Abstract: When a metal catalyst is used as a catalyst in a catalyst layer of a polymer electrolyte fuel cell, improvement in catalytic activity and improvement in durability of the metal catalyst are intended. The catalyst composition of the present invention comprises a metal catalyst, a carbon material having a nitrogen-containing group on which the metal catalyst is carried, and an ionomer.

Abstract: The present invention provides: a cellulose nanofiber enabling the provision of a high-performance sheet-like material; a method for producing the cellulose nanofiber; and a sheet-like material obtained from the cellulose nanofiber. A bamboo-derived cellulose nanofiber having a cellulose purity of at least 90%, a fiber diameter of 10-20 nm, and a crystallinity of at least 70% can be obtained by a method comprising: (1) a step for subjecting a bamboo material to an alkali treatment and a mechanical treatment to prepare bamboo fibers; (2) a step for delignificating the obtained bamboo fibers; (3) a step for mechanically spreading the delignificated bamboo fibers; (4) a step for removing hemicellulose from the spread bamboo fibers; and (5) a step for removing metal components from the bamboo fibers from which hemicellulose has been removed.