Solid Electrolyte Cells Research Articles

Low Temperature Electrochemical Reduction of NO and O2 on Pt Electrode Using YSZ, GDC and Lsgm Electrolyte

The pollutant NO mainly from diesel/gasoline engine exhausts without purification into environment can give rise to the acid rain and photochemical smog[1] which causes great potential safety hazard to human health and global environment. Accompanied by NO, there exists excess O2 in exhausts. Electrochemical reduction of NO and O2 can save the huge reducing agents storage system with the low operation temperatures simultaneously[2-3]. The exhaust temperature is low that high O2- conductivity is needed to guarantee high conversions of NO and O2 in the low temperature range. In this study, we fucused on the electrochemical reduction of NO and O2 in solid oxide electrolyte cell(SOEC) on symmetric Pt electrode with the temperature varying from 250℃ to 500℃ using three different electrolytes including YSZ, Ce0.9Gd0.1O1.95(GDC) and La0.9Sr0.1Ga0.8Mg0.2O2.85(LSGM). The GDC and LSGM electrolyte were prepared by tape-casting method and characterized by SEM after electrochemical tests. The symmetric cells were characterized by electrochemical measurements including linear sweep voltammetry(IV) and electrochemical impedance spectroscopy(EIS) at open circuit voltage(OCV). The polarization range was set from 2V to 0V containing 800ppm NO and 8% O2. The experiment testing temperatures and the concentrations of the NO and O2 are choosen according to the exhausts of the diesel or gasoline engine. The GDC and LSGM electrolyte showed higher electrochemical performance than YSZ by polarization measurements especially at low temperature of 250℃ to 350℃. The EIS experiment results were fitted well with equivalent circuit model R(C(RW)) containing the serial resistance Rs, electron transfer resistance Rt, double layer capacitance C and Warburg component W. It can be observed that the activation energy of the Rs and Rt were close to each other and the activation energy of the Rs were 0.581eV, 0.702eV and 0.719eV in GDC, LSGM and YSZ electrolytes. The EIS results yielded typical semi-infinite diffusive character in three electrolytes. The activation energy of the electron transfer process for the YSZ, GDC, and LSGM electrolytes were 1.057eV, 0.933eV and 1.031eV in 800ppm NO with 8% O2. And the YSZ electrolyte displayed the maxmium activation energy of electron transfer resistance Rt indicating the larger resistance of the charge transfer process. The gases in the Pt/YSZ/Pt cell showed the lowest diffusion coefficients obtained from the Warburg component in low frequency in the electrode resulted from largest charge transfer resistance that blocked the diffusion of the gases. This studies demonstrated that GDC and LSGM can be promising electrolytes for low temperature electrochemical removal of NO and provided theoretical guidance for the design of practical NOx elecrochemical application device at low temperatures.

(Invited) Applications of Solid Electrolyte Membranes in Heterogeneous Catalysis. Electrochemical Reaction and Separation

In addition to their applications in sensors, separators and solid oxide fuel cells, solid electrolytes have been used in the construction of solid state cell-reactors, in which catalytic reactions were studied. Depending on the reaction system, there was a variety of goals in these studies: a) to take advantage of the selective conduction of ions, b) improve the yield to the desired product and c) cogenerate electricity and value-added chemicals. Two examples of applications of solid state cell-reactors in heterogeneous catalysis are presented here, a) the production of ethylene and hydrogen from methane with simultaneous separation of hydrogen from the reaction mixture and b) the electrochemical synthesis of NH3. The production of hydrogen with simultaneous conversion of methane to C2 hydrocarbons was studied in a solid state oxygen ion (O2-) conducting cell at temperatures between 700 oC and 850 oC. Methane, diluted in nitrogen was introduced over the anode (Ag) and steam, also diluted in nitrogen, was introduced over the cathode (Pt). When oxygen was electrochemically “pumped” from the cathode to the anode, steam was electrolyzed to produce gaseous H2 while CH4 was converted to C2H6, C2H4 and CO2. At the anode, C2yields exceeding 8% were obtained while an up to 65% conversion of steam was achieved at the cathode. The electrochemical synthesis of ammonia was studied in a proton conducting solid electrolyte cell. The BaZr0.7Ce0.2Y0.1O2.9 (BZCY72) proton conducting ceramic was used as the electrolyte with a Ni-BZCY72 cermet and a Pt film serving as cathodic and anodic electrodes, respectively. The reaction was studied at atmospheric pressure and at temperatures between 450 oC and 700 oC, under both, open- and closed-circuit conditions. A peculiar reaction rate enhancement was observed when the cell returned to open-circuit after operating under closed-circuit for a certain time. A possible explanation of this new phenomenon is that a fraction of protons electrochemically transported to the cathode, is "stored" in the Ni-BZCY72 electrode in the form of a highly reactive hydride which, upon current interruption, reacts with adsorbed N species to produce ammonia.

Pilot Study of Desorption Kinetics of Adsorbate from an Adsorbent Granule

The possibility of a change in the desorption kinetics of an adsorbate from an adsorbent granule is demonstrated with use of solid-electrolyte cells. A description of the experimental bench created for measurement of kinetic curves is given for adsorbate adsorption from an adsorbent granule. Results of test changes in the kinetic curves are presented for oxygen desorption from a granule of a carbon-molecular sieve (UMS-1).

Preparation of ultra-fine Sm0.2Ce0.8O1.9 powder by a novel solid state reaction and fabrication of dense Sm0.2Ce0.8O1.9 electrolyte film

A novel solid state reaction was adopted to prepare Sm0.2Ce0.8O1.9 (SDC) powder. A mixed oxalate Sm0.2Ce0.8(C2O4)1.5·2H2O was synthesized by milling a mixture of cerium acetate hydrate, samarium acetate hydrate, and oxalic acid for 5h at room temperature. An ultra-fine SDC powder with the primary particle size of 5.5nm was obtained at 300°C. The ultra-low temperature for the formation of SDC phase was due to the atomic level mixture of the Sm3+ and Ce4+ ions. The crystal sizes of SDC powders at 300°C, 550°C, 800°C, and 1050°C were 5.5nm, 11.4nm, 24.1nm and 37.5nm, respectively. The sintering curves showed that the powder calcined at lower temperature was easier to be sintered owning to its smaller particle size. A solid oxide electrolytic cell (SOEC), comprising porous La0.8Sr0.2Cu0.1Fe0.9O3−δ (LSCF) for substrate, LSCF–SDC for active electrode, SDC for electrolyte, and LSCF–SDC for symmetric electrode, was fabricated by dip-coating and co-sintering techniques. An extremely dense SDC film with the thickness of 20μm was obtained at only 1200°C, which was about 100–300°C lower than the literatures׳ reports. The designed SOEC was proved to work effectively for decomposing NO (3500ppm, balanced in N2), 80% NO can be decomposed at 600°C.

Ammonia synthesis at atmospheric pressure in a BaCe0.2Zr0.7Y0.1O2.9 solid electrolyte cell

The catalytic and electrocatalytic synthesis of ammonia from its elements was studied in a proton conducting single-chamber solid electrolyte cell. The BaCe0.2Zr0.7Y0.1O2.9 (BCZY27) proton conducting ceramic was used as the electrolyte. A Ni-BCZY27 cermet and a Rh film were the two electrodes. The reaction was studied at atmospheric pressure and at temperatures between 450°C and 650°C, under both, open- and closed-circuit conditions. The highest improvement (40%) in the open-circuit rate was attained at 550°C and for PH2/PN2=1.0. The corresponding purely electrocatalytic rate (difference between closed-circuit and open-circuit rate) was 2.9×10−9mol⋅s−1⋅cm−2. This value is among the highest reported for electrochemical ammonia synthesis.

Low emission hydrogen generation through carbon assisted electrolysis

The conventional electrolysis process for hydrogen generation offers many advantages such as on-site on-demand generation, pure hydrogen that can be stored for latter use directly in fuel cells, and potential of direct coupling to a renewable source of energy. However, the process is very energy intensive. Therefore, at present hydrogen is produced mainly by Natural Gas reforming and coal gasification at temperatures in the vicinity of 800 °C. This method of hydrogen production involves the steps of reforming/gasification, shift reaction and gas separation at high temperatures to improve hydrogen yield and purity based on its application. This paper investigates the thermodynamic and practical energy benefits of single step water electrolysis process assisted by carbon, where part of the energy can come from the chemical energy of carbon. The process has been demonstrated in a solid state electrolytic cell operating at near room temperature. The paper also discusses the technology status and challenges to achieve high hydrogen generation rates.

Electrochemical activation of Au nanoparticles for the selective partial oxidation of methanol

An electrochemical catalyst based on Au nanoparticles dispersed in an yttria-stabilized zirconia (YSZ) matrix was prepared by reactive cosputtering of zirconium–yttrium and Au targets on a K-βAl2O3 solid electrolyte. The Au/YSZ catalyst film deposited on K-βAl2O3 was found to be active in the partial oxidation of methanol with a high selectivity toward methyl formate. This configuration allowed to electrochemically promote a highly dispersed Au catalyst by K+ ions and allowed to decrease the amount of metal used in the solid electrolyte cell. The back-spillover of K+ ions sharply increased the H2 and HCOOCH3 production rates up to more than 9 and 5 times, respectively. A number of experiments confirmed that the observed electro-promotional effect did not depend on the rate of K+ supply nor on the operation mode (galvanostatic or potentiostatic) and only depended on the promoter coverage (total applied charge). The stability of the Au–YSZ catalyst film under the explored conditions was also verified.

Coupling catalysis and electrocatalysis for hydrogen production in a solid electrolyte membrane reactor

This study reports the production of H2 via catalytic methane decomposition on Pt supported on yttria-stabilized zirconia together with its electrochemical regeneration in a solid electrolyte membrane reactor. Hence, a Pt-YSZporous/YSZ/Pt double-chamber solid electrolyte cell was prepared and tested under two reaction regimes. In the first regime, under open-circuit conditions, hydrogen and carbon are produced on the catalytically active Pt-YSZ porous catalyst via methane decomposition reaction (CH4 (g) → C (s)+2H2 (g)). In the second regime, under polarization conditions, steam is electrolyzed at the Pt cathode of the cell (H2O+2e−→H2+O2−) and the produced O2− ions were simultaneously electrochemically pumped to the Pt/YSZ porous catalyst (anode), thereby allowing removal of the previously deposited carbon (C (s)+O2−→CO2 (g)) and finally regenerating the Pt/YSZ porous catalyst film. We demonstrated that the carbon generated in the methane decomposition step serves as a depolarizating agent in the steam electrolysis process, thus decreasing the electrical energy input required for electrochemically producing pure H2. In addition, during the regeneration step, C2 hydrocarbons (e.g., ethane and ethylene) were obtained as a result of the electrocatalytic methane oxidative coupling on the Pt/YSZ porous catalyst film. The performance and durability of the system was also verified for long operation times in view of the possible practical application of this novel reactor configuration, which combines gas-phase catalysis and electrocatalysis for hydrogen production.

Low Power Consumption CO2 Gas Sensor Using Ionic Liquid

Recently, various gas sensors are investigated. Specially, CO2 gas sensor is worthy of the notice, because monitoring of CO2 gas concentration is important for energy-saving. For example CO2 gas concentration is required for 1000 ppm or less in space, such as office buildings, a building management method, a production plant, and an IT-related server room. An exhaust gas periodically compulsory in order to make the present condition and CO2 gas concentration below into a steady value. By minimizing the displacement volume of the air which is carrying out air-conditioning management using CO2 sensor, an air-conditioning system carries out efficient operation, and it aims at development of CO2 sensor corresponding to the low consumption power high integration interlocked with a sensor network system efficiently. However the conventional CO2 gas sensors have the following problems, 1) large power consumption, 2) large size and 3) long detection time. These problems are mainly caused by usage of a light source and heater. We are interested in the ionic liquids because the ionic liquids are 1) the conductivity is high at room temperature, 2) thermal and chemical property is high stable, 3) volatility is high and 4) adsorb polarity molecule gases as like CO2, NH3, SO2, and NO2. Therefore we develop CO2 sensor which converted CO2 concentration into ionic liquid which adsorbed CO2 specifically by impedance. Our sensor feature is that it isn't used light source and heater, it is used ionic response. It compares with conventional CO2 sensor, 1) low consumption power, 2) miniaturization, 3) high-speed response and 4) low consumption CO2 gas sensor using ionic liquids. We use ionic liquids of imidazolium salts, EMIMBF4, EMIMTFSI and DEMEBF4. The impedance of ionic liquids decreases along with increase of CO2 gas concentration. By measuring the impedance of ionic liquids, we can estimate CO2 gas concentration of the atmosphere. From the experiment, measurement resolution of CO2 gas concentration was 100 ppm. The power consumption of our proposed CO2 gas sensor is several tens of microwatts, and this value is 1/1000 smaller compared with conventional CO2 gas sensors (NDIR and Solid state electrolyte cell).

Measurement of non-isothermal oxygen potentials in a Cu–Fe–Ca–S–O liquid during reduction of chalcopyrite in lime and carbon mixtures

The reduction of Indian chalcopyrite concentrates from the Ghatshila mines with carbon was studied in the presence of lime in the temperature range of 1123–1573 K. An attempt was made to determine the oxygen potential corresponding to the selective separation of two metals, copper and iron, during the reduction of chalcopyrite by carrying out electro-motive force (emf) measurements under isochronal heating rate conditions using an yttria-stabilised zirconia solid electrolyte cell with Cu/Cu2O as the reference electrode. The isochronal rate data for oxygen potential measurements were analysed by comparing them with the data from isothermal kinetics studies on the reduction of natural and synthetic chalcopyrite minerals in the above temperature range. The analyses of phases formed were carried out using the X-ray powder diffraction and scanning electron microscopic techniques, which showed the presence of a new quinary solid solution CIII phase. The solid solution phase CIII [Cu2S-CII(FeS⋅CaO)] forms as a result of mixing between the two rhombohedral lattices: high-temperature form of Cu2S and CII (FeO⋅CaS) compounds. The mechanism of reduction of chalcopyrite with carbon in the presence of lime is illustrated by the explanation of the role of the intermediate phases, CII, CIII and matte phases.

Electrochemical Synthesis of Ammonia in Solid Electrolyte Cells

Developed in the early 1900's, the “Haber-Bosch” synthesis is the dominant NH3 synthesis process. Parallel to catalyst optimization, current research efforts are also focused on the investigation of new methods for ammonia synthesis, including the electrochemical synthesis with the use of solid electrolyte cells. Since the first report on Solid State Ammonia Synthesis (SSAS), more than 30 solid electrolyte materials were tested and at least 15 catalysts were used as working electrodes. Thus far, the highest rate of ammonia formation reported is 1.13×10−8 mol s−1 cm−2, obtained at 80°C with a Nafion solid electrolyte and a mixed oxide, SmFe0.7Cu0.1Ni0.2O3, cathode. At high temperatures (>500oC) the maximum rate was 9.5*10-9 mol s−1 cm−2 using Ce0.8Y0.2O2-δ -[Ca3(PO4)2 -K3PO4] as electrolyte and Ag-Pd as cathode. In this paper, the advantages and the disadvantages of SSAS vs the conventional process and the requirements that must be met in order to promote the electrochemical process into an industrial level, are discussed.

Failure of Solid Oxide Fuel Cells by Electrochemically Induced Pressure

It is well known that many electrochemical devices such as fuel cells, electrolyzers, batteries, etc. degrade under various operating conditions. Many devices are based on solid electrolytes. In many cases, degradation manifests as electrode delamination and/or cracking of the electrolyte. An apparently obvious conclusion often reached is that this must be due to weak interfaces and some approach to mechanical strengthening or toughening should alleviate the problem. It is the intent of this manuscript to show that such electrochemical degradation often occurs due to electrochemical-mechanical coupling effects which result in extremely large internal pressures. So large can be the pressures that no amount conventional strengthening or toughening can prevent degradation. In fact, even a perfect lattice can be disrupted by electrochemically induced pressure leading to failures. In order to prevent failures, it is necessary to fully understand the role of coupling and develop strategies of mitigating high pressure formation by optimizing ion and electron transporting properties of the membrane. This manuscript discusses a fundamental mechanism of electrochemical failure of solid oxide fuel cells, solid oxide electrolyzer cells, and oxygen separators based on oxygen ion conducting solid electrolytes. Experimental results on two types solid electrolyte cells are presented in support of the mechanism.

A novel method for measuring dissolved gases in liquids

In many chemical and biotechnological plants, such as biogas plants, the measurement of the concentrations of dissolved gases and volatile components in liquids is very helpful for process control and to indicate and prevent process instabilities. Conventional membrane-covered electrochemical sensors are often not suitable for this purpose. Here we describe a new method for parallel measuring dissolved gases in complex and even corrosive liquids providing excellent selectivity, sensitivity, high long-term stability and low maintenance. The measuring method is an innovative combination of gas stripping and chemical sensing. It consists in the sequence of the following three main steps: (1) membrane-free extraction of the dissolved components in a special vessel by means of an extraction gas stream, (2) chromatographic separation of the gas mixture and (3) detection of oxidizable and reducible components by means of a coulometrically operated high-temperature solid-electrolyte cell. In the extraction vessel the dissolved volatile constituents pass off by diffusion via the open interface from the sample medium into an extraction gas stream that is passed through the vessel.

Steam electrolysis with simultaneous production of C2 hydrocarbons in a solid electrolyte cell

The production of hydrogen from steam electrolysis with simultaneous conversion of methane to C2 hydrocarbons was investigated. The reaction system was studied in a solid state oxygen ion (O2−) conducting cell at temperatures between 700 °C and 840 °C. Methane and steam, diluted in nitrogen, were introduced over the anode (Ag) and the cathode (Pt), respectively. When oxygen was electrochemically “pumped” from the cathode to the anode, steam was electrolyzed to produce gaseous H2 and CH4 was converted to C2H4, C2H6 and CO2. The conversion of methane and the C2 yield increased when a perovskite of the form SrZr0.95Y0.05O3−a (SZY) was placed on the anodic electrode to serve as a methane coupling catalyst. At the anode, C2 yields exceeding 7.6% were obtained, while an up to 65% H2 yield was achieved at the cathode.

Simultaneous production of H2 and C2 hydrocarbons by using a novel configuration solid-electrolyte + fixed bed reactor

A novel combined single chamber solid electrolyte plus fixed bed reactor configuration was developed for the simultaneous production of H2 and C2 hydrocarbons from a humidified CH4 atmosphere. Hence, a Pt/YSZ/Ag solid electrolyte cell was placed on the top of an active oxidative coupling catalyst powder bed Ce–Na2WO4/SiO2. H2 was produced via steam electrolysis in a Pt cathode of the solid electrolyte cell (H2O + 2e− → H2 + O2−). Simultaneously, the produced O2− ions were electrochemically pumped to the Ag anode, leading to the C2s production, via oxidative coupling of CH4 (4CH4 + 3O2− → C2H4 + C2H6 + 3H2O + 6e−). Additionally, non-reacted O2− molecules desorbed to the gas phase (2O2− → O2+4e−) and reacted with CH4 in the catalyst bed leading to an increase of C2s yield. The influence of different reaction parameters was investigated together with long-term reaction experiments, confirming the stability of this configuration for its practical application. The obtained results demonstrated that the addition of an active catalyst bed strongly enhances both: the efficiency of the single chamber steam electrolysis and the oxidative coupling process.

Электролитическое получение нановолокон кремния из расплава KCl-KF-K2SiF6-SiO2 для композиционных анодов литий-ионных аккумуляторов

Silicon nano- and microwires have been obtained by KCl-KF-K2SiF6-SiO2 melt electrolysis in air; this material is suitable as anode component for lithium ion batteries. Optimal conditions of electrolysis were determined. Morphology, phase and chemical composition of silicon deposits were established. Electrochemical behavior of silicon nanowires as anode component was evaluated using solid polymer electrolyte cells.

Study on electrolytic reduction with controlled oxygen flow for iron from molten oxide slag containing FeO

A ZrO2-based solid membrane electrolytic cell with controlled oxygen flow was constructed: graphite rod /[O]Fe+C saturated / ZrO2(MgO)/(FeO) slag/iron crucible. The feasibility of extraction of iron from molten oxide slag containing FeO at an applied voltage was investigated by means of the electrolytic cell. The effects of some important process factors on the FeO electrolytic reduction with the controlled oxygen flow were discussed. The results show that: solid iron can be extracted from molten oxide slag containing FeO at 1450?C and an applied potential of 4V. These factors, such as precipitation and growth of solid iron dendrites, change of the cathode active area on the inner wall of the iron crucible and ion diffusion flux in the molten slag may affect the electrochemical reaction rate. The reduction for Fe2+ ions mainly appears on new iron dendrites of the iron crucible cathode, and a very small amount of iron are also formed on the MSZ (2.18% MgO partially stabilized zirconia) tube/slag interface due to electronic conductance of MSZ tube. Internal electronic current through MSZ tube may change direction at earlier and later electrolytic reduction stage. It has a role of promoting electrolytic reduction for FeO in the molten slag at the earlier stage, but will lower the current efficiency at the later stage. The final reduction ratio of FeO in the molten slag can achieve 99%. A novel electrolytic method with controlled oxygen flow for iron from the molten oxide slag containing FeO was proposed. The theory of electrolytic reduction with the controlled oxygen flow was developed.

Electrochemical impedance spectroscopy study of the oxygen evolution reaction on a gas-evolving anode composed of lead dioxide microfibers

The oxygen evolution reaction (OER) during the electrolysis of electrolyte-free water on a gas-evolving anode composed of lead dioxide microfibers (MF-β-PbO2) was studied in a solid polymer electrolyte cell using the electrochemical impedance spectroscopy (EIS) technique. EIS spectra were recorded as a function of the overpotential for the OER. Impedance spectra characterized by two time constants distributed in the low and high frequency domains indicated that both the charge transfer and adsorption of reaction intermediates affect the electrode kinetics. In addition, it was verified that morphological aspects do not comprise the main cause for the time constant observed in the high frequency domain. In trying to interpret the EIS findings, a transfer function was derived for the electrode mechanism of Pavlov and Monahov in order to permit the evaluation of the adsorption pseudocapacitance, the double-layer capacitance and the charge transfer and adsorption resistances. It was verified that the adsorption pseudocapacitance is potential-dependent while the double-layer capacitance is almost potential-independent. It was also verified that the adsorption resistance decreases exponentially upon increasing the overpotential, exhibiting Tafel-like behavior. The apparent charge transfer coefficient, the exchange current density and the kinetic rate constant were evaluated from the impedance data.

Production of Fischer–Tropsch liquid fuels from high temperature solid oxide co-electrolysis units

A model for high temperature co-electrolysis (HTCE) of carbon dioxide and water using solid oxide electrolytic cells (SOEC) for syngas production and subsequent conversion to liquid fuels by a Fischer–Tropsch (F–T) process is presented. The SOEC model is guided by experimental data from the literature, and the model is employed to explore the effect of temperature, pressure, and feedstock composition on syngas composition exiting the SOEC. The syngas is converted in a slurry bubble column F–T synthesis reactor in which the model approach of a once-through conversion of carbon monoxide is chosen, and the distribution of hydrocarbon products is determined by the Anderson–Schulz–Flory model. The overall system efficiency for liquid hydrocarbon fuels produced from electrical energy is found to be 54.8% HHV (51.0%-LHV). It is determined that operating the SOEC at low pressure (1.6 bar) versus higher pressure (5 bar) results in an efficiency gain of 2.6%. The economics of the production plant are evaluated for variations in electricity feedstock costs and operating capacity factors. The liquid fuels production costs range from 4.4 $/GGE to 15.0 $/GGE for electricity prices of 0.02 $/kWh to 0.14 $/kWh and a plant capacity factor of 90% to 40%, respectively.

Amorphous Titanium Sulfide Electrode for All-solid-state Rechargeable Lithium Batteries with High Capacity

Abstract Amorphous TiS3 active materials were prepared using a high-energy ball mill and first applied to all-solid-state cells with Li2S–P2S5 solid electrolyte. The solid-state cell operated as a rechargeable lithium battery with a high capacity of 400 mA h g−1 at room temperature. The cell exhibited a higher capacity than a solid-electrolyte cell with crystalline TiS2 and showed better cyclability than a liquid-electrolyte cell with crystalline TiS3.