NOVELTY - A fuel cell system (100) comprises an electrolysis cell (119) having an air cathode and coupled to a fuel cell (101). The fuel and electrolysis cells are designed so that power requirement of the electrolysis cell is covered by a power delivered from the fuel cell. The fuel cell has anode and cathode sides (102, 103) coupled to respective anode and cathode sides (120, 121) of the electrolysis cell. The cells are designed so that air from a aircraft cabin is conductable to cathode-sides. Hydrogen or reformate gas is conductable to fuel cell on the anode side.    USE - The fuel cell system is used for supplying a vehicle with drinking water and oxygen, and for use in an aircraft (claimed).    ADVANTAGE - The system is efficient in supplying drinking water and oxygen to a vehicle, e.g. aircraft. It is a high-integratibility system to generate pure oxygen, and increase the oxygen partial pressure, i.e. percentage distribution of the oxygen and nitrogen is altered in favor of the oxygen, in the respiration air of the passengers and crew of the aircraft, thus providing weight saving with regard to structural components of the cabin, flight altitude of 15500 m without additional structural reinforcement and the associated weight increase, and fuel savings. It increases passengers comfort, produces fresh water for the supply of water consumers found on the aircraft, reduces water load at aircraft takeoff and during climbing, provides weight savings, and a reduced power requirement when climbing.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for an aircraft with a fuel cell system. The fuel cell is a proton exchange membrane fuel cell. The electrolysis cell is a polymer membrane electrolysis cell with catalyst.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of the fuel cell system.    Fuel cell system (100)    Fuel cell (101)    Fuel cell anode and cathode sides (102, 103)    Electrolysis cell (119)    Electrolysis cell anode and cathode sides (120, 121)