Fanglin Chen

Sm0.5Sr0.5CoO3 cathodes for low-temperature SOFCs

The electrochemical properties of the interfaces between an Sm0.2Ce0.8O1.9 (samaria-doped ceria, SDC) electrolyte and porous composite cathodes consisting of Sm0.5Sr0.5CoO3 (SSC) and SDC have been investigated in anode-supported single cells at low temperatures (400–600 °C). The bilayer structures of the SDC electrolyte films (25 μm thick) and the NiO–SDC anode supports were formed by co-pressing and subsequent co-firing at 1350 °C for 5 h. The effect of composition, firing temperature, and microstructure of the composite cathodes on the electrochemical properties is systematically studied. Results indicate that the optimum firing temperature is about 950 °C, whereas the optimum content of SDC electrolyte in the composite cathodes is about 30 wt.%. It is noted that the addition of the proper amount of SDC to SSC dramatically improved the catalytic properties of the interfaces; reducing the interfacial resistance by more than one order of magnitude compared with an SSC cathode without SDC.

A Novel Electrode Material for Symmetrical SOFCs

5 ] The application of this new SOFC confi guration leads to a number of advantages. Possible sulfur poisoning or coke formation on the surface of the anode can be potentially eliminated by oper-ating the anode as a cathode; oxidant (typically air) will fl ush any sulfur or carbon species absorbed on the electrode, thereby regenerating the electrode from sulfur or coke deactivation. In addition, a redox stable cathode is also expected to enhance the cathode durability since O

Reduced-Temperature Solid Oxide Fuel Cells Fabricated by Screen Printing

Electrolyte films of samaria-doped ceria ~SDC, Sm0.2Ce0.8O1.9) are fabricated onto porous NiO-SDC substrates by a screen printing technique. A cathode layer, consisting of Sm0.5Sr0.5CoO3 and 10 wt % SDC, is subsequently screen printed on the electrolyte to form a single cell, which is tested at temperatures from 400 to 600°C. When humidified ~3% H2O) hydrogen or methane is used as fuel and stationary air as oxidant, the maximum power densities are 188 ~or 78! and 397 ~or 304! mW/cm at 500 and 600°C, respectively. Impedance analysis indicates that the performances of the solid oxide fuel cells ~SOFCs! below 550°C are determined primarily by the interfacial resistance, implying that the development of catalytically active electrode materials is critical to the successful development of high-performance SOFCs to be operated at temperatures below 600°C.

Sulfur‐Tolerant Redox‐Reversible Anode Material for Direct Hydrocarbon Solid Oxide Fuel Cells

A novel composite anode material consisting of K(2) NiF(4) -type structured Pr(0.8) Sr(1.2) (Co,Fe)(0.8) Nb(0.2) O(4+δ) (K-PSCFN) matrix with homogenously dispersed nano-sized Co-Fe alloy (CFA) has been obtained by annealing perovskite Pr(0.4) Sr(0.6) Co(0.2) Fe(0.7) Nb(0.1) O(3-δ) (P-PSCFN) in H(2) at 900 °C. The K-PSCFN-CFA composite anode is redox-reversible and has demonstrated similar catalytic activity to Ni-based cermet anode, excellent sulfur tolerance, remarkable coking resistance and robust redox cyclability.

Preparation of yttria-stabilized zirconia (YSZ) films on La0.85Sr0.15MnO3 (LSM) and LSM–YSZ substrates using an electrophoretic deposition (EPD) process

Preparation of high-quality yttria-stabilized zirconia (YSZ) electrolyte films on porous substrates is critical to the fabrication of high-performance solid-state ionic devices such as fuel cells and gas sensors. An electrophoretic deposition (EPD) process is investigated for the preparation of YSZ electrolyte films on both porous La0.85Sr0.15MnO3 (LSM) and porous LSM–YSZ composite substrates. The Pechini process is used for the preparation of fine LSM powders with an average particle size of about 0.1 μm. The processing parameters critically influencing the microstructures of green YSZ films are identified and optimized to obtain uniform, crack-free green YSZ films with high packing density of fine YSZ particles. Dense YSZ films with a thickness of about 10 μm have been successfully fabricated on both porous LSM and porous LSM–YSZ substrates when sintered at 1250°C for 2 h.

Mesoporous Catalytic Filters for Semiconductor Gas Sensors

Abstract An effective way to improve sensor selectivity and stability is the use of catalytic filters to block interfering and poisoning gas molecules from reaching the sensor surface. Mesoporous silica with high resistivity and hugh surface areas are ideally suited as a base material for this application. When impregnated with proper catalysts, mesoporous silica has a great potential to eliminate responses to undesired gases even of thin-film and/or micro-machined sensors. In this paper, we report our initial results on thick film SnO 2 -based gas sensors covered with a catalytic filter consisting of Pd and Pt loaded mesoporous silica. Results indicate that selective oxidation of CO in the catalytic filter leads to the elimination of CO interference to a CH 4 sensor with no perceptible deterioration in sensing performance.

Sr2Fe1.5Mo0.5O6 as Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells with La0.8Sr0.2Ga0.87Mg0.13O3 Electrolyte

The performance of Sr 2 Fe 15 Mo 0.5 O 6 (SFMO) as a cathode material has been investigated in this study. The oxygen ionic conductivity of SFMO reaches 0.13 S cm -1 at 800°C in air. The chemical diffusion coefficient (D chem ) and surface exchange constant (k ex ) of SFMO at 750°C are 5.0 x 10 -6 cm 2 s -1 and 2.8 x 10 -5 cm s -1 , respectively, suggesting that SFMO may have good electrochemical activity for oxygen reduction. SFMO shows a thermal expansion coefficient (TEC) of 14.5 x 10 -6 K -1 the temperature range of 200-760°C in air. The polarization resistance of the SFMO cathode is 0.076 Ω cm 2 at 800°C in air under open-circuit conditions measured on symmetrical cells with La 0.8 Sr 0.2 Ga 0.87 Mg 0.13 O 3 (LSGM) electrolytes. Dependence of SFMO cathode polarization resistance on the oxygen partial pressure and the cathode overpotentials at different temperatures are also studied. SFMO shows an exchange current density of 0.186 A cm -2 at 800°C in air. Single cells with the configuration of Ni-La 0.4 Ce 0.6 O 2 (LCO)ILCOILSGMISFMO show peak power densities of 349, 468, and 613 mW cm -2 at 750, 800, and 850°C, respectively using H 2 as the fuel and ambient air as the oxidant. These results indicate that SFMO is a promising cathode candidate for intermediate-temperature solid oxide fuel cells with LSGM electrolyte.

Enhancing grain boundary ionic conductivity in mixed ionic-electronic conductors

Mixed ionic–electronic conductors are widely used in devices for energy conversion and storage. Grain boundaries in these materials have nanoscale spatial dimensions, which can generate substantial resistance to ionic transport due to dopant segregation. Here, we report the concept of targeted phase formation in a Ce0.8Gd0.2O2−δ–CoFe2O4 composite that serves to enhance the grain boundary ionic conductivity. Using transmission electron microscopy and spectroscopy approaches, we probe the grain boundary charge distribution and chemical environments altered by the phase reaction between the two constituents. The formation of an emergent phase successfully avoids segregation of the Gd dopant and depletion of oxygen vacancies at the Ce0.8Gd0.2O2−δ–Ce0.8Gd0.2O2−δ grain boundary. This results in superior grain boundary ionic conductivity as demonstrated by the enhanced oxygen permeation flux. This work illustrates the control of mesoscale level transport properties in mixed ionic–electronic conductor composites through processing induced modifications of the grain boundary defect distribution.

Direct synthesis of methane from CO2–H2O co-electrolysis in tubular solid oxide electrolysis cells

Directly converting CO2 to hydrocarbons offers a potential route for carbon-neutral energy technologies. Here we report a novel design, integrating the high-temperature CO2–H2O co-electrolysis and low-temperature Fischer–Tropsch synthesis in a single tubular unit, for the direct synthesis of methane from CO2 with a substantial yield of 11.84%.

Preparation of Nd-doped BaCeO3 proton-conducting ceramic and its electrical properties in different atmospheres

Abstract Nd-doped BaCeO 3 was prepared by a conventional ceramic processing technique using a special procedure to reduce calcining and sintering temperatures and to avoid possible contamination. BaCe 0.9 Nd 0.1 O 3 − α single perovskite phase was formed when the mixture powders was calcined at T ≥1000 °C. Ball-milling of the calcined powders could well disperse agglomerates. Sintered at T ≥ 1300 °C, specimens with density ≥ 93% of the theoretical and without open porosity could be obtained. Electrical conductivity was measured in different dry atmospheres of Ar, air and O 2 and in moist air. The results showed that in dry Ar, air and O 2 , the conductivity values at a given temperature were similar, and the activation energies almost identical, possibly because Nd-doped BaCeO 3 demonstrated predominately oxygen ion conduction in these environments. In moist air, proton conduction might predominate, leading to an increase in conductivity and a decrease in activation energy.