Redox flow battery

A redox flow battery comprising a positive electrode, a negative electrode and a separation membrane,

• wherein a positive electrode electrolyte composed of an aqueous solution containing vanadium ions is supplied into a positive electrode chamber, and a negative electrode electrolyte composed of an aqueous solution containing vanadium ions is supplied into a negative electrode chamber, to carry out charging and discharging of the battery;
• and
• wherein zirconium or titanium coated with a noble metal or a compound thereof is used as a positive electrode material, and
• when the positive electrode material is zirconium coated with a noble metal or a compound thereof, the positive electrode electrolyte and the negative electrode electrolyte contain sulfuric acid;
• and
• when the positive electrode material is titanium coated with a noble metal or a compound thereof, the positive electrode electrolyte contains nitric acid and sulfuric acid, and has a nitric acid content of 0.5 mass % or more and 15 mass % or less based on the total amount of the electrolyte.