Fuel cell system and corresponding operating process

1. A fuel cell system comprising:

at least one fuel cell, which has at least two electrodes for connecting at least one electric user;

at least one temperature-measuring device for measuring an electrode temperature, which is correlated with a temperature at at least one of said electrodes or corresponds to the temperature at said at least one of said electrodes;

at least one reformer for generating a reformate gas for supplying the fuel cell;

at least one water feed means for feeding water to the reformate gas, between said reformer and said fuel cell; and

a controller comprising a control setting programmed to set a quantity of water fed to the reformate gas as a function of the measured electrode temperature.

2. A fuel cell system in accordance with claim 1 , further comprising:

at least one residual gas burner for burning anode waste gas and cathode waste gas, wherein said residual gas burner has a burner waste gas line, which is coupled with a cathode gas feed means for supplying the fuel cell with cathode gas in a heat-transmitting manner.

3. A fuel cell system in accordance with claim 1 , wherein said control is designed and/or programmed for the steps of controlling a quantity of fuel fed to the reformer and/or a quantity of oxidant gas fed to the reformer depending on at least one of:

the measured electrode temperature;

the conversion of fuel and/or oxidant gas at the fuel cell; and

such that a carbon formation limit temperature of the reformate gas is below the measured electrode temperature.

4. A motor vehicle fuel cell system comprising:

a fuel cell comprising two electrodes with a motor vehicle user electrical connection;

a temperature-measuring device for measuring an electrode temperature, which electrode temperature is correlated with a temperature at one of said electrodes or corresponds to the temperature at said one of said electrodes;

a reformer for generating a reformate gas for supplying the fuel cell;

a water feed feeding water to the reformate gas, between said reformer and said fuel cell; and

a controller comprising a control setting programmed to set a quantity of water fed to the reformate gas as a function of the measured electrode temperature.

5. A motor vehicle fuel cell system in accordance with claim 4 , wherein said control sets the quantity of water fed to the reformate gas depending on at least one of:

a reformate gas volume flow;

a conversion of fuel and/or oxidant gas at the fuel cell; and

a carbon formation limit temperature of the reformate gas being below the measured electrode temperature.

6. A motor vehicle fuel cell system in accordance with claim 4 , wherein said control sets a quantity of fuel fed to the reformer and/or a quantity of oxidant gas fed to the reformer depending on the measured electrode temperature.

7. A motor vehicle fuel cell system in accordance with claim 6 , wherein the quantity of water fed to the reformate gas and/or the quantity of fuel fed to the reformer and/or the quantity of oxidant gas fed to the reformer is set depending on the conversion of fuel and/or oxidant gas at the fuel cell.

8. A motor vehicle fuel cell system in accordance with claim 4 , wherein the water is fed to the reformate gas at least one of only above a preset minimum electrode temperature and only below a preset maximum electrode temperature.

9. A motor vehicle fuel cell system in accordance with claim 4 , wherein:

water from said water feed is fed into the reformat gas downstream of said reformer.

10. A motor vehicle fuel cell system in accordance with claim 4 , wherein:

said control sets the quantity of water fed to the reformate gas to a value that causes a carbon formation limit temperature of the reformat gas to be at a value below the measured electrode temperature.

11. A fuel cell system in accordance with claim 1 , wherein:

water from said water feed means is fed into the reformat gas downstream of said reformer.

12. A motor vehicle fuel cell system in accordance with claim 4 , wherein:

said control sets the quantity of water fed to the reformate gas to a value that causes a carbon formation limit temperature of the reformat gas to be at a value below the measured electrode temperature.

13. A fuel cell system comprising:

a fuel cell including two electrodes adapted to connect to an electrical user;

a temperature-measuring device measuring an electrode temperature, the electrode temperature being correlated with a temperature of one of said two electrodes;

a reformer connected to said fuel cell and receivable of fuel, generating a reformate gas from the fuel, and supplying the reformate fuel to said fuel cell;

a reformate gas line connecting said reformer to said fuel cell, and transporting the reformate gas from said reformer to said fuel cell;

a water feed feeding water into the reformate gas downstream of said reformer; and

a control setting configured to set a quantity of water fed to the reformate gas as a function of the measured electrode temperature.

14. A fuel cell system in accordance with claim 13 , wherein:

said water feed feeding the water into the reformate gas line at a location between said reformer and said fuel cell.

15. A fuel cell system in accordance with claim 13 , wherein:

said control is configured to set the quantity of water fed to the reformate gas to a value that causes a carbon formation limit temperature of the reformat gas to be at a value below the measured electrode temperature.

16. A fuel cell system in accordance with claim 13 , wherein:

said control is configured to set a quantity of fuel fed to the reformer and a quantity of oxidant gas fed to the reformer to maintain a carbon formation limit temperature of the reformate gas below the measured electrode temperature.

17. A fuel cell system in accordance with claim 13 , wherein:

said control is configured to set the quantity of water fed to the reformate gas and is configured to set a quantity of fuel fed to the reformer and is configured to set a quantity of oxidant gas fed to the reformer to maintain a carbon formation limit temperature of the reformate gas below the measured electrode temperature.

18. A fuel cell system in accordance with claim 13 , further comprising:

a recirculating line feeding anode waste gas from said fuel cell to said reformer;

said control is configured to use a conversion rate of cathode and anode gas of said fuel cell to determine a quantity of water in the anode waste which is fed to said reformer.

19. A fuel cell system in accordance with claim 18 , wherein:

said control is configured to set the quantity of water fed to the reformate gas and is configured to set a quantity of fuel fed to the reformer and is configured to set a quantity of oxidant gas fed to the reformer depending on the conversion rate of the cathode and anode gas of said fuel cell.

20. A fuel cell system in accordance with claim 15 , wherein:

said control is configured to stop feeding the water to the reformate gas when the measured electrode temperature is below a minimum electrode temperature, the minimum electrode temperature being a temperature below which a further reduction of the carbon formation limit temperature by feeding water to the reformate gas is no longer possible.