JP2020013662A - Gas diffusion layer used for gas diffusion electrode of metal-air battery or fuel cell, gas diffusion electrode using the same, and manufacturing method thereof - Google Patents
Gas diffusion layer used for gas diffusion electrode of metal-air battery or fuel cell, gas diffusion electrode using the same, and manufacturing method thereof Download PDFInfo
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Abstract
Description
本発明は、金属空気電池または燃料電池のガス拡散電極に使用されるガス拡散層とそれを用いたガス拡散電極およびその製造方法に関する。 The present invention relates to a gas diffusion layer used for a gas diffusion electrode of a metal-air battery or a fuel cell, a gas diffusion electrode using the same, and a method of manufacturing the same.
金属空気電池は、金属あるいは金属化合物を負極活物質とし、酸素を正極活物質として用いる化学反応のエネルギーを電気エネルギーとして取り出すエネルギーデバイスである。金属空気電池は正極活物質として空気中の酸素を利用するため、空気極を非常に薄くすることができ、電池に占める空気極の重量や体積は極めて小さい。したがって、通常の電池に必要な正極活物質を含む材料を電池内部に含まないため、現行の電池の中で大きなエネルギー密度をもつリチウムイオン電池と比較しても、その理論エネルギー密度は極めて大きい。金属空気電池は、自動車車載用電源、家庭や工場等の定置式分散電源、あるいは携帯電子機器用の電源等として利用することができる。 A metal-air battery is an energy device that extracts the energy of a chemical reaction using metal or a metal compound as a negative electrode active material and oxygen as a positive electrode active material as electric energy. Since a metal-air battery uses oxygen in the air as a positive electrode active material, the air electrode can be made very thin, and the weight and volume of the air electrode occupying the battery are extremely small. Therefore, since the material containing the positive electrode active material necessary for a normal battery is not included in the battery, the theoretical energy density is extremely high even in comparison with a lithium ion battery having a large energy density among existing batteries. The metal-air battery can be used as a power source for a vehicle, a distributed power source for a home or a factory, or a power source for a portable electronic device.
金属空気電池の空気極は、通常、ガス拡散電極が使用される。ガス拡散電極とは気体反応物質の電気化学的酸化還元反応を直接起こさせることができる電極である。空気極では空気中の酸素を活物質として使用し、その還元反応が進行する。低電流密度域では酸素還元反応の電荷移動が律速になり、一方、高電流密度域では、酸素供給が律速となって限界拡散電流密度に近づくにつれて急速に電圧が低下する（非特許文献１）。したがって、高出力な金属空気電池を得るためには活性の高い触媒を使用して酸素還元反応の電荷移動を円滑に進行させるだけでなく酸素がスムーズに拡散して大きな電流が得られるような構造が必要である。 A gas diffusion electrode is usually used as an air electrode of a metal-air battery. A gas diffusion electrode is an electrode that can directly cause an electrochemical redox reaction of a gaseous reactant. At the air electrode, oxygen in the air is used as an active material, and the reduction reaction proceeds. In the low current density region, the charge transfer of the oxygen reduction reaction is rate-determining, while in the high current density region, the oxygen supply is rate-limiting and the voltage drops rapidly as it approaches the critical diffusion current density (Non-Patent Document 1). . Therefore, in order to obtain a high output metal-air battery, a structure is used that not only facilitates the charge transfer of the oxygen reduction reaction using a highly active catalyst, but also allows a large current to be obtained by the smooth diffusion of oxygen. is necessary.
金属空気電池の正極に使用されるガス拡散電極は、一般的に電解液側から順に触媒層、ガス拡散層、集電体から構成される。触媒層は、例えば、触媒、親水性カーボン等の導電性を持つ触媒担体およびＰＴＦＥ等の結着材を含む。ガス拡散層は、例えば、疎水性カーボンおよびＰＴＦＥ等の結着材を含む。ガス拡散層は、スムーズなガス拡散パスを形成し、かつ電解液の漏出および空気側からの水分の混入を防ぐ（非特許文献２）。アセチレンガスから製造したカーボンブラック（アセチレンブラック）は、高ストラクチャーであるため粒子間空隙が発達してガスの拡散パスを有効に形成し、また、表面官能基が少なく疎水性が高いためガス拡散層に好適である。集電体は、酸素の拡散を妨げないようにＮｉメッシュ（非特許文献３）やカーボン繊維織布（特許文献１）が通常使用される。しかし、これらは金属線あるいは炭素繊維を編み込んだものであるため、その線同士あるいは繊維同士は固定されていないため電気的な接触が不安定であり、また、しなやかすぎるため接合しているガス拡散層との形状を保持できず、剥離してしまう虞がある。 A gas diffusion electrode used for a positive electrode of a metal-air battery generally includes a catalyst layer, a gas diffusion layer, and a current collector in order from the electrolyte side. The catalyst layer includes, for example, a catalyst, a conductive catalyst carrier such as hydrophilic carbon, and a binder such as PTFE. The gas diffusion layer includes, for example, a binder such as hydrophobic carbon and PTFE. The gas diffusion layer forms a smooth gas diffusion path and prevents leakage of the electrolytic solution and entry of moisture from the air side (Non-Patent Document 2). Carbon black (acetylene black) produced from acetylene gas has a high structure, so that intergranular voids develop to effectively form a gas diffusion path. In addition, the gas diffusion layer has a small surface functional group and high hydrophobicity. It is suitable for. As the current collector, a Ni mesh (Non-Patent Document 3) or a carbon fiber woven fabric (Patent Document 1) is usually used so as not to hinder the diffusion of oxygen. However, since these are braided metal wires or carbon fibers, the wires or fibers are not fixed, so the electrical contact is unstable. There is a possibility that the shape of the layer cannot be maintained and the layer is peeled off.
特許文献２では、ガス拡散電極としてＮｉ多孔体を使用し、この多孔体は、気孔率が５５〜８５％であることが好ましく、また孔径が２００μｍ以上５５０μｍ以下であることが好ましいとされている。このガス拡散電極は、プロトン伝導型固体高分子（Ｎａｆｉｏｎ等）を電解質として使用した固体高分子型燃料電池用であり、このＮｉ多孔体は孔径が大きくかつ撥水性を有さないため、金属空気電池用ガス拡散層に必要な電解液の漏出および空気側からの水分の混入を防ぐ機能を有さず、使用に適さない。 Patent Document 2 discloses that a Ni porous body is used as a gas diffusion electrode, and the porous body preferably has a porosity of 55 to 85% and a pore diameter of 200 μm or more and 550 μm or less. . This gas diffusion electrode is used for a polymer electrolyte fuel cell using a proton conductive solid polymer (such as Nafion) as an electrolyte. Since this Ni porous body has a large pore size and does not have water repellency, it is difficult to use metal air. It has no function to prevent leakage of electrolyte required for the gas diffusion layer for a battery and entry of moisture from the air side, and is not suitable for use.
特許文献３では非導電性不織布の片面側に特定の第１の導電層、前記片面とは反対の面側に特定の第２の導電層を形成することで、第２の導電層（導電性多孔質基材）を構成する導電性炭素材料として導電性炭素繊維を用いた場合にも、第２の導電層を構成する導電性炭素繊維が第１の導電層内に突き出すのを抑制することで、導電層をクラックの少ない膜とした燃料電池や金属空気電池等の電池が得られる導電性多孔質層を提供できることを見出しているが、二つの導電層を活物質である空気が拡散する必要があるため、ガス拡散距離が長くなってガス拡散性が低下して出力が小さくなる。 In Patent Literature 3, a specific first conductive layer is formed on one side of a non-conductive nonwoven fabric, and a specific second conductive layer is formed on a side opposite to the one side, thereby forming a second conductive layer (conductive type). Even when conductive carbon fibers are used as the conductive carbon material forming the porous substrate, the conductive carbon fibers forming the second conductive layer are prevented from protruding into the first conductive layer. Have found that it is possible to provide a conductive porous layer that can provide a battery such as a fuel cell or a metal-air battery in which the conductive layer has a film with less cracks. However, air as an active material diffuses between the two conductive layers. Because of the necessity, the gas diffusion distance becomes longer, the gas diffusivity decreases, and the output decreases.
以上のように、従来の金属メッシュやカーボン繊維織布を集電体として用いたガス拡散電極は、ガス拡散層と集電体との接触が不安定であり、容易に剥離する問題や、ガス拡散距離が長くなってガス拡散性が低下する問題があった。 As described above, the gas diffusion electrode using the conventional metal mesh or carbon fiber woven fabric as the current collector has a problem in that the contact between the gas diffusion layer and the current collector is unstable, and the gas is easily peeled off. There has been a problem that the diffusion distance becomes long and the gas diffusivity decreases.
本発明は、以上の事情に鑑みてなされたものであり、優れたガス拡散性を有し、かつ、剛性が高く電気的な接触が安定した金属空気電池または燃料電池のガス拡散電極に使用されるガス拡散層とそれを用いたガス拡散電極およびその製造方法を提供することを課題としている。 The present invention has been made in view of the above circumstances, and has excellent gas diffusion properties, and is used for a gas diffusion electrode of a metal-air battery or a fuel cell having high rigidity and stable electrical contact. It is an object to provide a gas diffusion layer, a gas diffusion electrode using the same, and a method for manufacturing the same.
本発明者らは、前記課題を解決するために鋭意検討した結果、カーボン材料と樹脂結着材を含む懸濁液を発泡金属に塗布し、これを加圧することで発泡金属とカーボン材料と樹脂結着材とが隙間なく一層を形成し、そのように成形された複合層は、発泡金属とカーボン材料が複雑に絡み合うため電気的接触が安定することを見出し、本発明を完成するに至った。 The present inventors have conducted intensive studies to solve the above problems, and as a result, applied a suspension containing a carbon material and a resin binder to a foam metal, and pressed the suspension to form a foam metal, a carbon material, and a resin. The binder and the binder formed one layer without any gaps, and the composite layer formed in such a manner was found to have stable electrical contact because the metal foam and the carbon material were intertwined in a complicated manner, and completed the present invention. .
すなわち本発明のガス拡散層は、金属空気電池または燃料電池のガス拡散電極に使用されるガス拡散層であって、発泡金属、カーボン材料、および樹脂結着材を含み、ガス拡散層における少なくとも一部に、カーボン材料および樹脂結着材が発泡金属に充填された複合層を有することを特徴としている。 That is, the gas diffusion layer of the present invention is a gas diffusion layer used for a gas diffusion electrode of a metal-air battery or a fuel cell, and includes a foamed metal, a carbon material, and a resin binder. The portion has a composite layer in which a carbon material and a resin binder are filled in a foam metal.
本発明のガス拡散電極は、前記ガス拡散層を有する。 The gas diffusion electrode of the present invention has the gas diffusion layer.
本発明の金属空気電池は、前記ガス拡散層を正極に有する。 The metal-air battery of the present invention has the gas diffusion layer on the positive electrode.
本発明の燃料電池は、前記ガス拡散層を正極に有する。 The fuel cell of the present invention has the gas diffusion layer on the positive electrode.
本発明のガス拡散電極の製造方法は、金属空気電池または燃料電池に使用されるガス拡散電極の製造方法であって、以下の工程（Ａ１）および（Ａ２）を含む：
（Ａ１）カーボン材料および樹脂結着材を分散させた懸濁液（ａ）を発泡金属に塗布し、厚み方向に加圧する第１工程；および
（Ａ２）工程（Ａ１）の後、樹脂結着材が軟化または流動する温度で厚み方向に加熱加圧する工程。
The method for manufacturing a gas diffusion electrode of the present invention is a method for manufacturing a gas diffusion electrode used for a metal-air battery or a fuel cell, and includes the following steps (A1) and (A2):
(A1) a first step in which a suspension (a) in which a carbon material and a resin binder are dispersed is applied to foam metal and pressed in the thickness direction; and (A2) a resin binder after the step (A1) A step of heating and pressing in the thickness direction at a temperature at which the material softens or flows.
前記方法における好ましい態様では、以下の工程（Ｂ）をさらに含む：
（Ｂ）工程（Ａ１）の後、懸濁液（ａ）を塗布した面に、さらにカーボン材料、樹脂結着材、および触媒を含む懸濁液（ｂ）を塗布し、厚み方向に加圧する工程。
A preferred embodiment of the above method further comprises the following step (B):
(B) After the step (A1), a suspension (b) containing a carbon material, a resin binder, and a catalyst is further applied to the surface to which the suspension (a) has been applied, and pressed in the thickness direction. Process.
前記方法における好ましい態様では、工程（Ａ２）において、工程（Ａ１）と（Ｂ）の後、懸濁液（ａ）および（ｂ）の各樹脂結着材が軟化または流動する温度で厚み方向に加熱加圧する。 In a preferred embodiment of the above method, in the step (A2), after the steps (A1) and (B), at a temperature at which the respective resin binders of the suspensions (a) and (b) soften or flow, the thickness direction is increased. Heat and press.
本発明によれば、優れたガス拡散性を有し、かつ、剛性が高く電気的な接触が安定した金属空気電池または燃料電池のガス拡散電極に使用されるガス拡散層とそれを用いたガス拡散電極およびその製造方法が提供される。そのような優れたガス拡散層によって、従来よりも支持体や補強材を簡素化でき、安価で、かつ出力が安定した金属空気電池や燃料電池の製造に資するものと期待される。 Advantageous Effects of Invention According to the present invention, a gas diffusion layer used for a gas diffusion electrode of a metal-air battery or a fuel cell having excellent gas diffusibility, and having high rigidity and stable electrical contact, and a gas using the same A diffusion electrode and a method for manufacturing the same are provided. Such an excellent gas diffusion layer is expected to contribute to the production of a metal-air battery or a fuel cell, which can simplify a support and a reinforcing material, is inexpensive, and has a stable output than before.
以下、本発明を詳細に説明する。
（ガス拡散層）
本発明のガス拡散層に使用される発泡金属は、ガス拡散電極の集電体として機能する。本発明のガス拡散層は、集電体となる発泡金属の空孔にカーボン材料が隙間なく充填され、カーボン材料が絡んだ構造となっているため電気的な接触が安定し、安定した電池出力が得られる。
Hereinafter, the present invention will be described in detail.
(Gas diffusion layer)
The foam metal used in the gas diffusion layer of the present invention functions as a current collector of the gas diffusion electrode. The gas diffusion layer of the present invention has a structure in which the carbon material is filled without gaps in the pores of the foamed metal serving as the current collector, and has a structure in which the carbon material is entangled. Is obtained.
発泡金属は、ガスによる小さな空間を多量に有する金属のセル状の構造物であり、気孔を大量に有している特徴を持ち、例えば、その７５〜９５％が空洞である。 The foamed metal is a metal cellular structure having a large amount of small space by gas, and has a feature of having a large amount of pores. For example, 75 to 95% of the cells are hollow.
発泡金属の材料としては、例えば、ニッケル、チタン、アルミニウムおよびそれらの合金等が挙げられる。これらの中でも、集電体としての機能面や価格等の観点を考慮すると、ニッケルを材料とする発泡ニッケルが好ましい。 Examples of the material of the foam metal include nickel, titanium, aluminum, and alloys thereof. Among these, foamed nickel made of nickel is preferable in view of the function as a current collector, the price, and the like.
アセチレンブラックのアグロメレートのような疎水性カーボン等のカーボン材料の径を考慮すると、これを充填する発泡金属の平均孔径はこれよりも十分に大きいことが必要であり、一方で孔径が大き過ぎると充填したカーボン材料と発泡金属との接着点が少なくなって導電パスが減少し、電極の剛性も低下する。このような点から、発泡金属の平均孔径は、２００μｍ以上５ｍｍ以下が好ましい。ここで平均孔径は、顕微鏡像から任意に選択した空孔１００個の平均値であり、各空孔の径は、最長径として求める。例えば発泡金属のうち、発泡ニッケルは、三角柱状の骨格が３次元に連なった、連続気孔を持つ金属多孔体である。 Considering the diameter of a carbon material such as hydrophobic carbon such as agglomerate of acetylene black, the average pore size of the foam metal to be filled with the material needs to be sufficiently larger than this. The number of bonding points between the carbon material and the foamed metal decreases, the number of conductive paths decreases, and the rigidity of the electrode also decreases. From such a point, the average pore diameter of the foamed metal is preferably 200 μm or more and 5 mm or less. Here, the average pore diameter is an average value of 100 pores arbitrarily selected from a microscope image, and the diameter of each pore is determined as the longest diameter. For example, among foamed metals, foamed nickel is a porous metal body having continuous pores in which triangular prism-shaped skeletons are three-dimensionally connected.
発泡金属のうち、発泡ニッケルの市販品としては、例えば、住友電気工業製「セルメット」、長峰製作所製「金属多孔質体」等が使用できる。発泡ニッケルの比表面積は２５０〜５８００ｍ２／ｍ３が好ましい。 Among the foamed metals, as commercially available products of foamed nickel, for example, "Celmet" manufactured by Sumitomo Electric Industries, "porous metal" manufactured by Nagamine Seisakusho, and the like can be used. The specific surface area of the foamed nickel is preferably from 250 to 5800 m 2 / m 3 .
本発明のガス拡散層に使用されるカーボン材料は、細孔形成によって導電パスを形成し、かつ電極内部への水の浸透を抑制する疎水性を付与する。 The carbon material used for the gas diffusion layer of the present invention forms a conductive path by forming pores, and imparts hydrophobicity that suppresses penetration of water into the inside of the electrode.
カーボン材料としては、疎水性カーボンが好ましい。疎水性カーボンは、表面に酸素官能基等を多数有する親水性カーボンとは異なり疎水性を有するものであり、例えば、カーボンブラック、カーボンナノチューブ、グラフェン等が挙げられる。その中でも、多孔質であり、電気抵抗が低く、安価である点から、カーボンブラックが好ましい。疎水性カーボンであるカーボンブラックの例としては、アセチレンブラック、ファーネスブラック等が挙げられる。 As the carbon material, hydrophobic carbon is preferable. Hydrophobic carbon has hydrophobicity unlike hydrophilic carbon having a large number of oxygen functional groups and the like on its surface, and examples thereof include carbon black, carbon nanotube, and graphene. Among them, carbon black is preferred because it is porous, has low electric resistance and is inexpensive. Examples of carbon black that is a hydrophobic carbon include acetylene black and furnace black.
カーボン材料の平均粒径は、２０ｎｍ以上５０ｎｍ以下が好ましい。このような平均粒径を持つカーボン材料は、前記したような発泡金属の空孔に充填した際に、緻密な導電パスを形成し、集電体となる発泡金属とカーボン材料が絡んだ構造となるため電気的な接触が安定し、安定した電池出力が得られる。ここで平均粒径は、走査透過電子顕微鏡による観察像において、任意の１００個の粒子を選択し、それぞれの外径を計測し、その数平均値として算出したものである。カーボンブラックは一般に、ストラクチャーを持つアグリゲート（１次凝集体）が、ファン・デルワールス力等の物理的な力によりアグロメレート（２次凝集体）を構成するが、カーボン材料がカーボンブラックである場合、平均粒径はアグリゲートの１次粒子の平均粒径である。 The average particle size of the carbon material is preferably from 20 nm to 50 nm. The carbon material having such an average particle size forms a dense conductive path when filled in the above-described pores of the foamed metal, and has a structure in which the foamed metal serving as a current collector and the carbon material are entangled. Therefore, the electrical contact is stable, and a stable battery output can be obtained. Here, the average particle diameter is obtained by selecting an arbitrary 100 particles in an image observed by a scanning transmission electron microscope, measuring the outer diameter of each particle, and calculating the number average value. In general, aggregates (primary aggregates) having a structure form agglomerates (secondary aggregates) by physical force such as van der Waals force. When the carbon material is carbon black, The average particle size is the average particle size of the primary particles of the aggregate.
本発明のガス拡散層に使用される樹脂結着材は、カーボン材料を結着させるバインダー機能と、ガス拡散層に撥水性を付与する機能を有する。 The resin binder used for the gas diffusion layer of the present invention has a binder function of binding a carbon material and a function of imparting water repellency to the gas diffusion layer.
樹脂結着材としては、撥水性を有する樹脂、例えばフッ素樹脂が挙げられる。その中でも、フッ素樹脂が好ましい。フッ素樹脂としては、例えば、ポリテトラフルオロエチレン（ＰＴＦＥ）、パーフルオロスルフォン酸ポリマー、ポリフッ化ビニリデン（ＰＶｄＦ）、テトラフルオロエチレン共重合体（ＦＥＰ）、（ＰＦＥ）等が挙げられる。その中でも、ポリテトラフルオロエチレン、パーフルオロスルフォン酸ポリマーが好ましい。 Examples of the resin binder include a resin having water repellency, for example, a fluororesin. Among them, a fluororesin is preferable. Examples of the fluorine resin include polytetrafluoroethylene (PTFE), perfluorosulfonic acid polymer, polyvinylidene fluoride (PVdF), tetrafluoroethylene copolymer (FEP), and (PFE). Among them, polytetrafluoroethylene and perfluorosulfonic acid polymer are preferable.
ガス拡散層に使用するカーボン材料と樹脂結着材の質量比は、樹脂結着材がバインダー機能、撥水付与機能を発揮する観点を考慮すると、３０：７０〜９５：５が好ましく、６０：４０〜９０：１０がより好ましい。 The mass ratio of the carbon material to the resin binder used in the gas diffusion layer is preferably 30:70 to 95: 5, and more preferably 60:60, in view of the fact that the resin binder exerts a binder function and a water-repellent function. 40-90: 10 is more preferable.
ガス拡散層の製造において添加する樹脂結着材の形態は、特に限定されないが、カーボン材料と混合されて分散する微粒子状が好ましく、カーボン材料と樹脂結着材を溶媒に分散した懸濁液をガス拡散層の製造に用いることができる。この場合、予めカーボン材料と樹脂結着材を水系溶媒に分散後、乾燥して溶媒を除去する等の方法によって、樹脂結着材を担持したカーボン材料を作製しておき、この樹脂結着材を担持したカーボン材料を有機溶媒に分散することによって懸濁液を調製してもよい。 The form of the resin binder added in the production of the gas diffusion layer is not particularly limited, but is preferably in the form of fine particles that are mixed and dispersed with a carbon material, and a suspension in which the carbon material and the resin binder are dispersed in a solvent is used. It can be used for manufacturing a gas diffusion layer. In this case, a carbon material supporting the resin binder is prepared in advance by a method such as dispersing the carbon material and the resin binder in an aqueous solvent, and then drying and removing the solvent. A suspension may be prepared by dispersing a carbon material carrying the compound in an organic solvent.
本発明のガス拡散層は、発泡金属、カーボン材料、および樹脂結着材を含み、ガス拡散層における少なくとも一部に、カーボン材料および樹脂結着材が発泡金属に充填された複合層を有する。 The gas diffusion layer of the present invention includes a foam metal, a carbon material, and a resin binder, and at least a part of the gas diffusion layer has a composite layer in which the carbon material and the resin binder are filled in the foam metal.
製造工程に応じて、ある態様では、本発明のガス拡散層は、発泡金属からなる層と、当該層から厚み方向に連続する複合層とを有する。この場合、カーボン材料および樹脂結着材が、製造工程における加圧によって発泡金属の空孔に一部充填されて、発泡金属の厚み方向のうち一部が複合層となる。別の態様では、厚み方向の全体が複合層である。この場合、カーボン材料および樹脂結着材が、製造工程における加圧によって発泡金属の空孔にほぼ全てが充填され、残りの発泡金属の空孔は押し潰されて、発泡金属のみからなる部分は殆ど確認できず、発泡金属の厚み方向の全体が複合層となる。従って厚み方向の全体が複合層であるとは、走査型電子顕微鏡の観察において、発泡金属の空孔に、カーボン材料および樹脂結着材が厚み方向の全体に分布し、特に炭素の元素マップにおいて、カーボン材料に由来する炭素が厚み方向の全体に確認されることを含む。例えば、ニッケル等の発泡金属の元素マップにおいて金属が分布する厚みのうち、８０％以上、９０％以上、あるいは９５％以上の範囲に、炭素の元素マップにおいて炭素が存在すること、およびカーボン材料の全てが発泡金属内に充填されることを含む。以上の態様の中でも、安定した電池出力が得られる点を考慮すると、後者のように発泡金属の厚み方向の全体が複合層となる態様が好ましい。 Depending on the manufacturing process, in one embodiment, the gas diffusion layer of the present invention has a layer made of a foamed metal and a composite layer continuous from the layer in the thickness direction. In this case, the carbon material and the resin binder are partially filled in the pores of the foam metal by pressurization in the manufacturing process, and a part of the foam metal in the thickness direction becomes a composite layer. In another aspect, the entirety in the thickness direction is a composite layer. In this case, the carbon material and the resin binder are almost completely filled into the pores of the foamed metal by the pressurization in the manufacturing process, the pores of the remaining foamed metal are crushed, and the portion composed of only the foamed metal is formed. Almost no confirmation was made, and the entire thickness of the foam metal in the thickness direction was a composite layer. Therefore, that the entire layer in the thickness direction is a composite layer means that, in the observation with a scanning electron microscope, the carbon material and the resin binder are distributed in the entire hole in the pores of the foamed metal in the thickness direction. And that carbon derived from the carbon material is confirmed in the entire thickness direction. For example, in the elemental map of a foamed metal such as nickel, the presence of carbon in the carbon element map in the range of 80% or more, 90% or more, or 95% or more of the thickness of the metal distribution, All including filling in the foam metal. Among the above embodiments, in consideration of the fact that a stable battery output is obtained, an embodiment in which the entire foam metal in the thickness direction is a composite layer as described above is preferable.
本発明のガス拡散層の厚みは、０．５ｍｍ以上１．５ｍｍ以下が好ましく、０．７ｍｍ以上１．３ｍｍ以下がより好ましい。発泡金属からなる層が存在する場合には当該層と、複合層との合計厚みはガス拡散の最短距離となるため、電解液の漏出および空気側からの水分の混入を抑制する限りにおいて、ガス拡散層は薄いほど空気中の酸素の拡散に有利であるが、ガス拡散層の厚みが上記範囲内であると、電解液の漏出および空気側からの水分の混入を抑制しつつガスが拡散し、金属空気電池や燃料電池の正極として好適である。このようにガス拡散層の厚みを小さくしても、本発明のガス拡散層は、集電体となる発泡金属の空孔にカーボン材料が隙間なく充填された構造であるため、剛性が高く、電気的な接触が安定し、安定した電池出力が得られる。 The thickness of the gas diffusion layer of the present invention is preferably 0.5 mm or more and 1.5 mm or less, more preferably 0.7 mm or more and 1.3 mm or less. When a layer made of a foamed metal is present, the total thickness of the layer and the composite layer is the shortest distance of gas diffusion, so that gas leakage is limited as long as leakage of electrolyte and mixing of moisture from the air side are suppressed. The thinner the diffusion layer, the better the diffusion of oxygen in the air.However, when the thickness of the gas diffusion layer is within the above range, the gas diffuses while suppressing leakage of the electrolyte and mixing of moisture from the air side. It is suitable as a positive electrode of a metal air battery or a fuel cell. Even if the thickness of the gas diffusion layer is reduced in this way, the gas diffusion layer of the present invention has a structure in which the carbon material is filled with voids of the foamed metal serving as the current collector without gaps, and thus has high rigidity. Electrical contact is stable, and a stable battery output is obtained.
（ガス拡散電極とその製造方法）
本発明のガス拡散電極は、以上に説明した本発明のガス拡散層を有している。さらに、このガス拡散層に隣接する触媒層を備えている。本発明のガス拡散電極は、本発明のガス拡散層の高い剛性によって、従来のガス拡散電極に使用される電極支持体を省略することが可能である。
(Gas diffusion electrode and its manufacturing method)
The gas diffusion electrode of the present invention has the gas diffusion layer of the present invention described above. Further, a catalyst layer adjacent to the gas diffusion layer is provided. In the gas diffusion electrode of the present invention, the electrode support used for the conventional gas diffusion electrode can be omitted due to the high rigidity of the gas diffusion layer of the present invention.
本発明のガス拡散電極における触媒層の構成は、特に限定されないが、例えば、触媒、担体、および樹脂結着材を含む。 The configuration of the catalyst layer in the gas diffusion electrode of the present invention is not particularly limited, but includes, for example, a catalyst, a carrier, and a resin binder.
触媒は、放電時には酸素還元反応、充電時には酸素酸化反応を促進させるものであれば特に限定されないが、例えば、白金等の貴金属触媒、金属酸化物触媒、カーボン触媒等が挙げられる。担体が親水性カーボン等である場合、担体自体が触媒機能を有するものであってもよい。 The catalyst is not particularly limited as long as it promotes an oxygen reduction reaction at the time of discharging and an oxygen oxidation reaction at the time of charging, and examples thereof include noble metal catalysts such as platinum, metal oxide catalysts, and carbon catalysts. When the carrier is a hydrophilic carbon or the like, the carrier itself may have a catalytic function.
担体としては、例えば、導電性のカーボン材料を用いることができる。導電性のカーボン材料としては、親水性カーボンが好ましい。親水性カーボンは、表面に酸素官能基等の親水性官能基を多数有するものであり、例えば、親水性カーボンブラック、表面を官能基で修飾したカーボンブラック、カーボンナノチューブ、グラフェン等が挙げられる。その中でも、多孔質であり、電気抵抗が低く、安価である点から、親水性カーボンブラックが好ましい。親水性カーボンブラックの例としては、ケッチェンブラック、Ｖｕｌｃａｎ等が挙げられる。 As the carrier, for example, a conductive carbon material can be used. As the conductive carbon material, hydrophilic carbon is preferable. The hydrophilic carbon has many hydrophilic functional groups such as oxygen functional groups on the surface, and examples thereof include hydrophilic carbon black, carbon black having a surface modified with a functional group, carbon nanotube, and graphene. Among them, hydrophilic carbon black is preferred because it is porous, has low electric resistance, and is inexpensive. Examples of hydrophilic carbon black include Ketjen Black, Vulcan and the like.
樹脂結着材としては、例えばフッ素樹脂等が挙げられる。フッ素樹脂としては、例えば、ガス拡散層に使用される樹脂結着材として前記に例示したものが挙げられる。 As the resin binder, for example, a fluorine resin or the like can be given. Examples of the fluororesin include those exemplified above as the resin binder used for the gas diffusion layer.
本発明のガス拡散電極を製造する方法は、好ましい態様において、本発明のガス拡散層を構成するカーボン材料および樹脂結着材を分散させた懸濁液（ａ）を発泡金属に塗布し、厚み方向に加圧する工程を含む。 In a preferred embodiment of the method for producing a gas diffusion electrode of the present invention, a suspension (a) in which a carbon material and a resin binder constituting a gas diffusion layer of the present invention are dispersed is applied to a foamed metal, Direction.
懸濁液（ａ）は、カーボン材料および樹脂結着材を含むものであれば特に限定されないが、予め、湿式分散によって微粒子状の樹脂結着材をカーボン材料に担持し、この樹脂結着材を担持したカーボン材料を、溶媒に分散して調製することが好ましい。この場合、樹脂結着材の粒径としては０．１〜０．５μｍが好ましい。溶媒としては、水や有機溶媒が好ましく、例えば、イソプロピルアルコール、エタノール、アセトン、n-ブタノール等のアルコール系溶媒、ベンゼン、ヘキサン等が挙げられる。 The suspension (a) is not particularly limited as long as it contains a carbon material and a resin binder. The resin binder is prepared by previously supporting a particulate resin binder on the carbon material by wet dispersion. Is preferably prepared by dispersing in a solvent a carbon material carrying the compound. In this case, the particle size of the resin binder is preferably 0.1 to 0.5 μm. As the solvent, water or an organic solvent is preferable, and examples thereof include alcohol solvents such as isopropyl alcohol, ethanol, acetone, and n-butanol, benzene, and hexane.
懸濁液（ａ）を発泡金属に塗布する方法としては、特に限定されないが、例えば、スプレー塗布、スクリーン印刷、バーコーター、スピンコーター、ブレードを用いた方法等が挙げられる。 The method for applying the suspension (a) to the foamed metal is not particularly limited, and examples thereof include spray coating, screen printing, a method using a bar coater, a spin coater, and a blade.
懸濁液（ａ）を発泡金属に塗布し、厚み方向に加圧する工程は、樹脂結着材が軟化または流動する温度で厚み方向に加熱加圧する工程、つまり樹脂結着材による結着を促進させるホットプレス工程であってもよいが、カーボン材料および樹脂結着材を発泡金属の空孔により多く充填させて複合層の厚みを大きくし、ガス拡散層の厚みをより小さくするためには、懸濁液（ａ）を発泡金属に塗布後、厚み方向に加圧した後（以下、懸濁液充填プレス工程とも言う。）、ホットプレス工程を行うことが好ましい。 The step of applying the suspension (a) to the foamed metal and pressing in the thickness direction is a step of heating and pressing in the thickness direction at a temperature at which the resin binder softens or flows, that is, promotes binding by the resin binder. Although it may be a hot pressing step, to increase the thickness of the composite layer by filling the carbon material and the resin binder into the pores of the foam metal more, to reduce the thickness of the gas diffusion layer, After applying the suspension (a) to the foamed metal and pressing it in the thickness direction (hereinafter also referred to as a suspension filling press step), it is preferable to perform a hot press step.
ホットプレス工程および懸濁液充填プレス工程に使用される装置は、加圧成形が可能な装置であれば特に限定されないが、例えば、油圧プレス機を用いることができる。油圧プレス機の一軸加圧成形によって電極の剛性が高まるため、大型電極の作製に好適であり、手動式の油圧プレスで作製可能であるため特殊な生産設備を必要とせず、シンプルな製造プロセスで大量生産に適している。 The apparatus used in the hot press step and the suspension filling press step is not particularly limited as long as it can perform pressure molding. For example, a hydraulic press machine can be used. The uniaxial pressing of a hydraulic press increases the rigidity of the electrode, making it suitable for the production of large electrodes.Since it can be produced by a manual hydraulic press, it does not require special production equipment and can be used in a simple manufacturing process. Suitable for mass production.
ガス拡散層と触媒層を形成するために、触媒層の成分を含む懸濁液（ｂ）を調製し、懸濁液（ａ）を塗布した面に、さらに懸濁液（ｂ）を塗布し、厚み方向に加圧してもよい。 In order to form a gas diffusion layer and a catalyst layer, a suspension (b) containing the components of the catalyst layer is prepared, and the suspension (b) is further applied to the surface on which the suspension (a) is applied. Alternatively, pressure may be applied in the thickness direction.
懸濁液（ｂ）は、例えば、カーボン材料、樹脂結着材、および触媒を含む。 The suspension (b) contains, for example, a carbon material, a resin binder, and a catalyst.
懸濁液（ａ）の発泡金属への塗布、懸濁液（ａ）を塗布した面への懸濁液（ｂ）の塗布と、ホットプレス工程、懸濁液充填プレス工程においては、これらの手順の前後は任意であり、加圧はホットプレス工程のみで行ってもよく、懸濁液充填プレス工程を含めて行ってもよい。例えば、懸濁液（ａ）の発泡金属への塗布、懸濁液（ａ）を塗布した面への懸濁液（ｂ）の塗布を行った後、ホットプレス工程で加圧する態様や、懸濁液（ａ）の発泡金属への塗布を行った後、懸濁液充填プレス工程を行い、その後懸濁液（ａ）を塗布した面への懸濁液（ｂ）の塗布、懸濁液充填プレス工程を行い、さらにホットプレス工程を行う態様等であってよいが、好ましい態様では、以下の工程（Ａ１）および（Ａ２）を含む：
（Ａ１）カーボン材料および樹脂結着材を分散させた懸濁液（ａ）を発泡金属に塗布し、厚み方向に加圧する工程（懸濁液充填プレス工程）；および
（Ａ２）工程（Ａ１）の後、樹脂結着材が軟化または流動する温度で厚み方向に加熱加圧する工程（ホットプレス工程）。
In the application of the suspension (a) to the foamed metal, the application of the suspension (b) to the surface on which the suspension (a) is applied, and the hot press step and the suspension filling press step, The order before and after the procedure is arbitrary, and the pressurization may be performed only in the hot press step or may be performed including the suspension filling press step. For example, after the suspension (a) is applied to the foam metal and the suspension (b) is applied to the surface to which the suspension (a) has been applied, the suspension is pressed in a hot press step, After the suspension (a) is applied to the foam metal, a suspension filling press step is performed, and then the suspension (b) is applied to the surface on which the suspension (a) is applied, and the suspension is applied. An embodiment in which a filling press step is performed and further a hot press step is performed may be performed, but a preferred embodiment includes the following steps (A1) and (A2):
(A1) A step of applying a suspension (a) in which a carbon material and a resin binder are dispersed to a foam metal and pressing in the thickness direction (suspension filling press step); and (A2) step (A1) Thereafter, a step of heating and pressing in the thickness direction at a temperature at which the resin binder softens or flows (hot pressing step).
さらに好ましい態様では、以下の工程（Ｂ）をさらに含む：
（Ｂ）工程（Ａ）の後、懸濁液（ａ）を塗布した面に、さらにカーボン材料、樹脂結着材、および触媒を含む懸濁液（ｂ）を塗布し、厚み方向に加圧する工程。
In a further preferred embodiment, the method further comprises the following step (B):
(B) After the step (A), a suspension (b) containing a carbon material, a resin binder, and a catalyst is further applied to the surface to which the suspension (a) has been applied, and pressed in the thickness direction. Process.
特に好ましい態様では、工程（Ａ２）において、工程（Ａ１）と（Ｂ）の後、懸濁液（ａ）および（ｂ）の各樹脂結着材が軟化または流動する温度で厚み方向に加熱加圧する。 In a particularly preferred embodiment, in the step (A2), after the steps (A1) and (B), the resin binders in the suspensions (a) and (b) are heated in the thickness direction at a temperature at which the resin binder softens or flows. Press.
懸濁液充填プレス工程における荷重は、特に限定されないが、工程（Ａ１）では１００〜５００ｋｇｆｃｍ−２が好ましく、３００〜４５０ｋｇｆｃｍ−２がより好ましい。工程（Ｂ）では１０〜５０ｋｇｆｃｍ−２が好ましく、３０〜４５ｋｇｆｃｍ−２がより好ましい。懸濁液充填プレス工程によって、カーボン材料同士が樹脂結着材によって結着されない状態で、カーボン材料および樹脂結着材を発泡金属の空孔により多く充填させて複合層の厚みを大きくし、ガス拡散層の厚みをより小さくすることができる。その結果として、電解液の漏出および空気側からの水分の混入を抑制しつつガスが拡散し、金属空気電池や燃料電池の正極として好適であると共に、ガス拡散層の厚みを小さくしても、集電体となる発泡金属の空孔にカーボン材料が隙間なく充填された構造であるため、剛性が高く、電気的な接触が安定し、安定した電池出力が得られる。 The load in the suspension filling press step is not particularly limited, but is preferably 100 to 500 kgfcm- 2 , and more preferably 300 to 450 kgfcm- 2 in the step (A1). In the step (B), 10 to 50 kgfcm- 2 is preferable, and 30 to 45 kgfcm- 2 is more preferable. In the suspension filling press step, in a state where the carbon materials are not bound by the resin binder, the carbon material and the resin binder are filled more in the pores of the foamed metal to increase the thickness of the composite layer, and the gas The thickness of the diffusion layer can be made smaller. As a result, the gas is diffused while suppressing leakage of the electrolyte and mixing of moisture from the air side, which is suitable as a positive electrode of a metal-air battery or a fuel cell, and even if the thickness of the gas diffusion layer is reduced, Since the carbon material has a structure in which the pores of the foamed metal serving as the current collector are filled without gaps, the rigidity is high, the electrical contact is stable, and a stable battery output is obtained.
以上において、加圧をホットプレス工程のみで行う場合や、懸濁液充填プレス工程を含めて行う場合に関わらず、ホットプレス工程を行う際における荷重は、特に限定されないが、５０〜３００ｋｇｆｃｍ−２が好ましく、１００〜２００ｋｇｆｃｍ−２がより好ましい。ホットプレス工程における温度は、特に限定されないが、ＰＴＦＥ等のフッ素樹脂の場合、その溶融温度以上で分解等が生じない範囲、例えば３３０〜３８０℃が好ましい。 In the above, regardless of the case where the pressurization is performed only by the hot press step or the case where the pressurization is performed including the suspension filling press step, the load at the time of performing the hot press step is not particularly limited, but is 50 to 300 kgfcm −2. Is preferable, and 100 to 200 kgfcm- 2 is more preferable. The temperature in the hot pressing step is not particularly limited, but in the case of a fluororesin such as PTFE, it is preferably in a range in which decomposition or the like does not occur at a melting temperature or higher, for example, 330 to 380 ° C.
ホットプレス工程や懸濁液充填プレス工程によって加圧を行った後、懸濁液（ａ）や（ｂ）の溶媒を除去するために、乾燥機等の加熱装置によって乾燥処理を行うことが好ましい。 After pressurizing by a hot press step or a suspension filling press step, it is preferable to perform a drying treatment by a heating device such as a drier in order to remove the solvent of the suspensions (a) and (b). .
（金属空気電池および燃料電池）
本発明のガス拡散電極は、金属空気電池および燃料電池に用いることができる。金属空気電池および燃料電池は、ガス拡散電極を正極に備えている。
(Metal air battery and fuel cell)
The gas diffusion electrode of the present invention can be used for a metal-air battery and a fuel cell. Metal-air batteries and fuel cells have a gas diffusion electrode on the positive electrode.
金属空気電池は、負極活物質として金属を用いるものであり、燃料電池は、負極活物質として水素などの金属以外の物質を用いるものである。 A metal-air battery uses a metal as a negative electrode active material, and a fuel cell uses a material other than a metal such as hydrogen as a negative electrode active material.
金属空気電池および燃料電池は、正極として空気極が設置され、電解質を介して、負極として金属空気電池では金属極、燃料電池では燃料極が設置される。 In a metal air battery and a fuel cell, an air electrode is provided as a positive electrode, and a metal electrode is provided as a negative electrode in a metal air battery and a fuel electrode is provided in a fuel cell as a negative electrode via an electrolyte.
電解質としては、水系の金属空気電池および燃料電池の場合、これらの電解液として通常用いられる水系電解液を用いることができる。 As the electrolyte, in the case of a water-based metal-air battery and a fuel cell, a water-based electrolyte commonly used as these electrolytes can be used.
金属空気電池における金属極としては、亜鉛、アルミニウム、マグネシウムなどの金属などを用いることができる。具体的な金属極の構造は、公知の金属空気電池と同様とすればよい。燃料電池における燃料極の構造についても特に限定はなく、公知の燃料電池の燃料極の構造と同様とすればよい。燃料極用の触媒としても、従来公知の金属、金属合金、金属錯体や、触媒微粒子を炭素材料や金属酸化物などの担体に担持した触媒などを用いることができる。 As the metal electrode in the metal-air battery, a metal such as zinc, aluminum, and magnesium can be used. The specific structure of the metal electrode may be the same as that of a known metal-air battery. The structure of the fuel electrode in the fuel cell is not particularly limited, and may be the same as that of a known fuel cell. As the catalyst for the fuel electrode, a conventionally known metal, metal alloy, metal complex, or a catalyst in which catalyst fine particles are supported on a carrier such as a carbon material or a metal oxide can be used.
正極である空気極側には、酸素または空気を供給あるいは自然拡散させればよい。また、燃料電池には、燃料極側に燃料となる物質を供給する必要がある。燃料物質としては、水素ガスの他、メタノールのようなアルコール類などが使用できる。 Oxygen or air may be supplied or spontaneously diffused to the air electrode side as the positive electrode. Further, it is necessary to supply a fuel cell with a substance serving as a fuel on the fuel electrode side. As the fuel substance, besides hydrogen gas, alcohols such as methanol can be used.
以下、実施例に基づき本発明をさらに詳しく説明するが、本発明はこれらの実施例に限定されるものではない。
［実施例１］
＜１＞ＰＴＦＥ担持疎水性カーボン、ＰＴＦＥ担持親水性カーボンの作製
ガス拡散層用の疎水性カーボンとして市販のアセチレンブラック（ＨＳ−１００、電気化学工業製）を蒸留水中に分散させ、６０質量％ＰＴＦＥディスパージョン（粒径：０．２２μｍ、Ｄ−２１０ｃ、ダイキン工業製）をアセチレンブラックに対して３０質量％となるように添加した。これを、超音波分散して、ＰＴＦＥディスパージョンをアセチレンブラックに均一に分散担持させ、混合液をろ過して１２０℃で乾燥してＰＴＦＥ担持疎水性カーボンを作製した。触媒層に用いる親水性カーボンとしては市販のカーボンブラック（ケッチェンブラック、ライオン製）を使用し、同様の方法でＰＴＦＥを担持した。なお、表面に酸素官能基を多数有するこの親水性カーボンは、触媒として酸素還元反応を促進する。
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.
[Example 1]
<1> Preparation of PTFE-supporting hydrophobic carbon and PTFE-supporting hydrophilic carbon Commercially available acetylene black (HS-100, manufactured by Denki Kagaku Kogyo) as a hydrophobic carbon for a gas diffusion layer was dispersed in distilled water, and 60% by mass PTFE was prepared. A dispersion (particle size: 0.22 μm, D-210c, manufactured by Daikin Industries, Ltd.) was added so as to be 30% by mass based on acetylene black. This was ultrasonically dispersed to uniformly disperse and support the PTFE dispersion in acetylene black, and the mixture was filtered and dried at 120 ° C. to produce PTFE-supported hydrophobic carbon. As the hydrophilic carbon used for the catalyst layer, commercially available carbon black (Ketjen Black, manufactured by Lion) was used, and PTFE was supported by the same method. This hydrophilic carbon having a large number of oxygen functional groups on the surface promotes an oxygen reduction reaction as a catalyst.
＜２＞ガス拡散電極の作製
２−プロパノールにＰＴＦＥ担持疎水性カーボンを分散させてカーボンインキを作製し、これを３．５×３．８ｃｍ２に切断した発泡ニッケル（厚み：１．６ｍｍ、セルメット＃７、住友電気工業製）に１ｃｍ２あたり１４ｍｇになるように塗布して乾燥させた。同様に２−プロパノール中に分散させたＰＴＦＥ担持親水性カーボンインキを、作製した発泡ニッケル−疎水性カーボンの疎水性カーボン上に１ｃｍ２あたり６ｍｇになるように塗布して乾燥させた後、これを電気炉で急加熱して３６０℃まで昇温させてＰＴＦＥを融解させ、油圧プレス機を用いて３８ｋｇｆｃｍ−２の荷重でプレスした後、急冷却した。最後に１２０℃に保持した乾燥機に移し、溶媒の２−プロパノールを完全に除去してガス拡散電極を得た。
<2> Preparation of Gas Diffusion Electrode A carbon ink was prepared by dispersing PTFE-supporting hydrophobic carbon in 2-propanol and cut into 3.5 × 3.8 cm 2 foamed nickel (thickness: 1.6 mm, Celmet) # 7, manufactured by Sumitomo Electric Industries, Ltd.) and dried at 14 mg / cm 2 . Similarly, a PTFE-supporting hydrophilic carbon ink dispersed in 2-propanol was applied onto the hydrophobic carbon of the produced foamed nickel-hydrophobic carbon in an amount of 6 mg / cm 2 and dried. The mixture was rapidly heated in an electric furnace to raise the temperature to 360 ° C. to melt the PTFE, pressed using a hydraulic press at a load of 38 kgfcm −2 , and then rapidly cooled. Finally, the mixture was transferred to a dryer maintained at 120 ° C., and 2-propanol as a solvent was completely removed to obtain a gas diffusion electrode.
＜３＞電池性能評価
上記のように作製したガス拡散電極（電極面積：１３．３ｃｍ２）を正極として、マグネシウム合金（Ｍｇ：９０％、Ａｌ：９％、Ｚｎ：１％、厚み：０．５ｃｍ、電極面積：３．８×５．８ｃｍ２）を負極としてセルに取り付け、電極間の距離を１ｃｍに固定し、２３質量％のＮａＣｌ水溶液に浸した状態で電子付加装置を正極、負極に接続して、電子負荷装置を用いて任意の定抵抗を接続し、電極間の電圧値と電流値を測定した。電子付加装置は菊水電子工業製ＰＬＺ６６４ＷＡを用いた。
<3> Battery Performance Evaluation Using the gas diffusion electrode (electrode area: 13.3 cm 2 ) prepared as described above as a positive electrode, a magnesium alloy (Mg: 90%, Al: 9%, Zn: 1%, thickness: 0.1%). 5 cm, electrode area: 3.8 × 5.8 cm 2 ) was attached to the cell as a negative electrode, the distance between the electrodes was fixed to 1 cm, and the electron adding device was immersed in a 23% by mass aqueous NaCl solution to form a positive electrode and a negative electrode. Then, an arbitrary constant resistance was connected using an electronic load device, and a voltage value and a current value between the electrodes were measured. The PLZ664WA manufactured by Kikusui Electronics Co., Ltd. was used as the electron addition device.
［実施例２］
実施例１と同様の方法によりＰＴＦＥ担持疎水性カーボン、ＰＴＦＥ担持親水性カーボンを作製した。実施例１と同サイズに切断した発泡ニッケルを金属やすりを用いて厚みが０．７ｍｍになるまで研磨した。２−プロパノールにＰＴＦＥ担持疎水性カーボンを分散させてカーボンインキを作製し、これを研磨した発泡ニッケルに１ｃｍ２あたり１４ｍｇになるように塗布して乾燥させた。同様に２−プロパノール中に分散させたＰＴＦＥ担持親水性カーボンインキを、作製した発泡ニッケル−疎水性カーボンの疎水性カーボン上に１ｃｍ２あたり６ｍｇになるように塗布して乾燥させた後、これを電気炉で急加熱して３６０℃まで昇温させてＰＴＦＥを融解させ、油圧プレス機を用いて３８ｋｇｆｃｍ−２の荷重でプレスした後、急冷却した。最後に１２０℃に保持した乾燥機に移し、溶媒の２−プロパノールを完全に除去してガス拡散電極を得た。電池性能評価は実施例１と同様の方法で行った。
[Example 2]
In the same manner as in Example 1, PTFE-supported hydrophobic carbon and PTFE-supported hydrophilic carbon were produced. Nickel foam cut to the same size as in Example 1 was polished with a metal file until the thickness became 0.7 mm. A carbon ink was prepared by dispersing PTFE-supporting hydrophobic carbon in 2-propanol, and this was applied to polished nickel foam at a concentration of 14 mg / cm 2 and dried. Similarly, a PTFE-supporting hydrophilic carbon ink dispersed in 2-propanol was applied onto the hydrophobic carbon of the produced foamed nickel-hydrophobic carbon in an amount of 6 mg / cm 2 and dried. The mixture was rapidly heated in an electric furnace to raise the temperature to 360 ° C. to melt the PTFE, pressed using a hydraulic press at a load of 38 kgfcm −2 , and then rapidly cooled. Finally, the mixture was transferred to a dryer maintained at 120 ° C., and 2-propanol as a solvent was completely removed to obtain a gas diffusion electrode. The battery performance evaluation was performed in the same manner as in Example 1.
［実施例３］
実施例１と同様の方法によりＰＴＦＥ担持疎水性カーボン、ＰＴＦＥ担持親水性カーボンを作製した。２−プロパノールにＰＴＦＥ担持疎水性カーボンを分散させてカーボンインキを作製し、これを実施例１と同じサイズに切断した発泡ニッケルに１ｃｍ２あたり１４ｍｇになるように塗布して乾燥させ、これを油圧プレス機を用いて３７６ｋｇｆｃｍ−２の荷重でプレスして発泡ニッケル／疎水性カーボン複合体を得た。同様に２−プロパノール中に分散させたＰＴＦＥ担持親水性カーボンインキを、作製した発泡ニッケル／疎水性カーボン複合体に１ｃｍ２あたり６ｍｇになるように塗布して乾燥させ、油圧プレス機を用いて１５０ｋｇｆｃｍ−２の荷重でプレスし、これを電気炉で急加熱して３６０℃まで昇温させてＰＴＦＥを融解させ、油圧プレス機を用いて３８ｋｇｆｃｍ−２の荷重でプレスした後、急冷却した。最後に１２０℃に保持した乾燥機に移し、溶媒の２−プロパノールを完全に除去してガス拡散電極を得た。電池性能評価は実施例１と同様の方法で行った。定電流測定は電流密度を２３ｍＡｃｍ−２に固定し、電池電圧を測定した。
[Example 3]
In the same manner as in Example 1, PTFE-supported hydrophobic carbon and PTFE-supported hydrophilic carbon were produced. A carbon ink was prepared by dispersing PTFE-supporting hydrophobic carbon in 2-propanol, and was applied to foamed nickel cut to the same size as in Example 1 so as to be 14 mg / cm 2 and dried. It was pressed with a load of 376 kgfcm- 2 using a press machine to obtain a foamed nickel / hydrophobic carbon composite. Similarly, PTFE-supporting hydrophilic carbon ink dispersed in 2-propanol was applied to the foamed nickel / hydrophobic carbon composite at a concentration of 6 mg / cm 2 , dried, and dried using a hydraulic press at 150 kgfcm. This was pressed with a load of -2 , rapidly heated in an electric furnace, heated to 360 ° C to melt the PTFE, pressed by a hydraulic press with a load of 38 kgfcm -2 , and then rapidly cooled. Finally, the mixture was transferred to a dryer maintained at 120 ° C., and 2-propanol as a solvent was completely removed to obtain a gas diffusion electrode. The battery performance evaluation was performed in the same manner as in Example 1. In the constant current measurement, the current density was fixed at 23 mAcm −2 , and the battery voltage was measured.
［比較例１］
実施例１と同様の方法によりＰＴＦＥ担持疎水性カーボン、ＰＴＦＥ担持親水性カーボンを作製した。２−プロパノールにＰＴＦＥ担持疎水性カーボンを分散させてカーボンインキを作製し、これを３．５×３．８ｃｍ２に切断したニッケルメッシュ（１００ｍｅｓｈ、ニラコ製）に１ｃｍ２あたり１４ｍｇになるように塗布し、同様に２−プロパノールに分散させたＰＴＦＥ担持親水性カーボンインキを、さらに疎水性カーボン上に１ｃｍ２あたり６ｍｇになるように塗布し、これを電気炉で急加熱し、温度を３６０℃まで昇温させてＰＴＦＥを融解させ、油圧プレス機を用いて３８ｋｇｆｃｍ−２の荷重でプレスした後、急冷却した。最後に１２０℃に保持した乾燥機に移し、溶媒の２−プロパノールを完全に除去してガス拡散電極を得た。電池性能評価は実施例１と同様の方法で行った。定電流測定は実施例３と同様の方法で行った。
[Comparative Example 1]
In the same manner as in Example 1, PTFE-supported hydrophobic carbon and PTFE-supported hydrophilic carbon were produced. PTFE-supporting hydrophobic carbon is dispersed in 2-propanol to prepare a carbon ink, which is applied to a nickel mesh (100 mesh, made by Nilaco) cut into 3.5 × 3.8 cm 2 so as to be 14 mg / cm 2. Then, a PTFE-supporting hydrophilic carbon ink similarly dispersed in 2-propanol was further applied on hydrophobic carbon so as to be 6 mg per 1 cm 2 , and this was rapidly heated in an electric furnace to a temperature of 360 ° C. The PTFE was melted by raising the temperature, pressed with a load of 38 kgfcm- 2 using a hydraulic press, and then rapidly cooled. Finally, the mixture was transferred to a dryer maintained at 120 ° C., and 2-propanol as a solvent was completely removed to obtain a gas diffusion electrode. The battery performance evaluation was performed in the same manner as in Example 1. The constant current measurement was performed in the same manner as in Example 3.
図１〜図４は走査型電子顕微鏡（ＪＳＭ−６４９０ＬＡ、日本電子製）を用いて観察したそれぞれ実施例１〜３、比較例１のガス拡散電極断面の二次電子線像、炭素およびニッケルの元素マップである。図５は発泡ニッケルの光学写真である。実施例１、２は部分的に発泡ニッケル／疎水性カーボン複合層を形成しているが、一部の発泡ニッケルは疎水性カーボンと複合しておらず、特徴的な発泡ニッケルの孔（１００〜５００μｍ）が確認できる。一方、実施例３で作製したガス拡散電極は、３７６ｋｇｆｃｍ−２でのプレスによって元の発泡ニッケルの特徴的な孔は確認できなくなり、疎水性カーボンが隙間なく充填され、圧縮されて潰れた発泡ニッケルと疎水性カーボンからなる複合層の一層を確認した。 1 to 4 are secondary electron beam images of the cross sections of the gas diffusion electrodes of Examples 1 to 3 and Comparative Example 1 observed using a scanning electron microscope (JSM-6490LA, manufactured by JEOL Ltd.), respectively. It is an element map. FIG. 5 is an optical photograph of nickel foam. In Examples 1 and 2, the nickel foam / hydrophobic carbon composite layer was partially formed, but some of the nickel foam was not composite with hydrophobic carbon, and the characteristic nickel foam holes (100 to 500 μm) can be confirmed. On the other hand, in the gas diffusion electrode manufactured in Example 3, the characteristic pores of the original foamed nickel cannot be confirmed by pressing at 376 kgfcm −2 , and the foamed nickel foam is filled with hydrophobic carbon without any gap, and is compressed and crushed. And one layer of a composite layer composed of hydrophobic carbon.
図６は実施例１〜３、比較例１のマグネシウム空気電池の電流密度−電圧特性である。空気中の酸素が正極活物質である金属空気電池や燃料電池は、空気極での酸素還元反応が進行するが、電流密度が大きくなると酸素供給が律速となって急激に電池電圧が低下する。したがって、電解液の漏出および空気側からの水分の混入を防ぐ限りは、ガス拡散層は薄いほど空気中の酸素の拡散に有利である。実施例１、２のガス拡散電極は、発泡ニッケルおよび発泡ニッケル／疎水性カーボン複合層を併せた厚みはそれぞれ１２５０μｍ、９６４μｍであるため、空気中の酸素が触媒層まで達するガス拡散パスの最短距離はそれぞれ１２５０μｍ、９６４μｍである。実施例３のガス拡散電極の発泡ニッケル／疎水性カーボン複合層の厚みは７２４μｍであるため、空気中の酸素が触媒層まで達するガス拡散パスの最短距離は７２４μｍである。実施例１〜３の電極はガス拡散パスの最短距離が短くなるほど、約１０ｍＡｃｍ−２以上の高電流密度域で高い電池電圧が得られ、その最高出力はそれぞれ４１．６、６８．１、８０．８ｍＷｃｍ−２となり、実施例２、３は、従来のニッケルメッシュを使用したガス拡散電極を用いたマグネシウム空気電池の最高出力４６．５ｍＷｃｍ−２より高い性能を示した。 FIG. 6 shows current density-voltage characteristics of the magnesium air batteries of Examples 1 to 3 and Comparative Example 1. In a metal-air battery or a fuel cell in which oxygen in the air is a positive electrode active material, the oxygen reduction reaction proceeds at the air electrode. However, as the current density increases, the supply of oxygen becomes rate-limiting and the battery voltage drops rapidly. Therefore, the thinner the gas diffusion layer, the better the diffusion of oxygen in the air, as long as the leakage of the electrolyte and the entry of moisture from the air side are prevented. In the gas diffusion electrodes of Examples 1 and 2, the combined thicknesses of the foamed nickel and the foamed nickel / hydrophobic carbon composite layer were 1250 μm and 964 μm, respectively. Are 1250 μm and 964 μm, respectively. Since the thickness of the foamed nickel / hydrophobic carbon composite layer of the gas diffusion electrode of Example 3 is 724 μm, the shortest distance of the gas diffusion path for oxygen in the air to reach the catalyst layer is 724 μm. In the electrodes of Examples 1 to 3, as the shortest distance of the gas diffusion path became shorter, a higher battery voltage was obtained in a high current density region of about 10 mAcm −2 or more, and the maximum outputs were 41.6, 68.1, and 80, respectively. 2.8 mWcm −2 , and Examples 2 and 3 exhibited higher performance than the maximum output of 46.5 mWcm −2 of the magnesium-air battery using the gas diffusion electrode using the conventional nickel mesh.
図７は実施例３および比較例１のマグネシウム空気電池の定電流特性である。実施例３のマグネシウム空気電池の電池電圧は比較的安定していたが、比較例１のマグネシウム空気電池は約３０分から電池電圧が減少し、約５０分で電池電圧が不安定になった。図８は定電流測定後の比較例１のガス拡散電極断面の二次電子線像である。部分的にガス拡散層である疎水性カーボンから集電体であるＮｉメッシュの剥離が確認されたため、メッシュがガス拡散層との接触形状を保持できずに電池電圧が不安定になったものと示唆された。 FIG. 7 shows the constant current characteristics of the magnesium air batteries of Example 3 and Comparative Example 1. Although the battery voltage of the magnesium-air battery of Example 3 was relatively stable, the battery voltage of the magnesium-air battery of Comparative Example 1 was reduced from about 30 minutes, and became unstable after about 50 minutes. FIG. 8 is a secondary electron beam image of the cross section of the gas diffusion electrode of Comparative Example 1 after the measurement of the constant current. Since the Ni mesh, which is the current collector, was partially separated from the hydrophobic carbon, which was the gas diffusion layer, the battery voltage became unstable because the mesh could not maintain the contact shape with the gas diffusion layer. It was suggested.
Claims (15)
発泡金属、カーボン材料、および樹脂結着材を含み、
前記ガス拡散層における少なくとも一部に、前記カーボン材料および前記樹脂結着材が前記発泡金属に充填された複合層を有する、ガス拡散層。 A gas diffusion layer used for a gas diffusion electrode of a metal-air battery or a fuel cell,
Including foam metal, carbon material, and resin binder,
A gas diffusion layer, comprising a composite layer in which the foamed metal is filled with the carbon material and the resin binder at least in a part of the gas diffusion layer.
（Ａ１）カーボン材料および樹脂結着材を分散させた懸濁液（ａ）を発泡金属に塗布し、厚み方向に加圧する工程；および
（Ａ２）前記工程（Ａ１）の後、前記樹脂結着材が軟化または流動する温度で厚み方向に加熱加圧する工程。 A method for producing a gas diffusion electrode used in a metal-air battery or a fuel cell, comprising the following steps (A1) and (A2):
(A1) a step of applying a suspension (a) in which a carbon material and a resin binder are dispersed to a foam metal and pressing in the thickness direction; and (A2) the step of bonding the resin after the step (A1). A step of heating and pressing in the thickness direction at a temperature at which the material softens or flows.
（Ｂ）前記工程（Ａ１）の後、前記懸濁液（ａ）を塗布した面に、さらにカーボン材料、樹脂結着材、および触媒を含む懸濁液（ｂ）を塗布し、厚み方向に加圧する工程。 The method for producing a gas diffusion electrode according to claim 13, further comprising the following step (B):
(B) After the step (A1), a suspension (b) containing a carbon material, a resin binder, and a catalyst is further applied to the surface to which the suspension (a) is applied, and Step of applying pressure.
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