JP7023478B2 - Solid fuel cell - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Law The Chemical Society of Japan Autumn Project 6th CSJ Chemistry Festa 2016 Proceedings

The present invention relates to solid fuel cells.

Since an expensive electrode material such as Pt and a scarce resource amount are used in the polymer electrolyte fuel cell, it is desired to highly activate the catalytic reaction and reduce the amount of the catalyst used.

By the way, the fuel cell reaction occurs at the interface between the electrode and the electrolyte, but the high activation of the fuel cell so far has been improved exclusively on the electrode material side such as alloying and core shelling.

For example, Non-Patent Document 1 below discloses a technique for activating an oxygen reduction reaction (ORR), which is important in a fuel cell reaction, by chemically adsorbing an alkylamine on the surface of platinum nanoparticles.

Langmuir 30,2936 (2014)

However, the technique described in Non-Patent Document 1 is based on chemical adsorption, and there is a problem that the reaction activity cannot be fully utilized due to the adsorption of alkylamine on the active site.

Therefore, in view of the above problems, it is an object of the present invention to provide a solid fuel cell capable of performing a more efficient oxygen reduction reaction.

The solid fuel cell according to one aspect of the present invention that solves the above problems is a solid fuel cell including a pair of electrodes and a solid electrolyte layer arranged between the pair of electrodes, and is an ammonium ion and a phosphonium ion. At least one of the above is present in at least one of the pair of electrodes by a non-covalent interaction.

As described above, according to the present invention, it is possible to provide a solid fuel cell capable of performing a more efficient oxygen reduction reaction.

It is sectional drawing of the fuel cell which concerns on embodiment. It is a figure which shows the image of the non-covalent interaction. It is a figure which shows the result of the ORR activity evaluation and the ERO activity evaluation which concerns on an Example. It is a figure which shows the result by CTR which concerns on Example. It is a figure which shows the result by XRV which concerns on Example. It is a figure which shows the image of the analysis result of the structure estimated from the result of an Example. It is a figure which shows the result of the ORR activity evaluation which concerns on an Example. It is a figure which shows the result of the ORR activity evaluation which concerns on an Example. It is a figure which shows the result of the ORR activity evaluation which concerns on an Example. It is a figure which shows the result of the ORR activity and the MOR activity which concerns on an Example. It is a figure which shows the result of the ORR activity which concerns on an Example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention can be implemented in many different embodiments, and is not limited to the specific examples described in the embodiments and examples shown below.

FIG. 1 is a schematic cross-sectional view of a solid fuel cell (hereinafter referred to as “the battery”) 1 according to the present embodiment. As shown in this figure, the battery 1 includes a pair of electrodes 2 and 3 and a solid electrolyte layer 4 arranged between the pair of electrodes 2 and 3, and the pair of electrodes 2 and 3. At least one of them is characterized by the presence of at least one of an ammonium ion and a phosphonium ion by a non-covalent interaction.

Further, in the present battery 1, separators 5 and 6 covering the pair of electrodes 2 and 3 are arranged outside the pair of electrodes 2 and 3. As a result, the space inside the battery 1 is separated from the outside. In a fuel cell, it is also a preferable example that a pair of electrodes and a plurality of sets of solid electrolyte layers arranged between them are arranged adjacent to each other, usually for the purpose of increasing the output.

The pair of electrodes 2 and 3 in the battery 1 have conductivity, and are electrically connected to each other via an external load. That is, as described later, the battery 1 can generate electric power between the pair of electrodes and supply electric power to the load.

Further, the materials of the pair of electrodes 2 and 3 in the battery 1 are conductive and have a catalytic function. Since the battery 1 has a catalytic function, one electrode generates hydrogen ions and electrons from hydrogen, while the other electrode combines hydrogen ions, oxygen and electrons to generate water. In the example of this figure, from the viewpoint of making the explanation easy to understand, one electrode 2 will be described as a fuel electrode (anode) for generating hydrogen ions and electrons, and the other electrode 3 will be described as an air electrode (cathode) for generating water.

Of the electrodes in the battery 1, the material of the anode is not particularly limited, but it is preferably one containing platinum, and more preferable examples include platinum powder, platinum-supported carbon, platinum-ruthenium alloy-supported carbon, and the like. Can be exemplified.

Further, among the electrodes in the present battery 1, the material of the cathode is not particularly limited, but it is preferably one containing platinum, and more preferable examples include platinum powder, platinum-supported carbon, and platinum-platinum alloy-supported carbon. Platinum-cobalt alloy-supported carbon, platinum-nickel alloy-supported carbon, and the like can be exemplified.

Further, in the present battery 1, as described above, at least one of ammonium ion and phosphonium ion is non-covalently interacted with at least one of the pair of electrodes 2 and 3, more specifically, on the surface on the solid electrolyte side. Existing. Here, the "non-covalent interaction" refers to an interaction that is not a covalent interaction, and more specifically, an interaction using at least one of van der Waals force and ionic electrostatic force, and further. Specifically, it means that the substance is in a positively charged state or in a cation state and exists in the vicinity of the electrode. In the present battery 1, by using this non-covalent interaction, more efficient reaction is possible without chemically adsorbing to the active site of the catalyst. An image diagram in this case is shown in FIG.

The example in this figure is just an image and may differ from the actual one. However, in this battery 1, the additive is not directly chemically adsorbed on the surface, but has a weak mutual non-covalent bond with the surface. By coexisting in the vicinity of the surface by action, the hydrogen bond network structure of water molecules near the surface is broken, and the reactants can easily reach the electrode surface, resulting in an oxygen reduction reaction (ORR) or an alcohol oxidation reaction. It is considered that (MOR, EOR, etc.) can be activated. At least one of the ammonium ion and the phosphonium ion in the present battery 1 is on the cathode, and any of them can activate ORR, MOR and the like.

Further, the ammonium ion in the present battery 1 is not limited as long as it has the above-mentioned function, but it is preferable that the compound as a whole is water-soluble, but has a hydrophobic site. Is preferable, and for example, alkylammonium ion and arylammonium ion are preferable. The ammonium ion is preferably a quaternary ammonium cation. Further, in the case of alkylammonium ion, tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion and the like can be exemplified, and in the case of arylammonium ion, tetraphenylammonium ion, tetrabenzylammonium ion and the like can be exemplified. Can be exemplified, but is not limited to this.

Further, the phosphonium ion in the present battery 1 is not limited as long as it has the above-mentioned function, but it is preferable that the compound as a whole is water-soluble, but has a hydrophobic site. Is preferable, and for example, alkylphosphonium ion and arylphosphonium ion are preferable. Further, in the case of alkylphosphonium ion, tetramethylphosphonium ion, tetraethylphosphonium ion, tetrapropylphosphonium ion, tetrabutylphosphonium ion and the like can be exemplified, and in the case of arylphosphonium ion, tetraphenylphosphonium ion, tetrabenzylphosphonium ion and the like can be exemplified. Can be exemplified, but is not limited to this.

The counter anion of the ammonium ion and the phosphonium ion is not limited, but is preferably at least one of a hydroxide ion, a fluoride ion, a perchlorate ion, and a sulfate ion.

Further, the solid electrolyte layer 4 in the present battery 1 is not limited as long as it can permeate hydrogen ions, but is preferably an ion exchange membrane as a polymer material, and more preferably. It is a cation exchange membrane.

(Operation of fuel cell)
Here, the operating principle of the battery 1 will be described.

First, hydrogen gas is supplied between the electrode 2 on the anode side and the separator. Then, hydrogen separates into hydrogen ions and electrons on the anode side. Then, hydrogen propagates in the solid electrolyte layer and moves to the cathode side, while electrons move to the electrode 3 on the cathode side via the load via the connected conductor.

On the other hand, oxygen is supplied to the cathode side, and the hydrogen ions and electrons are combined to generate water. That is, since the electrons generated in the electrodes on the anode side move to the cathode side to generate an electric current, the battery 1 exhibits the function as a battery.

In the present battery 1, at least one of ammonium ion and phosphonium ion is present in at least one of the pair of electrodes due to non-covalent interaction in the vicinity of the surface of the electrode, so that water molecules in the vicinity of the surface are present. It is considered that the hydrogen bond network structure can be disrupted so that the reactant can easily reach the electrode surface, and the oxygen reduction reaction (ORR) can be activated.

As described above, according to the present invention, it is possible to provide a solid fuel cell capable of performing a more efficient oxygen reduction reaction.

(Method of manufacturing electrodes)
The production of the present battery 1 is simple. Specifically, it is completed by sandwiching the solid electrolyte layer between a pair of electrodes, further arranging the solid electrolyte layer between the pair of separators, and fixing the respective positions.

However, in the present battery 1, as described above, at least one of ammonium ion and phosphonium ion needs to be present near the surface of at least one of the pair of electrodes due to non-covalent interaction. Therefore, it is necessary to devise in the electrode manufacturing process. The following is a brief explanation.

For the production of the electrode, the same method as the known electrode production method can be adopted except that at least one of ammonium ion and phosphonium ion is added. That is, the method for manufacturing the electrode in the present battery 1 is as follows: (1) Immerse the already manufactured electrode in an aqueous solution containing at least one of ammonium ion and phosphonium ion, or spray the aqueous solution on the electrode surface (2). An aqueous solution containing at least one of ammonium ion and phosphonium ion is sprayed on the catalyst or the catalyst is immersed in the aqueous solution and then molded as an electrode. (3) A method of adding during this period when forming a membrane / electrode assembly is adopted. Can be, but is not limited to.

In the step (1), the concentration of the compound in the aqueous solution containing at least one of ammonium ion and phosphonium ion can be appropriately adjusted depending on the ion to be used, the catalyst to be used and the like as long as it has the above function. From the viewpoint of preventing precipitation in a saturated state, for example, the range is preferably 0.001 mM or more and 0.5 M or less, more preferably 0.1 mM or more and 10 mM or less.

As described above, according to the present embodiment, it is possible to provide a solid fuel cell capable of performing a more efficient oxygen reduction reaction.

Here, based on the above embodiment, an electrode was actually manufactured and its effect was confirmed. This will be described in detail below.

(Evaluation of activity in Pt (111) in alkaline solution)
First, a platinum crystal substrate (Pt (111)) having a (111) plane is immersed in a 0.1 M tetramethylammonium hydroxide solution (alkaline solution) to evaluate oxygen reduction reaction (ORR) activity and ethanol oxidation reaction (111). EOR) Activity was evaluated.

Further, in the same manner as described above, the platinum crystal substrate having the (111) plane was immersed in a 0.1 M potassium hydroxide solution (alkaline solution) to evaluate the ORR activity and the ERO activity.

The above results are shown in FIG. According to the results shown in this figure, it was confirmed that the activity of tetramethylammonium hydroxide was improved as compared with the case of the potassium hydroxide solution.

Moreover, the sea level structure analysis of Pt (111) in the above tetramethylammonium hydroxide solution was performed using SXRD. These results are shown in FIGS. 4 to 6. FIG. 4 shows the result by CTR, FIG. 5 shows the result by XRV, and FIG. 6 shows the image of the analysis result of the interface structure assumed as a result. According to these results, tetramethylammonium hydroxide is not a covalent bond, but is located at a distance of about the size of a water molecule (about 4 angstroms), and is connected to at least one of the pair of electrodes by a non-covalent interaction. Confirmed that it is considered to exist.

Next, the concentration dependence of the ORR activity was carried out using a lithium hydroxide solution and tetrabutylammonium hydroxide.

Specifically, (A) 0.1 M solution of lithium hydroxide, (B) lithium hydroxide: tetrabutylammonium hydroxide = 100: 1 solution, (C) lithium hydroxide: tetrabutylammonium hydroxide = The ORR activity was evaluated in each of a 10: 1 solution, (D) lithium hydroxide: tetrabutylammonium hydroxide = 1: 1 solution, and (E) 0.1 M tetrabutylammonium hydroxide solution. The result is shown in FIG.

According to this result, although the activity of 0.1 M tetrabutylammonium hydroxide alone is inferior to that of 0.1 M lithium hydroxide, 0.1 M water is contained by containing a small amount of tetrabutylammonium hydroxide. It was confirmed that the activity was improved as compared with the case of lithium oxide.

Further, in the same manner as above, (A) 0.1 M potassium hydroxide solution, (B) potassium hydroxide: tetrabutylammonium hydroxide = 1000: 1 solution, (C) potassium hydroxide: tetrabutylammonium hydroxide. ORR activity was evaluated in each of (D) potassium hydroxide: tetrabutylammonium hydroxide = 10: 1 solution and (E) 0.1 M tetrabutylammonium hydroxide solution. .. The result is shown in FIG.

In this result as well, as in the case of lithium hydroxide, the activity of only 0.1 M tetrabutylammonium hydroxide is inferior to that of 0.1 M potassium hydroxide, but a small amount of tetrabutylammonium hydroxide is used. It was confirmed that the inclusion improved the activity as compared with the case of 0.1 M potassium hydroxide.

Next, (A) 0.1 M solution of tetramethylammonium hydroxide, (B) tetramethylammonium hydroxide: tetrabutylammonium hydroxide = 100: 1 aqueous solution, (C) tetramethylammonium hydroxide. The ORR activity was evaluated in each of the: tetrabutylammonium hydroxide = 10: 1 aqueous solution and (D) 0.1 M tetrabutylammonium hydroxide aqueous solution. The result is shown in FIG.

As a result, it was confirmed that by mixing tetramethylammonium hydroxide and tetrabutylammonium hydroxide, the ORR activity was improved as compared with the case of each alone.

(Evaluation of activity in Pt (111) in acidic solution)
Here, the platinum crystal substrate having the (111) plane is immersed in an acidic solution in which tetramethylammonium perchlorate is added (0.1 mM) to a 0.1 M perchloric acid solution, and the ORR is the same as the above alkaline solution. The activity was evaluated and the activity of the methanol oxidation reaction (MOR) was evaluated.

Further, the platinum crystal substrate having the same (111) plane as described above is immersed in an acidic solution obtained by adding tetrabutylammonium perchlorate (0.1 mM) to a 0.1 M perchloric acid solution to evaluate the ORR activity and MOR. The activity was evaluated.

Further, as a comparative example, a platinum crystal substrate having a (111) plane was immersed in a 0.1 M perchloric acid solution, and ORR activity evaluation and MOR activity evaluation were performed. These results are shown in FIG.

As shown in this figure, both the ORR activity and the MOR activity are more active depending on whether they are tetramethylammonium perchlorate or tetrabutylammonium perchlorate, as compared with the case of using only a 0.1 M perchloric acid solution. I was able to confirm the improvement.

From the above results, it was confirmed that the activity of the electrodes in the fuel cell is improved by allowing ammonium ions to be present in at least one of the pair of electrodes by non-covalent interaction.

(Activity evaluation in Pt (331))
The platinum crystal substrate having the (331) plane was evaluated for ORR activity in the same manner as tetrabutylammonium perchlorate in the above Pt (111). This result is shown in FIG.

As shown in this figure, it was confirmed that the activity was also improved by the addition of tetrabutylammonium perchlorate.

As described above, it has been confirmed that it is possible to provide a solid fuel cell capable of performing a more efficient oxygen reduction reaction by this example.

The present invention has industrial applicability as a solid fuel cell.

Claims (4)

With a pair of electrodes,
A solid fuel cell comprising a solid electrolyte layer disposed between the pair of electrodes.
A solid fuel cell in which ammonium ions of 0.001 mM or more and 10 mM or less are present in at least one of the pair of electrodes by a non-covalent interaction. The solid fuel cell according to claim 1, wherein the solid electrolyte layer is an ion exchange membrane. The solid fuel cell according to claim 1, wherein the ammonium ion is a quaternary ammonium cation. The solid fuel cell according to claim 1, wherein the ammonium ion is at least one of an arylammonium ion and an alkylammonium ion .

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