Guoliang Xiao

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

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.

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.

Effective Ionic Conductivity of a Novel Intermediate-Temperature Mixed Oxide-Ion and Carbonate-Ion Conductor

The discovery of new fast ionic conductors has been long pursued by solid state chemists due to the important roles they play in modern solid state ionic devices. The Sr- and Mg-doped LaGaO3 LSGM perovskite oxide-ion conductor discovered in the mid1990s is a good example illustrating the fruition of years’ of continual efforts in this area. The oxide-ion conductivity of LSGM at 800°C is as high as that of Y2O3-doped ZrO2 at 1000°C and is stable over a broad range of partial pressures of oxygen. As an electrolyte of the solid oxide fuel cell SOFC, these attributes connote higher chemical-to-electrical conversion efficiency or less performance loss at a given temperature and/or reduced operating temperature for a given performance. The latter is of practical importance because lowering the operating temperature of an SOFC could drastically improve the performance stability and reduce the system cost, the two foremost obstacles presently impeding the commercialization of the SOFC technology. The common features of existing good oxide-ion conductors such as ZrO2-, CeO2-, and LaGaO3-based oxides can be characterized by oxygen vacancies available in the lattice and cubic structure of high symmetry. 1-3

Releasing metal catalysts via phase transition: (NiO)0.05-(SrTi0.8Nb0.2O3)0.95 as a redox stable anode material for solid oxide fuel cells.

Donor-doped perovskite-type SrTiO3 experiences stoichiometric changes at high temperatures in different Po2 involving the formation of Sr or Ti-rich impurities. NiO is incorporated into the stoichiometric strontium titanate, SrTi0.8Nb0.2O3-δ (STN), to form an A-site deficient perovskite material, (NiO)0.05-(SrTi0.8Nb0.2O3)0.95 (Ni-STN), for balancing the phase transition. Metallic Ni nanoparticles can be released upon reduction instead of forming undesired secondary phases. This material design introduces a simple catalytic modification method with good compositional control of the ceramic backbones, by which transport property and durability of solid oxide fuel cell anodes are largely determined. Using Ni-STN as anodes for solid oxide fuel cells, enhanced catalytic activity and remarkable stability in redox cycling have been achieved. Electrolyte-supported cells with the cell configuration of Ni-STN-SDC anode, La0.8Sr0.2Ga0.87Mg0.13O3 (LSGM) electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode produce peak power densities of 612, 794, and 922 mW cm(-2) at 800, 850, and 900 °C, respectively, using H2 as the fuel and air as the oxidant. Minor degradation in fuel cell performance resulted from redox cycling can be recovered upon operating the fuel cells in H2. Such property makes Ni-STN a promising regenerative anode candidate for solid oxide fuel cells.

La0.7Sr0.3Fe0.7Ga0.3O3−δ as electrode material for a symmetrical solid oxide fuel cell

In this research, La0.7Sr0.3Fe0.7Ga0.3O3−δ (LSFG) perovskite oxide was successfully prepared using a microwave-assisted combustion method, and employed as both anode and cathode in symmetrical solid oxide fuel cells. A maximum power density of 489 mW cm−2 was achieved at 800 °C with wet H2 as the fuel and ambient air as the oxidant in a single cell with the configuration LSFG|La0.8Sr0.2Ga0.83Mg0.17O3−δ|LSFG. Furthermore, the cells demonstrated good stability in H2 and acceptable sulfur tolerance.

Enhanced reducibility and conductivity of Na/K-doped SrTi0.8Nb0.2O3

Donor and acceptor co-doped SrTiO3 materials have shown interesting features in their conductivity and reducibility. In this work, 10 mol% Na+ or K+ as acceptor dopants have been introduced into the A-site of donor-doped strontium titanate, SrTi0.8Nb0.2O3, and the doping impact on their properties has been studied. By doping with Na or K, the sinterability of SrTi0.8Nb0.2O3 in reducing atmospheres has been improved. Na0.1Sr0.9Ti0.8Nb0.2O3 and K0.1Sr0.9Ti0.8Nb0.2O3 show metallic conduction behavior after being sintered at 1400 °C in 5% H2/N2. Electrical conductivity reaches 1180 S cm−1 at 400 °C and 272 S cm−1 at 800 °C for K0.1Sr0.9Ti0.8Nb0.2O3, which is higher than that of Sr0.99Ti0.8Nb0.2O3 prepared under similar conditions, indicating the improved reducibility of acceptor doped SrTi0.8Nb0.2O3. Such improvement may be attributed to the improved oxide ionic conductivity and cation mobility at high temperatures. Reduced polarization resistance is also observed using Na0.1Sr0.9Ti0.8Nb0.2O3 and K0.1Sr0.9Ti0.8Nb0.2O3 as anodes on YSZ electrolytes, suggesting improved catalytic activity by Na/K-doping.

Mixed Oxide-Ion and Carbonate-Ion Conductors (MOCCs) as Electrolyte Materials for Solid Oxide Fuel Cells

A solid oxide fuel cell (SOFC) operating in the temperature window of 600-700C has long been pursued by the worldwide SOFC developers for it has the greatest potential to be developed into a commercial product. Not only does the stability of materials improve significantly in this intermediate temperature range, but also the cost can be reduced while still maintaining high energy efficiency by integrating the endothermic reformer with the exothermic SOFC stack. To reduce the operating temperature of a SOFC, two parallel approaches have been practiced in the past: making the electrolyte layer thinner and searching for new electrolyte materials with higher oxide-ion conductivity. In this presentation, we report a mixed oxide-ion and carbonate-ion conductor (MOCC) having a total ionic conductivity of ~0.25 S/cm at 650C. The MOCC is comprised of a solid oxide phase and a liquid carbonate phase. The solid oxide phase serves as an oxide-ion conductor with a welldefined porous structure, in which the liquid carbonate-ion conductor is filled and immobilized. It is highly expected that this kind of MOCC finds potential applications in fuel cells and CO2 separation/capture. A systematic characterization of microstructures, phase compositions, thermal and electrical properties of the developed MOCC is described. Excellent electrical performance of a fuel cell based on a MOCC electrolyte operating at 650C is also presented with CO2 and O2 as well as air as the oxidants and H2 as the fuel. ∗ To whom correspondence should be addressed: kevin.huang@sc.edu Abstract #1156, 218th ECS Meeting,