METHOD FOR OPERATING A FUEL CELL SYSTEM, AND CONTROL DEVICE

Abstract

The invention relates to a method for operating a fuel cell system comprising a fuel cell stack having an anode and a cathode, in which the following steps for oxidizing impurities present in the anode, in particular adsorbates, are performed: S1 Interrupt the supply of air to the cathode of the fuel cell stack and ramp down the cell voltage by electrochemically reducing residual oxygen present in the cathode, S2 Interrupt the supply of hydrogen to the anode and electrochemically pump residual hydrogen present in the anode to the cathode, and S3 Oxidize the impurities by increasing the anode potential.

The invention also relates to a control device for carrying out steps of the method according to the invention.

Claims

1. A method of operating a fuel cell system comprising a fuel cell stack having an anode and a cathode, in which the following steps are performed for oxidizing impurities present in the anode, the method comprising: (step S1) interrupting a supply of air to the cathode of the fuel cell stack and ramping down a cell voltage by electrochemically reducing residual oxygen present in the cathode, (step S2) interrupting a supply of hydrogen to the anode and electrochemically pumping residual hydrogen present in the anode to the cathode, and (step S3) oxidizing impurities by increasing the anode potential.

2. The method according to claim 1, wherein in step S3 the anode potential is increased to 0.4 V to 1.5 V, compared to the cathode potential.

3. The method according to claim 1, wherein in step S3 the anode potential is increased by a potential jump, a potential ramp or a cyclic potential ramp.

4. The method according to claim 1, wherein steps S1 to S3 are performed at regular time intervals.

5. The method according to claim 1, wherein steps S1 to S3 are performed when shutting down the fuel cell system.

6. The method according to claim 1, wherein steps S1 and S2 are performed simultaneously or during overlapping time periods.

7. The method according to claim 1, wherein in step S1 the reduction in the cell voltage is forced by power tapping and the power is fed into the vehicle system and/or a battery.

8. The method according to claim 1, wherein in step S2, the electrochemical pumping is effected by applying a current and/or a voltage.

9. The method according to claim 1, wherein after performing steps S1 to S3 hydrogen present in the cathode is pumped back to the anode before continuing normal operation of the fuel cell system.

10. A control device configured to operating a fuel cell system comprising a fuel cell stack having an anode and a cathode, by controlling: interruption of a supply of air to the cathode of the fuel cell stack and ramping down of a cell voltage by electrochemically reducing residual oxygen present in the cathode, interruption of a supply of hydrogen to the anode and electrochemically pumping of residual hydrogen present in the anode to the cathode, and oxidization of impurities by increasing the anode potential.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The invention and its advantages are explained in more detail below with reference to the accompanying drawings. Shown are:

[0036] FIG. 1 a flow diagram for depicting a preferred procedure of the method according to the invention, and

[0037] FIG. 2 a cyclic voltammogram of a Pt/C electrode poisoned by carbon monoxide.

DETAILED DESCRIPTION

[0038] The sequence shown in FIG. 1 comprises three steps, from S1 to S3, as an example.

[0039] In step S1, the supply of air to the cathode is initially interrupted by closing the valves at the inlet and outlet of the fuel cell stack so that a self-contained volume of oxygen remains on the cathode side. Then, by power tapping, the fuel cell reaction is further forced to reduce oxygen and bring the cell voltage below 0.2 V, preferably below 0.1 V, particularly preferably below 0.05 V.

[0040] In the following step 2, which can also be carried out simultaneously or at least during a time period overlapping with step S1, the hydrogen supply to the anode is first interrupted. Subsequently, the hydrogen present in the anode is introduced to the cathode side by electrochemical pumping.

[0041] In step S3, the oxidation of the parasitic adsorbate then takes place by increasing the anode potential, for example by a potential jump or by a cyclic potential ramp, also called cyclic voltammetry.

[0042] Carbon monoxide oxidation by cyclic voltammetry is depicted in the graph of FIG. 2 as an example, wherein curve A is attributable to a first cycle and curve B is attributable to a second cycle. Region 1 shows an oxidation peak. Region 2 shows the gain in active platinum surface after the first cycle.