Ni-YSZ cermet is commonly used as the anode of a solid oxide fuel cell (SOFC) because it has excellent electrochemical performance and is a cost effective anode material for coal-syngas fuel. However, coal-syngas contains trace contaminants, such as phosphine (PH 3 ), hydrogen sulfur (H 2 S), arsine (AsH 3 ) and stibine (SbH 3 ), and these can cause degradation of the SOFC. Ni-YSZ anode-supported SOFCs were exposed to syngas and H 2 fuel, while co-feeding PH 3 and chlorine Cl 2 impurities under a constant current load at 800°C. The cell degradation was postponed in syngas and highly mitigated in H 2 . In another test, a Ni-based filter was used to remove the PH 3 impurity. The results show that the filter can effectively remove 20 ppm PH 3 to a level which does not significantly degrade the SOFC over 400 h. The poisoning effects were evaluated by current-voltage scans and impedance spectroscopy, in addition to thermodynamic and chemical analyses. The post-mortem analyses of the cell and filter were performed by means of XRD and SEM/EDS.

Biogas is a renewable resource which comes from numerous sources, such as biomass, manure, sewage, municipal waste, green waste and energy crops. It is a variable mixture of CH 4 , CO 2 , N 2 and other gases. Ni-YSZ cermet is commonly used as the anode of a solid oxide fuel cell (SOFC) because it has excellent electrochemical performance and is cost effective. It can utilize not only hydrogen fuel, but also a clean synthesized biogas mixture of varying CH 4 and CO 2 concentrations with steam (H 2 O) and air (O 2 ). However, trace impurities, such as H 2 S, Cl 2 , and F 2 in biogas may cause degradation of cell performance. In this work, Ni-CeO 2 coated Ni-YSZ anode-supported cells were exposed to two different compositions of synthesized biogases (biogas) with 100 ppm Cl 2 under a constant current load at 850°C. The electrochemical performance was evaluated periodically using standard electrochemical methods. 20 ppm H 2 S impurity was also added to the fuel stream during the Cl 2 impurity testing and its effect was noted. Post-mortem analyses of the SOFC anode were performed using XRD, SEM and XPS. The results show that Cl 2 did not cause any electrochemical degradation of the cell during the 200 h test. However, after adding 20 ppm H 2 S, the cell started to degrade and eventually lost all its performance. The experimental data showed that 100 ppm Cl 2 impurity in the fuel gas can postpone the degradation caused by addition of the H 2 S impurity.

The mechanical properties of Ni-YSZ cermets at high temperature in reduction atmosphere were evaluated by the four points bending method. We studied the influences of reduction and thermal cycles, i.e. a cycle from R.T. to 800°C, to flexural strength and Young’s modulus. The flexural strength of Ni-YSZ at room temperature was lower than that of NiO-YSZ by about 10 to 20% mainly caused by the increment of porosity. But, the flexural strength of Ni-YSZ at 800°C was drastically decreased by an half of that at R.T. In addition, the stress–strain diagram of Ni-YSZ at 800°C indicated that it showed weak ductility. The maximum observed strain was over 0.5% at 30MPa. On the contrary, NiO-YSZ showed only brittlely at 800°C. The difference was caused by Ni metal in the Ni-YSZ cermets. Therefore, it was expected that Ni-YSZ is easily deformed in operation, though residual stress between an anode and an electrolyte was low. The influence of thermal cycles to flexural strength and Young’s modulus was not observed clearly. At the same time, the differences of microstructure were not observed. Therefore, it was concluded that the cycle does not change mechanical properties significantly.

The change in electrical conductivity of Ni-YSZ cermet used for the solid oxide fuel cell (SOFC) anode was investigated under methane, ethylene and n-butane feeding. Rectangular-shaped pellets have been prepared and exposed to gaseous mixtures including hydrocarbons and nitrogen with or without steam at 750 °C. In the absence of steam, carbon deposition occurred in the Ni-YSZ pellets and consequently the electrical conductivity decreased exponentially. When steam was fed (steam to carbon ratio = 2) to make carbon formation thermodynamically unfavorable, the electrical conductivity was kept constant, except for supplying butane. The effect of the mole fraction of methane on the change of electrical conductivity was also investigated in the CH 4 -N 2 system. When the molar concentration was increased, the rate of decrease of electrical conductivity was increased. The present study helps to understand the effect of carbon deposition on the electrical conductivity of Ni-YSZ anode.

This study explores the incorporation of ceria (CeO 2 ) into Ni/YSZ cermet anodes for solid oxide fuel cell performance with both syngas and n-butane/steam feeds to suppress carbon deposits and expand operability of Ni-based anodes with carbonaceous fuel feeds. CeO 2 was co-fired with Ni/YSZ cermets to form a porous anode support layer (1 mm thick), which was tested in SOFC button cells with dense YSZ electrolytes (10–20 μm thick) and porous LSM/YSZ cathodes (∼50 μm thick). The co-fired Ni/CeO 2 /YSZ anode-supported cells were tested from 700 to 800 °C on various fuels including syngas and n-butane with H 2 O added at a 1.5-to-1 and a 1-to-1 steam-to-carbon (S/C) ratio. Electrochemical characterization revealed that CeO 2 addition provided stable performance with high power densities at 800 °C — up to 0.6 W/cm 2 on syngas and 0.35 W/cm 2 on direct butane feeds — without significant carbon deposition as observed for Ni/YSZ anodes without CeO 2 . Testing with syngas at different H 2 and CO partial pressures indicated that high power densities can be maintained along an anode channel for up to 50% fuel conversion. The results indicate that CeO 2 addition to Ni/YSZ may provide a viable means for stable SOFC operation on either pre-reformed or direct light-hydrocarbon fuel feeds.

Micro-tubular Solid Oxide Fuel Cells (SOFCs) are fabricated and tested for analysis of electrochemical properties. The impedance spectra from individual 1.8 mm diameter, 1.2 cm length micro-tubular SOFCs are obtained for the intermediate temperature range of 450–550°C. The micro-tubular SOFC used is anode supported, consisting of a NiO and Gd 0.2 Ce 0.8 O 2−x (GDC) cermet anode, thin GDC electrolyte, and a La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−y (LSCF) and GDC composite cathode. The impedance information gained at cell operating temperatures of 450, 500, and 550°C yielded power density losses of 0.8, 2.3, and 4.6% respectively. Within the operating temperature range of 450–550 °C, the ceria based 1.8 mm micro-tubular SOFCs were found to have a power densities ranging between 180–740 mW/cm 2 .

Manufacturing cost remains one of the major issues facing the solid oxide fuel cell (SOFC) industry. In the anode supported SOFC design, the cermet anode constitutes around 90% of the total material required to build a cell, making the technology very sensitive to anode raw material price. A new patent-pending process called “nickel yttria reaction-sintered zirconia (NiYRSZ)” has been developed for manufacturing SOFC anodes at a fraction of the cost. Typically, the solid component of the anode consists of about 50/50 volume percent nickel and 8 mole percent yttria stabilized zirconia, the latter being a rather costly material. It was discovered that zirconia and yttria powders sintered in the presence of nickel oxide readily form the cubic phase at moderate temperature. Cells manufactured using this process show excellent microstructures for anode supports: a strong bond between the electrolyte and the anode, and a high porosity without addition of pore formers. The strength of the anode was 100 MPa making the material equivalent or slightly superior to an anode fabricated with the traditional NiO/8YSZ material of similar porosity. The resistivity of the material was measured at 850°C and found to be less than 2 mΩ·cm. Cell performance was also compared to cells manufactured with traditional material. Every indication is that SOFC anodes fabricated with this new method perform as well as anodes made with the conventional material set.

A simple and mass productive extrusion technique was applied to fabricate anode-supported micro-tubular solid oxide fuel cells (SOFCs). A standard NiO/8YSZ (Nickel oxide/8 mol % yttria stabilized zirconia) cermets anode, 8 YSZ electrolyte, and LSM (Lanthanum strontium manganite) cathode were used as the materials components. SEM (secondary electron microscopy) images indicated vacuum infiltration method successfully generated the thin electrolyte layer (10∼15 μm) with a structurally effective three phase boundaries. Fabricated unit cell showed the open circuit voltage of 1.12 V without any fuel leaking problems. Electrochemical tests showed a maximum power density up to 0.30 W/cm 2 at 800 °C, implying the excellent performance as micro-tubular SOFCs. This study verified that the extrusion aided by vacuum infiltration process could be a promising technique for mass production of microtubualr SOFCs.

Ceramic reactors, which convert materials and energy electrochemically, are expected to solve various environmental problems, and use of micro reactor design was shown to realize high performance reactor with high thermal durability operable at lower temperatures. Our research project “Advanced Ceramic Reactor” supported by NEDO targets to develop new fabrication technology for such micro reactors and modules using conventional, commercially available materials. In this study, fabrication technology of micro tubular ceramic reactors have been investigated for aiming solid oxide fuel cells (SOFCs) application, such as small distributed power generators, APU for vehicles, and portable power sources. So far, micro tubular SOFCs under 1 mm diam. using doped ceria electrolyte and Ni-ceria based cermet for tubular support has been successfully developed and evaluated. The single micro tubular SOFC showed cell performance of 0.46 W/cm 2 (@0.7 V) at 550 °C with H 2 fuel. Bundle design for such tubular cell was also proposed and fabricated. Discussion will cover fabrication technology of single tubular SOFC and bundle, and optimization of the cell and bundle design by considering gas pressure loss and current collecting loss.

Ni/YSZ cermet anode is required to simultaneously satisfy various properties as a key component of anode-supported type SOFC, since the cell performance is highly dependent upon anode properties. Ni/YSZ anode, with complicated structural features, consists of three different phases such as metallic Ni, YSZ ceramic and pores. Furthermore, the correlation between those structural features makes it difficult to independently optimize individual function of anode such as gas permeability, electrical conductivity and electrochemical activity. Thus, a great deal of efforts to establish structure-property-processing correlation has been made in this study in order to achieve improved anode performance. Critical process steps in anode fabrication were investigated in terms of raw material selection, mixing and granulation, and forming, judging from the performance evaluation of anode substrate. An optimized fabrication process, enabling to produce thin and large-area anode substrate with improved uniformity, will be presented with respect to multifunctional performance of Ni/YSZ anode, and resulting cell performance will be also discussed.

An experimental study is under way to assess the performance of solid-oxide cells operating in the steam electrolysis mode for hydrogen production over a temperature range of 800 to 900°C. Results presented in this paper were obtained from a ten-cell planar electrolysis stack, with an active area of 64 cm 2 per cell. The electrolysis cells are electrolyte-supported, with scandia-stabilized zirconia electrolytes (∼140 μm thick), nickel-cermet steam/hydrogen electrodes, and manganite air-side electrodes. The metallic interconnect plates are fabricated from ferritic stainless steel. The experiments were performed over a range of steam inlet mole fractions (0.1–0.6), gas flow rates (1000–4000 sccm), and current densities (0 to 0.38 A/cm 2 ). Steam consumption rates associated with electrolysis were measured directly using inlet and outlet dewpoint instrumentation. Cell operating potentials and cell current were varied using a programmable power supply. Hydrogen production rates up to 100 Normal liters per hour were demonstrated. Values of area-specific resistance and stack internal temperatures are presented as a function of current density. Stack performance is shown to be dependent on inlet steam flow rate.

Solid oxide fuel cell (SOFC) works at high temperature and is normally used in stationary devices which are of wide interest in the world market. The most currently SOFC developers utilize yttria-stabilized zirconia (YSZ) as electrolyte, strontium-doped lanthanum manganite (LSM) as cathode and a Ni/YSZ cermet obtained from NiO/YSZ in situ reduction as anode. The electrode performance is directly influenced by powder grain sizes, homogeneity, purity, and amount of Ni. Although physical mixture is a simpler procedure it hardly gives homogeneous materials as suitable to SOFC applications. Alternative chemical methods are sol-gel, impregnation and those derived from Pechini route. The present work compares thermal stability and hydrogen reducibility of NiO/YSZ composites prepared by impregnation (I), Pechini (P) and physical mixture (PM) procedures.