2009A1854                          BL14B2ᅛయ㧗ศᏊᙧ⇞ᩱ㟁ụ࡟࠾ࡅࡿ Pt-Co ྜ㔠ゐ፹ࡢຎ໬࡟క࠺㟁Ꮚᵓ㐀ኚ໬
Changes of Electronic Structure of Pt-Co Alloy Catalysts in Polymer
Electrolyte Fuel Cellᑠᯘ ṇ㉳ a,b, ᖸ㪉 ᑗ୍ a,c, ୹⩚ ⚽἞ a, ཎ⏣ ឿஂ a,b, ᑿᔱ ṇ἞ a,b,኱ῲ ༤ᐉ d, ୰᳃ ὒ஧ b, 㟷ᮌ ດ ba,bMasaki Kobayashi , Shoichi Hidaia,c, Hideharu Niwaa, Yoshihisa Haradaa,b, Masaharu Oshimaa,b,Hironori Ofuchid, Yoji Nakamorib, Tsutomu Aokibaᮾி኱Ꮫ ኱Ꮫ㝔ᕤᏛ⣔◊✲⛉, b ᮾி኱Ꮫᨺᑕග㐃ᦠ◊✲ᶵᵓ, c㻔ᰴ㻕ᮾⰪ⇞ᩱ㟁ụࢩࢫࢸ࣒,d㻔㈈㻕㧗㍤ᗘග⛉Ꮫ◊✲ࢭࣥࢱ࣮a School of Engineering, University of Tokyo, bSRRO, University of Tokyo,cToshiba Fuel Cell Power Systems Corporation, dJASRIṇᴟ࡟ Pt-Co ྜ㔠ゐ፹ࢆࠊ㈇ᴟ࡟ࡣ Pt-Ru ྜ㔠ゐ፹ࢆ⏝࠸ࡓ⭷᥋ྜయ㻔MEA㻕࡟ᑐࡋ࡚ຎ໬ຍ㏿ヨ㦂ࢆ⾜࠸ࠊຎ໬࡟క࠺㟁Ꮚᵓ㐀ኚ໬ࢆ X ⥺྾཰ᚤ⣽ᵓ㐀࡟ࡼࡗ࡚ㄪ࡭ࡓࠋṇᴟࡢ Co ࡣṇᴟ-㟁ゎ㉁⭷⏺㠃࡛㓟໬ࡋ࡚࠾ࡾࠊ㓟໬ Co ࡣຎ໬ヨ㦂࡟ࡼࡾቑ኱ࡍࡿࡇ࡜ࡀࢃ࠿ࡗࡓࠋࡇࢀࡣ⁐ฟࡋࡓCo ࡀ㓟໬ࡋ࡚࠸ࡿࡇ࡜ࢆ♧၀ࡍࡿࠋ⇕ฎ⌮ࢆ᪋ࡋࡓヨᩱ࡛ࡣ Co ࡢ㓟໬ࡀᢚ࠼ࡽࢀ࡚࠾ࡾࠊ᭱⾲㠃 Pt ᒙࡀ㓟໬ಖㆤᒙ࡜ࡋ࡚ാ࠸࡚࠸ࡿ࡜⪃࠼ࡽࢀࡿࠋ࣮࣮࢟࣡ࢻ㸸 ᅛయ㧗ศᏊᙧ⇞ᩱ㟁ụࠊṇᴟゐ፹ࠊⓑ㔠ྜ㔠ゐ፹ࠊຎ໬ࠊ㟁Ꮚᵓ㐀⫼ᬒ࡜◊✲┠ⓗ㸸ᅛయ㧗ศᏊᙧ⇞ᩱ㟁ụ㻔PEFC㻕ࡣ⏕ᡂ≀ࡀỈࡔࡅ࡛࠶ࡾࠊNOx ➼ࡢ᭷ᐖ≀㉁ࢆ᤼ฟࡋ࡞࠸ࡇ࡜࠿
ࡽ⎔ቃ࡟ඃࡋࡃࠊ᪂ࡓ࡞࢚ࢿࣝࢠ࣮ࢩࢫࢸ࣒࡜ࡋ࡚ᑟධẁ㝵࡟࠶ࡿࠋPEFC ࡣṇᴟ࡜㈇ᴟ࡜࡛㟁ゎ㉁ࢆᣳࢇࡔࢭࣝᵓ㐀㻔⭷᥋ྜయ㸸MEA㻕ࢆᣢࡕࠊṇᴟゐ፹ࡢᮦᩱࡸ㟁ゎ㉁࡟ࡼࡗ࡚⇞ᩱ㟁ụࡢຠ⋡ࢆ⾲ࡍ㓟⣲㑏ඖ཯ᛂάᛶࡀኚ໬ࡍࡿࠋ⌧ᅾࠊPEFC ࡢ㟁ᴟ࡟ࡣάᛶࡢ㧗࠸㔠ᒓ࡛࠶ࡿⓑ㔠㻔Pt㻕ࡀゐ፹࡜ࡋ࡚฼⏝ࡉࢀ࡚࠸ࡿࡀࠊPt ࡣ㧗౯࡛࠶ࡾࠊ㈨※ⓗ࡟ࡶ㝈⏺ࡀ࠶ࡿ࡜࠸ࡗࡓၥ㢟ࡀ࠶ࡿࠋࡲࡓࠊࡇࡢၥ㢟ࢆゎỴࡋᏳ౯࡞⇞ᩱ㟁ụࢆᐇ⌧ࡍࡿࡓࡵ࡟ࡣࠊཎᩱࡢ್ẁࢆୗࡆࡿࡇ࡜࡟ຍ࠼࡚ࠊ⇞ᩱ㟁ụࡀ㛗᫬㛫౑⏝ྍ⬟࡛࠶ࡿᚲせࡀ࠶ࡿࠋࡼࡗ࡚ࠊⓑ㔠ࡢ౑⏝㔞ࡀᑡ࡞ࡃ㛗᫬㛫✌ാࡍࡿ⇞ᩱ㟁ụࡢ㛤Ⓨࡀồࡵࡽࢀ࡚࠸ࡿࠋࡑࡇ࡛ Pt ࡢ౑⏝㔞ࢆᢚ࠼ࠊ࠿ࡘ Pt ࡼࡾࡶ㓟⣲㑏ඖ཯ᛂάᛶࡢ㧗࠸ⓑ㔠-㔠ᒓ㻔Pt-M㻕ྜ㔠㻔ࡇࡇ࡛ࠊM ࡣ 3d 㑄⛣㔠ᒓ㻕ゐ፹ࡀὀ┠ࢆ㞟ࡵࠊ┒ࢇ࡟◊✲ࡉࢀ࡚࠸ࡿ[1,2]ࠋ
ྜ㔠໬ࡍࡿ㔠ᒓࡣ Co ࡢ᫬ࡀ᭱ࡶάᛶࡀ኱ࡁࡃ࡞ࡿ[3]ࠋ
Pt-Co ゐ፹ࢆ⏝࠸ࡓ⇞ᩱ㟁ụࡢᐇ⏝໬࡟ྥࡅ࡚ࠊ㓟⣲㑏ඖάᛶ࠾ࡼࡧຎ໬ࡢᶵᵓࢆゎ᫂ࡋࠊ㟁ụ࡜ࡋ࡚ࡢᛶ⬟ࢆྥୖࡉࡏࡿࡇ࡜ࡀษᮃࡉࢀ࡚࠸ࡿࠋᡃࠎࡣࠊࡇࢀࡲ࡛࡟ヨᩱస〇ཬࡧ㟁Ẽ໬Ꮫᐃ࡟ࡼࡿホ౯ࠊ୪ࡧ࡟ᨺᑕගࢆ⏝࠸ࡓ㟁Ꮚ≧ែゎᯒࢆ⾜ࡗ࡚ࡁࡓ[4]ࠋ㟁ụࢆຎ໬ࡉࡏࡿ㐠㌿࡟ࡣࠊᐃᖖ㐠㌿࡜㟁ᅽࢧ࢖ࢡࣝ㐠㌿㻔㟁※ࡢ ON/OFF ࡟ᑐᛂ㻕ࡢ஧✀㢮ࡀ࠶ࡾࠊࡇࢀࡲ࡛࡟ᐃᖖ㐠㌿ࡢຠᯝࢆㄪ࡭࡚ࡁࡓࠋPt-Co ᚤ⢏Ꮚࢆ⏝࠸ࡓ PEFC ࡣ 6,700 ᫬㛫ࡢᐃᖖ㐠㌿࡟ࡼࡾࠊ⣙ 3㸣ࡢ㟁ᅽ㝆ୗࡀ㟁Ẽ໬Ꮫ ᐃࡼࡾほ ࡉࢀࡓࠋX ⥺྾཰ศගࢆ⏝࠸࡚㐠㌿᮲௳ࡀ␗࡞ࡿ 3 ✀㢮ࡢヨᩱ㻔ึᮇࠊ
ึⓎ㟁ᚋࠊ6,700 ᫬㛫౑⏝ᚋ㻕࡟ᑐࡋ࡚ࠊṇᴟゐ፹ࡢ Co ࡢ㟁Ꮚᵓ㐀ࡢኚ໬ࢆㄪ࡭࡜ࡇࢁࠊ㛗᫬㛫ࡢ㐠㌿࡟ࡼࡾ୕౯ࡢ㓟໬ Co ࡔࡅࡀቑຍࡍࡿࡇ࡜ࡀ᫂ࡽ࠿࡜࡞ࡗࡓࠋ᭦࡟ໟᣓⓗ࡟ຎ໬ࡢཎᅉࢆ᫂ࡽ࠿࡟ࡍࡿࡓࡵ࡟ࡣࠊCo ࡟ຍ࠼࡚㟁Ẽ໬Ꮫ཯ᛂ࡛⁐ฟࡍࡿ Pt ࡸ㟁ゎ㉁⭷࡟⁐ฟࡋࡓ Pt ཬࡧ Coࡢ㟁Ꮚ≧ែཬࡧᒁᡤᵓ㐀ࢆㄪ࡭ࡿᚲせࡀ࠶ࡿࠋ௒ᅇࡢᐇ㦂࡛ࡣࠊࡼࡾ⌧ᐇⓗ࡞㟁఩ࢧ࢖ࢡࣝヨ㦂ࢆ᪋ࡋࡓヨᩱ࡟ᑐࡋ࡚ࠊ᳨ฟ㛗ࡢὸ࠸㻔< 100 nm㻕㌿᥮㟁Ꮚ཰㔞ἲ㻔CEY㻕࡜᳨ฟ㛗ࡢ㛗࠸㻔䡚1 mm㻕⺯ගἲ䠄FY䠅ࢆ⏝࠸࡚ࠊṇᴟཬࡧ㈇ᴟࡢ୧᪉࠿ࡽගࢆධᑕࡍࡿࡇ࡜࡟ࡼࡾ Co ཬࡧ Pt ࡢ྾཰➃࡛ XAFSᐃࢆ⾜࠸ࠊຎ໬࡟క࠺ྛ㟁ᴟᒙࡢ㟁Ꮚ≧ែ㻔XANES㻕ཬࡧᒁᡤᵓ㐀㻔EXAFS㻕ኚ໬ࢆㄪ࡭ࡓࠋ

ᐇ㦂㸸ᐇ㦂࡟⏝࠸ࡓヨᩱࡣࠊṇᴟゐ፹࡟Ⅳ⣲ᆠᣢ Pt3Co ᚤ⢏Ꮚ㻔⏣୰㈗㔠ᒓࠊPt 47 wt.%㻕ࠊ㈇ᴟゐ፹࡟Ⅳ⣲ᆠᣢ PtRu ᚤ⢏Ꮚࠊ㟁ゎ㉁⭷࡟ࣇࢵ⣲໬ࢫࣝࣇ࢛ࣥ㓟⭷ࢆ⏝࠸ࡓ MEA ࡛࠶ࡿࠋࡲࡓࠊάᛶࢆྥୖࡉࡏࡿ⇕ฎ⌮ࢆ᪋ࡋࡓ Pt3Co ゐ፹ࢆ⏝࠸ࡓ MEA ࡜ࡢẚ㍑ࢆ⾜ࡗࡓࠋ㟁఩ࢧ࢖ࢡࣝヨ㦂࡛ࡣ 0.6 V - 1.0V ࢆ 10000 ᅇ⧞ࡾ㏉ࡋࡓࠋXAFS ᐃࡣᐊ ࡛⾜ࡗࡓࠋCEY ࡟࠾࠸࡚ࡣࠊṇᴟࡢ Co ࡢ≧ែࢆㄪ࡭ࡿࡓࡵ࡟ṇᴟഃ࠿ࡽගࢆධᑕࡋࠊFY ࡟࠾࠸࡚ࡣࠊṇᴟ࡜㟁ゎ㉁⭷ࡢ⏺㠃ࡸ⁐ฟࡋࡓ Co ࡢ≧ែࢆㄪ࡭ࡿࡓࡵ࡟㈇ᴟഃ࠿ࡽගࢆධᑕࡋ࡚ ᐃࡋࡓࠋFY ࡛ࡣヨᩱࡢධᑕゅ ș㻔ᆶ┤ධᑕࡢሙྜ ș=0㻕ࢆኚ࠼ࡿࡇ࡜࡛ࠊ᳨ฟ㛗ࢆኚ໬ࡉࡏࡓࠋ

Intensity (arb. units)

Intensity (arb. units)⤖ᯝ࠾ࡼࡧ⪃ᐹ㸸
ᅗ 1 ࡣ Pt-Co ゐ፹ࢆ⏝࠸ࡓ MEA ࡢ Co K XANES ࢫ࣌ࢡࢺࣝࢆ♧ࡍࠋࡲࡎࠊ㟁఩ࢧ࢖ࢡࣝヨ㦂๓ࡢ MEA300
CEY Cathodeo— FY Anode 45
ヨᩱ࡟╔┠ࡍࡿࠋCEY ࡛ᚓࡽࢀࡓࢫ࣌ࢡࢺࣝࡣ Co 㔠o
FY Anode 80ᒓࡢࡶࡢ࡟㏆ࡃࠊṇᴟࡢ Co ࡣ㔠ᒓⓗ࡛࠶ࡿࡇ࡜ࡀศ
࠿ࡿࠋFY ࡢࢫ࣌ࢡࢺࣝࢆぢࡿ࡜ 7720 eV ௜㏆ࡢࣆ࣮ࢡ
Heat-treated MEA
200 after cycling test
ࡀ CEY ࡟ẚ࡭࡚኱ࡁࡃ࡞ࡾࠊ7750 eV ࡢᵓ㐀ࡀᙅࡃ࡞Heat-treated MEAࡗ࡚࠸ࡿࠋ⏺㠃࡟ᩄឤ࡞ᩳධᑕ࡛ࡢ ᐃ࡛ࡣࠊࡇࢀࡽ
before cycling testࡢኚ໬ࡣࡼࡾ㢧ⴭ࡟࡞ࡗ࡚࠸ࡿࡇ࡜ࡀศ࠿ࡿࠋࡇࡢ⤖100ᯝࡣࠊṇᴟ-㟁ゎ㉁⏺㠃࡟㓟໬ࡋࡓ Co ࡀᏑᅾࡍࡿࡇ࡜
MEA after
cycling testࢆ♧၀ࡍࡿࠋḟ࡟㟁఩ࢧ࢖ࢡࣝヨ㦂ࢆ⾜ࡗࡓヨᩱ࡛ẚ㍑ࡍࡿࠋCEY ࡣ኱ࡁ࡞ኚ໬ࡣぢࡽࢀࡎࠊ㟁఩ࢧ࢖ࢡࣝMEA before
cycling testヨ㦂ᚋࡶṇᴟ࡛ࡣ Pt-Co ྜ㔠ࡀᏑᅾࡋ࡚࠸ࡿࡇ࡜ࢆ♧0ࡋࡓࠋFY ࡣ 45 ᗘ㓄⨨ࡼࡾࡶᩳධᑕ࡛ ᐃࡋࡓࢫ࣌ࢡࢺࣝ࡟ࡼࡾከࡃࡢ㓟໬ᡂศࡀぢࡽࢀࠊ㓟໬ᡂศࡢᙉᗘCoOࡣヨ㦂๓࡟ẚ࡭࡚኱ࡁࡃ࡞ࡗ࡚࠸ࡓࠋࡇࡢ⤖ᯝࡣࠊ㈇Pt-Co MEA-100
Co K XANESᴟഃ࡬⁐ฟࡋࡓ Co ࡀ㓟໬ࡋࡓࡇ࡜ࢆ♧၀ࡍࡿࠋCo metalḟ࡟⇕ฎ⌮ࢆࡋࡓヨᩱࢆẚ㍑ࡍࡿࠋ⇕ฎ⌮ࢆ᪋ࡋࡓ
7680
77207760㟁఩ࢧ࢖ࢡࣝ๓ࡢヨᩱࡢࢫ࣌ࢡࢺࣝࡣ CEY, FY ඹ࡟
Photon Energy (eV)Co 㔠ᒓ࡟㏆࠸ᵓ㐀ࢆࡋ࡚࠾ࡾࠊ⏺㠃࡛㓟໬ࡋࡓ Co ࡀ
ᅗ 1. Pt-Co ṇᴟゐ፹ࢆ⏝࠸ࡓ MEA ࡢぢࡽࢀ࡞࠿ࡗࡓࠋ㟁఩ࢧ࢖ࢡࣝࢆ⾜࠺࡜ FY ࡛㓟໬≀
Co K XAFS㸬ᡂศࡀቑ኱ࡍࡿࡀࠊ⇕ฎ⌮๓ࡢヨᩱ࡜ẚ࡭ࡿ࡜㓟໬ Coࡢ㔞ࡀᑡ࡞࠸ࡇ࡜ࡀศ࠿ࡿࠋࡇࢀࡽࡢ⤖ᯝࡣࠊ⇕ฎ⌮
CEY250࡟ࡼࡾṇᴟཬࡧṇᴟ-㟁ゎ㉁⭷⏺㠃㏆ഐࡢ Co ࡢ㓟໬ࡀCathodeᢚไࡉࢀࡓࡇ࡜ࢆ♧၀ࡋ࡚࠸ࡿࠋࡇࡢཎᅉࡢ୍ࡘ࡜ࡋ200࡚ࠊ⇕ฎ⌮࡛⏕ᡂࡉࢀࡿ᭱⾲㠃 Pt ࢫ࢟ࣥ[3]ࡀ㓟໬ಖㆤ
Heat-treated MEAᒙ࡜ࡋ࡚ാ࠸ࡓ࡜⪃࠼ࡽࢀࡿࠋ
after cycling test150
ᅗ 2 ࡣ CEY ࡛ ᐃࡋࡓ Pt L3 XANES ࢫ࣌ࢡࢺࣝࢆ♧Heat-treated MEA
before cycling testࡍࠋࢫ࣌ࢡࢺࣝࡢᙧ≧ࡣ⇕ฎ⌮ࡸ㟁఩ࢧ࢖ࢡࣝヨ㦂࡟
100
ࡼࡽࡎࠊPt 㔠ᒓ࡟ఝ࡚࠸ࡓࠋPt 5d ࣂࣥࢻࡢ✵Ꮝᩘ࡟ẚ
MEA after
౛ࡍࡿ 11560 eV ࡢࣆ࣮ࢡᙉᗘࡣࠊ⇕ฎ⌮๓ࡢヨᩱ࡛ࡣ
cycling test50㟁఩ࢧ࢖ࢡࣝヨ㦂࡟ࡼࡗ࡚~10%ࡢῶᑡࡀぢࡽࢀࡓࡀࠊ
MEA before⇕ฎ⌮ᚋࡢヨᩱ࡛ࡣ࡯ࡰኚࢃࡽ࡞࠿ࡗࡓࠋࡇࢀࡽࡢ⤖cycling test0ᯝࡣࠊṇᴟࡢ Pt ࡣຎ໬ヨ㦂ᚋࡶྜ㔠ࡢ≧ែࢆಖࡗ࡚࠾
Pt-Co MEA
Pt L3 XANESࡾࠊ⇕ฎ⌮ࢆ᪋ࡍࡇ࡜࡛ࡼࡾᏳᐃ໬ࡍࡿࡇ࡜ࢆ♧ࡋ࡚
Pt metal-50
࠸ࡿࠋ1152011540115601158011600
௨ୖࡢ⤖ᯝ࠿ࡽࠊPt-Co ゐ፹࡟࠾࠸࡚⪏ஂᛶࢆྥୖࡉ
Photon Energy (eV)ࡏࡿ࡟ࡣࠊPt ࢫ࢟ࣥᒙࡢᙧᡂࡀ᭷ຠ࡛࠶ࡿ࡜⪃࠼ࡽࢀ ᅗ 2. Pt-Co ṇᴟゐ፹ࢆ⏝࠸ࡓ MEA ࡢࡿࠋ
Pt L3 XAFS㸬௒ᚋࡢㄢ㢟㸸ᮏ ᐃ࠿ࡽࠊPt-Co ゐ፹࡟࠾ࡅࡿ⇕ฎ⌮࡟ࡼࡿ⪏ஂᛶྥୖࡢཎᅉ࡜ࡋ࡚ Pt ࢫ࢟ࣥᒙࡢᙧᡂࡀ♧၀ࡉࢀࡓࠋࡋ࠿ࡋ࡞ࡀࡽࠊPt-Co ゐ፹ࡢຎ໬ᶵᵓ࡟ࡘ࠸࡚ࡣࡲࡔ༑ศ࡞▱ぢࡀᚓࡽࢀ࡚࠸࡞࠸ࠋ௒ᚋࡣṇᴟ-㟁ゎ㉁⭷⏺㠃ࡢ㓟໬ Co ࡢᏑᅾ࡜ゐ፹ࡢຎ໬ࡢ㛵㐃ᛶࡸࠊゐ፹ࡢ⢏ᚄࢆኚ࠼࡚㟁Ẽ໬Ꮫⓗ⾲㠃✚ࢆኚ໬ࡉࡏࡓ᫬ࡢ㟁Ꮚ≧ែࡢኚ໬ࢆㄪ࡭ࡿࡇ࡜࡛ࠊࡼࡾ㧗⪏ஂ࡞ヨᩱࢆస〇ࡍࡿࡓࡵ࡟࡝ࡢᵝ࡞ࣉࣟࢭࢫࡀ㔜せ࠿ࢆ᫂ࡽ࠿࡟ࡋ࡚࠸ࡃᚲせࡀ࠶ࡿ࡜⪃࠼ࡽࢀࡿࠋཧ⪃ᩥ⊩㸸[1] S. Mukerjee and S. Srinvasan, J. Electroanal. Chem. 357, 201 㻔1993㻕.
[2] T. Toda, H. Igarashi, H. Uchida and M. Watanabe, J. Electrochem. Soc. 146, 3750㻌㻔1999㻕.
[3] V. R. Stamenkovic, B. S. Mun, M. Arenz, K. J. J. Mayrhofer, C. A. Lucas, G. Wang, P. N. Ross and N.
M. Markovic, Nature Mater. 6, 241㻌㻔2007㻕.
[4] M. Kobayashi, S. Hidai, H. Niwa, Y. Harada, M. Oshima, Y. Horikawa, T. Tokushima, S. Shin, Y.
Nakamori, T. Aoki, Phys. Chem. Chem. Phys. 11, 8226 㻔2009㻕.