▎ 摘　　要

NOVELTY - Air electrode catalyst comprises transition metal nitride nano-sheet which is carry/supported on the nitrogen addition graphene nano-sheet. USE - Air electrode catalyst for metal-air secondary batteries, catalyzing both reaction of oxygen generation and oxygen reduction (claimed). ADVANTAGE - The air electrode catalyst reduces the energy efficiency. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for: (1) a rechargeable and dischargeable metal-air secondary battery, which comprises air electrode as positive electrode; and (2) a method for preparing air electrode catalyst, which involves peeling transition-metal hydroxide layer from layered double hydroxide, where transition metal is selected from iron, cobalt, and nickel, and thickness of transition-metal hydroxide nanosheet is thinner than 10 nanometer; (3) mixing transition-metal hydroxide nanosheet and graphene oxide; (4) heating mixture in ammonia gas and nitriding simultaneously both transition metal and graphene oxide; and (5) collecting/recovering transition metal nitride nanosheets which is carry/supported on nitrogen addition graphene nanosheet.