[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] Highlights:• Conductivity measurements were carried out at different oxygen and vapor partial pressure.• Transport numbers were determined by defect equilibria model.• The Ba_4·3Ta_1·7O_8.55 electrolyte exhibits high protonic transport number of 0.64 at 700 °C in humidity air.• The predominance area diagrams for currieries conduction were plotted. -- Abstract: Ba₃Ca_1·18Nb_1·82O_9-δ(BCN18), which has a high conductivity and protonic conductive dominant above 600 °C, is regarded as a promising double perovskite-type proton conductor for solid oxide fuel cells, catalysis, and electrochemical sensors. To further increase the conduction properties of the double perovskite-type proton conductor, it can be considered to decrease the electronegativities of A and B site elements. In this study, Ba and Ta, which have lower electronegativities than those of Ca and Nb, were introduced to totally substitute Ca and Nb. The double perovskite-type proton conductor Ba_4·3Ta_1·7O_8.55 (BBT30) was prepared by solid-state sintering. We found that the total conductivities increased linearly with the increase of the temperature, with the total conductivities being in the range of 1.2 × 10⁻⁵−8.7 × 10⁻⁴ S cm⁻¹ in humid air at 400 °C−800 °C; the estimated activation energy of proton was obviously lower than those of oxide ion and hole. The standard molar hydration enthalpy of BBT30 was calculated to be −79.9 kJ/mol. Additionally, the transport numbers were determined systematically by defect equilibria model. Our results indicated that both the transport numbers of oxide ion and hole remarkably increased with increasing oxygen partial pressure, while the protonic conduction was always predominant in those atmospheric conditions, with the protonic transport number being 0.64 at 700 °C, and it was significantly higher than those of other double perovskite-type proton conductors. This indicates that BBT30 is an excellent candidate for an electrochemical sensor, and our work has demonstrated a new direction in developing a high conductivity and protonic transport number perovskite-type proton conductor.

[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.

[en] Highlights: • The structure and properties of SCBC were studied as cathodes for IT-SOFCs. • The introduction of Ca significantly improved the TEC and conductivity. • The SCBC exhibited good chemical compatibility and electrochemical properties. • The SCBC exhibited good anti-carbon dioxide poisoning capability. -- Abstract: Here, Sm_1–xCa_xBaCo₂O_5+δ (x = 0–0.4; SCBC) oxygen-deficient perovskites were synthesized by a sol–gel method and studied as potential novel cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). As an effective doping strategy, partial substitution of Ca for Sm in SmBaCo₂O_5+δ could reduce the thermal expansion coefficient (TEC) and improve the conductivity and catalytic activity of the oxygen reduction reaction (ORR). The x = 0–0.2 samples obtained after sintering at 1100 °C crystallized in an orthorhombic structure with the space group Pmmm and had good chemical compatibility with CeO₂-based electrolytes at 1000 °C for 10 h. The TECs of the SCBC samples decreased from 20.2 × 10⁻⁶ K⁻¹ (x = 0) to 17.7 × 10⁻⁶ K⁻¹ (x = 0.2). The area-specific resistances (ASRs) of the x = 0–0.4 cathodes were 0.163, 0.114, 0.075, and 0.090 Ω cm² at 700°C. Additionally, the x = 0.2 cathode showed good electrochemical stability in a CO₂-containing atmosphere. All results clearly indicated that double perovskite SCBC (x = 0–0.3) are promising cathode materials for IT-SOFCs.

[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] Highlights: • Five SOFC temperature control systems consider different control strategies and control points. • SOFC temperature performance in the horizontal and vertical directions are both considered. • Controlling average temperature benefits the system efficiency. • Two-side control strategy and average temperature as control point are suggested for SOFC thermal systems. Solid oxide fuel cell-gas turbine (SOFC-GT) hybrid systems are facing challenges in terms of fuel cell temperature control due to its significant effect on safe and efficient operation. In this study, five different temperature control systems are designed according to different SOFC control strategies and control points in anode and cathode ejector-based SOFC-GT hybrid systems. Firstly, three SOFC temperature control strategies including only anode-side control, only cathode-side control, and two-side control are compared. The comparison results indicate that the cathode-side temperature control strategy can effectively maintain the system efficiency. In addition, the two-side control strategy is better than one-side control strategies considering the safe operation of the anode and cathode differential temperature. Then, three SOFC temperature control points including input temperature, output temperature, and average temperature are chosen in order to investigate the effect of control variables. The comparison results indicate that maintaining the average temperature is better than the other temperature control points. Therefore, the two-side average temperature control system of SOFC is more appropriate to guarantee efficient and safe operation. The temperature distribution in SOFC is more feasible, and the efficiency of SOFC and the whole hybrid system is most efficient at a part load condition.

[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)