Fuel cell system and method for operating a fuel cell system

A method (M) for operating a fuel cell system (200), comprising:

• feeding (M1) an oxidation gas stream to a cathode inlet (213) of a cathode (210B) of a fuel cell (210) of the fuel cell system (200);
• feeding (M2) a cathode exhaust gas stream from a cathode outlet (214) of the cathode (210B) to an exhaust gas inlet (233) of the humidifier (230);
• discharging (M4) the cathode exhaust gas stream from the humidifier (230) via an exhaust gas outlet (234) of the humidifier (230);
• humidifying (M5) the oxidation gas stream in the humidifier (230) by means of the water extracted from the cathode exhaust gas stream;
• determining (M6) at least one of the following indicators for the moisture content of the cathode exhaust gas:
• a pressure drop between the cathode inlet (213) and the cathode outlet (214), a pressure drop between the exhaust gas inlet (233) and the exhaust gas outlet (234) of the humidifier (230), a first temperature difference of the cathode exhaust gas stream between the exhaust gas inlet (233) and the exhaust gas outlet (234) of the humidifier (230), a second temperature difference of the oxidation gas stream between the oxidation gas inlet (231) and the oxidation gas outlet (232) of the humidifier (230);
• and
• varying (M7) a moisture feed to the cathode inlet (213) and/or moisture removal from the cathode (210B) by adjusting at least one operating parameter of the fuel cell system (200) based on the at least one determined indicator.