Abstract: A solid electrolyte contains a lithium (Li) element, a phosphorus (P) element, a sulfur (S) element, and an X element, where X represents at least one element selected from the group consisting of a chlorine (Cl) element, a bromine (Br) element, and an iodine (I) element. The solid electrolyte has a peak attributed to a fluorine (F) element in surface analysis based on X-ray photoelectron spectroscopy. It is preferable that the ratio (quantitative value of F1s/quantitative value of P2p) of quantitative value of F1s (atom %) and quantitative value of P2p (atom %), calculated based on X-ray photoelectron spectroscopy with the total amount of Li1s, C1s, O1s, F1s, P2p, S2p, Cl2p, and Br3d being set to 100%, is 0.01 or more and 0.34 or less.

Abstract: A method for producing a sulfide solid electrolyte includes: a step of mixing a lithium (Li) element source, a phosphorus (P) element source, and a sulfur (S) element source, thereby obtaining a raw material composition; a step of firing the raw material composition, thereby obtaining a sulfide; a step of milling a slurry containing a solvent having fluorine atoms and the sulfide; and a step of drying the slurry. The sulfide in the slurry preferably has a concentration of 3 to 40 mass %. The step of milling a slurry is preferably a step of dry milling the sulfide, and mixing the dry milled sulfide and the solvent, thereby preparing the slurry.

Abstract: An electrode catalyst layer for a fuel cell includes a catalyst/support composite including a support and a catalyst supported thereon. The support contains a titanium oxide. The surface of the catalyst/support composite has an oxide of at least one element selected from the group consisting of niobium, tantalum, zirconium, and silicon. The ratio A2/A1 is from 0.35 to 1.70, wherein A1 is the atomic ratio of titanium on a surface of the catalyst layer and A2 is the atomic ratio of a total of niobium, tantalum, zirconium, and silicon on the surface of the catalyst layer, A1 and A2 being measured by X-ray photoelectron spectroscopy. The titanium oxide preferably has a composition TiOx (0.5 ? x < 2).

Abstract: A catalyst layer for a fuel cell contains a support and a catalyst supported on the support. The support contains a titanium oxide having a crystal phase of Ti2O. The ratio of total abundance of trivalent Ti and divalent Ti (W2) to abundance of tetravalent Ti (W1), W2/W1, is 0.1 or more as determined on the surface of the catalyst layer by X-ray photoelectron spectroscopy. The catalyst is preferably made of at least one metal selected from platinum, iridium, and ruthenium, or an alloy thereof. Also, the catalyst layer for a fuel cell preferably further contains an ionomer, and the ratio of mass of the ionomer (I) to mass of the catalyst-supporting support (S), I/S, is preferably 0.06 or more and 0.23 or less.