JP6324699B2 - Photoelectrode, method for producing the same, and marine microbial fuel cell equipped with the photoelectrode - Google Patents
Photoelectrode, method for producing the same, and marine microbial fuel cell equipped with the photoelectrode Download PDFInfo
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- GWEVSGVZZGPLCZ-UHFFFAOYSA-N titanium dioxide Inorganic materials O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 196
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 claims description 129
- 229910044991 metal oxide Inorganic materials 0.000 claims description 53
- 150000004706 metal oxides Chemical class 0.000 claims description 53
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- 239000007789 gas Substances 0.000 description 10
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 9
- 239000000843 powder Substances 0.000 description 9
- 230000000694 effects Effects 0.000 description 8
- 239000013535 sea water Substances 0.000 description 7
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- 239000010935 stainless steel Substances 0.000 description 6
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 239000013078 crystal Substances 0.000 description 3
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- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
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- GNRSAWUEBMWBQH-UHFFFAOYSA-N oxonickel Chemical compound [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 239000011941 photocatalyst Substances 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
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- 239000002344 surface layer Substances 0.000 description 2
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 2
- 229910001887 tin oxide Inorganic materials 0.000 description 2
- 229910052719 titanium Inorganic materials 0.000 description 2
- 239000010936 titanium Substances 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical compound [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 description 1
- 239000005751 Copper oxide Substances 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 229910006404 SnO 2 Inorganic materials 0.000 description 1
- 229910001069 Ti alloy Inorganic materials 0.000 description 1
- LCKIEQZJEYYRIY-UHFFFAOYSA-N Titanium ion Chemical compound [Ti+4] LCKIEQZJEYYRIY-UHFFFAOYSA-N 0.000 description 1
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 1
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- 229910000431 copper oxide Inorganic materials 0.000 description 1
- LBJNMUFDOHXDFG-UHFFFAOYSA-N copper;hydrate Chemical compound O.[Cu].[Cu] LBJNMUFDOHXDFG-UHFFFAOYSA-N 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
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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
Description
本発明は、光電極及びその製造方法に関し、特に海洋微生物燃料電池のアノード電極に用いられる光電極に関する。 The present invention relates to a photoelectrode and a method for producing the same, and more particularly to a photoelectrode used for an anode electrode of a marine microbial fuel cell.
海洋微生物燃料電池（Ｍｉｃｒｏｂｉａｌ Ｆｕｅｌ Ｃｅｌｌ；ＭＦＣ）は、自然海水中のバイオフィルム付着電極をカソード（正極）に、光触媒電極（光電極）をアノード（負極）にすることで発生する電位差を使った自然エネルギー利用型電池である（図１）。ＭＦＣでは、カソードで水及び微生物活動を促進する海水中有機物を、アノードでは水をそれぞれ活物質（燃料）とし、電解質は自然海水をそのまま利用する。 Marine Microbial Fuel Cell (MFC) is a natural fuel cell that uses a potential difference generated by using a biofilm-attached electrode in natural seawater as a cathode (positive electrode) and a photocatalytic electrode (photoelectrode) as an anode (negative electrode). It is an energy utilization type battery (FIG. 1). MFC uses water and organic matter in seawater that promotes microbial activity at the cathode, water as the active material (fuel) at the anode, and natural seawater as the electrolyte.
電気を取り出した後の反応生成物は水（Ｈ２Ｏ）の分解生成物のみであり、非プロトン（Ｈ＋）供給型ながら一般の燃料電池と同じ動作原理の低環境負荷型電源である。しかし、この電池は正極にバイオフィルムの微生物活性を利用することから発生電力が低く、実用化には光電極（負極）の電子伝達性の向上が必須とされている。また、光電極としてより防食性（耐食性）に優れた電極が求められている。 The reaction product after taking out electricity is only a decomposition product of water (H 2 O), and is a low environmental load type power source having the same operation principle as that of a general fuel cell while being aprotic (H + ) supply type. However, since this battery uses the microbial activity of the biofilm for the positive electrode, the generated power is low, and it is essential to improve the electron transfer property of the photoelectrode (negative electrode) for practical use. Further, there is a demand for an electrode that is more excellent in corrosion resistance (corrosion resistance) as a photoelectrode.
特許文献１及び非特許文献１には、金属材料の表面に異種元素（Ｆｅ、Ｖ等）を含む酸化チタン皮膜を形成し、さらにその表面に酸化チタン皮膜を形成した酸化チタン電極が開示されている。
特許文献２には反応性スパッタリング法を用いて、導電体上にルチル型酸化チタン層が配置され、その上にさらにアナターゼ型酸化チタン層が配置された光電気化学電池が開示されている。
Patent Document 1 and Non-Patent Document 1 disclose a titanium oxide electrode in which a titanium oxide film containing a different element (Fe, V, etc.) is formed on the surface of a metal material, and further a titanium oxide film is formed on the surface. Yes.
Patent Document 2 discloses a photoelectrochemical cell in which a rutile-type titanium oxide layer is disposed on a conductor and an anatase-type titanium oxide layer is further disposed thereon using a reactive sputtering method.
上述のように、光電極において、電極の防食性及び電極性能の向上を目的として、酸化チタン皮膜を二層構造にした電極が検討されている。しかしながら、その防食性及び電極性能には、依然として改善の余地があった。 As described above, in the photoelectrode, for the purpose of improving the anticorrosion property and electrode performance of the electrode, an electrode having a two-layer structure of the titanium oxide film has been studied. However, there is still room for improvement in the corrosion resistance and electrode performance.
そこで本発明では、金属酸化物層が形成された光電極であって、電極性能と防食性（耐久性）により優れた光電極を提供することを目的とする。 Therefore, an object of the present invention is to provide a photoelectrode having a metal oxide layer, which is superior in electrode performance and corrosion resistance (durability).
本発明者らは、バンドギャップの異なる金属酸化物層を積層することで、電極性能と耐久性に優れた光電極を得ることができることを見出し、本発明を完成するに至った。
すなわち本発明は、上記課題を解決するものであり、下記［１］〜［９］に関するものである。
The present inventors have found that a photoelectrode excellent in electrode performance and durability can be obtained by laminating metal oxide layers having different band gaps, and the present invention has been completed.
That is, this invention solves the said subject, and relates to following [1]-[9].
［１］ 基板と、前記基板上に設けられる金属酸化物層（Ａ）と、前記金属酸化物層（Ａ）上に設けられる金属酸化物層（Ｂ）とを含む光電極であって、前記金属酸化物層（Ａ）及び前記金属酸化物層（Ｂ）が共に光触媒作用を有し、前記金属酸化物層（Ａ）のバンドギャップが前記金属酸化物層（Ｂ）のバンドギャップよりも狭い、光電極。
［２］ 前記金属酸化物層（Ａ）がルチル型酸化チタン皮膜であり、前記金属酸化物層（Ｂ）がアナターゼ型酸化チタン皮膜である、前記［１］に記載の光電極。
［３］ 前記ルチル型酸化チタン皮膜の表面粗さが２〜４μｍであり、かつ前記ルチル型酸化チタン皮膜の膜厚が６０μｍ以上である、前記［２］に記載の光電極。
［４］ 基板と、前記基板上に設けられるルチル型酸化チタン皮膜と、前記ルチル型酸化チタン皮膜上に設けられるアナターゼ型酸化チタン皮膜とを含む光電極であって、前記ルチル型酸化チタン皮膜が溶射法によって形成された光電極。
［５］ 前記アナターゼ型酸化チタン皮膜の膜厚が１０〜８０μｍである、前記［２］〜［４］のいずれか１に記載の光電極。
［６］ 前記アナターゼ型酸化チタン皮膜がスキージ法、ゾル−ゲル法又は塗布法によって形成された、前記［２］〜［５］のいずれか１に記載の光電極。
［７］ 前記基板が耐食性金属である、前記［１］〜［６］のいずれか１に記載の光電極。
［８］ 前記［１］〜［７］のいずれか１に記載の光電極をアノード電極として備えた海洋微生物燃料電池。
［９］ 基板上にルチル型酸化チタン皮膜を溶射法により形成する工程、及び前記ルチル型酸化チタン皮膜上にアナターゼ型酸化チタン皮膜をスキージ法、ゾル−ゲル法又は塗布法により形成する工程を含む、光電極を製造する方法。
[1] A photoelectrode comprising a substrate, a metal oxide layer (A) provided on the substrate, and a metal oxide layer (B) provided on the metal oxide layer (A), Both the metal oxide layer (A) and the metal oxide layer (B) have a photocatalytic action, and the band gap of the metal oxide layer (A) is narrower than the band gap of the metal oxide layer (B). , Photoelectrode.
[2] The photoelectrode according to [1], wherein the metal oxide layer (A) is a rutile-type titanium oxide film and the metal oxide layer (B) is an anatase-type titanium oxide film.
[3] The photoelectrode according to [2], wherein the rutile type titanium oxide film has a surface roughness of 2 to 4 μm, and the rutile type titanium oxide film has a thickness of 60 μm or more.
[4] A photoelectrode including a substrate, a rutile-type titanium oxide film provided on the substrate, and an anatase-type titanium oxide film provided on the rutile-type titanium oxide film, wherein the rutile-type titanium oxide film is A photoelectrode formed by thermal spraying.
[5] The photoelectrode according to any one of [2] to [4], wherein the anatase-type titanium oxide film has a thickness of 10 to 80 μm.
[6] The photoelectrode according to any one of [2] to [5], wherein the anatase-type titanium oxide film is formed by a squeegee method, a sol-gel method, or a coating method.
[7] The photoelectrode according to any one of [1] to [6], wherein the substrate is a corrosion-resistant metal.
[8] A marine microbial fuel cell comprising the photoelectrode according to any one of [1] to [7] as an anode electrode.
[9] A step of forming a rutile type titanium oxide film on a substrate by a thermal spraying method and a step of forming an anatase type titanium oxide film on the rutile type titanium oxide film by a squeegee method, a sol-gel method or a coating method. A method of manufacturing a photoelectrode.
本発明によれば、光触媒作用を持つ金属酸化物層（Ａ）及び（Ｂ）のうち、バンドギャップの狭い方の金属酸化物層（Ａ）を基板上に設け、その上にバンドギャップの広い金属酸化物層（Ｂ）を設けることによって、金属酸化物層の光触媒作用を基板に効率よく伝え、電極性能の優れた光電極を得ることができる。また、上記構成とすることにより、金属酸化物層（Ｂ）から金属酸化物層（Ａ）に電子が移動し、電極の腐食も電気化学的に抑制することができることから、防食性能にも優れた光電極を得ることができる。 According to the present invention, of the metal oxide layers (A) and (B) having a photocatalytic action, the metal oxide layer (A) having the narrower band gap is provided on the substrate, and the wide band gap is provided thereon. By providing the metal oxide layer (B), the photocatalytic action of the metal oxide layer can be efficiently transmitted to the substrate, and a photoelectrode having excellent electrode performance can be obtained. In addition, by adopting the above configuration, electrons move from the metal oxide layer (B) to the metal oxide layer (A), and the corrosion of the electrode can also be suppressed electrochemically. A photoelectrode can be obtained.
本発明に係る光電極は、基板と、前記基板上に設けられる金属酸化物層（Ａ）と、前記金属酸化物層（Ａ）上に設けられる金属酸化物層（Ｂ）とを含み、前記金属酸化物層（Ａ）及び（Ｂ）は共に光触媒作用を有し、前記金属酸化物層（Ａ）のバンドギャップが前記金属酸化物層（Ｂ）のバンドギャップよりも狭いことを特徴とする。 The photoelectrode according to the present invention includes a substrate, a metal oxide layer (A) provided on the substrate, and a metal oxide layer (B) provided on the metal oxide layer (A), The metal oxide layers (A) and (B) both have a photocatalytic action, and the band gap of the metal oxide layer (A) is narrower than the band gap of the metal oxide layer (B). .
＜金属酸化物層（Ａ）及び（Ｂ）＞
バンドギャップの狭い金属酸化物層（Ａ）を基板上に設け、バンドギャップの広い金属酸化物層（Ｂ）を前記金属酸化物層（Ａ）上に設けることにより、金属酸化物層の光触媒作用を基板に効率よく伝えることができる。そのため、本発明では電極性能の優れた光電極を得ることができる。
また、金属酸化物層（Ａ）がポーラス構造等を取ることによって電解液が透過する場合には基板の腐食原因となることから、当該金属酸化物層（Ａ）を金属酸化物層（Ｂ）で完全に被覆することにより物理的な封孔作用を示すと共に、金属酸化物層（Ｂ）から金属酸化物層（Ａ）に電子が移動し、電極が腐食することを電気化学的に抑制して防食性にも優れた光電極を得ることができる。
<Metal oxide layers (A) and (B)>
By providing a metal oxide layer (A) having a narrow band gap on the substrate and providing a metal oxide layer (B) having a wide band gap on the metal oxide layer (A), the photocatalytic action of the metal oxide layer is achieved. Can be efficiently transmitted to the substrate. Therefore, in the present invention, a photoelectrode with excellent electrode performance can be obtained.
In addition, when the metal oxide layer (A) has a porous structure or the like and the electrolytic solution permeates, it causes corrosion of the substrate. Therefore, the metal oxide layer (A) is converted into the metal oxide layer (B). By covering completely with a metal, it exhibits a physical sealing action, and electrochemically suppresses the movement of electrons from the metal oxide layer (B) to the metal oxide layer (A) and corrosion of the electrode. Thus, a photoelectrode excellent in corrosion resistance can be obtained.
本発明における金属酸化物層（Ａ）及び（Ｂ）は光触媒作用を有する。具体的には、酸化チタン（ＴｉＯ２）、酸化スズ（ＳｎＯ２）、酸化亜鉛（ＺｎＯ）、酸化ニッケル（ＮｉＯ）、酸化銅（Ｃｕ２Ｏ）等が挙げられ、これらは様々な結晶構造を取ることができる。これらは一種を用いても、複数種を組み合わせて用いてもよい。中でも、酸化チタンが光電位の安定性の点から好ましい。 The metal oxide layers (A) and (B) in the present invention have a photocatalytic action. Specific examples include titanium oxide (TiO 2 ), tin oxide (SnO 2 ), zinc oxide (ZnO), nickel oxide (NiO), and copper oxide (Cu 2 O). These have various crystal structures. Can be taken. These may be used alone or in combination of two or more. Among these, titanium oxide is preferable from the viewpoint of the stability of the photopotential.
金属酸化物層（Ａ）及び（Ｂ）として酸化チタンを用いる場合、酸化チタンはルチル型、アナターゼ型及びブルカイト型の３種の結晶形態を取ることができるが、ルチル型とアナターゼ型が工業的に利用可能な点からより好ましい。ルチル型酸化チタンのバンドギャップは３．０ｅＶであり、アナターゼ型酸化チタンのバンドギャップは３．２ｅＶである。 When titanium oxide is used as the metal oxide layers (A) and (B), the titanium oxide can take three types of crystal forms of rutile, anatase and brookite, but the rutile and anatase types are industrial. It is more preferable from the point that it can be used. The band gap of rutile titanium oxide is 3.0 eV, and the band gap of anatase titanium oxide is 3.2 eV.
＜ルチル型酸化チタン皮膜＞
金属酸化物層（Ａ）としてルチル型酸化チタン皮膜を用いる場合、その表面粗さＲａは２〜４μｍが好ましく、２．６〜３．４μｍがより好ましい。表面粗さが上記範囲内にあれば、ルチル型酸化チタン皮膜はポーラス構造（多孔構造）を取っているということができ、皮膜の比表面積、すなわち反応面積が大きくなることから好ましい。
<Rutyl type titanium oxide film>
When a rutile type titanium oxide film is used as the metal oxide layer (A), the surface roughness Ra is preferably 2 to 4 μm, and more preferably 2.6 to 3.4 μm. If the surface roughness is within the above range, it can be said that the rutile-type titanium oxide film has a porous structure (porous structure), which is preferable because the specific surface area of the film, that is, the reaction area becomes large.
ルチル型酸化チタン皮膜の表面粗さは、溶射法を用いて皮膜を形成する場合には、溶射材とするルチル型酸化チタン粉末の粒子サイズや粉末の溶解条件、溶射距離、溶射雰囲気等を調整することにより制御することができる。また、表面粗さＲａは表面粗さ測定機により測定することができる。 The surface roughness of the rutile type titanium oxide film is adjusted by adjusting the particle size of rutile type titanium oxide powder used as the thermal spraying material, the melting conditions of the powder, the spraying distance, the spraying atmosphere, etc. Can be controlled. The surface roughness Ra can be measured with a surface roughness measuring machine.
ルチル型酸化チタン皮膜は基板との密着性が強いことが好ましい。またより低い光電位が得られる点から、皮膜の膜厚は６０μｍ以上であることが好ましく、８０μｍ以上であることがより好ましい。また膜厚の上限は３００μｍ以下が好ましく、１００μｍ以下がより好ましい。
皮膜の膜厚は、溶射法を用いて皮膜を形成する場合には、溶射材とするルチル型酸化チタン粉末の粒子サイズや粉末の溶解条件、溶射回数や溶射時間を調整することにより制御できる。またゾル−ゲル法やスキージ法等を用いて皮膜を形成する場合にも、重ね塗りを行う回数を調整することにより、皮膜の厚さを制御することができる。なお、膜厚はマイクロメーターおよびレーザー顕微鏡により測定することができる。
It is preferable that the rutile type titanium oxide film has strong adhesion to the substrate. Moreover, the film thickness of the film is preferably 60 μm or more, and more preferably 80 μm or more from the viewpoint of obtaining a lower photopotential. The upper limit of the film thickness is preferably 300 μm or less, more preferably 100 μm or less.
When the coating is formed using a thermal spraying method, the thickness of the coating can be controlled by adjusting the particle size of the rutile-type titanium oxide powder used as the thermal spraying material, the powder dissolution conditions, the number of thermal sprays, and the thermal spraying time. Moreover, also when forming a film | membrane using a sol-gel method, a squeegee method, etc., the thickness of a film | membrane can be controlled by adjusting the frequency | count of overcoating. The film thickness can be measured with a micrometer and a laser microscope.
上記特性を有するルチル型酸化チタン皮膜は、例えば溶射法、ゾル−ゲル法、固相法等により得ることができ、中でもより良好なポーラス構造を得られる点から溶射法が好ましい。溶射法の具体例としてはプラズマガスアーク溶射法、フレーム溶射法、電気溶射法、爆発溶射法等が挙げられるが、溶射に用いる材料（溶射材）の結晶構造を変化させずに溶射皮膜を形成することができれば、特にこれらに限定されない。 The rutile-type titanium oxide film having the above characteristics can be obtained by, for example, a thermal spraying method, a sol-gel method, a solid phase method or the like, and the thermal spraying method is preferable from the viewpoint of obtaining a better porous structure. Specific examples of the thermal spraying method include plasma gas arc spraying method, flame spraying method, electric spraying method, explosion spraying method, etc., but the sprayed coating is formed without changing the crystal structure of the material (spraying material) used for spraying. If possible, it is not limited to these.
溶射法とは、皮膜材料の粒子を加熱して溶解またはそれに近い状態とし、物体表面に吹き付けて皮膜を形成する表面処理法である。また、プラズマガスアーク溶射法とは、皮膜材料を溶解し、ガスと共に基板に高速で吹き付けることで成膜する方法である。
溶射法により皮膜を形成する場合、溶解した皮膜材料が基板に叩き付けられて成膜されるので、基板との密着性が高くなり、得られた皮膜はポーラス構造となる。また、膜の導電性は皮膜中の酸素欠陥の量により異なるが、溶射法ではこの酸素欠陥の量、すなわち導電性の制御が可能であることから、導電体に近い半導体を作製することができる。
The thermal spraying method is a surface treatment method in which particles of a coating material are heated to be dissolved or close to the state and sprayed on the surface of an object to form a coating. The plasma gas arc spraying method is a method of forming a film by melting a coating material and spraying it on a substrate together with a gas at a high speed.
When a film is formed by thermal spraying, the dissolved film material is struck against the substrate to form a film, so that the adhesion with the substrate is increased and the obtained film has a porous structure. In addition, although the conductivity of the film varies depending on the amount of oxygen defects in the film, since the amount of oxygen defects, that is, conductivity can be controlled by the thermal spraying method, a semiconductor close to a conductor can be manufactured. .
例えば、ルチル型酸化チタン皮膜を溶射法により形成する場合には、ルチル型の酸化チタンパウダーを溶射材とする。
ルチル型酸化チタンパウダーの粒子サイズは５０ｎｍ〜２００μｍが皮膜形成性の点から好ましく、１〜５０μｍがより好ましい。ルチル型酸化チタンパウダーの純度は高いほど好ましいが、９５％以上であればよく、９９％以上であればより好ましい。
For example, when a rutile type titanium oxide film is formed by a thermal spraying method, a rutile type titanium oxide powder is used as a thermal spray material.
The particle size of the rutile titanium oxide powder is preferably 50 nm to 200 μm from the viewpoint of film formation, and more preferably 1 to 50 μm. The purity of the rutile titanium oxide powder is preferably as high as possible, but it may be 95% or more, and more preferably 99% or more.
溶射法を用いる場合には、溶射材を溶解させる条件として２次キャリアガスにＮ２又はＣＯ２を用いることが好ましく、ＣＯ２がより好ましい。
溶射距離は５０〜２００ｍｍが皮膜の均一性の点から好ましく、６０〜１００ｍｍがより好ましい。
また、光電位の高い安定性が得られることから、溶射を２回以上行うことが好ましい。
When using the spraying method, it is preferable to use N 2 or CO 2 in the secondary carrier gas as a condition for dissolving the thermal spraying material, CO 2 is more preferable.
The spraying distance is preferably 50 to 200 mm from the viewpoint of film uniformity, and more preferably 60 to 100 mm.
Moreover, it is preferable to perform thermal spraying twice or more because stability with a high photopotential is obtained.
＜アナターゼ型酸化チタン皮膜＞
金属酸化物層（Ｂ）としてアナターゼ型酸化チタン皮膜を用いる場合、ルチル型酸化チタン皮膜上に、アナターゼ型酸化チタン皮膜を形成する。
先述したように、アナターゼ型酸化チタン皮膜のバンドギャップは３．２ｅＶであり、ルチル型酸化チタン皮膜のバンドギャップ３．０ｅＶよりも広いことから、本発明に係る光電極に好適に用いられる。
<Anatase type titanium oxide film>
When an anatase type titanium oxide film is used as the metal oxide layer (B), an anatase type titanium oxide film is formed on the rutile type titanium oxide film.
As described above, the band gap of the anatase-type titanium oxide film is 3.2 eV, which is wider than the band gap of 3.0 eV of the rutile-type titanium oxide film, so that it is suitably used for the photoelectrode according to the present invention.
アナターゼ型酸化チタン皮膜はルチル型酸化チタン皮膜を覆うことができればよいが、アナターゼ型酸化チタン皮膜の膜厚がナノオーダーである場合、皮膜が薄すぎてルチル型酸化チタン皮膜表面の孔（又は凹凸）を塞ぐ封孔効果が出にくい。そのため、アナターゼ型酸化チタン皮膜の膜厚は１０〜８０μｍであることが好ましく、５５〜７５μｍであることがより好ましい。また、上記範囲にすることにより、より低い光電位が得られることからも好ましい。
皮膜の膜厚はメンディングテープ又はエマルジョン厚さを変化することにより制御できる。また、膜厚はレーザー顕微鏡により測定することができる。
The anatase-type titanium oxide film only needs to be able to cover the rutile-type titanium oxide film. However, when the anatase-type titanium oxide film has a nano-order film thickness, the film is too thin and has pores (or irregularities) on the surface of the rutile-type titanium oxide film. ) Is difficult to seal. Therefore, the film thickness of the anatase-type titanium oxide film is preferably 10 to 80 μm, and more preferably 55 to 75 μm. In addition, the above range is preferable because a lower photopotential can be obtained.
The film thickness can be controlled by changing the thickness of the mending tape or emulsion. The film thickness can be measured with a laser microscope.
アナターゼ型酸化チタン皮膜を形成する方法は、ルチル型酸化チタン皮膜を覆うことができれば特に制限されないが、スキージ法、ゾル−ゲル法又は塗布法によって形成することが好ましい。
上記方法によれば、ルチル型酸化チタン皮膜に食い込む形でアナターゼ型酸化チタン皮膜が形成されるものと考えられることから、当該ルチル型酸化チタン皮膜表面の孔（又は凹凸）を塞ぐ封孔効果が期待できる。光電極をＭＦＣ用電極等に適用した場合、前記皮膜表面の孔（又は凹凸）から腐食が始まるものと考えられるので、当該封孔効果により光電極の防食性を高めることができ、非常に有用である。
The method for forming the anatase type titanium oxide film is not particularly limited as long as it can cover the rutile type titanium oxide film, but it is preferably formed by a squeegee method, a sol-gel method or a coating method.
According to the above method, since it is considered that the anatase type titanium oxide film is formed so as to bite into the rutile type titanium oxide film, the sealing effect of closing the pores (or irregularities) on the surface of the rutile type titanium oxide film is obtained. I can expect. When the photoelectrode is applied to an electrode for MFC, etc., it is considered that corrosion starts from the pores (or irregularities) on the surface of the film. Therefore, the anticorrosive property of the photoelectrode can be enhanced by the sealing effect, which is very useful. It is.
アナターゼ型酸化チタン皮膜は、ルチル型酸化チタン皮膜表面の孔（又は凹凸）を塞ぐ封孔効果を得て、かつルチル型酸化チタン皮膜を完全に被覆しやすいことから、スキージ法または塗布法で形成することがより好ましい。また、得られるアナターゼ型酸化チタン皮膜の膜厚を制御し、さらには皮膜表面を光触媒作用に適した平滑な面としやすいことから、スキージ法が特に好ましい。なお、スキージ法とは皮膜材料の溶液を基板に塗布、乾燥した後に焼結する成膜方法であるが、この方法で得られた皮膜は絶縁体に近い半導体を作製することができる。 Anatase-type titanium oxide film is formed by the squeegee method or coating method because it has a sealing effect to close the pores (or irregularities) on the surface of rutile-type titanium oxide film and it is easy to completely coat the rutile-type titanium oxide film. More preferably. In addition, the squeegee method is particularly preferable because the film thickness of the obtained anatase-type titanium oxide film is controlled and the surface of the film is easy to be a smooth surface suitable for photocatalytic action. Note that the squeegee method is a film forming method in which a solution of a film material is applied to a substrate, dried, and then sintered. A film obtained by this method can produce a semiconductor close to an insulator.
スキージ法によりアナターゼ型酸化チタン皮膜を形成する場合には、材料として用いられるアナターゼ型の酸化チタンペーストの粒子サイズは１０〜３００ｎｍが皮膜形成性の点から好ましい。また、乾燥条件は１００〜１５０℃で０．５〜１時間乾燥させることが好ましく、乾燥後３００〜４５０℃で０．５〜１時間焼成することが好ましい。焼成時の雰囲気は大気下でも不活性雰囲気下でもよい。
皮膜の膜厚は、後述する実施例に記載のメンディングテープ又はエマルジョンの厚さによって調整することができる。
When an anatase-type titanium oxide film is formed by a squeegee method, the particle size of the anatase-type titanium oxide paste used as a material is preferably 10 to 300 nm from the viewpoint of film formation. Moreover, it is preferable to make it dry at 100-150 degreeC for 0.5 to 1 hour, and it is preferable to bake at 300-450 degreeC for 0.5 to 1 hour after drying. The atmosphere during firing may be in the air or in an inert atmosphere.
The film thickness of the film can be adjusted by the thickness of the mending tape or emulsion described in Examples described later.
以上より、本発明におけるルチル型酸化チタン皮膜及びアナターゼ型酸化チタン皮膜は、酸化チタンによる光触媒作用を基板へ効率よく伝えることができ、電極としての性能が向上するとともに、電極の防食性も向上することができる。
また、ルチル型酸化チタン皮膜がポーラス構造を取ることによって反応面積が大きくなることから電極性能をさらに向上でき、アナターゼ型酸化チタンによる封孔効果によって防食性能をさらに向上できることから、より優れた光電極を得ることができる。
As described above, the rutile-type titanium oxide film and the anatase-type titanium oxide film in the present invention can efficiently transmit the photocatalytic action of titanium oxide to the substrate, improve the performance as an electrode, and improve the anticorrosion property of the electrode. be able to.
In addition, since the reaction area is increased due to the porous structure of the rutile titanium oxide film, the electrode performance can be further improved, and the anticorrosion performance can be further improved by the sealing effect of the anatase titanium oxide, so that a more excellent photoelectrode Can be obtained.
＜基板＞
本発明に係る酸化チタン電極に用いられる基板は光電極に一般的に用いられるものであれば特に制限されない。中でも耐食性の点から、耐食性金属であることが好ましく、具体的にはステンレス鋼（ＳＵＳ）や金属チタン、白金等の金属基板が好ましく用いられる。これらは一種を用いても、複数種を組み合わせて用いてもよい。
<Board>
If the board | substrate used for the titanium oxide electrode which concerns on this invention is generally used for a photoelectrode, it will not restrict | limit in particular. Among these, from the viewpoint of corrosion resistance, a corrosion-resistant metal is preferable, and specifically, a metal substrate such as stainless steel (SUS), metal titanium, or platinum is preferably used. These may be used alone or in combination of two or more.
＜電極＞
本発明に係る光電極は、図２（Ａ）に酸化チタン皮膜を例として示されるように、基板と、前記基板上に設けられるルチル型酸化チタン皮膜［金属酸化物層（Ａ）］と、前記ルチル型酸化チタン皮膜上に設けられるアナターゼ型酸化チタン皮膜［金属酸化物層（Ｂ）］とを含む。
電極全体の厚さは１００〜２００μｍが剥離耐久性の点から好ましく、１２０〜１４０μｍがより好ましい。
<Electrode>
The photoelectrode according to the present invention, as shown in FIG. 2A as an example of a titanium oxide film, a substrate, a rutile titanium oxide film [metal oxide layer (A)] provided on the substrate, Anatase-type titanium oxide film [metal oxide layer (B)] provided on the rutile-type titanium oxide film.
The thickness of the entire electrode is preferably 100 to 200 μm from the viewpoint of peeling durability, and more preferably 120 to 140 μm.
本発明に係る酸化チタン電極には、本発明における効果を妨げない限り、他に酸化スズ、酸化ニッケル、酸化銅等が含まれていてもよい。 The titanium oxide electrode according to the present invention may contain tin oxide, nickel oxide, copper oxide, etc. as long as the effects of the present invention are not hindered.
＜海洋微生物燃料電池：ＭＦＣ＞
本発明に係る光電極を用いた起電の仕組みを図３に示す。図３は、ルチル型酸化チタンとアナターゼ型酸化チタンに代表される、２種類の金属酸化物層（皮膜）からなるオーミックな接合状態にある半導体のバンド構造を模した図である。なお、オーミックとは、半導体で電荷移動に障壁がないことを意味する。
金属酸化物皮膜が光エネルギーｈν（Ｊ）を受けて、価電子帯から伝導帯へ電子が励起し、価電子帯にはホール（ｈ＋）が、伝導帯には電子（ｅ−）がそれぞれ過剰に生成する。過剰な当該ホール及び電子は各バンド帯末の曲がりにより、それぞれ金属酸化物内を移動して電解液界面付近にホール（ｈ＋）、基板との接合界面付近に電子（ｅ−）が帯電するようになる。この電子とホールの分離により内蔵電位の勾配ができ、そのエネルギー差が電極の起電力として取り出される。
<Marine microbial fuel cell: MFC>
The mechanism of electromotive force using the photoelectrode according to the present invention is shown in FIG. FIG. 3 is a diagram simulating a semiconductor band structure in an ohmic junction state composed of two types of metal oxide layers (films) represented by rutile titanium oxide and anatase titanium oxide. Note that ohmic means that there is no barrier to charge transfer in a semiconductor.
When the metal oxide film receives light energy hν (J), electrons are excited from the valence band to the conduction band, and holes (h + ) are present in the valence band and electrons (e − ) are present in the conduction band. Generate excessively. Excess holes and electrons move through the metal oxide due to the bending at the end of each band, and the holes (h + ) are charged near the electrolyte interface, and the electrons (e − ) are charged near the junction interface with the substrate. It becomes like this. The separation of the electrons and holes creates a gradient of the built-in potential, and the energy difference is taken out as an electromotive force of the electrode.
本発明に係る光電極は、海洋微生物燃料電池用のアノード電極として好適に用いられる。アノード電極では、図１に示すように２Ｈ２Ｏ＋４ｈ＋→Ｏ２＋４Ｈ＋といった電極反応が起こり、その電極電位はカロメル電極に対して−０．６Ｖ（−０．６Ｖ ｖｓ．ＳＣＥ）である。 The photoelectrode according to the present invention is suitably used as an anode electrode for a marine microbial fuel cell. In the anode electrode, as shown in FIG. 1, an electrode reaction of 2H 2 O + 4h + → O 2 + 4H + occurs, and the electrode potential is −0.6 V (−0.6 V vs. SCE) with respect to the calomel electrode.
アノード電極では、海洋中に存在する微生物が光触媒の存在の下、光を照射することによって有機物を電解し、反応生成物として水（Ｈ２Ｏ）の分解生成物が得られる。当該光触媒に、本発明における酸化チタン皮膜等、光触媒作用を有する金属酸化物層が用いられる。 In the anode electrode, microorganisms present in the ocean irradiate light in the presence of a photocatalyst to electrolyze organic matter, and a decomposition product of water (H 2 O) is obtained as a reaction product. As the photocatalyst, a metal oxide layer having a photocatalytic action such as a titanium oxide film in the present invention is used.
一方、カソード電極では、Ｏ２＋２Ｈ２Ｏ＋４ｅ−→４ＯＨ−といった電極反応が起こり、その電極電位はカロメル電極に対して＋０．４Ｖ（＋０．４Ｖ ｖｓ．ＳＣＥ）である。
以上より、ＭＦＣは１．０Ｖの起電力が得られる。
On the other hand, an electrode reaction such as O 2 + 2H 2 O + 4e − → 4OH − occurs at the cathode electrode, and the electrode potential is +0.4 V (+0.4 V vs. SCE) with respect to the calomel electrode.
From the above, MFC can obtain an electromotive force of 1.0V.
カソード電極は基板と、前記基板上に自然海水中のバイオフィルムを付着させたものを用いる。
カソード基板は耐食性金属材料であることが必要であるが、中でもステンレス鋼、チタン合金が好ましい。
前記基板を自然海水中に浸漬することにより、バイオフィルムが付着したカソード電極を得ることができる。
As the cathode electrode, a substrate and a biofilm in natural seawater attached on the substrate are used.
The cathode substrate is required to be a corrosion-resistant metal material, and stainless steel and titanium alloy are particularly preferable.
By immersing the substrate in natural seawater, a cathode electrode to which a biofilm is attached can be obtained.
海洋微生物燃料電池に用いられる電解質は自然海水をそのまま利用することができる。中でもタンク汲み上げ海水が有殻生物の付着を防止する点から好ましい。 Natural seawater can be used as it is for the electrolyte used in the marine microbial fuel cell. Among them, seawater pumped up from the tank is preferable from the viewpoint of preventing the attachment of shelled organisms.
本発明に係る海洋微生物燃料電池には、本発明における酸化チタン電極の効果を妨げない限り、他に配線およびその接合部、シール材等が含まれていてもよい。 As long as the marine microbial fuel cell according to the present invention does not interfere with the effect of the titanium oxide electrode according to the present invention, wiring, a joint portion thereof, a sealing material, and the like may be included.
以下、実施例により本発明を具体的に説明する。ただし、本発明はこれらの実施例のみに限定されるものではない。
＜実施例１＞
ルチル型酸化チタンパウダーを溶射材として、直径３６ｍｍのステンレス鋼基板（Ｔｙｐｅ３２９Ｊ４Ｌ）上に下記条件でプラズマガスアーク溶射法によりルチル型酸化チタン皮膜を形成した。溶射回数は２回とし、いずれも和光純薬工業社製の酸化チタン（ＩＶ）ルチル型、純度９９％）を用いた。
得られた皮膜の任意の２点について膜厚をレーザー顕微鏡により測定したところ、平均の膜厚は６４μｍであった。ステンレス鋼基板の組成を表１に、得られたルチル型酸化チタン皮膜の表面を観察した走査型電子顕微鏡（ＳＥＭ）写真を図４にそれぞれ示す。またＸ線回折測定（ＸＲＤ）により、得られた皮膜はルチル型の酸化チタンであることが確認された。
Hereinafter, the present invention will be described specifically by way of examples. However, the present invention is not limited to only these examples.
<Example 1>
A rutile type titanium oxide film was formed on a 36 mm diameter stainless steel substrate (Type 329J4L) by a plasma gas arc spraying method under the following conditions using rutile type titanium oxide powder as a thermal spray material. The number of times of thermal spraying was 2, and in each case, titanium (IV) rutile type manufactured by Wako Pure Chemical Industries, Ltd., purity 99%) was used.
When the film thickness was measured with a laser microscope at any two points of the obtained film, the average film thickness was 64 μm. Table 1 shows the composition of the stainless steel substrate, and FIG. 4 shows scanning electron microscope (SEM) photographs of the surface of the obtained rutile-type titanium oxide film. Further, it was confirmed by X-ray diffraction measurement (XRD) that the obtained film was a rutile type titanium oxide.
（プラズマガスアーク溶射条件）
アーク電流、電圧 ６５０Ａ、４０Ｖ
溶射距離 ８０ｍｍ
一次ガス Ａｒ：５０Ｌ／分
二次ガス ＣＯ２：６．４Ｌ／分
皮膜厚さ ８０〜１００μｍ
（酸化チタン粉末）
結晶系 ルチル型
酸化チタン純度 （溶射１回目）９９．９％
（溶射２回目）９５．２％（不純物 Ｆｅ２Ｏ３：０．７％、ＺｒＯ２：０．６％、ＳｉＯ２：１．１０％、Ａｌ２Ｏ３：０．４０％、Ｐ：０．０１％、Ｓ：０．０２％）
粒子サイズ 直径１０〜４４μｍ
(Plasma gas arc spraying conditions)
Arc current, voltage 650A, 40V
Thermal spraying distance 80mm
Primary gas Ar: 50 L / min Secondary gas CO 2 : 6.4 L / min Film thickness 80-100 μm
(Titanium oxide powder)
Crystalline purity of rutile type titanium oxide (1st thermal spraying) 99.9%
(2nd thermal spraying) 95.2% (impurity Fe 2 O 3 : 0.7%, ZrO 2 : 0.6%, SiO 2 : 1.10%, Al 2 O 3 : 0.40%, P: 0 .01%, S: 0.02%)
Particle size Diameter 10 ~ 44μm
次いで、ルチル型酸化チタン皮膜上にスキージ法によりアナターゼ型酸化チタン皮膜を形成した。スキージ法の手順を以下に示す。
上記で基板上に形成されたルチル型酸化チタン皮膜表面の左右の縁に厚さ６０μｍのメンディングテープを張ることで２６ｍｍ×２６ｍｍの正方形の溝を作り、当該溝内に酸化チタンペースト（ペクセルテクノロジー社製、ＰＥＣＣ−０１−０６）で均一な膜を作った。これを１５０℃で１時間乾燥させ、さらに４５０℃で１時間焼結することで、アナターゼ型酸化チタン皮膜を形成した。
得られた皮膜の任意の２点について膜厚をレーザー顕微鏡により測定したところ、平均の膜厚は６６μｍであった。なお、アナターゼ型酸化チタン皮膜でルチル型酸化チタン皮膜をすべて被覆することができなかったため、アナターゼ型酸化チタン皮膜で覆われていない部分については、シリコン系接着剤を塗布することで、ルチル型酸化チタン皮膜が表層に出ないようにした。
得られたアナターゼ型酸化チタン皮膜の表面を観察した光学顕微鏡写真を図５に示す。またＸ線回折測定（ＸＲＤ）により、得られた皮膜はアナターゼ型の酸化チタンであることが確認された。
以上の手順によりルチル型酸化チタンとアナターゼ型の酸化チタンの２種類の皮膜が異種積層された酸化チタン電極（以下、“Ｄｏｕｂｌｅ ｌａｙｅｒ ｆｉｌｍ”と称することがある。）を作製した（図２（Ａ））。
Next, an anatase-type titanium oxide film was formed on the rutile-type titanium oxide film by a squeegee method. The procedure of the squeegee method is shown below.
A square groove of 26 mm × 26 mm is made by applying a 60 μm thick mending tape to the left and right edges of the surface of the rutile-type titanium oxide film formed on the substrate, and titanium oxide paste (Peccel) is formed in the groove. A uniform film was made with PECC-01-06 from Technology. This was dried at 150 ° C. for 1 hour, and further sintered at 450 ° C. for 1 hour to form an anatase-type titanium oxide film.
When the film thickness was measured with a laser microscope at any two points of the obtained film, the average film thickness was 66 μm. In addition, since it was not possible to cover all the rutile titanium oxide film with the anatase type titanium oxide film, the rutile type oxide film was applied to the part not covered with the anatase type titanium oxide film by applying a silicon adhesive. The titanium film was prevented from appearing on the surface layer.
The optical microscope photograph which observed the surface of the obtained anatase type titanium oxide film is shown in FIG. Further, it was confirmed by X-ray diffraction measurement (XRD) that the obtained film was anatase type titanium oxide.
Through the above procedure, a titanium oxide electrode (hereinafter sometimes referred to as “Double layer film”) in which two types of coatings of rutile type titanium oxide and anatase type titanium oxide were laminated differently was produced (FIG. 2 (A). )).
＜比較例１＞
ステンレス鋼基板上にルチル型酸化チタン皮膜を形成せず、直接スキージ法で皮膜厚さ１２０μｍのアナターゼ型酸化チタン皮膜を形成した。基板表面の左右の縁に厚さ１２０μｍのメンディングテープを張って２６ｍｍ×２６ｍｍの正方形の溝を作る以外は実施例１におけるスキージ法と同様にして、アナターゼ型酸化チタン１種類のみの皮膜が形成された酸化チタン電極（以下、“Ｓｉｎｇｌｅ ｌａｙｅｒ ｆｉｌｍ”と称することがある。）を作製した（図２（Ｂ））。
<Comparative Example 1>
A rutile type titanium oxide film was not formed on a stainless steel substrate, but an anatase type titanium oxide film having a film thickness of 120 μm was formed by a direct squeegee method. A film of only one type of anatase-type titanium oxide is formed in the same manner as in the squeegee method in Example 1 except that a square groove of 26 mm × 26 mm is formed by stretching a 120 μm thick mending tape on the left and right edges of the substrate surface. A titanium oxide electrode (hereinafter sometimes referred to as “single layer film”) was fabricated (FIG. 2B).
＜表面粗さＲａ＞
実施例１において、アナターゼ型酸化チタン皮膜を形成する前のルチル型酸化チタン皮膜の表面粗さと、アナターゼ型酸化チタン皮膜を形成した後の表面粗さを測定した結果を表２に示す。
ここで表面粗さは、サーフコーダー製表面粗さ測定機ＳＥ−２３００を用い、以下の条件で測定を行った。
（測定条件）
測定距離 ４ｍｍ
駆動速度 ０．１ｍｍ／秒
カットオフ ０．８ｍｍ Ｇ
<Surface roughness Ra>
Table 2 shows the results of measuring the surface roughness of the rutile titanium oxide film before forming the anatase type titanium oxide film and the surface roughness after forming the anatase type titanium oxide film in Example 1.
Here, the surface roughness was measured under the following conditions using a surf coder surface roughness measuring machine SE-2300.
(Measurement condition)
Measuring distance 4mm
Drive speed 0.1mm / second cut-off 0.8mm G
表２より、溶射法により形成したルチル型酸化チタン皮膜よりも、スキージ法により形成したアナターゼ型酸化チタン皮膜の方がいずれの値についても小さく、表面が平滑であることが分かった。また、アナターゼ型酸化チタン皮膜はルチル型酸化チタン皮膜上に形成された状態で測定を行っていることから、下地となるルチル型酸化チタン皮膜表面の孔（凹凸）の影響を受けているにも関わらず、すべての値がルチル型酸化チタン皮膜よりも小さい結果となった。そのため、ルチル型酸化チタン皮膜表面の凹凸がアナターゼ型酸化チタン皮膜の形成により塞がれ、表面が平滑となったことが分かる。以上より、アナターゼ型酸化チタン皮膜の形成によって、ルチル型酸化チタン皮膜表面の孔に対する封孔効果が発現しているものと考えられる。 From Table 2, it was found that the anatase-type titanium oxide film formed by the squeegee method was smaller in both values and the surface was smoother than the rutile-type titanium oxide film formed by the thermal spraying method. In addition, since the anatase-type titanium oxide film is measured on the rutile-type titanium oxide film, it is affected by the pores (irregularities) on the rutile-type titanium oxide film surface. Regardless, all values were smaller than the rutile type titanium oxide film. Therefore, it can be seen that the irregularities on the surface of the rutile-type titanium oxide film were blocked by the formation of the anatase-type titanium oxide film, and the surface became smooth. From the above, it is considered that the formation of the anatase-type titanium oxide film exhibits a sealing effect on the pores on the surface of the rutile-type titanium oxide film.
＜光電位＞
得られた電極の光電位（Ｐｈｏｔｏ ｐｏｔｅｎｔｉａｌ）の経時変化を測定した結果を図６に示す。ここで光電位とは、電極に照射強度１０．５ｍＷ／ｃｍ２で標準光源のキセノン光を照射した場合の電極電位である。
図６より、実験開始から５分後に光照射を開始したところ、直ちに電極電位は低下し、その後５分以内に電位は一定の値に落ち着いた。実施例１、比較例１共に、実験終了（実験開始から２時間）までほぼ安定した光電位を示すものの、実施例１（Ｄｏｕｂｌｅ ｌａｙｅｒ ｆｉｌｍ）の方が、比較例１に比べて安定性が高いことが分かった。また、光を２時間照射した後の光電位は、比較例１が−４８０ｍＶ ｖｓ．ＳＣＥであったのに対して、実施例１では−６２０ｍＶ ｖｓ．ＳＣＥと１４０ｍＶ程度低く、光触媒能に優れ、良好な電極性能が得られることが分かった。
<Photo potential>
FIG. 6 shows the results of measuring the temporal change of the photopotential of the obtained electrode. Here, the photopotential is an electrode potential when the electrode is irradiated with xenon light as a standard light source at an irradiation intensity of 10.5 mW / cm 2 .
As shown in FIG. 6, when light irradiation was started 5 minutes after the start of the experiment, the electrode potential immediately decreased and the potential settled to a constant value within 5 minutes. Although both Example 1 and Comparative Example 1 show a substantially stable photopotential until the end of the experiment (2 hours from the start of the experiment), Example 1 (Double layer film) is more stable than Comparative Example 1. I understood that. Further, the photopotential after irradiation with light for 2 hours was −480 mV vs. Comparative Example 1. In contrast to SCE, in Example 1, -620 mV vs.. It was found that the SCE was about 140 mV lower, the photocatalytic ability was excellent, and good electrode performance was obtained.
また、得られた電極に対して光照射のオン−オフを２時間−２４時間のサイクルで５回繰り返した際の光電位と繰り返し数（Ｎｕｍｂｅｒ ｏｆ ｒｕｎ ｃｙｃｌｅｓ）との関係を測定した結果を図７に示す。ここで、光照射後６０〜１２０分における光電位を定常値であるとみなして用いた。なお、実施例１の電極、比較例１の電極について、同じ条件で２回測定を行い、再現性が得られるかについても併せて確認した。
その結果、比較例１（図７：●及び＋）では３サイクル目以降で光電位が上昇するのに対し、実施例１（図７：□及び×）では３サイクル目以降も低い光電位を保つことが分かった。なお、電極によって光電位の測定値に若干のバラツキは見られたものの、３サイクル目以降の光電位の傾向については再現性のある結果が得られた。
In addition, the results of measuring the relationship between the photopotential and the number of repetitions (Number of run cycles) when the on / off of light irradiation is repeated 5 times in a cycle of 2 hours to 24 hours for the obtained electrode are shown in FIG. 7 shows. Here, the photopotential at 60 to 120 minutes after light irradiation was used as a steady value. In addition, about the electrode of Example 1 and the electrode of the comparative example 1, it measured twice on the same conditions, and also confirmed whether reproducibility was acquired.
As a result, in Comparative Example 1 (FIG. 7: ● and +), the photopotential increases after the third cycle, whereas in Example 1 (FIG. 7: □ and X), the low photopotential is also maintained after the third cycle. I knew it would keep. In addition, although a slight variation was observed in the measured value of the photopotential depending on the electrode, a reproducible result was obtained for the tendency of the photopotential after the third cycle.
＜電極表面観察＞
上記で光照射を５サイクル繰り返した後の、実施例１に係る電極表面を光学顕微鏡で観察した（図８）。その結果、皮膜表面上で目視による点錆（腐食痕）は確認されなかった。一方、光照射を３サイクル繰り返した後の、比較例１に係る電極表面では、点錆（腐食痕）が確認された（図９）。
<Electrode surface observation>
The electrode surface according to Example 1 after repeating the light irradiation for 5 cycles as described above was observed with an optical microscope (FIG. 8). As a result, no spot rust (corrosion marks) was observed on the surface of the film. On the other hand, spot rust (corrosion marks) was confirmed on the electrode surface according to Comparative Example 1 after repeating light irradiation for 3 cycles (FIG. 9).
比較例１に係る電極において、赤錆が発生している部分は膜の剥離が生じているので、当該剥離部分の面積を測定することで点錆の発生している面積比率を算出した。その結果、点錆の発生面積比率は３．１４％（標準偏差１．１５３）であった。
具体的には、解像度７２ピクセル／インチの電極表面画像から、（赤錆部のピクセル数／全ピクセル数）を求め、点錆部の面積比率とした。点錆部の面積比率は同じ条件で作製した計３枚の電極に対し、電極１枚当たり５箇所、すなわち合計１５箇所について求め、その平均値を比較例１に係る電極の点錆部の面積比率とした。
In the electrode according to Comparative Example 1, since the film where the red rust was generated was peeled off, the area ratio where the point rust was generated was calculated by measuring the area of the peeled part. As a result, the area ratio of spot rust was 3.14% (standard deviation 1.153).
Specifically, (the number of pixels in the red rust portion / the total number of pixels) was determined from the electrode surface image with a resolution of 72 pixels / inch, and the area ratio of the point rust portion was obtained. The area ratio of the spot rust portion was obtained for a total of three electrodes prepared under the same conditions, 5 locations per electrode, that is, a total of 15 locations, and the average value was the area of the spot rust portion of the electrode according to Comparative Example 1. It was a ratio.
＜電極抵抗＞
実施例１及び比較例１に係る電極について、交流インピーダンス（ＥＩＳ）測定により電極抵抗の測定を行った。交流インピーダンス測定は以下の条件で行った。
その結果、実施例１の電極抵抗は２．８ｋΩであり、比較例１の電極抵抗は３．２６ｋΩであったことから、本発明に係る電極は電極抵抗が小さく、優れた電極性能が得られることが分かった。
<Electrode resistance>
For the electrodes according to Example 1 and Comparative Example 1, the electrode resistance was measured by AC impedance (EIS) measurement. The AC impedance measurement was performed under the following conditions.
As a result, since the electrode resistance of Example 1 was 2.8 kΩ and the electrode resistance of Comparative Example 1 was 3.26 kΩ, the electrode according to the present invention had a small electrode resistance, and excellent electrode performance was obtained. I understood that.
（交流インピーダンス測定条件）
測定装置 エヌエフ回路設計ブロック社製、ＦＲＡ５０１４
測定周波数 １ｍＨｚ〜１００ｋＨｚ
交流加算電流 ２．４μＡ
(AC impedance measurement conditions)
Measuring device NF Circuit Design Block, FRA 5014
Measurement frequency 1mHz ~ 100kHz
AC addition current 2.4μA
以上より、従来の光電極では光照射を繰返し行うことで発生する腐食によって酸化チタン等による光触媒反応が阻害されるのに対し、本発明に係る光電極では、光照射を繰返し行っても基板の腐食を防ぐことができることが分かった。
また、本発明に係る光電極では、プラズマガスアーク溶射法により形成されたルチル型酸化チタン皮膜が、中間層として表面層（アナターゼ型酸化チタン皮膜）の電子伝達を媒介（メディエーション）し、かつアナターゼ型酸化チタン皮膜が封止効果を示して腐食を抑制することで、光電極の光触媒能（電極性能）と耐久性（防食性）の両方を同時に向上させるものと考えられる。
As described above, in the conventional photoelectrode, the photocatalytic reaction due to titanium oxide or the like is inhibited by corrosion caused by repeated light irradiation, whereas in the photoelectrode according to the present invention, the substrate is not affected by repeated light irradiation. It has been found that corrosion can be prevented.
Further, in the photoelectrode according to the present invention, the rutile type titanium oxide film formed by the plasma gas arc spraying method mediates the electron transfer of the surface layer (anatase type titanium oxide film) as an intermediate layer, and anatase type. It is considered that both the photocatalytic ability (electrode performance) and durability (anticorrosiveness) of the photoelectrode are improved simultaneously by the titanium oxide film exhibiting a sealing effect and suppressing corrosion.
本発明に係る光電極は、バンドギャップの狭い金属酸化物層（Ａ）を基板上に形成し、その上にバンドギャップの広い異なる種類の金属酸化物層（Ｂ）を積層させることで、電極性能と耐久性（防食性）に共に優れた電極を得ることができる。そのため、本発明に係る光電極を海洋微生物燃料電池のアノード電極に適用することは特に有用であり、その技術的意義は極めて大きなものである。 The photoelectrode according to the present invention is formed by forming a metal oxide layer (A) having a narrow band gap on a substrate and laminating different types of metal oxide layers (B) having a wide band gap on the electrode. An electrode excellent in both performance and durability (anticorrosion) can be obtained. Therefore, it is particularly useful to apply the photoelectrode according to the present invention to the anode electrode of a marine microbial fuel cell, and its technical significance is extremely large.
１ ステンレス鋼基板
２ アナターゼ型酸化チタン皮膜（スキージ法による成膜）
３ ルチル型酸化チタン皮膜（プラズマガスアーク溶射法による成膜）
1 Stainless steel substrate 2 Anatase type titanium oxide film (deposition by squeegee method)
3 Rutile-type titanium oxide film (deposition by plasma gas arc spraying method)
Claims (6)
前記金属酸化物層（Ａ）及び前記金属酸化物層（Ｂ）が共に光触媒作用を有し、
前記金属酸化物層（Ａ）のバンドギャップが前記金属酸化物層（Ｂ）のバンドギャップよりも狭く、
前記金属酸化物層（Ａ）がルチル型酸化チタン皮膜であり、前記金属酸化物層（Ｂ）がアナターゼ型酸化チタン皮膜であり、
前記ルチル型酸化チタン皮膜の膜厚が６０μｍ以上であり、
前記アナターゼ型酸化チタン皮膜の膜厚が１０〜８０μｍであり、
前記アナターゼ型酸化チタン皮膜がスキージ法、ゾル−ゲル法又は塗布法によって形成された、光電極。 A photoelectrode comprising a substrate, a metal oxide layer (A) provided on the substrate, and a metal oxide layer (B) provided on the metal oxide layer (A),
Both the metal oxide layer (A) and the metal oxide layer (B) have a photocatalytic action,
It said metal band gap of the oxide layer (A) is rather narrower than the band gap of the metal oxide layer (B),
The metal oxide layer (A) is a rutile type titanium oxide film, and the metal oxide layer (B) is an anatase type titanium oxide film,
The rutile titanium oxide film has a thickness of 60 μm or more,
The anatase-type titanium oxide film has a thickness of 10 to 80 μm,
A photoelectrode in which the anatase-type titanium oxide film is formed by a squeegee method, a sol-gel method, or a coating method .
前記ルチル型酸化チタン皮膜上にアナターゼ型酸化チタン皮膜をスキージ法、ゾル−ゲル法又は塗布法により形成する工程を含む、光電極を製造する方法。
A photoelectrode comprising a step of forming a rutile type titanium oxide film on a substrate by a thermal spraying method, and a step of forming an anatase type titanium oxide film on the rutile type titanium oxide film by a squeegee method, a sol-gel method or a coating method. How to manufacture.
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