Xinge Zhang

Ni-SDC cermet anode for medium-temperature solid oxide fuel cell with lanthanum gallate electrolyte

The polarization properties and microstructure of Ni-SDC (samaria-doped ceria) cermet anodes prepared from spray pyrolysis (SP) composite powder, and element interface diffusion between the anode and a La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) electrolyte are investigated as a function of anode sintering temperature. The anode sintered at 1250°C displays minimum anode polarization (with anode ohmic loss), while the anode prepared at 1300°C has the best electrochemical overpotential, viz., 27 mV at 300 mA cm−2 operating at 800°C. The anode ohmic loss gradually increases with increase in the sintering temperature at levels below 1300°C, and sharply increases at 1350°C. Electron micrographs show a clear grain growth at sintering temperatures higher than 1300°C. The anode microstructure appears to be optimized at 1300°C, in which nickel particles form a network with well-connected SDC particles finely distributed over the surfaces of the nickel particles. The anode sintered at 1350°C has severe grain growth and an apparent interface diffusion of nickel from the anode to the electrolyte. The nickel interface diffusion is assumed to be the main reason for the increment in ohmic loss, and the resulting loss in anode performance. The findings suggest that sintering Ni-SDC composite powder near 1250°C is the best method to prepare the anode on a LSGM electrolyte.

High performance electrodes for reduced temperature solid oxide fuel cells with doped lanthanum gallate electrolyte I. Ni-SDC cermet anode

The reduced temperature solid oxide fuel cell (SOFC) with 0.5 mm thick La0.9Sr0.1Ga0.8Mg0.2O3−α (LSGM) electrolyte, La0.6Sr0.4CoO3−δ (LSCo) cathode, and Ni-(CeO2)0.8(SmO1.5)0.2 (SDC) cermet anode showed an excellent initial performance, and high maximum power density, 0.47 W/cm2, at 800°C. The results were comparable to those for the conventional SOFC with yttria-stabilized zirconia (YSZ) electrolyte, La(Sr)MnO3-YSZ cathode and Ni–YSZ cermet anode at 1000°C. Using an LSCo powder prepared by spray pyrolysis, and selecting appropriate sintering temperatures, the lowest cathodic polarization of about 25 mV at 300 mA/cm2 was measured for a cathode prepared by sintering at 1000°C. Life time cell test results, however, showed that the polarization of the LSCo cathode increased with operating time. From EPMA results, this behavior was considered to be related to the interdiffusion of the elements at the cathode/electrolyte interface. Calcination of LSCo powder could be a possible way to suppress this interdiffusion at the interface.

Interface reactions in the NiO–SDC–LSGM system

Abstract The reactivity of NiO–SDC (samaria-doped ceria) anode material with a Sr- and Mg-doped lanthanum gallate (LSGM) electrolyte was studied by X-ray diffraction (XRD) and electrical measurements. It was found that a LaNiO3-based compound in hexagonal structure formed in binary powder mixtures of NiO and LSGM after firing at 1150°C. Reaction between SDC and LSGM was also observed. Several SDC peaks merged with the adjacent LSGM peaks during firing, and a SrLaGa3O7 compound was identified as a reaction product. Reaction between LSGM and SDC could cause more than 50% loss in the ionic conductivity of LSGM–SDC electrolytes sintered at 1350°C. The measured conductivity of an LSGM electrolyte with a NiO–LSGM anode prepared at 1350°C was extremely low, indicating that the LaNiO3-based new phase is highly insulating. The reaction between NiO and SDC was not so obvious in comparison with NiO–LSGM and SDC–LSGM binary mixtures.

Interactions of a La0.9Sr0.1Ga0.8Mg0.2O3−δ electrolyte with Fe2O3, Co2O3 and NiO anode materials

Abstract In this study, the interactions of a Sr- and Mg-doped lanthanum gallate (LSGM with composition La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3− δ ) electrolyte with Fe 2 O 3 , Co 2 O 3 and NiO as the anode starting materials were investigated. It was found that the order of reactivity of the LSGM with the three oxides was Co 2 O 3 >NiO>Fe 2 O 3 , and La-containing oxides were detected in these binary powder mixtures after firing. The anode performance was greatly influenced by the interaction. The Fe 2 O 3 –LSGM anode, mixed with 40 vol.% LSGM powder and sintered at 1150°C, exhibited the highest initial performance in comparison with NiO–LSGM and Co 2 O 3 –LSGM anodes. It seems that Fe 2 O 3 is a possible anode starting material for a LSGM-based solid oxide fuel cell.

Thin Film Solid Oxide Fuel Cells Deposited by Spray Pyrolysis

Two techniques of spray pyrolysis, namely, electrostatic and pneumatic spray deposition, were used to deposit samaria-doped ceria (SDC) electrolyte and lanthanum strontium cobalt ferrite (LSCF) cathode on cermet or metal supported anodes for solid oxide fuel cells (SOFCs) operated at reduced temperature. The deposition processes, the properties of the deposited films, and the electrochemical performances of the fabricated cells are reported in this paper. The deposited SDC electrolytes were dense and gas-tight, and had good adhesion to the underlying anodes. The deposited LSCF cathode had a preferred morphology to facilitate the transport of oxygen gas and effective contact with the electrolyte. Button cell testing indicated that the SOFCs with electrolyte or cathode deposited by spray pyrolysis had good electrochemical performance. This study demonstrated that spray pyrolysis is a cost-effective process for fabricating thin film SOFCs, especially metal supported SOFCs.

Spray Pyrolysis Deposition of Electrolyte and Anode for Metal-Supported Solid Oxide Fuel Cell

Metal-supported solid oxide fuel cells (SOFCs) offer many advantages, including increased robustness, improved thermal shock resistance, and decreased cost. However, fabricating metal-supported SOFCs using conventional techniques is both very difficult and very costly. In this study, two processes of spray pyrolysis deposition, pneumatic spray deposition and electrostatic spray deposition, were used to deposit samaria-doped ceria (SDC) electrolytes on different substrates and NiO-SDC anodes on porous stainless steel substrates. A cathode layer was subsequently applied on the electrolyte by stencil printing for electrochemical testing. The test results indicated that the electrolyte had reasonable cell performance, but the topography of the anode needed optimization. It was also discovered that the porous ferritic stainless steel 430 substrate used in this study did not have sufficient oxidation resistance as the substrate of a metal-supported SOFC.

Enhancement of Solid Oxide Fuel Cell Performance by La0.6Sr0.4Co0.2Fe0.8O3 − δ Double-Layer Cathode

NiO-Sm 0.2 Ce 0.8 O 19 (SDO/SDC/La 0.6 Si 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) cells with either a single-layer or a double-layer cathode were fabricated and tested. The single-layer LSCF cathode was made by stencil printing, while the double-layer cathode was prepared by depositing a thin porous layer on the SDC electrolyte using electrostatic spray deposition (ESD) before stencil printing. The cells were tested with moist hydrogen as fuel and air as oxidant. The maximum power density increased from 0.81 to 0.91 W cm -2 at 650°C and 1.04-1.18 W cm -2 at 700°C when the ESD-LSCF layer was introduced. The interfacial area specific resistances (ASRs) of electrodes for both cells were also measured under open-circuit condition. In comparison to that in the single-layer cathode cell, the electrode ASRs were reduced to half with the addition of the ESD-LSCF cathode layer.

Preparation and Characterization of Nanocrystalline Ba2In2 − x M x O5 − δ ( M = Ce , Zr )

Nanocrystalline, oxygen-deficient perovskite materials-Ce-doped Ba 2 In 2 O 5-δ (BIC) and Zr-doped Ba 2 In 2 O 5-δ (BIZ) powders-have been successfully synthesized via reactive spray deposition technique processing. The mean particle size, surface areas, and phases of BIC and BIZ powders were analyzed. The transmission electron microscopy images showed a particle size of ∼ 10 nm and the existence of nanopowder agglomeration. The sintering studies of the nanopowders of BIC and BIZ indicated that the grain size increases significantly with calcining temperatures beyond 1250°C. The BIC sintered at 1250°C showed much higher electrical conductivities than that sintered at 1500°C.

Development Status of SOFC Cell and Stack Technology at NRC-IFCI

Solid Oxide Fuel Cell (SOFC) development was started at the National Research Council of Canada’s Institute for Fuel Cell Innovation (NRCIFCI) in 2003 with the goal to develop the next generation of SOFC’s for Canadian Industry. To accomplish this task, work focused on the development of low temperature cermet and metal supported cells, direct deposition methods, low temperature sintering, seal and stack technology. As of November 2006, 5 cm x 5 cm cermet supported cell performance has been improved to 900 mW/cm at 600°C. These components have been incorporated into short stacks developed at IFCI to continue the push to commercialize this technology. At the same time, direct deposition technology has progressed rapidly to the point where metal supported 5 x 5 cells can be fabricated using sintering temperatures below 850°C. Results of this work will be presented, along with the development path at IFCI.