Diagnostic system, fuel cell system having a diagnostic system, and method for determining cathode gas contamination

A fuel cell system comprising:

• a fuel cell stack;
• and
• a diagnostic system connected to a cathode supply line that supplies a cathode gas and an anode supply line that supplies an anode gas;
• wherein the diagnostic system includes a diagnostic fuel cell having a cathode side and an anode side, the diagnostic fuel cell connectable on the cathode side with the cathode supply line and on the anode side with the anode supply line and a detection unit which is configured to detect a measured value or a measured value time curve of the diagnostic fuel cell when in operation with the cathode gas and the anode gas.

A method for determining a cathode gas contamination in a fuel cell system, comprising:

• connecting a diagnostic system having a diagnostic fuel cell to a cathode supply line and an anode supply line of the fuel cell system;
• operating the diagnostic fuel cell of the diagnostic system with cathode gas provided by the cathode supply line and with anode gas provided by the anode supply line;
• detecting a measured value or a measured value time curve of the diagnostic fuel cell;
• comparing the detected measured value or the detected measured value time curve with a predefined nominal value or a predefined nominal value time curve;
• and
• outputting a deviation value or a deviation signal as a function of a deviation determined between the detected measured value or the detected measured value time curve and the nominal value or the nominal value time curve.