JP2002289266A - Air electrode and air cell using the same as positive electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop air electrode catalyst which is less expensive and has less oxygen overvoltage than platinum catalyst and to provide an inexpensive air electrode having high charging/discharging efficiency and an air cell by using the air electrode catalyst. SOLUTION: The air electrode catalyst for an air electrode of the air cell operating in acidic atmosphere is mainly composed of carbon and metal sulphide. The metal sulphide is preferably NiS. The air call preferably comprises an air electrode using the electrode catalyst mainly composed of carbon and metal sulphide as a positive electrode, a proton exchange film as electrolyte, and a hydrogen storage alloy electrode as a negative electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an air electrode and an air battery using the air electrode as a positive electrode.

[0002]

2. Description of the Related Art MH / PEM / Air (MH = hydrogen storage alloy, PEM = proton exchanger) using an air electrode as a positive electrode, a proton exchange membrane (PEM membrane) as an electrolyte, and a hydrogen storage alloy electrode as a negative electrode , Air = air) Since the inside of the proton exchange membrane of the electrolyte and the surface thereof are in an acidic atmosphere, a catalyst is necessary for the operation of the air electrode constituting the positive electrode. Are almost exclusively available.

[0003]

However, platinum catalysts are very expensive, and using them in large quantities results in high costs.

Further, when charging the MH / PEM / Air battery, oxygen is generated at the air electrode. At that time, in the case of a platinum catalyst having a large oxygen overvoltage, there is a problem that the charging voltage is increased and the charge / discharge efficiency is reduced.

The present invention solves the above-mentioned problems of the prior art, develops an air electrode catalyst which is less expensive than a platinum catalyst and has a small oxygen overvoltage, and is inexpensive and uses the air electrode catalyst. An object of the present invention is to provide an air electrode and an air battery having excellent charge / discharge efficiency.

[0006]

SUMMARY OF THE INVENTION The present invention provides an MH / PEM
An air electrode catalyst for an air electrode of an air battery operated in an acidic atmosphere such as a / Air battery is constituted by using carbon and metal sulfide as main materials to solve the above problem.

That is, metal sulfide is less expensive than platinum and has a smaller oxygen overvoltage, so that it is possible to provide an air electrode catalyst that is less expensive than a platinum catalyst and has a smaller oxygen overvoltage, and is therefore less expensive and more fully charged. An air electrode and an air battery having high discharge efficiency can be provided.

[0008]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, metal sulfide
For example, NiS, NiS_Two, Ni_ThreeS _Four, Ni
_0.3Co_0.7S_Two, CoS, FeS, MoS_Two, Ag_Two
S, Sb_TwoS_Three, Sb_TwoS_Five, SnS, MnS, W
S_Two, PbS and ZnS
At least one kind, particularly containing Ni, Co, Fe, etc.
Sulfide is a transition metal whose constituent metal is the same as Pt
It is preferable because it is relatively inexpensive.

The carbon is not particularly limited. For example, graphite, carbon black, charcoal, activated carbon and the like can be used. In preparing the air electrode catalyst, the ratio between the carbon and the metal sulfide is preferably 70:30 to 30:70 by weight, and particularly preferably 60:40 to 40:60. That is, by setting the ratio of carbon to metal sulfide within the above range, the balance between the specific surface area of the cathode catalyst, which is associated with the reaction area, and the amount of metal sulfide in the cathode catalyst is optimized, and the cost and the charge are reduced. It is possible to provide an air electrode having excellent discharge efficiency, and it is possible to suppress excessive wetting of the air electrode by the water repellency of carbon and to maintain a favorable three-phase interface as a reaction point.

In preparing the cathode, it is preferable to keep the cathode catalyst in a molded state.
In preparing the air electrode catalyst, it is preferable to use polytetrafluoroethylene, in addition to the carbon and metal sulfide, for the purpose of assisting water repellency and exhibiting the effect as a binder. As the polytetrafluoroethylene, an aqueous dispersion may be used in preparing the air electrode catalyst. Further, for the same purpose as polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and the like can also be used.

In the present invention, the mixing and stirring of the constituent materials of the air electrode catalyst are carried out in the presence of water. At that time, it is preferable to add an organic solvent. As the organic solvent,
For example, alcohol, acetone, hexane and the like can be used, but lower alcohols such as butanol, ethanol and 2-propanol are particularly preferable. this is,
This is because these lower alcohols change the surface potential of the catalyst constituent material and cause agglomeration more strongly.

In the addition of the organic solvent, it is preferable to add the constituent material of the air electrode catalyst to water, mix and stir, add the organic solvent, and heat and mix. The temperature during mixing and stirring after the addition of the organic solvent is 150
To 200 ° C. is preferable, and under these conditions, atomization and sedimentation of the air electrode catalyst suitably proceeds.

The above-mentioned carbon and metal sulfide may not only be mixed as described above, but may also be formed into a complex in advance. For example, if the above-mentioned metal sulfide is made into a colloid liquid in advance, and the colloid liquid containing the metal sulfide is mixed with carbon, it is possible to make a state in which the surface of the carbon particles is coated with fine particles of metal sulfide. it can. Then, it may be mixed with polytetrafluoroethylene or the like as described above to prepare an air electrode catalyst.

In the above description, the air electrode catalyst is prepared in a state containing polytetrafluoroethylene in addition to the above-mentioned carbon and metal sulfide. However, in the present invention, the air electrode catalyst is prepared by using carbon and metal sulfide. It may be composed of a material and, in place of polytetrafluoroethylene,
The air electrode catalyst may be formed using polyvinylidene fluoride, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or the like exemplified above. That is, in the present invention, the configuration in which the air electrode catalyst is mainly composed of carbon and metal sulfide means that the air electrode catalyst may be composed only of carbon and metal sulfide, or that other than carbon and metal sulfide. May include other materials such as polytetrafluoroethylene.

The production of an air electrode using the above-mentioned air electrode catalyst can be performed in substantially the same manner as in the case of using a conventional air electrode catalyst. To illustrate, for example, the above-mentioned air electrode catalyst is formed into a current collector made of nickel, titanium, stainless steel, molybdenum, a net made of carbon having excellent conductivity such as tantalum or carbon, foil, expanded metal, punching metal, or the like. After application and pressure molding, heat treatment is performed as necessary. However, the above method is merely an example, and the air electrode may be manufactured by another method.

In order to form an air battery using the air electrode, the air electrode can be used as a positive electrode, and a hydrogen storage alloy, a carbon nanotube, a metal such as aluminum or zinc can be used as a negative electrode active material. As the electrolyte, a proton exchange membrane, an alkaline aqueous solution, or the like can be used. In the present invention, MH / PEM / using the above air electrode as a positive electrode, using a hydrogen storage alloy electrode as a negative electrode, and using a proton exchange membrane as an electrolyte is used. The effect is most remarkably exhibited in the Air battery.

The hydrogen storage alloy used as the active substance of the hydrogen storage alloy electrode constituting the negative electrode is, for example, L
AB ₅ -type hydrogen absorbing alloy represented by ANI _5, ZnMn
₂ or AB ₂ type hydrogen storage alloy represented by the substituents thereof, Mg ₂ Ni or A ₂ B type hydrogen storage alloys of magnesium-based typified by derivatives thereof, such as a solid solution-type V based hydrogen storage alloy is used. Further, as the proton exchange membrane, for example, Nafion (trade name, manufactured by DuPont),
It is preferable to use a fluorine-based resin such as Flemion (trade name, manufactured by Asahi Glass Co., Ltd.) or Aciplex (trade name, manufactured by Asahi Kasei Co., Ltd.), and to form a proton-exchange resin film having a proton exchange ability with a skeleton.

[0018]

Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only these examples. In the following examples, the percentages when indicating concentrations and the like are weight percentages unless otherwise specified.

Example 1 As a material for an air electrode catalyst, 0.25 g of carbon, NiS
A sample weighed in advance of 0.33 g was put into 30 ml of distilled water and stirred. After 10 minutes, 0.42 g of a 60% aqueous polytetrafluoroethylene dispersion (0.1% as solids).
252 g) and stirred for 20 minutes. Finally n-
After adding 8 ml of butanol and stirring for 20 minutes, 200 ml
C. and further stirred for 20 minutes to settle the air electrode catalyst and remove the supernatant to obtain an air electrode catalyst.

The air electrode catalyst produced as described above is applied to a current collector made of a titanium net, dried, pressed and integrated with a polytetrafluoroethylene sheet to form the air electrode catalyst shown in FIG. Was fabricated, and a model cell shown in FIG. 2 was assembled using the air electrode.

Here, the air electrode shown in FIG. 1 will be described. In the air electrode 1, the above-mentioned air electrode catalyst 2 is press-bonded to a current collector 3 made of a titanium net, and the periphery thereof is solidified with an epoxy resin 4, and the air electrode 1 is solidified with an epoxy resin 4. It is configured by being integrated with the polytetrafluoroethylene sheet 5 in a state. In the air electrode 1 shown in FIG. 1, the periphery of the air electrode catalyst 2 is solidified with the epoxy resin 4, but it is not always necessary to solidify the periphery of the air electrode catalyst 2 with the epoxy resin 4, The polytetrafluoroethylene sheet 5 can be replaced with a sheet made of another material as long as it performs the same function (repels water but allows air to pass).

Next, the model cell shown in FIG. 2 will be described. In FIG. 2, the inner wall 8 of the cell container 6 of the model cell and the air electrode 1 are shown in a separated state.
An outer wall portion 7 provided with an air hole 7a is disposed outside the air electrode 1 (right side in FIG. 2), and an inner wall portion 8 has a flange shape. In FIG. In the actual model cell, the air electrode 1 fits into the space of the inner wall portion 8, and the outer wall portion 7 is disposed outside the air electrode 1. On the left side), a separator 11, a reference electrode 12 made of Ag-AgCl, a separator 11 and a counter electrode 13 made of platinum are arranged, and the separator 11, the reference electrode 12, the counter electrode 13 and the like are 1 mol / mol.
1 is immersed in an electrolytic solution 14 composed of an aqueous sulfuric acid solution, an O-ring 15 is disposed between the inner wall portion 8 and the outer wall portion 7, and the electrolytic solution 14 is provided on the outer wall portion 7, the inner wall portion 8, and the side wall portion. 9
And the bottom wall 10 are accommodated in the internal space of the cell container 6, thereby forming a model cell.

The model cell shown in FIG. 2 incorporating the air electrode manufactured in Example 1 was used to confirm the function of the air electrode to reduce oxygen in the air. Specifically, 35 mA / c
After applying a current of m ² , the air hole of the model cell body was shut off after the air electrode potential was stabilized. After the air electrode potential was stabilized again, the air hole was opened and the behavior of the air electrode potential was examined. The result is shown in FIG.

As is apparent from the results shown in FIG. 3, the transition of the air electrode potential to the hydrogen generation potential due to the air hole cutoff and the recovery of the air electrode potential due to the subsequent opening of the air hole were observed. It was confirmed that the electrode had a function of reducing oxygen in the air. To explain this in detail, the application of electric current causes polarization, which lowers the air electrode potential. While the air hole is open, the air electrode potential is kept almost at that level, and when the air hole is shut off, the air electrode potential drops to the hydrogen generation potential. Then, when the air hole is opened, the air electrode potential is restored to the potential before the air hole was shut off. Therefore, it can be determined that the air electrode of the first embodiment has a function of reducing oxygen in the air.

COMPARATIVE EXAMPLE 1 5% platinum-supported carbon 0.2
5 g was put into 30 ml of distilled water and stirred. Ten minutes later,
60% polytetrafluoroethylene aqueous dispersion 0.18
g (0.108 g as a solid content) and stirring for 20 minutes, then add 8 ml of n-butanol and stir for 20 minutes, then heat to 200 ° C. and stir for another 20 minutes to precipitate the air electrode catalyst. After removing the supernatant, an air electrode catalyst was obtained. In the same manner as in Example 1, a model cell was assembled in the same manner as in Example 1 except that an air electrode was formed by coating, drying, and pressing a current collector made of a titanium net, and the air electrode was used.

FIG. 4 shows the polarization characteristics measured at 25 ° C. in the model cells incorporating the air electrodes of Example 1 and Comparative Example 1, respectively. As shown in FIG.
In Comparative Example 1, although the polarization characteristics were slightly inferior to Comparative Example 1 using platinum-supported carbon as the air electrode catalyst, Comparative Example 1
It showed a polarization characteristic almost the same as that of the above, and it was clear that it had a sufficient catalytic function as an air electrode catalyst instead of a platinum catalyst.

Example 2 An MH / PEM / Air model cell was assembled using the air electrode of Example 1 described above, and its cycle characteristics were examined.

The used hydrogen storage alloy has a composition of MmNi
_3.48 Co _0.74 Mn _0.4 Al _0.3 (where Mm is La:
(A misch metal containing 33%, Ce: 47%, Pr: 5%, and Nd: 15%). The hydrogen storage alloy electrode is composed of 20 g of the hydrogen storage alloy and 2.55 g of carboxymethyl cellulose 2%. 0.56 g of a 60% aqueous polytetrafluoroethylene dispersion was added, and 2 ml of pure water was further added and mixed well to prepare a paste containing the hydrogen storage alloy. The obtained paste containing the hydrogen storage alloy was emptied. It was prepared by coating, filling and drying a porous substrate made of a nickel foam having a porosity of 95% by volume.

As the proton exchange membrane, Nafion
(Nafion) 117 (trade name, manufactured by DuPont, a proton exchange membrane formed from a hydrolyzate of a copolymer of tetrafluoroethylene and perfluorosulfonylethoxyvinyl ether) was used.

The MH / PEM / Air model cell was assembled using the air electrode as a positive electrode, a hydrogen storage alloy electrode as a negative electrode, and a proton exchange membrane as an electrolyte. In assembling, first, a proton exchange membrane as an electrolyte is interposed between the air electrode and the hydrogen storage alloy electrode, and pressurized at 140 ° C. for 3 minutes at a pressure of 125 kg / cm ² to integrate them. As shown in FIG. 5, a laminated electrode body was manufactured.

Referring to the laminated electrode body shown in FIG. 5, reference numeral 21 denotes a positive electrode comprising the air electrode of the first embodiment,
Reference numeral 22 denotes an electrolyte made of a proton exchange membrane, 23 denotes a negative electrode made of the above-mentioned hydrogen storage alloy electrode, and 23a denotes a lead body thereof. 24 is a platinum reference electrode;
The platinum reference electrode 24 is provided for monitoring the potential of the platinum reference electrode 24 by being brought into contact with the electrolyte 22 made of a proton exchange membrane. The platinum reference electrode 24 is provided at an end of the electrolyte 22. As shown in the figure, the laminate is mainly composed of a cathode 21 composed of an air electrode, an electrolyte 22 composed of a proton exchange membrane, and a negative electrode 23 composed of a hydrogen storage alloy electrode.

FIG. 6 schematically shows a model cell using a laminated electrode body 25 mainly composed of a cathode 21 composed of the air electrode, an electrolyte 22 composed of a proton exchange membrane, and a negative electrode 23 composed of a hydrogen storage alloy electrode. FIG.
5 is shown in a perspective view, the other part is shown in a cross-sectional view, and the model cell is shown separated at the laminated electrode body 25. In FIG. 6, a polytetrafluoroethylene sheet 26 is crimped on the outside (the right side in FIG. 6) of the laminated electrode body 25 (however, it is shown in a separated state in FIG. 6). 6, an outer wall portion 28 having an air hole 28a is disposed on the inner wall portion 29.
Has a flange shape, and is shown in FIG. 6 in a state separated from the laminated electrode body 25 as described above.
In an actual model cell, the laminated electrode body 25 fits into the space of the inner wall 29, and the outer wall 28 is arranged outside the space. Then, the cell container 27 includes the outer wall portion 28 and the inner wall portion 2.
9, a side wall 30, a bottom wall 31, etc., a space formed by them is filled with water 32, and an O-ring 33 is disposed between the outer wall 28 and the inner wall 29. Thereby, a model cell is configured.

Comparative Example 2 An MH / PEM / Air model cell was assembled in the same manner as in Example 2 except that the air electrode of Comparative Example 1 was used as the air electrode.

With respect to the model cells of Example 2 and Comparative Example 2, at 25 ° C., 10 mA at 0.1 mA / cm ² .
After charging for 1 hour and stopping for 1 hour, charging and discharging were repeated to discharge to 0.1 V in 10 hours, and the cycle characteristics were examined.
FIG. 7 shows the result.

As shown in FIG. 7, in Example 1, the discharge voltage was stable at about 0.5 V, and the charge voltage was around 1.6 V, which was lower than that of Comparative Example 1 using a platinum catalyst. Thus, the effect of using a metal sulfide having a small oxygen overpotential has been exhibited.

[0036]

As described above, according to the present invention, it is possible to provide an air electrode which is less expensive than an air electrode using a platinum catalyst, has a small oxygen overvoltage, and has a high charge / discharge efficiency. By using such an air battery, an air battery that is less expensive and has higher charge and discharge efficiency can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating an air electrode according to a first embodiment.

FIG. 2 is a cross-sectional view schematically showing a model cell assembled using the air electrode shown in FIG. 1 in a partially separated state.

FIG. 3 is a diagram showing a discharge curve of the air electrode at 25 ° C. in a model cell assembled using the air electrode of Example 1.

FIG. 4 is a diagram showing discharge polarization characteristics of an air electrode at 25 ° C. of a model cell assembled using the air electrode of Example 1 and the air electrode of Comparative Example 1, respectively.

FIG. 5 is a perspective view schematically showing a state in which a laminated electrode body mainly composed of a cathode composed of an air electrode, an electrolyte composed of a proton exchange membrane, and a negative electrode composed of a hydrogen storage alloy electrode of Example 1 is separated. .

6 is a diagram schematically showing a model cell using the laminated electrode body shown in FIG. 5, wherein the laminated electrode body is shown in a perspective view in a state where it is separated from other members, and other parts are sectional views Indicated by

FIG. 7 is a diagram showing cycle characteristics at 25 ° C. in an MH / PEM / Air-based model cell assembled using the air electrode of Example 1 and the air electrode of Comparative Example 1, respectively.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Air electrode 2 Air electrode catalyst 3 Current collector 4 Epoxy resin 5 Polytetrafluoroethylene sheet 6 Cell container 7 Outer wall 7a Air hole 8 Inner wall 9 Side wall 10 Bottom wall 11 Separator 12 Reference electrode 13 Counter electrode 14 Electrolyte 15 O-ring 21 Positive electrode 22 Electrolyte 23 Negative electrode 23a Lead 24 Platinum reference electrode 25 Stacked electrode 26 Polytetrafluoroethylene sheet 27 Cell container 28 Outer wall 28a Air hole 29 Inner wall 30 Side wall 31 Bottom wall 32 Water 33 O- ring

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinsuke Shibata 1-1-88 Ushitora, Ibaraki City, Osaka Prefecture Inside Hitachi Maxell Co., Ltd. (72) Inventor Stone Army 1-188 Ushitora, Ibaraki City, Osaka Hitachi Within Maxell Co., Ltd. (72) Inventor Ryu Nagai 1-88 Ushitora, Ibaraki-shi, Osaka Prefecture F-term within Hitachi Maxell Co., Ltd. 5H018 AA10 AS03 BB08 DD08 EE05 EE11 5H032 AA01 AS05 BB05 CC11 CC17 EE08

Claims (3)

[Claims] 1. An air electrode for electrochemically reducing oxygen in air and generating oxygen, wherein an air electrode catalyst mainly composed of carbon and metal sulfide is used. 2. The method according to claim 1, wherein the metal sulfide is NiS, NiS_Two,
Ni_ThreeS_Four, Ni_{0. Three}Co_0.7S_Two, CoS, FeS,
MoS_Two, Ag_TwoS, Sb_TwoS_Three, Sb_TwoS _Five, Sn
S, MnS, WS_TwoThe group consisting of PbS and ZnS
At least one member selected from the group consisting of:
Item 7. The air electrode according to Item 1. 3. An air battery using the air electrode according to claim 1 or 2 as a positive electrode, using a proton exchange membrane as an electrolyte, and using a hydrogen storage alloy electrode as a negative electrode.