Ni-SDC Cermet Research Articles

Electrode properties of doped Pr<sub>2</sub>NiO<sub>4</sub>-based oxide cathode for intermediate-temperature SOFCs

K2NiF4-type Pr2NiO4 doped with Cu, Cu–Ga, or Co (Pr2Ni0.9Cu0.1O4, Pr2Ni0.75Cu0.25O4, Pr1.91Ni0.71Cu0.24Ga0.05O4, or Pr2Ni0.9Co0.1O4) were synthesized by a solid-state reaction for use as cathodes in an intermediate-temperature (500–700°C) solid oxide fuel cell (IT-SOFC). Pr2NiO4, Pr2Ni0.9Cu0.1O4, Pr2Ni0.75Cu0.25O4, Pr1.91Ni0.71Cu0.24Ga0.05O4, and Pr2Ni0.9Co0.1O4 crystallize in the space group Bmab. Single test cells with samarium oxide doped ceria (SDC) as the electrolyte, Ni-SDC cermet as the anode, and the above-mentioned cathode material were fabricated for cell performance measurements at 700°C. Current interruption measurements and electrochemical impedance spectroscopic analysis revealed that the cathode properties of Pr2NiO4, Pr2Ni0.9Cu0.1O4, Pr2Ni0.75Cu0.25O4, and Pr1.91Ni0.71Cu0.24Ga0.05O4 were comparable to that of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and the cathode properties of Pr2NiO4 were improved by doping with Cu or Cu–Ga at the Ni site of Pr2NiO4.

Improved power generation performance of solid oxide fuel cells using doped LaGaO3 electrolyte films prepared by screen printing method II. Optimization of Ni–Ce0.8Sm0.2O1.9 cermet anode support

A Ni and Sm-doped ceria (Ce0.8Sm0.2O1.9, SDC) cermet anode as a porous support of doped LaGaO3 film prepared by a wet coating and co-firing process was investigated. Different preparation methods and compositions were used to improve the power density of intermediate temperature solid oxide fuel cells. NiO–SDC precursor powder with fine particles and a porous microstructure with high surface area was synthesized by a modified impregnation method and compared with that synthesized by a ball milling method. In addition, an open circuit voltage, which is almost equal to the theoretical value of 1.1 V, and maximum power densities of 835, 277, and 67 mW cm−2 at 700, 600, and 500 °C, respectively, were achieved on a single cell supported by a 75 wt% Ni–SDC cermet anode when a 60 μm thick Sr- and Mg-doped lanthanum gallate (LSGM) electrolyte was used. The improved power density was explained by the enlarged reaction area for the anode as a result of the low polarization resistance of the anode by high porosity and uniform distribution of Ni and SDC particles. Although a small amount of Ni diffused to the interface between the La-doped ceria (LDC) buffer layer and the LSGM electrolyte film, an adverse reaction that deteriorates cell performance seemed to be suppressed, and thus, reasonably high power density was achieved on the cell using the LSGM film prepared by the screen printing method with optimization of the anode substrate structure and composition.

Influence of Tertiary Phases Incorporated into Ni-Based Cermets by Solution Precursor Plasma Spraying (SPPS) on Anode Stability

The Solution Precursor Plasma Spray (SPPS) process was successfully used to deposit cermet coatings which exhibit fine microstructures with high surface area. MgO addition in Ni-YSZ and Ni-SDC cermets results in the solid solution (Ni,Mg)O formation, and nickel particles are finer than without magnesia. In contrast, small tin additions do not influence the microstructure. Influences of MgO and Sn on the chemical stability of cermets in anodic operating conditions are also discussed. It was found that MgO addition helps to prevent carbon deposition, whereas tin does not influence its rate.

Electro-catalytic activity of Dy2O3 as a solid oxide fuel cell anode material

Cermet anodes composed of Ni and Dy2O3 have been applied as anode for intermediate-temperature solid oxide fuel cells. Although the oxide ion conductivity of Dy2O3 is negligible compared to that of doped ceria (DCO), Ni–Dy2O3 cermet anodes have displayed very high performance comparable to that of the commonly used Ni–SDC cermet anode. Temperature programmed reduction study suggests that the catalytic activity of the Ni–Dy2O3 cermet might be originated from the hydrogen adsorption ability on the Dy2O3 surface, promoting hydrogen spillover process, and consequently enhancing the electrochemical oxidation of the fuel. Further, the electrochemical catalytic activity of Au-based cermet anode confirms that hydrogen adsorption capability is as important as oxygen-ion conductivity for the ceramic component in a cermet anode.

Electrode Properties of the Ruddlesden–Popper Series, Lan+1NinO3n+1 (n=1, 2, and 3), as Intermediate‐Temperature Solid Oxide Fuel Cells

The Ruddlesden–Popper phases, Lan+1NinO3n+1 (n=1, 2, and 3), were synthesized by a solid‐state reaction for use as cathodes in an intermediate‐temperature (500°–700°C) solid oxide fuel cell. The samples crystallized into an orthorhombic layered perovskite structure. The overall electrical conductivity increased with the increase of n in the intermediate temperature range. Single test‐cells, which consisted of samarium‐oxide‐doped ceria (SDC; Sm0.2Ce0.8Ox) as an electrolyte, Ni–SDC cermet (Ni–SDC) as an anode, and Lan+1NinO3n+1 as a cathode, were fabricated for measurements of cell performance at 500°–700°C. Current interruption measurements revealed that both the ohmic and overpotential losses at 700°C decreased with the increase of n. La4Ni3O10 was found to exhibit the best cathode characteristics in the Lan+1NinO3n+1 series. Maximum test‐cell power densities with La4Ni3O10 (n=3) were 10.2, 36.5, and 88.2 mW/cm2 at 500°, 600°, and 700°C, respectively.

Self-rising synthesis of Ni–SDC cermets as anodes for solid oxide fuel cells

Ni–SDC cermets have been obtained using a self-rising approach by two different ways, one-step direct synthesis (OS) and ball milling the separately prepared NiO and SDC powders (BM). The results showed that self-rising approach was an efficient way for the synthesis of porous materials composed of evenly distributed uniform size nanocrystals. The as-synthesized powders have been applied as anodes for solid oxide fuel cells, whose electrochemical properties have been systematically studied. Cells with anodes from the BM method showed better performance compared with those of the OS method, achieving a maximum power density of 400 mW cm −2 at 600 °C.

The Effect of Particle Size on the Microstructure and the Effective Reaction Zone of SOFC Cermet Anodes

Ni-SDC cermet SOFC anodes with different microstructures were prepared and the overpotential and the ohmic loss were measured. Anodes with coarse particles and small pores showed intermediate performance and little dependence on flow rate, whereas that with large pores showed a large dependence on flow rate and high performance at high flow rate. Anodes with fine particles showed lowest overpotential at low current density. Ohmic loss was large for the thick electrode with small pores, and for that with large pores, when flow rate was low. It is considered that different particle size and pore size lead to the difference in effective reaction zone, thus showing different dependence to the flow rate.

Microstructural Characteristics of SDC Electrolyte Film Supported by Ni–SDC Cermet Anode

As a promising electrolyte material for intermediate-temperature solid oxide fuel cells operated at a temperature of , a (SDC) film supported by a Ni–SDC cermet anode was prepared through electrophoretic deposition. Detailed microstructural features of the electrolyte film were studied. In the region away from the interface, the microstructure of the SDC film is similar to that of the SDC bulk sample, containing nanosized domains embedded in a fluorite matrix. However, in the region near the interface, the diffusion of Ni from the cermet anode to the electrolyte film was observed with a depth of about . Furthermore, the reduction in Ce and a high degree of oxygen vacancy ordering can be noticed in the interfacial region at the electrolyte side. It is suggested that these microstructural features could have negative impacts on the ionic conductivity of the electrolyte films.

Reaction Process in the Ni-SDC Cermet Anode

The reaction process for the Ni-SDC cermet anode on the ScSZ electrolyte was examined by impedance spectrometry with wet hydrogen fuels and results were compared with previously obtained data for the Ni-ScSZ anode. Area specific conductivities (σSDC) for each rate controlling steps were obtained from the impedance spectra. Hydrogen and water vapor pressure (PH2 and PH2O, respectively) dependencies and temperature (T) dependence of σ for the Ni-SDC are compared with those of the Ni-ScSZ. Three rate controlling steps were observed for the Ni-SDC anode. The σSDC obtained at the lowest frequency region (σLSDC) shows slightly negative dependence on the T and it was proportional to the PH2O. The σMSDC obtained in the middle frequency region is activated with increasing PH2, PH2O and T. This process should be associated with the electrochemical oxidation reaction step accompanied with charge transfer. The σHSDC obtained at the highest frequency region is independent on both PH2 and PH2O, but it is activated with increasing temperature. This process appears only in the Ni-SDC anode, and therefore, it is reasonable to assume formation of proton at the Ni/SDC interface. The difference in reaction processes between the Ni-SDC anode and the Ni-ScSZ anode is discussed.

Steam reforming on Ni-samaria-doped ceria cermet anode for practical size solid oxide fuel cell at intermediate temperatures

Direct internal and external reforming operations on Ni-samaria-doped ceria (SDC) anode with the practical size solid oxide fuel cell (SOFC) at intermediate temperatures from 600 to 750 °C are carried out to reveal the reforming activities and the electrochemical activities, being compared with the hydrogen-fueled power generation. The cell performance with direct internal and external steam reforming of methane and their limiting current densities were almost the same irrespective of the progress of reaction in the methane reformate at 700 and 750 °C. The durability test for 5.5 h at 750 °C with direct internal reforming operation confirmed that the cell performance did not deteriorate. The operation temperature of the cell controlled the reforming activities on the anode, and the large size electrode gave rise to high conversion due to the slow space velocity of the steam reforming. Direct internal steam reforming attained sufficient level of conversion for SOFC power generation with methane at 700 and 750 °C on the large Ni-SDC cermet anode.

Microstructure and Effective Thickness of Cermet Anode for SOFC

The effective thickness or the active thickness of Ni-SDC cermet SOFC anode was investigated for two types of anode with different microstructure. One was prepared by using large particle, and the other by small particle. The performance of each cells were measured for various anode thickness. The performance of the anode increased by increasing the anode thickness when prepared by large particles. The dependence of the anode thickness was as large as 120μm. On the other hand, the anode prepared by small particles showed little dependence on anode thickness. This large effective thickness of the electrode was achieved probably due to the high sintering temperature. Although this structure may not be typical, it indicates an alternative method for the improvement of the anodic performance of SOFC.

Direct Internal Steam Reforming at SOFC with Anode Prepared Using NiO-SDC Composite Particles

The dependence of anode catalytic activities on the fuel species and the operating temperatures was investigated for use in the direct internal steam-reformed power generation. The SOFCs employing Ni-SDC cermet anode fabricated from the NiO-SDC composite particles were operated in the temperature range of 700-1000{degree sign}C by feeding the humidified hydrogen and methane as fuels. The cell performances with humidified hydrogen fuel were higher than those with humidified methane fuel at every operation temperature. The performances at 700 and 800{degree sign}C were much lower than that at 1000{degree sign}C when the humidified methane fuel was supplied. Considering the results of the electrochemical characterization and the microstructural observation of anode, the methane conversion and the deposited carbon appeared to significantly affect the cell performances.

Double Layer-Type Electrodes for Reversible Solid Oxide Fuel Cells

We have developed double layer-type (catalyst layer/current collecting layer) electrodes for reversible SOFCs operating at medium-temperature. As the H2 catalyst layer (anode for SOFC and cathode for steam electrolysis) interfaced with YSZ solid electrolyte, mixed conducting samaria-doped ceria (CeO2)0.8 (SmO1.5)0.2 particles were employed in combination with Ni metal electrocatalysts (10 to 20 vol.% of nanometer-size Ni) highly dispersed on their surfaces. The current collecting porous layer of Ni-SDC cermet (60 vol.% of micrometer-size Ni) was formed on the catalyst layer. The H2-electrode with 10 vol.% Ni in the catalyst layer exhibited high performance, due to the effective enhancement of the reaction rate by increasing both the active reaction sites and the electronic conductance.

Studies on synthetic conditions of spray pyrolysis by acids addition for development of highly active Ni-SDC cermet anode

NiO-Ce 0.8Sm 0.2O 1.9 (SDC) composite particles were synthesized by spray pyrolysis method using the starting solutions containing the components for NiO-SDC and various amounts of nitric acid or acetic acid. It was found that the particles had the smooth surface due to the presence of the dissociated acetic acid in the starting solution and the large specific surface area due to the presence of the nitrate ion in the starting solution. SOFC single cell performance using the composite particles for an anode was examined at the operating temperature of 750 °C to clarify the relationship between particle morphology and cell performance. The NiO-SDC composite particles which had smooth surfaces with large specific surface areas gave reproducibly high SOFC performances. It was considered that the morphologies and the specific surface areas of NiO-SDC composite particles played an important role of realizing a high performance anode.

Chemical and redox stabilities of a solid oxide fuel cell with BaCe 0.8Y 0.2O 3− α functioning as an electrolyte and as an anode

The operation of a solid oxide fuel cell (SOFC) based on BaCe 0.8Y 0.2O 3− α (BCY20) at 800 °C was studied without using an anode material. A porous, Ce-rich phase with a fluorite structure was formed at a depth of approximately 10 μm from the BCY20 surface by heat treatment at 1700 °C. This was due to the vaporization of BaO from the BCY20 surface. This treatment improved the cell performance and chemical stability to CO 2 because the Ce-rich phase functioned as an electrically conducting and protective layer. The heat-treated BCY20 also had better chemical and redox stabilities over a Ni–Ce 0.8Sm 0.2O 1.9 (SDC) cermet anode attached to the SDC electrolyte. The cell with the heat-treated BCY20 operated well on unhumidified methane, ethane, propane, and butane without carbon deposition, while the cell with the Ni–SDC cermet anode degraded within a few hours. Moreover, the BCY20 showed higher tolerance to 10 ppm H 2S and stability over 20 times redox cycling in comparison to the Ni–SDC cermet anode.

The impact of NiO on microstructure and electrical property of solid oxide fuel cell anode

Ni-Ce(0.8)Sm(0.2)O(1.9) (Ni-SDC) cermet was selected as anode material for reduced temperature (800 degrees C) solid oxide fuel cells in this study. The influence of NiO powder fabrication methods for Ni-SDC cermets on the electrode performance was investigated so that the result obtained can be applied to make high-quality anode. Three kinds of NiO powder were synthesized with a fourth kind being available in the market. Four types of anode precursors were fabricated with these NiO powders and Ce(0.8)Sm(0.2)O(1.9) (SDC), and then were reduced to anode wafers for sequencing measurement. The electrical conductivity of the anodes was measured and the effect of microstructure was investigated. It was found that the anode electrical conductivity depends strongly on the NiO powder morphologies, microstructure of the cermet anode and particle sizes, which are decided by NiO powder preparation technique. The highest electrical conductivity is obtained for anode cermets with NiO powder synthesized by NiCO(3).2Ni(OH)(2).4H(2)O or Ni(NO(3))(2).6H(2)O decomposition technique.

Electrochemical performance of gel-cast NiO–SDC composite anodes in low-temperature SOFCs

NiO–Ce 0.8Sm 0.2O 1.9 (SDC) composites were synthesized using gel-casting technique. The electrochemical performance of the gel-cast (GC) Ni–SDC cermet as anode was investigated contrast with that fabricated from traditional mechanical mixing (MM) technique using fuel cells with about 35 μm-thick SDC electrolyte and Sm 0.5Sr 0.5CoO 3–SDC cathode. Maximum power density of the cell with GC anode achieved 491 mW cm −2 at 600 °C, over 100 mW cm −2 larger than that with MM anode, inferring high catalytic activity of the GC anode. Impedance measurements on the fuel cell at open circuit showed that the anodic interfacial polarization resistance of the GC anode was 0.1 Ω cm 2 lower than that of the MM anode. Long-term stability of the cell with GC anode in hydrogen was also performed, which showed that it can stabilize at least 7 days.

Gel-cast NiO–SDC composites as anodes for solid oxide fuel cells

NiO–SDC(Ce 0.8 Sm 0.2 O 1.9 ) composites were synthesized using gel-casting technique with nitrate precursors. The composite oxides were formed after the gels were fired at 350 °C in flowing air. No reaction between NiO and CeO 2 occurs as analyzed using X-ray diffraction (XRD). The average particle size was about 50 nm and specific surface area was 10 m 2 g −1 , when the powder was fired at 900 °C for 2 h. NiO–SDC cermets were prepared by firing the composites at 1350 °C. The electrical conductivities and porosities of the cermets were measured, for example, 360 S cm −1 at 600 °C for a cermet with 30% porosity, 35 vol.% Ni, and 35 vol.% SDC. And the electrochemical performance of Ni–SDC cermet as an anode was investigated using a fuel cell with 25-μm thick SDC electrolyte and Sm 0.5 Sr 0.5 CoO 3 -SDC cathode. Maximum power density was 618 mW cm −2 and 491 mW cm −2 at 650 and 600 °C, respectively, inferring high catalytic activity of the Ni–SDC anode. Impedance measurements on the fuel cell at open circuit showed that the interfacial polarization resistance of the Ni–SDC anode was negligible compared to the resistance of cathode and electrolyte.

Intermediate Temperature Solid Oxide Fuel Cells with Doped Lanthanum Gallate Electrolyte, La(Sr)CoO3 Cathode, and Ni-SDC Cermet Anode

Intermediate Temperature Solid Oxide Fuel Cells with Doped Lanthanum Gallate Electrolyte, La(Sr)CoO3 Cathode, and Ni-SDC Cermet Anode

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 La 0.9Sr 0.1Ga 0.8Mg 0.2O 3− 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.