A perovskite-type composite oxide powder is a perovskite-type composite oxide powder represented by a general formula ABO.sub.3-δ (where δ represents an amount of deficiency of oxygen and 0≤δ<1), an element contained in an A site is La, elements contained in a B site are Co and Ni and a crystallite size determined by a Williamson-Hall method is equal to or greater than 20 nm and equal to or less than 100 nm. In this way, when the perovskite-type composite oxide powder is used as an air electrode material for a fuel cell, an air electrode in which the resistance thereof is low and the conductivity thereof is high can be obtained.

The cathode active material is capable of reducing cathode resistance of a secondary battery by enhancing electron conductivity thereof without reducing discharge capacity of the secondary battery. The method for manufacturing a cathode active material includes: mixing transition metal-containing composite compound particles containing lanthanum with a lithium compound to obtain a lithium mixture; calcinating the lithium mixture at a temperature equal to or lower than the melting point of the lithium compound; and then subjecting the lithium mixture to main firing at a firing temperature within a range of 725° C. to 1000° C. Lithium carbonate is preferably used as the lithium compound, and in this case, the calcination temperature is within a range of 600° C. to 723° C. It is preferable to obtain the transition metal-containing composite compound particles containing lanthanum by a coprecipitation method and to uniformly disperse a lanthanum element in the particles.

A composition consisting essentially of a perovskite crystalline structure includes ions of a first metal M1 which occupies an A-site of the perovskite crystalline structure and ions of a second metal M2 which occupies a B-site of the perovskite crystalline structure. M2 has two oxidation states capable of forming a redox couple suitable for reversibly catalyzing an oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER). The composition also includes ions of a third metal M3 at least a portion of which substitutes for M1 in the A-site of the perovskite crystalline structure, and at least a portion of which optionally also substitutes for M2 in the B-site of the perovskite crystalline structure. At least some of the ions of M3 have a different oxidation state to the ions of M1. The composition also includes atoms of an element X, which is a chalcogen.

A composite oxide powder including a composition formula (1), wherein the ratio α/β of a surface area value α(m.sup.2/g) calculated by a BET one-point method to a surface area value β(m.sup.2/g) calculated from a formula (2) is greater than 1.0 and equal to or less than 1.5 and the surface area value α is equal to or less than 20 m.sup.2/g. ABO.sub.3-δ (1) (wherein A is one or more types of elements (La, Sr, Sm, Ca and Ba), B is one or more types of elements (Fe, Co, Ni and Mn) and 0≤δ<1); and surface area value β(m.sup.2/g)=specific surface area value γ- surface area value ε(2) (the specific surface area value γ(m.sup.2/g) is a value in a total pore size range measured by a mercury intrusion method.The specific surface area value ε(m.sup.2/g) is a value in a range of pore sizes that are larger than a 50% cumulative particle size.

Pyrochlore-based solid mixed oxide materials suitable for use in catalysing a hydrocarbon reforming reaction are disclosed, as well as methods of preparing the materials, and their uses in hydrocarbon reforming processes. The materials contain a catalytic quantity of inexpensive nickel and exhibit catalytic properties in dry reforming reactions that are comparable—if not better—than those observed using expensive noble metal-containing catalysts. Moreover, the Pyrochlore-based solid mixed oxide materials can be used in low temperature dry reforming reactions, where other catalysts would become deactivated due to coking. Accordingly, the catalytic materials represent a sizeable development in the industrial-scale reforming of hydrocarbons.

Disclosed herein are doped perovskite oxides. The doped perovskite oxides may be used as a cathode material in an electrochemical cell to electrochemically generate ammonia from N.sub.2. The doped perovskite oxides may be combined with nitride compounds, for instance iron nitride, to further increase the efficiency of the ammonia production.

An electrode assembly includes a composite body which includes an active material layer containing an active material constituted by a transition metal oxide, a solid electrolyte layer (solid electrolyte portion) containing a solid electrolyte, and a multiple oxide molded body (multiple oxide portion) containing at least one of a metal multiple oxide represented by the following general formula (1): Ln.sub.2Li.sub.0.5M.sub.0.5O.sub.4 (wherein Ln represents a lanthanoid, and M represents a transition metal) and a derivative thereof, and a current collector which is provided on one face (one of the faces) of the composite body by being bonded to the active material layer, wherein in the composite body, the multiple oxide molded body, the active material layer, and the solid electrolyte layer are formed in contact with each other in this order from the side of the one face of the composite body.

Provided is a new 5 V-class spinel-type lithium-manganese-containing composite oxide capable of achieving both the expansion of a high potential capacity region and the suppression of gas generation. Proposed is the spinel-type lithium-manganese-containing composite oxide comprising Li, Mn, O and two or more other elements, and having an operating potential of 4.5 V or more at a metal Li reference potential, wherein a peak is present in a range of 14.0 to 16.5° at 2θ, in an X-ray diffraction pattern measured by a powder X-ray diffractometer (XRD) using CuKα1 ray.

Provided is a new 5 V class spinel-type lithium manganese-containing composite oxide which enables the expansion of a high potential capacity region and the suppression of gas generation. The 5 V class spinel-type lithium manganese-containing composite oxide has an operating potential of 4.5 V or more at a metal Li reference potential, and contains Li, Mn, O and two or more other elements. The spinel-type lithium manganese-containing composite oxide is characterized in that, in an electronic diffraction image from a transmission electron microscope (TEM), a diffraction spot observed in the Fd-3m structure as well as a diffraction spot not observed in the Fd-3m structure are confirmed.

An electrochemical half-cell includes an electrical terminal lead in contact with a solid electrolyte, wherein the solid electrolyte includes a doped high-entropy oxide. The electrochemical half-cell can be used as either a reference half-cell or a measuring half-cell. Methods of manufacturing the solid electrolyte and the electrochemical half-cell are further disclosed.