Kenji Murata

Morphology Control of Ni-YSZ Cermet Anode for Lower Temperature Operation of SOFCs

Abstract A NiO–Y2O3 stabilized ZrO2 (YSZ) composite particles for solid oxide fuel cell (SOFC) anode was fabricated by advanced mechanical method in dry process. The processed powder achieved better homogeneity of NiO and YSZ particles, where submicron NiO particles were covered with finer YSZ particles. A Ni–YSZ cermet anode fabricated from the NiO–YSZ composite particles showed the porous structure in which Ni and YSZ grains of less than several hundred nano-meter as well as micron-size pores were uniformly dispersed. The cermet anode achieved high electrical performance at low temperature operation (

Direct EPD of YSZ Electrolyte Film onto Porous NiO-YSZ Composite Substrate for Reduced-Temperature Operating Anode-Supported SOFC

Electrophoretic deposition (EPD) was used for the fabrication of anode-supported yttria-stabilized zirconia (YSZ) electrolyte films. For the EPD, thin layers of graphite were pre-coated on the surface of a nonconducting porous NiO-YSZ composite anode substrate. Uniform YSZ green films were formed on the reverse sides, which did not have the graphite layers. The specimens were transformed into dense bodies ∼5 to 10 μm thick after being co-fired with the substrates. The cell performance of the ∼5 μm thick dense YSZ films supported on the anode substrates was tested using a La(Sr)Co(Fe)O 3 cathode. Maximum output power densities of ∼0.19, ∼0.61, and ∼1.02 W/cm 2 were attained at 600, 700, and 800°C, respectively.

Long life sealed nickel-zinc cell using a new separator

Abstract Because of internal shorting due to zinc (Zn) dendrite formation at the Zn electrode, nickel-zinc (NiZn) secondary cell cycle life is somewhat less than the NiCd cell cycle life. To solve this problem, a new kind of separator was developed which consisted of nylon non-woven cloth coated with poly(vinyl alcohol) (PVA) containing boric acid. This separator has a high ionic conductivity, but is resistant to zincate ion penetration. A large number of additives, effective for Zn dendrite suppression, was also tested. From them, bismuth oxide (Bi 2 O 3 ) was selected and added, together with calcium hydroxide (Ca(OH) 2 ), to the Zn electrode. A charging method, applying an intermittent anodic pulse, was found to be effective to reduce the Zn electrode shape change and prolong the cycle life of this cell. By using these materials and investigating a cell construction containing an electrolytic solution and hydrogen gas absorber, sizes AA, C, and D sealed NiZn cells were developed whose charging and discharging cycle life achieved over 500 cycles, for a size C cell.

Electrophoretic Fabrication and Cell Performance of Dense Sr- and Mg-Doped LaGaO3-Based Electrolyte Films

Dense films of (La, Sr)(Ga, Mg)O 3 compound, known as a superior oxide ion conductor, were fabricated successfully by electrophoretic deposition of the ceramic powders on graphite substrates followed by sintering with controlled heating profile. Thickness of the electrolyte films was varied in a range of ca. 40-80 μm with the deposition time. Ion conductivities of the films thus fabricated were 1.80 × 10 - 2 S/cm at 600°C and 5.75 X 10 - 2 S/cm at 730°C, and were comparable to those of bulky specimens prepared in a conventional manner. A single cell was constructed on the lanthanum gallate based film with doped lanthanum cobaltite for a cathode and Ni-yittria-doped ceria for an anode. Maximum output power densities of 0.34 W/cm 2 at 600°C and 0.50 W/cm 2 at 700°C were attained, respectively.

Formation of strontium-doped lanthanum manganite (La0.8Sr0.2MnO3) by mechanical milling without media balls

This paper reports a study of the phase evolution induced by mechanical milling of a mixture of industrial grade La2O3, SrCO3 and Mn3O4 powders under a humid atmosphere. In this milling, no media balls were employed and the mechanical activation was applied through friction among particles in the powder mixture. Under humid atmosphere (relative humidity 70% at 25°C), X-ray diffraction peak intensities of La2O3, SrCO3 and Mn3O4 decreased, and the specific surface area of the powder mixture increased at the early stage of the milling (less than 10 min). In further milling, the perovskite strontium-doped lanthanum manganite (LSM) started to appear. Differential thermal analysis suggests that the present mechanical activation brought about the decomposition of SrCO3. Single-phase LSM was obtained by annealing of the milled powder mixture at a relatively lower temperature of 900°C and its particle size was about 100 nm. The present mechanical milling resulted in considerably lower contamination release from milling media.

Microstructural control of Ni–YSZ cermet anode for planar thin-film SOFCs

A Ni–Y2O3-stabilized ZrO2 (Ni–YSZ) cermet anode was fabricated for solid oxide fuel cells (SOFCs) by conventional ceramic processing using NiO–YSZ composite particles. Microstructures of the anode were carefully characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Ni–YSZ cermet anode consists of fine YSZ connections with a continuous pore structure, which provides paths for the conduction of oxygen ions on the surface of the Ni network, as well as that of electrons and gaseous species. No amorphous phases were present at the interface between Ni and YSZ, and there was an orientation relationship between the Ni and YSZ grains, (111)Ni//(111)YSZ. The cermet anode showed high electrical performance at 800°C. These results indicate that the electrochemical activity of the Ni–YSZ cermet anode is enhanced with the present microstructure.

Enhanced electrochemical activity and long-term stability of Ni–YSZ anode derived from NiO–YSZ interdispersed composite particles

Nickel oxide–yttira stabilized zirconia (NiO–YSZ) interdispersed composite (IC) particles were prepared by mechanochemical processing using NiO and YSZ nanoparticles. Transmission electron microscopy (TEM) revealed that primary particles of YSZ (75 nm) and NiO (160 nm) were presented alternately in the composite particles. Specific surface area (SSA) decreased from 8.6 to 7.1 m 2 /g during the mechanochemical processing. The SSA reduction suggested that the chemically bound NiO/YSZ hetero-interfaces were formed during the processing. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) visualized that the anode made from the IC particles consisted of a three-dimensional textured structure of fine Ni and YSZ networks (grain size approximately 500 nm) with 34 vol% porosity. The anode demonstrated not only low polarization of 152 mV at 1 A/cm 2 even under operation at 700°C, but also long-term stability for 920 h.

Microstructural Control of LSM/YSZ Composite Cathode for Lower Temperature Operation of SOFC

La0.8Sr0.3MnO3(LSM)/Y2O3 stabilized ZrO2(YSZ) composite powders were mechanically prepared. By changing the mechanical device or processing time, three composite powders with different size distributions were obtained. Then the powders were formed into cathodes of solid oxide fuel cells (SOFCs). The microstructures of the cathodes were carefully characterized by scanning electron microscope (SEM). Losses by internal resistance (IR) and by polarization between the electrolyte and cathode were measured with the current interruption technique. The cathode fabricated by using the powder with the narrowest particle size distribution showed fine grains, uniform porous structure and good contact with the electrolyte layer, thereby resulting in low IR and polarization losses. In contrast, the cathode fabricated from the powder with the broadest particle size distribution contained a large mass of coarse particles and had less uniform structure in the grains and pores, thereby resulting in relatively high IR and polarization losses.