NOVELTY - The device (10a) has a redox unit (12a) performing redox reaction with consumption and/or production of first gas i.e. hydrogen gas, and/or second gas i.e. oxygen gas. The redox unit comprises a gas purification unit (20a) for freeing the first gas of contamination by the second gas and/or freeing the second gas of contamination by the first gas. The gas purification unit comprises a catalyst unit (22a) for catalyzing reaction of oxygen gas and hydrogen gas into water. The catalyst unit includes catalyst elements (26a, 28a) comprising platinum metal partly.    USE - Redox device i.e. hydrogen-oxygen redox device such as regenerative fuel cell system.    ADVANTAGE - The device can transport heat of reaction evolved on operation of the fuel cell by a heating unit so as to avoid overheating phenomenon of the fuel cell. The gas purification unit can be arranged close at a zone in which hydrogen gas or oxygen gas is formed, and/or at an entry zone into a reaction region so as to provide high degree of operational safety of the redox device and reduce cost of operation by dispensing a stock of inert flushing gas and a passage of inert flushing gas. The device can arrange the catalyst element in lines or at inlets of the lines into gas spaces or form catalyst layers at sides of electrodes facing away from reaction zones so as to improve operational safety of the device. The catalyst element is made of platinum or noble metals such as ruthenium, rhodium, palladium, osmium, iridium, nickel and darmstadtium, so that the catalyst element can be formed as a chemically resistant catalyst element with high catalysis activity, thus improving purifying performance of the gas purification unit. The device is formed as a regenerative fuel cell system due to presence of the redox unit to realize accumulator function. The device can release waste heat of reaction by recombination of hydrogen and oxygen in the gas spaces, and can be utilized for heating the redox unit, so that energy consumption for heating the redox unit to operating temperature can be reduced.    DETAILED DESCRIPTION - The redox unit is configured as a fuel cell i.e. alkaline fuel cell (16a), an electrolyzer for producing hydrogen gas and/or oxygen gas or a fuel cell-electrolyzer pair. An INDEPENDENT CLAIM is also included for a method for operating a redox device in closed operation.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of a redox device.    Redox device (10a)    Redox unit (12a)    Alkaline fuel cell (16a)    Gas purification unit (20a)    Catalyst unit (22a)    Catalyst elements (26a, 28a)