Ceramic Cathode Research Articles

Improvements in co-electrolysis performance and long-term stability of solid oxide electrolysis cells based on ceramic composite cathodes

The co-electrolysis of CO2 and H2O was performed using a solid oxide electrolysis cell with yttria-stabilized zirconia (YSZ) as the electrolyte and a La0.7Sr0.2Cr0.5Mn0.5O3 (LSCM)-YSZ composite as the cathodic material. The LSCM-YSZ composite cathode showed better co-electrolysis performance than did a La0.7Sr0.3V0.9O3 (LSV)-YSZ composite cathode, suggesting that the catalytic activity of LSCM is higher than that of LSV. After small amounts of CeO2 and Pd had been added as catalysts to the two composite electrodes, the LSCM-YSZ cathode showed better co-electrolysis performance than that of the LSV-YSZ composite electrode. The long-term stability of the co-electrolysis performance of the LSCM-YSZ composite cathode was higher than that of the LSV-YSZ composite cathode. These results show that the electrolysis performance of composite cathodes containing highly active materials such as CeO2 and Pd as catalysts can be improved further by choosing the proper base material.

Perovskite cathodes for NaBH4/H2O2 direct fuel cells

Perovskite-type oxides are evaluated as cathodes for hydrogen peroxide (H2O2) reduction in direct borohydride fuel cells (DBFCs). The study is conducted on button-type ceramic electrodes of LaCoO3 (LC), La0.84Sr0.16CoO3 (LSC), La0.8Sr0.2Fe0.8Co0.2O3 (LSFC), and La0.7Sr0.3MnO3 (LSM), thus avoiding cross-contributions of carbon or nickel catalyst supports. Cyclic voltammetry shows that LSM has the highest activity for H2O2 reduction in alkaline solution, with the other three materials showing minimal (LC) to none (LSC, LSFC) electroactivity. The data also suggest that only LC and LSM are stable within the tested potential window, although the alteration of the samples surface is apparent in scanning electron microscopy images collected after the electrochemical measurements. The analysis of LSM by chronopotentiometry in light of the Sand equation indicates ca. 1 electron involved in the H2O2 reduction. A demonstration DBFC employing a single phase LSM ceramic cathode yields a peak power density of 8.2mWcm−2 at 28mAcm−2, at 45°C. This value is about 60% of that obtained with a commercial platinum foil electrode, which is a notable feature and demonstrates the potential of LSM as an alternative low cost cathode for DBFCs.

Efficient carbon dioxide electrolysis in a symmetric solid oxide electrolyzer based on nanocatalyst-loaded chromate electrodes

Abstract Composite cathode based on redox-stable La0.75Sr0.25Cr0.5Mn0.5O3−δ (LSCM) can be handled to perform for direct CO2 electrolysis without a flow of reducing gas over the electrode; however, the insufficient electrocatalytic activity of the ceramic composite cathode still limits the electrode performances and current efficiencies. In this case, catalytic-active iron nanocatalyst and iron oxide catalyst were loaded into the LSCM-based composite cathode and anode, respectively, to improve the electrode performances. Then efficient direct CO2 electrolysis was demonstrated by using the symmetric solid oxide electrolyzer based on LSCM loaded with 2 wt% Fe2O3 at 800 °C. The dependences of conductivity of LSCM were studied on temperature and oxygen partial pressure and further correlated to the electrode performance. The loading of nanocatalyst considerably improves the electrode performance and the current efficiency of CO2 electrolysis was accordingly enhanced by approximately 75% for the impregnated LSCM-based electrode at 800 °C. The synergistic effect of catalyst-active iron nanoparticles and redox-stable LSCM perovskite ceramic leads to the excellent stability and better cathode performance for the direct CO2 electrolysis at high temperatures.

Microstructure and Property of Plasma Sprayed TiB<sub>2</sub> Wettable Coatings on Carbon Cathodes

In this work, fine-lamellar structured TiB2 ceramic wettable cathode coatings were deposited on carbon cathodes of aluminium oxide reduction cells by atmosphere plasma spraying (APS). Cathode carbon blocks consisting of coatings 800 μm thick of plasma sprayed TiB2 finepowder on carbon substrate were fabricated. In order to investigate the results of coating, the microstructure and phase composition of the wettable cathode coating were characterized by scanning electron microscopy (SEM). It is found that TiB2 fine-powders were partly oxidized during the plasma spraying process. The coating was mostly formed by a matrix of fully molten particles where the presence of semi-molten feedstock agglomerates. The APS method is believed to be a good choice to deposit TiB2 wettable cathode coating with high performance and reliability.

Composite Ag-La0.8Sr0.2MnO3-σ Cathode for Solid Oxide Fuel Cells

Abstract Composite cathodes for solid oxide fuel cells composed of metallic silver dispersed in ceramic (La0:8Sr0:2MnO3-σ) matrix were prepared on the surface of solid electrolyte by two-step procedure. First the matrix of controlled porosity was created by sintering mixture of La0:8Sr0:2MnO3-σ powder with the organic polymer beads then the matrix was saturated with AgNO3 solution and sintered again. Such obtained cathodes showed higher electrical conductivity and lower charge transfer resistance in oxygen reduction reaction in comparison to pure ceramic cathodes

Silver-Based Current Collectors for Industrial Applications

A major issue for the use of ceramic cathodes in solid oxide fuel cells (SOFCs) is their limited conductivity and fragility. Therefore silver based current collectors were used to obtain highly conductive cathodes. Incorporation of oxide particles prevents densification and led to porous films with enhanced stability and excellent electrochemical properties.

Effect of humidification on the performance of intermediate-temperature proton conducting ceramic fuel cells with ceramic composite cathodes

The effect of variations in flow rate and the humidity content of the cathode and anode gases on the performance of BaCe0.85Y0.15O3−δ electrolyte-based proton conducting ceramic fuel cell with ceramic composite cathodes are studied. Increased flow rate of gases has positive effect but the presence of humidity in the cathode/anode gases has negative effect on the performance. The effect of humidity is more pronounced when it is present in the cathode gas than when it is present in the anode gas. Also, the effect of humidity is dependent on the nature of the cathode material; in the case of La0.8Sr0.2MnO3–Gd0.1Ce0.9O1.95 cathode some of the reaction sites are occupied by H2O vapor and which leads to increase in the charge transfer resistance. Replacing La0.8Sr0.2MnO3–Gd0.1Ce0.9O1.95 with La0.8Sr0.2MnO3–BaCe0.85Y0.15O3−δ cathode leads to an increase in the effective area of three phase boundary, which mitigates the adverse effects of humidity to a certain extent.

Production of Nanopowders Using Nanosecond Electron Beam

Frequency nanosecond electron accelerators type URT has been developed for use in radiation technologies. The accelerator includes a thyratron, a pulse transformer and a semiconductor opening switch. The accelerating voltage is up to 0.9 MV, FWHM pulse length is up to 60 ns, and the repetition rate is up to 250 Hz. A metal ceramic cathode, which is used in the accelerator, provides an electron beam cross section up to 16 cm in diameter or rectangular with the dimensions of 45 * 5cm2 at a maximum density of the pulse current equal to 2 A/cm2. Thus, a family of nanosecond electron accelerators has been developed for use in radiation technologies applied to layers up to 0.4 g/cm2 thick, such as production of nanopowders from gas and liquid precursors. Experiments on the irradiation of silver nitrate solutions in various liquids by a URT-0.5 accelerator facilitated the development of technology for producing silver nanopowders (NPs). The powder yield and particle size as a function of the irradiation mode has been established. An increase in the adsorbed dose results in an increased powder yield; however, the particle size decreases and the powder agglomeration rate increases. Therefore, the targeted production of silver NPs with a mean particle size in the range of 90–1100 nm is possible. Besides to produce TiO2 and SiO2 NPs the gas precursors were used.

Mesoporous Nitrogen-Doped Carbon-Glass Ceramic Cathodes for Solid-State Lithium–Oxygen Batteries

The composite of nitrogen-doped carbon (N-C) blend with lithium aluminum germanium phosphate (LAGP) was studied as cathode material in a solid-state lithium-oxygen cell. Composite electrodes exhibit high electrochemical activity toward oxygen reduction. Compared to the cell capacity of N-C blend cathode, N-C/LAGP composite cathode exhibits six times higher discharge cell capacity. A significant enhancement in cell capacity is attributed to higher electrocatalytic activity and fast lithium ion conduction ability of LAGP in the cathode.

52.3: A Use of Electrically Conductive Oxide Ceramic (12CaO·7Al2O3 Electride) Electrode having Low Work Function and Low Sputtering Yield for Fluorescent Lamps

AbstractA significantly low cathode fall voltage of 140 V and a high sputtering resistance at the driving current as large as 20 mA were observed for the cold cathode fluorescent lamps that comprise the ceramic cathode electrodes made of 12CaO·7Al2O3 electride. The electride is a subnanoporous compound having a work function of 2.4 eV and electrical conductivity of 1670 S/m. The electrode was also found to be applicable to hot cathodes for glow and arc discharges.

Lifetime extension of ferroelectric cathodes for microwave tubes

The lifetime of a microwave tube with a ferroelectric cathode was investigated. The repeatability of the radiation output was measured as a function of the cathode lifetime. In this experimental research, two barium titanate ceramic cathodes were studied with different operating parameters. The emission current density was ∼0.6A/cm2. Current pulses of 0.5–1.5A with ∼0.5μs, and Duty factor <10−4 were used. The microwave tube used was a gyrotron operating at ∼7GHz. The tube was operated in a repetitive mode and even after ∼107 pulses the cathode still operates and microwave radiation is obtained. The pulse charge was fairly stable during the experiments. Nevertheless, the rate of missing pulses and irregularity between successive pulses increases and becomes the limiting factor for the cathode lifetime. It is concluded that the practical limitation for ferroelectric cathode lifetime in microwave tubes in the suggested configuration is not the degradation in the pulse charge, but the growing rate of missing pulses.

Research progress in TiB2 wettable cathode for aluminum reduction

Titanium diboride wettable cathodes are regarded as ideal for aluminum reduction because of their excellent wettability with molten aluminum. The TiB2 inert wettable cathode materials for aluminum reduction may be divided into three groups: pure TiB2 ceramic cathode, TiB2 composite cathode, and TiB2 coating. This paper briefly describes international research progress on TiB2 inert wettable cathodes as well as problems faced, and concentrates on the activities of Central South University, Changsha, China, in researching the ambient-temperature solidified TiB2 cathode coating. At the same time, the results of the coating applied in many aluminum smelters in China are presented, and the pattern of cathode surface of 160 kA cells coated with the ambient-temperature-solidified TiB2 cathode coating after one year operation is discussed in comparison with the normal cells.

Properties of ceramic honeycomb cathodes

A high current electron beam was emitted from slabs of ceramic honeycomb that were placed 2mm in front of the primary electron emitters. Inside the ceramic honeycomb pores, the primary electrons are multiplied many folds by a secondary emission process creating plasma from which the electron beam was emitted. Measurements show that there was no anode-cathode gap closure during the pulse duration and a uniform current density distribution was observed on the anode. Contrary to the measurements of “conventional” large area field emission cathodes, no transit time instability was observed.

Tungsten coatings by chemical solution deposition for ceramic electrodes in fluorescent tubes

In the lighting industry, the concept of ceramic cold cathodes provided with an inside tungsten coating is under consideration to be applied in mercury-free fluorescent lamps for advertising purposes. In this regard, the applicability of chemical solution deposition to fabricate metallic films on the inner surface of alumina tubules was established. The technique involves the preparation of tungsten oxide layers from a peroxotungstic acid precursor solution and their subsequent reduction to tungsten in the presence of hydrogen. Diverse characterisation of the precursor and the intermediates was carried out in order to determine the influence of their properties on the quality of the final coatings. By acquiring the optimum process parameters, highly-conducting tungsten films were obtained. The temperatures allowing for conversion of the oxide to the metal as well as for sintering of the derived tungsten films were observed to be substantially lower than in bulk processes. Electrode prototypes of the described type were accordingly realised and operated successfully in a fluorescent tube test setup, thus proving the feasibility of the hitherto theoretical idea.

Ceramic Technologies for Anode-Supported Solid Oxide Fuel Cells

One of the most promising technologies for future applications of solide oxide fuel cells (SOFC)is the so-called “anode-supported” configuration: a dense yttria-stabilised zirconia (YSZ) ceramic electrolyte is deposited as a thin film over a porous Ni / YSZ cermet substrate anode, followed by a porous ceramic cathode such as La1-xSrxMnO3 (LSM). In this paper, a short review is made of the current technologies available to achieve this particular architecture, and to optimise the service behaviour. Then, alternative materials and fabrication technologies, as well as their possible impact on performance, are proposed and investigated.

Thermal Degradation of Selected Alloys for SOFC Interconnectors

Oxide growth and thermal degradation of three ferritic SOFC interconnector alloys have been investigated. The materials included a standard grade (alloy 430) and two alloys (Crofer 22 APU, ZMG 232) specifically designed for interconnector service. All alloys appear to follow parabolic oxidation up to 500 h at 740{degree sign}C in air. During oxidation, a consistent decrease of iron and increase of chromium and manganese were observed in the surface oxide. Some chromium transport was detected on the cathode side surface of the cell after 500 h at 740{degree sign}C. The results emphasise the importance of appropriate coating of the interconnectors, to prevent chromium poisoning on the cathode. A natural coating material would be similar or compatible with the ceramic cathode. Such a coating also has the additional advantage that simpler and cheaper steel grades could be used as the interconnector material.

Operation of an LSGMC Electrolyte-Supported SOFC with Composite Ceramic Anode and Cathode

An all-perovskite-based intermediate-temperature fuel cell was fabricated from materials synthesized using glycine-nitrate process (GNP) combustion synthesis and modified Pechini synthesis routes. Yttrium-doped strontium titanate (SYT) was chosen as the conductive ceramic anode component to avoid problems associated with Ni-based anodes. La0.8 Sr0.2 Ga0.8 Mg0.1 Co0.1 O3-δ electrolyte-supported solid oxide fuel cells (SOFCs) with composite ceramic anode and cathode exhibit a relatively high power density of 0.246 Wcm at 800°C at 0.5 V. © 2007 The Electrochemical Society.

Chromium Poisoning of SOFC Cathodes: Influence of the LSM-YSZ Structure

The structure of the cathode strongly influences the degree and rate at which a (La 0.8 Sr 0.2 ) 0.98 MnO 3 (LSM) - 8% YSZ ceramic cathode assembly will exhibit chromium poisoning effects. Under cathodic polarization at 600°C (under flowing, dry air), porous films of LSM on dense YSZ in contact with a 430 stainless steel (430SS) contact will lose a significant degree of activity, especially at a high overpotential of -0.5 V vs. Pt/air. Under the same conditions, similar film thicknesses, and using the same materials, structurally graded cathodes composed of 50:50 LSM:YSZ topped with a 100% LSM contact layer exhibit high activity whether a Pt or 430SS contact is employed. Under the same conditions, patterned, fully dense, ca. 80 nm thick LSM films on dense YSZ also show relatively stable activity in the presence of either a Pt or 430SS contact. Electron microprobe analyses of the surfaces of the samples clearly show that Cr 2 O 3 is deposited at and around the perimeter of the cathode film for all samples polarized using a 430SS contact. However, little if any Cr species were found beneath the porous 50:50 LSM:YSZ film, in contrast to the porous LSM film samples, where large concentrations of Cr species were observed at what ostensibly is the buried LSM-YSZ-air triple-phase boundary (TPB). Thus, the stability of the 50:50 LSM:YSZ composite samples seems to be linked to the absence of Cr species at the buried TPB. The same cannot be said for the dense LSM sample, as other factors must be contributing to its resistance to Cr poisoning.

Repetitively pulsed, high energy KrF lasers for inertial fusion energy

Krypton fluoride (KrF) lasers produce highly uniform beams at 248 nm, allow the capability of ‘zooming’ the spot size to follow an imploding pellet, naturally assume a modular architecture and have been developed into a pulsed-power-based industrial technology that readily scales to a fusion power plant sized system. There are two main challenges for the fusion power plant application: to develop a system with an overall efficiency of greater than 6% (based on target gains of 100) and to achieve a durability of greater than 3 × 108 shots (two years at 5 Hz). These two issues are being addressed with the Electra (700 J, 5 Hz) and Nike (3000 J, single shot) KrF lasers at the Naval Research Laboratory. Based on recent advances in pulsed power, electron beam generation and transport, hibachi (foil support structure) design and KrF physics, wall plug efficiencies of greater than 7% should be achievable. Moreover, recent experiments show that it may be possible to realize long lived electron beam diodes using ceramic honeycomb cathodes and anode foils that are convectively cooled by periodically deflecting the laser gas. This paper is a summary of the progress in the development of the critical KrF technologies for laser fusion energy.

Stability and Reactivity of LSGM Electrolytes With Nickel-Based Ceramic Cathodes

The surface of La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM 9182) has been examined through the use of secondary-ion mass spectrometry before and after surface modification by mechanical polishing. It was found that the cation stoichiometry varied at the surface in both cases. The effect of this change on the performance of the cathode material La2NiO4+δ was assessed through ac impedance spectroscopy of symmetrical cells prepared by depositing La2NiO4+δ on the surface of pellets of La0.9Sr0.1Ga0.8Mg0.2O3−δ. An improvement in the cathode performance of these cells at temperatures above 500°C was found on electrolytes with elevated levels of strontium and magnesium at the surface.