A resistive oxygen sensor using a thick film of ceria doped with Hf (Ce_0.9Hf_0.1O₂ sensor) was fabricated and its sensing properties were investigated. The Ce_0.9Hf_0.1O₂ thick film had a single fluorite phase and a porous structure with 1-2μm particles. The Ce_0.9Hf_0.1O₂ sensor had much a lower resistance than the Ce_0.9Zr_0.1O₂ sensor or CeO₂ sensor. The temperature dependence of the resistance of the Ce_0.9Hf_0.1O₂ sensor was smaller than that of the Ce_0.9Zr_0.1O₂ sensor or CeO₂ sensor.

Zinc oxide which is one of the well known materials for photocatalyst, though not so wider than titanium oxide, is cheaper and could be prepared easily through wet process. It is well kown that the zinc oxide dissolves in acidic or alkalic medium. So zinc oxide could be available if the environment is limited to gaseous phase. The purpose of this research is to develop and examine the zinc oxide photocatalyst containing nano particlulate titanium oxide. Thus prepared specimen showed that higher photocatalytic activity than titanium oxide, and photocatalytic activity was observed also under visible light irradiation.

We have operated the single-cells in the stack structure using methane as a fuel under high fuel utilizations. Methane fuel was supplied directly to the cell-stack after addition of steam at a steam to carbon ratio of 2. A steam-reforming reaction was conducted directly on the anode (direct internal reforming: DIR). In the case of the single-cell with the anode-substrate having relatively high porosity, stack voltage was found to be 0.767 V at fuel utilization of 75%, at which d.c. energy conversion efficiency is 50.2% (H HV). A maximum energy conversion efficiency, 53.6%, was achieved at fuel utilization of 86% and cell voltage of 0.712 V. This methane-to-electricity conversion efficiency will be high enough for practical applications. For anode-supported SOFCs, concentration polarization loss in the anode can be a crucial problem because fresh fuel and electrochemical reaction products have to diffuse through a thick anode substrate in the opposite direction between the flow field (fuel distribution channel) and the anode/ electrolyte interface. Limiting current density with a diluted CO at a fixed current density was measured and analyzed to investigate the diffusion characteristics of a fuel in the anode-substrates. Diffusion parameters obtained by the analysis were verified by measurement of the limiting current density with diluted H₂ and voltage response for depolarization process after current-interruption.

A cyclic indole trimer (CIT) was studied electrochemically and was proposed as a new category of redox capacitor electrode material. ln a sulfuric acid aqueous media, the CIT electrode showed electrochemical redox activity at wide potential window between 0 and 1V vs. Ag/AgCl. The wide redox system is attributed to two redox couples, anion doping/undoping with electron transfer and proton undoping/doping. Specific capacity obtained for the CIT electrode was 55 Ah kg^－1(198 Fg^－1), which is three times higher than that for the polyindole (21 Ah kg^－1). More importantly, the CIT electrode maintained its high capacity of 52 Ah kg^－1 (187 Fg^－1) after 100,000 cycling, while the capacity decreased down to 5 Ah kg^－1 for the polyindole electrode.

Under a pulse anodization mode, a dielectric Ta₂O₅ film and a conducting polypyrrole film were formed on a nanoporous Ta pellet anode (average pore size: 250 nm, specific surface area: 4,000 cm² g^－1, capacitance: 50,000μFV g^－1). At a first pulse, Ta metal was anodized to form dielectric Ta₂O₅ nano film (1.6~ 14 nm in thickness) on nano-porous Ta pellet. With subsequent pulses, the polypyrrole film was deposited uniformly and compactly (average thickness: 70~230 nm) on the Ta₂O₅/Ta nano-porous layer. The thickness of polypyrrole film was controlled by tuning current and charge of the pulse. The polypyrrole film on the Ta₂O₅/Ta nano-porous layer showed low resistivity of 2×10^－1Ω persquare. By AC impedance analysis, low equivalent series resistance (400 mΩ at 100 kHz) was demonstrated for a sample electrolytic capacitor with nano-porous Ta₂O₅/Ta anode with polypyrrole coating layer.

Resistive oxygen sensors using cerium oxide thick film and Pt electrodes were fabricated. The cerium oxide thick films were prepared by screen-printing. The Pt electrodes were prepared by 2 methods: screen-printing and sputtering with a metal mask. The difference of the sensitivity of the sensors using Pt electrodes prepared by 2 methods was investigated. As a result, the oxygen sensor using the electrodes prepared by sputtering with metal mask had better sensitivity than that using the electrodes prepared by screen-printing.

Mg₂Ge thin film was prepared from mechanically alloyed powder of Mg₂Ge by vacuum evaporating method and evaluated as a negative electrode material for rechargeable lithium batteries. The thin film prepared at the substrate temperature of 300℃ was almost stoichiometric in composition and homogeneous in structure. Although the irreversible capacity was observed for the initial charging-discharging in the Mg₂Ge film electrode, the charge-discharge cycling was possible and about 70% capacity was preserved after 50 cycles at the current of 0.075 mA cm^－2. Especially this film electrode was found to have a high-rate battery performance as compared with the powder electrode.