Sensory detection of gases has become increasingly important especially for emission control and environmental monitoring. This article reviews how well a design concept using foreign receptors works for developing three types of solid state gas sensors. For oxide-semiconductor gas sensors, noble metals, metal oxides or even metal carbonates can works as an effective receptor material to recognize reducing gases when finely dispersed on the base oxide grains. Alkaline metal salts of oxyacids can work as indispensable receptors to oxidic gases like CO₂, NO₂ and SO₂ for potentiometric solid electrolyte gas sensors, while semiconducting oxides provide useful receptors to reducing or oxidizing gases when used as a sensing electrode for mixed potential type solid electrolyte gas sensors. Several gas sensors thus developed are demonstrated together with brief discussion.

Thiol derivatized aza-15-crown-5-ether (15C5) was synthesized and modified on a gold electrode surface as the self-assembled monolayer. The effects of the alkali metal ions on the CV response of the Fe(CN)₆³⁻ probe ion at the modified electrode were investigated with changing alkali metal ion. The CV response was decreased in the order of Rb⁺≥K⁺>Li⁺≫Na⁺. The results are discussed in relation to the interaction between the crown ring and the alkali metal ions.

The quatemary spinel LiMn_2−xMg_xO₄ in which a part of Mn is replaced by Mg (x=0~0.5) are prepared, and Mn valence was determined by chemical analysis. The effect of electrodle characteristics of the positive electrode active materials was investigated. The lattice parameter α decreased and Mn valence increased with increasing Mg content. Substitution a part of Mn with Mg brought to a good cycle performance in spite of some decrease on the initial capacity.

For alkaline batteries, it is important to investigate prospective materials with higher energy density and lower cost. We paid attention to the reaction of quinone compounds and investigated the electrochemical properties of these compounds in alkaline solution and discussed the possibility for a negative active material of alkaline secondary batteries. In alkaline solutioll, most of these materials, e.g. p-benzoquinone, dissolved, while only chloranilic acid (C₆Cl₂(OH)₂O₂) did not. We have found that chloranilic acid is the most possible candidate for the negative active materials of alkaline batteries because of its insolubility to alkaline solutions. There were three couples of peaks in cyclic voltammogram (−1.2〜−0.1V vs. Ag/AgCl) for the electrode of chloranilic acid. With cathodic scan of cyclic voltammogram on −0.8V vs. Ag/AgCl, the color of solution changed. It seems that this change is caused by the influence of dissolved products, which was formed by electrochemical redox reaction ofchlorallilic acid around −1.0V vs. Ag/AgCl. When the charge-discharge test was conducted in the potential range between −0.45V and −0.8V, no colored substance was formed in the solution and the discharge capacity reached to approximate150 mAhg⁻¹ at the first cycle. From these results, on chloranilic acid, it was suggested that there was a possibility of application for a negative active material of alkaline secondary batteries.

To improve the durability of the platinized titanium anode, TiO₂ gel prepared by sol-gel method was used as the binder between Pt film and Ti substrate. The durability of Pt/TiO₂/Ti and Pt/Ti electrodes after amealing at 200, 300, 400 and 550°C were examined in 1M H₂SO₄ solution at an anodic current density of 200A/dm², temperature being at 60°C. When the anode with TiO₂ binder was annealed at 550°C, the durability of Pt/Ti anodes was improved by a factor of about 3, compared with usual type anode annealed at 200°C. It was found that TiO₂ binder began to crystallize from amorphous to anatase structure at around 300°C. We assumed that a mixed phase of Pt, TiO₂ and Ti could be formed at temperatures over 300°C.

Aiming at the application of photovoltaic cells, β-FeSi₂-Si composite films were fabricated to increase the number of the generated carriers with the energy below the band-gap of silicon. A composite film consisted of nano-particles of β-FeSi₂ and amorphous-Si was fabricated using an alternate sputtering method, and the particle size of β-FeSi₂ could be controlled within the range of 3nm~80nm by varying the sputtering time. It was shown that the composite film had the absorption property of the direct transition type. The band-gaps of composite films with particle diameters of 5 and 3nm were 0.95 and 0.97eV respectively, though that of β-FeSi₂ thin film was 0.87eV. The blue shift of the band-gap by the quantum size effect was seen. Spectral responses of the β-FeSi₂-Si composite heterostructure were investigated. The photoyield was increased in the range of 0.98~1.05eV compared to noble a-Si film, Moreover, the decrease of the barrier height by the quantum size effect was indicated by the comparison with the theoretical values. It was suggested that the carrier excited by the β-FeSi₂ nano-particle was taken out as a photocurrent by moving to a-Si thin film and passing over the heterodiode side.

The effect of temperature and gas atmosphere on corrosion behavior of type 316L stainless steel in a molten Li₂CO₃-Na₂CO₃ eutectic has been investigated. When the CO₂ partial pressure was higher than 0.02 atm and the temperature was lower than 843K, the severe corrosion (localized corrosion) occurred. However, once the sample had been kept for some periods in the melt under N₂ (or N₂+5%H₂O), no severe corrosion occurred, even though the atmosphere shifted to the localized corrosion condition subsequently. From this result, it was revealed that localized corrosion was avoidable by forming LiFeO₂ layer on the metal surface in advance. Especially, the addition of H₂O into the atmosphere could become effective method to prevent localized corrosion.

It became clear that carbon fibers exhibited different graghitizability even treated at the same temperature depending on their precursor, and highly graphitized carbon fibers had high corrosion resisitibility in hot phosphoric acid. Therefore, it was concluded that the corrosion resisitibility of the PAFC electrode substrate in the hot phosphoric acid can be improved by use of highly graphitizable carbon fiber as a raw materia1. Under a mild corrosion condition, graghitizability of the fiber surface was important for improving corrosion resisitibility. Results showed that the corrosion of the carbon fiber occurred from a part of low graphitizability of the surface, and the carbon surface layer was converted to oxidized carbon compounds. In addition, specific surface area of the carbon fibers increased by corrosion to form micropores or surface roughness showing the extent of such changes depended greatly upon the graghitizability of the carbon fiber