Regeneration method and fuel cell system

Abstract

The invention relates to a regeneration method (100) for regenerating a contaminated fuel cell stack (201). The regeneration method (100) comprises:-introducing (101) a repair agent into the fuel cell stack (201); flushing (103) the repair agent from the fuel cell stack (201), the repair agent comprising a moving anion or a precursor of a moving anion.

Description

Technical Field

[0001] The invention relates to a regeneration method and a fuel cell system according to the appended claims. Background Art

[0002] A fuel cell is an electrochemical converter that converts hydrogen (H 2 ) and oxygen (O 2 ) is converted into water (H 2 O), electricity and heat.

[0003] The porous electrode of a proton exchange membrane (PEM) fuel cell is usually referred to as a catalyst layer, and is typically composed of nano-metal particles (catalysts) composed of platinum or platinum alloys supported on larger carbon particles. These carbon particles facilitate electron and heat transfer, high dispersion of active platinum or alloy metals, and sufficient mass transport due to their porosity.

[0004] Furthermore, the catalyst layer is impregnated with an ionomer to ensure its proton conductivity.

[0005] A three-phase boundary is required for the electrochemical reaction, which is formed by the contact of platinum, ionomer and reactants.

[0006] In the membrane and electrodes of a fuel cell, contaminants, especially metal ions, can accumulate during the service life of the fuel cell for various reasons. These reasons can include, for example, corrosion of the metal bipolar plates (e.g., Fe 2+ / 3+ ions), and the transport of these ions in the aqueous phase into the membrane electrode assembly (MEA); degradation reactions of the catalyst in the catalyst layer, depending on the alloy used; additives such as those used as free radical scavengers; or other contaminants or impurities, such as those resulting from the manufacturing process or from the operation of the fuel cell system.

[0007] The accumulation of positively charged ions (cations) is accompanied by a decrease in the proton concentration in the ion-containing polymer phase, which is a cation exchange material having a predetermined number of immobilized negatively charged counterions (anions).

[0008] Especially at high loads (current density), this leads to a reduction in the ionic conductivity and thus to a loss in efficiency of the fuel cell (lower voltage at a given current density), since the metal cations migrate into the cathode electrode and reduce the proton conduction there without themselves participating in the electrochemical reaction.

[0009] An exception is the noble metal ions, especially platinum ions, which are electrochemically reduced to metallic platinum at high loads and are thus exchanged for protons again. Therefore, in the degradation process, the chemically less active noble metal ions (such as Co 2+ 、Ni 2+ and / or Fe 2+ / 3+ ) accumulation is seen as a key issue.

[0010] It is presumed that the accumulated cations are mostly retained in the ion-conducting phase of the membrane electrode assembly, since they are fixed there due to the opposite charge of the anionic groups of the ionic polymer.

[0011] Known countermeasures are mostly limited to preventing or delaying the accumulation of metal cations in the membrane electrode assembly, for example by selecting catalyst materials, preventing / delaying degradation reactions or avoiding the transport of contaminants from the flow field into the membrane electrode assembly. Summary of the invention

[0012] Within the scope of the present invention, a regeneration method and a fuel cell system are proposed. Further features and details of the invention can be derived from the corresponding dependent claims, the description and the drawings. Here, the features and details described in connection with the regeneration method according to the invention are of course also applicable to the fuel cell system according to the invention and vice versa, so that the disclosures about the individual inventive aspects can always be referred to one another.

[0013] The invention is used, in particular, to provide a robust fuel cell system.

[0014] Therefore, according to a first aspect of the present invention, a regeneration method for regenerating a contaminated fuel cell stack is proposed, which comprises introducing a repair agent into the fuel cell stack and flushing the repair agent out of the fuel cell stack, wherein the repair agent contains mobile anions or a precursor of mobile anions.

[0015] In the context of the present invention, mobile anions are understood in particular to be free anions which are dissolved in solution, for example. In the context of the present invention, precursors or precursors of mobile anions are in particular immediately chemical compounds from which mobile anions can be formed in the fuel cell stack.

[0016] The present invention is based on the principle that mobile anions are introduced into the ion-containing polymer phase of a membrane electrode assembly (MEA) or a fuel cell without introducing additional cations that are not protons. These mobile anions can be discharged from the ion-containing polymer phase of the membrane electrode assembly together with the mobile cations in the form of salt pairs or aggregates, because these units are electrically neutral and are therefore no longer fixed by the ion polymer containing fixed anions.

[0017] Flushing is achieved by water produced in the fuel cell reaction under appropriately selected operating conditions and by fluids, such as gas and / or liquid water, flowing through the individual fuel cell flow fields. In this process, pollutants in the form of interfering metal cations are flushed out of the fuel cell together with anions introduced by the repair agent in the form of salt pairs, complexes or aggregates. Excess anions leave the fuel cell in protonated form.

[0018] In particular, the substances forming the repair reagent are selected and, if necessary, combined / mixed so that the affinity of the anions for the cations to be removed is neither too low nor too high, so that the cations can be discharged as efficiently as possible, while preventing the anions from leaving in protonated form and also avoiding local precipitation as sparingly soluble salts, which would prevent discharge but would release the interfering ions again in further operation. Unless the sparing solubility is sufficient to cause permanent binding of the interfering cations. In particular, the components of the repair reagent are optimized so that the cations with beneficial effects (e.g. Ce used as free radical scavengers) are not 3+ ) will not be washed away, or will only settle temporarily.

[0019] In particular, the repair agent is introduced into the cathode subsystem and, if appropriate, into the anode subsystem of the fuel cell stack.

[0020] It can be provided that the repair agent is gaseous and comprises an electrically neutral base gas, in particular carbon dioxide and / or nitrogen tetroxide, which decomposes into protons and anions when dissolved in water.

[0021] Carbon dioxide is particularly suitable for use as a remediation agent due to its low flammability and low cost.

[0022] It can also be provided that the base gas is converted or convertible into anionic species in the dissolved state and upon application of a voltage electrochemically.

[0023] Gases that can be converted into anionic species by voltage, such as dinitrogen tetroxide, can be activated, ie, converted into their anionic species, by the voltage provided in the fuel cell stack, so that the gas reacts where it should react in the fuel cell stack.

[0024] In the case of a liquid repair agent, this is introduced, for example, in pulses or as a spray, in order to ensure a regular oxygen supply.

[0025] It can also be provided that the repair reagent comprises at least one acid in an aqueous phase.

[0026] Acids such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, citric acid, oxalic acid, or ethylenediaminetetraacetic acid maximize the removal of cations from the fuel cell stack because the acids bind to the cations and can be flushed out of the fuel cell stack along with the cations.

[0027] Additionally, the acid can regulate reaction conditions that favor the reaction of the cation with the repair agent, such as a low pH.

[0028] It can also be provided that the repair agent comprises at least one complexing agent in the aqueous phase.

[0029] The complexing agent maximizes the removal of cations from the fuel cell stack because the complexing agent binds the cations and can be flushed out of the fuel cell stack together with the cations.

[0030] It can also be provided that the at least one acid and / or the at least one complexing agent is present in dissolved ionic or molecular form.

[0031] Depending on the repair agent, it can comprise, for example, a carrier substance in gaseous or liquid form, in which additives, such as acids and / or complexing agents, can be dissolved or contained in molecular form.

[0032] It can also be provided that the repair agent comprises a solution which comprises a substance, in particular ammonium carbonate, which can be converted into a neutral or anionic substance by applying an electrical voltage.

[0033] By means of substances which are convertible into neutral or anionic species when a voltage is applied, the regulating reaction for regeneration of the fuel cell stack can be controlled by the voltage acting on the fuel cell stack.

[0034] It can also be provided that the flushing of the repair agent and the contaminants takes place by means of water produced in the fuel cell stack.

[0035] In order to flush out the repair agent, the fuel cell stack can, for example, be switched into an operating state in which a particularly large amount of liquid water is produced.

[0036] It can also be arranged that, when flushing is carried out under wet and cold operating conditions, the battery voltage is adjusted to below a preset regeneration value.

[0037] Lowering the cell voltage below a preset regeneration value leads to a reduction of other pollutants adsorbed on the catalyst surface, such as sulfates or sulfonates, so that a plurality of, for example, independent regeneration processes can be carried out simultaneously in the same regeneration process.

[0038] For example, the regeneration method is implemented within the framework of a reconditioning protocol, which can also address other reversible aging effects. It is particularly advantageous to combine it with a procedure for reducing and flushing contaminants on the catalyst surface. In this procedure, a low cell voltage is set under wet and cold operating conditions, for example at 40°C and 100% relative air humidity, so that a large amount of liquid water is generated in the catalyst layer. In this state, the reconditioning agent is introduced on the cathode side via the medium supply system of the fuel cell stack in the form of a mixture with air or oxygen.

[0039] Alternatively, an alternative or additional introduction can also be carried out on the anode side. After the application of the remediation agent, the wet cold operating conditions are still maintained for a preset duration in order to flush out the remediation agent and the contaminants.

[0040] It may also be provided that, during or after the introduction of the repair agent, the voltage acting on the fuel cell stack is increased to above a preset adjustment value to induce a reaction between the repair agent and the pollutants present in the fuel cell stack.

[0041] According to a second aspect of the present invention, the present invention relates to a fuel cell system for energy conversion, the fuel cell system comprising a fuel cell stack, a metering system for metering a repair agent into the fuel cell stack, and a computing unit, wherein the computing unit is configured to control the metering system and the fuel cell stack to implement a possible configuration of the repair method according to the present invention.

[0042] Further advantages, features and details of the invention can be gathered from the following description, in which exemplary embodiments of the invention are described in detail with reference to the accompanying drawings. The features mentioned in the claims and in the description can be essential to the invention individually or in any combination. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A possible configuration of the regeneration method according to the present invention is shown;

[0044] Figure 2 A schematic diagram shows a possible configuration of a fuel cell system according to the present invention. DETAILED DESCRIPTION

[0045] exist Figure 1 1 shows a regeneration method 100 for regenerating a fuel cell stack. The regeneration method 100 comprises an introduction step 101, in which a repair agent is introduced, for example injected, into the fuel cell stack.

[0046] Furthermore, the regeneration method 100 comprises a flushing step 103 in which the remediation agent together with any contaminants which may be dissolved in the remediation agent are flushed out of the fuel cell stack.

[0047] According to the invention, it is provided that the repair agent contains mobile anions or precursors of mobile anions, so that the repair agent binds to contaminants that are present in the form of cations, in particular metal cations.

[0048] exist Figure 2 2 shows a fuel cell system 200. The fuel cell system 200 comprises a fuel cell stack 201, a metering system 203 for metering a repair agent into the fuel cell stack 201, and a computing unit 205.

[0049] The metering system 203 may include, for example, a storage tank (especially a pressure tank), a valve, and a pump.

[0050] The computing unit 205 may be, for example, a computer, a control device, a processor or any other programmable circuit.

[0051] The computing unit 205 is configured to control the metering system 203 and the fuel cell stack 201 so that the Figure 1 Repair method 100.

[0052] Optionally, the metering unit 203 and / or the computing unit 205 can be connected to the fuel cell system 200 via the interface 207, so that the metering unit 203 and / or the computing unit 205 can be connected to the fuel cell system 200 in a workshop, for example, to implement the method according to the invention. Figure 1 Repair method 100.

Claims

1. A regeneration method (100) for regenerating a contaminated fuel cell stack (201), wherein: The regeneration method (100) comprises: - introducing (101) a repair agent into the fuel cell stack (201); - Flushing (103) the repair agent out of the fuel cell stack (201), wherein the repair agent comprises mobile anions or precursors of mobile anions.

2. The regeneration method (100) according to claim 1, characterized in that: The repair agent is gaseous and comprises an electrically neutral base gas, in particular carbon dioxide and / or nitrogen tetroxide, which decomposes into protons and anions when dissolved in water.

3. The regeneration method (100) according to claim 2, characterized in that: The base gas can be converted electrochemically into anionic species in a dissolved state and upon application of a voltage.

4. The regeneration method (100) according to any one of the preceding claims, characterized in that The repair reagent includes at least one acid in an aqueous phase.

5. The regeneration method (100) according to any one of the preceding claims, characterized in that The repair reagent comprises at least one complexing agent in an aqueous phase.

6. The regeneration method (100) according to claim 4 or 5, characterized in that: The at least one acid and / or the at least one complexing agent are present in dissolved proton and anion or molecular form.

7. The regeneration method (100) according to any one of the preceding claims, characterized in that The repair reagent comprises a solution comprising a substance, particularly ammonium carbonate, which can be converted into a neutral or anionic substance by applying an electric voltage.

8. The regeneration method (100) according to any one of the preceding claims, characterized in that The flushing (103) of the repair reagents and contaminants is achieved by water produced in the fuel cell stack (201).

9. The regeneration method (100) according to any one of the preceding claims, characterized in that When flushing (103) is performed under wet and cold operating conditions, the battery voltage is adjusted to be lower than a preset regeneration value.

10. The regeneration method (100) according to any one of the preceding claims, characterized in that During or after the introduction of the repair agent, the voltage applied to the fuel cell stack (201) is increased to above a preset regulation value to induce a reaction between the repair agent and pollutants present in the fuel cell stack (201).

11. A fuel cell system (200) for energy conversion, the fuel cell system (200) comprising: - a fuel cell stack (201); - a metering system (203) for metering a repair agent into the fuel cell stack (201); - a computing unit (205), wherein the computing unit (205) is configured to control the metering system (203) and the fuel cell stack (201) in order to implement the repair method according to any one of claims 1 to 10.

12. A fuel cell system (200) for energy conversion, the fuel cell system (200) comprising: - a fuel cell stack (201); - an interface (207) for connection to a metering system (03) for metering a repair agent into the fuel cell stack (201).

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