JP5679639B2 - Gas diffusion electrode and manufacturing method thereof - Google Patents
Gas diffusion electrode and manufacturing method thereof Download PDFInfo
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- JP5679639B2 JP5679639B2 JP2009136659A JP2009136659A JP5679639B2 JP 5679639 B2 JP5679639 B2 JP 5679639B2 JP 2009136659 A JP2009136659 A JP 2009136659A JP 2009136659 A JP2009136659 A JP 2009136659A JP 5679639 B2 JP5679639 B2 JP 5679639B2
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- oxide
- gas diffusion
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- YHBDIEWMOMLKOO-UHFFFAOYSA-I pentachloroniobium Chemical compound Cl[Nb](Cl)(Cl)(Cl)Cl YHBDIEWMOMLKOO-UHFFFAOYSA-I 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 239000012466 permeate Substances 0.000 description 1
- 150000002978 peroxides Chemical class 0.000 description 1
- KRIOVPPHQSLHCZ-UHFFFAOYSA-N phenyl propionaldehyde Natural products CCC(=O)C1=CC=CC=C1 KRIOVPPHQSLHCZ-UHFFFAOYSA-N 0.000 description 1
- 150000003057 platinum Chemical class 0.000 description 1
- CFQCIHVMOFOCGH-UHFFFAOYSA-N platinum ruthenium Chemical compound [Ru].[Pt] CFQCIHVMOFOCGH-UHFFFAOYSA-N 0.000 description 1
- FHMDYDAXYDRBGZ-UHFFFAOYSA-N platinum tin Chemical compound [Sn].[Pt] FHMDYDAXYDRBGZ-UHFFFAOYSA-N 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000005518 polymer electrolyte Substances 0.000 description 1
- 150000004032 porphyrins Chemical class 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 235000010333 potassium nitrate Nutrition 0.000 description 1
- 239000004323 potassium nitrate Substances 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 1
- 239000000376 reactant Substances 0.000 description 1
- 238000010992 reflux Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 229910052895 riebeckite Inorganic materials 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- KKCBUQHMOMHUOY-UHFFFAOYSA-N sodium oxide Chemical compound [O-2].[Na+].[Na+] KKCBUQHMOMHUOY-UHFFFAOYSA-N 0.000 description 1
- 229910001948 sodium oxide Inorganic materials 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 230000007480 spreading Effects 0.000 description 1
- 238000003892 spreading Methods 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 125000004434 sulfur atom Chemical group 0.000 description 1
- 239000002887 superconductor Substances 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 229910001936 tantalum oxide Inorganic materials 0.000 description 1
- TXEYQDLBPFQVAA-UHFFFAOYSA-N tetrafluoromethane Chemical compound FC(F)(F)F TXEYQDLBPFQVAA-UHFFFAOYSA-N 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- 229910001930 tungsten oxide Inorganic materials 0.000 description 1
- GPPXJZIENCGNKB-UHFFFAOYSA-N vanadium Chemical compound [V]#[V] GPPXJZIENCGNKB-UHFFFAOYSA-N 0.000 description 1
- 239000002759 woven fabric Substances 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
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- 229910006290 γ-MnOOH Inorganic materials 0.000 description 1
Landscapes
- Electrodes For Compound Or Non-Metal Manufacture (AREA)
Description
本発明は電気化学プロセスに用いるガス拡散電極に関し、特にアルカリ、酸性水溶液での水素酸化、酸素還元、イオン交換膜を用いた燃料電池、食塩電解における酸素還元用ガス拡散陰極を提供することを目的とする。 The present invention relates to a gas diffusion electrode used in an electrochemical process, and in particular, to provide a hydrogen diffusion in an alkali or acidic aqueous solution, oxygen reduction, a fuel cell using an ion exchange membrane, and a gas diffusion cathode for oxygen reduction in salt electrolysis. And
ガス電極は反応原料であるガス成分の酸化あるいは還元を行うための電気化学用電極で、特に燃料電池用として盛んに開発が行われている。電解質として、リン酸、溶融塩、固体電解質などがあるが、近年、低温作動型として固体高分子電解質（イオン交換膜）型燃料電池が注目されている。 The gas electrode is an electrochemical electrode for oxidizing or reducing a gas component that is a reaction raw material, and has been actively developed especially for a fuel cell. Examples of the electrolyte include phosphoric acid, molten salt, and solid electrolyte. In recent years, a solid polymer electrolyte (ion exchange membrane) type fuel cell has attracted attention as a low-temperature operation type.
[燃料電池]
燃料電池は化学エネルギーを電気エネルギーに変換可能なクリーンかつ高効率な発電システムである。水素や有機炭素原料の酸化反応と、空気中の酸素の還元反応を組み合わせることにより、その起電力から電気エネルギーを得るものであり、特に1960年代の低温型宇宙用電池としての実用化で注目された後、最近、燃料電池自動車、小型可搬電源、家庭用電源として再び注目されている。
[Fuel cell]
A fuel cell is a clean and highly efficient power generation system that can convert chemical energy into electrical energy. By combining the oxidation reaction of hydrogen and organic carbon raw materials with the reduction reaction of oxygen in the air, electric energy is obtained from the electromotive force. Particularly, it has been attracting attention for practical use as a low-temperature space battery in the 1960s. Recently, it has been attracting attention again as a fuel cell vehicle, a small portable power source, and a household power source.
酸性電解質型における水素/酸素燃料電池の反応は以下のとおりである。
アノード： ２Ｈ2→４Ｈ+＋４ｅ- (1)
カソード： Ｏ2＋４Ｈ+＋４ｅ-→２Ｈ2Ｏ (2)
The reaction of the hydrogen / oxygen fuel cell in the acidic electrolyte type is as follows.
Anode: 2H 2 → 4H + + 4e - (1)
Cathode: O 2 + 4H + + 4e − → 2H 2 O (2)
アルカリ性電解質型の場合は、
アノード：４ＯＨ-＋Ｈ2→４Ｈ2Ｏ＋４ｅ- (3)
カソード：Ｏ2＋２Ｈ2Ｏ＋４ｅ -→ ４ＯＨ- (4)
正味の反応： ２Ｈ2＋Ｏ2→２Ｈ2Ｏ (5)
For alkaline electrolyte type,
Anode: 4OH − + H 2 → 4H 2 O + 4e − (3)
Cathode: O 2 + 2H 2 O + 4e − → 4OH − (4)
Net reaction: 2H 2 + O 2 → 2H 2 O (5)
燃料として水素のみならず、リチウム、亜鉛を負極とする2次電池の開発も期待されている。また原料として、メタノール、エタノール、エチレングリコール、などの他の有機物質も利用可能である。 The development of secondary batteries that use lithium as a negative electrode as well as hydrogen as a fuel is also expected. In addition, other organic substances such as methanol, ethanol, and ethylene glycol can be used as raw materials.
アノード（メタノール原料の場合）：ＣＨ3ＯＨ+Ｈ2→６Ｈ+＋ＣＯ2＋６ｅ- （６） Anode (in the case of methanol raw material): CH 3 OH + H 2 → 6H + + CO 2 + 6e − (6)
水素酸化、メタノール酸化のアノード触媒、及び、酸素還元のカソード触媒として、白金などの貴金属が一般的に使用される。水素アノード触媒では、原料水素に含まれるＣＯなどの吸着物質が触媒特性に影響を与えるため、各種除去装置により原料中のＣＯ混入率は１０ｐｐｍ以下に制御されている。メタノール燃焼電池では、反応過程においてメタノール酸化で生じるＣＯなどの吸着による性能劣化が生じる。また、ＣＯが存在しない場合でも、長時間の使用により、触媒金属のシンタリングが進行し、性能が劣化することが報告されている。 A noble metal such as platinum is generally used as an anode catalyst for hydrogen oxidation, methanol oxidation, and a cathode catalyst for oxygen reduction. In the hydrogen anode catalyst, since an adsorbing substance such as CO contained in the raw material hydrogen affects the catalyst characteristics, the CO contamination rate in the raw material is controlled to 10 ppm or less by various removing devices. In the methanol combustion battery, performance deterioration occurs due to adsorption of CO or the like generated by methanol oxidation in the reaction process. Further, it has been reported that, even when CO is not present, catalytic metal sintering proceeds and performance deteriorates due to long-term use.
白金などの単体触媒ではこのような欠点があるため、２元系又は多元系の触媒が開発され、優れた特性を発揮することが古くから報告されている。代表的な組成としてＰｔ−Ｒｕ合金触媒がＣＯ耐性に優れていることはよく知られており２〜３ｎｍの粒子サイズを有するＰｔ−Ｒｕ触媒をカーボン上に分散させた場合に、合金化によるＣＯ耐性向上が確認されている。その原因としては、２元化のために添加された触媒に吸着した酸素種が、主触媒である白金表面の吸着種ＣＯと反応して、ＣＯ2となる反応を促進する機構の発現（Bifunctional mechanism）や、過電圧の小さいＣＯ2が生成し得ない電位（或いはＣＯが除去されない電位）においても合金効果が生じることから、合金化により表面電子エネルギーレベルが変化し、ＣＯとの結合を弱めるように作用する機構（Intrinsic mechanism）などが提案されている(J. Applied Electrochem. 31, 325-334 (2001) 参照)。
触媒サイズの一般的な傾向としては、小さいほど活性が増大するが、５ｎｍ以下では結晶、露出割合、電子構造の変化、原料供給速度などの影響を受け、触媒性能が変化することも知られている。
Since single catalysts such as platinum have such disadvantages, binary or multi-component catalysts have been developed and have been reported for a long time to exhibit excellent characteristics. It is well known that a Pt—Ru alloy catalyst is excellent in CO resistance as a typical composition. When a Pt—Ru catalyst having a particle size of 2 to 3 nm is dispersed on carbon, CO by alloying is known. Improved resistance has been confirmed. This is because the oxygen species adsorbed on the catalyst added for binary reaction reacts with the adsorbed species CO on the platinum surface, which is the main catalyst, to promote the reaction to become CO 2 (Bifunctional). mechanism) and potentials where CO 2 with low overvoltage cannot be generated (or potentials where CO is not removed), the alloying effect occurs, so that the surface electron energy level changes due to alloying and weakens the bond with CO. Intrinsic mechanisms have been proposed (see J. Applied Electrochem. 31, 325-334 (2001)).
As a general tendency of the catalyst size, the smaller the activity, the higher the activity, but it is also known that the catalyst performance changes at 5 nm or less due to the influence of crystal, exposure ratio, electronic structure change, raw material supply rate, etc. Yes.
合金触媒及びその製法について、これまでに多くの特許技術が開示されている。米国特許第３４２８４９０号明細書では、金属合金を冶金的に製作し、これを酸洗浄した後、更に合金化しない金属を溶解することで三次元的に面積の大きい触媒を作製できることが開示されている。特開平２−６１９６１号公報では白金−鉄−銅からなる三元系触媒とその高温熱処理による製法が開示されている。特開平２−１１１４４０号公報では白金−ルテニウムの、特開平２−１１１４５２号公報では白金-スズ成分の開示がある。特開平５-４７３８９号公報 にも合金化の技術が開示されている。特開平６−２４６１６１号公報では酸素を微量添加した不活性雰囲気での焼成方法が開示されている。特開平１０−６９９１４号公報では合金化としての熱処理技術が開示されている。特開２００１−５２７１８号公報は炭素−白金の合金化処理で白金の格子定数は減少し、触媒活性が増加するが、格子サイズを安定化するような処理方法について開示している。特開２００３−２２６９０１号公報は不活性雰囲気下でのアルコールによる加熱還流による製法を開示している。 Many patented technologies have been disclosed so far for alloy catalysts and processes for producing them. In U.S. Pat. No. 3,428,490, it is disclosed that a metal alloy is produced metallurgically, and after this is acid cleaned, a non-alloyed metal can be dissolved to produce a catalyst having a large three-dimensional area. Yes. Japanese Patent Laid-Open No. 2-61961 discloses a ternary catalyst composed of platinum-iron-copper and a method for producing the same by high-temperature heat treatment. JP-A-2-111440 discloses platinum-ruthenium, and JP-A-2-111252 discloses a platinum-tin component. Japanese Patent Laid-Open No. 5-47389 also discloses an alloying technique. JP-A-6-246161 discloses a firing method in an inert atmosphere to which a small amount of oxygen is added. Japanese Patent Application Laid-Open No. 10-69914 discloses a heat treatment technique as alloying. Japanese Patent Laid-Open No. 2001-52718 discloses a treatment method in which the lattice constant of platinum is reduced and the catalytic activity is increased by the carbon-platinum alloying treatment, but the lattice size is stabilized. Japanese Patent Application Laid-Open No. 2003-226901 discloses a production method by heating and refluxing with alcohol in an inert atmosphere.
金属(合金含む)超微粉末を製造する方法として、気相化学反応法、液相還元析出法などが一般的である。前者では金属化合物を気化し、不活性雰囲気での熱分解法や、水素ガスによる気相還元法が主流となっている。 As a method for producing metal (including alloy) ultrafine powder, a gas phase chemical reaction method, a liquid phase reduction precipitation method, or the like is generally used. In the former, a metal compound is vaporized, and a thermal decomposition method in an inert atmosphere and a gas phase reduction method using hydrogen gas are mainly used.
白金や白金合金の作製法については多種な方法が提案されている。その中でCravilier、Wieckowski、Adzicらは、清浄なルテニウムなどの貴金属基板上に既知量（多くは単原子層を形成するくらいの濃度）の異種貴金属（例えば白金）水溶液を滴下すると、二種の金属の酸化還元電位の差を駆動力として単原子層（濃度が濃い場合は多原子層）の金属析出が起こることを明らかにしている。参考文献として、（ａ）M. J. Llorka, J. M. Feliu, A. Aldaz and J. Clavilier, J. Electroanal. Chem., 1993, 351, 299、（ｂ）S. Park, A. Wieckowski and M. J. Weaver, J. Am. Chem. Soc., 2003, 125, 2282、（ｃ）S. R. Brankvic, J. MacBreen and R. R. Adzic, Surf. Sci., 2001, 479, L363などがある。 Various methods for producing platinum and platinum alloys have been proposed. Among them, Cravilier, Wieckowski, Adzic and others drop two kinds of aqueous solutions of dissimilar noble metals (eg platinum) on known noble metal substrates such as ruthenium (of which concentration is often enough to form a monoatomic layer). It has been clarified that metal deposition occurs in a monoatomic layer (a polyatomic layer when the concentration is high) using the difference in redox potential of the metal as a driving force. References include (a) MJ Llorka, JM Feliu, A. Aldaz and J. Clavilier, J. Electroanal. Chem., 1993, 351, 299, (b) S. Park, A. Wieckowski and MJ Weaver, J. Am. Chem. Soc., 2003, 125, 2282, (c) SR Brankvic, J. MacBreen and RR Adzic, Surf. Sci., 2001, 479, L363.
当初は金属粒子そのものが触媒として利用されたが、導電性基体（触媒基体）としてカーボン粉末に合金触媒を展開することで大幅な触媒使用量の低減が可能となった。カーボンへの固着は水溶液で分散し、還元剤と触媒イオンを混合し、表面に触媒を固着した後、熱処理を施すのが一般的であるが、処理工程が煩雑である。触媒の製法は、不活性雰囲気下、高温処理による合金触媒の製法が主に紹介されており、より安価に大量生産できる方法が求められている。 Initially, metal particles themselves were used as a catalyst, but by using an alloy catalyst on carbon powder as a conductive substrate (catalyst substrate), it was possible to significantly reduce the amount of catalyst used. Fixing to carbon is generally performed by dispersing in an aqueous solution, mixing a reducing agent and catalyst ions, fixing the catalyst on the surface, and then performing heat treatment, but the processing steps are complicated. As a method for producing a catalyst, a method for producing an alloy catalyst by high-temperature treatment under an inert atmosphere is mainly introduced, and a method capable of mass production at a lower cost is demanded.
燃料電池では、貴金属と卑金属の合金でかつ超微粉末を得、かつ、これを用いた高性能な電池用触媒を得るために、より安全かつ安価な製造技術の開発が重要であり、また、電極基体と合金触媒の接合に関しても改良の余地が残されている。 In fuel cells, it is important to develop safer and cheaper manufacturing technology in order to obtain an ultrafine powder of an alloy of noble metal and base metal and to obtain a high-performance battery catalyst using this. There is still room for improvement in joining the electrode substrate and the alloy catalyst.
[貴金属触媒以外の技術]
白金に替わる安価な触媒の検討は以前から行われており、白金等の貴金属は、高い電位においても安定で、かつ触媒能が高いため、各種の電気化学システムの電極用触媒に用いられている。しかし、白金の価格が高いことや資源量が限られていることから、白金を代替できる高活性の触媒が要望されている。水電解、有機電解、燃料電池などの分野において酸性電解質中で用いられる電気化学システム用の電極触媒として有用である。
酸性電解質に使用するガス電極における触媒に関しては、以下例示するように、多くの非貴金属触媒の開発が進められた。
[Technologies other than precious metal catalysts]
Inexpensive catalysts to replace platinum have been studied for a long time, and noble metals such as platinum are stable at high potentials and have high catalytic ability, so they are used as catalysts for electrodes in various electrochemical systems. . However, since the price of platinum is high and the amount of resources is limited, a highly active catalyst that can replace platinum is desired. It is useful as an electrode catalyst for electrochemical systems used in acidic electrolytes in fields such as water electrolysis, organic electrolysis, and fuel cells.
As for the catalyst in the gas electrode used for the acidic electrolyte, many non-noble metal catalysts have been developed as exemplified below.
特許文献１は、次の触媒を開示している。
燃料電池用負極触媒として優れた性能を有し、且つ、白金と比較して安価であって、しかも一酸化炭素の存在する雰囲気下においても優れた触媒活性を維持できる、燃料電池用の新規な触媒物質を提供する。金微粒子を含む燃料電池用負極触媒、更に、チタン、バナジウム、ガリウム、ジルコニウム、ニオブ、セリウム、タンタル、インジウム及びこれらの金属の酸化物からなる群から選ばれた少なくとも１種の成分、及び／又は白金、ルテニウム及びルテニウムの酸化物からなる群から選ばれた少なくとも一種の成分を含む燃料電池用負極触媒が開示されている。
Patent Document 1 discloses the following catalyst.
A novel fuel cell anode catalyst that has excellent performance as a negative electrode catalyst for fuel cells, is inexpensive compared with platinum, and can maintain excellent catalytic activity even in an atmosphere containing carbon monoxide. Provide catalytic material. A negative electrode catalyst for fuel cells containing fine gold particles, and at least one component selected from the group consisting of titanium, vanadium, gallium, zirconium, niobium, cerium, tantalum, indium and oxides of these metals, and / or A fuel cell negative electrode catalyst comprising at least one component selected from the group consisting of platinum, ruthenium and ruthenium oxides is disclosed.
特開２００５−６３６７７号公報では遷移金属であるモリブデンの窒化物について開示されている。特開２００５−４４６５９号公報では、遷移金属である鉄の窒化物と貴金属の混合物が報告されている。特開２００９−８２９０９号公報では、ＺｒＯ1/2Ｎを用いて触媒能及び安定性に優れた電極触媒が提案された。 Japanese Patent Application Laid-Open No. 2005-63677 discloses molybdenum nitride which is a transition metal. Japanese Patent Application Laid-Open No. 2005-44659 reports a mixture of iron nitride and noble metal, which is a transition metal. In JP 2009-82909 A, an electrode catalyst excellent in catalytic ability and stability using ZrO 1/2 N has been proposed.
特許文献２では、Ｌａ、Ｔａ、Ｎｂ、Ｔｉ、Ｚｒからなる群から選択される少なくとも一つの遷移金属元素を含むオキシナイトライドからなる金属オキシナイトライド電極触媒が開示されている。
ＷＯ２００６／０１９１２８では、酸素欠損を有するＺｒＯ2、Ｔａ2Ｏ5、Ｎｂ2Ｏ5、ＳｎＯ2、ＴｉＯ2、Ｖ2Ｏ5、ＭｏＯ3、ＷＯ3のうち、少なくとも一つの遷移金属酸化物を主触媒とし金を助触媒とし、酸性電解質に接触して可逆水素電極電位に対して０．４Ｖより高い電位で使用されることを特徴とする耐食性酸素還元用電極触媒が開示され、この触媒は、遷移金属酸化物及び金を微粒子として、又は遷移金属酸化物を金微粒子に被覆した微粒子として、電子伝導性粉末である触媒担体上に分散させるなどの形態で使用できる。
Patent Document 2 discloses a metal oxynitride electrode catalyst made of oxynitride containing at least one transition metal element selected from the group consisting of La, Ta, Nb, Ti, and Zr.
In WO2006 / 019128, at least one transition metal oxide of ZrO 2 , Ta 2 O 5 , Nb 2 O 5 , SnO 2 , TiO 2 , V 2 O 5 , MoO 3 and WO 3 having oxygen deficiency is mainly used. Disclosed is a corrosion-resistant oxygen reduction electrode catalyst characterized in that it is used as a catalyst with gold as a co-catalyst and in contact with an acidic electrolyte and used at a potential higher than 0.4 V with respect to the reversible hydrogen electrode potential. The transition metal oxide and gold can be used as fine particles, or as fine particles obtained by coating the transition metal oxide with gold fine particles and dispersed on a catalyst carrier that is an electron conductive powder.
特許文献３は、次の触媒を開示している。
安価で酸性電解質中で使用しうる電極触媒として、ＭＸm/x〔式中、Ｍは、チタン原子、ランタン原子、タンタル原子、ニオブ原子またはジルコニウム原子を、Ｘは、窒素原子、ホウ素原子、炭素原子または硫黄原子をそれぞれ示し、ｍはＭの価数を、ｘはＸの価数をそれぞれ示す。〕で示される化合物の粉末を部分酸化することを特徴とし、例えば酸素を含む雰囲気中で上記粉末を焼成して部分酸化したものを提案している。
Patent Document 3 discloses the following catalyst.
As an electrode catalyst that can be used in an acidic electrolyte at a low price, MX m / x [wherein M is a titanium atom, lanthanum atom, tantalum atom, niobium atom or zirconium atom, X is a nitrogen atom, boron atom, carbon Each represents an atom or a sulfur atom, m represents the valence of M, and x represents the valence of X. The powder of the compound represented by the above formula is partially oxidized, and for example, a powder obtained by firing and partially oxidizing the powder in an atmosphere containing oxygen has been proposed.
特許文献４は、二酸化ケイ素に白金またはその合金と、セリウム、ランタンおよびタンタルから選ばれる少なくとも１種の元素の酸化物を担持した電極触媒であって、より実用性の高い燃料電池を製造可能な電極触媒、この電極触媒を用いた電極組成物および燃料電池を開示している。 Patent Document 4 is an electrode catalyst in which platinum or an alloy thereof and an oxide of at least one element selected from cerium, lanthanum, and tantalum are supported on silicon dioxide, and a more practical fuel cell can be manufactured. An electrode catalyst, an electrode composition using the electrode catalyst, and a fuel cell are disclosed.
特表２００８−５４５６０４では、ゼロ価又は部分的に荷電した白金原子の原子的薄層によって少なくとも部分的に被包されている金属酸化物コアで構成され、或いは代わりに、又はさらに、前記金属酸化物コアが、ゼロ価又は部分的に荷電した白金クラスターに結合している、白金-金属酸化物複合粒子が提案されている。 In JP 2008-545604, the metal oxide core is composed of, or alternatively or additionally, a metal oxide core that is at least partially encapsulated by an atomic thin layer of zero-valent or partially charged platinum atoms. Platinum-metal oxide composite particles have been proposed in which the product core is bound to zero-valent or partially charged platinum clusters.
[ガス拡散電極の工業電解への応用（特に食塩電解）]
ガス拡散電極は、反応物質としてのガスを電極表面に供給し、該電極上でガスの酸化ないし還元反応を進行させることを特徴とし、燃料電池用として開発されてきたが、近年、工業電解に利用することが検討され始めている。例えば、酸素還元反応を行なうための疎水性陰極が過酸化水素の電解製造装置に利用されている。又、アルカリ製造や酸、アルカリ回収プロセスでは、陽極での酸素発生の代替として水素酸化反応（水素陽極）、或いは陰極での水素発生の代替として酸素還元反応（酸素陰極）を、ガス拡散電極を用いて行い、消費電力の低減を図っている。亜鉛採取等の金属回収、亜鉛メッキの対極としても水素陽極による減極が可能であることが報告されている。
[Application of gas diffusion electrode to industrial electrolysis (especially salt electrolysis)]
Gas diffusion electrodes have been developed for use in fuel cells, characterized by supplying gas as a reactant to the electrode surface and allowing gas oxidation or reduction reaction to proceed on the electrode. It is beginning to be considered for use. For example, a hydrophobic cathode for performing an oxygen reduction reaction is used in an electrolytic production apparatus for hydrogen peroxide. Also, in alkali production, acid and alkali recovery processes, hydrogen oxidation reaction (hydrogen anode) as an alternative to oxygen generation at the anode, or oxygen reduction reaction (oxygen cathode) as an alternative to hydrogen generation at the cathode, gas diffusion electrode This is done to reduce power consumption. It has been reported that depolarization with a hydrogen anode is possible as a counter electrode for metal recovery such as zinc extraction and galvanization.
工業用原料として重要である水酸化ナトリウム（苛性ソーダ）及び塩素は主として食塩電解法により製造されている。この電解プロセスは、水銀陰極を使用する水銀法、及びアスベスト隔膜と軟鉄陰極を使用する隔膜法を経て、イオン交換膜を隔膜とし、過電圧の小さい活性陰極を使用するイオン交換膜法に移行してきた。この間、水酸化ナトリウム１トンの製造に要する電力原単位は２０００ｋＷｈまで減少した。しかしながら、水酸化ナトリウム製造は電力多消費産業であるため、更なる電力原単位の削減が求められている。 Sodium hydroxide (caustic soda) and chlorine, which are important as industrial raw materials, are mainly produced by the salt electrolysis method. This electrolysis process has gone through the mercury method using a mercury cathode and the diaphragm method using an asbestos diaphragm and a soft iron cathode, and then has shifted to an ion exchange membrane method using an active cathode with a small overvoltage using an ion exchange membrane as a diaphragm. . During this time, the power consumption required to produce 1 ton of sodium hydroxide was reduced to 2000 kWh. However, since sodium hydroxide production is a power intensive industry, there is a need for further reduction in power intensity.
従来の電解方法における陽極、陰極反応はそれぞれ式（７）及び（８）の通りであり、理論分解電圧は２．１９Ｖとなる。
２Ｃｌ- → Ｃｌ2 ＋ ２ｅ- （７）
２Ｈ2Ｏ ＋ ２ｅ- → ２ＯＨ- ＋ Ｈ2 （８）
The anode and cathode reactions in the conventional electrolysis method are as shown in equations (7) and (8), respectively, and the theoretical decomposition voltage is 2.19V.
2Cl − → Cl 2 + 2e − (7)
2H 2 O + 2e − → 2OH − + H 2 (8)
陰極で水素発生反応を行わせる代わりに酸素陰極を用いれば、反応は式（９）の通りになり、理論的には１．２３Ｖ、実用的電流密度範囲でも０．８Ｖ程度の槽電圧を低減することができ、水酸化ナトリウム１トン当たり７００ｋＷｈの電力原単位の低減が期待できる。
Ｏ2 ＋ ２Ｈ2Ｏ ＋ ４ｅ- → ４ＯＨ- （９）
If an oxygen cathode is used instead of performing a hydrogen generation reaction at the cathode, the reaction is as shown in equation (9), which theoretically reduces the cell voltage to about 1.23 V and about 0.8 V even in a practical current density range. And a reduction of 700 kWh per unit of sodium hydroxide can be expected.
O 2 + 2H 2 O + 4e − → 4OH − (9)
このため、１９８０年代からガス拡散電極を利用する食塩電解プロセスの実用化が検討されているが、このプロセスを実現させるためには高性能かつ該電解系における充分な安定性を要する酸素陰極の開発が不可欠である。
食塩電解での酸素ガス陰極の経緯については、「食塩電解酸素陰極に関する国内外の状況」、ソーダと塩素、第45巻、85（1994）に詳しい。
For this reason, the practical use of a salt electrolysis process using a gas diffusion electrode has been studied since the 1980s. In order to realize this process, development of an oxygen cathode that requires high performance and sufficient stability in the electrolysis system is required. Is essential.
The history of oxygen gas cathodes in salt electrolysis is detailed in “Domestic and Domestic Oxygen Cathodic Conditions”, Soda and Chlorine, Vol. 45, 85 (1994).
しかしながらこれらの工業電解系は燃料電池の場合と比較して、操業条件が過酷であるために、ガス拡散電極の寿命や性能が十分に得られないという問題点がある。
アルカリ性電解質では、貴金属以外の触媒が利用可能である。スピネル型、ペロブスカイト型、パイロクロア型の金属酸化物や二酸化マンガン（特にγ-ＭｎＯＯＨが最良）などが優れているとされる。金属キレート錯体も高活性であり、Ｎｉ、Ｃｏ、Ｆｅイオンを中心金属とするポルフィリン、フタロシアニンなどの配位錯体は特に検討が進んでいる。これらを熱処理した触媒も活性が向上することが報告されている（非特許文献１）。しかしながら、これらの酸化物、有機配位子触媒では２電子還元が主に進行し易いため、使用される電極、膜などの劣化を引き起こす可能性がある。銀触媒成分は耐久性があり汎用されているが、２電子還元が一部進行し、上記劣化を完全には防止できない。
However, these industrial electrolytic systems have the problem that the operating conditions of the gas diffusion electrode cannot be sufficiently obtained because the operating conditions are severer than in the case of a fuel cell.
For alkaline electrolytes, catalysts other than noble metals can be used. Spinel-type, perovskite-type, pyrochlore-type metal oxides and manganese dioxide (especially γ-MnOOH is best) are considered excellent. Metal chelate complexes are also highly active, and coordination complexes such as porphyrins and phthalocyanines that have Ni, Co, and Fe ions as the central metal have been particularly studied. It has been reported that the activity of these heat-treated catalysts is improved (Non-patent Document 1). However, these oxides and organic ligand catalysts tend to cause two-electron reduction to proceed mainly, which may cause deterioration of electrodes and films used. Although the silver catalyst component is durable and widely used, two-electron reduction partially proceeds and the above deterioration cannot be completely prevented.
特許文献５では、酸素還元ガス拡散陰極を用いる食塩電解において、陰極にて生成し電極性能を低下させる過酸化水素の対策を講じた酸素還元ガス拡散電極として、銀とマンガン酸化物を含む電極触媒層が提案されている。 In Patent Document 5, an electrode catalyst containing silver and manganese oxide is used as an oxygen reducing gas diffusion electrode in which sodium hydrogen is generated in the cathode electrolysis using an oxygen reducing gas diffusion cathode and measures against hydrogen peroxide are generated to reduce electrode performance. Layers have been proposed.
特許文献６には、食塩電解でのガス拡散電極触媒としては、高温アルカリ中で安定であり、安価であり、セル電圧の小さい電極として、疎水性材料及び炭素材料からなる多孔性の導電性基体３の上に、銀及びパラジウムを触媒層とする提案がある。 In Patent Document 6, a porous conductive substrate made of a hydrophobic material and a carbon material is used as a gas diffusion electrode catalyst in salt electrolysis, which is stable in high temperature alkali, inexpensive, and has a low cell voltage. 3 is a proposal to use silver and palladium as a catalyst layer.
上記特許文献記載の技術では、酸性電解質系の触媒開発において白金が利用されてきたが、貴金属の価格は非常に高いため、その使用量を最低限に減らす必要があり、非金属触媒に注目が集まっている。しかしながら安定性、寿命などについては課題が残っていたため、対策として微量の貴金属で高性能を達成する技術を確立する方向も重要であるといえる。 In the technology described in the above-mentioned patent document, platinum has been used in the development of an acidic electrolyte catalyst. However, since the price of noble metals is very high, it is necessary to reduce the amount used, and attention is paid to non-metallic catalysts. Gathered. However, problems remain with respect to stability, life, etc., so it can be said that it is important to establish a technology that achieves high performance with a small amount of precious metal as a countermeasure.
主触媒である白金族金属と酸化物が混合された触媒に関して多くの提案はあるが、該触媒の上に酸化物を被覆することにより、水素酸化反応や、酸素還元反応の活性が高まる作用があることは、これまで報告されていない。アルカリ性電解質型においても、銀、パラジウムなどの高価な金属が多量に用いられているため、このような新規な技術を活用し触媒量を減少させることが不可欠である。 There are many proposals regarding a catalyst in which a platinum group metal and an oxide are mixed as the main catalyst, but by covering the catalyst with an oxide, the activity of hydrogen oxidation reaction and oxygen reduction reaction is enhanced. There has been no report so far. Even in the alkaline electrolyte type, a large amount of expensive metal such as silver or palladium is used, so it is indispensable to reduce the amount of catalyst by utilizing such a novel technique.
これらの従来技術以外の関連技術について説明する。
特許文献７は、有機溶媒を用いたＴａ、Ｎｂの多孔性センサー材料の製造方法として、金属または金属合金上に、ニオブ層またはタンタル層を電着するために、五塩化ニオブまたは五塩化タンタルを含み、水と酸素を除いた炭酸プロピレン溶液で、０〜１２０℃の温度で周期的な電流反転により電析する技術が開示されている。
Related technologies other than these conventional technologies will be described.
In Patent Document 7, as a method for producing a porous sensor material of Ta and Nb using an organic solvent, niobium pentachloride or tantalum pentachloride is used for electrodeposition of a niobium layer or a tantalum layer on a metal or metal alloy. A technique of electrodeposition by cyclic current reversal at a temperature of 0 to 120 ° C. in a propylene carbonate solution containing water and oxygen is disclosed.
特許文献８は、ハロゲンを添加した有機溶媒を電解析出用溶液に使用することにより、金属種の溶解度で制約されることなく各種金属薄膜を作製する技術が開示されている。ケトン，アルコール類或いはこれらの混合物からなる有機溶媒にハロゲンを添加することにより、電解析出用溶液に金属又は合金製の陽極及び導電性陰極を浸漬し、直流電解によって陽極から金属イオンを溶出させ、金属薄膜又は金属化合物薄膜として陰極に析出させる。陽極材料に種々の金属や合金を使用できるが、Ｔｉ，Ｚｒ，Ｈｆ，Ｖ，Ｎｂ，Ｔａ，Ｍｏ，Ｗ，Ｃｒ，Ａｌから選ばれたバルブメタル又はその合金を陽極に使用すると、該バルブメタルが金属の皮膜となって陰極表面に堆積する。ただし、電極触媒としての利用は想定していない。 Patent Document 8 discloses a technique for producing various metal thin films without being restricted by the solubility of metal species by using an organic solvent to which halogen is added for an electrolytic deposition solution. By adding halogen to an organic solvent consisting of a ketone, alcohol or a mixture thereof, a metal or alloy anode and a conductive cathode are immersed in the electrolytic deposition solution, and metal ions are eluted from the anode by DC electrolysis. Then, it is deposited on the cathode as a metal thin film or a metal compound thin film. Various metals and alloys can be used for the anode material. When a valve metal selected from Ti, Zr, Hf, V, Nb, Ta, Mo, W, Cr, and Al or an alloy thereof is used for the anode, the valve metal Becomes a metal film and is deposited on the cathode surface. However, utilization as an electrode catalyst is not assumed.
特許文献９には、触媒として、オゾン水合成のための電解用電極技術が報告されている。平滑な基体上に白金、金、又は、導電性をもつ金属酸化物、例えば、酸化イリジウム、酸化パラジウム、又は、酸化ルテニウム、酸化物超伝導体などの上に、酸化チタン、酸化タンタル、酸化タングステン、酸化ハフニウム、酸化ニオブなどの表面層を形成する。表面酸化物がＴａＯxのような酸素欠損した酸化物であることが報告されている。しかし、酸素還元、水素酸化反応に対しての活性向上、ガス拡散電極としての利用に関しては開示がない。 Patent Document 9 reports an electrode technology for electrolysis for ozone water synthesis as a catalyst. Platinum, gold, or a conductive metal oxide such as iridium oxide, palladium oxide, ruthenium oxide, oxide superconductor, etc. on a smooth substrate, titanium oxide, tantalum oxide, tungsten oxide A surface layer of hafnium oxide, niobium oxide or the like is formed. It has been reported that the surface oxide is an oxygen-deficient oxide such as TaOx. However, there is no disclosure regarding oxygen reduction, activity improvement for hydrogen oxidation reaction, and utilization as a gas diffusion electrode.
特許文献１０は、導電性基材上の触媒層上に形成された水素吸着性層を含む水素発生用電極が開示されている。水素が関与する反応への効果は、水素原子のスピルオーバー、逆スピルオーバー現象として説明される。ただし、酸素還元に対しての活性向上に関しては開示がない。 Patent Document 10 discloses a hydrogen generating electrode including a hydrogen adsorbing layer formed on a catalyst layer on a conductive substrate. The effect on the reaction involving hydrogen is explained as a spillover or reverse spillover phenomenon of hydrogen atoms. However, there is no disclosure regarding improvement of activity against oxygen reduction.
本発明では、電極活性、安定性を向上させる目的で、鋭意検討の結果、従来の主触媒層の上に少量の助触媒層を形成させることにより、前記水素ガス酸化および酸素ガス還元活性が大幅に向上することを見出したものである。 In the present invention, as a result of intensive investigations for the purpose of improving electrode activity and stability, the hydrogen gas oxidation and oxygen gas reduction activities are greatly improved by forming a small amount of promoter layer on the conventional main catalyst layer. Has been found to improve.
本発明は、導電性基材表面に形成した主触媒粒子の上にＴａ、Ｔｉ、Ｎｂ、Ｚｒ、Ｗから選択される少なくとも１種の金属及び／又は金属酸化物を含んで成る助触媒層を形成したことを特徴とするガス拡散電極である。前記主触媒粒子を構成する物質は、Ｐｔ、Ｉｒ、Ｒｕ、Ｐｄ、Ｒｈなどの白金族金属、銀やその化合物、又はそれの白金族金属、銀と化合物に、ランタン系金属、弁金属、鉄系金属、銀から選択される１種類の金属及び/又は金属酸化物とすることができる。 The present invention provides a promoter layer comprising at least one metal and / or metal oxide selected from Ta, Ti, Nb, Zr, and W on the main catalyst particles formed on the surface of the conductive substrate. A gas diffusion electrode characterized by being formed. Substances constituting the main catalyst particles include platinum group metals such as Pt, Ir, Ru, Pd, and Rh, silver and compounds thereof, or platinum group metals, silver and compounds thereof, lanthanum metals, valve metals, iron One type of metal and / or metal oxide selected from the group metals and silver can be used.
助触媒層を構成する金属は、Ｔａ、Ｔｉ、Ｎｂ、Ｚｒ、Ｗから選ばれる少なくとも１種類の組成であり、該助触媒層は平均付着量が元素として０．１ｍｍｏｌ／ｍ2から１ｍｍｏｌ／ｍ2となるように形成することが望ましい。主触媒粒子の形成後、有機溶媒を用いためっきにより、多孔性かつ疎水性を有する電極内部の適切な位置に助触媒層を形成できる。 The metal constituting the promoter layer has at least one composition selected from Ta, Ti, Nb, Zr, and W. The promoter layer has an average deposition amount of 0.1 mmol / m 2 to 1 mmol / m as an element. It is desirable to form so as to be 2 . After the formation of the main catalyst particles, the promoter layer can be formed at an appropriate position inside the porous and hydrophobic electrode by plating using an organic solvent.
本発明の助触媒となる金属の表面には自然酸化膜が形成され、金属および酸化物からなることが確認されている。この場合、酸化物は実質上微量であるが、本発明では助触媒層を形成する有効な成分とみなしている。本発明の機構については不明な点があるが、ＴａＯｘとＴａ2Ｏ5とが共存し、導電性を発現すると同時に、酸素化学種のスピルオーバー現象に寄与していると推定されている。つまり本発明は水素のスピルオーバーでは説明できない触媒効果がＴａ層等の助触媒層にあることを示唆し、本発明ではこれを助触媒作用と呼ぶ。 It has been confirmed that a natural oxide film is formed on the surface of the metal serving as the co-catalyst of the present invention, and consists of a metal and an oxide. In this case, although the amount of oxide is substantially minute, in the present invention, it is regarded as an effective component for forming the promoter layer. Although there is an unclear point about the mechanism of the present invention, it is presumed that TaOx and Ta 2 O 5 coexist, exhibit conductivity, and contribute to the oxygen species spillover phenomenon. In other words, the present invention suggests that a catalytic effect that cannot be explained by hydrogen spillover is present in the promoter layer such as the Ta layer, and in the present invention, this is called promoter activity.
ガス電極の触媒表面に、有機溶媒にて触媒性を有さないＴａ金属などのめっきを施すと、触媒の活性を向上できること、また、担体であるカーボン微粉末の一部の表面もＴａめっきされること、触媒のみならずカーボン減耗も防止され、長期的安定性に貢献できることを見出した。 If the catalyst surface of the gas electrode is plated with Ta metal or the like that does not have catalytic properties with an organic solvent, the activity of the catalyst can be improved, and the surface of a part of the carbon fine powder that is the carrier is also Ta-plated. It has been found that not only the catalyst but also carbon depletion can be prevented, contributing to long-term stability.
本発明のガス拡散電極は、主電極触媒である貴金属、銀などの高価な材料表面にＴａなどの活性の小さい金属層を、有機溶媒を用いためっき法などにより形成し、これを助触媒層とした電極触媒を用いることで、主電極触媒単独の高価なガス拡散電極より、安価で活性の高いガス拡散電極を提供できる。更に該ガス拡散電極は、副反応で生成する過酸化水素等の活性酸素種の生成を抑制し、電極の劣化が防止される。従って電気化学システムの安定化と電極寿命の長期化を達成できる。 In the gas diffusion electrode of the present invention, a metal layer having a small activity such as Ta is formed on a surface of an expensive material such as a noble metal or silver as a main electrode catalyst by a plating method using an organic solvent, and this is formed as a promoter layer. By using the electrode catalyst described above, it is possible to provide a gas diffusion electrode that is cheaper and more active than the expensive gas diffusion electrode of the main electrode catalyst alone. Further, the gas diffusion electrode suppresses the generation of active oxygen species such as hydrogen peroxide generated by the side reaction, and the deterioration of the electrode is prevented. Therefore, stabilization of the electrochemical system and extension of the electrode life can be achieved.
以下本発明を詳細に説明する。 The present invention will be described in detail below.
[導電性基材]
導電性基材は、カーボンから成るクロス、繊維焼結体等の多孔性材料を用いることが望ましい。該基体はガス、液の供給、除去のため、適度の多孔性を有しかつ十分な導電性を保つことが好ましい。厚さ０．０１〜５ｍｍ、空隙率が３０〜９５％、代表的孔径が０．００１〜１ｍｍが好ましい。カーボンクロスは数μｍの細いカーボン繊維を数百本の束とし、これを織布としたものであるが、気液透過性に優れた材料である。カーボンペーパーはカーボン原料繊維を製紙法にて薄膜の前駆体とし、これを焼結したものであるが、これも使用に適する材料である。上記基体材料の表面は一般的に疎水性であり、酸素ガスの供給の観点からは好ましい材料であるが、生成した水酸化ナトリウムの排出の目的からは不適当な材料である。また、該材料の疎水性は運転とともに低下するため、長期的に十分なガス供給能を維持するために、疎水性バインダーを添加することが知られている。
[Conductive substrate]
As the conductive base material, it is desirable to use a porous material such as a cloth made of carbon or a fiber sintered body. The substrate preferably has moderate porosity and sufficient conductivity for supplying and removing gas and liquid. The thickness is preferably 0.01 to 5 mm, the porosity is 30 to 95%, and the typical pore diameter is 0.001 to 1 mm. The carbon cloth is made of a bundle of several hundreds of fine carbon fibers of several μm, which is used as a woven fabric, and is a material excellent in gas-liquid permeability. Carbon paper is obtained by using carbon raw material fibers as a thin film precursor by a paper manufacturing method and sintering it, and is also a material suitable for use. The surface of the base material is generally hydrophobic and is a preferable material from the viewpoint of supplying oxygen gas, but is inappropriate for the purpose of discharging the generated sodium hydroxide. In addition, since the hydrophobicity of the material decreases with operation, it is known to add a hydrophobic binder in order to maintain a sufficient gas supply capability for a long period of time.
前述の通り、導電性基材は高導電性であることが好ましい。前記カーボン材料は導電性ではあるが、金属に比較すれば劣っており、１ｍΩｃｍ以下にすることは困難である。性能を改善し高導電性化する目的で、プレス加工を施すことが好ましい。プレス加工は、カーボン材料を圧縮することによって全体の導電性を高めるとともに、圧力を加えて使用した際の導電性変化を低減させ、かつ、主触媒粒子と導電性基材間の接合度が向上することによる導電性向上に寄与する。また、導電性基材および主触媒粒子の圧縮、及び主触媒粒子と導電性基材の接合度の向上によって、原料酸素ガスの供給能力も向上する。プレス加工装置としては、ホットプレス、ホットローラーなどの公知の装置を利用できる。プレス条件としては、室温〜３６０℃にて、圧力０．１〜５ＭＰａが望ましい。 As described above, the conductive substrate is preferably highly conductive. Although the carbon material is conductive, it is inferior to metals, and it is difficult to make it 1 mΩcm or less. For the purpose of improving performance and increasing conductivity, it is preferable to perform press working. Press working increases the overall conductivity by compressing the carbon material, reduces the change in conductivity when used under pressure, and improves the degree of bonding between the main catalyst particles and the conductive substrate. This contributes to improving the conductivity. Further, the supply capacity of the raw material oxygen gas is improved by the compression of the conductive base material and the main catalyst particles and the improvement in the degree of bonding between the main catalyst particles and the conductive base material. As the press working apparatus, a known apparatus such as a hot press or a hot roller can be used. As pressing conditions, room temperature to 360 ° C. and a pressure of 0.1 to 5 MPa are desirable.
[主触媒粒子]
主触媒粒子は、Ｐｔ、Ｉｒ、Ｒｕ、Ｐｄ、Ｒｈ、Ａｇから選択される少なくとも1種類以上の金属又はその酸化物を含み、前記導電性基材上に形成される。具体例としては、Ｐｔ単独、Ｒｕ−Ｐｔ、Ｒｕ酸化物などがある。また、主触媒粒子は、これら白金族金属や銀及び/又はその金属酸化物以外に、ランタン系金属、バルブ金属、鉄系金属から選択される少なくとも1種類の金属及び/又は金属酸化物を含んで、合金や複合酸化物を構成していても良い。具体例としては、Ｐｔ―Ａｇ、Ｐｄ−Ａｇ 、Ｒｕ−Ｎｉ酸化物、Ｐｔ―Ｃｅ酸化物、Ｒｕ−Ｃｅ酸化物、Ｐｔ-Ｌａ酸化物、Ｒｕ−Ｌａ酸化物などがある。
[Main catalyst particles]
The main catalyst particles include at least one metal selected from Pt, Ir, Ru, Pd, Rh, and Ag or an oxide thereof, and are formed on the conductive substrate. Specific examples include Pt alone, Ru—Pt, and Ru oxide. The main catalyst particles contain at least one metal and / or metal oxide selected from lanthanum-based metals, valve metals, and iron-based metals in addition to these platinum group metals and silver and / or metal oxides thereof. Thus, an alloy or a composite oxide may be formed. Specific examples include Pt—Ag, Pd—Ag, Ru—Ni oxide, Pt—Ce oxide, Ru—Ce oxide, Pt—La oxide, Ru—La oxide, and the like.
例えば食塩電解での酸素還元触媒は、高温アルカリ中で安定であり、安価であることが好ましく、主反応である酸素還元による水酸イオン生成の触媒として、通常銀或いは銀合金（銅、白金、パラジウム少量を含有していても良い）を選択する。これらは市販されている粉末も使用できるが、既知方法に従って作製しても良い。銀触媒、合金触媒は、例えば硝酸銀、あるいは硝酸銀と硝酸パラジウムなどの水溶液に、還元剤を混合して合成する湿式法が好ましい。また、蒸着、スパッターなどの乾式法により合成することもできる。 For example, an oxygen reduction catalyst in salt electrolysis is preferably stable in high temperature alkali and inexpensive, and usually silver or a silver alloy (copper, platinum, May contain a small amount of palladium). Commercially available powders can be used for these, but they may be prepared according to known methods. The silver catalyst or alloy catalyst is preferably a wet method in which, for example, silver nitrate or an aqueous solution of silver nitrate and palladium nitrate is mixed with a reducing agent for synthesis. It can also be synthesized by a dry method such as vapor deposition or sputtering.
本発明の主触媒粒子も、粒子に上記の触媒を展開することにより、触媒表面積を有効に拡大することができる、通常、ファーネスブラック、アセチレンブラックなどと称される微粒子状の炭素微粒子が用いられる。炭素粒子の粒径は０．０１〜１μmが好ましい。 The main catalyst particles of the present invention can also effectively expand the surface area of the catalyst by spreading the above catalyst on the particles. Usually, fine carbon particles called furnace black, acetylene black or the like are used. . The particle size of the carbon particles is preferably 0.01 to 1 μm.
[触媒スラリー]
前記のような組成を有する主触媒粒子は、通常スラリーとして多孔性導電性基材に塗布し、固着する。つまり各触媒の粉末を、疎水性バインダー及び水、ナフサ等の溶剤と混合しペーストとし、前記基体に塗布、固着する。疎水性バインダー材料としては、フッ化ピッチ、フッ化黒鉛、フッ素樹脂が好ましく、特に耐久性のあるフッ素樹脂を２００℃から４００℃の温度において焼成して使用することは均一かつ良好な性能を得るために好ましい方法である。フッ素成分の粉末の粒径は０．００５〜１μｍが好ましい。塗布、乾燥、焼成は数回に分けて実施すると、均質な触媒層が得られるので特に好ましい。
[Catalyst slurry]
The main catalyst particles having the above composition are usually applied as a slurry to a porous conductive substrate and fixed. That is, the powder of each catalyst is mixed with a hydrophobic binder and a solvent such as water and naphtha to form a paste, which is applied and fixed to the substrate. As the hydrophobic binder material, fluorinated pitch, fluorinated graphite, and fluororesin are preferable. In particular, use of a durable fluororesin after baking at a temperature of 200 ° C. to 400 ° C. provides uniform and good performance. Therefore, it is a preferable method. The particle size of the fluorine component powder is preferably 0.005 to 1 μm. It is particularly preferable to apply the coating, drying and firing in several times since a homogeneous catalyst layer can be obtained.
[助触媒層とその製法]
助触媒層は使用状況における安定性があり、貴金属に比較して安価な材料であることが不可欠であり、Ｔａ、Ｔｉ、Ｎｂ、Ｚｒ、Ｗから選ばれる少なくとも１種類以上の金属及び／又は酸化物とする。
助触媒層の平均付着量は、主触媒粒子の表面積に対する助触媒層構成元素が、０．１ｍｍｏｌ／ｍ2から１ｍｏｌ／ｍ2となるようにすることが好ましい。１ｍｏｌ／ｍ2以上であると電解の進行の妨げになり、０．１ｍｍｏｌ／ｍ2以下であると触媒促進という特異的な効果が低下する。
[Cocatalyst layer and its production method]
The co-catalyst layer is stable in use, and is indispensable to be an inexpensive material as compared with a noble metal. At least one metal selected from Ta, Ti, Nb, Zr, and W and / or oxidation It is a thing.
The average adhesion amount of the promoter layer is preferably such that the constituent element of the promoter layer relative to the surface area of the main catalyst particles is 0.1 mmol / m 2 to 1 mol / m 2 . If it is 1 mol / m 2 or more, the progress of electrolysis is hindered, and if it is 0.1 mmol / m 2 or less, the specific effect of catalyst promotion is reduced.
主触媒粒子上に形成する助触媒層は次に示すいずれかの形成技術を用いて形成することができる。 The promoter layer formed on the main catalyst particles can be formed using any of the following forming techniques.
溶融めっきは、溶融金属中に基材を浸漬し、溶融金属を基材表面に付着させる方法である。必要に応じて付着過程において電流を流す。Ｔａの場合、たとえばＬｉＦ−ＮａＦ（モル％として６０：４０）の溶融塩にＫ2Ｔａ2Ｆ7を添加し、電気炉にてＡｒ雰囲気下８００℃に維持し、電流を流すことによりＴａ 層を形成できる。 Hot dipping is a method in which a substrate is immersed in molten metal and the molten metal adheres to the surface of the substrate. If necessary, an electric current is passed during the adhesion process. In the case of Ta, for example, K 2 Ta 2 F 7 is added to a molten salt of LiF—NaF (mol%: 60:40), maintained at 800 ° C. in an Ar atmosphere in an electric furnace, and a Ta layer is formed by flowing current. Can be formed.
五塩化タンタルとアルキルイミダゾリウムクロライドと弗化リチウムなどのアルカリ金属またはアルカリ土類金属の弗化物からなる溶融塩を電解浴に用い、低温の溶融塩電解浴を用いて、めっき法によりタンタル膜を形成することも知られている（特開２００１−２７９４８６号公報）。 A molten salt made of fluoride of alkali metal or alkaline earth metal such as tantalum pentachloride, alkylimidazolium chloride and lithium fluoride is used as an electrolytic bath, and a tantalum film is formed by plating using a low temperature molten salt electrolytic bath. It is also known to form (Japanese Patent Laid-Open No. 2001-279486).
次いで、CVDと称される化学蒸着法があり、半導体製造工程で汎用されている成膜技術である。低温で気化した金属塩と高温に加熱された固体との接触において、熱分解反応、水素還元反応、高温不均化反応等によって目的とする金属或いは金属化合物を析出させる方法である。例えば、無機塩の水素還元反応を利用する場合、Nbは水素によるNbCl5から低次のＮｂ3Ｃｌ8の生成とその高温不均化反応による分解を繰り返しながら析出される。一方、ＴａはＴａＣｌ5から水素によって直接還元される。 Next, there is a chemical vapor deposition method called CVD, which is a film forming technique widely used in semiconductor manufacturing processes. In this method, a target metal or metal compound is precipitated by a thermal decomposition reaction, a hydrogen reduction reaction, a high temperature disproportionation reaction, or the like in contact between a metal salt vaporized at a low temperature and a solid heated to a high temperature. For example, when a hydrogen reduction reaction of an inorganic salt is used, Nb is precipitated while repeatedly generating low-order Nb 3 Cl 8 from NbCl 5 by hydrogen and decomposing it by a high temperature disproportionation reaction. On the other hand, Ta is directly reduced by hydrogen from TaCl 5 .
ＰＶＤと称される物理蒸着法も使用され、真空蒸着、スパッターリング、イオンプレーティングなどの手法があり、既存の市販装置を用いることができる。真空蒸着法は物理蒸着法の一態様であり、減圧された空間の中で、蒸着すべき金属を加熱し基材表面に付着させる。通常１０-1〜１０-2Ｐａの範囲で制御する。スパッターリングも物理蒸着法の一態様であり、真空蒸着に比較して、低温で高融点物質の膜が得られる、大面積にわたって均一な膜が成形できる、合金組成に対応できる、応答性が速く制御しやすい、などの特徴を有し普及が進んでいる。イオンプレーティングもまた物理蒸着法の一態様であり、減圧したガス中の放電状態下でプラズマ化した金属イオンを電場で加速させ、負に分極した基材に蒸着させる方法である。スパッターリングより付き回り、均一性の点で品質良好な膜を得ることが可能である。 A physical vapor deposition method called PVD is also used, and there are techniques such as vacuum vapor deposition, sputtering, and ion plating, and existing commercial equipment can be used. The vacuum vapor deposition method is an embodiment of a physical vapor deposition method, in which a metal to be vapor-deposited is heated and adhered to the substrate surface in a decompressed space. Usually, it is controlled in the range of 10 −1 to 10 −2 Pa. Sputtering is also an aspect of physical vapor deposition. Compared to vacuum vapor deposition, a film of a high melting point material can be obtained at a low temperature, a uniform film can be formed over a large area, can respond to an alloy composition, and has a quick response. It is popular because it is easy to control. Ion plating is also an embodiment of a physical vapor deposition method, which is a method of accelerating metal ions, which are plasmatized under a discharge state in a decompressed gas, with an electric field and depositing them on a negatively polarized substrate. It is possible to obtain a film having a good quality in terms of uniformity by following the spatter ring.
上記の成膜方法は、製作条件が厳しく、装置費用もかかり必ずしも容易な手段ではない。 一方、有機溶媒を用いためっき法は、装置が安価で成膜が容易であり、工業化に有利である。水溶液ではめっきが困難なＴａなどの金属も容易に成膜が可能であることが報告されている。 The film forming method described above is not an easy means because the manufacturing conditions are strict and the apparatus cost is high. On the other hand, a plating method using an organic solvent is advantageous for industrialization because the apparatus is inexpensive and film formation is easy. It has been reported that a metal such as Ta, which is difficult to be plated with an aqueous solution, can be easily formed.
めっきに使用する有機溶媒としては、ポリカーボネートや、ＣＨ3ＣＯＲで表される構造を有するメチルケトン系のものが好ましく、例えば、アセトン、メチルエチルケトン、アセトフェノン等またはこれらの混合物を用いることができる。 The organic solvent used for plating is preferably a polycarbonate or a methyl ketone-based one having a structure represented by CH 3 COR. For example, acetone, methyl ethyl ketone, acetophenone, or a mixture thereof can be used.
電解質としては、目的の金属めっきを妨げるものでなければ特に限定はない。Ｌｉ、Ｎａ、ＫなどのカチオンのＣｌＯ4塩などが好ましい。それらの濃度は０．００２Ｍ〜０．１Ｍであることが好ましく、０．００５Ｍ〜０．０５Ｍであることが特に好ましい。
めっきする対象の金属イオンは、陽極溶解により補給することが可能である。また、金属塩を溶解させておくことも好ましい。金属イオン濃度は０．００２ｍｏｌ／Ｌ〜０．１ｍｏｌ／Ｌであることが好ましく、０．００５ｍｏｌ／Ｌ〜０．０５ｍｏｌ／Ｌであることが特に好ましい。
The electrolyte is not particularly limited as long as it does not interfere with the target metal plating. A ClO 4 salt of a cation such as Li, Na, or K is preferred. Their concentration is preferably 0.002M to 0.1M, particularly preferably 0.005M to 0.05M.
Metal ions to be plated can be replenished by anodic dissolution. It is also preferable to dissolve the metal salt. The metal ion concentration is preferably 0.002 mol / L to 0.1 mol / L, and particularly preferably 0.005 mol / L to 0.05 mol / L.
めっき時の電流密度は１ｍＡ／ｃｍ2〜１Ａ／ｃｍ2の範囲が好ましい。これより小さいと生産性が劣り、これより大きいと良質なめっき層が得られない。
有機溶媒温度は０℃〜７０℃であることが好ましく、１５℃〜５０℃であることがより好ましい。温度がこれよりも低いと溶液のイオン溶解度が低下し、また、７０℃を超えると溶液が蒸発し利用が困難となる。
助触媒となる金属の表面には自然酸化膜が形成されて安定化している。必要に応じて、熱処理を加えることができる。
Current density during plating is preferably in the range of 1mA / cm 2 ~1A / cm 2 . If it is smaller than this, the productivity is inferior, and if it is larger than this, a high-quality plated layer cannot be obtained.
The organic solvent temperature is preferably 0 ° C to 70 ° C, more preferably 15 ° C to 50 ° C. If the temperature is lower than this, the ionic solubility of the solution decreases, and if it exceeds 70 ° C., the solution evaporates and it becomes difficult to use.
A natural oxide film is formed on the surface of the metal serving as a cocatalyst and stabilized. If necessary, heat treatment can be applied.
[陽極]
陽極材料は、特に限定されないが、白金、チタン、ジルコニウム、ニオブ、タンタル、タングステン等の金属、それらの合金であることが好ましい。陽極形状は、特に限定されず、板状、棒状、筒状、網状等が好ましい。
[anode]
The anode material is not particularly limited, but is preferably a metal such as platinum, titanium, zirconium, niobium, tantalum, or tungsten, or an alloy thereof. The anode shape is not particularly limited, and a plate shape, a rod shape, a cylindrical shape, a net shape, and the like are preferable.
[陰極]
陰極としては、めっき法等で、主触媒粒子及び助触媒層を形成したガス拡散電極を用いる。
[cathode]
As the cathode, a gas diffusion electrode in which main catalyst particles and a promoter layer are formed by a plating method or the like is used.
[電気化学セル]
本発明のガス拡散電極は、食塩電解などの各種工業電解用の電気化学セルの電極として使用できる。
本ガス拡散電極とイオン交換膜を密着させる必要がある場合、前もってそれらを機械的に結合させておくか、或いは電解時に圧力を与える。圧力としては０．０１ＭＰａ〜３ＭＰａが好ましい。カチオン交換膜としてはフッ素樹脂系の膜が耐食性の面から最適である。アルカリ型燃料電池の場合、耐久性に優れた市販のアニオン交換膜を用いることができる。
食塩電解セルで本発明の電極を使用する場合、陽極はＤＳＥ、ＤＳＡと呼ばれる貴金属酸化物を有するチタン製の不溶性電極であり、膜と密着して用いることができるよう多孔性であることが好ましい。
[Electrochemical cell]
The gas diffusion electrode of the present invention can be used as an electrode for electrochemical cells for various industrial electrolysis such as salt electrolysis.
When the gas diffusion electrode and the ion exchange membrane need to be brought into close contact with each other, they are mechanically bonded in advance or pressure is applied during electrolysis. The pressure is preferably 0.01 MPa to 3 MPa. As the cation exchange membrane, a fluororesin-based membrane is optimal from the viewpoint of corrosion resistance. In the case of an alkaline fuel cell, a commercially available anion exchange membrane having excellent durability can be used.
When using the electrode of the present invention in a salt electrolysis cell, the anode is an insoluble electrode made of titanium having a noble metal oxide called DSE or DSA, and is preferably porous so that it can be used in close contact with the membrane. .
[セル構造・運転方法]
食塩電解セルについて説明する。酸素ガス拡散電極を電解槽に配置する際に、陰極を支え、また電気的導通を補助する目的として導電性支持材を用いることができる。支持材としては、適切な均一性かつクッション性を有することが好ましい。ニッケル、ステンレスなどの金属メッシュ、スプリング、板ばね、ウェブ状などの公知材料を使用すればよい。
銀以外の材料を使用する場合には銀めっきを施すことが耐食性の観点から好ましい。
[Cell structure and operation method]
The salt electrolysis cell will be described. When the oxygen gas diffusion electrode is disposed in the electrolytic cell, a conductive support material can be used for the purpose of supporting the cathode and assisting electrical conduction. The support material preferably has appropriate uniformity and cushioning properties. A known material such as a metal mesh such as nickel or stainless steel, a spring, a leaf spring, or a web may be used.
In the case of using a material other than silver, it is preferable to perform silver plating from the viewpoint of corrosion resistance.
酸素供給量は４電子還元において理論的に消費される量の１．０５〜２倍が好適である。必要に応じて酸素ガスは加湿する。加湿方法としてはセル入口に７０〜９５℃に加温された加湿装置を設け、酸素ガスを通すことで自由に制御できる。現在市販されているイオン交換膜の性能では、陽極水の濃度を１５０〜２００ｇ／Ｌに保つと加湿する必要がない。一方新規に開発された膜では加湿する必要がない。水酸化ナトリウム濃度は２５〜４０ｗｔ％が適当であり、基本的にはイオン交換膜の特性によって決まる。 The oxygen supply amount is preferably 1.05 to 2 times the amount theoretically consumed in the 4-electron reduction. If necessary, oxygen gas is humidified. The humidification method can be freely controlled by providing a humidifier heated to 70 to 95 ° C. at the cell inlet and passing oxygen gas. In the performance of ion exchange membranes currently on the market, it is not necessary to humidify the anode water when the concentration of the anode water is kept at 150 to 200 g / L. On the other hand, the newly developed membrane does not need to be humidified. The sodium hydroxide concentration is suitably 25 to 40 wt%, and basically depends on the characteristics of the ion exchange membrane.
本発明の燃料電池の一例を添付図面に基づいて説明する。図１Ａは、助触媒層形成前のガス拡散電極を例示する概略図、図１Ｂは、助触媒層形成後のガス拡散電極を例示する概略図、図２は、ガス拡散電極を使用する燃料電池の概略断面図である。 An example of the fuel cell of the present invention will be described with reference to the accompanying drawings. 1A is a schematic view illustrating a gas diffusion electrode before formation of a promoter layer, FIG. 1B is a schematic view illustrating a gas diffusion electrode after formation of a promoter layer, and FIG. 2 is a fuel cell using the gas diffusion electrode. FIG.
図２に示すように、高分子固体電解質として機能するイオン交換膜１の両面には、それぞれガス拡散電極である板状の酸素極（カソード）２及び水素極（アノード）３が密着している。両極２、３は、例えば炭素繊維製の多孔性クロス基材にＰｔ製の主触媒粒子とフッ素樹脂製粒子を担持させ（図１Ａ）、その後、この基材を、塩化タンタルを溶解させた有機溶媒中に浸漬し置換めっきにより作製できる。 As shown in FIG. 2, a plate-like oxygen electrode (cathode) 2 and a hydrogen electrode (anode) 3 which are gas diffusion electrodes are in close contact with both surfaces of an ion exchange membrane 1 which functions as a polymer solid electrolyte. . The bipolar electrodes 2 and 3 are made of an organic material in which Pt main catalyst particles and fluororesin particles are supported on a porous cloth base material made of, for example, carbon fiber (FIG. 1A), and then the base material is dissolved in tantalum chloride. It can be prepared by immersion plating in a solvent.
前記酸素極２及び水素極３のそれぞれのイオン交換膜１とは反対面の周縁には、額縁状の酸素極用ガスケット４と水素極用ガスケット５が密着している。当該酸素極用ガスケット４と水素極用ガスケット５のそれぞれの内縁側には、多孔性の酸素極用集電体６と水素極用集電体７が、酸素極２及び水素極３に接触するように設置されている。
前記酸素極用ガスケット４には、イオン交換膜に向かう側に複数の凹面が形成された酸素極フレーム８の周縁が接触し、この酸素極フレーム８と酸素極２間に酸素極室９が形成されている。
A frame-shaped oxygen electrode gasket 4 and a hydrogen electrode gasket 5 are in close contact with the peripheral edges of the oxygen electrode 2 and the hydrogen electrode 3 opposite to the ion exchange membrane 1. A porous oxygen electrode current collector 6 and a hydrogen electrode current collector 7 are in contact with the oxygen electrode 2 and the hydrogen electrode 3 on the inner edge sides of the oxygen electrode gasket 4 and the hydrogen electrode gasket 5, respectively. It is installed as follows.
The oxygen electrode gasket 4 is in contact with the periphery of an oxygen electrode frame 8 having a plurality of concave surfaces on the side facing the ion exchange membrane, and an oxygen electrode chamber 9 is formed between the oxygen electrode frame 8 and the oxygen electrode 2. Has been.
他方、前記水素極用ガスケット５には、イオン交換膜に向かう側に複数の凹面が形成された水素極フレーム１０の周縁が接触し、この水素極フレーム１０と水素極３間に水素極室１１が形成される。
１２は酸素極フレーム８の上部に横向きに開口された酸素ガス供給口、１３は酸素極フレーム８の下部に横向きに開口された未反応酸素ガス及び生成水取出口、１４は水素極フレーム１０の上部に横向きに開口された水素ガス供給口、１５は水素極フレーム１０の下部に横向きに開口された未反応水素ガス取出口である。
On the other hand, the peripheral edge of the hydrogen electrode frame 10 having a plurality of concave surfaces formed on the side facing the ion exchange membrane is in contact with the hydrogen electrode gasket 5, and the hydrogen electrode chamber 11 is interposed between the hydrogen electrode frame 10 and the hydrogen electrode 3. Is formed.
Reference numeral 12 denotes an oxygen gas supply port opened laterally at the upper part of the oxygen electrode frame 8, reference numeral 13 denotes unreacted oxygen gas and generated water outlet opened laterally at the lower part of the oxygen electrode frame 8, and reference numeral 14 denotes an outlet of the hydrogen electrode frame 10. A hydrogen gas supply port 15 that is opened laterally at the upper part, and 15 is an unreacted hydrogen gas outlet that is opened laterally at the lower part of the hydrogen electrode frame 10.
図３は、本発明のガス拡散陰極を装着した２室型（ゼロギャップタイプ）食塩電解槽を例示する概略図である。
２室法電解槽２１は、パーフルオロスルホン酸系の陽イオン交換膜２２により、陽極室２３と陰極ガス室２４と区画されている。陽イオン交換膜２２の陽極室２３側には、多孔性の寸法安定性陽極２５が密着し、陽イオン交換膜２２の陰極室側には、前述したガス拡散陰極２６が密着して設置されている。前記ガス拡散陰極２６は、カ−ボン粉末とＰＴＦＥを混合させシ−ト状に成形した多孔性導電性基材表面に、主触媒上に助触媒を形成させた触媒からなっている。
FIG. 3 is a schematic view illustrating a two-chamber type (zero gap type) salt electrolytic cell equipped with the gas diffusion cathode of the present invention.
The two-chamber electrolytic cell 21 is divided into an anode chamber 23 and a cathode gas chamber 24 by a perfluorosulfonic acid cation exchange membrane 22. A porous dimensionally stable anode 25 is in close contact with the anode chamber 23 side of the cation exchange membrane 22, and the gas diffusion cathode 26 is in close contact with the cathode chamber side of the cation exchange membrane 22. Yes. The gas diffusion cathode 26 is made of a catalyst in which a promoter is formed on the main catalyst on the surface of a porous conductive base material formed by mixing carbon powder and PTFE into a sheet shape.
この電解槽２１の陽極室２３に食塩水を、陰極ガス室２４に湿潤酸素含有ガスをそれぞれ供給しながら両極間に通電すると、陽極室２３で生成するナトリウムイオンが陽イオン交換膜２２を透過して陰極ガス室２４内のガス拡散陰極２６に到達する。一方陰極ガス室２４に供給される酸素含有ガス中の酸素は、ガス拡散陰極２６の電極触媒層中の主触媒粒子や助触媒層により水酸イオンに還元されて前記ナトリウムイオンと結合して水酸化ナトリウムを生成し、酸素含有ガスとともに供給される水分に溶解して水酸化ナトリウム水溶液が生成する。この際、過酸化水素や他の活性酸素種が生成するが、電極主触媒上に助触媒が存在することにより前記過酸化水素の生成が抑制され、長期間安定して食塩電解を継続することを可能にする。 When a saline solution is supplied to the anode chamber 23 of the electrolytic cell 21 and a wet oxygen-containing gas is supplied to the cathode gas chamber 24 while energizing between both electrodes, sodium ions generated in the anode chamber 23 permeate the cation exchange membrane 22. To the gas diffusion cathode 26 in the cathode gas chamber 24. On the other hand, oxygen in the oxygen-containing gas supplied to the cathode gas chamber 24 is reduced to hydroxide ions by the main catalyst particles and the promoter layer in the electrode catalyst layer of the gas diffusion cathode 26 and combined with the sodium ions to form water. Sodium oxide is produced and dissolved in water supplied together with the oxygen-containing gas to produce an aqueous sodium hydroxide solution. At this time, hydrogen peroxide and other active oxygen species are generated. However, the presence of a promoter on the electrode main catalyst suppresses the generation of hydrogen peroxide, and continues salt electrolysis stably for a long period of time. Enable.
［実施例］
次に本発明によるガス拡散電極の製造及び使用等に関する実施例（参考例）及び比較例を説明するが、本発明はこれらに限定されるものではない。
[Example]
Next, examples (reference examples) and comparative examples relating to production and use of the gas diffusion electrode according to the present invention will be described, but the present invention is not limited thereto.
[参考例１、参考例２]
本例は、Ｐｔ板表面にめっきしたＴａ層から成る電極状部材が活性を有することを示すものであり、本発明に必須の導電性基材を含まない。
[Reference Example 1, Reference Example 2]
This example shows that an electrode-like member composed of a Ta layer plated on the surface of a Pt plate has activity, and does not include an electroconductive substrate essential for the present invention.
電解質として１ＭのＬｉＣｌＯ4を含むポリカーボネートに塩化タンタルを０．１Ｍ溶解させた。この溶液にＰｔ板を浸漬し、室温にて、０．２Ｃ／ｃｍ2の電気量を流し、前記Ｐｔ板上にＴａをめっきした。図４にその表面の電子顕微鏡写真を示したが、樹脂状に析出したＴａが観察された。図５はＸＰＳであり、左側のグラフはＴａ(４ｆエネルギーレベル)で、右側のグラフはピーク分離データである。これらのデータから、自然酸化によりＴａ酸化物が生成していることが分かる（ＴａＯｘとＴａ2Ｏ5）。更に０．１Ｍ硫酸中、室温下で０．０１Ｖ／ｓでサイクリックボルタンメトリーを計測した（図６）。Ｔａを被覆したＰｔ板（参考例１、実線ｂ）では、Ｔａを被覆していないＰｔ板（参考例２、破線ａ）に比較して、水素の吸脱着電流（Ａｇ／ＡｇＣｌ基準電極にて−０．１Ｖ付近）、および、酸素含有種の吸脱着電流（Ａｇ／ＡｇＣｌ基準電極にて０．５Ｖ付近）のいずれもが増大した。触媒性の乏しいＴａで覆われているにもかかわらず、３〜５倍程度の電流増加が観察された。 0.1M tantalum chloride was dissolved in polycarbonate containing 1M LiClO 4 as an electrolyte. A Pt plate was immersed in this solution, an electric quantity of 0.2 C / cm 2 was passed at room temperature, and Ta was plated on the Pt plate. FIG. 4 shows an electron micrograph of the surface. Ta precipitated in a resinous form was observed. FIG. 5 shows XPS, the graph on the left is Ta (4f energy level), and the graph on the right is peak separation data. From these data, it can be seen that Ta oxide is generated by natural oxidation (TaOx and Ta 2 O 5 ). Furthermore, cyclic voltammetry was measured in 0.01 M sulfuric acid at 0.01 V / s at room temperature (FIG. 6). The Pt plate coated with Ta (Reference Example 1, solid line b) has a hydrogen adsorption / desorption current (Ag / AgCl reference electrode) as compared with the Pt plate not coated with Ta (Reference Example 2, broken line a). Both -0.1 V) and the adsorption / desorption current of oxygen-containing species (around 0.5 V at the Ag / AgCl reference electrode) increased. Despite being covered with Ta with poor catalytic properties, a current increase of about 3 to 5 times was observed.
同様のＴａ被覆したＰｔ板と被覆のないＰｔ板について、回転リングディスク装置による電位−電流関係図を測定した(図７)。参考例１及び参考例２のディスク電極の酸素還元電流電位をそれぞれ実線ａ及び破線ｂで示した。又参考例１及び参考例２のリング電極の過酸化水素の酸化電流電位を、それぞれ実線a’及び破線ｂ’で示した）。
Ｔａ被覆したＰｔ板は、Ｐｔよりも活性が高く、電位として、見掛け上で１００ｍＶ以上、貴の電位にシフトした。Ｔａｆｅｌ勾配は電流密度の小さい範囲で６０ｍＶ、大きい範囲で１２０ｍＶと、Ｐｔと同様の値を示し、交換電流密度が増大したことを示した。酸素の２電子還元により生じる過酸化水素が１．２Ｖに設定したリング電極における酸化電流を測定することで、Ｐｔでは電流効率が２．５％であったのに対して、Ｔａ被覆したＰｔ板では０．９％と低くなり、過酸化水素生成が抑制されたことが分かった。4電子還元が速やかに進行することは、過酸化物の生成が抑制され、電極あるいはセル構成部品の劣化が進行しにくいことを示す。
For the same Ta-coated Pt plate and uncoated Pt plate, the potential-current relationship diagram was measured by the rotating ring disk device (FIG. 7). The oxygen reduction current potentials of the disk electrodes of Reference Example 1 and Reference Example 2 are indicated by a solid line a and a broken line b, respectively. The oxidation current potential of hydrogen peroxide on the ring electrodes of Reference Example 1 and Reference Example 2 is shown by a solid line a ′ and a broken line b ′, respectively).
The Ta-coated Pt plate had higher activity than Pt, and the potential was shifted to a noble potential of 100 mV or more in appearance. The Tafel gradient showed 60 mV in the small current density range and 120 mV in the large current range, which was the same value as Pt, indicating that the exchange current density was increased. By measuring the oxidation current at the ring electrode where the hydrogen peroxide generated by the two-electron reduction of oxygen was set to 1.2 V, the current efficiency was 2.5% for Pt, whereas the Pt plate coated with Ta , It was found to be as low as 0.9%, indicating that the production of hydrogen peroxide was suppressed. The rapid progress of 4-electron reduction indicates that the generation of peroxide is suppressed, and the deterioration of the electrode or cell component is unlikely to proceed.
また、１Ｍの硝酸カリウムを窒素ガスで脱気し、１．８ｍＭのＫ3Ｆｅ（ＣＮ）6のフェリシアンカリウムを溶解し、室温下にて０．０１Ｖ／ｓで、参考例１（実線ａ’）及び参考例２（破線a）のサイクリックボルタンメトリーを測定した（図８）。参考例１のＴａめっきしたＰｔ板では、参考例２のＰｔ板に比較して、３分の１〜４分の１に電流が減少した。これは、このような一般の電気化学反応に対しては、Ｔａの助触媒作用がないことを示している。 Further, 1M potassium nitrate was degassed with nitrogen gas, 1.8 mM K 3 Fe (CN) 6 ferricyan potassium was dissolved, and 0.01 V / s at room temperature, Reference Example 1 (solid line a ′ ) And Reference Example 2 (broken line a) were measured for cyclic voltammetry (FIG. 8). In the Pt plate plated with Ta in Reference Example 1, the current decreased to 1/3 to 1/4 compared with the Pt plate in Reference Example 2. This indicates that Ta does not have a cocatalyst action for such a general electrochemical reaction.
［実施例１］
炭素繊維（バラード社製）製クロスの片面に、炭素粉末（米国キャボット社製バルカンＸＣ−72）とテトラフルオロカーボン樹脂の水懸濁液（三井デュポンフロロケミカル株式会社製３０Ｊ）から成る混合ペーストを塗布し、大気中３００ ℃で焼成した。次に白金を担持した炭素粉末を用いて上記シートの反対面から同様の手法にて塗布した。投影面積あたりの白金量は１ｇ／ｍ2であった。その後、空気中３００℃で焼成して樹脂を熱処理した。次に１ＭのＬｉＣｌＯ4を含むポリカーボネート（ＰＣ）に塩化タンタルを０．１Ｍ溶解させた。室温にて、０．５Ｃ／ｃｍ2の電気量を流し、Ｐｔを形成したガス電極上にＴａをめっきした。助触媒量は０．５ｇ／ｍ2であった。
[Example 1]
A mixed paste consisting of carbon powder (Vulcan XC-72, manufactured by Cabot, USA) and an aqueous suspension of tetrafluorocarbon resin (30J, manufactured by Mitsui DuPont Fluorochemical Co., Ltd.) is applied to one side of a cloth made of carbon fiber (Ballard). And fired at 300 ° C. in the atmosphere. Next, it applied with the same method from the opposite surface of the said sheet | seat using the carbon powder which carry | supported platinum. The amount of platinum per projected area was 1 g / m 2 . Thereafter, the resin was heat treated by baking at 300 ° C. in air. Next, 0.1M tantalum chloride was dissolved in polycarbonate (PC) containing 1M LiClO 4 . An electric quantity of 0.5 C / cm 2 was passed at room temperature, and Ta was plated on the gas electrode on which Pt was formed. The amount of cocatalyst was 0.5 g / m 2 .
この電極の触媒面にナフィオン液（米国アルドリッチ社製）を塗布しガス電極を２枚作製した。イオン交換膜（米国デュポン社製ナフィオン１１２ ）の両面に、前記２枚のガス電極の触媒面側が接触するよう配置し、圧力０．２ＭＰａ、温度１２０℃で５分間ホットプレスして接合した。この電極を電解槽に組み込み、片側に水蒸気で飽和した８０℃の水素ガスを、反対側に水蒸気で飽和した80℃の酸素ガスを供給して燃料電池として作動させた。８０℃、１００Ａ／ｄｍ2 で０．６ Ｖの出力が得られた。７５０時間を経過しても性能に変化はなかった。 Nafion liquid (manufactured by Aldrich, USA) was applied to the catalyst surface of this electrode to produce two gas electrodes. The two gas electrodes were placed on both sides of an ion exchange membrane (Nafion 112 manufactured by DuPont, USA) so that the catalyst surface sides were in contact with each other, and hot pressed at a pressure of 0.2 MPa and a temperature of 120 ° C. for 5 minutes for bonding. This electrode was installed in an electrolytic cell, and 80 ° C. hydrogen gas saturated with water vapor was supplied to one side, and 80 ° C. oxygen gas saturated with water vapor was supplied to the other side to operate as a fuel cell. An output of 0.6 V was obtained at 80 ° C. and 100 A / dm 2 . There was no change in performance after 750 hours.
［比較例１］
Ｔａめっきを行わなかった電極で同様の電池評価を実施したところ、初期は０．６３Ｖの出力が得られたものの、７５０時間後には０．５Ｖまで低下した。
[Comparative Example 1]
When the same battery evaluation was carried out with an electrode that was not subjected to Ta plating, an output of 0.63 V was obtained in the initial stage, but it decreased to 0.5 V after 750 hours.
［実施例２］
銀粉末（福田金属箔工業株式会社製ＡｇＣ−Ｈ、０．１μｍ）と、ＰＴＦＥ水懸濁液（三井フロロケミカル株式会社製３０Ｊ）を体積比１：１で混合し十分攪拌後、該混合懸濁液を、銀として投影面積当り５００ｇ／ｍ2となるように厚さ０．４ｍｍのカーボンクロス基体に塗布し、電気炉中３１０℃で１６分焼成後、プレス機にて、圧力０．２ＭＰａでプレス加工を行い、ガス拡散陰極を作製した。
その後有機溶媒中でめっきを行い、塩化タンタル溶液(濃度)を５ｗｔ％溶解したＰＣ溶液を作製し、１Ｃ／ｃｍ2の電気量を流し、実施例１と同様にＴａ層めっきを析出させた。助触媒量は０．９ｇ／ｍ2であった。
[Example 2]
Silver powder (AgC-H manufactured by Fukuda Metal Foil Industry Co., Ltd., 0.1 μm) and PTFE water suspension (30J manufactured by Mitsui Fluorochemical Co., Ltd.) are mixed at a volume ratio of 1: 1, and after sufficient stirring, the mixed suspension is mixed. The suspension was applied as silver to a carbon cloth substrate having a thickness of 0.4 mm so as to have a projected area of 500 g / m 2, and fired at 310 ° C. for 16 minutes in an electric furnace. A gas diffusion cathode was produced by pressing.
Thereafter, plating was carried out in an organic solvent to prepare a PC solution in which 5 wt% of a tantalum chloride solution (concentration) was dissolved, and an electric quantity of 1 C / cm 2 was applied to deposit Ta layer plating as in Example 1. The amount of cocatalyst was 0.9 g / m 2 .
陽極として酸化ルテニウムを主成分とするＤＳＥ、イオン交換膜としてフレミオンＦ８０２０（旭硝子社製）を用い、厚さ０．４ｍｍの親水化処理を行ったカーボンクロスを親水層とし、この親水層をガス拡散陰極と前記イオン交換膜間に挟み、前記陽極及びガス拡散陰極を内向きに押圧し、イオン交換膜が鉛直方向に位置するように、各部材を密着固定して電解槽を構成した。
陰極室水酸化ナトリウム濃度が３２ｗｔ％となるように陽極室食塩濃度を調整し、又陰極には酸素ガスを理論量の約１．２倍の割合で供給、陽極液の液温を９０℃、電流密度60Ａ／ｄｍ2で電解を行ったところ、初期の槽電圧は２．１５Ｖであった。１００日間電解を継続したところ、初期からの槽電圧、過電圧の上昇はほとんど無く、電流効率は約９６％に維持された。
Using DSE mainly composed of ruthenium oxide as an anode and Flemion F8020 (manufactured by Asahi Glass Co., Ltd.) as an ion exchange membrane, a carbon cloth subjected to a hydrophilic treatment with a thickness of 0.4 mm is used as a hydrophilic layer, and this hydrophilic layer is gas-diffused. The electrolytic cell was configured by sandwiching between the cathode and the ion exchange membrane, pressing the anode and the gas diffusion cathode inward, and closely fixing each member so that the ion exchange membrane was positioned in the vertical direction.
The sodium chloride concentration in the anode chamber was adjusted so that the sodium hydroxide concentration in the cathode chamber was 32 wt%, and oxygen gas was supplied to the cathode at a rate of about 1.2 times the theoretical amount. The liquid temperature of the anolyte was 90 ° C., When electrolysis was performed at a current density of 60 A / dm 2 , the initial cell voltage was 2.15V. When electrolysis was continued for 100 days, there was almost no increase in cell voltage and overvoltage from the beginning, and the current efficiency was maintained at about 96%.
［比較例２］
Ｔａめっきを行わなかった電極で実施例２と同様の電解評価を実施したところ、初期の槽電圧は２．１５Ｖであったが、１００日間電解を継続したところ、初期からの槽電圧がやや増加し、３０ｍＶの過電圧上昇が発生し、電流効率は約９４%に減少した。
[Comparative Example 2]
When the same electrolytic evaluation as in Example 2 was performed on the electrode not subjected to Ta plating, the initial cell voltage was 2.15 V, but when electrolysis was continued for 100 days, the cell voltage increased slightly from the initial stage. Then, an overvoltage increase of 30 mV occurred, and the current efficiency decreased to about 94%.
１ イオン交換膜
２ 酸素極
３ 水素極
９ 酸素極室
１１ 水素極室
２１ ２室法電解槽
２２ 陽イオン交換膜
２３ 陽極室
２４ 陰極ガス室
２５ 陽極
２６ ガス拡散陰極
1 Ion exchange membrane 2 Oxygen electrode 3 Hydrogen electrode
9 Oxygen electrode chamber 11 Hydrogen electrode chamber 21 Two-chamber electrolytic cell 22 Cation exchange membrane 23 Anode chamber 24 Cathode gas chamber 25 Anode 26 Gas diffusion cathode
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