JP3723902B2 - Electrode for oxygen reduction and electrochemical device using the same - Google Patents

Description

【０１０４】
本発明の炭化物を有効成分として含む空気極をプラス極として用いた発電セルａ、ｂでは、白金板をプラス極に用いた発電セルｃ、ｄに比べて開放電圧が０．２〜０．４Ｖ高い電圧を得ることができた。このことは、ビール酵母を炭化した炭化物を有効成分として含む空気極よりなるプラス極は、グルコースあるいはメタノールと直接接触しても酸化反応を起こさず、酸素の還元反応で決定される電位を与えるので、発電セルは高い電圧を与えることを示す。これに対し、白金板よりなるプラス極は、グルコースあるいはメタノールと直接接触すると酸化反応を起こすため、グルコースあるいはメタノールの酸化反応と酸素の還元反応で決定される低い電位を与えるために発電セルが低い電圧を与えていると考えられる。
【０１０５】
なお、電解質に可溶な燃料物質としてグルコースあるいはメタノールを用いたが、グルコースの他の糖類（たとえば、フルクトース、マンノース、スターチ、セルロールなど）、あるいはメタノールの他のアルコール類（たとえば、エタノール、プロパノール、ブタノール、グリセロールなど）を用いても同様な結果が得られる。また、電解質としてｐＨ６．８の０．１Ｍリン酸緩衝液に代えて、０．１ＮＫＯＨ水溶液またはＮａＣｌを３質量％溶解した塩水を用いても同様な結果が得られる。
【０１０６】
（実施例９）
発電セルの組み立て
図４に示す構成の発電セルＡおよび発電セルＢを組み立てた。
【０１０７】
図４において正極として作用する空気極１１は、発電セルＡでは、実施例１で得た試験電極１を用いて作製した。図４において、１５は負極リード、１６は正極リード、１７は透明のシリコンラバーよりなる封止材である。
【０１０８】
図４において負極として作用する光触媒電極は、ガラス基板６、ＩＴＯ薄膜７、酸化チタン（ＴｉＯ_２）微粒子膜８、および色素分子層９より成っている。厚さ１ｍｍのガラス基板６上に表面抵抗が１０オーム／ｃｍ^２のインジウム・錫酸化物（ＩＴＯ）薄膜７が形成された光透過性導電性基板を用意し、平均粒径が１０ｎｍのＴｉＯ_２粒子を１１質量％分散したポリエチレングリコールを３０質量％含むアセトニトリル溶液を、浸漬法によりＩＴＯ薄膜上に塗布し、８０℃で乾燥したのち、空気中で４００℃で１時間焼成することで厚さ約１０μｍのＴｉＯ_２微粒子膜８を形成した。次に、ＴｉＯ_２微粒子膜を、以下に示されるルテニウム金属錯体色素分子９を１０ｍＭ溶解したエタノール中に浸漬することで、色素分子９をＴｉＯ_２微粒子膜８に添着した。さらに、４−ｔｅｒｔ−ブチルピリジンに浸漬したのち、アセトニトリルで洗浄したのち乾燥することで上記光触媒電極を作製した。
【０１０９】
【化１】

【０１１０】
電解液・燃料液１０として、ｐＨ７．０の０．１Ｍリン酸緩衝溶液に、燃料のメタノール５質量％、補酵素ニコチンアミドヌクレオチド（ＮＡＤＨ）を５ｍＭ、アルコールデヒドロゲナーゼ（ＡＤＨ）を１６．０Ｕ／ｍｌ、アルデヒドデヒドロゲナーゼ（ＡｌＤＨ）を１．０Ｕ／ｍｌおよびホルメートデヒドロゲナーゼ（ＦＤＨ）を０．３Ｕ／ｍｌを溶解したものを用いた。電解液・燃料液１０は、電解液・燃料液注入口１３ａより注入され、発電後、排出口１３ｂより排出される。空気は、酸素透過性撥水膜１２を通して外部より発電セル内部に供給される。
【０１１１】
図４に記載されている発電セルの構造について説明する。この発電セルの負極側は、主としてガラス基板６からなり、このガラス基板６の表面にはＩＴＯ薄膜７が積層されている。ＩＴＯ薄膜７には、負極リード１５が設けられている。発電セルの正極側は、主として板状の空気極１１からなり、空気極１１の表面には酸素透過性撥水膜１２が積層されている。空気極１１の内部からは正極リード１６が伸び出している。このようなガラス基板６の表面および板状の空気極１１の裏面とを向かい合わせにし、これらの間に封止材１７を介してガラス基板６と空気極１１とを貼り合わせることにより発電セルが形成されている。
【０１１２】
ガラス基板６と空気極１１との間には、空気極１１側に電解液（または燃料液）１０が、ガラス基板６側に酸化チタンからなる微粒子が分散された微粒子薄膜８が位置している。そして、電解液（または燃料液）１０と微粒子薄膜８との間には、色素分離層９が挟まれている。
【０１１３】
また、封止材１７には、封止材１７を貫通する電解液・燃料液注入口１３ａおよび電解液・燃料液排出口１３ｂが設けられている。これらの電解液・燃料液注入口１３ａおよび電解液・燃料液排出口１３ｂには、液バルブ１４ａ・１４ｂがそれぞれ設けられている。これらの電解液・燃料液注入口１３ａおよび電解液・燃料液排出口１３ｂを介して、ガラス基板６と空気極１１との間に電解液（または燃料液）１０を外部から注入および外部に排出することができるように設計されている。
【０１１４】
なお、発電セルＢは、実施例２で得た試験電極３を用いて作製した空気極を使用した以外は、発電セルＡと同じ構成となるように作製した。
【０１１５】
発電セルの動作特性
発電セルを電解液・燃料液で満たしたのち、ガラス基板６側より太陽光シュミレータ（ＡＭ１．５、１００ｍＷ／ｃｍ^２）からの光を照射し、発電セルの起電力（ＯＣＶ）および、１００μＡの一定電流で発電セルを２０分間放電した際の発電セルの電圧を測定した。ＯＣＶは、発電セルＡでは０．８０Ｖ、発電セルＢでは０．６５Ｖであった。また、２０分間放電後の発電セルの電圧は、発電セルＡでは０．７５Ｖ、発電セルＢでは０．５５Ｖであった。このように高い起電力が得られるとともに、放電に際しても、高い電圧を維持することができた。
【０１１６】
なお、本実施例では、発電セルの負極として光触媒電極を用い、メタノールを燃料とする電池を示したが、負極として、亜鉛、マグネシウム、アルミニウムなどの金属を用いても、本発明に従う酸素還元用電極と組み合わせることで、電気化学素子として起電力ならびに放電時の電池電圧が高い電池を得ることができる。【Technical field】
[0001]
The present invention relates to an oxygen reduction electrode used in a reaction for reducing oxygen and an electrochemical device using the same.
[Background]
[0002]
Oxygen (O₂) Is reduced by electrolytic reaction, it is known that one-electron reduction, two-electron reduction, or four-electron reduction occurs. One-electron reduction produces superoxide. In the two-electron reduction, hydrogen peroxide is generated. In the 4-electron reduction, water is produced (for example, JACEK KIPKOWSKI, edited by PHILIP N. ROSS, ELECTROCATALYSIS, WILEY-VCH Publishing, 1998, pages 204-205).
[0003]
When the oxygen reduction reaction is used as a positive electrode reaction of a battery, it is required to obtain a battery having a large capacity, a high voltage and a high output current. In this case, the oxygen reduction reaction requires that a) move as many electrons as possible, b) make the potential as positive as possible, and c) suppress overvoltage as much as possible. For this purpose, it is preferable to use a catalyst that allows the four-electron reduction reaction to proceed at a high potential with a small overvoltage. One such catalyst is platinum (Pt).
[0004]
However, platinum has the following problems. (1) Platinum is an expensive noble metal and is disadvantageous in terms of cost. In addition, (2) platinum exhibits an activity not only for reduction of oxygen but also for an oxidation reaction of a fuel substance such as ethanol and hydrogen, so that the reaction selectivity is poor. For this reason, in actual use, the place where the oxidation reaction and the reduction reaction are performed must be separated by a separator or the like. (3) The surface of platinum is easily inactivated by carbon monoxide or a hydroxyl group, and it may be difficult to maintain high catalytic activity.
[0005]
Thus, several efforts have been made to develop a catalyst that can replace platinum.
[0006]
For example, JP-B-2-030141 or JP-B-2-030142 discloses a porous molded body of a conductive powder and a fluororesin carrying a metal chelate compound such as iron phthalocyanine and cobalt porphyrin having oxygen gas reducing ability. The catalyst which consists of is proposed. Further, it is known that by using a dimer (binuclear complex) of a metal chelate compound, a high oxygen reducing ability (4-electron reducing ability) can be achieved, and it can be expected to be applied to a large output air battery.
[0007]
For example, an oxygen reduction catalyst technology using a macrocyclic complex having a transition metal such as Cr, Mn, Fe, and Co as a central metal such as a cobalt porphyrin binuclear complex has been disclosed (JACEK KIPKOWSKI, PHILIP N. ROSS editing, ELECTROCATALYSIS, WILEY-VCH publication, 1998, pp. 232-234).
[0008]
Japanese Patent Application Laid-Open No. 11-253811 discloses a manganese complex catalyst for oxygen reduction. This complex serves as a catalyst for performing a four-electron reduction reaction of oxygen with high selectivity. This document states that the manganese atom has a valence of 2 to 7 and catalyzes the oxygen reduction reaction in a potential range of minus 0.5 V to plus 2 V.
[0009]
When these catalysts are actually used, the catalyst is often supported on a carrier having excellent stability. When used in electrode reactions of electrochemical devices, carbon materials are widely used as conductive carriers. For example, carbon materials such as carbon black, activated carbon, graphite, conductive carbon, and glassy carbon are used. It is known that these carbon materials usually cause a two-electron reduction reaction when oxygen is electrolytically reduced to give hydrogen peroxide.
DISCLOSURE OF THE INVENTION
However, if a high potential is to be obtained by using such a catalyst, a metal complex having a central metal atom having a large valence is required. Since such metal complexes are highly reactive, they react with members (for example, electrolytes, electrode leads, current collectors, battery cases, separators, gas permselective membranes, etc.) that the metal complexes come into contact with, and deteriorate these members There is a difficulty that causes.
[0010]
As for the carbon material used as a carrier, it is known that coconut shell activated carbon, wood carbide, etc. have an action of decomposing hydrogen peroxide. For example, as an activated carbon having high performance as a hydrogen peroxide decomposition catalyst, carbide of acrylic fiber, carbide of beer lees, and the like are disclosed (Japanese Patent Laid-Open Nos. 7-024315 and 2003-001107).
[0011]
However, regarding the catalytic action of the carbon material itself, only a generally known electrode reaction (that is, a two-electron reduction reaction) is known. The catalytic action and effectiveness as an electrode catalyst for reducing oxygen are not particularly disclosed.
[0012]
The main object of the present invention is to provide an electrode for oxygen reduction which gives a 4-electron reduction reaction with higher selectivity in the reaction of reducing oxygen.
[0013]
It is a further object of the present invention to provide a stable oxygen reduction electrode that exhibits little oxidation activity with respect to a fuel substance soluble in an electrolyte.
[0014]
That is, the present invention relates to the following oxygen reduction electrode and an electrochemical device using the same.
[0015]
1. A method for producing an oxygen reduction electrode used for 4-electron reduction of oxygen, wherein (1) a first step of obtaining a carbide by carbonizing a yeast-containing substance and (2) an electrode material containing the carbide A production method comprising a second step of producing the oxygen reduction electrode.
2. Yeast-containing substances are brewer's yeast, wine yeast, sake yeast, whiskey yeast, baker's yeast, food yeast, beer squeezed rice cake, sake brewer's sake, wine squeezed squeezed rice cake, whiskey brewed squeezed rice cake, corn juice squeezed Item 2. The method according to Item 1, wherein the method is at least one of koji and soy sauce koji.
3. Item 2. The method according to Item 1, wherein in the first step, the yeast-containing substance is carbonized at 300 ° C. or more and 1200 ° C. or less in an atmosphere having an oxygen concentration of 10% by volume or less.
-The manufacturing method of said claim | item 3 which carbonizes the said yeast containing substance by 500 degreeC or more and 1000 degrees C or less in the atmosphere where oxygen concentration is 10 volume% or less in a 1st process.
The manufacturing method according to Item 3, wherein the atmosphere is an inert gas atmosphere.
6). Item 2. The method according to Item 1, wherein the carbide is further activated in the first step.
7). In the second step, after the electrode material is molded into a predetermined shape to obtain a molded body, the oxygen reduction electrode is produced by laminating or pressing the molded body on a conductor substrate. The manufacturing method as described in.
8). Item 2. The electrode according to Item 1, wherein in the second step, the electrode material is made into a paste to obtain a paste containing the electrode material, and then the electrode for oxygen reduction is manufactured by coating the paste on a conductive substrate. Manufacturing method.
9. Item 2. The method according to Item 1, wherein an inorganic compound containing at least one of phosphorus (P) and calcium (Ca) is added to at least one of the yeast-containing substance, carbide, and electrode material.
10. The carbide is about 1000 to 1200 cm^-1The manufacturing method of said claim | item 1 which shows the infrared absorption of carbon (C) -oxygen (O) -carbon (C) expansion-contraction of the range.
11. The carbide is about 1600 cm^-1The manufacturing method of said claim | item 1 which shows the infrared absorption of the symmetrical expansion | contraction of carbon (C) = carbon (C).
12 The carbide is about 1700 cm^-1The manufacturing method of said claim | item 1 which shows the infrared absorption of the expansion-contraction of carbon (C) = oxygen (O).
13. The carbide is about 3000 cm^-1The manufacturing method of said claim | item 1 which shows the infrared absorption of the expansion-contraction of oxygen (O) -hydrogen (H).
14 The carbide is about 1000 to 1200 cm^-1Infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretch in the range, about 1600 cm^-1Carbon (C) = infrared absorption of symmetric stretching of carbon (C), about 1700 cm^-1Carbon (C) = infrared absorption of oxygen (O) stretching and about 3000 cm^-1The manufacturing method of said claim | item 1 which shows the infrared absorption of the expansion-contraction of oxygen (O) -hydrogen (H).
15. Item 2. The method according to Item 1, wherein at least one of a metal and an oxide thereof is added to at least one of the yeast-containing substance, carbide, and electrode material.
16. The oxide is of the general formula MnO_y(Where y is the number of oxygen atoms determined by the valence of manganese (Mn) and is less than 2).Item 15Manufacturing method.
17. An electrode containing a carbide obtained by carbonizing a yeast-containing substance, the electrode for oxygen reduction used for 4-electron reduction of oxygen.
18. Item 18. The oxygen reduction electrode according to Item 17, comprising an inorganic compound containing at least one of phosphorus (P) and calcium (Ca).
19. The carbide is about 1000 to 1200 cm^-1Item 18. The oxygen reduction electrode according to Item 17, which exhibits infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretching in a range.
20. The carbide is about 1600 cm^-1Item 18. The oxygen reduction electrode according to Item 17, which exhibits infrared absorption of symmetric stretching of carbon (C) = carbon (C).
21. The carbide is about 1700 cm^-1Item 18. The oxygen reduction electrode according to Item 17, which shows infrared absorption of carbon (C) = oxygen (O) stretching.
22. The carbide is about 3000 cm^-1Item 18. The oxygen reduction electrode according to Item 17, which exhibits infrared absorption of stretching of oxygen (O) -hydrogen (H).
23. The carbide is about 1000 to 1200 cm^-1Infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretch in the range, about 1600 cm^-1Carbon (C) = infrared absorption of symmetric stretching of carbon (C), about 1700 cm^-1Carbon (C) = infrared absorption of oxygen (O) stretching and about 3000 cm^-1Item 18. The oxygen reduction electrode according to Item 17, which exhibits infrared absorption of stretching of oxygen (O) -hydrogen (H).
24. Item 18. The oxygen reduction electrode according to Item 17, comprising at least one of a metal and an oxide thereof.
25. The oxide is MnO_yItem 25. The oxygen reduction electrode according to Item 24, wherein y is a manganese lower oxide represented by (wherein y is the number of oxygen atoms determined by the valence of manganese (Mn) and less than 2).
26. Item 18. The oxygen reduction electrode according to Item 17, wherein the carbide is particulate, and an electrode material containing the carbide is supported on a conductive substrate.
27. Item 27. The oxygen reduction electrode according to Item 26, wherein the conductive substrate is breathable.
28. Item 18. The oxygen reduction electrode according to Item 17, which is used for electrochemically reducing molecular oxygen in a neutral aqueous electrolyte.
29. An electrochemical device comprising: a) a positive electrode that reduces oxygen by four electrons; b) a negative electrode; and c) an electrolyte, wherein the positive electrode includes a carbide obtained by carbonizing a yeast-containing substance.
30. 30. The electrochemical element according to item 29, wherein the positive electrode includes an inorganic compound containing at least one of phosphorus (P) and calcium (Ca).
31. The carbide is about 1000 to 1200 cm^-130. The electrochemical element according to item 29, which exhibits infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretch in a range.
32. The carbide is about 1600 cm^-1Item 30. The electrochemical element according to Item 29, which exhibits infrared absorption of symmetrical stretching of carbon (C) = carbon (C).
33. The carbide is about 1700 cm^-1Item 30. The electrochemical element according to Item 29, which exhibits infrared absorption of stretching of carbon (C) = oxygen (O).
34. The carbide is about 3000 cm^-1Item 30. The electrochemical element according to Item 29, which exhibits infrared absorption of oxygen (O) -hydrogen (H) stretching.
35. The carbide is about 1000 to 1200 cm^-1Infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretch in the range, about 1600 cm^-1Carbon (C) = infrared absorption of symmetric stretching of carbon (C), about 1700 cm^-1Carbon (C) = infrared absorption of oxygen (O) stretching and about 3000 cm^-1Item 30. The electrochemical element according to Item 29, which exhibits infrared absorption of oxygen (O) -hydrogen (H) stretching.
36. 30. The electrochemical element according to item 29, wherein the positive electrode contains at least one of a metal and an oxide thereof.
37. The oxide is MnO_y37. The electrochemical element according to item 36, wherein y is a manganese lower oxide represented by the formula (wherein y is the number of oxygen atoms determined by the valence of manganese (Mn) and less than 2).
38. 30. The electrochemical element according to item 29, wherein the carbide is in the form of particles, and an electrode material containing the carbide is supported on a conductive substrate to constitute the positive electrode.
39. 39. The electrochemical element according to Item 38, wherein the conductive substrate is air permeable.
40. Item 30. The electrochemical element according to Item 29, wherein the electrolyte is a neutral aqueous electrolyte.
41. 30. The electrochemical element according to item 29, wherein the negative electrode reaction is an oxidation reaction in which electrons are electrochemically extracted from a fuel substance soluble in the electrolyte.
42. 30. The electrochemical element according to Item 29, wherein the electrolyte contains at least one of saccharides and alcohols.
43. A method for performing 4-electron reduction of oxygen,
a) a battery providing step for providing a battery comprising a carbide obtained by carbonizing a yeast-containing substance; b) a negative electrode; and c) an electrolyte; and
Oxygen supplying step of performing 4-electron reduction of oxygen by supplying oxygen to the positive electrode
A reduction method comprising:
44. 44. The reduction method according to item 43, wherein the positive electrode contains an inorganic compound containing at least one of phosphorus (P) and calcium (Ca).
45. The carbide is about 1000 to 1200 cm^-144. The reduction method according to Item 43, which shows infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretch in the range.
46. The carbide is about 1600 cm^-144. The reduction method according to Item 43, which shows infrared absorption of symmetric stretching of carbon (C) = carbon (C).
47. The carbide is about 2100 cm^-144. The reduction method according to Item 43, which shows infrared absorption of stretching of carbon (C) = oxygen (O).
48. The carbide is about 3000 cm^-144. The reduction method according to Item 43, which shows infrared absorption of oxygen (O) -hydrogen (H) stretching.
49. The carbide is about 1000 to 1200 cm^-1Infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretch in the range, about 1600 cm^-1Carbon (C) = infrared absorption of symmetric stretching of carbon (C), about 2100 cm^-1Carbon (C) = infrared absorption of oxygen (O) stretching and about 3000 cm^-144. The reduction method according to Item 43, which shows infrared absorption of oxygen (O) -hydrogen (H) stretching.
50. 44. The reduction method according to item 43, wherein the positive electrode contains at least one of a metal and an oxide thereof.
51. The oxide is MnO_y51. The reduction method according to item 50, wherein y is a manganese lower oxide represented by the formula (wherein y is the number of oxygen atoms determined by the valence of manganese (Mn) and less than 2).
52. 44. The reduction method according to item 43, wherein the carbide is in the form of particles and an electrode material containing the carbide is supported on a conductive substrate to constitute the positive electrode.
53. 53. The reduction method according to 52 above, wherein the conductive substrate is breathable.
54. Item 44. The reduction method according to Item 43, wherein the electrolyte is a neutral aqueous electrolyte.
55. 44. The reduction method according to item 43, wherein the negative electrode reaction is an oxidation reaction in which electrons are electrochemically extracted from a fuel substance soluble in the electrolyte.
56. 44. The reduction method according to item 43, wherein the electrolyte contains at least one of saccharides and alcohols.
[Brief description of the drawings]
[0016]
FIG. 1 is a diagram showing voltage (electromotive force) -current characteristics with respect to an oxygen reduction reaction in test electrodes 1 and 2 and each comparison electrode.
FIG. 2 is a graph showing voltage (electromotive force) -current characteristics with respect to an oxygen reduction reaction in test electrodes 3, 4, 5, 6 and each comparison electrode.
FIG. 3 is a cross-sectional view of a triode electrode cell in the measurement of an example of the present invention.
FIG. 4 is a cross-sectional view of a power generation cell according to another embodiment of the present invention.
[Explanation of symbols]
[0017]
1 Air electrode
1a Air electrode mixture
1b Fluororesin porous sheet
1c Electrode lead
2 Counter electrode
3 Reference electrode
4 Electrolyte
5 Glass cell
6 Glass substrate
7 ITO thin film
8 TiO₂Fine particle film
9 Dye molecular layer
10 Electrolyte / Fuel solution
11 Air electrode
12 Oxygen permeable water repellent film
13a Electrolyte / fuel injection port
13b Electrolyte / fuel outlet
14a, 14b Liquid valve
15 Negative lead
16 Positive lead
17 Sealing material
BEST MODE FOR CARRYING OUT THE INVENTION
[0018]
1. Oxygen reduction electrode and method for producing the same
The electrode for oxygen reduction of the present invention has (1) a first step of obtaining a carbide by carbonizing a yeast-containing substance, and (2) a production method having a second step of producing an electrode using an electrode material containing the carbide. It is produced by.
[0019]
(1) First step
In the first step, carbide is obtained by carbonizing the yeast-containing substance.
[0020]
Yeast
The yeast-containing substance may be yeast-derived substances such as yeast pomace, as well as yeast itself. These can be used alone or in combination of two or more.
[0021]
Examples of yeast that can be used include various yeasts such as beer yeast, wine yeast, sake yeast, whiskey yeast, baker's yeast, and dietary yeast.
[0022]
Examples of the squeezed lees include beer squeezed lees, sake lees, squeezed soup squeezed for wine production, wort squeezed sachet for whiskey production, corn soup squeezed soy sauce, and soy sauce lees. When these squeezes are used, merits such as effective use of resources and reduction of raw material costs can be obtained.
[0023]
Among these yeast-containing substances, those containing a relatively large amount of phosphorus and calcium when carbonized are preferred. When such a yeast is used, a higher oxygen reduction effect can be obtained. For example, at least one of brewer's yeast and its squeezed can be suitably used.
[0024]
In this invention, another additive can also be mix | blended with a yeast containing material as needed. The amount added can be appropriately determined according to the type of additive.
[0025]
For example, in order to improve the handleability of carbide, an organic binder (polyvinyl alcohol, butyral resin, etc.) or an inorganic binder (silicic anhydride, etc.) can be added.
[0026]
Moreover, a solvent can also be mix | blended with a yeast containing material. For example, an organic solvent such as phenol or a phenol derivative (for example, mononitrophenol, dinitrophenol, trinitrophenol, resilcinol, 1,4-di-hydroxybenzene, m-cresol, p-cresol, or the like) can be used.
[0027]
Carbonization and activation treatment
Carbide is made by carbonizing the yeast-containing substance. Usually, a carbide can be obtained by heat-treating the yeast-containing substance. The heat treatment conditions can be appropriately set according to the composition of the yeast-containing substance to be used, the characteristics of the desired carbide, and the like.
[0028]
The heat treatment temperature can be generally set in the range of about 300 ° C. or more and 1200 ° C. or less. When it exceeds 1200 ° C., graphitization proceeds, and therefore, it is preferable to treat at a temperature lower than that. More preferably, it is in the range of 500 ° C. or higher and 1000 ° C. or lower. By setting it to 500 ° C. or higher, better conductivity can be imparted. In addition, by setting the temperature to 1000 ° C. or lower, the above-described C—O—C bond or the like for imparting oxygen reduction activity and allowing the reaction to be efficiently performed can remain in the carbon component.
[0029]
What is necessary is just to set heat processing time suitably according to the heat processing temperature, the kind and quantity of the yeast containing material to be used, etc. so that carbonization may fully advance.
[0030]
As the heat treatment atmosphere, it is preferable to keep the oxygen concentration low or substantially no oxygen in order to prevent the yeasts from burning when heated at about 300 ° C. or higher. Specifically, the atmosphere is preferably set to an atmosphere having an oxygen concentration of 10% by volume or less, more preferably 1% by volume or less. In particular, an inert gas atmosphere (nitrogen, argon, helium, etc.) or vacuum is desirable.
[0031]
After the carbonization treatment, it is desirable to activate the obtained carbide. The activation process increases the specific surface area of the carbide to improve the activity, enhances the affinity with the reactants, enhances the affinity with other materials during loading, and adjusts the acidity of the surface. Can be.
[0032]
The method of activation processing can be implemented in accordance with a well-known method. For example, 1) a gas activation method using water vapor, carbon dioxide, or the like, and 2) a chemical activation method using ammonium chloride, zinc chloride, potassium hydroxide, or the like can be used. The temperature of the activation treatment varies depending on the treatment method. For example, in the gas activation method, the same temperature as the carbonization treatment is preferable. In the chemical activation method, the treatment can be performed at room temperature or in the range up to the same temperature as the carbonization treatment after being exposed to the chemical.
[0033]
(2) Second step
In the second step, an electrode is produced using an electrode material containing the carbide.
[0034]
carbide
The carbide generally includes an organic component having a structure derived from a yeast-containing substance (such as a structure derived from a fiber or a sugar of yeast).
[0035]
In particular, the carbide has a wave number of 1000 cm in infrared absorption spectroscopy.^-1To 1200cm^-1Range of about 1100cm^-1Carbon (C) -oxygen (O) -carbon (C) stretch absorption and / or about 1600 cm^-1It is preferable that the unsaturated carbon (C) = carbon (C) symmetrical stretching absorption. This is a characteristic not found in other activated carbon, carbon black and the like, and is unique to the present invention.
[0036]
Further, although it is not clear whether the carbide is derived from a carbon component or an inorganic component in infrared absorption spectroscopy, it is about 1700 cm due to a hydrophilic carbonyl group.^-1Carbon (C) = oxygen (O) stretching absorption and / or about 3000 cm due to hydroxyl group^-1It is preferable that oxygen (O) -hydrogen (H) stretching absorption in the vicinity is exhibited.
[0037]
By using a carbide containing a component exhibiting these absorptions, it is possible to contribute more effectively by improving the electrode characteristics. Such a carbide composition generally includes a carbon component and an inorganic component.
[0038]
The carbon component may be either crystalline or amorphous, but is particularly preferably amorphous. Moreover, it is preferable that the said carbon component has electroconductivity generally.
[0039]
Inorganic components vary depending on the composition of the yeast-containing substance used, but generally include phosphorus (P), calcium (Ca), potassium (K), magnesium (Mg) and the like as components derived from yeasts. . More preferably, P and Ca are contained as main components. These inorganic components may be present in the form of oxides, phosphates, carbonates and the like. The total content of inorganic components in the carbide also varies depending on the type of yeast-containing substance used, but usually contains 10% by mass or more, preferably 20% by mass or more. In this respect, it differs from activated carbon, carbon black, etc., in which the total content of inorganic components is several mass%.
[0040]
In addition, content of an inorganic component is measured by the ash content at the time of CHN elemental analysis of the carbide, and the element amount can be measured by fluorescent X-ray elemental analysis, ion chromatography analysis, or the like.
[0041]
In the present invention, in order to supplement the inorganic components, compounds containing these inorganic components can be added separately. In particular, an inorganic compound containing at least one of phosphorus and calcium can be suitably used. In addition to phosphoric acid, sodium phosphate, potassium phosphate, sodium hydrogen phosphate, calcium hydrogen phosphate, calcium carbonate, calcium oxide, calcium hydroxide, one or more of phosphate, inorganic calcium salt, etc. are used. be able to.
[0042]
Moreover, although the compound containing an inorganic component can be mix | blended with any of the said yeast containing substance or carbide | carbonized_material, it is desirable to mix | blend especially with a yeast containing substance.
[0043]
The form of the carbide is not limited as long as it has the physical properties as described above, but it is usually preferable to be granular or powder (powder). When the carbide is a granular material, it is preferable to have a particle size that passes 200 mesh or more of the Tyler sieve. Furthermore, the maximum particle diameter (diameter) is particularly preferably 20 μm or less, more preferably 1 μm or more and 20 μm or less. In general, since the reduction reaction occurs on the surface of the granular material, if it exceeds 20 μm, the efficiency with respect to the use amount may decrease. The particle size may be adjusted using a known pulverizer, classifier or the like.
[0044]
Electrode material
An electrode is produced using the electrode material containing the carbide. In the electrode material, various materials can be blended as necessary to improve electrode characteristics and the like. These materials can be blended in advance with the yeast-containing substance as long as the effects of the present invention are not hindered.
[0045]
For example, at least one of a metal and an oxide thereof can be blended in order to further enhance the ability to take up oxygen or release oxygen (oxygen exchange ability). For example, Mn₂O₃, Mn₃O₄, Mn₅O₈, Γ-MnOOH (Mn₃O₄And Mn₅O₈Manganese lower oxides such as MnO_y(Y is the number of oxygen atoms determined by the valence of manganese and is less than 2); ruthenium oxide, Cu_x-1Sr_xTiO₃(X = 0 to 0.5), La_xSr_1-xMnO₃(X = 0-0.5), SrTiO₃In addition to perovskite oxides such as vanadium oxide and platinum black.
[0046]
Among these, manganese lower oxides are preferable in that they have high hydrogen peroxide decomposition activity, little deterioration, and low cost. Manganese lower oxide is manganese oxide whose valence of manganese atom is less than 4. This is particularly preferable from the viewpoint of effective utilization of resources, for example, since the manganese dioxide positive electrode of the used manganese dry battery can be used as it is or can be fired.
[0047]
The addition amount of the metal or oxide thereof can be appropriately determined according to the type of metal acid or compound used, desired electrode characteristics, etc., but it is 1% by weight or more and 50% by weight in the finally obtained electrode. % Or less, particularly 5% to 20% by weight.
[0048]
In addition, various additives can be added to the electrode material. Examples of additives include 1) adjustment of affinity with other materials, 2) adjustment of acidity of the surface (electrode surface), 3) provision of catalytic activity, 4) provision of promoters, 5) reduction of overvoltage, etc. It can be used for the purpose. As such an additive, any of organic materials, inorganic materials, composite materials thereof, and mixtures thereof can be used depending on the purpose of addition. More specifically, metals or alloys such as platinum, cobalt, ruthenium, palladium, nickel, gold, silver, copper, platinum-cobalt alloy, platinum-ruthenium alloy; carbon materials such as graphite and activated carbon; copper oxide, nickel oxide Metal oxides such as cobalt oxide, ruthenium oxide, tungsten oxide, molybdenum oxide, manganese oxide, lanthanum-manganese-copper perovskite oxide; having porphyrin rings such as iron phthalocyanine, cobalt phthalocyanine, copper phthalocyanine, manganese phthalocyanine, zinc phthalocyanine Metal complexes such as metal phthalocyanine or metal porphyrin, ruthenium ammine complex, cobalt ammine complex, and cobalt ethylenediamine complex can be used.
[0049]
The central metal element of the metal complex is not limited, but at least one of platinum, ruthenium, cobalt, manganese, iron, copper, silver and zinc is particularly preferable. By using these metal elements, the oxygen reduction reaction can proceed with a smaller overvoltage. The valence of the metal element is preferably 4 or less. By setting the valence to 4 or less, the oxidizing power of the catalyst can be more effectively suppressed. As a result, it is possible to effectively prevent deterioration of the constituent elements of the electrochemical element (for example, electrolyte, electrode lead, current collector, battery case, separator, gas selective permeable membrane, etc.).
[0050]
The addition amount of the additive can be appropriately determined according to the type of material used, desired electrode characteristics, and the like, but it is 1% by weight to 80% by weight, particularly 20% by weight or more in the finally obtained electrode. It is desirable to make it 60% by weight or less.
[0051]
The electrode material may contain a material added to a known electrode material. For example, fluororesin binders such as polytetrafluoroethylene and Nafion, resin binders such as polyvinyl alcohol and polyvinyl butyral, conductive aids such as graphite, conductive carbon, hydrophilic carbon black, hydrophobic carbon black, etc. It can be added as appropriate.
[0052]
Electrode fabrication
The electrode may be manufactured according to a known electrode manufacturing method using the above electrode material. For example, a method of laminating or press-bonding a preformed electrode material formed on a conductive substrate (current collector), a method of coating a paste containing an electrode material on a conductive substrate, and mixing a conductive material and an electrode material Then, it can be produced by a molding method or the like.
[0053]
The conductive substrate is, for example, a carbon paper made by carbon fiber papermaking; a metal mesh such as a stainless steel mesh or a nickel mesh; a carbon powder, a metal powder or the like joined together with a synthetic resin binder such as a fluororesin binder to form a sheet A conductive composite material sheet or the like that has been processed can be used effectively.
[0054]
Moreover, when preparing the said paste, a paste can be obtained by melt | dissolving a binder in a suitable solvent. For example, when polytetrafluoroethylene is used as the binder, alcohols such as ethanol can be used as the solvent. What is necessary is just to determine the density | concentration of a binder suitably according to the kind etc. of binder to be used.
[0055]
Redox electrode
The present invention also includes an oxidation-reduction electrode obtained by the production method of the present invention. That is, an electrode containing a carbide obtained by carbonizing a yeast-containing substance, and an oxygen reduction electrode used to reduce oxygen by four electrons is included. Therefore, what is necessary is just to employ | adopt what was hung up above as components, such as the said yeast containing substance and a carbide | carbonized_material, in the electrode which concerns on this invention.
[0056]
In the oxygen reduction electrode of the present invention, the content of the carbide is not limited, and can be appropriately set according to the use of the electrode, the purpose of use, and the like. In particular, it is desirable that the above-mentioned carbide is contained in the electrode in an amount of 1% by weight to 80% by weight, particularly 20% by weight to 60% by weight. By setting to such a range, more excellent 4-electron reduction performance can be obtained.
[0057]
In the oxygen reduction electrode of the present invention, when this is used as a positive electrode of a battery, the following reaction occurs.
[0058]
In the oxygen reduction electrode of the present invention, O₂+ H₂O + 2e⁻→ OH⁻+ HO^2-A two-electron reduction reaction (1) of oxygen represented by (in alkaline solution) occurs, and hydrogen peroxide (H₂O₂HO in alkaline solution^2-Hydrogen peroxide ions represented by Furthermore, the generated hydrogen peroxide ions are 2HO.^2-→ O₂+ 2OH⁻Is caused to generate oxygen again. This oxygen undergoes two-electron reduction again to generate hydrogen peroxide ions.
[0059]
One molecule of oxygen generates one molecule of hydrogen peroxide ions by the two-electron reduction reaction (1). One molecule of the generated hydrogen peroxide ions gives 1/2 molecule of oxygen by the decomposition reaction (2). The ½ molecule of oxygen molecule generates ½ molecule of hydrogen peroxide ions by the two-electron reduction reaction (1). The generated ½ molecule peroxide ion regenerates ¼ molecule oxygen by the decomposition reaction (2). The 1/4 molecule of oxygen molecules generates 1/4 molecule of hydrogen peroxide ions by the two-electron reduction reaction (1). The generated 1/4 molecule peroxide ion gives 1/8 molecule oxygen by the decomposition reaction (2). Thus, the two-electron reduction reaction (1) and the decomposition reaction (2) occur repeatedly.
[0060]
That is, 2 electrons, 1 electron, 1/2 electron, 1/4 electron, 1/8 electron,..., (1/2) n electrons (n → infinity) for reduction of one molecule of oxygen. A total of four electrons are used, which is substantially the same as when one molecule of oxygen has undergone a four-electron reduction reaction at the potential of a two-electron reduction reaction. In other words, O₂+ 2H₂O + 4e⁻→ 4OH⁻The result is the same as that of the reaction.
[0061]
Regarding the action of the carbides of yeast-containing substances, the two-electron reduction reaction of oxygen molecules occurs in the carbon component, and the hydrogen peroxide generated at that time is immediately decomposed by the inorganic component, and the generated oxygen is immediately reduced by two-electrons. It is thought that 4-electron reduction substantially occurs by repeating the reaction. Such a reaction is considered to occur due to the presence of the carbon component and the inorganic component in the vicinity. Probably, elements such as phosphorus and calcium, which are inorganic main components mixed with carbon components, have various oxidation states, and thus have a high oxygen exchange capacity and promote the decomposition of hydrogen peroxide.
[0062]
In addition, in the vicinity of the carbon component, in addition to the high affinity for oxygen, the affinity for water is also high, so it is considered that the two-electron reduction reaction is also promoted. In addition, the carbon component itself has C—O—C bonds, C═O bonds, OH groups, etc., and has a high affinity for oxygen and hydrogen peroxide, as well as an affinity for water. Is considered to be progressing. In addition, since other inorganic components such as silicon are also present in an oxidized state, it may be possible to act as a promoter to promote the reaction. In any case, it is considered that the 4-electron reduction reaction proceeds selectively by the synergistic action of each component.
[0063]
As described above, the electrode for oxygen reduction according to the present invention provides an oxygen reduction pathway for electrochemical reduction using oxygen as an electrode reactant by electrochemical catalysis by a carbide of a yeast-containing substance. The reaction can occur with high selectivity (selectivity close to 100%).
(2) Electrochemical element
The electrochemical device of the present invention includes a) a positive electrode in which a reduction reaction of oxygen is a positive electrode reaction, b) a negative electrode, and c) an electrolyte, and the positive electrode includes a carbide obtained by carbonizing a yeast-containing substance. Features.
[0064]
That is, in the electrochemical device of the present invention, the electrode according to the present invention is basically used as the positive electrode. As a negative electrode, well-known electrodes, such as platinum, zinc, magnesium, aluminum, iron, can be used, for example.
[0065]
For the electrochemical element of the present invention, known constituent elements of the electrochemical element can be applied except that the oxygen reduction electrode of the present invention is used as the positive electrode. For example, known or commercially available electrolytes, separators, containers, electrode leads, and the like can be used.
[0066]
In particular, the electrolyte may be either an electrolytic solution or a solid electrolyte, but an electrolytic solution can be particularly preferably used. When using an electrolytic solution, the solvent may be either water or an organic solvent. Among these, it is preferable to use an aqueous solution as the electrolytic solution. The pH of the electrolytic solution is not limited, but is preferably in the neutral region of pH 6 to pH 9. In the present invention, it is desirable to use a neutral aqueous solution as the electrolyte in that higher activity can be obtained.
[0067]
It is desirable that the electrolyte contains a fuel substance. In particular, the fuel substance is preferably dissolved in a neutral aqueous solution. The reaction of the negative electrode at this time is preferably an oxidation reaction in which electrons are electrochemically extracted from the fuel substance dissolved in the electrolyte. The fuel substance is not particularly limited as long as it is soluble in the electrolyte to be used (particularly a neutral aqueous solution), but is preferably at least one of saccharides and alcohols. Examples of the saccharide include glucose, fructose, mannose, starch, cellulose and the like. Examples of alcohols include methanol, ethanol, propanol, butanol, glycerol and the like.
[0068]
The content (concentration) of the fuel substance in the electrolyte depends on the type of fuel used, the type of solvent, etc., but is generally about 0.01% by weight to 100% by weight, particularly 1% by weight to 20% by weight. Is desirable.
[0069]
In the electrochemical device of the present invention, the oxidation-reduction electrode is used, for example, by placing it at a place where three phases of 1) a gas containing oxygen, 2) a liquid made of an electrolyte solution, and 3) a solid made of a conductive material are in contact. Is preferred. Thus, by arranging the electrode according to the present invention (especially, a carbide of yeast) at the intersection of the ion path and the electron path, the electrochemical reduction of oxygen can be caused smoothly with a small overvoltage (resistance). And a large current value can be obtained.
[0070]
The oxygen-reducing electrode of the present invention exhibits little oxidation activity with respect to saccharides or alcohols, which are fuels soluble in an electrolyte. For this reason, the electrode according to the present invention is used as a positive electrode (positive electrode), a saccharide or alcohol solution is used as an electrolyte, and a negative electrode (negative electrode) for oxidizing saccharides or alcohols is used to constitute a power generation cell. can do. In this case, even if the positive electrode side and the negative electrode side are not separated by a separator, the voltage of the power generation cell does not decrease even if saccharides or alcohols, which are fuels dissolved in the electrolyte, are in direct contact with the positive electrode. Of course, in the electrochemical device of the present invention, a separator may be used as necessary.
[0071]
In the electrochemical device of the present invention, an electrode containing a carbide obtained by carbonizing a yeast-containing substance is used as the positive electrode, and thus the 4-electron reduction reaction of oxygen as described above occurs. In other words, a four-electron reduction reaction of oxygen can be performed by using the electrochemical element of the present invention.
【The invention's effect】
[0072]
The electrode for oxidation-reduction in the present invention can obtain an electrode capable of efficiently performing oxygen reduction electrochemically by using a carbide of a yeast-containing substance.
[0073]
That is, the electrode according to the present invention exhibits a substantial four-electron reduction reaction action that has not been known in conventional carbon-based materials that catalyze the two-electron reduction reaction of oxygen molecules.
[0074]
When the electrode according to the present invention is disposed at the intersection of the ion path and the oxygen path, the electrochemical reduction of oxygen can be caused smoothly with a small overvoltage (resistance). As a result, an electrochemical element capable of obtaining a large electromotive force and a large current value can be provided.
[0075]
In particular, the electrode according to the present invention is a substitute for a noble metal catalyst such as platinum, which is a conventional four-electron reduction catalyst, because the reduction reaction of oxygen molecules proceeds substantially with four electrons. As a result, 1) it is inexpensive, 2) there is no need to separate the place where the oxidation reaction / reduction reaction is performed by a separator, etc., and 3) it is possible to suppress inactivation of the catalyst due to poisoning or the like. It becomes possible to provide an electrode.
[0076]
Moreover, since the support itself catalyses the reduction reaction electrochemically by using the carbide obtained by carbonizing the yeast-containing substance as a catalyst carrier for the oxidation-reduction electrode, the amount of noble metal catalyst such as platinum used. Can also be reduced.
[0077]
Furthermore, it is thought that the effect which suppresses the performance fall by the poisoning etc. of noble metal catalysts, such as platinum, is also possessed, and it becomes possible to aim at a higher performance improvement.
[Industrial applicability]
[0078]
ADVANTAGE OF THE INVENTION According to this invention, the electrode for oxygen reduction excellent also in the stability which gives a 4-electron reductive reaction with the selectivity close | similar to 100% substantially with respect to the electrochemical reduction of oxygen can be provided. Such an electrode for oxygen reduction can be used for an oxygen electrode, an air electrode, or the like of an electrochemical device using an oxygen reduction reaction as a positive electrode reaction. For example, it is suitably used for zinc-air batteries, aluminum-air batteries, sugar-air batteries and other air batteries; oxyhydrogen fuel cells, methanol fuel cells and other fuel cells; enzyme sensors, oxygen sensors and other electrochemical sensors; be able to.
[0079]
As described above, the electrode of the present invention and the manufacturing method thereof are methods suitable for production on an industrial scale, and are highly practical.
【Example】
[0080]
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the scope of the present invention is not limited to the examples.
[0081]
Example 1
Preparation of test electrodes 1 and 2
After carbonizing the beer pomace material containing brewer's yeast at 800 ° C. in a nitrogen atmosphere, test electrodes 1 and 2 were produced using the carbide obtained by performing steam activation at 900 ° C.
[0082]
Fixed carbon of the obtained carbide was about 64% by mass. Ash content in elemental analysis was about 30% by mass. Of these, about 30% by mass of phosphorus (P), 23% by mass of calcium (Ca), 7% by mass of magnesium (Mg), 3% by mass of potassium (K), silicon by silicon X-ray analysis. It was found that (Si) was about 20% by mass and that P and Ca were the main components. In addition, as a characteristic absorption by infrared spectroscopy, the wave number is about 1110 cm.^-1C—O—C absorption having an absorption peak at about 1570 cm^-1C = C absorption having an absorption peak at about 1705 cm^-1C = O absorption having an absorption peak at 3000 cm^-1Nearby broad OH absorption was observed. These are not carbon-only complete carbides, but are derived from the molecular structure of the yeast-containing material before carbonization.
[0083]
The obtained carbide was pulverized so that the maximum diameter was 10 μm or less. 25 μg of this powder was dispersed in 5 μl of an ethanol solution in which 0.05% by mass of proton-conductive Nafion (product name “Nafion 112” manufactured by DuPont, the same applies hereinafter) was dissolved. The obtained dispersion is dropped on a breathable conductive substrate so as to cover the entire surface, dried with warm air to evaporate ethanol, and the dispersion is further dropped again to evaporate the ethanol and carbide and Nafion. A test electrode was prepared.
[0084]
As the air-permeable conductive substrate, carbon paper having a thickness of 0.36 mm (product name “TGPH-120” manufactured by Toray, the same shall apply hereinafter) was used. 2.25 mg / cm2 of a mixture comprising 1 part by weight of carbon black particles and 0.1 part by weight of a polytetrafluoroethylene (PTFE) binder²A waterproof carbon paper base obtained by holding the carbon paper on the carbon paper and a carbon paper base that was not waterproofed were used.
[0085]
4.2 mg / cm of carbide is formed on the surface of the waterproof carbon paper substrate by the method described above.²The test electrode 1 coated so as to be obtained was obtained. In addition, the carbide is 2 mg / cm on the carbon paper substrate by the method described above.²A test electrode 2 formed so as to be obtained was obtained.
[0086]
(Example 2)
Preparation of test electrode 3
After carbonizing beer squeezed koji material containing brewer's yeast at 800 ° C. in a nitrogen atmosphere, steam activation was performed at 900 ° C. 4 parts by weight of the obtained carbide (average particle size of about 5 μm) was mixed with manganese lower oxide (Mn₃O₄And Mn₅O₈, 4 parts by weight of an average particle size of about 10 μm), 1 part by weight of carbon black, and 0.2 part by weight of a fluororesin binder (PTFE). Using this mixture, a sheet using a nickel-plated stainless steel wire mesh (thickness: 0.15 mm, 25 mesh) of a breathable conductive substrate as a core was produced. Next, a fluororesin porous sheet (porosity: about 50%, thickness: 0.2 mm) was pressure-bonded to one side of the sheet to produce a test electrode 3 having a thickness of about 3 mm.
[0087]
(Example 3)
Preparation of test electrode 4
5 parts by weight of brewer's yeast and 0.1 part by weight of calcium hydrogen phosphate were mixed with 0.1 part by weight of anhydrous silicic acid binder and molded and solidified. The resulting mixture was carbonized at 900 ° C. under a nitrogen atmosphere. The obtained carbide was pulverized so that the maximum diameter was 20 μm or less. 25 μg of the obtained powder was dispersed in 5 μl of an ethanol solution in which 0.05% by mass of Nafion was dissolved. This dispersion was dropped onto the waterproof carbon paper substrate used in Example 1 so as to cover the entire surface, dried with warm air, and ethanol was evaporated to prepare a test electrode 4 containing carbide and Nafion. Carbide is 2mg / cm²It formed so that it might become.
[0088]
Example 4
Preparation of test electrode 5
After carbonizing beer yeast at 800 ° C. in a nitrogen atmosphere, steam activation was performed at 900 ° C. to obtain a carbide. The carbide was pulverized so that the maximum diameter was 10 μm or less. The obtained powder was impregnated with a 3 mmol / L ethanol solution of chloroplatinic acid to give a platinum salt. This was reduced by adding sodium borohydride at room temperature to carry platinum. The platinum loading at this time was about 10% by mass. 25 μg of the carbide added with platinum was dispersed in 5 μl of an ethanol solution in which 0.05% by mass of proton conductive Nafion was dissolved. This dispersion is dropped onto the waterproof carbon paper substrate used in Example 1 so as to cover the entire surface, and dried with warm air to evaporate ethanol, and then the dispersion is added again to evaporate ethanol. As a result, a test electrode 5 containing carbide and Nafion was produced. In this test electrode 5, the carbide is 2 mg / cm.²The platinum amount at that time is about 0.2 mg / cm²Met.
[0089]
(Example 5)
Preparation of test electrode 6
The test electrode 6 was produced using the carbide | carbonized_material obtained by carbonizing the wort pomace material for whiskey manufacture containing yeast at 800 degreeC under nitrogen atmosphere, and then steam-activating at 900 degreeC. The carbide was pulverized so that the maximum diameter was 10 μm or less. 25 μg of this powder was dispersed in 5 μl of an ethanol solution in which 0.05% by mass of proton-conductive Nafion was dissolved. This dispersion is dropped onto a breathable conductive substrate made of carbon paper having a thickness of 0.36 mm so as to cover the entire surface, dried by warm air to evaporate ethanol, and the dispersion is further dropped again. The test electrode 6 containing carbide and Nafion was prepared by evaporating ethanol. Carbon carbide is 2 mg / cm on the carbon paper substrate.²It carried so that it might become.
[0090]
(Comparative Example 1)
Preparation of comparative electrodes 1, 2, 3, 4 and 5
25 μg of carbon black powder having a platinum loading of 50% by mass was dispersed in 5 μl of an ethanol solution in which 0.05% by mass of proton-conductive Nafion was dissolved. 2.25 mg / cm of a mixture comprising 1 part by weight of carbon black particles as a breathable conductive substrate and 0.1 part by weight of a polytetrafluoroethylene (PTFE) binder.²This dispersion is dropped onto a waterproof carbon paper substrate held on a carbon paper with a thickness of 0.36 mm so as to cover the entire surface, dried with warm air to evaporate ethanol, and further the dispersion is By dropping again and evaporating ethanol, the amount of platinum was about 0.35 mg / cm2.²The comparative electrode 1 was prepared.
[0091]
At this time, platinum was reduced to about 0.2 mg / cm2 by performing the same treatment except that carbon black powder having a platinum loading of 30% by mass was used instead of the carbon black powder described above.²Comparative electrode 2 was prepared.
[0092]
In addition, the above-mentioned waterproof carbon paper substrate was formed on the comparative electrode 3, the carbon paper alone was formed on the comparative electrode 4, and an ethanol solution of proton conductive Nafion without the above-mentioned carbide was formed on the carbon paper substrate to obtain the comparative electrode 5. .
[0093]
(Example 6)
Evaluation of electrode characteristics of test electrodes 1 and 2
A three-electrode cell having the configuration shown in FIG. 3 was constructed, and the oxygen reduction characteristics at the test electrode were evaluated by voltage-current characteristics. In FIG. 3, 1 is an air electrode, 1a is a test electrode or a comparison electrode, 1b is a fluororesin porous sheet, 1c is an electrode lead, 2 is a counter electrode, 3 is a reference electrode, 4 is an electrolyte, and 5 is an air electrode. This is a glass cell having an opening with a diameter of 16 mm. As shown in FIG. 3, the air electrode 1 is disposed in the opening of the glass cell 5 so that the surface on the fluororesin porous sheet 1 b side is exposed to the atmosphere, and the other surface is in contact with the electrolytic solution 4. As the electrolytic solution 4, a 0.1 M phosphate buffer solution having a pH of 7.0 was used. The counter electrode 2 was platinum, and the reference electrode 3 was an Ag / AgCl (saturated KCl) electrode. The test electrode or comparative electrode 1a and the fluororesin porous sheet 1b were brought into close contact with each other.
[0094]
FIG. 1 shows a comparison of voltage-current characteristics when the test electrodes 1 and 2 and each comparison electrode are the air electrode 1. The applied current is measured while being maintained for at least 10 minutes, and the electromotive force is corrected by cell resistance and expressed on the basis of a standard hydrogen electrode (NHE). The test electrodes 1 and 2 had a small overvoltage and a high electromotive force compared to the comparative electrode 3 made of carbon black, and an electromotive force comparable to that of the comparative electrodes 1 and 2 made of platinum catalyst. This is comparable to the four-electron reduction reaction in platinum because the carbon used in the test electrode is substantially reduced by four electrons while oxygen is reduced by two electrons in the conventional carbon-based material. It is considered that the characteristics were obtained.
[0095]
(Example 7)
Evaluation of electrode characteristics of test electrodes 3, 4, 5 and 6
Similarly to Example 6, a three-electrode cell having the configuration shown in FIG. 3 was constructed, and the reduction characteristics of oxygen at the test electrode were evaluated by voltage-current characteristics.
[0096]
FIG. 2 shows a comparison of voltage-current characteristics when the test electrodes 3, 4, 5 and 6 and each comparison electrode are the air electrode 1. As compared with the comparative electrode 3 made of carbon black, each test electrode has a small overvoltage and a high electromotive force as in Example 6, and it can be seen that oxygen is catalyzed by an action close to a four-electron reduction reaction.
[0097]
In the test electrode 3, since the manganese lower oxide contained in the air electrode has a strong action of decomposing hydrogen peroxide generated by the two-electron reduction reaction of oxygen molecules, the effect of the four-electron reduction reaction is substantially increased. An electromotive force almost equal to that of the reference electrode 1 made of platinum was obtained.
[0098]
In the test electrode 4, a high electromotive force was obtained as an electrochemical catalytic effect in the granular material even in the carbide formed by molding and solidifying. For this reason, it is expected that the handleability can be improved, for example, by forming a molded body of carbide to form an electrode without using a granular material.
[0099]
In the test electrode 5, a high electromotive force is obtained with respect to the comparison electrode 2 in which the amount of platinum adhering to the carbide is the same. This is because, in addition to the added platinum, the reducing action of the carbide obtained by carbonizing the yeast is added to cause an efficient reduction reaction. By using this carbide as a catalyst carrier, the amount of expensive noble metal catalyst used can be reduced.
[0100]
Further, when the holding time of the electromotive force in the air electrode using the test electrode 5 is compared with that of the comparative electrode 1, the test electrode 5 is 5 times or more than the comparative electrode 1 in the time until the electromotive force is reduced by 10%. It was confirmed that it was retained for a long time. One of the major causes of this decrease in electromotive force is due to poisoning of platinum as a catalyst. The test electrode 5 has a small amount of platinum, so there is little decrease in electromotive force. However, since it has an effect that simply exceeds the difference in the amount of platinum (test electrode 5: comparative electrode 1 = 0.2: 0.35), It cannot be explained, and other effects are thought to have contributed. Although the effect is not clear, it is considered that the carbide effectively suppresses the poisoning of platinum due to the effect of advancing the four-electron reduction reaction of oxygen.
[0101]
In the test electrode 6, it turns out that the effect of 4-electron reduction reaction is acquired similarly also in the carbide | carbonized_material derived from yeast other than brewer's yeast.
[0102]
(Example 8)
Evaluation of power generation cell characteristics
The air electrode including the test electrode 1 of Example 1 is used as a positive electrode (positive electrode), platinum as a counter electrode is used as a negative electrode (negative electrode), and a 0.1M phosphate buffer solution having a pH of 6.8 in which 100 mM of glucose is dissolved is used as an electrolyte. Cell a was configured. Using the same positive electrode and negative electrode as in the power generation cell a, a power generation cell b using 0.1 M phosphate buffer solution having a pH of 6.8 in which 3% by mass of methanol was dissolved was constituted. Further, the power generation cell c and the power generation cell d were configured in the same manner except that the air electrode was a platinum plate Pt and used as a positive electrode. Table 1 shows the open circuit voltage of each power generation cell and the voltage when the power generation cell is discharged at a constant current value of 1 mA for 10 hours.
[0103]
[Table 1]

[0104]
In the power generation cells a and b using the air electrode containing the carbide of the present invention as an active ingredient as the positive electrode, the open circuit voltage is 0.2 to 0.4 V compared to the power generation cells c and d using the platinum plate as the positive electrode. A high voltage could be obtained. This is because a positive electrode composed of an air electrode containing carbonized carbonized beer yeast as an active ingredient does not cause an oxidation reaction even when directly contacted with glucose or methanol, and gives a potential determined by a reduction reaction of oxygen. This indicates that the power generation cell gives a high voltage. On the other hand, the positive electrode made of a platinum plate causes an oxidation reaction when directly in contact with glucose or methanol, so that the power generation cell is low to give a low potential determined by the oxidation reaction of glucose or methanol and the reduction reaction of oxygen. It is thought that voltage is given.
[0105]
In addition, although glucose or methanol was used as a fuel substance soluble in the electrolyte, other saccharides of glucose (for example, fructose, mannose, starch, cellulose, etc.) or other alcohols of methanol (for example, ethanol, propanol, Similar results can be obtained using butanol, glycerol and the like. Similar results can be obtained by using a 0.1 NKOH aqueous solution or a salt solution in which 3% by mass of NaCl is dissolved in place of the 0.1 M phosphate buffer having a pH of 6.8 as the electrolyte.
[0106]
Example 9
Assembling the power generation cell
A power generation cell A and a power generation cell B having the configuration shown in FIG. 4 were assembled.
[0107]
In FIG. 4, the air electrode 11 acting as the positive electrode was produced in the power generation cell A using the test electrode 1 obtained in Example 1. In FIG. 4, 15 is a negative electrode lead, 16 is a positive electrode lead, and 17 is a sealing material made of transparent silicon rubber.
[0108]
In FIG. 4, the photocatalytic electrode acting as the negative electrode is composed of a glass substrate 6, an ITO thin film 7, titanium oxide (TiO 2).₂) It consists of a fine particle film 8 and a dye molecule layer 9. The surface resistance is 10 ohm / cm on the glass substrate 6 having a thickness of 1 mm.²A light-transmitting conductive substrate on which an indium tin oxide (ITO) thin film 7 is formed is prepared, and TiO having an average particle diameter of 10 nm is prepared.₂An acetonitrile solution containing 30% by mass of polyethylene glycol in which 11% by mass of particles are dispersed is applied on the ITO thin film by a dipping method, dried at 80 ° C., and then baked at 400 ° C. for 1 hour in air. 10 μm TiO₂A fine particle film 8 was formed. Next, TiO₂By immersing the fine particle film in ethanol in which 10 mM of the ruthenium metal complex dye molecule 9 shown below is dissolved, the dye molecule 9 is converted into TiO 2.₂Attached to the fine particle film 8. Furthermore, after dipping in 4-tert-butylpyridine, the photocatalyst electrode was produced by washing with acetonitrile and drying.
[0109]
[Chemical 1]

[0110]
As electrolyte solution / fuel solution 10, 0.1% phosphate buffer solution of pH 7.0, 5% by mass of fuel methanol, 5 mM coenzyme nicotinamide nucleotide (NADH), 16.0 U / ml alcohol dehydrogenase (ADH) Aldehyde dehydrogenase (AlDH) dissolved in 1.0 U / ml and formate dehydrogenase (FDH) dissolved in 0.3 U / ml were used. The electrolytic solution / fuel solution 10 is injected from the electrolytic solution / fuel solution injection port 13a, and is discharged from the discharge port 13b after power generation. Air is supplied from the outside into the power generation cell through the oxygen permeable water repellent film 12.
[0111]
The structure of the power generation cell shown in FIG. 4 will be described. The negative electrode side of the power generation cell is mainly composed of a glass substrate 6, and an ITO thin film 7 is laminated on the surface of the glass substrate 6. The ITO thin film 7 is provided with a negative electrode lead 15. The positive electrode side of the power generation cell is mainly composed of a plate-like air electrode 11, and an oxygen permeable water repellent film 12 is laminated on the surface of the air electrode 11. A positive electrode lead 16 extends from the inside of the air electrode 11. Such a power generation cell is formed by making the front surface of the glass substrate 6 and the back surface of the plate-like air electrode 11 face each other, and bonding the glass substrate 6 and the air electrode 11 with a sealing material 17 therebetween. Is formed.
[0112]
Between the glass substrate 6 and the air electrode 11, an electrolyte solution (or fuel solution) 10 is located on the air electrode 11 side, and a fine particle thin film 8 in which fine particles of titanium oxide are dispersed is located on the glass substrate 6 side. . A dye separation layer 9 is sandwiched between the electrolytic solution (or fuel solution) 10 and the fine particle thin film 8.
[0113]
Further, the sealing material 17 is provided with an electrolyte / fuel liquid inlet 13 a and an electrolyte / fuel liquid outlet 13 b that penetrate the sealing material 17. Liquid valves 14a and 14b are provided in the electrolyte / fuel solution inlet 13a and the electrolyte / fuel solution discharge port 13b, respectively. Through these electrolyte / fuel liquid inlet 13a and electrolyte / fuel outlet 13b, electrolyte (or fuel) 10 is injected between the glass substrate 6 and the air electrode 11 from the outside and discharged outside. Designed to be able to.
[0114]
The power generation cell B was manufactured to have the same configuration as the power generation cell A except that an air electrode manufactured using the test electrode 3 obtained in Example 2 was used.
[0115]
Power cell operating characteristics
After filling the power generation cell with the electrolyte / fuel solution, the solar simulator (AM1.5, 100 mW / cm from the glass substrate 6 side)²), And the voltage of the power generation cell when the power generation cell was discharged for 20 minutes at a constant current of 100 μA was measured. The OCV was 0.80 V for power generation cell A and 0.65 V for power generation cell B. Moreover, the voltage of the power generation cell after 20 minutes of discharge was 0.75 V in the power generation cell A and 0.55 V in the power generation cell B. Thus, a high electromotive force was obtained, and a high voltage could be maintained during discharge.
[0116]
In this example, a battery using a photocatalyst electrode as a negative electrode of a power generation cell and methanol as a fuel is shown. However, even if a metal such as zinc, magnesium, or aluminum is used as a negative electrode, oxygen reduction according to the present invention is used. By combining with an electrode, a battery having a high electromotive force and a battery voltage during discharge can be obtained as an electrochemical element.

Claims (56)

A method for producing an oxygen reduction electrode used for 4-electron reduction of oxygen, wherein (1) a first step of obtaining a carbide by carbonizing a yeast-containing substance and (2) an electrode material containing the carbide A production method comprising a second step of producing the oxygen reduction electrode. Yeast-containing substances are brewer's yeast, wine yeast, sake yeast, whiskey yeast, baker's yeast, food yeast, beer squeezed rice cake, sake brewer's sake, wine squeezed squeezed rice cake, whiskey brewed squeezed rice cake, corn juice squeezed The production method according to claim 1, which is at least one of koji and soy sauce koji. The production method according to claim 1, wherein in the first step, the yeast-containing substance is carbonized at 300 ° C to 1200 ° C in an atmosphere having an oxygen concentration of 10% by volume or less. The production method according to claim 3, wherein in the first step, the yeast-containing substance is carbonized at 500 ° C or more and 1000 ° C or less in an atmosphere having an oxygen concentration of 10% by volume or less. The manufacturing method according to claim 3, wherein the atmosphere is an inert gas atmosphere. The manufacturing method according to claim 1, wherein in the first step, the carbide is further activated. In the second step, the electrode material for oxygen reduction is manufactured by forming the electrode material into a predetermined shape to obtain a molded body, and then laminating or press-bonding the molded body to a conductor substrate. The manufacturing method as described in. 2. The oxygen reduction electrode according to claim 1, wherein in the second step, the electrode material is made into a paste to obtain a paste containing the electrode material, and then the electrode for oxygen reduction is manufactured by coating the paste on a conductive substrate. Manufacturing method. The manufacturing method of Claim 1 which adds the inorganic compound containing at least 1 sort (s) of phosphorus (P) and calcium (Ca) to at least any one of the said yeast containing substance, a carbide | carbonized_material, and an electrode material. The method of claim 1, wherein the carbide exhibits infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretching in the range of about 1000 to 1200 cm ⁻¹ . The manufacturing method according to claim 1, wherein the carbide exhibits infrared absorption of symmetrical stretching of carbon (C) = carbon (C) of about 1600 cm ⁻¹ . The manufacturing method according to claim 1, wherein the carbide exhibits infrared absorption of stretching of carbon (C) = oxygen (O) of about 1700 cm ⁻¹ . The manufacturing method of Claim 1 in which the said carbide | carbonized_material shows the infrared absorption of the expansion-contraction of oxygen (O) -hydrogen (H) of about 3000 cm < ^-1 >. Infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretch in the range of about 1000 to 1200 cm ⁻¹ , about 1600 cm ⁻¹ carbon (C) = symmetric stretch of carbon (C) infrared absorption, expansion and contraction of the infrared absorption of carbon about 1700cm ^-1 (C) = oxygen (O), in and around 3000 cm ^-1 oxygen (O) - claim showing the infrared absorption of the expansion and contraction of the hydrogen (H) 1. The production method according to 1. The manufacturing method of Claim 1 which adds at least 1 sort (s) of a metal and its oxide to at least any one of the said yeast containing substance, carbide | carbonized_material, and an electrode material. 16. The oxide according to claim 15 , wherein the oxide is a manganese lower oxide represented by the general formula MnO _y (where y is the number of oxygen atoms determined by the valence of manganese (Mn) and less than 2). Production method. An electrode containing a carbide obtained by carbonizing a yeast-containing substance, the electrode for oxygen reduction used for 4-electron reduction of oxygen. The oxygen reduction electrode according to claim 17, comprising an inorganic compound containing at least one of phosphorus (P) and calcium (Ca). The oxygen-reducing electrode according to claim 17, wherein the carbide exhibits infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretching in a range of about 1000 to 1200 cm ⁻¹ . The oxygen-reducing electrode according to claim 17, wherein the carbide exhibits infrared absorption of symmetrical stretching of carbon (C) = carbon (C) of about 1600 cm ⁻¹ . The oxygen-reducing electrode according to claim 17, wherein the carbide exhibits infrared absorption of stretching of carbon (C) = oxygen (O) of about 1700 cm ⁻¹ . The oxygen reduction electrode according to claim 17, wherein the carbide exhibits infrared absorption of stretching of oxygen (O) -hydrogen (H) of about 3000 cm ⁻¹ . Infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretch in the range of about 1000 to 1200 cm ⁻¹ , about 1600 cm ⁻¹ carbon (C) = symmetric stretch of carbon (C) infrared absorption, expansion and contraction of the infrared absorption of carbon about 1700cm ^-1 (C) = oxygen (O), in and around 3000 cm ^-1 oxygen (O) - claim showing the infrared absorption of the expansion and contraction of the hydrogen (H) 18. The electrode for oxygen reduction according to 17. The oxygen reduction electrode according to claim 17, comprising at least one of a metal and an oxide thereof. 25. The manganese lower oxide represented by MnO _y (wherein y is the number of oxygen atoms determined by the valence of manganese (Mn) and less than 2). Electrode for oxygen reduction. The electrode for oxygen reduction according to claim 17, wherein the carbide is particulate, and an electrode material containing the carbide is supported on a conductive substrate. 27. The oxygen reduction electrode according to claim 26, wherein the conductive substrate is breathable. 18. The oxygen reduction electrode according to claim 17, which is used for electrochemical reduction of molecular oxygen in a neutral aqueous electrolyte. An electrochemical device comprising: a) a positive electrode that reduces oxygen by four electrons; b) a negative electrode; and c) an electrolyte, wherein the positive electrode includes a carbide obtained by carbonizing a yeast-containing substance. 30. The electrochemical device according to claim 29, wherein the positive electrode contains an inorganic compound containing at least one of phosphorus (P) and calcium (Ca). 30. The electrochemical device of claim 29, wherein the carbide exhibits infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretch in the range of about 1000 to 1200 cm ⁻¹ . 30. The electrochemical device of claim 29, wherein the carbide exhibits infrared absorption of a symmetric stretch of about 1600 cm < ^-1 > carbon (C) = carbon (C). 30. The electrochemical device of claim 29, wherein the carbide exhibits infrared absorption of carbon (C) = oxygen (O) stretch of about 1700 cm ⁻¹ . 30. The electrochemical device according to claim 29, wherein the carbide exhibits infrared absorption of oxygen (O) -hydrogen (H) stretching at about 3000 cm < ^-1 >. Infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretch in the range of about 1000 to 1200 cm ⁻¹ , about 1600 cm ⁻¹ carbon (C) = symmetric stretch of carbon (C) infrared absorption, expansion and contraction of the infrared absorption of carbon about 1700cm ^-1 (C) = oxygen (O), in and around 3000 cm ^-1 oxygen (O) - claim showing the infrared absorption of the expansion and contraction of the hydrogen (H) 29. The electrochemical device according to 29. 30. The electrochemical device according to claim 29, wherein the positive electrode contains at least one of a metal and an oxide thereof. The oxide according to claim 36, wherein the oxide is a manganese lower oxide represented by MnO _y (wherein y is the number of oxygen atoms determined by the valence of manganese (Mn) and less than 2). Electrochemical element. 30. The electrochemical device according to claim 29, wherein the carbide is particulate, and an electrode material containing the carbide is supported on a conductive substrate to constitute the positive electrode. The electrochemical device according to claim 38, wherein the conductive substrate is breathable. 30. The electrochemical element according to claim 29, wherein the electrolyte is a neutral aqueous electrolyte. 30. The electrochemical device according to claim 29, wherein the reaction of the negative electrode is an oxidation reaction in which electrons are electrochemically extracted from a fuel substance soluble in the electrolyte. 30. The electrochemical device according to claim 29, wherein the electrolyte contains at least one of saccharides and alcohols. A method for performing 4-electron reduction of oxygen,
a) a positive electrode containing a carbide obtained by carbonizing a yeast-containing substance, b) a negative electrode and c) a battery providing step for providing a battery containing an electrolyte, and four-electron reduction of oxygen by supplying oxygen to the positive electrode A reduction method including an oxygen supply step. 44. The reduction method according to claim 43, wherein the positive electrode contains an inorganic compound containing at least one of phosphorus (P) and calcium (Ca). 44. The reduction method of claim 43, wherein the carbide exhibits infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretch in the range of about 1000 to 1200 cm ⁻¹ . 44. The reduction method according to claim 43, wherein the carbide exhibits infrared absorption of a symmetric stretch of about 1600 cm ⁻¹ of carbon (C) = carbon (C). 44. The reduction method according to claim 43, wherein the carbide exhibits infrared absorption of stretch of carbon (C) = oxygen (O) of about 2100 cm ⁻¹ . 44. The reduction method according to claim 43, wherein the carbide exhibits infrared absorption of oxygen (O) -hydrogen (H) stretching at about 3000 cm ⁻¹ . Infrared absorption of carbon (C) -oxygen (O) -carbon (C) stretch in the range of about 1000 to 1200 cm ⁻¹ , about 1600 cm ⁻¹ carbon (C) = symmetric stretch of carbon (C) An infrared absorption, an infrared absorption of about 2100 cm ^-1 carbon (C) = oxygen (O) stretch, and an infrared absorption of about 3000 cm ^-1 oxygen (O) -hydrogen (H). 44. The reduction method according to 43. 44. The reduction method according to claim 43, wherein the positive electrode contains at least one of a metal and an oxide thereof. 51. The manganese lower oxide according to claim 50, wherein the oxide is MnO _y (wherein y is the number of oxygen atoms determined by the valence of manganese (Mn) and less than 2). Reduction method. 44. The reduction method according to claim 43, wherein the carbide is in the form of particles, and an electrode material containing the carbide is supported on a conductive substrate to constitute the positive electrode. 53. The reduction method according to claim 52, wherein the conductive substrate is breathable. 44. The reduction method according to claim 43, wherein the electrolyte is a neutral aqueous electrolyte. 44. The reduction method according to claim 43, wherein the negative electrode reaction is an oxidation reaction in which electrons are electrochemically extracted from a fuel substance soluble in the electrolyte. 44. The reduction method according to claim 43, wherein the electrolyte contains at least one of saccharides and alcohols.

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