JP2005276711A - Method of restoring fuel cell catalyst and restoring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a apparatus of restoring fuel cell catalyst in which a degraded catalyst layer of a fuel cell is restored in a simple manner. <P>SOLUTION: This method of restoring a fuel cell catalyst includes a first step of adhering Pt ions onto a carbon black carrier on the side of degraded electrode, and a second step of providing hydrogen and gas containing hydrogen to an electrode opposite to the degraded electrode and reducing the Pt ions adhered to the carbon black carrier to Pt by applying a voltage between both electrodes. In the restoring apparatus, a water container 40, a Pt compound aqueous solution container 42 and an acid aqueous solution container 44 are coupled to the fuel cell 30 via a liquid supply passage 32, and thus the catalyst layer on the side of the degraded electrode receives supplies from the respective containers. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of repairing a catalyst when a fuel cell catalyst such as a polymer electrolyte fuel cell is deteriorated, and a fuel cell catalyst repairing apparatus suitable for carrying out this repairing method.

  In recent years, reserves of fossil fuels have drastically decreased, and development of alternative fuels has been demanded. As an alternative fuel for fossil combustion, hydrogen, which can be easily generated and has a low environmental impact, has attracted attention. As an energy source using hydrogen gas, a fuel cell which does not generate carbon dioxide during power generation and is a clean energy source has attracted attention, and various developments have been actively conducted.

  A polymer electrolyte fuel cell, which is a type of fuel cell, includes a pair of electrodes supplied with a fuel gas such as hydrogen or an oxidant gas such as air, and an electrolyte membrane sandwiched between the electrodes, such as platinum. It is made to react electrochemically on this catalyst and generate electricity.

  A conventional polymer electrolyte fuel cell has proton conductivity and can selectively move hydrogen ions, a hydrogen electrode (anode electrode) to which hydrogen gas as fuel is supplied, It comprises an oxygen electrode (cathode electrode) to which air is supplied as an oxidant.

  The hydrogen electrode has a catalyst layer mainly composed of carbon powder supporting a platinum-based metal catalyst and a gas diffusion layer composed of a porous member having pores, and one surface of the electrolyte membrane, It arrange | positions so that a catalyst layer may closely_contact | adhere. Similarly, the oxygen electrode is composed of a catalyst layer mainly composed of carbon powder supporting a platinum-based metal catalyst and a gas diffusion layer composed of a porous member having pores, and the other side of the electrolyte membrane. It arrange | positions so that a catalyst layer may closely_contact | adhere to this surface. In addition, the hydrogen electrode and the oxygen electrode are electrically connected through an external circuit, and separators that form flow paths for the respective gases are installed outside the hydrogen electrode and the oxygen electrode.

  In the polymer electrolyte fuel cell, hydrogen ions generated by the reaction between the hydrogen gas supplied to the hydrogen electrode and the metal catalyst supported on the catalyst layer move to the oxygen electrode through the electrolyte membrane, and are supplied to the oxygen electrode. Electricity is generated by causing an electrochemical reaction on the catalyst with oxygen in the air. Electricity generated in the polymer electrolyte fuel cell is supplied to an external device via an external circuit.

  Normally, hydrogen gas or air that is supplied to the hydrogen electrode or oxygen electrode and does not contribute to the reaction is discharged through the discharge port. In addition, the electrolyte membrane has proton conductivity, selectively transmits only hydrogen ions, and plays a role of blocking gas movement between the electrodes.

  In a solid polymer electrolyte fuel cell, there is an electrode containing a solid polymer electrolyte (polytetrafluoroethylene), carbon particles, and a catalytic material. In this electrode, the catalytic material is separated from the proton conduction path on the carbon particle surface and Teflon ( Since it is located in the (R) skeleton, only the catalyst material of the proton conduction pathway is involved in the reaction, and the catalyst material of the Teflon (R) skeleton is not involved in the reaction.

  In order to solve such a problem, in the electrode including a solid polymer electrolyte (polytetrafluoroethylene), carbon particles, and a catalyst material, the catalyst material is contacted with the proton conduction path and the proton conduction path of the solid polymer electrolyte. A fuel cell supported mainly on the surface of the metal and a manufacturing method thereof have been proposed. (Patent Document 1)

  Such a fuel cell is excellent in that the utilization factor of the catalyst substance is increased. However, when the fuel cell is operated for a relatively long period of time, there is a problem that the performance of the electrode, particularly the cathode electrode, is deteriorated. That is, on the cathode side of the fuel cell, a phenomenon in which Pt used as a catalyst material causes sintering on carbon particles as conceptually shown in FIG. 5A, conceptually shown in FIG. 5B. As shown, a phenomenon in which Pt is eluted from the carbon particles occurs.

The reason for this seems to be that the oxidation potential and elution potential of Pt are close to the cathode potential of the fuel cell, as shown below.
Pt oxidation potential _{of: Pt + H 2 O → PtOH} + H + at0.98V (vs.NHE) Pt elution potential ^{of: Pt → Pt 2+ + 2e -} at1.2V (vs.NHE)

  For this reason, the surface area of individual Pt particles on the carbon particles is significantly reduced by sintering of Pt, and the amount of Pt particles supported on the carbon particles is reduced by elution of Pt from the carbon particles, so that the catalytic reaction A significant decrease, that is, the catalyst has deteriorated.

JP 2000-173626 A

  In order to solve the above problems, an object of the present invention is to provide a fuel cell catalyst repair method and a fuel cell catalyst repair device capable of repairing a deteriorated catalyst layer in a fuel cell by a simple method. .

  The method for repairing a fuel cell catalyst according to claim 1 of the present invention includes a first step of depositing Pt ions on the carbon black support on the deteriorated electrode side, and hydrogen or a hydrogen-containing gas on the opposite electrode to the deteriorated electrode. And a second step of reducing the Pt ions deposited on the carbon black support to Pt by applying a voltage between the electrodes and applying a voltage between the electrodes.

  According to the method of repairing a fuel cell catalyst of the present invention as set forth in claim 1, Pt ions deposited on a carbon black support are efficiently converted by applying a voltage between both electrodes in the presence of hydrogen. Can be reduced to Pt.

  The method for repairing a fuel cell catalyst of the present invention according to claim 2 is characterized in that an aqueous solution of a Pt compound is supplied to the catalyst layer, and Pt ions generated from the aqueous solution of the Pt compound are deposited on the carbon black support. A method for repairing a fuel cell catalyst according to claim 1.

  According to the method for repairing a fuel cell catalyst of the present invention as set forth in claim 2, Pt ions are simply deposited on the carbon black support simply by supplying an aqueous solution of the Pt compound to the catalyst layer.

In the method for repairing a fuel cell catalyst of the present invention according to claim 3, the aqueous solution of the Pt compound is Pt (NH ₃ ) ₄ Cl ₂ , and the Pt ion is Pt (NH ₃ ) ₄ 2 ⁺ . The method for repairing a fuel cell catalyst according to claim 2, wherein:

According to the method for repairing a fuel cell catalyst of the present invention according to claim 3, Pt (NH ₃ ) ₄ Cl ₂ can be used as an aqueous solution of a Pt compound, and only by supplying this aqueous solution to the catalyst layer, Pt ions are easily deposited on the carbon black support.

  According to a fourth aspect of the present invention, there is provided a method of repairing a fuel cell catalyst according to the present invention, wherein after the first step, water is supplied to the diffusion layer and / or separator adjacent to the catalyst on the deteriorated electrode side to The method for repairing a fuel cell catalyst according to any one of claims 1 to 3, wherein Pt ions adhering to the catalyst are removed.

  According to the method for repairing a fuel cell catalyst of the present invention described in claim 4, Pt ions attached to the diffusion layer and / or the separator are removed by water, and the removed Pt ions are reused as necessary. The

  According to a fifth aspect of the present invention, there is provided a method for repairing a fuel cell catalyst according to the present invention, wherein after the second step, an acidic aqueous solution is supplied to the catalyst layer on the deteriorated electrode side, The method for repairing a fuel cell catalyst according to any one of claims 1 to 3, wherein the aqueous solution is removed.

  According to the method for repairing a fuel cell catalyst of the present invention according to claim 5, the aqueous solution of the Pt compound is removed from the catalyst layer and the polymer electrolyte membrane adjacent to the catalyst layer, and the removed aqueous solution of the Pt compound is removed as necessary. Will be reused.

  According to a sixth aspect of the present invention, there is provided an apparatus for repairing a fuel cell catalyst comprising: a liquid supply path and a liquid discharge path connected to a cathode electrode side of the fuel cell; And a fuel cell catalyst repairing device comprising switching means for sequentially supplying any one of the acidic aqueous solution.

  According to the fuel cell catalyst repair device of the present invention described in claim 6, water, an aqueous solution of a Pt compound, and an acidic aqueous solution are supplied to the catalyst layer through a liquid supply path connected to the cathode electrode side, and carbon Pt ions are deposited on the black carrier, and unnecessary Pt ions are removed by water or an acidic aqueous solution.

  According to a seventh aspect of the present invention, there is provided a fuel cell catalyst repair device for returning at least one of water, an aqueous solution of a Pt compound, and an acidic aqueous solution to a liquid discharged from the cathode side of the fuel cell to the liquid discharge path. 7. The fuel cell catalyst repair device according to claim 6, further comprising switching means.

  According to the fuel cell catalyst repairing apparatus of the present invention described in claim 7, the liquid used for repairing the deteriorated catalyst layer is recovered and reused.

  In the method for repairing a fuel cell catalyst according to the present invention, in a deteriorated catalyst layer, Pt decreased due to elution can be replenished to repair the catalyst layer. The fuel cell catalyst repair device of the present invention connects a liquid supply path and a liquid discharge path to a fuel cell, and can easily repair the fuel cell catalyst by a liquid supply operation and a discharge operation.

  The method for repairing a fuel cell catalyst according to the present invention includes a first step of attaching Pt ions on a carbon black support on the deteriorated electrode side, supplying hydrogen to an opposite electrode to the deteriorated electrode, and applying a voltage between the two electrodes. And a second step of reducing Pt ions applied to the carbon black support to Pt. Since the deteriorated electrode is usually a cathode electrode, the first step deposits Pt ions on the carbon black carrier on the cathode electrode side.

As a method for depositing Pt ions on the carbon black support, a method of supplying an aqueous solution of a Pt compound to the cathode electrode side is desirable. A typical example of the aqueous solution of the Pt compound is Pt (NH ₃ ) ₄ Cl _2, but PtCl ₂ , Pt (CN) ₂ , PtO ₂ , H ₂ PtCl _6, etc. can also be used. However, H ₂ PtCl ₆ is particularly preferred from the viewpoint of ease of handling and ease of dissolution in water.

  It is preferable to adjust the concentration of the Pt compound according to the degree of deterioration of the catalyst layer of the deteriorated electrode, such as the type and supply amount of the aqueous solution of the Pt compound supplied to the deteriorated electrode.

FIG. 1 is an explanatory view conceptually showing the state at this time. <A) is an aqueous solution of a Pt compound supplied to the surface of the carbon black support 10 of the catalyst layer, for example, Pt (NH ₃ ) ₄ Cl ₂ 12. (B) shows a state in which Pt ions 14 made of Pt (NH ₃ ) ₄ ²⁺ are attached on the carbon black support 10.

The aqueous solution of Pt compound such as Pt (NH ₃ ) ₄ Cl ₂ flowing down the catalyst layer on the cathode electrode side and discharged to the outside can be reused. Thereafter, if necessary, water is allowed to flow through a separator, a diffusion layer or the like adjacent to the catalyst layer, and an excess aqueous solution of the Pt compound attached to the separator, the diffusion layer or the like can be removed. The removed aqueous solution of the Pt compound such as Pt (NH ₃ ) ₄ Cl ₂ can be reused and the original performance of the separator and the diffusion layer can be maintained.

Next, the present invention includes a second step of applying a voltage between both electrodes to reduce Pt ions attached on the carbon black support to Pt. As shown in FIG. 2, in this step, in FIG. 2A, Pt ions such as Pt (NH ₃ ) ₄ ²⁺ adhering to the carbon black support in the catalyst layer on the deteriorated electrode 20 side are as shown in FIG. As shown in <B>, hydrogen or a gas containing hydrogen is supplied to the electrode 22 on the side opposite to the deteriorated electrode 20, and a voltage is applied between the electrodes by the secondary battery 24.

As a result, Pt ions such as Pt (NH ₃ ) ₄ ²⁺ adhering to the carbon black carrier are reduced to form Pt fine particles. FIG. 2 (B) shows the reduction reaction when Pt (NH ₃ ) ₄ Cl ₂ is used as the aqueous solution of the Pt compound. That is, fine particles of Pt are generated by Pt (NH ₃ ) ₄ ²⁺ + 2e ⁻ → Pt + 4NH ₃ .

  In the reduction reaction with hydrogen gas, it is necessary to adjust the reduction temperature, the reduction time, and the like. However, depending on the reduction time and the reduction temperature, the solid polymer electrolyte may be deteriorated. In the present invention, since the reduction is performed by applying a voltage between the two electrodes via the secondary battery while supplying hydrogen or a hydrogen-containing gas, there is no possibility of degrading the solid polymer electrolyte.

  The voltage applied between both electrodes is preferably +0.1 to -2.0 V, more preferably -0.2 to -0.1 V, and still more preferably -0.4 to -0.8 V. When this voltage is higher than +0.1 V, there is a problem such as platinum does not precipitate, and when it is lower than −2.0 V, problems such as reduction deterioration of each material and generation of hydrogen tend to occur. The time during which the voltage is applied between both electrodes should be selected in consideration of the degree of deterioration of the deteriorated catalyst layer, that is, the amount of eluted Pt, but is preferably 1 to 60 minutes, for example, 5 to 20 minutes. Is more preferable.

Next, an acidic aqueous solution is allowed to flow to the deteriorated electrode side to remove an aqueous solution of a Pt compound such as Pt (NH ₃ ) ₄ Cl ₂ remaining in the solid polymer electrolyte membrane or the catalyst layer. Here, examples of the acidic aqueous solution include a sulfuric acid aqueous solution, a phosphoric acid aqueous solution, a perchloric acid aqueous solution, and a hydrochloric acid aqueous solution in consideration of decomposition and damage of the solid polymer electrolyte membrane. Among these, an aqueous sulfuric acid solution is most preferable from the viewpoint of anion adsorption and anion stability. The concentration of the acidic aqueous solution is preferably 0.01 to 2.0M, more preferably 0.05 to 1.0M. The acidic aqueous solution discharged from the deteriorated electrode side can be discharged as it is, or can be recovered and reused.

  Through the above steps, the Pt fine particles lost by elution from the carbon black support are newly supported on the carbon black support to restore the catalyst layer.

  FIG. 3 is a schematic configuration diagram showing a preferred embodiment of the fuel electrode catalyst repair device of the present invention. In the repairing device shown in FIG. 3, the liquid supply path 32 connected to one side of the fuel cell 30 and the cathode electrode has a water container 40, a Pt compound aqueous solution container 42, a switching valve 34, a pump 36, and a switching valve 38, respectively. An acidic aqueous solution container 44 is connected. The liquid container 50, the Pt compound aqueous solution container 42, and the acidic aqueous solution container 44 are connected to the other side of the cathode electrode of the fuel cell 30 through the switching valve 46 and the switching valve 48.

  In this repair device, when the catalyst layer on the cathode electrode side deteriorates, an aqueous solution of Pt compound is introduced from the Pt compound water container 42 to the cathode electrode side catalyst layer through the switching valve 34 by the operation of the pump 36. . After a predetermined time, water is introduced from the water container 40 into the catalyst layer on the cathode electrode side by the operation of the switching valve 34. Next, after a predetermined time, the acidic aqueous solution is introduced from the acidic aqueous solution container 44 into the catalyst layer on the cathode electrode side by the operation of the switching valve 34. In addition, during each operation, in order to remove each liquid more completely, each liquid is introduced into the catalyst layer on the cathode electrode side, and then is switched to the catalyst layer on the cathode electrode side by operating the switching valve 38. Air is introduced and the catalyst layer is dried to remove the liquid more completely.

  In these series of operations, each liquid discharged from the catalyst layer on the cathode electrode side may be discharged out of the repair device via the liquid discharge path 50, but as shown in the figure, the switching valve 48 is used. Then, it can be returned to each container again by the operation of the switching valve 46 and reused.

Examples of the present invention will be described below.
<Catalyst layer configuration>
40% by mass Pt supported carbon (Tanaka Kikinzoku Kogyo Co., Ltd.)
5% by mass Nafion solution (manufactured by Aldrich)
Ratio of Nafion to carbon = mass ratio 1.0

<Repair operation>
[Pt (NH ₃ ) ₄ Cl ₂ 1 g, water 30 ml] was poured, and a voltage of −0.5 V was applied for 10 min (hydrogen at the counter electrode 500 cc / min)
Replacement with 0.1 MH ₂ SO ₄ 30 min
Replacement with distilled water for 30 min

The catalyst layer having the above structure was repaired by the repairing operation.
FIG. 4 shows a cyclic voltammogram of the electrode by the catalyst layer before and after the repair (regeneration) at this time.
<Measurement conditions>
Anode: Hydrogen 500cc / min normal pressure,
Cathode: nitrogen 500 cc / min normal pressure,
Humidification: anode 60 ° C, cathode 60 ° C
Cell temperature: 40 ° C
Potentio galvanostat is used. 0.05 to 1.4 V is applied to the cathode side with respect to the anode side. Operating speed: 50 mV / s

  According to the repair method of the present invention from FIG. 4, it was found that the deteriorated catalyst layer shows a large output current due to the generation of new Pt after repair (regeneration).

It is a schematic block diagram which shows in principle the behavior of Pt at the time of supplying the aqueous solution of Pt compound to a catalyst layer in the restoration | repair method of the fuel cell catalyst of this invention. It is explanatory drawing which shows the adhesion of Pt component at the time of supplying the aqueous solution of Pt compound to a catalyst layer in the restoration | repair method of the fuel cell catalyst of this invention, and reduction | restoration of a Pt component. It is a schematic block diagram which shows one preferable embodiment of the repair apparatus of the fuel cell catalyst of this invention. It is a graph which shows the measurement result of an Example. It is a figure which shows the state of sintering and elution of Pt in the conventional polymer electrolyte fuel cell schematically.

Explanation of symbols

30 fuel cell 32 liquid supply path 34 switching valve 36 pump 38 switching valve 40 water container 42 Pt compound aqueous solution container 44 acidic aqueous solution container 46 switching valve 48 switching valve 50 liquid discharge path

Claims (7)

  A first step of depositing Pt ions on the carbon black carrier on the deteriorated electrode side, supplying hydrogen or a hydrogen-containing gas to the opposite electrode to the deteriorated electrode, and applying a voltage between the two electrodes to And a second step of reducing Pt ions attached to the Pt to Pt.   2. The method for repairing a fuel cell catalyst according to claim 1, wherein an aqueous solution of a Pt compound is supplied to the catalyst layer, and Pt ions generated from the aqueous solution of the Pt compound are deposited on the carbon black support. _{3. The} method of repairing a fuel cell catalyst according to claim 2, wherein the aqueous solution of the Pt compound is Pt (NH ₃ ) ₄ Cl ₂ , and the Pt ion is Pt (NH ₃ ) ₄ ^2+. .   The Pt ions attached to the diffusion layer and / or separator are removed by supplying water to the diffusion layer and / or separator adjacent to the catalyst layer on the deteriorated electrode side after the first step. The method for repairing a fuel cell catalyst according to any one of claims 1 to 3.   The aqueous solution of Pt compound is removed from the catalyst layer and the polymer electrolyte membrane adjacent thereto by supplying an acidic aqueous solution to the catalyst layer on the deteriorated electrode side after the second step. The method for repairing a fuel cell catalyst according to any one of the preceding claims.   A liquid supply path and a liquid discharge path are connected to the cathode electrode side of the fuel cell, respectively, and switching means for sequentially supplying any of water, an aqueous solution of a Pt compound, and an acidic aqueous solution to the liquid supply path is provided. To repair the fuel cell catalyst.   The fuel cell catalyst repair according to claim 6, further comprising switching means for returning at least one of water, an aqueous solution of a Pt compound, and an acidic aqueous solution to the liquid discharged from the cathode side of the fuel cell in the liquid discharge path. apparatus.

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