Regeneration method and fuel cell system

Abstract

The presented invention relates to a regeneration method (100) for regenerating a contaminated fuel cell stack (201), comprising: - introducing (101) a reconditioning reagent into the fuel cell stack (201); and - flushing (103) the reconditioning reagent from the fuel cell stack (201), the reconditioning reagent containing mobile anions or precursors of mobile anions.

Description

[Technical Field]

[0001] The present invention relates to a regeneration method and a fuel cell system as claimed in the accompanying claims. [Background technology]

[0002] A fuel cell is an electrochemical energy converter that converts, for example, hydrogen (H2) and oxygen (O2) into water (H2O), electrical energy, and heat.

[0003] The porous electrodes of PEM fuel cells, often referred to as catalyst layers, consist of nanometal particles (catalysts), typically made of platinum or platinum alloys, supported on relatively large carbon particles that provide electron and heat transport, high dispersion of the active platinum or alloy metal, and sufficient mass transport due to their porosity.

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

[0005] For the electrochemical reaction to occur, a three-phase interface is required, which is formed by contact between platinum, the ionomer, and the reactants.

[0006] Fuel cell membranes and electrodes can accumulate contaminants, especially metal ions, over the life of the fuel cell for a variety of reasons. These reasons include corrosion of the metal bipolar plates (e.g., Fe 2+ / 3+ ions) and the transport of these ions into the aqueous phase within the MEA, catalyst degradation reactions in the catalyst layers, depending on the alloy used, these could be additives used for example as radical scavengers, or other contaminations or pollutants, e.g., from the manufacturing process or 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 ionomer-containing phase, which is a cation exchange material containing a certain amount of immobilized negatively charged counterions (anions).

[0008] In particular, at relatively high loads (current densities), metal cations migrate to the cathode electrode where they reduce proton conductivity without themselves contributing to the electrochemical reaction, resulting in a reduction in ionic conductivity and a concomitant loss of fuel cell efficiency (lower voltage at a given current density).

[0009] The exceptions are noble metal ions, especially platinum ions, which at high loadings are electrochemically reduced back to metallic Pt and thereby exchanged for protons again. Therefore, during the degradation process, chemically less noble metal ions, such as CO 2+ , Ni 2+ and / or Fe 2+ / 3+ accumulation is considered more serious.

[0010] It is postulated that the accumulated cations remain mostly in the ion-conducting phase of the MEA because they are held there by the opposite charges of the anionic groups of the ionomer.

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

[0012] Within the scope of the presented invention, a regeneration method and a fuel cell system are presented. Further features and details of the invention will become apparent from the respective dependent claims, the following description and the drawings. In that case, features and details explained in the context of the regeneration method according to the invention are naturally also valid in the context of the fuel cell system according to the invention and vice versa, whereby reference is always made to or can be made to each other in relation to the disclosure of the individual inventive aspects.

[0013] The presented invention is particularly useful for providing a robust fuel cell system.

[0014] Thus, according to a first aspect of the presented invention, a regeneration method for regenerating a contaminated fuel cell stack is presented, the regeneration method comprising introducing a reconditioning reagent into the fuel cell stack and rinsing the reconditioning reagent from the fuel cell stack, the reconditioning reagent containing a mobile anion or a precursor or precursor of the mobile anion.

[0015] In the context of the presented invention, mobile anions are to be understood in particular as free anions dissolved, for example in solution. In the context of the presented invention, precursors or precursors of mobile anions are to be understood in particular as chemical compounds capable of forming mobile anions in a fuel cell stack.

[0016] The presented invention is based on the principle that mobile anions can be incorporated into the ionomer-containing phase of an MEA or fuel cell without simultaneously incorporating other cations that are not protons.

[0017] These mobile anions can be removed from the ionomer-containing phase of the MEA in the form of salt pairs or blocks along with the mobile cations, since such units are electrically neutral and therefore no longer retained by the ionomer containing the immobilized anions.

[0018] Rinsing is carried out by the water produced in the fuel cell reaction under suitable operating conditions, as well as by fluids, such as gas and / or liquid water, flowing through the flow field of each fuel cell. In this case, contaminants in the form of interfering metal cations are washed out of the fuel cell in the form of salt pairs, complexes, or aggregates together with the anions carried by the reconditioning reagent. Excess anions leave the fuel cell in protonated form.

[0019] In particular, the substances forming the reconditioning reagent are selected, and possibly combined / mixed, so that the affinity between the anions and the cations to be removed is neither too strong nor too weak, in order to allow the most efficient possible removal of the cations for the release of the anions in protonated form, while avoiding local precipitation as sparingly soluble salts. Sparingly soluble salts may prevent removal, but may liberate the interfering ions again in further processes. This is unless the sparing solubility is sufficient to provide persistent binding of the interfering cations. In particular, the composition of the reconditioning reagent is determined by the presence of, for example, Ce, which is used as a radical scavenger. 3+ The method is optimized so that beneficial cations such as ammonium nitrate are not rinsed away or are only temporarily precipitated.

[0020] In particular, the reconditioning reagent is introduced into the cathode subsystem of the fuel cell stack, and in some cases into the cathode and anode subsystems.

[0021] The reconditioning reagent is gaseous and may be intended to include electrically neutral basic gases, particularly carbon dioxide and / or dinitrogen tetroxide, which dissociate into protons and anions when dissolved in water.

[0022] Carbon dioxide is particularly well suited for use as a reconditioning reagent due to its low flammability and low cost.

[0023] It is further contemplated that the basic gas is in solution and is electrochemically converted or convertible to anionic species upon application of a voltage.

[0024] A gas that can be converted to an anionic species by a voltage, such as dinitrogen tetroxide, can be activated, i.e., converted to its anionic species, by a voltage provided to the fuel cell stack, so that it reacts where it should react, i.e., in the fuel cell stack.

[0025] In the case of a liquid reconditioning reagent, this may be pulsed or introduced as an atomized mist, for example to ensure a regular oxygen supply.

[0026] It is further contemplated that the reconditioning reagent comprises at least one acid in the aqueous phase.

[0027] 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 they bind the cations and can be flushed out of the fuel cell stack along with the cations.

[0028] Furthermore, the acid provides for the adjustment of reaction conditions, such as a low pH value, which are favorable for the reaction of the cation with the reconditioning reagent.

[0029] Furthermore, the reconditioning reagent may be contemplated to comprise at least one complexing agent in the aqueous phase.

[0030] The complexing agent maximizes the removal of cations from the fuel cell stack as it binds the cations and can be flushed out of the fuel cell stack along with the cations.

[0031] Furthermore, it can be contemplated that the at least one acid and / or the at least one complexing agent are present as dissolved ions or molecules.

[0032] Depending on the reconditioning reagent, which may comprise a carrier substance, for example in gaseous or liquid form, additives such as acids and / or complexing agents may be dissolved therein or may contain molecules therein. It is further contemplated that the reconditioning reagent comprises a solution containing a substance that can be converted into a neutral or anionic substance by applying a voltage, in particular ammonium carbonate.

[0033] Depending on the substance, which can be or is converted into a neutral or anionic substance by applying a voltage, the conditioning reaction for regenerating the fuel cell stack can be controlled via the voltage applied to the fuel cell stack.

[0034] Furthermore, it may be contemplated that rinsing of reconditioning reagents and contaminants is performed with water produced in the fuel cell stack.

[0035] To rinse out the reconditioning reagent, for example, the fuel cell stack can be switched to an operating state in which particularly large amounts of liquid water are produced.

[0036] Furthermore, it may be contemplated that when rinsing, a cell voltage below a predetermined regeneration value is set under wet and cold operating conditions.

[0037] Reducing the cell voltage below a predetermined regeneration value causes reduction of other contaminants adsorbed on the catalyst surface, such as sulfates or sulfonates, thereby carrying out multiple, e.g., independent, regeneration processes simultaneously within the same regeneration method. For example, the regeneration method can be implemented within a reconditioning protocol that also removes other reversible aging effects. It is particularly advantageous to combine it with a procedure for reducing and flushing contaminants from the catalyst surface. This procedure results in low cell voltages under cold, humid operating conditions, e.g., 100% relative humidity in the air and 40°C, which leads to the production of large amounts of liquid water in the catalyst layer. The reconditioning reagent is then introduced into the cathode side of the fuel cell stack via the media supply, mixed with air or oxygen.

[0038] Optionally, alternative or additional introduction on the anode side is also possible. After dispensing the reconditioning reagent, the cool, humid operating conditions are continued for a predetermined duration to rinse away the reconditioning reagent and contaminants.

[0039] Furthermore, it may be contemplated that, upon or after the introduction of the reconditioning reagent, the voltage applied to the fuel cell stack may be increased above a predetermined adjustment value in order to initiate a reaction between the reconditioning reagent and contaminants present in the fuel cell stack.

[0040] According to a second aspect, the presented invention relates to a fuel cell system for converting energy, comprising a fuel cell stack, a dosier system for dosing a reconditioning reagent to the fuel cell stack, and a computing unit, the computing unit being configured to control the dosier system and the fuel cell stack in order to carry out possible embodiments of the presented reconditioning method.

[0041] Other advantages, features and details of the invention will become apparent from the following description in which exemplary embodiments of the invention are explained in detail with reference to the drawings, in which the features mentioned in the claims and in the description can each alone or in any combination be essential to the invention. [Brief explanation of the drawings]

[0042] [Figure 1] 1 is a diagram of a possible embodiment of the presented playback method; [Figure 2] 1 is a schematic diagram of a possible embodiment of the fuel cell system presented. DETAILED DESCRIPTION OF THE INVENTION

[0043] 1, a regeneration method 100 for regenerating a fuel cell stack is shown. The regeneration method 100 includes an introduction step 101 in which a reconditioning reagent is introduced, ie, for example, sprayed, into the fuel cell stack.

[0044] Additionally, the regeneration method 100 includes a rinsing step 103 in which the reconditioning reagent is washed from the fuel cell stack, possibly along with contaminants dissolved in the reconditioning reagent.

[0045] In accordance with the present invention, it is contemplated that the reconditioning reagent contains mobile anions or precursors of mobile anions, whereby the reconditioning reagent binds contaminants in the form of cations, particularly metal cations.

[0046] 2, a fuel cell system 200 is shown comprising a fuel cell stack 201, a dosing system 203 for dosing a reconditioning reagent to the fuel cell stack 201, and a calculation unit 205.

[0047] The dispensing system 203 may include, for example, a tank, particularly a pressure tank, a valve, and a pump.

[0048] The computing unit 205 can be, for example, a computer, a controller, a processor, or any other programmable circuit.

[0049] The calculation unit 205 is configured to control the metering system 203 and the fuel cell stack 201 such that the reconditioning method 100 according to FIG. 1 is performed.

[0050] Optionally, a metering unit 203 and / or a calculation unit 205 can be connected to the fuel cell system 200 via an interface 207, so that the metering unit 203 and / or the calculation unit 205 can be connected to the fuel cell system 200, for example in a factory, in order to perform the readjustment method 100 according to FIG. 1. [Explanation of symbols]

[0051] 100 How to readjust and play 101 Implementation Steps 103 Rinse step 200 Fuel Cell System 201 Fuel Cell Stack 203 Dosing System 205 computing units 207 Interface

Claims

1. A regeneration method (100) for regenerating a contaminated fuel cell stack (201), comprising: The regeneration method (100) comprises: - introducing (101) a reconditioning reagent into said fuel cell stack (201); - rinsing (103) the reconditioning reagent from the fuel cell stack (201), The regeneration method, wherein the reconditioning reagent contains a mobile anion or a precursor of a mobile anion.

2. 2. The regeneration method (100) according to claim 1, characterized in that the reconditioning reagent is gaseous and comprises an electrically neutral basic gas, in particular carbon dioxide and / or dinitrogen tetroxide, which dissociates into protons and anions when dissolved in water.

3. 3. The regeneration method (100) of claim 2, wherein the basic gas, in a dissolved state, is electrochemically convertible to an anionic species upon application of a voltage.

4. 4. The regeneration method (100) according to any one of claims 1 to 3, characterized in that the reconditioning reagent comprises at least one acid in the aqueous phase.

5. 5. The regeneration method (100) according to any one of claims 1 to 4, characterized in that the reconditioning reagent comprises at least one complexing agent in the aqueous phase.

6. 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 as dissolved protons and anions or molecules.

7. 7. The regeneration method (100) according to any one of claims 1 to 6, characterized in that the reconditioning reagent comprises a solution containing a substance, in particular ammonium carbonate, that can be converted into a neutral or anionic substance by applying a voltage.

8. The regeneration method (100) according to any one of claims 1 to 7, characterized in that the rinsing (103) of the reconditioning reagent and contaminants is carried out with water produced in the fuel cell stack (201).

9. The regeneration method (100) according to any one of claims 1 to 8, characterized in that when rinsing (103), cell voltages below a predetermined regeneration value are adjusted under wet and cold operating conditions.

10. 10. The regeneration method (100) according to any one of claims 1 to 9, characterized in that, during or after the introduction of the reconditioning reagent, a voltage applied to the fuel cell stack (201) is increased above a predetermined adjustment value in order to initiate a reaction between the reconditioning reagent and contaminants present in the fuel cell stack (201).

11. A fuel cell system (200) for converting energy, comprising: The fuel cell system (200) said fuel cell stack (201); a dosing system (203) for dosing a reconditioning reagent to said fuel cell stack (201); a calculation unit (205), A fuel cell system, wherein the calculation unit (205) is configured to control the metering system (203) and the fuel cell stack (201) to perform the readjustment method according to any one of claims 1 to 10.

12. A fuel cell system (200) for converting energy, comprising: The fuel cell system (200) a fuel cell stack (201), an interface (207) for connection to a dosing system (03) for dosing a reconditioning reagent to said fuel cell stack (201).

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