCl-PbCl2 electrolyte. Electric field plotting is applied. The distributions of the bulk current density are graphically illustrated, and the electrical conductivities of the melts are estimated.

Mechanistic Studies of Liquid Metal Anode SOFCs: I. Oxidation of Hydrogen in Chemical - Electrochemical Mode

Liquid metal anode (LMA) solid oxide fuel cells (SOFCs) are a promising type of high temperature fuel cell suitable for the direct oxidation of gaseous or solid fuel. Depending upon the operating conditions they can be run in four different modes. In this first of a series of studies concerning the mechanism of reaction and species transport in LMA SOFCs, the oxidation of hydrogen fuel in a liquid tin anode has been investigated. An electrochemical model is developed based upon fast dissolution of hydrogen in a molten tin anode, slow, rate-determining homogeneous reaction of hydrogen with oxygen dissolved in the liquid tin, followed by anodic oxygen injection under diffusion control to replace the oxygen removed by reaction (so-called Chemical - Electrochemical mode or CE mode). Experimentally-generated data are used to validate the model. The model has introduced a new key parameter, , which takes a value between zero and unity; its value is determined by geometric and convective factors in the cell as well as the partial pressure of the supplied hydrogen fuel. Current output of the cell is proportional to the value of .

A Rotating Electrolyte Disc (RED) for Operation in Liquid Metal Anode SOFCs

not Available.

A Rotating Electrolyte Disc (RED) for Operation in Liquid Metal Anode SOFCs

A novel Rotating Electrolyte Disc (RED) apparatus has been developed to determine parameters controlling mass transport of dissolved oxygen (and other gases) and oxidised species including metal oxide in liquid metal anode SOFCs. The validity of the concept and design for high temperature studies was first demonstrated by testing the setup in an aqueous system at ambient temperature (equimolar solution of ferrous and ferric chloride in KCl as supporting electrolyte). The diffusion coefficients have been determined for Fe2+ and Fe3+ by measuring the limiting oxidation and reduction diffusion-controlled currents. The obtained data have been compared with appropriate literature data. Preliminary testing of RED in molten tin electrodes is discussed.

A review of liquid metal anode solid oxide fuel cells

A review of liquid metal anode solid oxide fuel cells

Simulation of the electric field in an electrolytic cell with a liquid metal anode

The influence of the temperature and the level of liquid metal electrodes on the direct current distribution over the surface of the liquid metal anode and the electrolyte KCl-PbCl2 volume in a cylindrical electrolytic cell is studied by simulating the electric field.

Production of Silicon by Solid Oxide Membrane-Based Electrolysis Process

ABSTRACTThe solid oxide membrane (SOM) electrolysis process has been successfully tested on a laboratory scale to produce silicon directly from silica in a cost-effective and eco-friendly way. A one-end-closed yttria-stabilized zirconia (YSZ) tube was employed to separate a molten salt containing dissolved silica from a liquid metal anode placed inside the YSZ tube. When an applied electric potential between a liquid tin cathode in the molten salt and the anode exceeds the dissociation potential of silica, oxygen ions are transported out of the molten salt through the YSZ membrane and oxidized at the anode while the silicon cations in the flux are reduced to silicon on the surface of the liquid tin cathode. A potentiodynamic scan (PDS) was performed to determine the dissociation potential of silica in the molten salt system. Electrolysis was performed at 1.05 V for 8 hours. The presence of high-purity silicon crystals on the surface of liquid tin cathode was confirmed by scanning electron microscopy (SEM) and electron dispersive X-ray spectroscopy (EDS).

A review of liquid metal anode solid oxide fuel cells

This review discusses recent advances in a solid oxide fuel cell (SOFC) variant that uses liquid metal electrodes (anodes) with the advantage of greater fuel tolerance and the ability to operate on solid fuel. Key features of the approach are discussed along with the technological and research challenges that need to be overcome for scale-up and commercialisation.

Electrochemical Characterization of Liquid Metal Anode Solid Oxide Fuel Cell

A liquid tin anode solid oxide fuel cell is operated at 900 °C with a variety of fuel feeds, including argon, hydrogen, coal and a coal-water slurry. Characterization of anode performance is carried out by open circuit potential monitoring, linear potential sweeps, and electrochemical impedance spectroscopy combined with equivalent circuit modeling. A cathode symmetric cell is analyzed and modeled to isolate impedance contributions resulting from ionic resistance, cathode mass transport, and cathode charge transfer; results are used to isolate anode mass transport and charge transfer impedances in the fuel cell. Open circuit potential measurements under hydrogen fuel indicate that the dominant anode reaction is electrochemical oxidation of H2, while oxidation of Sn to SnO2 becomes the principal anodic process when the cell is fed with argon, coal, or coal-water slurry. Some chemical reduction of SnO2 to Sn by chemical reaction with coal is indicated by the cell potential.

Electrochemical Characterization of Liquid Metal Anode Solid Oxide Fuel Cell

not Available.

Basic properties of a liquid tin anode solid oxide fuel cell

An unconventional high temperature fuel cell system, the liquid tin anode solid oxide fuel cell (LTA-SOFC), is discussed. A thermodynamic analysis of a solid oxide fuel cell with a liquid metal anode is developed. Pertinent thermochemical and thermophysical properties of liquid tin in particular are detailed. An experimental setup for analysis of LTA-SOFC anode kinetics is described, and data for a planar cell under hydrogen indicated an effective oxygen diffusion coefficient of 5.3×10−5cm2s−1 at 800°C and 8.9×10−5cm2s−1 at 900°C. This value is similar to previously reported literature values for liquid tin. The oxygen conductivity through the tin, calculated from measured diffusion coefficients and theoretical oxygen solubility limits, is found to be on the same order of that of yttria-stabilized zirconia (YSZ), a traditional SOFC electrolyte material. As such, the ohmic loss due to oxygen transport through the tin layer must be considered in practical system cell design since the tin layer will usually be at least as thick as the electrolyte.

A solid oxide membrane electrolyzer for production of hydrogen and syn-gas from steam and hydrocarbon waste in a single step

This paper describes a novel solid oxide membrane (SOM) electrolyzer that can utilize the energy value in any hydrocarbon waste or reductant to lower the energy requirement for hydrogen production from steam. The SOM electrolyzer consists of a one-end closed oxygen-ion-conducting yttria stabilized zirconia (YSZ) tube with Ni–YSZ cathode coated on the outside and liquid metal anode inside the tube. The SOM electrolyzer is operated by feeding steam on the cathodic side and hydrocarbon reductant in the liquid metal anode. By feeding hydrocarbon waste it is possible to lower the chemical potential of oxygen in the liquid metal such that the SOM electrolyzer can spontaneously dissociate steam and generate hydrogen on the cathodic side and oxidize the hydrocarbon waste on the anodic side to produce syn-gas. The rate of these reactions can be increased by applying a small potential across the electrodes.

Solid Oxide Membrane Electrolyzer Utilizing the Energy Value in Solid and Gaseous Reductant for Hydrogen Production

This paper describes a novel Solid Oxide Membrane (SOM) electrolyzer that can utilize the energy value in any carbon and hydrocarbon reductant to lower the energy requirement for hydrogen production from steam. The Solid Oxide Membrane (SOM) electrolyzer consists of a one-end closed oxygen-ion conducting yttria stabilized zirconia (YSZ) tube with Ni-YSZ cathode coated on the outside and liquid metal anode inside the tube. In the SOM electrolyzer steam is reduced at the cathode and the oxygen produced on the anodic side reacts with the reductant supplied in the liquid metal anode. In the present study the SOM electrolyzer is evaluated using solid carbon and humidified hydrogen as reductant.

Electrochemical Characterization of a Solid Oxide Membrane Electrolyzer for Production of High-Purity Hydrogen

A laboratory-scale solid oxide membrane (SOM) steam electrolyzer that can potentially use energy value in waste or any source of carbon or hydrocarbon to produce high-purity hydrogen has been fabricated and evaluated. The SOM electrolyzer comprises an oxygen-ion-conducting yttria-stabilized zirconia (YSZ) electrolyte with a Ni-YSZ cermet cathode coated on one side and liquid-metal anode on the other side. The SOM electrolyzer is operated at 1000 °C by providing a steam-rich gas feed to the Ni-YSZ cermet cathode and feeding a reductant source into the liquid-metal anode. The steam is reduced over the cathode, and oxygen ions are transported through the YSZ electrolyte and are oxidized at the molten metal electrode by the reductant feed. The advantage of SOM electrolyzer over the state-of-the-art solid oxide electrolyzer is its ability to use solid, liquid, and gaseous reductant feed in the liquid-metal anode to reduce the oxygen chemical potential and drive the reaction for hydrogen production. In this study, an electrochemical process model for a SOM electrolyzer was developed. The condition of the liquid-metal anode with reductant was simulated by bubbling humidified hydrogen (3 pct H2O) in the liquid metal, and the electrochemical performance of the SOM electrolyzer was modeled. The experimental data were curve-fitted into the model to identify the various polarization losses. It showed that the performance of the SOM electrolyzer was dominated by the ohmic resistance of the YSZ membrane. Based on the results of this study, future work is needed toward increasing the performance efficiency of the SOM electrolyzer.