High-temperature Electrochemical Cells Research Articles

Revisiting the ionic conductivity of solid oxide electrolytes: A technical review

Oxygen-ionic and proton-conducting oxides are an important class of functional materials for their applications as electrolytes in various high-temperature electrochemical cells, including solid oxide fuel cells (SOFCs), solid oxide electrolysis...

A Deeper Insight into Stability of Pt-Alloy Nanoparticles as Oxygen Reduction Reaction Electrocatalysts

One of the links in the chain of creating a carbon-neutral society is undoubtedly hydrogen-powered vehicles. However, due to a very high price of platinum (Pt), which is used as an electrocatalyst for the hydrogen oxidation reaction (HOR) at the anode, as well as the oxygen reduction reaction (ORR) at the cathode of the proton exchange membrane fuel cell (PEMFC), their massive production is still unfeasible. Moreover, a very slow kinetics of the ORR and consequently the need for larger quantities of electrocatalyst makes this issue even higher. Therefore, in the fuel cell community there is a lot of effort to reduce the use of Pt. The most promising solution on that path seems to be carbon supported Pt-based nanoalloys, where part of Pt is replaced by a less noble and at the same time less expensive metal (e.g. Co, Cu, Fe, Ni).1 Nevertheless, although the ORR activity of carbon supported Pt-based alloys has been extensively studied and already proven, their stability is still an unsolved area. Here will be presented the latest findings regarding the stability of the carbon supported intermetallic Pt-alloy nanoparticles (Pt-M/C, where M = Co, Cu or Ni) obtained by utilization of advanced, in-house designed methodologies such as the high-temperature accelerated degradation tests (HT-ADTs) and the high-temperature electrochemical flow cell coupled to an inductively coupled plasma mass spectrometry (HT-EFC-ICP-MS).2,3 Whereas the former enables ADT to be performed in a liquid electrolyte half-cell using a standard rotating disk electrode at temperatures of up to 80 °C, the latter allows for precise (ppb range) time-temperature-and-potential resolved measurements of dissolution of metals. By simulating close-to-real operational conditions, these technologies enabled to show that in addition to the carbon corrosion, which follows the Arrhenius law and increases exponentially with temperature,3,4 also Pt dissolution, as well as less noble metal dissolution, increases with increasing temperature.2,3 However, with an increase in temperature, not only the dissolution of Pt, but also the rate of its re-deposition (due to the Ostwald ripening) is increased at the same time.2,3,5 Furthermore, the widening of the potential window results in an exponential growth of temperature impact on metals dissolution.2,3 These previous findings about the dependence of the stability of Pt and less noble metal on the temperature and potential window2 will be upgraded with new information about the impact of some other non-intrinsic as well as intrinsic properties on the stability of metal nanoparticles in the carbon supported Pt-nanoalloys. In other words, the effect of a different number of cycles of the degradation tests on the behavior of Pt and less noble metal in the operational potential window (i.e. 0.6-0.95 V) at the high temperature (60 °C) will be presented. In continuation, the influence of the type of crystal structure on the stability of Pt-alloy nanoparticles will also be discussed. References 1 L. J. Moriau, A. Hrnjić, A. Pavlišič, A. R. Kamšek, U. Petek, F. Ruiz-Zepeda, M. Šala, L. Pavko, V. S. Šelih, M. Bele, P. Jovanovič, M. Gatalo, N. Hodnik, iScience 2021, 102102.2 T. Đukić, L. J. Moriau, L. Pavko, M. Kostelec, M. Prokop, F. Ruiz-Zepeda, M. Šala, G. Dražić, M. Gatalo, N. Hodnik, ACS Catal. 2022, 12, 101–115.3 T. Đukić, L. Pavko, P. Jovanovič, N. Maselj, M. Gatalo, N. Hodnik, Chem. Commun. , DOI:10.1039/d2cc05377b.4 N. Maselj, M. Gatalo, F. Ruiz-Zepeda, A. Kregar, P. Jovanovič, N. Hodnik, M. Gaberšček, J. Electrochem. Soc. 2020, 167, 114506.5 A. Kregar, M. Gatalo, N. Maselj, N. Hodnik, T. Katrašnik, J. Power Sources 2021, 514, 230542.

Engineering lanthanum into Pt doped CeO2 for Intermediate temperature solid oxide fuel cells

Platinum doped oxides with extremely low utilization of noble metal and excellent catalytic activity have gained attention in high-temperature electrochemical cells. However, platinum ions tend to be reduced in reducing atmospheres, resulting in the catalyst deactivation. In this work, lanthanum is introduced into Pt-CeO2, which aims to deal with the above problem and provides an approach to promote Pt-CeO2 based catalysts for intermediate temperature solid oxide fuel cells. In specific, lanthanum doped Pt-CeO2 catalysts are prepared and infiltrated into the anode. The results show the highest peak power density with 10 mol% lanthanum doped Pt-CeO2 among all samples. In-situ ambient pressure X-ray photoemission spectroscopy investigation reveals that the reducibility of CeO2 can be tailored by lanthanum dopants, which leads to exceptional stability of active Pt2+ in reducing atmospheres. Our results foster the development of more stable and inexpensive Pt-CeO2 for intermediate temperature solid oxide fuel cells.

Na6Li4MO4(CO3)4 (M = W and Mo): An Alternative Electrolyte for High-Temperature Electrochemical Cells.

Two new acentric oxycarbonates Na6Li4MO4(CO3)4 (M = W and Mo) were synthesized via a conventional solid-state route. Their structure was determined from X-ray diffraction data on single crystals. Na6Li4MO4(CO3)4 (M = W and Mo) crystallizes in the acentric cubic P-43m space group (a ≈ 7.15 Å). It is composed of MLi4O16 units built from MO4 and LiO4 tetrahedra and linked by CO32- groups to form a three-dimensional framework in which Na+ ions are inserted. We showed from differential scanning calorimetry and powder X-ray diffraction experiments that the melting is congruent (T ∼525 °C). In the solid and molten forms, conductivity was measured for both oxycarbonates by electrochemical impedance spectroscopy with three various gas compositions (CO2 100 vol %, CO2-air 70-30 vol %, and CO2-air 20-80 vol %). Each time, the stability of the electrical behavior was checked via heating and cooling cycles. The conductivity of both solid and molten phases is purely ionic and in the same order of magnitude as for the classical molten alkali electrolyte made of Li-Na or Li-K carbonates. As activation energies are also comparable, those new oxycarbonates appear to be promising electrolytes for electrochemical devices.

Electrochemical Cells for Novel Routes to Ammonia

Ammonia is an extremely important chemical compound. Annual production exceeds 180 million tons of which ~80% is used for fertilizer production. The conventional production route is CO2 intensive and almost 2% of global anthropogenic CO2 emissions stems from ammonia synthesis. This will have to change over the coming decades to ensure the politically targeted emission reductions.The synthesis gas a mixture of N2 and H2 will have to be produced in a green and sustainable manner eventually only relying on green power and sustainable synthesis routes as discussed in [1]. High temperature electrochemical cells can play a role in this, not only for providing a green stream of hydrogen, but also in realizing the required N2 as discussed in [2]. Here, a special mode of operating an SOEC was proposed including feeding some air together with the steam to the SOEC cathode to produce directly a N2/H2 mixture suitable for down-stream ammonia synthesis. This can be done with excellent efficiency [2].Here, we shall present a different and in several aspects advantageous route for providing N2 for green ammonia synthesis. It is suggested to produce the N2 by electrochemical pumping the oxygen out of an air stream. The overall energy efficiency of the concept will be discussed in detail. However, the motivation to pursue this route relies on that it would be applicable on “small” scale. Considering the scale of renewable electricity sources it would be advantageous if also ammonia synthesis could be scaled down to match the small scale and distributed nature of renewable electricity generation. Here, a technology that scales just like the electrochemical routes to be applied for the Hydrogen production would be advantageous. Whereas cryogenic distillation is an energy efficient route to provide N2 it is a technology, that would not scale down well.A solid oxide cell for electrochemical production of N2 by oxygen extraction from air was developed. 5*5 cm pieces were prepared and characterized both with respect to electrochemical performance and long term durability as tracked over 2000 hr. The cells are based on a ~10 micron CGO (Ce0.9Gd0.1O2) electrolyte sandwiched between composite supports (electrodes) made in either LSCF/CGO, or LSF/CGO. (LSCF=La0.6Sr0.4Co0.2Fe0.8O3- δ , LSF= La0.6Sr0.4FeO3- δ). To boost performance at low temperature the electrodes were infiltrated with Pr-oxide [3]. The performance with the different supports is compared at a range of temperatures and current densities with and without infiltration. Both materials were found to perform well and enable current densities ~0.8 A/cm2 at ~ 150 mV polarization, when tested at 700 oC. A 90% pure N2 stream can be produced with at a cell voltage below 150mV at temperatures from 700-800 ºC. As illustrated in Fig. 1, a purer N2 stream with 96% N2 could be produced at a cell voltage below 200 mV. Also a 98% pure N2 stream was demonstrated. Moreover, the cells were demonstrated to operate without degradation over a 2000 hr. period.The results are quite promising in terms of the excellent durability demonstrated and in terms of absolute energy consumption. For comparison with literature, the energy consumption is related to the removed oxygen rather than the produced N2. At 150 mV the energy consumption is ca. 0.7 kWh/m3 of oxygen extracted. This compares well with performance reported by Wang et al. [4] describing a similar concept. The energy consumption is ca. twice what it takes to produce the oxygen via cryogenic distillation. Here, it should be noted, however, that all the produced heat (0.7 kWh/m3) can be directly utilized in synthesizing the H2 needed for the ammonia due to the endothermic nature of steam splitting. Hence, the energy invested in producing the N2 is not really wasted in this case, as also discussed in [2].The results of detailed electrochemical testing will be presented and the factors limiting cell performance will be discussed. Finally, an analysis of what dictates the optimal point of operation in terms of energy consumption and component volume and reliability is presented. Acknowledgment The work was supported by the EU commission via project; ARENHA, H2020 GRANT AGREEMENT: 862482. References Campion, N., Nami, H., Swisher, P. R., Hendriksen, P. V., & Münster, M. (2023). Renewable and Sustainable Energy Reviews, 173, 113057. 2022.John Bøgild Hansen and Peter Vang Hendriksen 2019 ECS Trans. 91 2455.Hendriksen, P. V., Khoshkalam, M., Tong, X., Tripkovic, D., Faghihi-Sani, M. A., & Chen, M. 2019 ECS Transactions, 91, 1413-1424.Mei Wang, Kamil Maciej Nowicki, and John Thomas Sirr Irvine, Journal of The Electrochemical Society, 2022, 169, 064509 Figure 1

Theoretical analysis of mixed open-circuit potential for high temperature electrochemical cells electrodes

The Nernst equilibrium potential calculates the theoretical OCV, which estimates the best performance achievable by an electrochemical cell. When multiple semi-reactions (or multiple ionic species) are active in one of the electrodes, the calculation of the theoretical OCV is not straightforward, since different Nernst potentials are associated to each semi-reaction. In this paper, analytical equations for calculation of the theoretical OCV are developed, using the mixed potential theory. The case of H2 and CO co-oxidation (or H2O and CO2 co-reduction) in solid oxide cells is used as a reference case, but similar conclusions can be drawn for other equivalent cases. OCV data from literature are used to calibrate and validate the model. The relative reaction rate of H2 and CO semi-reactions is estimated within the calibration process, and the result is in line with assumptions and suggestions given by other authors. The validation procedure shows predicted OCV values in line with experimental literature data, except for mixtures with relatively large CH4 concentration (e.g., 8%), for which the OCV is significantly underestimated. This is expected when thermochemical reactions, in parallel to electrochemical reactions occur, since the additional H2 produced by internal steam methane reforming is not accounted within the local mixed potential model. A fuel cell polarization model is developed based on the results from the calibration procedure, and it is used to predict the polarization behavior of an SOFC fed with a H2-H2O-CO-CO2 fuel mixture. It is found that either H2 or CO may be reduced rather than oxidized via an equivalent electrochemical water-gas-shift reaction.

(Invited) Opportunities for Bulk Silicon As a High Capacity Lithium Host

Silicon, the earth’s second most abundant element ushered in new age of computing capability. More recently, silicon is enjoying a second wave of technological adoption as a constituent of lithium-ion battery negative electrodes; made possible in practice by reducing the dimensions to the nanoscale and/or compositing with traditional carbon-based lithium host materials. The large lithium capacity and subsequent volumetric expansion and mechanical fracture have been documented extensively and the nano and composite routes mentioned above provide strategies to overcome this obstacle. We take a new exploratory approach elevating the working temperature to demonstrate reversible alloying and dealloying of lithium and silicon, in its most basic bulk form, a wafer. The brittle nature of silicon may be made more elastic when operated above its brittle-to-ductile transition temperature, potentially leading to more elastic behavior capable of maintaining its structure with modulation of its volume. Here was explore lithium alloying/dealloying into bulk silicon at elevated temperature to assess the efficiently and reversibility of silicon in this environment. While a contrived experiment, we are learning more about lithium diffusion into silicon and may provide a thermal preconditioning of silicon electrode materials to support long cycle for lithium-ion batteries. Additionally, the developmental improvements of a high temperature electrochemical cell will be conveyed along with demonstration of an electrolyte salt, LiTFI, in the molten form. Last, micro computed tomography 3D images will be presented to show crack formation and progression when alloying a bulk silicon wafer with lithium at elevated temperatures.

The CO Tolerance of Pt/C and Pt-Ru/C Electrocatalysts in a High-Temperature Electrochemical Cell Used for Hydrogen Separation.

This paper describes an experimental evaluation and comparison of Pt/C and Pt-Ru/C electrocatalysts for high-temperature (100–160 °C) electrochemical hydrogen separators, for the purpose of mitigating CO poisoning. The performances of both Pt/C and Pt-Ru/C (Pt:Ru atomic ratio 1:1) were investigated and compared under pure hydrogen and a H2/CO gas mixture at various temperatures. The electrochemically active surface area (ECSA), determined from cyclic voltammetry, was used as the basis for a method to evaluate the performances of the two catalysts. Both CO stripping and the underpotential deposition of hydrogen were used to evaluate the electrochemical surface area. When the H2/CO gas mixture was used, there was a complex overlap of mechanisms, and therefore CO peak could not be used to evaluate the ECSA. Hence, the hydrogen peaks that resulted after the CO was removed from the Pt surface were used to evaluate the active surface area instead of the CO peaks. Results revealed that Pt-Ru/C was more tolerant to CO, since the overlapping reaction mechanism between H2 and CO was suppressed when Ru was introduced to the catalyst. SEM images of the catalysts before and after heat treatment indicated that particle agglomeration occurs upon exposure to high temperatures (>100 °C)

An Operando calorimeter for high temperature electrochemical cells

Operando calorimetry has previously been utilized to study electrochemical reactions and degradation in electrochemical cells such as batteries. Calorimetric data can provide important information on the lifetime and thermal properties of electrochemical cells in practical engineering applications such as thermal management. High temperature electrochemical cells such as solid oxide fuel cells or electrolyzers can also benefit from operando calorimetry, but to the authors’ knowledge such capabilities have not been commercially developed. Herein, an operando calorimeter is reported that is capable of simultaneous calorimetry and electrochemistry at temperatures up to 1000 °C and in both oxidizing and reducing atmospheres. The calorimeter is constructed by modifying a commercial apparatus originally designed to study high temperature electrochemical cells in various gas environments. A grey-box, nonlinear system identification model is utilized to analyze both electrochemical and calorimetric data of BaZr0.8Ce0.1Y0.1O3 based electrochemical cells and achieve a calorimeter electrochemical cell power sensitivity of 16.1 ± 11.7 mW. This operando calorimeter provides the capability to study thermal behaviour of electrochemical cells at elevated temperatures.

Deposition and Electrical and Structural Properties of La0.6Sr0.4CoO3 Thin Films for Application in High-Temperature Electrochemical Cells

Low-temperature deposition of electroceramic thin films allows the construction of new devices and their integration with existing large-scale fabrication methods. Developing a suitable low-cost deposition method is important to further advance the development of microdevices. In this work, we deposited a 1-μm-thick La0.6Sr0.4CoO3−δ (LSC) perovskite with high electrical conductivity on sapphire substrates at 400°C and analyzed its electrical, morphological and structural properties as a function of temperature in the range of 400–1100°C. The results show that spray pyrolysis can be used to deposit high-quality reproducible layers with the desired chemical and phase composition. Upon heating to around 600°C, the residual C–O and C=O species are removed, and the deposited layers crystallize and become conducting. The dependence of electrical conductivity versus processing temperature has a complex character—the maximum conductivity is found for layers processed at 800°C. An analytical model of stress distribution was used to predict stress to which the bi-layer material would be exposed to while being cooled down from the annealing temperature to room temperature. The high electronic conductivity and high-quality microstructure of the LSC layers, which can be adjusted with the appropriate heat treatment procedure, make them suitable for applications in electrochemical devices applied in integrated energy modules, including electrodes or contacts.

A Bismuth Attack at Grain-Boundaries of Ceria-Based Electrolytes

Bismuth is a common additive of commercial silver pastes for enhancing metallization effect; silver paste is also commonly used in high-temperature electrochemical cells as a current collector or contact layer. We here report that the minor amount of bismuth in commercial silver pastes can transport to the interface of electrode/Gd-doped CeO2 (GDC) electrolyte and seriously corrode grain-boundaries (GBs) of the GDC electrolyte, a commonly used intermediate-temperature electrolyte, causing significant ionic conductivity degradation. A comprehensive electron microscopic analysis reveals that the Bi-corrosion takes place along GBs of GDC electrolyte acting as “washing flux” agent, causing grain separation and thus blocking ionic conduction. It is also found that electrical field enhances the “Bi-washing” effect, leading to a faster degradation in full-cell than in half-cell. Overall, the use of commercial silver paste as a current collector for CeO2-based electrolytes in long-term testing should be cautioned.

(Invited) High-Temperature Electrosynthesis of Hydrogen and Chemicals

High-temperature electrochemical cells based on solid electrolytes have been considered for synthesis and production of hydrogen and a variety of other fuels and chemicals. Solid oxide electrolysis cells (SOECs) for example, are being developed for hydrogen production (from water), syngas production (from mixtures of water and carbon dioxide) and oxygen recovery (from water or carbon dioxide for space applications). The main attractive features of the SOEC are its simple chemistry, environmental compatibility and high electrical-to-hydrogen efficiency. Solid oxide fuel cell (SOFC type cells have been investigated for production of chemicals and cogeneration of electricity and chemicals (in this case, the cell is referred to as CSOFC); examples include production of C2 hydrocarbons and syngas from methane. The key features of the CSOFC include its high selectivity and the possibility to produce valuable chemicals such as hydrocarbons using methane-rich gases from non-fossil origins. Current state-of-the-art SOECs and CSOFCs, both fundamentally derived from the more advanced conventional SOFC technology are still in their feasibility/development stage. This paper discusses certain aspects in selected materials, performance and operation of the SOEC for hydrogen production from water and the CSOFC for production of C2 hydrocarbons from methane.

Modified coin cells to evaluate the electrochemical properties of solid-state fluoride-ion batteries at 150 °C

In the scope of developing new chemistries for electrochemical energy systems, rechargeable solid-state fluoride-ion batteries are attractive devices owing to their high theoretical energy density. State of the art of fluoride ion conductors require the use of high temperature electrochemical cells to overcome the low ionic conductivity of the electrolyte at room temperature. In this work, we modify a coin cell to evaluate the electrochemical properties of fluoride-ion batteries at elevated temperature, over long periods of time and outside a glovebox. The coin cell is covered by a high-temperature epoxy resin that enables efficient sealing and therefore protection against air atmosphere at 150°C. The suitability of the setup is confirmed by electrochemical investigation performed on a symmetrical cell assembled with composite electrodes made of Bi and BiF3. Notably, a reversible capacity of around 190mAh/g after 3 cycles is reached with the modified coin cell setup.

Methods for Determining the Working Electrode Interfacial Area for Electroanalytical Measurements of Metal Ions in Molten LiCl-KCl

Voltammetry is a promising approach to determining the concentration of actinides and rare earths in molten chloride salts for real time or near real time monitoring of nuclear fuel electrorefining. In this process, actinides and rare earths accumulate in eutectic LiCl-KCl from reaction of UCl3 with spent nuclear fuel. Monitoring the salt composition is key in order to maintain optimal process conditions, to determine when to treat or discard salt, and to safeguard the process against nuclear material diversion. Voltammetry methods such as cyclic voltammetry (CV), chronopotentiometry (CP), chronoamperometry (CA), normal pulse voltammetry (NPV), and square wave voltammetry (SWV) have been extensively reported in the literature for application to molten LiCl-KCl typically containing one rare earth or actinide chloride. Our studies have expanded the salt matrices to include quaternary salts with two electrochemically active metal chlorides. We believe this to be the first step in determining if these basic electrochemical analysis methods can be applied to salts containing many components with similar standard reduction potentials. In the simpler ternary salt systems, classic diffusion limited rate equations such as those derived by Randles-Sevcik and Berzins-Delahay have been applied to correlate CV peak height to concentration. Application of these equations requires knowledge of both the diffusion coefficient of the salt compound in the LiCl-KCl and the interfacial area between the working electrode and salt. In our experimental investigations, we have determined that both of these quantities can be difficult to establish a priori. Diffusion coefficients for metal chlorides in molten LiCl-KCl appear to vary with concentration. And the high temperature electrochemical cells located in insulated furnaces make it challenging to precisely determine the electrode-salt interfacial area. In this paper, we focus on empirical evaluation of methods for determining this area—ranging from the simplest approach of dipping a cold electrode into the molten salt to measure the film height to more elaborate approaches such as using a vertical electrode actuator, coating the electrodes with glass, and integrating a pre-peak which may represent formation of a monolayer of metal on the electrode. Salt mixtures investigated include LiCl-KCl-UCl3, LiCl-KCl-UCl3-MgCl2, LiCl-KCl-ThCl4-LaCl3, LiCl-KCl-LaCl3-GdCl3, and LiCl-KCl-LaCl3-MgCl2. It will be shown that with accurate determination of the electrode-salt interfacial area that concentration correlations can be developed with error as low as 2-3%. Both using differential insertion depth with the vertical electrode translator and using glass-coated working electrodes are promising approaches—the latter of which is believed to be more easily implemented in a production operation scenario.

Electrochemical Measurement of Li2O in Molten LiCl Salt

Nuclear fuel reprocessing is an important technology designed to increase the sustainability of nuclear power generation, as well as minimize long-lived radioactive waste production. There are multiple reprocessing schemes, most notably PUREX and pyroprocessing. While PUREX and related aqueous separation processes technically have superior maturity due to large scale implementation in France, Japan, Great Britain, and Russia, pyroprocessing has attracted substantial interest in recent years largely based on the perception that it represents a much lower proliferation threat and is ideally suited for metallic fast reactor fuel recycle. The Republic of Korea in particular has invested a tremendous amount of research funding over the last decade to develop pyroprocessing for spent fuel from commercial pressurized water reactors. Pyroprocessing utilizes a high temperature electrochemical cell called an electrorefiner to separate actinides from fission products. To apply this technology to oxide fuel, as in the case of the Korean spent fuel, an oxide reduction step must precede electrorefining. The current leading technology for oxide reduction is a high temperature electrolytic process carried out in molten lithium chloride salt. Electrolytic reduction relies on a lithium cycle, which consists of oxidation of lithium metal to lithium oxide at the cathode and reduction of the lithium oxide back to lithium metal at the anode. The net result is that uranium oxide is reduced to uranium metal, and oxygen gas is evolved. Lithium oxide concentration in the molten salt electrolyte is an important process variable. If it decreases, it can be a sign of lithium oxide accumulation in the fuel basket and will result in increased anode potential that ultimately leads to anode degradation. Currently, the only proven way of measuring lithium oxide concentration in lithium chloride involves sampling followed by acid-base titration. Measuring lithium oxide concentration in real time is an important objective to maintain optimal process control. The technique being developed for this purpose involves measuring the change in the open circuit potential (OCP) between a molten pool of a lead-lithium alloy and a Ni/NiO reference electrode. Because OCP measures equilibrium potential, this method can be combined with the Nernst Equation to continuously measure lithium oxide concentration. Mixtures of lithium chloride and lithium oxide were prepared with lithium oxide concentrations ranging from 0.00 to 2.75 wt%. A lead-lithium pool containing 2.0 wt% lithium was placed below the molten salt pool. After the salt melted it was allowed an hour to equilibrate, then an OCP measurement was obtained. As expected, the OCP increased with increasing concentration of Li2O. The measured sensitivity was about 200 mV for a Li2O concentration change from 0 to 2.5 wt%. Achieving repeatable and stable reference electrode potential is key to making accurate measurements from this method. The reference electrodes were made of high-density MgO tubes with low density, porous MgO plugs. Nickel wire and NiO powder were inserted into these tubes. The reference potential varied significantly between different sets of reference electrodes, which is hypothesized to be due to variations in the thickness of the porous MgO plugs. Methods for standardizing the reference electrodes have been attempted, and the results will be discussed. Another factor that may effect this measurement is the solubility of lithium metal in the zero oxidation state in the molten LiCl. Lithium solubility measurements were made in LiCl-Li2O with varying concentrations of Li2O. The results varied from 0.7 to 1.5 mole%. This low level of solubility is expected to cause minimal loss of lithium from the lead-lithium sensor. And experiments with different volumes of salt over a fixed volume of lead-lithium confirmed that the measured OCP is relatively insensitive to any decrease in the lithium concentration in the lithium-lead pool.

(Invited) High-Temperature Electrosynthesis of Hydrogen and Chemicals

High-temperature electrochemical cells based on solid electrolytes have been considered for synthesis and production of hydrogen and a variety of other fuels and chemicals. Solid oxide electrolysis cells (SOECs), for example, are being developed for hydrogen production (from water), syngas production (from mixtures of water and carbon dioxide) and oxygen recovery (from water or carbon dioxide for space applications). The main attractive features of the SOEC are its simple chemistry, environmental compatibility and high electrical-to-hydrogen efficiency. Solid oxide fuel cell (SOFC) type cells have been investigated for production of chemicals and cogeneration of electricity and chemicals (in this case, the cell is referred to as CSOFC); examples include production of C2 hydrocarbons and syngas from methane. The key features of the CSOFC include its high selectivity and the possibility to produce valuable chemicals such as hydrocarbons using methane-rich gases from non-fossil origins. Current state-of-the-art SOECs and CSOFCs, both fundamentally derived from the more advanced conventional SOFC technology, are still in their feasibility/development stage. This paper discusses certain aspects in selected materials, performance and operation of the SOEC for hydrogen production from water and the CSOFC for production of C2 hydrocarbons from methane.

Experimental investigation of electrical and optical phenomena during combustion of two-layer energetic condensed (Zr + CuO + LiF)–(Zr + BaCrO4 + LiF) systems

Electrical and optical phenomena in the process of combustion of heterogeneous energetic condensed systems (ECSs) of the (Zr + CuO + LiF)–(Zr + BaCrO4 + LiF) type that represent the model of a high-temperature electrochemical cell (HEC) are experimentally investigated. It is found that combustion of the systems studied generates a pulsed electrical signal with a half-width duration of ~1.0 s. The maximum value of the signal amplitude reaches 1.2–1.5 V. The electrical signal occurs at the start of combustion and lasts until the end of the reaction. For the first time, the flame emission spectrum in the visible spectral range (λ ~ 300–700 nm) is recorded during combustion of the given systems. X-ray phase analysis is carried out for input components of the charge carrier source (anode) and the receiver of the charge carriers (cathode), the products of combustion of the electrodes, and the HEC model. An experimental facility for simultaneous recording of a number of physical properties of condensed energy systems during combustion is created. A technique of recording electrical signals and optical emission spectra in the course of combustion is developed.

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

High Temperature Electrochemical Hydrogen Pump Cell Using a PBI Membrane at High Current Densities

The ability of an electrochemical hydrogen pump cell employing a polybenzimidazole membrane imbibed with phosphoric acid to purify hydrogen rich streams has been investigated. It has been found that pure hydrogen can be produced from diluted hydrogen and from typical reformate feeds with less than 5 kW-hrs required per kilogram of hydrogen pumped. The performance of these cells does not degrade under pure hydrogen over 24 hours for current densities up to 0.4 A/cm2. However, in less than 10 hours, the polarization effects had increased by 10% under pure hydrogen at 1.0 A/cm2 and by 50% under reformate at 0.2 A/cm2. However, the performance degradation caused by the presence of CO was observed to be reversible by switching the cell polarization and flows.

Ab initio study of phase competition in (La1 − c,Src)CoO3 solid solutions

(La1−c,Src)CoO3 (LSC) solid solutions are promising materials for high temperature electrochemical cells and cathodes of solid oxide fuel cells. The Density Functional Theory (DFT) was applied to calculate the energies of the different superstructures in LSC which are stable with respect to formation of anti-phase domains. The energy parameters determining the relative stability of the cubic superstructures (phases) are extracted from these calculations. Using the Concentration Wave formalism and the energy parameters for different phases from DFT calculations, the temperature dependences of the long-range order parameters were obtained characterizing the order–disorder transformations.