JP2023097112A - Non-noble metal electrode for water electrolysis and production method thereof - Google Patents
Non-noble metal electrode for water electrolysis and production method thereof Download PDFInfo
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- 238000005868 electrolysis reaction Methods 0.000 title claims abstract description 67
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 48
- 229910000510 noble metal Inorganic materials 0.000 title claims abstract description 31
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 25
- 239000002131 composite material Substances 0.000 claims abstract description 116
- 238000007747 plating Methods 0.000 claims abstract description 61
- 229910017091 Fe-Sn Inorganic materials 0.000 claims abstract description 45
- 229910017142 Fe—Sn Inorganic materials 0.000 claims abstract description 45
- 239000002243 precursor Substances 0.000 claims abstract description 20
- 239000000463 material Substances 0.000 claims abstract description 12
- 239000000758 substrate Substances 0.000 claims abstract description 12
- 150000003841 chloride salts Chemical class 0.000 claims abstract description 5
- 238000000034 method Methods 0.000 claims description 20
- 239000010970 precious metal Substances 0.000 claims description 15
- 229910052718 tin Inorganic materials 0.000 claims description 7
- 229910052742 iron Inorganic materials 0.000 claims description 6
- 229910052759 nickel Inorganic materials 0.000 claims description 6
- 230000003197 catalytic effect Effects 0.000 abstract description 25
- 238000000151 deposition Methods 0.000 abstract 5
- 230000008021 deposition Effects 0.000 abstract 2
- 239000011135 tin Substances 0.000 description 74
- 238000005259 measurement Methods 0.000 description 35
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 28
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 27
- 239000001301 oxygen Substances 0.000 description 27
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- 229910052739 hydrogen Inorganic materials 0.000 description 26
- 239000001257 hydrogen Substances 0.000 description 26
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 25
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 23
- 238000006243 chemical reaction Methods 0.000 description 22
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- 239000013078 crystal Substances 0.000 description 7
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- 238000001878 scanning electron micrograph Methods 0.000 description 5
- DHMQDGOQFOQNFH-UHFFFAOYSA-N Glycine Chemical compound NCC(O)=O DHMQDGOQFOQNFH-UHFFFAOYSA-N 0.000 description 4
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 4
- 239000003054 catalyst Substances 0.000 description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 4
- 238000004364 calculation method Methods 0.000 description 3
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- 238000010586 diagram Methods 0.000 description 2
- LLQVGQZFZSRDAV-UHFFFAOYSA-L dichloroiron dihydrate Chemical compound O.O.Cl[Fe]Cl LLQVGQZFZSRDAV-UHFFFAOYSA-L 0.000 description 2
- XPPKVPWEQAFLFU-UHFFFAOYSA-J diphosphate(4-) Chemical compound [O-]P([O-])(=O)OP([O-])([O-])=O XPPKVPWEQAFLFU-UHFFFAOYSA-J 0.000 description 2
- 235000011180 diphosphates Nutrition 0.000 description 2
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- LAIZPRYFQUWUBN-UHFFFAOYSA-L nickel chloride hexahydrate Chemical compound O.O.O.O.O.O.[Cl-].[Cl-].[Ni+2] LAIZPRYFQUWUBN-UHFFFAOYSA-L 0.000 description 2
- 230000008520 organization Effects 0.000 description 2
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910002555 FeNi Inorganic materials 0.000 description 1
- 101000993059 Homo sapiens Hereditary hemochromatosis protein Proteins 0.000 description 1
- 229910021578 Iron(III) chloride Inorganic materials 0.000 description 1
- 229910001030 Iron–nickel alloy Inorganic materials 0.000 description 1
- 241000080590 Niso Species 0.000 description 1
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- OSOVKCSKTAIGGF-UHFFFAOYSA-N [Ni].OOO Chemical compound [Ni].OOO OSOVKCSKTAIGGF-UHFFFAOYSA-N 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000000970 chrono-amperometry Methods 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
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- 238000007599 discharging Methods 0.000 description 1
- 239000010411 electrocatalyst Substances 0.000 description 1
- 238000003487 electrochemical reaction Methods 0.000 description 1
- 239000006260 foam Substances 0.000 description 1
- 239000002803 fossil fuel Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 229910052741 iridium Inorganic materials 0.000 description 1
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 1
- UGKDIUIOSMUOAW-UHFFFAOYSA-N iron nickel Chemical compound [Fe].[Ni] UGKDIUIOSMUOAW-UHFFFAOYSA-N 0.000 description 1
- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical compound Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 description 1
- SURQXAFEQWPFPV-UHFFFAOYSA-L iron(2+) sulfate heptahydrate Chemical compound O.O.O.O.O.O.O.[Fe+2].[O-]S([O-])(=O)=O SURQXAFEQWPFPV-UHFFFAOYSA-L 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
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- 230000007246 mechanism Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000003541 multi-stage reaction Methods 0.000 description 1
- 229910000483 nickel oxide hydroxide Inorganic materials 0.000 description 1
- RRIWRJBSCGCBID-UHFFFAOYSA-L nickel sulfate hexahydrate Chemical compound O.O.O.O.O.O.[Ni+2].[O-]S([O-])(=O)=O RRIWRJBSCGCBID-UHFFFAOYSA-L 0.000 description 1
- 229940116202 nickel sulfate hexahydrate Drugs 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 230000027756 respiratory electron transport chain Effects 0.000 description 1
- 229910052707 ruthenium Inorganic materials 0.000 description 1
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- 238000003756 stirring Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- YJBKVPRVZAQTPY-UHFFFAOYSA-J tetrachlorostannane;dihydrate Chemical compound O.O.Cl[Sn](Cl)(Cl)Cl YJBKVPRVZAQTPY-UHFFFAOYSA-J 0.000 description 1
- 125000000101 thioether group Chemical group 0.000 description 1
- FWPIDFUJEMBDLS-UHFFFAOYSA-L tin(II) chloride dihydrate Chemical compound O.O.Cl[Sn]Cl FWPIDFUJEMBDLS-UHFFFAOYSA-L 0.000 description 1
- HPGGPRDJHPYFRM-UHFFFAOYSA-J tin(iv) chloride Chemical compound Cl[Sn](Cl)(Cl)Cl HPGGPRDJHPYFRM-UHFFFAOYSA-J 0.000 description 1
- 229910052723 transition metal Inorganic materials 0.000 description 1
- 150000003624 transition metals Chemical class 0.000 description 1
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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
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
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- Electrodes For Compound Or Non-Metal Manufacture (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
- Electroplating And Plating Baths Therefor (AREA)
- Inert Electrodes (AREA)
Abstract
Description
本発明は、本発明は、水の電気分解による水素等の電解製造に用いる電極に関し、特に、非貴金属で高い触媒活性及び高耐久性を有した電極及びその製造法に関する。 TECHNICAL FIELD The present invention relates to an electrode for use in the electrolytic production of hydrogen or the like by electrolysis of water, and more particularly to a non-precious metal electrode having high catalytic activity and high durability, and a method for producing the same.
今日、化石燃料の枯渇が問題視される中、クリーンで且つ、持続可能な代替エネルギー源を探すことが急務とされている。この問題の解決策として、水素キャリア社会の実現が挙げられる。水素キャリア社会では、水電解を通してＣＯ２を排出しない水素を生産し、その水素をエネルギーが必要な際に、燃料電池等を用いエネルギーへと変換することができる。すなわち、水素自身が新たなエネルギー媒体となる。炭素社会から脱却できるこの水素キャリア社会を構築するため、現在、世界中で水素燃料の生産コストを削減する努力がなされている。水素生産コスト削減のため、中でも、水電解で使用される電極の性能を上げることがキーテクノロジーとされている。 As depletion of fossil fuels is regarded as a problem today, there is an urgent need to find clean and sustainable alternative energy sources. A solution to this problem is the realization of a hydrogen carrier society. In the hydrogen carrier society, hydrogen that does not emit CO 2 can be produced through water electrolysis, and the hydrogen can be converted into energy using a fuel cell or the like when energy is required. That is, hydrogen itself becomes a new energy medium. In order to build this hydrogen carrier society that can escape from the carbon society, efforts are currently being made to reduce the production cost of hydrogen fuel all over the world. In order to reduce the cost of hydrogen production, among other things, improving the performance of the electrodes used in water electrolysis is considered a key technology.
現在、水素キャリア社会実現のために国が示している水素基本戦略では、水素製造コストの単価を20 円／Ｎｍ３以下に抑えることを目標として掲げている。水素製造コストには水電解装置の運転に関する設備費、維持費、人件費等、が考慮されているが、中でも電気代が大きく寄与するとされている。できるだけ、安価で水素を製造するためには、水の電解反応を生じさせるための電気代を如何に節約するかが問われ、本発明のような電極の高機能化が重要視される。国立研究開発法人新エネルギー・産業技術総合開発機構（ＮＥＤＯ）では水電解においてセル電流密度600 mA/cm２にて1.8 V以下の電解電圧となるようなセルの構築を目標として掲げており、この値を目標に電極開発がなされている。 At present, the government's Basic Hydrogen Strategy for the realization of a hydrogen carrier society aims to keep the unit cost of hydrogen production below 20 yen/ Nm3 . Equipment costs, maintenance costs, personnel costs, and the like related to the operation of the water electrolyzer are taken into account in the hydrogen production cost, and among others, it is said that the electricity cost contributes greatly. In order to produce hydrogen as inexpensively as possible, how to save the cost of electricity for causing the electrolysis reaction of water is a question, and high functionality of the electrode as in the present invention is important. The New Energy and Industrial Technology Development Organization (NEDO), a national research and development agency, has set a goal of constructing a cell that produces an electrolysis voltage of 1.8 V or less at a cell current density of 600 mA/ cm2 in water electrolysis. Electrodes are being developed with the goal of achieving these values.
特に、水電解の性能を上げることにおけるボトルネックは、水電解装置の陰極で行われる水素発生反応及び陽極で行われるＯＥＲ（酸素発生反応）である。両反応は多段階反応であり、本質的に遅い反応速度を有することが知られているが、特にＯＥＲは４つのプロトン共役電子移動が含まれているため、陽極の高効率化が求められている。これら問題点から、水電解を商用運転させるとなると、Ｐｔ（白金）、 Ｒｕ（ルテニウム）及びＩｒ（イリジウム）ベースの酸化物などの貴金属系の電極を使用しているのが現状である。しかしながら、これらの電極はコストが高く、希少性があり、耐久性が低いなどの欠点により、大規模な使用が大幅に制限されている。
そこで、安価な触媒金属としてＮｉ（ニッケル）やＣｏ（コバルト）等の非貴金属が広く用いられてきた。そして、特許文献１では、「溶解性電極触媒」という名称でＮｉにＳｎ（スズ）を複合させた非貴金属のＮｉ－Ｓｎ複合膜に関する発明が開示されている。この発明では、水素発生反応(２Ｈ＋＋２ｅ-＝Ｈ２)を伴う陰極として使用した際、電解中にＳｎが選択的に溶解し、電解時間が増すごとにつれ、電極表面の表面積が増大し、活性が維持されるという機能を発揮することができる。
また、貴金属電極の代替となる電極として非貴金属のＮｉ－Ｆｅ（ニッケル鉄）合金などの遷移金属が注目されており、これらは活性が高く、安価でかつ、地殻資源として豊富であるという理由から、これまで多くの検討がなされてきた。そして、非特許文献１では、表面積を増大させる狙いから、Ｎｉ－Ｆｅ合金にＳｎを添加する研究も開示されている（非特許文献１）。
この非特許文献１では、電解中に生じるＮｉＯＯＨ（オキシ水酸化ニッケル）の電気伝導率を向上させ、酸素過電圧を低減させることができるＮｉ－Ｆｅ合金化の効果と電極表面の凹凸形成に寄与するＳｎを複合化させたＮｉ－Ｆｅ－Ｓｎ複合電極に関する技術が開示されている。
In particular, the bottleneck in improving the performance of water electrolysis is the hydrogen evolution reaction that takes place at the cathode of the water electrolysis device and the OER (oxygen evolution reaction) that takes place at the anode. Both reactions are multi-step reactions and are known to have inherently slow reaction kinetics. In particular, OER involves four proton-conjugated electron transfers, so high efficiency of the anode is required. there is Due to these problems, when it comes to commercial operation of water electrolysis, the current situation is to use noble metal electrodes such as Pt (platinum), Ru (ruthenium) and Ir (iridium) based oxides. However, drawbacks such as high cost, scarcity and low durability of these electrodes severely limit their large-scale use.
Therefore, non-precious metals such as Ni (nickel) and Co (cobalt) have been widely used as inexpensive catalyst metals. Patent Document 1 discloses an invention related to a non-noble metal Ni—Sn composite film in which Sn (tin) is combined with Ni under the name of “soluble electrode catalyst”. In the present invention, when used as a cathode with a hydrogen evolution reaction (2H + +2e − =H 2 ), Sn is selectively dissolved during electrolysis, and as the electrolysis time increases, the surface area of the electrode surface increases, It can exhibit the function of maintaining activity.
In addition, transition metals such as non-precious Ni-Fe (nickel iron) alloys are attracting attention as electrodes that can be substituted for noble metal electrodes, because they are highly active, inexpensive, and abundant as crustal resources. has been extensively studied so far. Non-Patent Document 1 also discloses a study of adding Sn to a Ni—Fe alloy for the purpose of increasing the surface area (Non-Patent Document 1).
In this non-patent document 1, it contributes to the effect of Ni-Fe alloying that can improve the electrical conductivity of NiOOH (nickel oxyhydroxide) generated during electrolysis and reduce the oxygen overvoltage and the formation of unevenness on the electrode surface. A technique relating to a Ni--Fe--Sn composite electrode in which Sn is compounded has been disclosed.
しかしながら、特許文献１に開示される発明では、酸素発生反応(４ＯＨ-＝２Ｈ２Ｏ＋Ｏ２＋４ｅ-)に伴う陽極として使用すると、前述の水素発生反応のメカニズムとは異なるため、Ｎｉ－Ｓｎ複合膜を陽極に使用しても十分な活性及び耐久性は得られないという課題があった。
また、非特許文献１に開示される技術では、電気めっき法を用いたＮｉ－Ｆｅ－Ｓｎ複合電極の作製方法として、めっき電流密度を20 mA/cm２とし、めっき浴中に含まれるＮｉ、Ｆｅ、Ｓｎの３元素の前駆体としては硫酸塩を用いている。このような方法で作製した電極では、膜中の結晶子サイズが微細化しておらず、ＥＣＳＡ（電気化学的活性表面積）が増大せず、十分な触媒活性は得られないという課題があった。そして、実際に商用運転を模擬したセルにこれら電極を使用すると、高い触媒活性が得られず、あるいは一定時間を過ぎると触媒活性が低下してしまうという課題があった。
なお、ＥＣＳＡとは、ＢＥＴ法（ＢＥＴの吸着等温式に基づく表面積測定法）などで算出する物理的な表面積とは異なり、溶液中で電気化学反応を行うことができる電極中の反応場の表面積のことを言う。測定方法としては、サイクリックボルタンメトリー（ＣＶ）解析からＣｄｌ（電気二重層静電容量）を算出する方法が一般的である。
本発明はかかる従来の事情に対処してなされたものであり、貴金属電極の代替となる材料・製造コストの安い非貴金属電極を採用した水電解反応に関わり、触媒活性度が高く、その高い触媒活性度を長時間に亘って維持可能な高い耐久性を備えた水電解用の非貴金属電極とその製造方法を提供することを目的とする。
However, in the invention disclosed in Patent Document 1, when used as an anode accompanying the oxygen evolution reaction (4OH - = 2H 2 O + O 2 + 4e - ), the mechanism of the hydrogen evolution reaction is different from that of the above-mentioned hydrogen evolution reaction. is used as the anode, there is a problem that sufficient activity and durability cannot be obtained.
In addition, in the technique disclosed in Non-Patent Document 1, as a method for producing a Ni--Fe--Sn composite electrode using an electroplating method, the plating current density is set to 20 mA/cm 2 and Ni contained in the plating bath, Sulfate is used as a precursor of the three elements of Fe and Sn. The electrode produced by such a method has the problem that the crystallite size in the film is not refined, the ECSA (electrochemically active surface area) is not increased, and sufficient catalytic activity is not obtained. When these electrodes are used in cells simulating actual commercial operation, there is a problem that high catalytic activity cannot be obtained, or the catalytic activity decreases after a certain period of time.
Note that ECSA is different from the physical surface area calculated by the BET method (surface area measurement method based on the adsorption isotherm of BET), etc., and the surface area of the reaction field in the electrode that can perform an electrochemical reaction in a solution. say about As a measuring method, a method of calculating C dl (electric double layer capacitance) from cyclic voltammetry (CV) analysis is generally used.
The present invention has been made in response to such conventional circumstances, and is related to a water electrolysis reaction that employs a non-precious metal electrode that is a substitute for a noble metal electrode and has a low manufacturing cost, and has a high catalytic activity and a high catalyst. An object of the present invention is to provide a highly durable non-noble metal electrode for water electrolysis that can maintain activity over a long period of time, and a method for producing the same.
上記目的を達成するため、第１の発明である水電解用の非貴金属電極は、基材と、この基材上に設けられたＮｉ－Ｆｅ－Ｓｎ複合膜と、を有し、前記Ｎｉ－Ｆｅ－Ｓｎ複合膜は、Ｎｉ、Ｆｅ及びＳｎの合計を100質量％としたとき、Ｆｅ含有率が3 ～ 15質量％、Ｎｉ含有率が50 ～ 65質量％、Ｓｎ含有率が30 ～ 50質量％であることを特徴とするものである。
上記構成の水電解用の非貴金属電極では、Ｎｉ－Ｆｅ－Ｓｎ複合膜の高いＦｅ含有率によって膜中の結晶子サイズが減少するように作用し、これによって電極としての反応場が増加するという作用を有する。
In order to achieve the above object, a first invention provides a non-noble metal electrode for water electrolysis, comprising a base material and a Ni--Fe--Sn composite film provided on the base material, wherein the Ni-- The Fe—Sn composite film has a Fe content of 3 to 15 mass%, a Ni content of 50 to 65 mass%, and a Sn content of 30 to 50 mass%, where the total of Ni, Fe, and Sn is 100 mass%. %.
In the non-precious metal electrode for water electrolysis with the above structure, the high Fe content of the Ni-Fe-Sn composite film acts to reduce the crystallite size in the film, which increases the reaction field as an electrode. have an effect.
第２の発明である水電解用の非貴金属電極は、第１の発明において、前記Ｎｉ－Ｆｅ－Ｓｎ複合膜は、電気化学有効表面積（ＥＣＳＡ）が1.0 ～ 2.9 m２/gの範囲であることを特徴とするものである。
上記構成の水電解用の非貴金属電極では、ＥＣＳＡが十分大きいため、電極としての反応場が増加するという作用を有する。
The second invention is a non-noble metal electrode for water electrolysis, wherein the Ni--Fe--Sn composite film has an electrochemical effective surface area (ECSA) in the range of 1.0 to 2.9 m 2 /g in the first invention. It is characterized by
Since the non-noble metal electrode for water electrolysis having the above structure has a sufficiently large ECSA, it has the effect of increasing the reaction field as the electrode.
第３の発明である水電解用の非貴金属電極は、第１又は第２の発明において、前記Ｎｉ－Ｆｅ－Ｓｎ複合膜は、(102)面の結晶子サイズが15 ～ 100 Åであることを特徴とするものである。
上記構成の水電解用の非貴金属電極では、Ｎｉ－Ｆｅ－Ｓｎ複合膜の結晶子サイズが小さいため、電極としての反応場が増加するという作用を有する。
A third invention is a non-noble metal electrode for water electrolysis, wherein the Ni-Fe-Sn composite film has a (102) plane crystallite size of 15 to 100 Å in the first or second invention. It is characterized by
In the non-noble metal electrode for water electrolysis having the above structure, the Ni--Fe--Sn composite film has a small crystallite size, so that the reaction field as an electrode increases.
第４の発明である水電解用の非貴金属電極は、第１乃至第３のいずれか１つの発明において、前記Ｎｉ－Ｆｅ－Ｓｎ複合膜は、電流密度400 mA/cm２で18時間、電流密度500 mA/cm２で18時間、電流密度600 mA/cm２で18時間、電流密度700 mA/cm２で18時間、電流密度800 mA/cm２で58時間、合計130時間の運転が継続できる耐久性を有することを特徴とするものである。
上記構成の水電解用の非貴金属電極では、長時間の運転が継続されるように作用する。
A fourth invention is a non-noble metal electrode for water electrolysis according to any one of the first to third inventions, wherein the Ni--Fe--Sn composite film is applied at a current density of 400 mA/cm 2 for 18 hours. Continuous operation for 18 hours at a density of 500 mA/ cm2 , 18 hours at a current density of 600 mA/ cm2 , 18 hours at a current density of 700 mA/ cm2 , and 58 hours at a current density of 800 mA/ cm2 for a total of 130 hours. It is characterized by its durability.
The non-precious metal electrode for water electrolysis having the above configuration functions to continue operation for a long period of time.
第５の発明である水電解用の非貴金属電極の製造方法では、基材上に前駆体となる塩化物塩を湿式成膜法によって配置する工程と、前記湿式成膜法によってＮｉ－Ｆｅ－Ｓｎ複合膜を成膜する成膜工程と、を有し、前記成膜工程におけるめっき電流密度は40 ～ 100 mA/cm２であることを特徴とするものである。
上記構成の水電解用の非貴金属電極の製造方法では、前駆体として塩化物塩を湿式成膜法によって配置する工程と、めっき電流密度を40 ～ 100 mA/cm２として成膜する工程が、Ｎｉ－Ｆｅ－Ｓｎ複合膜のＦｅ含有率を高め、結晶子を微細化してＥＣＳＡを十分に増大させるように作用し、電極としての反応場を増加させるように作用する。また、長時間運転を可能とする高い耐久性を備えたＮｉ－Ｆｅ－Ｓｎ複合膜を成膜するように作用する。
In the method for producing a non-noble metal electrode for water electrolysis, which is the fifth invention, a step of disposing a chloride salt as a precursor on a substrate by a wet film-forming method, and Ni--Fe-- by the wet film-forming method. and a film forming step of forming a Sn composite film, wherein the plating current density in the film forming step is 40 to 100 mA/cm 2 .
In the method for producing a non-precious metal electrode for water electrolysis having the above configuration, the steps of disposing a chloride salt as a precursor by a wet film-forming method and forming a film at a plating current density of 40 to 100 mA/cm 2 are performed. It acts to increase the Fe content of the Ni--Fe--Sn composite film, refine the crystallites, sufficiently increase the ECSA, and act to increase the reaction field as an electrode. It also acts to form a Ni--Fe--Sn composite film with high durability that enables long-term operation.
第１の発明に係る水電解用の非貴金属電極では、高い触媒活性度を発揮することが可能である。 The non-precious metal electrode for water electrolysis according to the first invention can exhibit high catalytic activity.
第２の発明に係る水電解用の非貴金属電極においても、高い触媒活性度を発揮することが可能である。 The non-precious metal electrode for water electrolysis according to the second invention can also exhibit high catalytic activity.
第３の発明に係る水電解用の非貴金属電極においても、高い触媒活性度を発揮することが可能である。 The non-noble metal electrode for water electrolysis according to the third invention can also exhibit high catalytic activity.
第４の発明に係る水電解用の非貴金属電極では、第１の発明乃至第３の発明における高い触媒活性度に関する効果に加えて、高い耐久性を発揮することが可能である。 The non-precious metal electrode for water electrolysis according to the fourth invention can exhibit high durability in addition to the effect of high catalytic activity in the first to third inventions.
第５の発明に係る水電解用の非貴金属電極の製造方法では、高い触媒活性度と高い耐久性を発揮することが可能な水電解用の非貴金属電極を製造することが可能である。 In the method for producing a non-noble metal electrode for water electrolysis according to the fifth invention, it is possible to produce a non-noble metal electrode for water electrolysis that can exhibit high catalytic activity and high durability.
以下に、本発明の実施の形態に係る水電解用の非貴金属電極及びその製造方法について図１及び図２を参照しながら説明する。
図１は本実施の形態に係る水電解用の非貴金属電極の製造方法のフロー図である。
図１において、ステップＳ１は基材の前処理工程である。本実施の形態において使用される基材は、アルカリ溶液中でも耐食性を有するＮｉが好ましいが、実際に溶液中に暴露される箇所は基材表面を被覆した膜であるため、Ｃｕ（銅）やＡｌ（アルミニウム）等の安価な材料でもよい。但し、基材は反応時に発生する気体の泡離れを効率よく行うため、メッシュ状であることが望ましい。
このステップＳ１の基材の前処理工程の前処理としては、脱脂処理と活性化処理を行う。
具体的には、例えば脱脂処理としては、１分間程度のアルカリ電解脱脂処理を行うが、この処理では基材表面の油分等のいわゆるコンタミ成分を取り除くことを目的としている。処理の内容としては、アルカリ溶液中で、カソードに処理対象の基材を設置し、アノードにはＰｔプレートを設置してカソードの電流密度20 ～ 50 mA/cm２で１分間程度通電するものである。
また、活性化処理としては、塩化第二鉄が含まれた塩酸中で浸漬させ、基材表面に形成されている酸化被膜を取り除く処理を行う。
EMBODIMENT OF THE INVENTION Below, it demonstrates, referring FIG.1 and FIG.2 for the non-noble metal electrode for water electrolysis and its manufacturing method which concern on embodiment of this invention.
FIG. 1 is a flowchart of a method for manufacturing a non-precious metal electrode for water electrolysis according to this embodiment.
In FIG. 1, step S1 is a pretreatment step for the substrate. The substrate used in the present embodiment is preferably Ni, which has corrosion resistance even in an alkaline solution. Inexpensive materials such as (aluminum) may also be used. However, it is desirable that the substrate be mesh-like in order to efficiently release bubbles of gas generated during the reaction.
Degreasing treatment and activation treatment are performed as the pretreatment of the base material pretreatment process in step S1.
Specifically, as the degreasing treatment, for example, an alkaline electrolytic degreasing treatment is performed for about one minute, and this treatment is intended to remove so-called contaminants such as oil on the base material surface. The contents of the treatment consisted of placing the base material to be treated on the cathode and placing the Pt plate on the anode in an alkaline solution and applying current at the cathode current density of 20 to 50 mA/cm 2 for about 1 minute. be.
As the activation treatment, the substrate is immersed in hydrochloric acid containing ferric chloride to remove the oxide film formed on the surface of the substrate.
ステップＳ２は、基材上へ前駆体である塩化物塩を配置する工程である。具体的には、湿式成膜法として基材をめっき浴へ浸漬する工程である。めっき浴組成は、0.06 mol/dm３のＮｉＣｌ２・６Ｈ２Ｏ（塩化ニッケル６水和物）、0.02 mol/dm３のＳｎＣｌ２・２Ｈ２Ｏ（塩化スズ２水和物）、0.02 mol/dm３のＦｅＣｌ３・２Ｈ２Ｏ（塩化鉄２水和物）、0.025 mol/dm３のＫ２Ｐ２Ｏ７（ピロリン酸）、0.1 mol/dm３のＣ２Ｈ５ＮＯ２（グリシン）で、ｐＨが７となるように、ＨＣｌ（塩酸）とＮａＯＨ（水酸化ナトリウム）を用いて調整する。
なお、めっき組成としては上記の値に特定されるのではなく、ＮｉＣｌ２・６Ｈ２Ｏ（塩化ニッケル６水和物）は0.001 ～ 0.5 mol/dm３、ＳｎＣｌ２・２Ｈ２Ｏ（塩化スズ２水和物）は0.001 ～ 0.5 mol/dm３、ＦｅＣｌ３・２Ｈ２Ｏ（塩化鉄２水和物）は0.01 ～ 0.1 mol/dm３、Ｋ２Ｐ２Ｏ７（ピロリン酸）は0.1 ～ 1 mol/dm３、Ｃ２Ｈ５ＮＯ２（グリシン）は0.05 ～ 1 mol/dm３であれば電析による成膜に望ましい条件となる。
Step S2 is a step of disposing a chloride salt, which is a precursor, on the substrate. Specifically, it is a step of immersing the substrate in a plating bath as a wet film forming method. The plating bath composition is 0.06 mol/ dm3 NiCl2.6H2O (nickel chloride hexahydrate), 0.02 mol/ dm3 SnCl2.2H2O (tin chloride dihydrate), 0.02 mol / dm3 dm 3 FeCl 3 .2H 2 O (iron chloride dihydrate), 0.025 mol/dm 3 K 2 P 2 O 7 (pyrophosphate), 0.1 mol/dm 3 C 2 H 5 NO 2 (glycine) , pH is adjusted to 7 using HCl (hydrochloric acid) and NaOH (sodium hydroxide).
The plating composition is not limited to the above values, but NiCl 2 .6H 2 O (nickel chloride hexahydrate) is 0.001 to 0.5 mol/dm 3 , SnCl 2 .2H 2 O (
ステップＳ３は、本実施の形態に係る水電解用の非貴金属電極（以下、Ｎｉ－Ｆｅ－Ｓｎ電極ともいう。）を構成する複合膜（以下、単にＮｉ－Ｆｅ－Ｓｎ複合膜ともいう。）を基材上に成膜する工程である。めっきの浴温度は50 ℃として常時撹拌しながら行う。電解条件は、電流密度を80 mA/cm２で２時間めっきする。このようにしてＮｉ－Ｆｅ－Ｓｎ複合膜が基材上に成膜される。
なお、めっきの浴温度及びめっき電流密度は上記の値に特定されるものではなく、めっき浴温度は20 ～ 90 ℃であればよく、めっき電流密度は40 ～100 mA/cm２であればよい。
以上のようなステップＳ１～Ｓ３を経て水電解用の非貴金属電極が作製される。
作製されたＮｉ－Ｆｅ－Ｓｎ複合膜が形成されたＮｉ－Ｆｅ－Ｓｎ電極の表面のＳＥＭ画像を図２（ａ）に示す。本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極の複合膜は10 μｍ程度の粒子が凝集し、カリフラワー状の凹凸が形成されていることがわかる。
また、Ｎｉ－Ｆｅ－Ｓｎ複合膜の組成を、エネルギー分散型成分分析装置によって定量した。その結果、Ｎｉ、Ｆｅ及びＳｎの合計組成濃度を100 質量％としたとき、Ｆｅ含有量は5.32 質量％ 、Ｎｉ含有量は59.15 質量％ 、Ｓｎ含有量は35.53 質量％であった。
In step S3, a composite film (hereinafter simply referred to as a Ni-Fe-Sn composite film) constituting a non-noble metal electrode for water electrolysis (hereinafter also referred to as a Ni-Fe-Sn electrode) according to the present embodiment is is a step of forming a film on the base material. The plating bath temperature is set at 50°C and the plating is always stirred. The electrolysis conditions are plating at a current density of 80 mA/cm 2 for 2 hours. Thus, a Ni--Fe--Sn composite film is formed on the substrate.
The plating bath temperature and plating current density are not limited to the above values, and the plating bath temperature may be 20 to 90 ° C., and the plating current density may be 40 to 100 mA/cm 2 . .
A non-precious metal electrode for water electrolysis is produced through steps S1 to S3 as described above.
A SEM image of the surface of the Ni--Fe--Sn electrode on which the Ni--Fe--Sn composite film was formed is shown in FIG. 2(a). In the composite film of the Ni--Fe--Sn electrode according to the present embodiment, particles of about 10 μm are aggregated to form cauliflower-like irregularities.
Also, the composition of the Ni--Fe--Sn composite film was quantified by an energy dispersive component analyzer. As a result, when the total composition concentration of Ni, Fe and Sn is 100% by mass, the Fe content was 5.32% by mass, the Ni content was 59.15% by mass, and the Sn content was 35.53% by mass.
次に、本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極の複合膜の特性について、図３乃至図９を参照しながら、従来技術に係る非貴金属電極であるＮｉ－Ｆｅ電極の基材上に成膜されたＮｉ－Ｆｅ複合膜及び従来技術に係る非貴金属電極であるＮｉ－Ｓｎ電極の基材上に成膜されたＮｉ－Ｓｎ複合膜と比較する。
＜従来技術に係る複合膜の作製＞
水電解用の非貴金属電極を構成するＮｉ－Ｆｅ－Ｓｎ複合膜の製造方法と条件と統一するためにめっき浴の組成を除いて図１に示す製造方法によって作製した。
すなわち、Ｎｉ－Ｆｅ複合膜は、図１のステップＳ３においてＳｎＣｌ２・２Ｈ２Ｏを除いためっき浴組成とし、その他は図１のステップＳ１～Ｓ３に示される工程を実施して作製した。このようにして作製されたＮｉ－Ｆｅ複合膜が形成されたＮｉ－Ｆｅ電極の表面のＳＥＭ画像を図２（ｂ）に示す。
このＮｉ－Ｆｅ複合膜では、凹凸のない滑らかな表面ではあるが、電気めっき処理時の内部応力に起因すると思われるクラックが形成されていることがわかる。
Ｎｉ－Ｓｎ複合膜も、図１のステップＳ３においてＦｅＣｌ３・２Ｈ２Ｏを除いためっき浴組成として、その他は図１のステップＳ１～Ｓ３に示される工程を実施して作製した。このようにして作製されたＮｉ－Ｓｎ複合膜が形成されたＮｉ－Ｓｎ電極の表面のＳＥＭ画像を図２（ｃ）に示す。
このＮｉ－Ｓｎ複合膜では、Ｎｉ－Ｆｅ－Ｓｎ複合膜と同様に10 μｍ程度の粒子が凝集し、カリフラワー状の凹凸が形成されていることがわかる。
Next, with reference to FIGS. 3 to 9, the characteristics of the composite film of the Ni—Fe—Sn electrode according to the present embodiment will be described. A Ni--Fe composite film deposited and a Ni--Sn composite film deposited on a substrate of a Ni--Sn electrode, which is a non-noble metal electrode according to the prior art, are compared.
<Preparation of composite membrane according to conventional technology>
In order to unify the manufacturing method and conditions of the Ni--Fe--Sn composite film constituting the non-noble metal electrode for water electrolysis, the manufacturing method shown in FIG. 1 was used except for the composition of the plating bath.
That is, the Ni--Fe composite film was produced by using a plating bath composition excluding SnCl 2 .2H 2 O in step S3 of FIG. 1, and performing the other steps shown in steps S1 to S3 of FIG. FIG. 2(b) shows a SEM image of the surface of the Ni--Fe electrode on which the Ni--Fe composite film thus produced is formed.
Although the Ni--Fe composite film has a smooth surface without irregularities, it can be seen that cracks are formed which are thought to be caused by internal stress during the electroplating process.
The Ni—Sn composite film was also produced by performing the steps shown in steps S1 to S3 of FIG. 1, with the plating bath composition excluding FeCl 3 .2H 2 O in step S3 of FIG. FIG. 2(c) shows a SEM image of the surface of the Ni—Sn electrode on which the Ni—Sn composite film thus produced was formed.
It can be seen that in this Ni--Sn composite film, particles of about 10 μm are agglomerated to form cauliflower-like irregularities, as in the Ni--Fe--Sn composite film.
＜本実施の形態と従来技術に係る複合膜の結晶構造の比較＞
図３を参照しながら、本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極の複合膜と従来技術に係るＮｉ－Ｆｅ電極とＮｉ－Ｓｎ電極の複合膜の結晶構造を比較して説明する。
結晶構造はＸＲＤ（Ｘ線回折）装置を用いて解析した。Ｘ線源としてＣｕＫα放射線（λ＝0.154051ｎｍ）を使用した。また、解析条件としては、40 kVのビーム電圧と30 mAのビーム電流下で1°/分のスキャン速度とし、25°から80°までの2θ（回折角）領域に亘って回折されたＸ線を測定した。
図３は、本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極の複合膜(c)に加え、従来のＮｉ－Ｆｅ電極の複合膜(a)及びＮｉ－Ｓｎ電極の複合膜(b)の結晶構造の解析結果を示すグラフである。横軸は２θ（回折角）を示しており、縦軸は回折Ｘ線の強度を示している。
その結果、Ｎｉ－Ｆｅ複合膜ではＦｅＮｉ３（ICSD No.01-077-7971 a＝3.55Å、b＝3.55Å、c＝3.55Å、V＝44.706Å３）に帰属されることがわかった。Ｎｉ－ＦｅのようにＳｎを添加していない複合膜では、シャープな回折パターンが得られ結晶性を有していることが分かった。
一方、Ｎｉ－Ｓｎ複合膜及びＮｉ－Ｆｅ－Ｓｎ複合膜は、43°付近にＮｉ３Ｓｎ２（ICSD No.01-072-2561 a＝4.103Å、b＝4.103Å、c＝5.178Å、V＝75.491Å３）の(101)、(102)、(110) に帰属されるブロードなピークが存在することからアモルファスに近い構造をとることが確認された。
<Comparison of the crystal structure of the composite film according to the present embodiment and the conventional technology>
With reference to FIG. 3, the crystal structures of the composite film of the Ni--Fe--Sn electrode according to the present embodiment and the composite film of the Ni--Fe and Ni--Sn electrodes according to the prior art will be compared and explained.
The crystal structure was analyzed using an XRD (X-ray diffraction) device. CuKα radiation (λ=0.154051 nm) was used as the X-ray source. The analysis conditions were a beam voltage of 40 kV, a beam current of 30 mA, and a scan rate of 1°/min. was measured.
FIG. 3 shows crystals of a conventional Ni—Fe electrode composite film (a) and a Ni—Sn electrode composite film (b) in addition to the Ni—Fe—Sn electrode composite film (c) according to the present embodiment. It is a graph which shows the analysis result of a structure. The horizontal axis indicates 2θ (diffraction angle), and the vertical axis indicates the intensity of diffracted X-rays.
As a result, it was found that the Ni—Fe composite film was attributed to FeNi 3 (ICSD No.01-077-7971 a=3.55 Å, b=3.55 Å, c=3.55 Å, V=44.706 Å 3 ). It was found that a composite film such as Ni—Fe to which Sn was not added gave a sharp diffraction pattern and had crystallinity.
On the other hand, the Ni—Sn composite film and the Ni—Fe—Sn composite film have Ni 3 Sn 2 (ICSD No.01-072-2561 a=4.103 Å, b=4.103 Å, c=5.178 Å, V = 75.491 Å 3 ), which is attributed to (101), (102), and (110), confirming that it has an almost amorphous structure.
＜本実施の形態と従来技術に係る複合膜の酸素過電圧の測定比較＞
図４を参照しながら、各複合膜の触媒性能を比較するために、本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極の複合膜と従来技術に係るＮｉ－Ｆｅ電極とＮｉ－Ｓｎ電極の複合膜及びbareＮｉの酸素過電圧を測定し比較した結果について説明する。
図４は本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極の複合膜、従来技術に係るＮｉ－Ｆｅ電極及びＮｉ－Ｓｎ電極の複合膜と、bareＮｉに対するＬＳＶ測定を実施した結果をまとめたグラフである。横軸の電圧では、未補償溶液抵抗（iR）の補償を行っている。すなわち、作用電極と参照電極の間の溶液抵抗に比例した電位降下分を考慮して、実測した電圧(V)から発生した電流値(i)×溶液抵抗(Ru)を差し引く補正を行っている。また、溶液抵抗はポテンショスタット（電気化学測定装置）では直接認識できないことからポジティブフィードバック法（正帰還）を採ってフィードバック率を60 ％として求めている。
ＬＳＶ測定は、1.0 MのＫＯＨの水溶液中で、1 mV/sのスキャン速度で開回路電位から実行した。過電圧（η）の算出は、電流密度10 mA/cm２に到達するまでに要する電位をη１０＝Ｅ（ＲＨＥ）-1.23 V（酸素発生理論電位）として計算した。この酸素過電圧が低いほど触媒性能が高いとして評価できる。
具体的には、図４おいて、縦軸の電流密度10 mA/cm２における電圧はＮｉ－Ｆｅ－Ｓｎ複合膜で1.523 mVとなり、過電圧（η１０）はη１０＝1.523-1.23で293 mVとなる。同様に他の複合膜の過電圧も計算すると、Ｎｉ－Ｆｅ－Ｓｎ複合膜（η１０＝293 mV）＜Ｎｉ－Ｆｅ複合膜（η１０＝303 mV）＜Ｎｉ－Ｓｎ複合膜（η１０＝337 mV）＜Ｎｉ膜（η１０＝351 mV）の順となり、Ｎｉ－Ｆｅ－Ｓｎ複合膜を形成するＮｉ－Ｆｅ－Ｓｎ電極の酸素触媒活性が最も優れていることが確認できた。
したがって、本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極は、他の非貴金属電極を備える従来技術に比較して、陽極の酸素発生反応に顕著に優れた効果を発揮する。
<Comparison of Oxygen Overvoltage Measurements of Composite Films According to the Present Embodiment and Conventional Technology>
With reference to FIG. 4, in order to compare the catalytic performance of each composite film, the composite film of the Ni—Fe—Sn electrode according to the present embodiment and the composite film of the Ni—Fe electrode and the Ni—Sn electrode according to the prior art were used. The results of measuring and comparing the oxygen overvoltages of the film and bareNi will be described.
FIG. 4 is a graph summarizing the results of LSV measurement for the composite film of the Ni—Fe—Sn electrode according to the present embodiment, the composite film of the Ni—Fe electrode and the Ni—Sn electrode according to the prior art, and bareNi. be. The voltage on the horizontal axis compensates for the uncompensated solution resistance (iR). That is, considering the potential drop proportional to the solution resistance between the working electrode and the reference electrode, correction is performed by subtracting the generated current value (i) × solution resistance (Ru) from the actually measured voltage (V). . In addition, since the solution resistance cannot be directly recognized by a potentiostat (electrochemical measuring device), a positive feedback method (positive feedback) is adopted and the feedback rate is determined as 60%.
LSV measurements were performed from an open circuit potential in an aqueous solution of 1.0 M KOH with a scan rate of 1 mV/s. The overvoltage (η) was calculated by setting the potential required to reach a current density of 10 mA/cm 2 as η 10 =E(RHE)-1.23 V (theoretical potential for oxygen generation). It can be evaluated that the lower the oxygen overvoltage, the higher the catalytic performance.
Specifically, in FIG. 4, the voltage at a current density of 10 mA/cm 2 on the vertical axis is 1.523 mV for the Ni—Fe—Sn composite film, and the overvoltage (η 10 ) is 293 mV at η 10 =1.523-1.23. becomes. Similarly, when the overvoltages of other composite films are calculated, Ni—Fe—Sn composite film (η 10 =293 mV)<Ni—Fe composite film (η 10 =303 mV)<Ni—Sn composite film (η 10 =337 mV) mV)<Ni film (η 10 =351 mV), and it was confirmed that the Ni—Fe—Sn electrode forming the Ni—Fe—Sn composite film has the highest oxygen catalytic activity.
Therefore, the Ni--Fe--Sn electrode according to the present embodiment exhibits a remarkably superior effect on the oxygen evolution reaction at the anode as compared with the prior art including other non-precious metal electrodes.
＜本実施の形態と従来技術に係る複合膜の水素過電圧の測定比較＞
図５を参照しながら、各複合膜の触媒性能を比較するために、本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極の複合膜と従来技術に係るＮｉ－Ｆｅ電極とＮｉ－Ｓｎ電極の複合膜及びＮｉ膜の水素過電圧を測定し比較した結果について説明する。
図５は本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極の複合膜、従来技術に係るＮｉ－Ｆｅ電極及びＮｉ－Ｓｎ電極の複合膜と、bareＮｉに対するＬＳＶ測定を実施した結果をまとめたグラフである。ＬＳＶ測定は、1.0 MのＫＯＨの水溶液中で、1 mV/sのスキャン速度で開回路電位から実行した。過電圧（η）は、水素発生理論電位が0 V（vsＲＨＥ）であるため、電流密度10 mA/cm２に到達するまでに要する電位の絶対値を採用した。この水素過電圧も低いほど触媒性能が高いとして評価できる。
図５において、電流密度10 mA/cm２における水素過電圧（η１０）はＮｉ－Ｆｅ－Ｓｎ複合膜（η１０＝15 mV）＜Ｎｉ－Ｓｎ複合膜（η１０＝76 mV）＜Ｎｉ－Ｆｅ複合膜（η１０＝170 mV）＜bareＮｉ（η１０＝271 mV）の順となり、Ｎｉ－Ｆｅ－Ｓｎ複合膜を形成するＮｉ－Ｆｅ－Ｓｎ電極の水素触媒活性が最も優れていることが確認できた。
したがって、本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極は、他の非貴金属電極を備える従来技術に比較して、陰極の水素発生反応にも顕著に優れた効果を発揮する。
<Measurement Comparison of Hydrogen Overvoltage of Composite Membrane According to Present Embodiment and Conventional Technology>
With reference to FIG. 5, in order to compare the catalytic performance of each composite film, the composite film of the Ni--Fe--Sn electrode according to the present embodiment and the composite film of the Ni--Fe electrode and the Ni--Sn electrode according to the prior art The results of measuring and comparing the hydrogen overvoltages of the film and the Ni film will be described.
FIG. 5 is a graph summarizing the results of LSV measurement for the composite film of the Ni—Fe—Sn electrode according to the present embodiment, the composite film of the Ni—Fe electrode and the Ni—Sn electrode according to the prior art, and bareNi. be. LSV measurements were performed from an open circuit potential in an aqueous solution of 1.0 M KOH with a scan rate of 1 mV/s. As the overvoltage (η), the absolute value of the potential required to reach a current density of 10 mA/cm 2 was adopted, since the hydrogen generation theoretical potential is 0 V (vsRHE). It can be evaluated that the lower the hydrogen overvoltage, the higher the catalytic performance.
In FIG. 5, the hydrogen overvoltage (η 10 ) at a current density of 10 mA/cm 2 is Ni—Fe—Sn composite film (η 10 =15 mV)<Ni—Sn composite film (η 10 =76 mV)<Ni—Fe Composite membrane (η 10 = 170 mV) < bareNi (η 10 = 271 mV), confirming that the Ni-Fe-Sn electrode forming the Ni-Fe-Sn composite membrane has the best hydrogen catalytic activity. did it.
Therefore, the Ni--Fe--Sn electrode according to the present embodiment exhibits a remarkably superior effect on the hydrogen generation reaction at the cathode as compared with the conventional technology provided with other non-noble metal electrodes.
＜本実施の形態と従来技術に係る複合膜の耐久性の評価＞
図６を参照しながら、各複合膜の耐久性能を比較するために、本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極の複合膜と従来技術に係るＮｉ－Ｆｅ電極とＮｉ－Ｓｎ電極の複合膜に対し、クロノアンペロメトリー解析を実施して耐久性能を比較した結果について説明する。クロノアンペロメトリー解析では、電流密度400 mA/cm２で18時間、電流密度500 mA/cm２で18時間、電流密度600 mA/cm２で18時間、電流密度700 mA/cm２で18時間、電流密度800 mA/cm２で58時間、合計130時間、定電流測定を行い、電位変動を記録した。
図６は、本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極の複合膜、Ｎｉ－Ｆｅ電極及びＮｉ－Ｓｎ電極の複合膜の定電流測定（クロノアンペロメトリー解析）結果を示すグラフである。図６の横軸は時間（ｈ）であり縦軸は電位を示している。図６からＮｉ－Ｆｅ－Ｓｎ複合膜では測定時間中の電位の増加が少なく、Ｎｉ－Ｆｅ複合膜やＮｉ－Ｓｎ複合膜のように電流密度700 mA/cm２を超えた時点（横軸の72 hを超えた時点）からの急激な電位の増加現象も見られず、耐久性能が最も高いことが確認でき、最大で130 時間の継続運転が可能であることも確認できた。
さらに、Ｎｉ－Ｆｅ複合膜及びＮｉ－Ｓｎ複合膜では、測定当初からＮｉ－Ｆｅ－Ｓｎ複合膜よりも電位が高く、また、１時間当たりにおける電位の増加量もＮｉ－Ｆｅ－Ｓｎ複合膜よりも大きく、前述のとおり700 mA/cm２を超えた時点から急激に電位が増加して制御不能となる等の不具合が生じた。
したがって、本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極は、他の非貴金属電極を備える従来技術に比較して、耐久性にも顕著に優れた効果を発揮する。
<Evaluation of durability of composite membranes according to the present embodiment and conventional technology>
With reference to FIG. 6, in order to compare the durability performance of each composite film, the composite film of the Ni--Fe--Sn electrode according to the present embodiment and the composite of the Ni--Fe electrode and the Ni--Sn electrode according to the prior art The result of comparing durability performance by performing chronoamperometric analysis on the membrane will be described. In chronoamperometric analysis, current density of 400 mA/ cm2 for 18 hours, current density of 500 mA/ cm2 for 18 hours, current density of 600 mA/ cm2 for 18 hours, current density of 700 mA/ cm2 for 18 hours. , a current density of 800 mA/cm 2 for 58 hours, a total of 130 hours, and constant current measurements were performed to record potential fluctuations.
FIG. 6 is a graph showing the results of constant current measurement (chronoamperometry analysis) of the Ni--Fe--Sn electrode composite film, the Ni--Fe electrode, and the Ni--Sn electrode composite film according to the present embodiment. The horizontal axis of FIG. 6 represents time (h) and the vertical axis represents potential. From FIG. 6, the Ni--Fe--Sn composite film shows little increase in potential during the measurement time, and when the current density exceeds 700 mA/cm 2 like the Ni--Fe composite film and the Ni--Sn composite film (horizontal axis After 72 hours), no sudden increase in potential was observed, confirming that the durability performance was the highest, and that continuous operation for up to 130 hours was possible.
Furthermore, in the Ni-Fe composite film and the Ni-Sn composite film, the potential is higher than the Ni-Fe-Sn composite film from the beginning of the measurement, and the increase in potential per hour is also higher than that of the Ni-Fe-Sn composite film. As described above, the potential increased sharply from the point of exceeding 700 mA/cm 2 , causing problems such as uncontrollability.
Therefore, the Ni--Fe--Sn electrode according to the present embodiment exhibits a remarkably superior effect in terms of durability as compared with the prior art including other non-precious metal electrodes.
＜本実施の形態と従来技術に係る複合膜の商用条件における性能評価＞
商用条件での電解を模擬した水電解システムを構築し、前述の製造方法によって得られたＮｉ－Ｆｅ－Ｓｎ電極をＮｉ電極に代えてアノード（陽極）に使用した際と、Ｎｉ電極に代えてカソード（陰極）に使用した際の二極式電極セルの電解電圧の値を、従来技術に係るＮｉ－Ｆｅ電極とＮｉ－Ｓｎ電極及びＮｉ電極と比較しながら評価した。
まず、図７（ａ）に商用条件での電解を模擬した水電解システムの構成概念図と、図７（ｂ）に製作した実際の水電解システムの写真を示す。
図７（ａ）において、本評価の装置として、溶液抵抗を最小限に抑えるため、隔膜（日本アグフアマテリアルズ社製 Zirfon perl UTP 500）に電極を押し付け、隔膜と電極との距離を小さくしたゼロギャップ構造の電解セルを採用した。
その内部構造は、陰極室(Cathode cell)、陰極の集電体(Current collector)、クッション材(Ni mesh for cushioning)、陰極（Cathode）、隔膜(Diaphragm)、陽極（Anode）、陽極の集電体(Current collector)、陽極室(Anode cell)と並び、クッション材が陰極を隔膜へ押し付ける役割を果たし、ゼロギャップ構造が構築される仕組みとなっている。
ＫＯＨ溶液は、溶液タンク（図７（ｂ）のＫＯＨ tank）から電磁駆動定量ポンプ（イワキ社製 EHNC-BR；図７（ｂ）のPump）を用いて極室へ供給され、再び溶液タンクへ排出される構造となっている。
なお、商用条件を再現するため、30 wt％のＫＯＨ溶液を作製し、恒温槽（アズワン社製 TR-1）を用い、80 ℃に常時保温された溶液を極槽内へ供給することとした。両極室の上下には、ＫＯＨ溶液の供給及び排出用のフランジが設けられており、供給用の極室下部のフランジと電磁駆動定量ポンプ、排出用の極室上部のフランジと溶液タンクの間はPTFEチューブにより接続されている。排出用の極室上部のフランジ（図７（ａ）のFlange）と溶液タンクの間のPTFEチューブは二又となっているが、これは運転中、極室内部で発生した気体を極室外へ排出するためである。本評価装置の接液部分の材質は、ＫＯＨ溶液タンク、溶液送入のためのPTFEチューブ、隔膜を除き全てbareＮｉとした。
<Performance evaluation of composite membranes according to the present embodiment and conventional technology under commercial conditions>
A water electrolysis system simulating electrolysis under commercial conditions was constructed, and when the Ni-Fe-Sn electrode obtained by the above-described manufacturing method was used as an anode (anode) instead of the Ni electrode, and instead of the Ni electrode The value of the electrolysis voltage of the bipolar electrode cell when used as a cathode (cathode) was evaluated while comparing Ni--Fe, Ni--Sn and Ni electrodes according to the prior art.
First, FIG. 7(a) shows a conceptual diagram of a water electrolysis system simulating electrolysis under commercial conditions, and FIG. 7(b) shows a photograph of an actual water electrolysis system manufactured.
In FIG. 7(a), in order to minimize the solution resistance, the electrode was pressed against the diaphragm (
Its internal structure consists of a cathode cell, a current collector of the cathode, a Ni mesh for cushioning, a cathode, a diaphragm, an anode, and a current collector of the anode. Together with the current collector and the anode cell, the cushioning material plays a role in pressing the cathode against the diaphragm, creating a zero-gap structure.
The KOH solution is supplied from the solution tank (KOH tank in FIG. 7(b)) to the electrode chamber using an electromagnetically driven metering pump (EHNC-BR manufactured by Iwaki; Pump in FIG. 7(b)), and then to the solution tank again. It is designed to be ejected.
In order to reproduce commercial conditions, a 30 wt% KOH solution was prepared, and a constant temperature bath (AS ONE TR-1) was used to supply the solution, which was constantly kept at 80 °C, into the pole bath. . Flanges for supplying and discharging the KOH solution are provided above and below the bipolar chamber, between the flange at the bottom of the electrode chamber for supply and the electromagnetically driven metering pump, and between the flange at the top of the electrode chamber for discharge and the solution tank Connected by PTFE tube. The PTFE tube between the flange at the top of the electrode chamber for discharge (Flange in Fig. 7(a)) and the solution tank is bifurcated. It is for discharge. The wetted parts of this evaluation apparatus were all made of bare Ni except for the KOH solution tank, the PTFE tube for feeding the solution, and the diaphragm.
評価方法を以下に説明する。本評価装置の運転は、電解電圧の測定時を除き、セル電流密度を常時100 mA/cm２に保持し、３日間の連続運転を行った。電解電圧の測定は、両極槽の集電体にデジタルマルチメーターを接触させ、その際に表示される電圧値の値をセル電流密度（100，200，300，400，500，600 mA/cm２）ごとに計測することとした。電流密度の調整は、直流電源（菊水電子工業社製 PAS10-35）を用いた。電解電圧の測定回数は、所定の時間（10時と15時）に1日２回実施し、３日間の合計である計６回分の電圧値の平均値をセルの電解電圧値とした。 Evaluation methods are described below. The evaluation apparatus was operated continuously for 3 days while maintaining the cell current density at 100 mA/cm 2 at all times except when measuring the electrolysis voltage. The electrolysis voltage is measured by contacting the current collector of the bipolar tank with a digital multimeter, and measuring the voltage value displayed at that time with the cell current density (100, 200, 300, 400, 500, 600 mA/cm 2 ) was measured. A DC power supply (PAS10-35 manufactured by Kikusui Electronics Co., Ltd.) was used to adjust the current density. The electrolysis voltage was measured twice a day at predetermined times (10:00 and 15:00), and the average value of the voltage values for a total of six measurements over three days was taken as the electrolysis voltage value of the cell.
図８及び図９を参照しながら電解電圧の測定値について説明する。図８は本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極、Ｎｉ－Ｆｅ電極及びＮｉ－Ｓｎ電極を二極式電極セルの陽極に用いた商用条件での電極性能評価結果を示すグラフであり、図９は同様に陰極に用いた商用条件での電極性能評価結果を示すグラフである。
商用条件での電解を模擬した本水電解システムでは、電流密度を制御し、各電流密度における電圧値をそれぞれの電極に対して測定した。図４や図５に示された結果は実験室レベルでの性能評価となるが、温度80 ℃、ＫＯＨ濃度30 wt％と商用条件である極環境での試験となる。
各電極における電解電圧の値は、図８の陽極ではＮｉ－Ｆｅ－Ｓｎ電極＜Ｎｉ－Ｆｅ電極＜Ｎｉ－Ｓｎ電極＜Ｎｉ電極の順となり、Ｎｉ－Ｆｅ－Ｓｎ電極が全てのセル電流密度において最も低い電解電圧の値を示した。
また、図９の陰極においてもＮｉ－Ｆｅ－Ｓｎ電極＜Ｎｉ－Ｓｎ電極＜Ｎｉ－Ｆｅ電極＜Ｎｉ電極の順となり、やはりＮｉ－Ｆｅ－Ｓｎ電極が全てのセル電流密度において最も低い電解電圧の値を示した。
国立研究開発法人新エネルギー・産業技術総合開発機構では水電解においてセル電流密度600 mA/cm２にて1.8 V以下の電解電圧となるようなセルの構築を目標として掲げており、陽極としてのＮｉ－Ｆｅ－Ｓｎ電極は1.81 Vと＋10 mV高い性能まで迫っていることがわかる。すなわち、他の非貴金属電極を備える従来技術に貴金属電極を含めて比較しても、特に陽極としての顕著な触媒活性に基づく有用性を明確に示している。
Measured values of the electrolytic voltage will be described with reference to FIGS. 8 and 9. FIG. FIG. 8 is a graph showing electrode performance evaluation results under commercial conditions using the Ni—Fe—Sn electrode, Ni—Fe electrode, and Ni—Sn electrode according to the present embodiment as the anode of a bipolar electrode cell. FIG. 9 is a graph showing the electrode performance evaluation results under commercial conditions similarly used for the cathode.
In this water electrolysis system simulating electrolysis under commercial conditions, the current density was controlled and the voltage value at each current density was measured for each electrode. Although the results shown in FIGS. 4 and 5 are performance evaluations at the laboratory level, they are tests in an polar environment, which is a commercial condition of a temperature of 80° C. and a KOH concentration of 30 wt%.
The value of the electrolysis voltage at each electrode is in the order of Ni--Fe--Sn electrode <Ni--Fe electrode <Ni--Sn electrode <Ni electrode at the anode in FIG. It showed the lowest electrolysis voltage value.
Also, in the cathode of FIG. 9, the order is Ni—Fe—Sn electrode<Ni—Sn electrode<Ni—Fe electrode<Ni electrode, and the Ni—Fe—Sn electrode has the lowest electrolysis voltage at all cell current densities. showed the value.
The New Energy and Industrial Technology Development Organization has set a goal of constructing a cell in which the electrolysis voltage is 1.8 V or less at a cell current density of 600 mA/ cm2 in water electrolysis. It can be seen that the -Fe-Sn electrode is approaching 1.81 V and +10 mV high performance. In other words, even when the noble metal electrode is compared with the prior art provided with other non-noble metal electrodes, the usefulness based on the remarkable catalytic activity especially as an anode is clearly shown.
＜めっき電流密度の異なるＮｉ－Ｆｅ－Ｓｎ複合膜の作製＞
次に、本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極の複合膜を、めっき電流密度を変化させて作製して比較する。
めっき浴組成は図１を参照しながら説明したＮｉ－Ｆｅ－Ｓｎ電極の製造方法における組成と同一の組成を用い、ｐＨの調整方法も同一である。めっきも浴温度を50 ℃として同一の条件で常時攪拌しながら行った。また、電解条件は、電流密度を10,20,30,40,60,80,100 mA/cm２で各２時間めっきした。得られたＮｉ－Ｆｅ－Ｓｎ複合膜の組成は、エネルギー分散型成分分析装置によって定量した。
７種類のめっき電流密度で作製したＮｉ－Ｆｅ－Ｓｎ複合膜の組成に関する成分分析結果を表１に示す。表１からめっき電流密度が少なくとも30 mA/cm２以上でＦｅが含有されることがわかる。表１から明らかなとおり、Ｆｅが含有されることで酸素過電圧が低下している。特に、めっき電流密度が40 mA/cm２で更に大きく酸素過電圧が低下し、結晶子サイズが急激に小さくなっている。
したがって、高い触媒活性を得るためには、特にＦｅの含有率が重要であると考えられ、その値は約3質量％以上である必要と考えられる。一方、上限値は特に定める必要はないとも考えられるが、ＮｉやＳｎの含有率からすれば15％程度が妥当と考えられる。また、表１から理解されるとおり、Ｎｉの含有率は50 ～ 65質量％、Ｓｎの含有率は30 ～ 50質量％である必要がある。
このような含有比率を備えたＮｉ－Ｆｅ－Ｓｎ複合膜でなければ電解中に生じるＮｉＯＯＨの高い電気伝導率が得られず、ＮｉＦｅ含有による高い触媒活性は得られない。また、Ｓｎの含有率（30 ～ 50質量％）に示すとおりでなければ電極表面の凹凸を増大させる効果と耐久性を有する効果の両方を満足させることができない。
一方、電流密度が100 mA/cm２以上の範囲では成膜した複合膜自体が高電流密度で作製した際によく見受けられる不良めっき特有の「焦げ」を形成するため十分な活性が得られない。
<Preparation of Ni—Fe—Sn composite films with different plating current densities>
Next, composite films of Ni--Fe--Sn electrodes according to the present embodiment are produced by changing the plating current density and compared.
The composition of the plating bath is the same as that in the Ni--Fe--Sn electrode manufacturing method described with reference to FIG. 1, and the pH adjustment method is also the same. Plating was also carried out under the same conditions with a bath temperature of 50° C. while constantly stirring. Electrolytic conditions were current densities of 10, 20, 30, 40, 60, 80 and 100 mA/cm 2 for 2 hours each. The composition of the obtained Ni--Fe--Sn composite film was quantified by an energy dispersive component analyzer.
Table 1 shows the result of component analysis on the composition of the Ni--Fe--Sn composite films produced at seven different plating current densities. From Table 1, it can be seen that Fe is contained when the plating current density is at least 30 mA/cm 2 or more. As is clear from Table 1, the oxygen overvoltage is lowered by containing Fe. In particular, when the plating current density is 40 mA/cm 2 , the oxygen overvoltage is further reduced and the crystallite size is rapidly reduced.
Therefore, in order to obtain high catalytic activity, it is considered that the content of Fe is particularly important, and it is considered that the value should be about 3% by mass or more. On the other hand, although it is not considered necessary to set the upper limit in particular, considering the content of Ni and Sn, about 15% is considered appropriate. Further, as understood from Table 1, the Ni content must be 50 to 65% by mass, and the Sn content must be 30 to 50% by mass.
Unless the Ni--Fe--Sn composite film has such a content ratio, NiOOH generated during electrolysis cannot obtain high electrical conductivity, and high catalytic activity due to the NiFe content cannot be obtained. Moreover, unless the content of Sn (30 to 50% by mass) is as shown, it is not possible to satisfy both the effect of increasing the unevenness of the electrode surface and the effect of providing durability.
On the other hand, when the current density is in the range of 100 mA/cm 2 or higher, sufficient activity cannot be obtained because the deposited composite film itself forms "burnt" peculiar to defective plating, which is often seen when it is produced at a high current density. .
７種類のめっき電流密度で作製したＮｉ－Ｆｅ－Ｓｎ複合膜の(102)面における結晶子サイズを算出した結果を表１に示すが、めっき電流密度が増加するにつれて結晶子サイズが減少することがわかった。また、その値は、めっき電流密度100 mA/cm２において、17.1 Åと最小の値を有することがわかった。
結晶子サイズは微細化されるほどＥＣＳＡが増大して反応場が増大するのでより小さい方が望ましいが、100 Å以下であればよく、100 Åよりも大きくなるとＥＣＳＡが増大せず、過電圧の低減には至らない。より好ましい結晶子サイズは後述するＮｉ－Ｆｅ－Ｓｎ複合膜の酸素過電圧として大きく減少しているめっき電流密度40 mA/cm２近傍の結晶子サイズである30 Åから焦げを生じないめっき電流密度である100 mA/cm２近傍の結晶子サイズである15 Åである。
Table 1 shows the results of calculating the crystallite size in the (102) plane of the Ni—Fe—Sn composite film produced at seven different plating current densities. I found out. It was also found to have a minimum value of 17.1 Å at a plating current density of 100 mA/cm 2 .
As the crystallite size becomes finer, the ECSA increases and the reaction field increases, so it is desirable that the crystallite size is smaller. does not reach A more preferable crystallite size is a plating current density of 30 Å, which is a crystallite size near the plating current density of 40 mA/ cm2 , which greatly decreases as the oxygen overvoltage of the Ni-Fe-Sn composite film described later, and a plating current density that does not cause scorching. It is 15 Å, which is the crystallite size near a certain 100 mA/cm 2 .
＜本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極の複合膜の酸素過電圧の測定比較＞
図１０は本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極の複合膜でめっき時の電流密度を変化させた場合の酸素過電圧測定のためのＬＳＶ測定結果を示すグラフである。
Ｎｉ－Ｆｅ－Ｓｎ複合膜の酸素過電圧（η）の算出は、前述のとおり電流密度10 mA/cm２に到達するまでに要する電位をη１０＝Ｅ（ＲＨＥ）-1.23 V（酸素発生理論電位）で計算した。その結果、80 mA/cm２(η１０＝293 mV)＜100 mA/cm２(η１０＝296 mV)＜60 mA/cm２(η１０＝302mV)＜40 mA/cm２(η１０＝320 mV) ＜30 mA/cm２(η１０＝346 mV)＜10 mA/cm２(η１０＝362 mV)＜20 mA/cm２(η１０＝366 mV)の順となり、40 mA/cm２から急激に過電圧が減少していることがわかる。これは、40 mA/cm２以降、Ｆｅが十分に複合膜中に含有され、膜中の結晶子サイズが微細化し、反応場が増加したためと考えられる。
したがって、Ｎｉ－Ｆｅ－Ｓｎ電極の複合膜の成膜工程におけるめっき電流密度としては40 ～ 100 mA/cm２が望ましいと考えられる。
<Measurement comparison of oxygen overvoltage of composite film of Ni—Fe—Sn electrode according to the present embodiment>
FIG. 10 is a graph showing LSV measurement results for oxygen overvoltage measurement when the current density during plating is changed in the composite film of the Ni--Fe--Sn electrode according to the present embodiment.
To calculate the oxygen overvoltage (η) of the Ni-Fe-Sn composite film, the potential required to reach a current density of 10 mA/cm 2 as described above is η 10 = E (RHE) - 1.23 V (theoretical potential for oxygen generation ). As a result, 80 mA/cm 2 (η10 = 293 mV) < 100 mA/cm 2 (η10 = 296 mV) < 60 mA/cm 2 (η 10 = 302 mV) < 40 mA/cm 2 (η 10 = 320 mV ) < 30 mA/cm 2 (η 10 = 346 mV) < 10 mA/cm 2 (η 10 = 362 mV) < 20 mA/cm 2 (η 10 = 366 mV), and from 40 mA/cm 2 It can be seen that the overvoltage is rapidly reduced. This is probably because Fe was sufficiently contained in the composite film after 40 mA/cm 2 , the crystallite size in the film became finer, and the reaction field increased.
Therefore, the plating current density of 40 to 100 mA/cm 2 is considered desirable in the process of forming the composite film of the Ni--Fe--Sn electrode.
＜電気化学的活性表面積の測定＞
本実施の形態に係るＮｉ－Ｆｅ－Ｓｎ電極の複合膜のＥＣＳＡは、Ｃｄｌに基づいて算出した。Ｃｄｌの算出には、ＣＶ測定を用い、0 ～ 0.1 V（vs. Ｈｇ／ＨｇＯ）の電位範囲で2 ～ 10 mV/sのスキャンレートで電流応答を測定した。図１１～図１４にその結果を示す。そして、各スキャンレートにおける電流密度（ｊ＝ ｊａｎｏｄｉｃ＋|ｊ|ｃａｔｈｏｄｉｃ／２）をプロットし、その傾きをＣｄｌとした(図１５)。
図１５に示すとおり、めっき電流密度が10 mA/cm２でＣｄｌ＝1.8 mF/cm２、20 mA/cm２でＣｄｌ＝3.9 mF/cm２、30 mA/cm２でＣｄｌ＝2.0 mF/cm２、40 mA/cm２でＣｄｌ＝5.6 mF/cm２、60 mA/cm２でＣｄｌ＝10.6 mF/cm２、80 mA/cm２でＣｄｌ＝11.5 mF/cm２、100 mA/cm２でＣｄｌ＝16.3 mF/cm２となった。
ＥＣＳＡは式（１）を用いて算出した。
ＥＣＳＡ＝Ｃｄｌ／Ｃｓ （１）
ここでのＣｓは比静電容量であり、1.0 M ＫＯＨにおいて0.040 mF/cm２の値を使用した。また、めっき膜重量として、めっき電流密度10 mA/cm２時で0.0115g、めっき電流密度20 mA/cm２時で0.0115g、めっき電流密度30 mA/cm２時で0.0125g、めっき電流密度40 mA/cm２時で0.0143g、めっき電流密度60 mA/cm２時で0.0141g、めっき電流密度80 mA/cm２時で0.0134g、めっき電流密度10 mA/cm２時で0.0142gを使用した。
その結果、ＥＣＳＡはめっき電流密度が増加するにつれ増大し、最大で、めっき電流密度100 mA/cm２の場合において2.9 m２/gと算出された。また、めっき電流密度とＥＣＳＡの対応は、それぞれ、10 mA/cm２で0.4 m２/g 、20 mA/cm２で0.8 m２/g、30 mA/cm２で0.4 m２/g、40 mA/cm２で1.0 m２/g、60 mA/cm２で1.9 m２/g、80 mA/cm２で2.1 m２/gとなった。これはめっき電流密度が増加するにつれ結晶子サイズが微細化することと一致し、Ｆｅが含有されることにより、反応場が増大したことが明らかと言える。
<Measurement of electrochemically active surface area>
The ECSA of the composite film of the Ni--Fe--Sn electrode according to this embodiment was calculated based on Cdl . CV measurements were used to calculate C dl and current responses were measured at a potential range of 0 to 0.1 V (vs. Hg/HgO) at a scan rate of 2 to 10 mV/s. The results are shown in FIGS. 11 to 14. FIG. Then, the current density (j= janodic +|j| cathodic /2) at each scan rate was plotted, and the slope was taken as Cdl (FIG. 15).
As shown in FIG. 15, C dl =1.8 mF/cm 2 at a plating current density of 10 mA/cm 2 , C dl =3.9 mF/cm 2 at 20 mA/cm 2 , and C dl =2.0 at 30 mA/cm 2 . mF/ cm2 , Cdl = 5.6 mF/ cm2 at 40 mA/ cm2 , Cdl = 10.6 mF/ cm2 at 60 mA/ cm2 , Cdl = 11.5 mF/ cm2 at 80 mA/ cm2 , C dl =16.3 mF/cm 2 at 100 mA/cm 2 .
ECSA was calculated using Equation (1).
ECSA=C dl /C s (1)
Cs here is the specific capacitance and a value of 0.040 mF/cm 2 in 1.0 M KOH was used. The weight of the plating film was 0.0115 g at a plating current density of 10 mA/ cm2 , 0.0115 g at a plating current density of 20 mA/ cm2 , 0.0125 g at a plating current density of 30 mA/ cm2 , and a plating current density of 40. 0.0143 g at a plating current density of 60 mA/ cm2 , 0.0141 g at a plating current density of 80 mA/ cm2 , and 0.0142 g at a plating current density of 10 mA/ cm2 . .
As a result, the ECSA increased as the plating current density increased, and was calculated to be 2.9 m 2 /g at the maximum when the plating current density was 100 mA/cm 2 . Correspondence between plating current density and ECSA is 0.4
＜Ｎｉ－Ｆｅ－Ｓｎ電極の複合膜の前駆体の違いによる比較＞
１）組成濃度の比較
本実施の形態においては、図１を参照しながら説明したとおり、前駆体として塩化物を使用しているが、非特許文献１で開示された技術と同様に比較対象として硫化物を使用した場合について説明する。
まず、前駆体として硫酸塩を用いたＮｉ－Ｆｅ－Ｓｎ複合膜の作製に用いためっき浴組成は、前述の塩酸塩を用いためっき浴組成のうち、ＮｉＣｌ２・６Ｈ２Ｏに代えてＮｉＳＯ４・６Ｈ２Ｏ（硫酸ニッケル６水和物）とし、ＦｅＣｌ３・２Ｈ２Ｏに代えてＦｅＳＯ４・７Ｈ２Ｏ（硫酸鉄７水和物）とした以外はモル濃度も含めて同一とした。さらに、ｐＨの調整方法も同一であり、めっき浴温度50 ℃及びめっき処理時の80 mA/cm２の電流密度と２時間の処理時間も同一である。
得られたＮｉ－Ｆｅ－Ｓｎ複合膜の組成をエネルギー分散型成分分析装置によって定量した結果、Ｎｉ、Ｆｅ及びＳｎの合計組成濃度を100 質量％としたとき、Ｆｅ含有量は1.22 質量％ 、Ｎｉ含有量は59.95 質量％、Ｓｎ含有量は38.81 質量％であった。但し、Ｆｅ含有量の1.22 質量％はＦｅが検出された箇所での数値であり、検出されない部分の方が多くを占めていた。
前駆体が塩化物の場合のＦｅ含有量が5.32 質量％であるのに対し、硫化物の場合は検出されない部分も多く、検出された箇所でも1.22 質量％と特に低く、反応場が増大せず十分な触媒活性は発揮されない可能性が高い。
<Comparison of Ni—Fe—Sn Electrode Composite Film Precursors>
1) Comparison of composition concentration In the present embodiment, as described with reference to FIG. 1, chloride is used as a precursor. A case of using sulfide will be described.
First, the plating bath composition used for the preparation of the Ni—Fe—Sn composite film using sulfate as a precursor was NiSO 4.6H 2 O (nickel sulfate hexahydrate) was used, and FeSO 4.7H 2 O (iron sulfate heptahydrate) was used instead of FeCl 3.2H 2 O. . Furthermore, the pH adjustment method is the same, the plating bath temperature is 50° C., the current density is 80 mA/cm 2 during plating, and the treatment time is 2 hours.
The composition of the obtained Ni--Fe--Sn composite film was quantified by an energy dispersive component analyzer. The content was 59.95 mass % and the Sn content was 38.81 mass %. However, the Fe content of 1.22% by mass is the value at the portion where Fe was detected, and the portion where Fe was not detected accounted for the majority.
When the precursor is chloride, the Fe content is 5.32% by mass, whereas in the case of sulfide, there are many parts where it is not detected, and even where it is detected, it is a particularly low 1.22% by mass, and the reaction field does not increase. It is highly likely that sufficient catalytic activity will not be exhibited.
２）酸素過電圧の比較
次に、図１６に前駆体を塩化物にした場合と硫化物にした場合のそれぞれで作製されたＮｉ－Ｆｅ－Ｓｎ電極の複合膜に対する酸素過電圧測定のためのＬＳＶ測定結果のグラフを示す。
硫酸塩を前駆体として作製したＮｉ－Ｆｅ－Ｓｎ複合膜の酸素過電圧（η）の算出も同様に、電流密度10 mA/cm２に到達するまでに要する電位をη１０＝Ｅ（ＲＨＥ）-1.23 V（酸素発生理論電位）で計算した。その結果、酸素過電圧η１０＝310 mVとなっており、塩化物を前駆体として作製したＮｉ－Ｆｅ－Ｓｎ複合膜の酸素過電圧η１０＝293 mVよりも17 mV高く、触媒性能が低下していたことがわかった。
すなわち、前駆体が硫酸塩（硫化物）の場合には、十分に優位な効果は発揮することができず、高い触媒活性を発揮させるためには前駆体は塩化物であることが望ましいことが判明した。
2) Comparison of oxygen overvoltage Next, LSV measurement for oxygen overvoltage measurement for composite films of Ni—Fe—Sn electrodes prepared using chloride and sulfide precursors in FIG. A graph of the results is shown.
Calculation of the oxygen overvoltage (η) of the Ni--Fe--Sn composite film prepared using sulfate as a precursor is similarly carried out using η 10 =E(RHE)− Calculated at 1.23 V (theoretical potential for oxygen evolution). As a result, the oxygen overvoltage η 10 = 310 mV, which is 17 mV higher than the oxygen overvoltage η 10 = 293 mV of the Ni—Fe—Sn composite film prepared using chloride as a precursor, indicating a decrease in catalytic performance. I found out.
That is, when the precursor is a sulfate (sulfide), a sufficiently superior effect cannot be exhibited, and in order to exhibit high catalytic activity, it is desirable that the precursor be a chloride. found.
３）電気化学的活性表面積（ＥＣＳＡ）の比較
次に、前駆体に硫化物を用いたＮｉ－Ｆｅ－Ｓｎ電極の複合膜（めっき電流密度80 mA/cm２）のＥＣＳＡは、前駆体に塩化物を用いたＮｉ－Ｆｅ－Ｓｎ複合膜と同様にＣｄｌに基づいて算出した。Ｃｄｌの算出には、ＣＶ測定を用い、0 ～ 0.1 V（vs. Ｈｇ／ＨｇＯ）の電位範囲で2 ～ 10 mV/sのスキャンレートで電流応答を測定した。図１７にその結果を示す。そして、各スキャンレートにおける電流密度（ｊ＝ ｊａｎｏｄｉｃ＋|ｊ|ｃａｔｈｏｄｉｃ／２）をプロットし、その傾きをＣｄｌとした(図１８)。
図１８に示されるとおりＣｄｌは3.3 mF/cm２であり、ＥＣＳＡは塩化物の場合と同様に式（１）を用いて算出した。
Ｃｓとして、1.0 M ＫＯＨにおいて0.040 mF/cm２の値を使用し、めっき膜重量が0.0145gであることからＥＣＳＡは0.52 m２/gと算出された。
前駆体が塩化物の場合では、めっき電流密度が80 mA/cm２で成膜されたＮｉ－Ｆｅ－Ｓｎ複合膜におけるＥＣＳＡが2.1 m２/gであり、前駆体を硫化物として成膜したＮｉ－Ｆｅ－Ｓｎ複合膜よりも格段に大きな数値であることが理解でき、反応場の拡大と高い触媒活性も期待できる。
3) Comparison of electrochemically active surface area ( ECSA ) It was calculated based on C dl in the same manner as the Ni--Fe--Sn composite film using the material. CV measurements were used to calculate C dl and current responses were measured at a potential range of 0 to 0.1 V (vs. Hg/HgO) at a scan rate of 2 to 10 mV/s. The results are shown in FIG. Then, the current density (j= janodic +|j| cathodic /2) at each scan rate was plotted, and the slope was taken as Cdl (FIG. 18).
C dl was 3.3 mF/cm 2 as shown in FIG. 18, and ECSA was calculated using equation (1) as in the case of chloride.
Using a value of 0.040 mF/cm 2 in 1.0 M KOH as C s and a plating film weight of 0.0145 g, the ECSA was calculated to be 0.52 m 2 /g.
When the precursor is a chloride, the Ni--Fe--Sn composite film formed at a plating current density of 80 mA/cm 2 has an ECSA of 2.1 m 2 /g, and the precursor is a sulfide. It can be understood that the numerical value is much larger than that of the Ni--Fe--Sn composite film, and expansion of the reaction field and high catalytic activity can be expected.
以上１）から３）で述べたとおり、Ｎｉ－Ｆｅ－Ｓｎ電極の複合膜の前駆体の違いによって、Ｆｅ含有量、酸素過電圧及びＥＣＳＡのいずれも顕著な差が生じており、前駆体として硫化物よりも塩化物で成膜する方が十分に高い触媒性能を発揮させることができると考えられる。 As described in 1) to 3) above, the difference in the precursor of the composite film of the Ni—Fe—Sn electrode causes a significant difference in all of the Fe content, oxygen overvoltage, and ECSA. It is considered that a sufficiently high catalyst performance can be exhibited by forming a film with a chloride rather than a substance.
以上説明したとおり、請求項１乃至請求項５に記載された発明は水電解用の電極及び燃料電池の電極やその製造方法として広く利用することが可能である。 As described above, the inventions described in claims 1 to 5 can be widely used as electrodes for water electrolysis, electrodes for fuel cells, and manufacturing methods thereof.
Claims (5)
前記湿式成膜法によってＮｉ－Ｆｅ－Ｓｎ複合膜を成膜する成膜工程と、を有し、前記成膜工程におけるめっき電流密度は40 ～ 100 mA/cm２であることを特徴とする水電解用の非貴金属電極の製造方法。 A step of disposing a chloride salt as a precursor on a substrate by a wet film-forming method;
a film forming step of forming a Ni-Fe-Sn composite film by the wet film forming method, wherein the plating current density in the film forming step is 40 to 100 mA/cm 2 . A method for producing a non-noble metal electrode for electrolysis.
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