Abstract Nitrogen-doped and sulfur-doped mechanochemically synthesized multilayer graphene (N-doped and S-doped MSMG) were prepared by planetary ball-milling, and they were used in bifunctional gas diffusion electrodes (GDEs) for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Graphite, melamine, and elemental sulfur were used as raw materials. The surface area-normalized linear sweep voltammograms revealed that the N-doped and S-doped MSMG have higher intrinsic ORR/OER activity than the undoped MSMG. When the MSMG samples were used in GDEs, the N-doped and S-doped MSMG showed higher OER activity but lower ORR activity than the undoped MSMG. We analyzed the relationship between the specific surface area, intrinsic ORR/OER activity, and ORR/OER activity of GDEs and found that both the intrinsic ORR activity and surface area are important in the fabrication of GDEs with high ORR activity and that the intrinsic OER activity rather than the surface area is important in the fabrication of GDEs with high OER activity. The GDE fabricated from the S-doped MSMG showed the highest ORR/OER bifunctional activity among the MSMG-based GDEs, and its ORR/OER bifunctional activity was higher than the GDEs fabricated from other materials, such as reduced graphene oxide and electroconductive oxides.

© 2019 The Electrochemical Society. In this study, the influence of the oxygen partial pressures (PO2) on the sensor response to H2 of SnO2 resistive-type gas sensors was evaluated under various humid atmospheres. SnO2 nanoparticles of 8–15 nm in diameter were synthesized using a hydrothermal technique followed by calcination at 600°C. Additionally, a large amount of pores with diameters greater than 10 nm was confirmed in the nanoparticles. The electrical resistance at 350°C was decreased with decreasing the PO2, and the electrical resistance in the presence of 10 ppm H2 was much smaller than that in the absence of H2 in both dry and humid atmospheres regardless of the PO2. Furthermore, the sensor response to 10 ppm H2 at 350°C increased with decreasing PO2 in both dry and humid atmospheres. Thus, decreasing the amount of oxygen adsorption enhanced the effect of rooted hydroxyl formation on the SnO2 surface through a combustion reaction between H2 and adsorbed oxygen and improved the sensor response to H2. These results are important for understanding the fundamental mechanisms of gas detection and for the material surface design of highly sensitive resistive-type semiconductor gas sensors.

Manufacturing of advanced functional materials should also rely on the green chemistry principles like utilization of natural renewable resources. Marine environment offers plenty of renewable raw materials like chitin and its derivative chitosan. The paper presents how urea treatment has influenced several textural, chemical, and electrocatalytic properties of N-doped activated carbons (N-ACs) obtained from chitosan and chitin. The materials were subjected to an activation procedure (with different activators) as well as nitrogenation by premixing the precursors with water solutions of urea. Raw and premixed precursors were carbonized in the temperature range of 700-800 °C. The urea treatment resulted in a spectacular increase in the nitrogen content by weight (up to 68%) and an improvement of the surface area (up to 42%) along with total/micro-/mezo-pore volume (up to 49%). Some urea-modified N-ACs were capable of reducing oxygen in an alkaline solution as effectively as a Pt-loaded carbon material. The highest number of electrons transferred to O2 molecule was found to be equal to 3.76 for a chitosan derived sample. This ability of chitosan and chitin derived N-rich activated carbons was studied by means of the method named rotating ring disc electrode.

To investigate the effect of aging at 580 °C in wet air (humid aging) on the oxygen adsorption on the surface of SnO2 particles, the electric properties and the sensor response to hydrogen in dry and humid atmospheres for SnO2 resistive-type gas sensors were evaluated. The electric resistance in dry and wet atmospheres at 350 °C was strongly increased by humid aging. From the results of oxygen partial pressure dependence of the electric resistance, the oxygen adsorption equilibrium constants (K1 for O- adsorption, K2 for O2- adsorption) were estimated on the basis of the theoretical model of oxygen adsorption. The K1 and K2 in dry and wet atmospheres at 350 °C were increased by humid aging at 580 °C, indicating an increase in the adsorption amount of both O- and O2-. These results suggest that hydroxyl poisoning on the oxygen adsorption is suppressed by humid aging. The sensor response to hydrogen in dry and wet atmosphere at 350 °C was clearly improved by humid aging. Such an improvement of the sensor response seems to be caused by increasing the oxygen adsorption amount. Thus, the humid aging offers an effective way to improve the sensor response of SnO2 resistive-type gas sensors in dry and wet atmospheres.

Polyoxometallates (POMs) have been attracting much attention as homogeneous molecular catalysts because of their excellent photocatalytic activities. However, the poor sensitivities of POMs to visible light limit their utilization of solar energy. Here, we studied photoinduced electron transfer (PET) from a Ru complex to POMs such as S1W10O368-, W10O324-, SiW12O404- , and PMo12O403- to use them for photoenergy storage and photocatalysis driven by visible light. A hydrophobic Ru complex ([Ru(nbpy)(3)](2+); nbpy = 4,4'-dinoyl-2,2'-hipyridyl) was coupled with POMs that were hybridized with dioctadecyldimethylammonium (DODA) in chloroform. Photoluminescence (PL,) quenching and lifetime measurements indicate that PET efficiently occurred from the Ru complex to the POMs/DODA hybrids in chloroform by excitation with visible light. The PET led to the formation of one electron reduced POMs that store photoexcited electrons. The stored/charged electrons can be discharged in a subsequent reaction that can proceed under dark conditions. The Ru complex-POM hybrid system in chloroform was used to reduce metal ions in a water phase at a liquid/liquid interface Under visible light irradiation. The one-electron reduced POM that was formed by PET could reduce metal ions to produce metal particles, suggesting the applicability of this system for photocatalytic reactions. under visible light irradiation.

We conducted ring-opening polymerization of silacyclobutane monomers 1-[2-(2,4-dioxa-3-pentanoyl)ethyl]-1-methylsilacyclobutane (SBMC) and 1,1-di[2-(2,4-dioxa-3-pentanoyl)ethyl]silacydobutane (SBDC) to obtain polySBMC and polySBDC, respectively, and measured their ionic conductivity with addition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium trifluoromethanesulfonate (LiOTf). The ionic conductivity of both polySBMC and polySBDC increased with the increase in the amount of LiTFSI added. The ionic conductivity of polySBMC decreased with the increase in the amount of LiTOf, and that of polySBDC decreased after an increase. PolySBMC and polySBDC showed ionic conductivity of 6.1 x 10(-5) and 1.5 x 10(-4) S/cm at 3 degrees C, respectively, after the addition of 4 mol equiv of LiTFSI per cyclic carbonate. Differential scanning, calorimetry analysis of the polymer revealed that the polymers with a high LiTFSI content formed a crystalline phase around room temperature, but the glass transition temperatures of the amorphous phases were kept low. Infrared analysis suggested the existence of a strong interaction between carbonate carbonyl groups and lithium cations.

Vanadium oxide (V2O5) was successfully loaded on tin dioxide (SnO2) nanoparticles using an impregnation method to improve the sensor response for detecting combustible gases in a humid atmosphere. As seen from field-emission scanning electron microscopy images, appropriate pores for gas diffusion are formed on the nanoparticles. The sensor response to combustible gases such as hydrogen and ethanol were evaluated at elevated temperatures in a humid atmosphere, showing clear improvement with 1 wt% V2O5 loading on the SnO2 nanoparticles. The improvement in performance was attributed to the role of V2O5 as an oxygen provider in the air atmosphere with combustible gas and the ability for V2O5 to undergo reduction. Thus, adding a catalytic metal oxide provides a simple way to overcome hydroxyl poisoning on a SnO2 surface. (C) 2016 Elsevier B.V. All rights reserved.

© 2016 The Ceramic Society of Japan and the Korean Ceramic Society ZnO nanocrystals (NCs) were synthesized by heating Zn (II) acetylacetonate in oleic acid/oleylamine in the presence of 1,2-hexadecanediol at 220 °C. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements revealed the formation of monodispersed ZnO NCs of ca. 7 nm. ZnO NC assembled films were fabricated on a glass substrate by deposition with the colloidal ZnO NCs dispersed in toluene. The film composed of the NCs showed good optical transparency in the visible to near-infrared region. A device coupling the ZnO NC film with a p-type Cu 2 ZnSnS 4 (CZTS) NC film exhibited an obvious diode-like current–voltage behavior. The results suggest that the transparent ZnO film has a potentiality to be used for an n-type window layer in some optoelectronic applications.

In this study, we prepared thermally stable SnO2 nanocrystals (ca. 4 nm) in a mixture of Sncl(4), tetraethylene glycol (TEG), and tetrabutylammonium hydroxide (TBAH) tinder reflux and obtained a highly sensitive semiconductor gas sensor. It has been determined both theoretically and experimentally that the synthesis of oxide Semiconductor nanoparticles is an important factor in highly sensitive semiconductor gas sensors. However, as-synthesized nanocrystals generally grow large during calcination at high temperature, and this thermal crystal growth reduces the sensor response. Therefore,. to refine the response of the semiconductor gas sensor,:we synthesized thermally stable SnO2 nanocrystals by heating under reflux a SnCl4 TBAH-TEG mixture. The obtained SnO2 nanocrystals exhibited high thermal stability even when Calcined at a. temperature up, to 600 degrees C. The gas-sensing films fabricated from the thermally stable SnO2 nanocrystals exhibited a high sensor response to hydrogen due to their small crystal size, and a change in their surface property as compared with conventional SnO2 nanocrystals synthesized via hydrothermal treatment.

The type and amounts of oxygen adsorption species at various atmospheric humidity levels are important factors in improving the sensitivity to combustible gases and stability to humidity changes of SnO2-based resistive-type gas sensors. We investigated the effect of antimony (Sb) doping of SnO2 nanoparticles on the stability of the sensitivity to humidity changes and oxygen adsorption species under humid atmosphere. No significant degradation of the sensitivity to hydrogen of Sb-SnO2 sensors was observed between 16 and 96 RH%, while an undoped SnO2 sensor showed gradually decreasing responses with increasing humidity. An evaluation of oxygen adsorption species under humid atmosphere showed a transition from O2- to O- with increasing humidity from 16 to 96 RH%. However, the O2- adsorption sites were maintained on the surfaces of the Sb-SnO2, even as the humidity increased. Moreover, the extent of oxygen adsorption on the Sb-SnO2 was not obviously changed with increasing humidity. These results indicate that Sb atoms function as hydroxyl absorbers and also generate O2- adsorption sites in their vicinity. Additionally, Pd loading on the Sb-SnO2 further enhanced the sensor response under humid atmosphere, while maintaining the stability to humidity changes. Therefore, we successfully imparted stability to the sensitivity of SnO2 nanoparticles during humidity changes, representing an important improvement with applications to the development of high performance, practical, resistive-type gas sensors.

The simultaneous improvement of sensor response and response/recovery kinetics is important for repeated gas monitoring using high-performance semiconductor gas sensors. In this study, we attempted to add two different types of catalysts to the SnO2 nanoparticles to enhance their responsive properties and investigated the impact of each catalyst on co-loaded SnO2 nanoparticles. V2O5 and Pd were loaded on sphere-type SnO2 nanoparticles by a simple impregnation method, and we evaluated the effect on the sensor response to H-2 and recovery speed. Separately, V2O5 and Pd loading effectively enhance the sensor response and rapid recovery reaction, respectively, because V2O5 provides SnO2 with reactive adsorbed oxygen, and Pd enhances the catalytic activity on the particle surface. Further, V2O5- and Pd-co-loaded SnO2 shows both high sensor response and rapid recovery reaction. Thus, co-loaded SnO2 is improved by V2O5 and Pd simultaneously, and the two loadings are complementary. In particular, V2O5 loading reduces the recovery speed due to the re-oxidization of V2O5 on SnO2. However, Pd accelerates V2O5 re-oxidization by catalytic activity and the recovery kinetics of the co-loaded SnO2. Therefore, this fundamental investigation offers a suitable material design for additives, which can be applied to manufacture high-performance electrochemical devices such as semiconductor gas sensors.

We successfully prepared SnO2 nanoparticles of two different sizes by hydrothermal synthesis and calcination at 400 degrees C to evaluate the oxygen adsorption equilibrium constant K(O2-ad) on a particle surface. The K(O2-ad) values were calculated from the relationship between the electric resistance and the oxygen partial pressure (P-O2). The K(O2-ad) values of 7 and 17 nm SnO2 nanoparticles were almost in the same range when the donor densities of these nanoparticles are the same. Additionally, the sensor responses of these nanoparticles to hydrogen were affected by the surface-area-to-volume ratio because the K(O2-ad) values are the same. Thus, we propose that the K(O2-ad) value can be evaluated on the basis of the relationship between the electric resistance and P-O2.

The p-type nanocrystals (NCs) of copper-based chalcogenides, such as CuInSe2 and Cu2ZnSnS4, have attracted increasing attention in photovoltaic applications due to their potential to produce cheap solution-processed solar cells. Herein, we report the synthesis of copper antimony-sulfide (CAS) NCs with different crystal phases including CuSbS2, Cu3SbS4, and Cu12Sb4S13. In addition, their morphology, crystal phase, and optical properties were characterized using transmission electron microscopy, X-ray diffractometry, UV vis near-IR spectroscopy, and photoemission yield spectroscopy. The morphology, crystal phase, and electronic structure were significantly dependent on the chemical composition in the CAS system. Devices were fabricated using particulate films consisting of CAS NCs prepared by spin coating without a high-temperature treatment. The CAS NC-based devices exhibited a diode-like current voltage characteristic when coupled with an n-type CdS layer. In particular, the CuSbS, NC devices exhibited photovoltaic responses under simulated sunlight, demonstrating its applicability for use in solution-processed solar cells.

Real-time monitoring of specific gas concentrations with a compact and portable gas sensing device is required to sense potential health risk and danger from toxic gases. For such purposes, we developed an ultrasmall gas sensor device, where a micro sensing film was deposited on a micro heater integrated with electrodes fabricated by the microelectromechanical system (MEMS) technology. The developed device was operated in a pulse-heating mode to significantly reduce the heater power consumption and make the device battery-driven and portable. Using clustered Pd/SnO2 nanoparticles, we succeeded in introducing mesopores ranging from 10 to 30 nm in the micro gas sensing film (area: phi 150 mu m) to detect large volatile organic compounds (VOCs). The micro sensor showed quick, stable, and high sensor responses to toluene at ppm (parts per million) concentrations at 300 degrees C even by operating the micro heater in a pulse-heating mode where switch-on and -off cycles were repeated at one-second intervals. The high performance of the micro sensor should result from the creation of efficient diffusion paths decorated with Pd sensitizers by using the clustered Pd/SnO2 nanoparticles. Hence we demonstrate that our pulse-driven micro sensor using nanostructured oxide materials holds promise as a battery-operable, portable gas sensing device.

Selective oxygen separation from air was performed using perovskite-type oxide membranes made of Ba0.95La0.05FeO3-delta. We demonstrated that surface modification of Ba0.95La0.05FeO3-delta membranes with La1-xSrxFeO3-delta catalyst layers led to an increase in oxygen permeation fluxes at 700-930 degrees C. We studied the effects of oxygen vacancy amounts, surface area, particles size, surface treatment of La1-xSrxFeO3-delta on the oxygen permeability of the membranes fitted with La1-xSrxFeO3-delta catalyst layers. Among the catalyst layers tested, the membranes fitted with La0.9Sr0.1FeO3-delta (x=0.1) showed the highest oxygen permeation flux probably because of its higher porosity and uniform morphology without open voids, which would increase the number of surface reaction sites. The obtained results suggest the feasibility of further upgrading the membrane performance by using surface catalyst layers having a homogeneous morphology and a different composition from that of the mother membrane. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Pd particles of different nanosizes were loaded on the SnO2 surface by using different Pd precursors for the purpose of investigating the Pd size effect on gas sensing properties in humid atmosphere. One kind of Pd-loaded SnO2 natioparticle was characterized by smaller Pd particles (2.6 nm) with high dispersion, while another kind was characterized by larger Pd particles (5-10 nm) with low dispersion. It was found that both kinds of Pd on the SnO2 surface let the mainly, adsorbed oxygen species change from O- to O2- in humid atmosphere at 350 degrees C. In addition, the water vapor poisoning effect on electric resistance and sensor response was greatly reduced by loading Pd. Interestingly; for the CO response at 350 degrees C, Pd-SnO2 with small Pd size showed almost constant sensor response with varying humidity (0.5-4 vol % H2O). While the CO response of Pd-SnO2 with large Pd site even increased with increasing amount of water vapor. Moreover, the former CO response was increased from 300 to 350 degrees C, but the later response decreased with increase in operating temperature. These behaviors were analyzed by temperature programed reduction (TPR) in H-2 and CO atmospheres, and they were supported by the different catalytic activities of different nanosized Pd particles.

Recently, the process by which energy is transferred from photoexcited semiconductor nanocrystals, called quantum dots (QDs), to other semiconductors has attracted much attention and has potential application in solar energy conversion (i.e., QD-sensitized solar cells). Sensitization of wide band gap polyoxometalates (POMs) to visible light by using CuInS2 QDs dispersed in an organic solution is demonstrated herein. Photoluminescence quenching and lifetime studies revealed efficient electron transfer from the CuInS2 QDs to POMs, such as SiW12O40 and W10O32, that were hybridized with a cationic surfactant. CuInS2 QDs function as an antenna that absorbs visible light and supplies electrons to the POMs to enable certain photocatalytic reactions, including noble-metal-ion reduction. The photoenergy storage capabilities of the QD-POM system, in which electrons photogenerated in QDs by visible-light excitation are trapped and accommodated by POMs to form reduced POM, are also demonstrated. Electrons stored in the POM can be later discharged through reductive reactions, such as oxygen reduction, in the dark.

Using the same protocol for precipitation of tin hydroxide and its hydrothermal treatment (HT), we synthesize SnO2 from three precursors - tin(IV) acetate, tin(IV) hydroxide acetate and tin(IV) chloride pentahydrate. After annealing on sensor substrates the materials were found to be very similar from structural point of view. However, their sensing properties (responses to CO and H-2 as a function of humidity) were discovered to be very different, which was related to different impurity level in the samples. High amount of chlorine and potassium (ca. 300 ppmw) in two samples corresponded well to notably high water vapor effect. Differences in surface areas (within 20-60 m(2)/g) and pore volumes (between 0.11 and 0.19 cm(3)/g), found for the materials in question, seem to play minor role if the impurities are present. (C) 2015 Elsevier B.V. All rights reserved.

The effect of water vapor on Pd-loaded SnO2, sensor was investigated through the oxygen adsorption behavior and sensing properties toward hydrogen and CO under different humidity conditions. On the basis of the theoretical model reported previously, it was found that the mainly adsorbed oxygen species on the SnO2, surface in humid atmosphere was changed by loading Pd, more specifically, for neat SnO2, was O-, while for 0.7% Pd-SnO, was O2-. The water vapor poisoning effect on electric resistance and sensor response was reduced by loading Pd. Moreover the sensor response in wet atmosphere was greatly enhanced by loading Pd. It seems that the electron depletion layer by p-n junction of PdO-SnO2, may impede OH- adsorption.

Inhibition of hydroxyl poisoning of SnO2 nanoparticles is important to develop a highly sensitive combustible gas sensor that functions in a humid atmosphere. For this purpose, we incorporated Al into SnO2 nanoparticles (Al-doped SnO2) by a precipitation method, and fabricated a thick-film-type sensor using a screen printing method. Bare SnO2 nanoparticles and Al2O3-loaded SnO2 nanoparticles were also prepared for comparison. The oxygen adsorption amount clearly decreased after Al doping and Al2O3 loading, according to temperature programmed desorption measurements. Al doping enhanced the sensor response (sensitivity) to H-2, CO and C2H5OH in a humid atmosphere by almost five to ten times. Al2O3 loading also slightly increased the sensor response to each gas in a humid atmosphere. The enhancement of the sensor response was attributed to both Al and Al2O3 acting as hydroxyl absorbers on the surface of the nanoparticles, thereby providing an oxygen adsorption site for surface combustion reactions in a humid atmosphere. Based on the relationship between the sensor response and C2H5OH concentration, it was estimated that Al-doped SnO2 can detect less than one ppm C2H5OH in a humid atmosphere. Therefore, doping with Al, which protects and holds the adsorbed oxygen on the surface of the SnO2, is important as a surface modification to obtain humidity-tolerant semiconductor gas sensors.

Neat and Pd-loaded WO3 sensors were fabricated from lamellar-structured nanoparticles. The sensing mechanism of hydrogen was investigated. Oxygen adsorption properties were studied through the resistive responses and TPD measurements. It was observed that oxygen adsorption was significantly enhanced by Pd loading from the viewpoint of p-n junction for PdO-WO3. In the presence of H-2, the resistive response to oxygen for Pd-loaded WO3 was obviously different from that of neat WO3, which demonstrated a relatively weak response to oxygen. It was concluded that Pd loading not only promoted the sensor response but also made the sensing mechanism different from that of neat WO3. It was proposed that with Pd loading, the surface lattice oxygen near Pd sites was involved for the sensing process of H-2.

Gas sensing with nanosized oxide materials is attracting much attention because of its promising capability of detecting various toxic gases at very low concentrations. In this study, using clustered SnO2 nanoparticles formed by controlled particle aggregation, we fabricated highly sensitive gas sensing films to detect large gas molecules such as toluene. A hydrothermal method using stanic acid (SnO2 center dot nH(2)O) gel as a precursor produced monodispersed SnO2 nanoparticles of ca. 5 nm at pH 10.6. Decreasing the solution pH to 9.3 formed SnO2, clusters of ca. 45 nm that were assemblies of the monodispersed nanoparticles, as determined by dynamic light scattering, X-ray diffraction, and transmission electron microscopy analyses. Porous gas sensing films were successfully fabricated by a spin-coating method using the clustered nanoparticles due to the loose packing of the larger aggregated particles. The sensor devices using the porous films showed improved sensor responses (sensitivities) to H-2 and CO at 300 degrees C. The enhanced sensitivity resulted from an increase in the film's porosity, which promoted the gas diffusivity of the sensing films. Pd loading onto the clustered nanoparticles further upgraded the sensor response due to catalytic and electrical sensitization effects of Pd. In particular, the Pd-loaded SnO2 nanoparticle clusters showed excellent sensitivity to toluene, able to detect it at down to low ppb levels.

Tungsten trioxide (WO3) is one of the important multifunctional materials used for photocatalytic, photoelectrochemical, battery, and gas sensor applications. Nanostructured WO3 holds great potential for enhancing the performance of these applications. Here, we report highly sensitive NO2 sensors using WO3 nanolamellae and their sensitivity improvement by morphology control using SnO2 nanoparticles. WO3 nanolamellae were synthesized by an acidification method starting from Na2WO4 and H2SO4 and subsequent calcination at 300 degrees C. The lamellae were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), which clearly showed the formation of single-crystalline nanolamellae with a c-axis orientation. The stacking of each nanolamella to form larger lamellae that were 50-250 nm in lateral size and 15-25 nm in thickness was also revealed. From pore size distribution measurements, we found that introducing monodisperse SnO2 nanoparticles (ca. 4 nm) into WO3 lamella-based films improved their porosity, most likely because of effective insertion of nanoparticles into lamella stacks or in between assemblies of lamella stacks. In contrast, the crystallite size was not significantly changed, even by introducing SnO2. Because of the improvement in porosity, the composites of WO3 nanolamellae and SnO2 nanoparticles displayed enhanced sensitivity (sensor response) to NO2 at dilute concentrations of 20-1000 ppb in air, demonstrating the effectiveness of microstructure control of WO3 lamella-based films for highly sensitive NO2 detection. Electrical sensitization by SnO2 nanoparticles was also considered.

Water isotope exchange in the presence of CO on two undoped tin dioxides has been studied using modulation excitation diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and resistance measurements at 300 degrees C. Our results reveal that the material synthesized from tin tetrachloride (SnO2Cl) manifests higher affinity to chemisorbed water than that made from tin hydroxide acetate (SnO2Ac). The latter was shown to exhibit a strong correlation between the evolution of surface OH groups (bridging type, involved in hydrogen bonding) and electric resistance upon increasing concentration of CO. Water desorption kinetics, being independent of CO concentration for both materials, was found to be slower for SnO2Cl by ca. 30% with respect to SnO2Ac. High affinity to water as well as low sensor signals to CO in humid air reported for SnO2Cl were proposed to originate from traces of Cl ions (about 0.15 wt % for SnO2Cl and 0.03 wt % for SnO2Ac) and not microstructure, which has been confirmed to be similar for both materials. Two types of water adsorption and two CO sensing mechanisms are proposed for SnO2Cl and SnO2Ac on the basis of the results.

The gas sensing properties of polyhedral alpha-Fe2O3 particles were investigated. The polyhedral alpha-Fe2O3 particles were synthesized via a modified polyol method with the addition of an extra amount of NaBH4 in ethylene glycol, and fabricated to a thick gas sensing film after calcination at 500 degrees C and 900 degrees C. The polyhedral alpha-Fe2O3 particles exhibited a p-type nature, which is a new result opposite to other results of recent reports of semiconductor gas sensors using alpha-Fe2O3. In particular, we suggest that the difference between structure and morphology of alpha-Fe2O3 particles can lead to p-type and n-type characterization. In addition, we suggested that Na ions from NaBH4 were incorporated into alpha-Fe2O3 oxide. They are the cause of the generation of holes in alpha-Fe2O3 oxide that led to the p-type nature of alpha-Fe2O3 oxide. The measurement of the sensor response to hydrogen, carbon monoxide, toluene, propane and ethanol revealed that the sensor device synthesized using polyhedral alpha-Fe2O3 particles is sensitive to hydrocarbons and ethanol. Importantly, the sensor device using polyhedral alpha-Fe2O3 particles calcined at 900 degrees C was strongly sensitive to ethanol due to the porous structure of the alpha-Fe2O3 particles.

In the present research, large iron oxide microparticles with large sizes in the range of 1-5 mm have been facilely synthesized by a modified polyol method with NaBH4 as a versatile strong reducing agent. We found that the highly homogeneous iron oxide microparticles' novel structure is the best pure crystal phase of alpha-Fe2O3 in terms of polyhedral morphology and shape in existence. There are no diffraction peaks of other crystal phases from impurities in alpha-Fe2O3 microparticle products in the crystal growth. Interestingly, a new method of heat treatment or atomic surface deformation allowed for the discovery of a new large alpha-Fe2O3 structure with controlled specific alpha-Fe2O3 oxide grains in the crystal structure. The severe surface deformation of sharp, polyhedral, large alpha-Fe2O3 microparticles under a sintering treatment was found to give un-sharp, polyhedral large alpha-Fe2O3 microparticles with specific grains and boundaries.

Solution-processed photovoltaic (PV) devices based on semiconductor nanocrystals (NCs) such as Cu2ZnSnS4 (CZTS) and CuInS2 (CIS) are attracting much attention for use in next-generation solar cells. However, the performance of NC-based devices is hindered by insulating surface-capping ligands that limit transfer/transport of charged carriers. Here, to remove surface-capping ligands (long-chain fatty amines) from NCs, we use the strong alkylating agent methyl iodide, which converts primary amines to quaternary amines that have low coordinating affinity to the NC surface. X-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy analyses confirm the successful removal of capping ligands from the CZTS surface after treatment with methyl iodide without changing the crystal structure of CZTS. CZTS and CIS NC-based devices treated with methyl iodide exhibit a reproducible PV response under simulated sunlight. The developed route can potentially enhance the performance of NC-based devices used in a broad range of applications.

Oxygen adsorption plays key roles in resistive-type SnO2 gas sensors that can very sensitively detect combustible gases such as CO and hydrocarbons. Thus, exact evaluation of the electric resistance of SnO2 in response to oxygen is important to understand the oxygen adsorption mechanism. However, infinitesimal impurities contained in even high-grade commercial oxygen cylinders impose great effect on the sensitivity of SnO2. In this study, we designed an experimental system, which composed of gas pretreatment chambers including a Pt/Al2O3 combustion catalyst and a zeolite adsorbent, for exact analysis of gas sensing properties. Our experimental system allowed for the accurate determination of the dependence of the electrical resistance (R) on oxygen partial pressure (PO2) by removing impurities in sample gases. According to the linear correlation between R versus PO21/4, we concluded that oxygen adsorbed on the SnO2 surface in the form of O2- at 350 and 450 degrees C in extremely dry conditions that was achieved using the experimental system. The competitive adsorption on the SnO2 surface in the form of O- and O2- was suggested at 300 degrees C. (C) 2014 The Electrochemical Society. All rights reserved.

An impregnation method has been proposed to prepare Pd-loadedWO3 nanolamellae for the gas sensing application. WO3 nanolamellaewere synthesized via an acidificationmethod and impregnatedwithH(2)Pd(2)Cl(4) solution followed by an ammoniawashing treatment. Themicrostructure and H2 sensing characteristics of the Pd-loaded WO3 nanolamellae were investigated. Electronmicroscopy studies revealed that PdO particles have been deposited on the surfaces ofWO(3) with a diameter ranging from3 to 15 nm. With quite a small amount of Pd, the sensor resistivity was greatly enhanced and it demonstrated an extremely large response to the reduced gas. It was found that sensing response at low temperature increased dramatically with a rise in the gas concentration for Pd-loaded sensors. However, the sensor response at high temperature quickly saturated with increasing the H-2 concentration for larger amount of Pd loading. An enhanced combustion effect of Pd and chemical adsorbed water could be responsible for such a saturation of sensing response at high temperatures. (C) 2013 Elsevier B.V. All rights reserved.

The discharge/charge performance of Li-air cell using the carbon-supported LaMn0.6Fe0.4O3 nanoparticle as a cathode catalyst was investigated in this study. The carbon-supported LaMn0.6Fe0.4O3 nanoparticle was prepared via a reverse homogeneous precipitation method, and fabricated to air electrode. Li-air cell was constructed using air electrode, Li metal foil and 1.0 M LiPF6 in propylene carbonate as a cathode, anode and electrolyte, respectively. As the result, the carbon-supported LaMn0.6Fe0.4O3 nanoparticle exhibited both the oxygen evolution activity and the oxygen reduction activity in the non-aqueous electrolyte. The investigation about the presence and absence of the catalytic layer and the gas diffusion layer revealed that each layer is indispensable for the excellent electrode performance, and that the catalytic layer and the gas diffusion layer has a important role to supply the electrolyte and the oxygen gas, respectively. The investigation about the amount of the catalytic layer and the effect of the oxygen concentration revealed that the oxygen diffusability into the air electrode strongly affects to the discharge capacity of Li-air cells. (C) 2013 Elsevier B.V. All rights reserved.

Gas sensing is an important application of metal oxides. The gas sensor response of metal oxide films is greatly influenced by particle size, pore size, thickness, and surface states. To study the effects of particle and pore sizes of sensing films on sensitivity, we fabricated SnO2-based films with different particle and pore sizes and studied sensor responses to three different gases: H2, CO, and H2S with different Knudsen diffusion coefficients. The pore size radii of the gas sensing films were successfully controlled from 2.8 to 5.5 nm using SnO2 nanoparticles of different sizes (4-17 nm diameter) that were synthesized by seed-mediated growth under hydrothermal conditions. Sensor response to H2 increased with decreasing particle size because of the formation of an electron depletion layer within the nanosized crystals. In contrast, the response to CO and H 2S increased with increasing particle size and the resultant pore size. Using the Knudsen diffusion-surface reaction equation, we simulated a gas concentration profile within the films, which revealed that the diffusion of CO and H2S is limited by small pores because of their lower diffusion rates compared with H2. We show that controlling the pore size of the sensing films produces ultrasensitive films, and a large resistance change by 4 orders of magnitude is achieved in response to a low concentration of H 2S (5 ppm). © 2013 American Chemical Society.

Carbon-supported La1-xCaxMn1-yFeyO3 nanoparticles were synthesized, and their oxygen reduction activities and electronic states were investigated. A reverse micelle method using KIvInO, as a source of high valence state Mn successfully yielded carbon-supported La1-xCaxMn1-yFeyO3 nanoparticles even when calcined under a reducing atmosphere. The oxygen reduction activity of carbonsupported La1-xCaxMn1-yFeyO3 exceeded that of carbon-supported Pt nanoparticles when the Ca composition was limited to the range of 0.4 to 0.8. X-ray photoelectron spectroscopy (XPS) measurements of La1-xCaxMn1-yFeyO3 particle surfaces revealed the existence of Mn+, which is important in the oxygen reduction activity. Depth analysis of La1-xCaxMn1-yFeyO3 nanoparticles by XPS revealed the formation of a CaCO3 impurity and an A-site deficient perovskite-type oxide containing a high surface concentration of Mn4+.

A catalytic combustion-type gas sensor using a positive temperature coefficient (PTC) thermistor, which shows a sharp resistance change around Curie temperature, was developed for the detection of hydrogen. La-doped BaTiO 3 (Ba0.998 La0.002 TiO3) was prepared through a solid-state method and an oxalic acid method. La-doped BaTiO3 obtained by the oxalic acid method showed improved PTC properties, due to the formation of fine particles, as compared to that prepared with the solid-state method. The resulting sensor device showed a fairly high H2 sensitivity in the range of 100-1000 ppm. In addition, the H 2 sensitivity and response speed were improved by coating a Pt/SiO2 catalyst on the sensor device because the catalytic combustion efficiency of H2 was improved by the catalyst coating. © 2013 The American Ceramic Society.

To develop a portable gas sensor with low power consumption, we deposited a micro size sensing film (100 × 100 μm2) on a Si substrate with an integrated micro heater and electrodes constructed using micro-electro- mechanical system (MEMS) technology. TiO2 nanotubes ca. 500nm long with a 50 nm diameter were used to sense and detect volatile organic compounds (VOCs). We demonstrate that the MEMS sensor responded well to ethanol and toluene in air at elevated temperatures, such as 500 °C, which suggests that it is a promising battery-operable micro gas sensor for detecting VOCs. © 2013 The Japan Society of Applied Physics.

In recent years, the recovery of noble metals from waste has become very important because of their scarcity and increasing consumption. In this study, we attempt the photochemical recovery of noble metals from solutions using inorganic organic hybrid photo-catalysts. These catalysts are based on polyoxometalates such as PMo12O403-, SiW12O404-; and gamma-SiW10O368- coupled with a cationic surfactant, dimethyldioctadecylammonium (DODA). The three different photocatalysts dissolved in chloroform were successful in photoreducing gold ions dissolved in water in a two-phase (chloroform/water) system under UV irradiation (lambda < 475 nm). The gamma-SiW10O36/DODA photocatalyst exhibited the best activity and recovered gold from solution efficiently. It was suggested that one-electron reduced gamma-SiW10O369- formed by the UV irradiation reduced gold ions. As a result, large two-dimensional particles (gold nanosheets) were produced using the gamma-SiW10O36/DODA photocatalyst, indicating that the reduction of gold ions occurred at the interface between chloroform and water. The gamma-SiW10O36/DODA photocatalyst was able to recover metals such as platinum, silver, palladium, and copper from deaerated solutions. The selective recovery of gold is possible by controlling pH and oxygen concentration in the reaction system.

In our present research, bottom-up self-assembly of gold (Au) nanoparticles on a flat copper (Cu) substrate is performed by a facile method. The very interesting evidence of self-assembly of Au nanoparticles on the top of the thin assembled layer was observed by scanning electron microscopy (SEM). We had discovered one of the most general and simple methods for the self-assembly of metal nanoparticles. The general physical and chemical mechanisms of the evaporation process of the solvents can be used for self-assembly of the as-prepared nanoparticles. The important roles of molecules of the used solvents are very critical to self-assembly of the as-prepared Au nanoparticles in the case without using any polymers for those processes. It is clear that self-assembly of such one nanosystem of the uniform Au nanoparticles is fully examined. Finally, an exciting surface plasmon resonance (SPR) phenomenon of the pure Au nanoparticles in the solvent was fully discovered in their exciting changes of the narrow and large SPR bands according to synthesis time. The SPR was considered as the collective oscillation of valence electrons of the surfaces of the pure Au nanoparticles in the solvent by incident ultraviolet-visible light. Then, the frequency of light photons matches the frequency of the oscillation of surface electrons of the Au nanoparticles that are excited.

We have already demonstrated that an air electrode using LaMnO3-supported on LaNiO3 efficiently works as a bi-functional air electrode for oxygen reduction and evolution. In order to improve the bi-functional activity, high specific surface area of nano-LaNiO3 was prepared by a new route using ZnO particles as an aggregation inhibitor. Nano-sized LaNiO3 (ca. 40 nm) was successfully prepared after removing ZnO by KOH solution from a LaNiO3-ZnO mixture prepared by a reverse homogeneous precipitation (RHP) method. The result showed that increasing the surface area of LaNiO3 support is very effective in improving both the oxygen reduction and evolution activities. (C) 2012 Elsevier B.V. All rights reserved.

A stable sol suspension of Pd-loaded SnO2 nanocrystals, which is valid for both fundamental studies of semiconductor gas sensor and fabrications of a micro gas sensor, was fabricated by the photochemical deposition of PdCl42- onto SnO2 in an aqueous solution. UV light was irradiated on a mixture of a SnO2 sol obtained through a hydrothermal treatment of stannic acid gel in the presence of PdCl42- and ethanol/water at pH 2. A stable sol suspension of Pd-loaded SnO2 was successfully obtained by controlling the pH of the above suspension to 10.5 after UV irradiation. Thin-film type sensor devices (film thickness similar to 200 nm) using Pd-loaded SnO2 nanocrystal were successfully fabricated by a spin-coating method. Gas sensing measurements showed that the deposition of Pd on the SnO2 nanocrystals resulted in large electrical sensitization effect The maximum gas sensitization effect was obtained at 0.125 mol % Pd loading. Moreover, the Pd loading lowered the temperature, in which the maximum sensor response to H-2 was obtained, due to the efficient catalytic combustion of H-2 on Pd.

To verify theoretical model based on the surface depletion effect of oxide semiconductor in small crystallite, the SnO2 particles of different crystallite size and donor density were prepared by controlling heat-treatment temperature and Fe3+ doping concentration, respectively. In addition, Fe3+-doped SnO2 was compared with Fe2O3-loaded SnO2 to discuss the effect of donor density. The electrical resistance and sensor response of prepared SnO2 films were measured in various partial pressures of oxygen and hydrogen. As results, both undoped- and Fe3+-doped SnO2 showed the volume depletion in the oxygen concentration of more than 2.5% at 350 degrees C. The dependence of electrical resistance on oxygen partial pressure for smaller crystallite had steeper slope. Furthermore Fe3+-doping improved the sensor response to hydrogen, while the Fe2O3-loading did not work. Good agreement between experimental data the volume depletion theory was found. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.107204jes] All rights reserved.

Detection of volatile organic compounds (VOCs) has attracted considerable attention for indoor air quality and human breath analysis. Here, resistive-type gas sensors with porous films made of Au-loaded TiO2 nanotubes were developed for the detection of large-sized VOCs. Well-dispersed Au nanoparticles (10 to 20 nm) were photo-chemically deposited on TiO2 nanotubes (80 nm in diameter, 700 nm in length) prepared by a hydrothermal method. The device using the Au-loaded TiO2 nanotubes showed improved sensor responses to ethanol and toluene (50 ppm) in air at 500 degrees C. This suggested that Au nanoparticles deposited on the surface of TiO2 nanotubules without aggregation. We also demonstrated that the device could be used for the detection of large-sized VOC molecule, i.e., 2,6-diisopropylphenol (propofol), an intravenously administered hypnotic drug for induction and maintenance of anesthesia. The Au-loaded TiO2 nanotubes would offer a way to continuously monitor a change in the concentration of VOCs in exhaled air for medical diagnostics. (C) 2011 The Ceramic Society of Japan. All rights reserved.

Porous gas sensing films composed of TiO2 nanotubes were fabricated for the detection of volatile organic compounds (VOCs), such as alcohol and toluene. In order to control the microstructure of TiO2 nanotubular films, ball-milling treatments were used to shorten the length of TiO2 nanotubes and to improve the particle packing density of the films without destroying their tubular morphology and crystal structure. The ball-milling treatment successfully modified the porosity of the gas sensing films by inducing more intimate contacts between nanotubes, as confirmed by scanning electron microscopy (SEM) and mercury porosimetry. The sensor using nanotubes after the ball-milling treatment for 3 h exhibited an improved sensor response and selectivity to toluene (50 ppm) at the operating temperature of 500 degrees C. However, an extensive ball-milling treatment did not enhance the original sensor response, probably owing to a decrease in the porosity of the film. The results obtained indicated the importance of the microstructure control of sensing layers in terms of particle packing density and porosity for detecting large sized organic gas molecules. (C) 2010 Elsevier B.V. All rights reserved.

We investigated the H-2 sensing properties of a catalytic combustion-type hydrogen sensor using a BaTiO3-based positive temperature coefficient (PTC) thermistor as a transducer. In this sensor, catalytic combustion of H-2 on Pt electrodes or a catalyst layer induces a remarkable change in the electric resistance as a sensor signal when the operating temperature is set near the Curie temperature of BaTiO3 (120 degrees C). However, the sensor response to H-2 is relatively low at lower H-2 concentrations because of lower combustion efficiency near 120 degrees C. In this study, Ba-0.9(Bi0.5Na0.5)(0.1)Ti0.999Nb0.001O3 (BNN-BT) with a higher Curie temperature (146 degrees C) was used as a transducer to increase the operating temperature and thus improve the sensor response. The sensor using BNN-BT and a Pt/SiO2 combustion catalyst showed improved sensor responses particularly at lower H-2 concentrations. It also showed good response and recovery behaviors in response to 100-1000 ppm H-2 in air.

The loading of noble metals was carried out to enhance the gas sensing characteristics of TiO2 nanotube-based sensors. Using a photochemical deposition method, Au nanoparticles were successfully deposited on TiO 2 nanotubes prepared by a hydrothermal method in a highly-dispersed state. The sensor device using a porous film composed of the Au-loaded (0.5 wt%) TiO2 nanotubes exhibited improved sensor responses to 10-50 ppm toluene in air at 500 °C. The sensor response was about two times higher than that of a sensor using commercial TiO2 nanoparticles (degussa P-25). The results demonstrate that the Au loading is a very efficient method for improving the sensing characteristics of TiO2 nanotube-based sensors operative at high temperatures. Copyright © 2011 American Scientific Publishers.

The durability of carbon-supported La-Mn-based perovskites for the oxygen reduction reaction in strong alkaline solutions was investigated. Carbon-supported perovskite-type oxide nanoparticles were prepared by using a reverse micelle method. The durability of the carbon-supported LaMnO(3) nanoparticles was compared with that of carbon-supported LaMnO(3) prepared by the mechanical mixing of LaMnO(3) with the carbon support. As a result, the durability of the carbon-supported LaMnO(3) nanoparticles was less than that of the carbon-supported LaMnO(3) prepared by the mixing method due to a difference in the surface area of LaMnO(3), which has an effect on the oxygen reduction reaction. In order to improve the durability of the carbon-supported LaMnO(3) nanoparticles, Ca and Fe were substituted at the A-sites and B-sites of the perovskite lattice, respectively. As a result, it was found that the partial substitution of Ca and Fe is effective in improving the durability of LaMnO(3) under cathodic polarization in strong alkaline solutions. In particular, the substitution of Ca at the A-site not only improved the durability of the oxide but also enhanced the oxygen reduction activity owing to an increase in the average valence state of the B-sites of the perovskite lattice. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3551499]

Carbon supported-electrocatalysts are principally used as catalytic layers for air electrodes of metal air batteries. However, these types of air electrodes are problematic because the carbon support can be oxidized to water soluble organic compounds under anodic polarization for a charge process. In this study, we have investigated to use LaNiO3 as a possible electrode material to replace the carbon support because LaNiO3 has both high electric conductivity and high oxygen evolution activity. LaNiO3 was prepared by a reverse homogeneous precipitation method, and then LaMnO3, which is active for oxygen reduction reactions, was successfully loaded onto the LaNiO3 by using a reverse micelle method. LaNiO3 had a much higher stability against anodic polarization as compared to carbon support. The LaMnO3/LaNiO3 composite electrode showed excellent bi-functional oxygen reduction/evolution activity in an alkaline solution and this makes it a highly potential candidate for use in rechargeable metal-air batteries. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3562564] All rights reserved.

To obtain a highly active and low-cost oxygen reduction electrode, as compared with a Pt-loaded carbon electrode, a nano-sized La-Mn-based perovskite-type oxide on a carbon support was prepared through the reverse-micelle method. An gas diffusion oxygen reduction electrode using nano-sized La(0.4)Ca(0.6)Mn(0.9)Fe(0.1)O(3) as a electrocatalyst allowed a electrode potential as high as -50 mV (vs Hg/HgO) in 9 mol/l NaOH at 500 mA cm(-2). This electrode potential is much higher than the electrode potential of carbon-supported Pt nanoparticles at the same current density. This result suggests that nano-sized La(0.4)Ca(0.6)Mn(0.9)Fe(0.1)O(3) is a promising candidate as an alternative oxygen reduction catalyst of Pt nanoparticles. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3561762] All rights reserved.

A solid-state CO2 sensor device using a metal-insulator-silicon carbide (MISiC) capacitor combined with a Li2CO3-BaCO3 auxiliary layer was fabricated and tested for its basic sensing properties. The MISiC-based CO2 sensor attached with the carbonate showed typical capacitance-voltage (C-V) properties in air at 400 degrees C, and the sensor device responded well to changes in CO2 concentration in air at 400 degrees C. The sensor signals were directly proportional to the logarithm of CO2 concentration. The results suggested that an electrochemical reaction of CO2 occurred at the interface between the carbonate layer and the electrode, causing the applied voltage to shift in response to CO2. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3512998] All rights reserved.

In order to enhance the response speed, noble metal (Ru) loading into the WO3-NaNO2 sensing layer for the field effect transistor (FET)-based NO2 sensors was investigated. The sensing layer was prepared by heat-treating the mixture powder of NaNO2 and noble metal (Ru)-loaded WO3 at 300 degrees C. The effects of loading amounts of the noble metal on NO2 sensing performances as well as the microstructure of the sensing layer have been examined. It was found that the optimization of the noble metal loading amount into the sensing layer was important for the improvement of 90% response-and recovery-times. Field emission scanning electron microscopy observations revealed that the sensing layer became porous with increasing noble metal loading amounts. However, extensive addition of Ru (above 0.2 wt% to WO3) into the sensing layer resulted in the degradation of sensing characteristics, although the sensing layer showed a highly porous structure. According to theoretical analysis based on Knudsen gas diffusion reported by Matsunaga et al., the diffusion of gas molecules into such a porous sensing layer is very fast. Therefore the obtained results suggested that the improvement of the response-and recovery-speeds is owing to the large contribution of noble metal nanoparticle to the electrochemical promotion rather than the diffusion of NO2 gas into the sensing layer. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3525625] All rights reserved.

In order to investigate the effect of the microstructure on the oxygen permeation in Ba0.95La0.05FeO3-delta membranes, three different methods such as solid-state reaction, nitrate and acetate decomposition (NAD), and amorphous malic acid precursor (AMP) methods were used to fabricate membranes with different grain sizes. The grain size of the membranes was successfully controlled from 35 to 829 mu m2 via sintering at 1175 degrees-1275 degrees C. The oxygen permeation fluxes through the Ba0.95La0.05FeO3-delta membranes increased with a decrease in the grain size. The AMP method, using malic acid as a complexing agent, produced a membrane having the highest oxygen permeability (3.10 cm3 center dot(min center dot cm2)-1 at 930 degrees C) and the smallest grain size. The results obtained again confirmed the significant importance of microstructure control in designing high-performance oxygen permeable membranes.

High oxygen permeability was achieved using an asymmetric Ba0.95La0.05FeO3-delta membrane. In this membrane, oxygen diffuses physically through pores of a porous support and oxygen permeates electrochemically through a dense layer. The oxygen permeation flux of the asymmetric Ba0.95La0.05FeO3-delta membrane reached more than 10 cm(3) (STP) min(-1) cm(-2) from a test gas containing 50% oxygen at 930 degrees C.

In this study, gas diffusion electrodes (GDEs) with two catalyst layers were fabricated and tested for their electrode performance for oxygen reduction in an alkaline solution. The LaMnO3/carbon black catalyst layers were fabricated using a reverse micelle method to finely disperse the LaMnO3 particles onto the carbon matrices, for which commercial Ketjen Black (KB) (1270 m(2) g(-1)) and Vulcan XC-72R (VX) (254 m(2) g(-1)) were used. The three-layer-structured GDE with the two LaMnO3/KB and LaMnO3/VX catalyst layers exhibited a superior oxygen reduction activity when compared to that of a conventional GDE with only one LaMnO3/KB catalyst layer. Pore size distribution and gas permeability measurements revealed that the LaMnO3/VX layer was more porous and had higher gas permeability than the LaMnO3/KB layer. These results suggest that the intermediate layer of LaMnO3/VX can efficiently supply oxygen to reaction sites dispersed in the LaMnO3/KB and LaMnO3/VX catalyst layers, which consequently leads to an improvement in the electrode performance.

In order to reduce the electric resistance of the WO3 sensing film fabricated from the ion-exchange method, lamellar-structured and Re-doped WO3 was prepared through the acidification method. The mixed solution of Na2WO4 and Re2O7 was dropped into the mixed solution of H2SO4 and HCHO. Then the obtained gel was deposited on alumina substrate with An electrode for thick film devices and calcined at 300 degrees C. The size of the Re-doped WO3 particles was smaller in one order in magnitude than that of the WO3 by the ion-exchange method. The electric resistance of Re-doped WO3 device in air showed minimum value at the 4 at% Re doping due to the increase in the donor density in the WO3 crystal. As a result, the Re-doped WO3 device exhibited low electric resistance less than 10(8) Omega even in the 800 ppb NO2. Such a low electric resistance device is suitable for the detection of the wide range of NO2. (C) 2010 The Ceramic society of Japan. All rights reserved.

Preparation and morphology control of TiO2 nanostructured films for gas sensor applications were investigated. To examine the effect of the morphology of sensing films on the sensing characteristics, TiO2 with different morphologies, nanoparticles and nanotubes, were used for the film preparation. TiO2 nanotubes were prepared by a hydrothermal treatment of TiO2 nanoparticles in a NaOH solution at 160, 200, and 230 degrees C for 24 h and subsequent washing with an HCl solution. Uniform sized TiO2 nanotubes of 1 mu m in length and 50 nm in diameter were formed at 230 degrees C. The sensing films composed of nanotubes prepared at 230 degrees C showed a high sensor response to toluene at 500 degrees C as compared with those composed of TiO2 nanoparticles. Scanning electron microscope (SEM) analysis and pore size distribution measurements indicated that the sensing films composed of the TiO2 nanotubes had a high porous morphology with a peak pore size of around 200 rim, which can promote the diffusion of toluene deep inside the films and improve the sensor response. The obtained results demonstrated the importance of microstructure control of sensing layers for improving the sensitivity to large size molecules like volatile organic compounds (VOCs). (C) 2009 Elsevier B.V. All rights reserved.

Mixed potential-type gas sensors with a BiCuVOx (Bi2Cu0.1V0.9O5.35) oxygen conductor fitted with composite electrodes made of perovskite-type oxide (La0.6Sr0.4Co0.8Fe0.2O3) and BiCuVOx, were tested for their organic gas sensing properties. A planar-type BiCuVOx-based device, in which thin sensing electrode and thick counter electrode are attached, exhibited good sensing characteristics to low ethanol concentrations (4-30 ppm) at 400 degrees C. The electromotive force (EMF) of the device had a linear relation to the logarithm of ethanol concentration. The 90% response and recovery times of the device were short, i.e., less than 1 min. Moreover, the planar structure Successfully eliminated any oxygen interference. The ethanol sensing mechanism is based on the mixed potential generation from the simultaneous anodic oxidation of ethanol and the cathodic reduction of oxygen, at the BiCuVOx/electrode interface. (c) 2008 Elsevier B.V. All rights reserved.

A reverse micelle method was investigated for preparing nano-sized PdO loaded on SnO(2) nanoparticles. PdO-SnO(2) nano-composite was prepared by precipitating Pd(OH)(2) and Sn(OH)(4) inside a reverse micelle. The microstructure and the gas sensing properties of obtained nanoparticles were investigated. Although the particle size of SnO(2) was as same as ca. 10 nm at each observed sample, the particle size of PdO got larger as increasing with loading amount of PdO because of agglomeration of PdO nanoparticles each other. As a result of the gas sensing measurement, it was found that the particle size of PdO on SnO(2) nanoparticle influences the gas sensing property closely. That is, the sensor response declined gradually with increasing the particle size of PdO although the maximum of the sensor response was obtained in PdO=0.1 mol%. In this method, small amount of PdO loading can be achieved as compared with PdO-loaded SnO(2) sensor prepared by the conventional impregnation method. (C) 2008 Elsevier B.V. All rights reserved.

To explore oxygen permeable materials, oxygen permeation properties of partially A-site substituted BaFeO3-delta perovskites were investigated. Ba sites in BaFeO3-delta were substituted with cations such as Na, Rb, Ca, Y, and La by 5%. The partial substitution with Ca, Y, and La, whose ionic radii are smaller than that of Ba, succeeded in stabilizing a cubic perovskite structure that is a highly oxygen permeable phase, as revealed by X-ray diffraction analysis. This can be explained in terms of a decrease in the tolerance factor (t). Among the Ba0.95M0.05FeO3-delta (M = Na, Rb, Ca, Y, and La) membranes tested, Ba0.95La0.05FeO3-delta showed the highest oxygen permeability at 600-930 degrees C, owing to the stabilization of the cubic phase without the formation of impurity phases. From chemical analysis, the oxygen permeability of Ba1-xLaxFeO3-delta membranes was correlated with the amount of oxygen defects (delta) in the lattice. The oxygen permeation flux of Ba0.95La0.05FeO3-delta membrane was significantly increased by reducing its thickness. Furthermore, a Ba0.975La0.025FeO3-delta membrane exhibited good phase stability under He flow at elevated temperatures. The obtained results indicate the promising properties of Ba1-xLaxFeO3-delta membranes as a cobalt-free material that has a high oxygen permeability, good phase stability, and low cost. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3231690] All rights reserved.

To improve the stability of Na(3)Zr(2)Si(2)PO(12) (NASICON)-based potentiometric CO(2) sensors fitted with carbonate/Au layers (sensing electrode), mixed conducting oxides of Li(0.4)CoO(2) and Na(0.6)CoO(2) were examined for their applicability to solid-reference electrodes in terms of their stability against CO(2) and humidity. Compared with the Na(0.6)CoO(2) electrode, the Li(0.4)CoO(2) electrode showed far better stability against CO(2). When the Li(0.4)CoO(2) electrode was coated with a layer of glass, the electrode showed no response to CO(2) (200-2000 ppm) and little interference from humidity [21-86% relative humidity (RH)] at 450 degrees C. A CO(2) sensor device using Li(2)CO(3)-BaCO(3) and a glass-coated Li(0.4)CoO(2) showed stable electromotive force (emf) responses to CO(2) in humid air (86% RH) at 450 degrees C. The emf of the device was also stable even after it was exposed to humid air (86% RH) containing CO(2) (400 ppm) at room temperature for 1-2 days. The present study indicates the promising features of the glass-coated Li(0.4)CoO(2) as a stable solid-reference material for NASICON-based CO(2) sensors. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3216044] All rights reserved.

To fabricate more excellent NO2 sensor with high sensor response and good linearity between the sensor response and NO2 concentration, the microstructure of WO3 lamellae was controlled by adding nano-particles of SnO2. It was found that the sintering of WO3 lamellae was inhibited by adding nano-particles of SnO2. The device using WO3 lamellae added a small amount of SnO2 nano-particles had the highest sensor response, exhibiting a high sensor response (S = 60-540) even to dilute NO2 (100-1000 ppb) in air at 200 degrees C.

Partially Zr-substituted BaFe1-yZryO3-delta membranes were developed as a Co-free oxygen permeable membrane. In order to stabilize the cubic perovskite structure, Fe sites in BaFeO3-delta were partially substituted with Zr4+. In the substitution range of y = 0.01-0.1, the cubic perovskite structure was stabilized even at room temperature. Among the membranes prepared, a BaFe0.975Zr0.025O3-delta material (y = 0.025) showed the highest oxygen permeation flux of 1.30 cm(3) (standard temperature pressure) min(-1) cm(-2) at 930 degrees C under an air/He gradient. The oxygen permeation flux was higher than that of partially Ce-substituted BaFe1-yCeyO3-delta membranes reported previously. From the results obtained by chemical and scanning electron microscope analyses, it appears that the oxygen permeability for BaFe1-yZryO3-delta membranes was well correlated with the amount of oxygen defects in the lattice as well as the grain size. In addition, the oxygen permeation flux of the BaFe0.975Zr0.025O3-delta membrane was significantly increased after decreasing the thickness of the membrane from 2.0 to 0.4 mm. For thin membranes (0.4-1.0 mm), the thickness dependence of the oxygen permeability deviated from the Wagner equation, suggesting that the oxygen permeation of BaFe0.975Zr0.025O3-delta is controlled by not only bulk diffusion of oxide ions but also their surface reactions. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3086763] All rights reserved.

Tungsten trioxide (WO3) was prepared by acidification of Na2WO4 with acid solutions such as H2SO4, HCI, and HNO3 (pH 0.5 to -0.8)and tested forits NO2 sensing properties. Acidification with strong acid solutions (pH -0.5, -0.8) was found to produce lamellar-structured WO3 particles, which consisted of nano-sized crystalline plates that were 100-350nm in lateral size and 20-50nm in thickness, as observed by XRD and SEM analyses. The sizes of the primary and secondary particles were decreased by decreasing the pH of the acid solution used. This was accompanied by an increase in the specific surface area. The NO2 responses of the prepared WO3 lamellae were dependent on their morphology. The device using smaller WO3 lamellae prepared with a H2SO4 solution (pH -0.8) had the highest sensor response, exhibiting a high sensor response (S=150-280), even to dilute NO2 (50-1000 ppb) in air at 200 C. The use of smaller lamellae resulted in a decrease in the electrical resistance of the device, probably due to intimate contact between smaller lamellar particles, which allowed the detection of NO2 in a rather wide concentration range. In addition, the developed device showed high NO2 selectivity without substantial interference from NO. (c) 2008 Elsevier B.V. All rights reserved.

To achieve a high oxygen permeation rate at medium and high temperature, an asymmetrically structured membrane, in which a thin dense layer (30 mu m) made of La0.6Ca0.4CoO3-delta (LCC) and BaFe0.975Zr0.025O3-delta (BFZ) was formed on a porous LCC support, was fabricated and tested for its oxygen permeability. The oxygen permeation flux significantly increased by mixing BFZ with LCC and reached a fairly high value of 1.60 cm(3) min(-1) cm(-2) even at 780 degrees C.

The perovskite-type SmFeO(3) powders were prepared by the four different methods, named decomposition method of heteronuclear cyano complexes (CN), polymer precursor method (PP), reverse micelle method (RM) and reverse homogenous precipitation method (RHP), and their catalytic activities were evaluated with a CO oxidation reaction. The surface areas and the surface chemical compositions of Sm, Fe, O and C were strongly dependent on the preparation methods and calcination temperatures. On the basis of such the characteristics on the surface the factors controlling the catalytic activity are discussed. (C) 2008 Elsevier B.V. All rights reserved.

A FET type NO(2) sensor fitted with NaNO(2)-RU/WO(3) as a new auxiliary (sensing) layer was fabricated and tested for its NO(2) sensing properties. The developed device responded to dilute NO(2) of ppb concentrations (20-300 ppb) at 130 and 170 degrees C. The sensor signal (V(GS); gate-source voltage) is linearly proportional to the logarithm of NO(2) Concentration, exhibiting the Nernstian response. It was found that the response speed was improved at lower operating temperature by adding Ru to the NaNO(2)WO(3) auxiliary layer. It was suggested that Ru nanoparticles deposited in the auxiliary layer with a porous morphology improved the rate of adsorption and electrochemical reaction of NO(2) occurring at the interface between the Au gate electrode and auxiliary layer.

To achieve high-efficiency oxygen permeation using mixed (ionic and electronic) conducting perovskite-type oxides, we examined asymmetric-structured membranes of La0.6Ca0.4CoO3 in which a thin dense membrane was deposited on a porous support. The La0.6Ca0.4CoO3 porous support was fabricated using irregular-shaped precursor particles prepared through an oxalate method. The fabricated support had good gas permeability and thermal stability, showing sufficient properties as a support for dense thin membranes. A dense membrane of 10 mu m thickness was successfully formed on the porous support by coating a La0.6Ca0.4CoO3 Slurry and subsequent densification by sintering. The deposited thin membrane was gastight and free from clacks, as revealed by gas permeation tests and SEM observations. The asymmetric membrane exhibited a high oxygen permeability of 1.66 cm(3) (STP, standard temperature and pressure) min(-1) cm(-2) at 930 degrees C, which was four times higher than that of a typical sintered-disk type membrane with 1200/mu m thickness, demonstrating its feasibility as a high-performance oxygen separation membrane.

An asymmetric-structured membrane, in which a dense thin La0.6Ca0.4CoO3 layer of 10 mu m was deposited on porous La0.6Ca0.4CoO3 support by a slurry dropping method, were tested for its oxygen permeability at 630-930 degrees C. In order to increase the oxygen permeability, porous La0.6Ca0.4CoO3 and SrCo0.8Fe0.2O3-delta oxygen evolution layers were attached on the dense layer. It was found that the asymmetric structured membranes with the porous oxygen evolution layers showed remarkably higher oxygen permeability as compared with a conventional sintered disk-type membrane (1200 mu m). This suggests that oxygen permeation through membranes of 10 mu m in thickness is rate-determined by both bulk O2- diffusion and oxygen evolution reaction. The maximum oxygen permeability reached 4.77 cm(3) (STP) min(-1) cm(-2) (3.54 x 10(-6) Mol cm(-2) s(-1)) at 930 degrees C for the asymmetric membrane with porous La0.6Ca0.4CoO3 oxygen evolution layer of 10 mu m in thickness (STP= Standard Temperature and Pressure). Further improvements in the oxygen permeability would be achieved through control of the micro-structure of the oxygen evolution layers. (C) 2008 Elsevier B.V. All rights reserved.

A high-speed gas-switching system. in which a low-dead volume chamber (0.6 cm(3)) was connected to a gas flow apparatus equipped with a high-speed gas-switching valve operative at a rate of 30 ms, was designed to investigate the real response and recovery properties of semiconductor gas sensors. The developed system allowed rapid replacement of the gas atmosphere in the chamber where a gas sensor device was placed within 0.3 s. it was revealed that the response speed of the sensor device based on a SnO2 porous film (pore size at maximum population: 37 nm) was remarkably fast, reaching a response time of less than 1 s for H-2 and CO detection at 250 and 350 degrees C. This suggests that the diffusion and surface reaction of H-2 and CO are quite fast in the porous film. On the other hand, the recovery speed was not comparably fast and the resistance of the device did not recover to the original state within 20 s after switching the gas atmosphere in the chamber from the sample gases to air. This is possibly due to the slow desorption of the H2O and CO2 that were formed by the surface reaction of H-2 and CO, respectively with the adsorbed oxygen on SnO2. (c) 2008 Elsevier B.V. All rights reserved.

A potentiometric organic gas sensor-based on BiCuVOx (Bi2Cu0.1V0.9O5.35) solid electrolyte was investigated. Electromotive force (EMF) of the sensor device, in which a BiCuVOx sintered disk is fitted with composite electrodes of BiCuVOx/La0.6Sr0.4Co0.78Ni0.02- Fe0.2O3, was measured in the presence of various organic gases at 350-500 degrees C. The device responded to volatile organic compounds (VOC) of formaldehyde, toluene, and ethanol, but showed little sensitivities to methane, propane, propene, CO, and H-2. The EMF of the sensor was linear to the logarithm of organic gas concentrations, suggesting that the generation of EMF is explained on the basis of the mixed potential theory. The observed good sensitivity toward VOC derives from the good oxide ion conductivity of BiCuVOx and proper electro-catalytic activity of the perovskite oxide electrode even at lower temperature. (c) 2008 Elsevier B.V. All rights reserved.

To improve the stability of a NASICON (Na3Zr2Si2PO12; Na+ conductor)-based potentiometric CO2 sensor under humid conditions, a composite of BiCuVOx (Bi2Cu0.1V0.9O5.35) and perovskite-type oxide (La0.6Sr0.4Co0.78Ni0.02Fe0.2O3) was used as a solid-reference electrode. The CO2 sensing properties and stability of a NASICON-based planar device fitted with Li2CO3-BaCO3 (auxiliary phase) and the composite reference electrode were examined under humid conditions. The planar device mounted on an alumina substrate with a Pt heater showed stable electromotive force (emf) responses to changes in the CO2 concentration (100-400 ppm) at 400 and 450 degrees C in humid air without degradation. The sensor device also exhibited a good warming-up characteristic, i.e., the emf of the device quickly reached a steady and constant value when the sensor operation was restarted even after the sensor was exposed to humid air (86% relative humidity at 25 degrees C) at room temperature for a long time. (C) 2008 The Electrochemical Society.

A laminated solid-reference electrode of BiCuVOx (Bi2Cu0.1V0.9O5.35)/perovskite-oxide (La0.6Sr0.4Co0.78Ni0.02 Fe0.2O3) was developed for a NASICON (Na3Zr2Si2PO12; Na+ conductor)-based potentiometric CO2 sensor. The fabricated electrochemical cell expressed as, CO2, O-2/Au (sensing electrode)/Li2CO3-BaCO3 (auxiliary phase)/NASICON/BiCuVOx/BiCuVOx-perovskite-oxide (reference electrode)/O-2, responded well to changes in CO2 concentration (100-400 ppm) at 450 degrees C under high humid conditions (88%RH). The potential of the developed reference electrode was stable and exhibited little interference by water vapor. Furthermore, the reference electrode potential did not response to CO2 even after the BiCuVOx layer was contaminated with carbonate, indicating a good stability of BiCuVOx against CO2. The sensor device attached with the laminated solid-reference electrode showed a good warming-up characteristic, i.e., the electromotive force (EMF) of the device reached a steady and constant value when the sensor operation is re-started even after the sensor was exposed to humid air containing CO2 at room temperature.

Two ways of reverse micelle (RM) method were investigated to prepare carbon-supported nano-sized LaMnO3 with high oxygen reduction activity. Hydrolysis precipitation in reverse micelle (HP-RM) method could give nano-sized particles of LaMnO3 easily because the particles size decreased with decreasing R-w (=[H2O]/[surfactant]) value as well as nitrate concentration. The electrode prepared by the resulting particles showed high oxygen reduction activity as compared with that prepared by mechanical mixing-method. Furthermore, it was found that new RM method (ROP-RM) using KMnO4 as an oxidizer gave higher oxygen reduction activity than the HP-RM method, although particle size of LaMnO3 obtained by the ROP-RM method was almost same as that by RM-HP method. (C) 2007 Published by Elsevier B.V.

A novel method by combining NAC-FAS (NAnometer-sized Crystal Formation in Alcoholic Solutions) method and mechanical milling treatment was successfully applied for dispersing perovskite type oxide LaMnO3 finely on carbon support. Microscopic observation revealed that nano-sized oxide particles were dispersed fairly well in the carbon support. The gas diffusion-type electrode prepared by means of reducing number and quantity of chemicals exhibited more excellent oxygen reduction activity than the electrodes containing LaMnO3 prepared by RHP (Reverse Homogeneous Precipitation) method. It allowed current density as high as 300 mA cm(-2) at -80 mV (vs. Hg/HgO) in 8 M KOH at 60 degrees C under air flow.

La1-xSrxMn0.8Fe0.2O3+delta (x = 0-0.4) and La0.8Sr0.2Mn1-yFeyO3+delta (y = 0-0.8) supported on carbon were successfully prepared by a reverse micelle method. Aqueous solutions dissolving nitrates of constituent metals of the intended oxides and tetramethylammonium hydroxide (precipitant) were separately transformed into reverse micelle dispersions by using poly(oxyethylene)(5)-lauryl ether (surfactant) and cyclohexane (oil). These dispersions were mixed together to derive a reverse micelle dispersion containing mixed hydroxides as precursors of the oxides, into which carbon powder suspended in cyclohexane was put under agitation. The suspension was destabilized with ethanol, and the resulting precipitate (carbon-supported precursors) was calcined in N-2 atmosphere to prevent the carbon matrix from being combusted. Single-phase oxides supported on carbon were obtained by calcination at 700degreesC unless the oxides were free of Fe. Oxygen reduction activity of the gas-diffusion-type electrodes fabricated with thus prepared carbon-supported oxides increased sharply and decreased gradually with increasing x and y, respectively. Among the prepared oxides, the greatest activity, i.e., 500 mA/cm(2) at -67 mV (vs. Hg/HgO electrode) in 9 M NaOH at 85degreesC under O-2 flow, was achieved by the oxide with x = 0.4 and y = 0.2. Optimal loading on carbon as well as durability under oxygen reduction conditions were tested for selected oxides. 17 wt % La0.6Sr0.4Mn0.8Fe0.2O3+delta loading electrode was compared with 27.7 wt % Pt-loading electrode in an oxygen reduction activity, and it was found that the former electrode was better than the Pt loading electrode. (C) 2004 The Electrochemical Society.

Reverse micelle (RM) based synthesis of carbon-supported perovskite type oxide (LaMnO3) was investigated. By using cyclohexane as oil phase, six kinds of nonionic surfactants were tested for the formation of the revere micelle dispersions containing aqueous solutions of mixed nitrates of La3+ and Mn2+ (RM-N) and tetramethylammonium hydroxide (RM-A) at the water/surfactant molar ratio (R-W) of 3. RM-A was found to be more difficult to form compared with RM-N or the RM containing pure water. At a temperature range of 5-25degreesC, it was given only by the surfactants with hydrophilic-lipophilic balance (HLB) values of 10.0-10.9. Phase diagrams of oil-surfactant-alkaline solution (or pure water) were constructed at 5 and 15degreesC for the best two surfactants, i.e., poly-(oxyetylene)(6)-nonylphenyl ether and poly-(oxyetylene)(5)-lauryl ether. Mixing RM-N and RM-A together gave the RM containing a mixed hydroxides-precursor (RM-P), which was further converted into carbon-supported LaMnO3 through a series of treatments including the addition of carbon powder and calcination in N-2 atmosphere at 600degreesC. The size of RM-P as well as that of the LaMnO3 grains supported on carbon could be controlled well by selecting R-W. The carbon-supported LaMnO3 proved to be highly active for the electrochemical reduction of oxygen. (C) 2004 The Electrochemical Society.

本研究では、メカノケミカル法でグラフェンを合成し、そのグラフェンの物性を明らかにするとともに、電気化学エネルギーデバイスへと応用展開することに取り組む。具体的には、メカノケミカル法により合成したグラフェンについて、以下の２点を明らかにする。
① 酸素還元・酸素発生に対して高い活性を示す要因を明らかにする ② 酸素還元・酸素発生反応以外の電気化学反応への適用可能性を探る
①について本年度は、メカノケミカル法により合成したグラフェンの電気化学特性（酸素還元活性および酸素発生活性）と欠陥構造の関係を調査した。メカノケミカル法により合成したグラフェンの酸素還元と酸素発生活性を計測し、得られた酸素還元電流および酸素発生電流を電極材料の表面積で規格化して「比活性」を定義した。また、メカノケミカル法により合成したグラフェンの原子配列に生じる欠陥構造をラマン分光法で評価した。そして、比活性と欠陥構造とを関連付けて考察した結果、メカノケミカル法により合成したグラフェンが酸素還元・酸素発生に対して高い活性を示す要因は、メカノケミカル法により導入された多数の欠陥にあることが推察された。また、メカノケミカル法により合成したグラフェンにおいては、酸素還元反応には比表面積の増大が重要であるが、酸素発生反応には比表面積の増大は特に有効でないことが明らかとなった。②について本年度は、メカノケミカル法により合成したグラフェンをスズ系酸化物と複合化することで大きな二酸化炭素還元電流が得られることを明らかにした。

Stable electrode materials under oxygen evolution reaction (charging reaction of metal air battery) was investigated for the construction of metal-air secondary batteries. It was found that Niobium doped-TiO2 (Nb-TiO2) is stable under oxygen evolution reaction. LaNi0.5Mn0.5O3 addition was effective for improving both the oxygen reduction reaction activity and oxygen evolution reaction activity of Nb-TIO2. It was also found that graphene is stable for under oxygen evolution reaction. NiCo2O4 was effective for improving the oxygen evolution reaction activity of Nb-TiO2.

In order to improve the electrode potential for the oxygen reduction reaction of air electrode, the effect of the composition of La-Mn based perovskite-type oxides on the oxygen reduction activity and the effect of the doubly loading of LaMnO3 and Pt on the carbon-support were investigated. As the result of substituting Ca and Fe for LaMnO3 nanoparticles, the optimum oxygen reduction activity was obtained at Ca=0.4 and Fe=0.1 because the valence state of B-sipe in the perovskite-type oxide was well optimized. The doubly loading of LaMnO3 and Pt on the carbon-support revealed that Pt is effective to improve the on-set potential for the oxygen reduction reaction, and that LaMnO3 is effective to reduce the overpotential for oxygen reduction reaction.

In this study, basic understandings of oxide semiconductor toward establishment of micro gas sensors for environmental protection have been investigated. Especially depletion state of semiconductors due to controlling grain size and donor density, relationship between donor density and amount of oxygen adsorption, masking effect on oxide surface, receptor function and its optimal loading method, etc. were researched. As one of the results, the VOC sensor in ppb level to toluene was prepared based on the obtained theories and experiments.

Metal-air batteries have higher theoretical energy densities compared with other chemical batteries because they utilize oxygen in the air as one of their electroactive materials. Therefore, metal-air batteries have been paid attention as a next generation energy device. However, air electrodes in metal air batteries are problematic because the carbon black can be oxidized to water soluble organic compounds, under anodic polarization. Therefore, we have looked at the use of LaNiO_3 as a possible electrode material to replace carbon black because LaNiO_3 has both high conductivity and high oxygen evolution activity. As the result, we found that LaNiO_3 has a much higher stability against anodic polarization when compared to carbon black, and that fabrication of LaMnO_3/LaNiO_3 composite made air electrodes to work as bi-functional electrodes.

Various kinds of gas sensors have been developed or proposed and some of them have been recognized as key devices to monitor, handle or control of gases for various purposes. In this study, importance of structure control in nano- and meso-level for high-sensitive semiconductor gas sensor to VOCs, which are large size molecules, was indicated through brief effects by receptor function, transducer function and utility factor. For receptor function, it was challenged to load each colloidal particle of SnO_2 with foreign metal like Pd by a reverse micelle method and a surface modification method for surface modification. It was found that the particle size of PdO on SnO_2 nano-particle influences the gas sensing property closely. Small amount of PdO loading can be achieved as compared with PdO-loaded SnO_2 sensor prepared by the conventional impregnation method. For transducer function, doping each particle with other oxides for valence control was also challenged. We investigated the effects of Fe^3^+ doping in SnO_2 on the crystalline size, electric resistance, and sensor response. The Fe^3+ doping was found to decrease the carrier concentration and crystalline size. The dependence of electrical resistance on oxygen partial pressure and the sensor response to H_2are well explained in terms of the proposed theory. For utility factor, by increasing pore size through an increase in grain size and introducing macropores through forming small clusters (secondary particles) of grains, the target gas reacts with the oxide surface on its way of diffusion into the sensor device. The prepared SnO_2cluster sols were useful for fabrication of thin film type gas sensor including the microstructure with larger pores. From the sensing properties, it was found that such cluster sols have high potentiality as a precursor solution to prepare high order structure controlled devices for high performance. In order to develop high-sensitive gas sensors, it was expressed that the three key factors should be fused together in one sensor device.