METHOD FOR OPERATING A FUEL CELL SYSTEM, AND ANALYSIS UNIT FOR A FUEL CELL SYSTEM

The invention relates to a method for operating a fuel cell system with at least one fuel cell which is supplied with hydrogen via an anode path and oxygen via a cathode path, wherein anode exhaust gas exiting the fuel cell is recirculated, but from time to time a part of the anode exhaust gas is introduced into an exhaust gas path, which conducts the cathode exhaust gas, by purging the exhaust gas out of the anode path, and wherein the hydrogen concentration of the exhaust gas is measured in the exhaust gas path using a hydrogen sensor. According to the invention, the hydrogen and/or nitrogen concentration of the anode gas in the anode path before the last purge is calculated on the basis of the measured hydrogen concentration, the quantity of gas introduced into the exhaust gas path from the cathode path and from the anode path, and the quantity of hydrogen which is freshly supplied to the anode path. The invention further relates to an analysis unit for a fuel cell system for carrying out the method according to the invention.