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[en] Highlights: • Two-step sintering of BCZY vis-à-vis conventional and Zn-aided sintering was evaluated. • Conventional sintering was ineffective and density decreased with decreasing sintering time. • Two-step sintering was found very effective yielding 95% relative density. • Zn-doping also improved the densification but the conductivity was adversely affected. • Two-step sintered samples showed highest conductivity.
[en] Solid oxide fuel cells (SOFC) are complex devices that offer great advantages over conventional manner in which electrical energy is produced. Many of these advantages revolve around the environmental impact and particularly energy efficiency. However, progress in the field of these devices operating at high temperatures require the continuous search for new materials with advanced properties, optimization in manufacturing, cutting edge technologies for the processing of its main components (anode-electrolyte-cathode-seal) and low manufacturing costs. Here, the perovskite structure material LaxSr1-xCryMn1-yO3-δ (LSCM) is efficient, stable redox environments, has low manufacturing cost and is optimized for SOFC applications. Its properties compare favorably with the compound Ni/YSZ using hydrogen as a fuel; and when methane is used, it requires only 3% moisture to prevent carbon formation, which is much lower compared to when used Ni/YSZ (50% moisture). The LSCM material allows a SOFC cell operate at intermediate temperatures around 700°C. This article provides a brief review of the excellent properties and potential presented by this perovskite. (Author)
[en] High temperature proton conductor (HTPC) oxides are attracting extensive attention as electrolyte materials alternative to oxygen-ion conductors for use in solid oxide fuel cells (SOFCs) operating at intermediate temperatures (400-700 0C). The need to lower the operating temperature is dictated by cost reduction for SOFC pervasive use. The major stake for the deployment of this technology is the availability of electrodes able to limit polarization losses at the reduced operation temperature. This review aims to comprehensively describe the state-of-the-art anode and cathode materials that have so far been tested with HTPC oxide electrolytes, offering guidelines and possible strategies to speed up the development of protonic SOFCs. (topical review)
[en] Solid Oxide Fuel Cells (SOFC) and High Temperature Electrolysis (HTE) work on two opposite processes. The basic equations (Nernst equation, corrected by a term of over-voltage) are thus very similar, only a few signs are different. An operational model, based on measurable quantities, was finalized for HTE process, and adapted to SOFCs. The model is analytical, which requires some complementary assumptions (proportionality of over-tensions to the current density, linearization of the logarithmic term in Nernst equation). It allows determining hydrogen production by HTE using a limited number of parameters. At a given temperature, only one macroscopic parameter, related to over-voltages, is needed for adjusting the model to the experimental results (SOFC), in a wide range of hydrogen flow-rates. For a given cell, this parameter follows an Arrhenius law with a satisfactory precision. The prevision in HTE process is compared to the available experimental results. (authors)
[en] In this work, we propose the use of electro-spinning technique for the synthesis of ceramic fibers that can be used as SOFC's electrodes. In particular, the increase of ceramic fibers production capacity (up to one order of magnitude) has been demonstrated through the replacement of a single injector by a multiple injector (equipped with 10 needles). Moreover, the diameters, lengths, glass sizes and surface area of the obtained fibers indicate that these fibers could be used to manufacture highly porous electrodes that can be easily infiltrated, having micro-structure where the oxygen reduction reaction region takes place is maximized and also the gases and charges transportations properties are improved.
[es]En este trabajo se propone el empleo de la técnica de electro-hilado para la síntesis de fibras cerámicas que puedan ser empleadas como constituyentes de electrodos de pilas de combustible de óxido sólido. Concretamente se ha demostrado el aumento en la capacidad de producción de fibras cerámicas (en un orden de magnitud) gracias a la sustitución de un inyector simple por uno múltiple (provisto de 10 agujas). Además, los diámetros, longitudes, tamaños de cristal y área superficial de las fibras obtenidas indican que estas podrían ser empleadas para fabricar electrodos con una microestructura altamente porosa, fácilmente infiltrable y donde se maximice la región donde tiene lugar la reacción de reducción de oxígeno y el transporte de gases y cargas.
[en] The current state of the art in fuel cell system development will be reviewed with an emphasis of the critical issues on heat transfer. The heat transfer issues for both PEM based systems and SOFC based fuel cell systems will be addressed. For systems that are based on hydrocarbon fuels a reforming step is needed and critical heat transfer issues are also present in this fuel processing part of the system where the primary feedstock is converted to reformate. Also, in both the PEM and SOFC fuel cell itself, heat transfer is a critical issue. It will be shown what are the implications of the fuel cell heat transfer to the total system architecture for the various fuel cell applications (stationary power, transport). The heat transfer issues in fuel cell system development will be clarified with several examples
[en] The Technical University of Munich investigates the degradation effects observed on SOFCs when fired with product gases from biomass gasification processes. The TUM has concentrated its research on tubular SOFCs. For this purpose tubular electrolyte-supported SOFCs have been manufactured using commercially available electrolyte tubes, anode foil and cathode paste. The tubular SOFCs were first run with hydrogen and synthetic fuels. Once stable and reproducible results were achieved, tests with product gas from four different biomass gasifiers have started. These gasifiers have been coupled to a gas cleaning device which includes sulphur and particle removal and pre-reforming. Different operation conditions of the gasifiers and the gas cleaning device have been realized and the corresponding fuel cell degradations have been analysed. (authors)
[en] 'Full text:' The 5 kW SOFC system has been under development at Fuel Cell Technologies Ltd. (FCT) since 2001. The power output and thermal capacity were chosen after considering typical load data for residential, remote and small commercial applications. A specification for a system was developed in conjunction with target market customers, and much useful feedback into the operability, reliability and maintainability of the system was incorporated. A single prototype was designed and built in 2002 utilizing tubular cells manufactured by Siemens Westinghouse Power Corporation (SWPC). FCT was responsible for system integration and Balance of Plant while SWPC was responsible for the generator which incorporated the cell stack, recuperator, insulation systems and reformer. This prototype was successfully tested at FCT in 2002 and was rapidly followed by four first generation or 'Alpha' demonstration units. The design methodology for the 5 kW system will be described, including the testing carried out to verify performance and reliability of the various subsystems. Results of safety and reliability analyses will also be included leading to an overall description of the design. In the presentation, the performance and design of these first generation units will be described. We will also present some site operating results. As this program was being completed, the second generation or 'Beta' unit was being designed and developed at FCT, with the goal of incorporating the lessons learned on site. This improved unit will be described and the results of early demonstration results of the Beta units will be incorporated into the presentation. It is anticipated that this will show the improved performance of a highly reliable and safe combined heat and power SOFC system. (author)
[en] Solid Oxide Fuel Cells (SOFC) are being widely studied due to their possible utilization to produce electrical energy in a wide power range (from 1 kW up to few hundreds of kW).The principle of operation of this kind of fuel cells involves reduction of O2 in the cathode oxygen ions (O2-) diffusion of oxygen through the electrolyte and fuel oxidation in the anode.Commercial SOFC must work at temperature higher than to 1000 degree C to enable the O2- diffusion.Therefore, it is necessary to investigate new materials that enable to decrease the operation temperature, improving SOFC performance and cost. La1-xSrxCo1-yFeyO3-δ (LSCF) perovskites are good candidates for SOFC cathodes because these materials present high ionic and electronic conductivity. LSCF cathodes are adequate to fabricate Ce1-xGdxO2-δ electrolyte SOFC due to its low chemical reactivity with this material and its similar thermal expansion coefficient. In this work we present a study of microstructural and electrochemical characteristics of films for SOFC cathodes. La0.4Sr0.6Co0.8Fe0.2O3-δ compounds were prepared by the acetate reaction method.Then, cathodes were deposited onto a Ce0.9Gd0.1O2-δ electrolyte disk by dip coating and spray techniques.Structural characterization is made by X-ray diffraction XRD and scanning electron microscopy (SEM).Electrochemical properties are characterized by complex impedance measurements.Finally, the relation between structural characteristics and electrical properties is discussed
[en] Highlights: ► Three new trigeneration systems (SOFC-trigeneration, biomass-trigeneration, and solar-trigeneration systems) are thermodynamically examined and assessed. ► The overall exergy efficiency for the SOFC-trigeneration system becomes the highest. ► The maximum costs per exergy unit for the SOFC-trigeneration system is approximately 38 $/GJ. ► The solar-trigeneration system offers the best thermoeconomic performance. - Abstract: In this part II of the study, three new trigeneration systems are examined. These systems are SOFC-trigeneration, biomass-trigeneration, and solar-trigeneration systems. This study reveals that the maximum trigeneration-exergy efficiencies are about 38% for the SOFC-trigeneration system, 28% for the biomass-trigeneration system and 18% for the solar-trigeneration system. Moreover, the maximum cost per exergy unit for the SOFC-trigeneration system is approximately 38 $/GJ, for the biomass-trigeneration system is 26 $/GJ, and for the solar-trigeneration system is 24 $/GJ. This study reveals that the solar-trigeneration system offers the best thermoeconomic performance among the three systems. This is because the solar-trigeneration system has the lowest cost per exergy unit. Furthermore, the solar-trigeneration system has zero CO2 emissions and it is based on a free renewable energy source