Jun Akikusa

Effect of SO2 Concentration on Degradation of Sm0.5Sr0.5CoO3 Cathode

A trace amount of SO2 in air is not a negligible factor on degradation of SOFC cathode. SO2 acts like Cr vapors which cause Cr-poisoning, and easily reacts with the strontium component in lanthanum-cobaltite based SOFC cathodes. Effects of SO2 concentration on degradation of an Sm0.5Sr0.5CoO3 (SSC) cathode were investigated in order to evaluate degradation of SSC cathode in an accelerated mode. Three different concentrations of SO2 (100 ppm, 1 ppm, and 5 ppb) were supplied to the cathode with air during cell tests at T = 1073 K Degradation of SSC cathode was accelerated with increasing SO2 concentration. In the thin SO2 conditions (1 ppm and 5 ppb SO2), SO2 in air was captured on the surface of the SSC cathode. SO2 reacted with the strontium component in the SSC cathode to form SrSO4. In the thick SO2 condition (100 ppm SO2), SO2 reacted with the strontium and samarium components. Too excess SO2 concentration in air was not suitable to examine cathode degradation in an accelerated mode because other degradation modes were appeared. One ppm - SO2 in air was applicable to accelerate the degradation of SSC cathode.

Characterization of solid oxide fuel cell using doped lanthanum gallate

Abstract The power-generation characteristics and the electrode overpotential of the solid oxide fuel cell (SOFC) using doped lanthanum gallate perovskite-type oxide as an electrolyte were measured at temperatures below that of the typical SOFC using yttria-stabilized zirconia (YSZ) as an electrolyte. The oxide ion conductivity of the electrolyte, La 0.8 Sr 0.2 Ga 0.8 Mg 0.15 Co 0.05 O 3− δ (LSGMC), was much higher than that of YSZ. A single cell using LSGMC of 205 μm in thickness showed a power density of 380 mW/cm 2 at a current density of 0.5 A/cm 2 and a temperature of 650°C by using air and dry hydrogen as oxidant and fuel, respectively. The overpotential of anode was larger than that of the cathode and dominated the overall overpotential. The IR-drop measured by current-interrupting method was in good agreement with the value estimated from the electrical conductivity of the electrolyte. The experimental results indicate that LSGMC is a promising material as an electrolyte for a low-temperature SOFC. The characteristics of electrodes are further discussed in terms of the composition and particle size of the starting powders.

Sulfur Poisoning of SOFC Cathodes

In order to examine degradation of solid oxide fuel cell (SOFC) cathodes due to a trace of SO x in air, sulfur poisoning of SOFC cathodes was investigated in an accelerated mode using SO 2 -concentrated air at T = 1073 K. Two different cathode materials, Sm 0.5 Sr 0.5 CoO 3 (SSC) and (La 0.85 Sr 0.15 ) 0.95 MnO 3 (LSM), were fired on button-type La 0.8 Sr 0.2 Ga 0.8 Mg 0.15 Co 0.05 O 3-δ electrolytes. SO 2 -concentrated air (98 ppm SO 2 -air mixture) was selected as the source of sulfur in order to accelerate degradations due to sulfur poisoning. By exposure to SO 2 , the performance of SSC cathode rapidly declined, because both ohmic and polarization resistances increased. The performance of the LSM cathode slightly decreased after exposure to SO 2 , and the performance recovered by interrupting the feed of SO 2 . Secondary phases such as strontium sulfate were formed on SSC cathode after exposing SO 2 and were not clearly detected on LSM cathode. The LSM cathode was more stable in SO 2 concentrated air than the SSC cathode. This can be explained by the difference in the activity of strontium oxide in LSM and SSC.

Development of a Low Temperature Operation Solid Oxide Fuel Cell

Lowering operation temperature of the solid oxide fuel cell (SOFC) would promote the commercialization of a power-generation module in terms of the manufacturing cost, lifetime, reliability, etc. Mitsubishi Materials Corporation and Oita University have been jointly developing a planar-type SOFC which could operate at a temperature of about 700°C. As an electrolyte, lanthanum gallate (LaGaO 3 ) with substitution of Sr for the La site and Mg and Co for the Ga site was used at this temperature. So far we have established a technique for large-seale cell production, and currently we are examining the performance of a commercial-size cell as large as 154 mm in diam. The obtained cell attained an output power of 31 W with an effective electrode area of 177 cm - at 650°C. Furthermore, a stack of two cells has been tested and the use of stainless steel for the separator was found to be possible during the examined time period at this temperature. The internal CH 4 reforming on the cell has been examined, and the cell output performance using methane [steam/carbon ratio (S/C) = 2] was about 93% of the power density of the cell using hydrogen.

Development of Intermediate-Temperature SOFC Module Using Doped Lanthanum Gallate

An intermediate temperature solid oxide fuel cell (SOFC) module was developed using electrochemically active cells composed of (La, Sr)(Ga, Mg, Co)O 3 electrolyte, Ni-(Ce, Sm)O 2 anode, and (Sm, Sr)CoO 3 cathode. Seal-less planar type stack design was employed. The first generation module successfully provided the output power of I kW with thermal self-sustainability below 800°C. Maximum electrical efficiency obtained with this module was 43%[LHV] together with the corresponding fuel utilization of 78%. Dynamic performance tests demonstrated the capability of output power alteration from 0.6 to 1 kW while maintaining a high electrical conversion efficiency. Further testing and modification of the module for methane fuel utilization are in progress.

SOFC Module and System Development by Means of Sealless Metallic Separators with Lanthanum Gallate Electrolyte

The third-generation 1-kW e -class module was developed with an automatic control system. A conversion efficiency of 48% ac/lower heating value [ac/LHV] was achieved with an exhaust heat recovery unit. An endurance test using the third-generation 1-kW e module was done for over 1000 h and no degradation of the power generation performance was observed. In parallel, a single-cell unit, which includes one cell and two metallic separators, was tested for over 10000 h and the degradation rate of the terminal voltage was found to be 1-2%/1000 h. In the direction of scale-up, a triple-stack module of 3-kW e output was developed. A partial load as well as excess loads on the module were tested and the output power of 1-5 kW e was attained under thermally self-sustainable conditions. It was found that a high efficiency of 55% dc/lower heating value [dc/LHV] was obtained under stable operation. Ongoing research of the fourth-generation 1-kW e module has resulted in the conversion efficiency of 58% [dc/LHV].

Effect of surface treatment for aluminum foils on discharge properties of lithium-ion battery

Aluminum foils having thicknesses of 10−20 μm are commonly employed as current collectors for cathode electrodes in Li-ion batteries. The effects of the surface morphology of the foil on battery performance were investigated by using a foil with roughened surface by chemical etching and a plain foil with smooth surface on both sides. For high-conductivity LiCoO2 active materials with large particle size, there are no significant differences in battery performance between the two types of foils. But for low-conductivity LiFePO4 active materials with small particle size, high-rate discharge properties are significantly different. The possibility shows that optimizing both the surface morphology of the aluminum foil and particle size of active material leads to improvement of the battery performance.

Development of Intermediate-Temperature Solid Oxide Fuel Cells Using Doped Lanthanum Gallate Electrolyte

Intermediate-temperature(IT) solid oxide fuel cells(SOFCs) were developed using lanthanum gallate electrolyte, samarium cobaltite cathode and the cermet anode of nickel and ceria. High efficiency operation below 800°C was enabled using planar disk type cells with unique seal less stack design. The first 10 kW-class combined heat and power (CHP) system provided AC output power of 10 kW with electrical and overall efficiency of 41 and 82 %HHV, respectively. Optimization of cell-stack components to increase the output power density is in progress.