JP6863764B2 - Electrode catalyst, membrane electrode assembly and polymer electrolyte fuel cell - Google Patents
Electrode catalyst, membrane electrode assembly and polymer electrolyte fuel cell Download PDFInfo
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- JP6863764B2 JP6863764B2 JP2017023278A JP2017023278A JP6863764B2 JP 6863764 B2 JP6863764 B2 JP 6863764B2 JP 2017023278 A JP2017023278 A JP 2017023278A JP 2017023278 A JP2017023278 A JP 2017023278A JP 6863764 B2 JP6863764 B2 JP 6863764B2
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- tin oxide
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- 239000003054 catalyst Substances 0.000 title claims description 122
- 239000000446 fuel Substances 0.000 title claims description 32
- 239000012528 membrane Substances 0.000 title claims description 20
- 239000005518 polymer electrolyte Substances 0.000 title claims description 16
- 239000000654 additive Substances 0.000 claims description 102
- 230000000996 additive effect Effects 0.000 claims description 102
- 239000011247 coating layer Substances 0.000 claims description 76
- 229910001887 tin oxide Inorganic materials 0.000 claims description 73
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 claims description 72
- 229910000510 noble metal Inorganic materials 0.000 claims description 59
- 239000002245 particle Substances 0.000 claims description 35
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 claims description 28
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 27
- 239000010410 layer Substances 0.000 claims description 16
- 229910052787 antimony Inorganic materials 0.000 claims description 14
- WATWJIUSRGPENY-UHFFFAOYSA-N antimony atom Chemical compound [Sb] WATWJIUSRGPENY-UHFFFAOYSA-N 0.000 claims description 14
- 229910052715 tantalum Inorganic materials 0.000 claims description 14
- 239000007787 solid Substances 0.000 claims description 13
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 claims description 13
- 229910052731 fluorine Inorganic materials 0.000 claims description 10
- 239000011737 fluorine Substances 0.000 claims description 10
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims description 7
- 229910052721 tungsten Inorganic materials 0.000 claims description 7
- 239000010937 tungsten Substances 0.000 claims description 7
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 claims description 5
- 229910052801 chlorine Inorganic materials 0.000 claims description 5
- 239000000460 chlorine Substances 0.000 claims description 5
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 4
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 4
- 229910052750 molybdenum Inorganic materials 0.000 claims description 4
- 239000011733 molybdenum Substances 0.000 claims description 4
- 229910052758 niobium Inorganic materials 0.000 claims description 4
- 239000010955 niobium Substances 0.000 claims description 4
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 claims description 4
- 229910052698 phosphorus Inorganic materials 0.000 claims description 4
- 239000011574 phosphorus Substances 0.000 claims description 4
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 claims 1
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 34
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 26
- 229910052718 tin Inorganic materials 0.000 description 26
- 239000010419 fine particle Substances 0.000 description 19
- 239000010936 titanium Substances 0.000 description 17
- 150000001875 compounds Chemical class 0.000 description 16
- 238000000034 method Methods 0.000 description 16
- 229910052697 platinum Inorganic materials 0.000 description 16
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 15
- 239000000243 solution Substances 0.000 description 15
- 229910052719 titanium Inorganic materials 0.000 description 15
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 14
- 238000010438 heat treatment Methods 0.000 description 12
- 238000009792 diffusion process Methods 0.000 description 11
- 239000007789 gas Substances 0.000 description 10
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 9
- 229910006404 SnO 2 Inorganic materials 0.000 description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 9
- 239000001301 oxygen Substances 0.000 description 9
- 229910052760 oxygen Inorganic materials 0.000 description 9
- 229920000557 Nafion® Polymers 0.000 description 8
- 230000001965 increasing effect Effects 0.000 description 7
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 6
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 6
- 125000004429 atom Chemical group 0.000 description 6
- 239000013078 crystal Substances 0.000 description 6
- 239000007788 liquid Substances 0.000 description 6
- -1 perfluoroalkyl sulfonic acid Chemical compound 0.000 description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 5
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 5
- 239000007864 aqueous solution Substances 0.000 description 5
- 229910052799 carbon Inorganic materials 0.000 description 5
- 239000000084 colloidal system Substances 0.000 description 5
- 230000000052 comparative effect Effects 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 239000001257 hydrogen Substances 0.000 description 5
- 229910052739 hydrogen Inorganic materials 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 238000005259 measurement Methods 0.000 description 5
- 229920000642 polymer Polymers 0.000 description 5
- 239000002244 precipitate Substances 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 230000003197 catalytic effect Effects 0.000 description 4
- 239000011259 mixed solution Substances 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 4
- 239000004810 polytetrafluoroethylene Substances 0.000 description 4
- 238000010248 power generation Methods 0.000 description 4
- 239000000725 suspension Substances 0.000 description 4
- 238000001308 synthesis method Methods 0.000 description 4
- YUOWTJMRMWQJDA-UHFFFAOYSA-J tin(iv) fluoride Chemical compound [F-].[F-].[F-].[F-].[Sn+4] YUOWTJMRMWQJDA-UHFFFAOYSA-J 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 239000006229 carbon black Substances 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 239000004020 conductor Substances 0.000 description 3
- 239000002737 fuel gas Substances 0.000 description 3
- 229910052736 halogen Inorganic materials 0.000 description 3
- 150000002367 halogens Chemical class 0.000 description 3
- 239000007800 oxidant agent Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 229920000049 Carbon (fiber) Polymers 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 241000282341 Mustela putorius furo Species 0.000 description 2
- 229910000990 Ni alloy Inorganic materials 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 229910010413 TiO 2 Inorganic materials 0.000 description 2
- 230000003213 activating effect Effects 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000004917 carbon fiber Substances 0.000 description 2
- 239000003575 carbonaceous material Substances 0.000 description 2
- 239000006185 dispersion Substances 0.000 description 2
- 238000003411 electrode reaction Methods 0.000 description 2
- 239000004744 fabric Substances 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- PCLURTMBFDTLSK-UHFFFAOYSA-N nickel platinum Chemical compound [Ni].[Pt] PCLURTMBFDTLSK-UHFFFAOYSA-N 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 231100000572 poisoning Toxicity 0.000 description 2
- 230000000607 poisoning effect Effects 0.000 description 2
- 229920005597 polymer membrane Polymers 0.000 description 2
- 238000000634 powder X-ray diffraction Methods 0.000 description 2
- 239000010970 precious metal Substances 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- HPGGPRDJHPYFRM-UHFFFAOYSA-J tin(iv) chloride Chemical compound Cl[Sn](Cl)(Cl)Cl HPGGPRDJHPYFRM-UHFFFAOYSA-J 0.000 description 2
- XJDNKRIXUMDJCW-UHFFFAOYSA-J titanium tetrachloride Chemical compound Cl[Ti](Cl)(Cl)Cl XJDNKRIXUMDJCW-UHFFFAOYSA-J 0.000 description 2
- 238000004627 transmission electron microscopy Methods 0.000 description 2
- 238000001132 ultrasonic dispersion Methods 0.000 description 2
- 229910001233 yttria-stabilized zirconia Inorganic materials 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 229910000531 Co alloy Inorganic materials 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
- CLBRCZAHAHECKY-UHFFFAOYSA-N [Co].[Pt] Chemical compound [Co].[Pt] CLBRCZAHAHECKY-UHFFFAOYSA-N 0.000 description 1
- ZKIHCVGCBDREBT-UHFFFAOYSA-N [F].[W] Chemical compound [F].[W] ZKIHCVGCBDREBT-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 238000000889 atomisation Methods 0.000 description 1
- 239000011324 bead Substances 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 239000003638 chemical reducing agent Substances 0.000 description 1
- 238000000975 co-precipitation 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
- 238000000366 colloid method Methods 0.000 description 1
- 239000012698 colloidal precursor Substances 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 238000007865 diluting Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 238000004993 emission spectroscopy Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- UQSQSQZYBQSBJZ-UHFFFAOYSA-N fluorosulfonic acid Chemical compound OS(F)(=O)=O UQSQSQZYBQSBJZ-UHFFFAOYSA-N 0.000 description 1
- 125000000524 functional group Chemical group 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 239000010931 gold Substances 0.000 description 1
- 239000001307 helium Substances 0.000 description 1
- 229910052734 helium Inorganic materials 0.000 description 1
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 1
- 239000011261 inert gas Substances 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
- 229910052742 iron Inorganic materials 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- 238000004949 mass spectrometry Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000001000 micrograph Methods 0.000 description 1
- 150000007522 mineralic acids Chemical class 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000004570 mortar (masonry) Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- UYXRCZUOJAYSQR-UHFFFAOYSA-N nitric acid;platinum Chemical compound [Pt].O[N+]([O-])=O UYXRCZUOJAYSQR-UHFFFAOYSA-N 0.000 description 1
- 229910052762 osmium Inorganic materials 0.000 description 1
- SYQBFIAQOQZEGI-UHFFFAOYSA-N osmium atom Chemical compound [Os] SYQBFIAQOQZEGI-UHFFFAOYSA-N 0.000 description 1
- SOQBVABWOPYFQZ-UHFFFAOYSA-N oxygen(2-);titanium(4+) Chemical class [O-2].[O-2].[Ti+4] SOQBVABWOPYFQZ-UHFFFAOYSA-N 0.000 description 1
- DCKVFVYPWDKYDN-UHFFFAOYSA-L oxygen(2-);titanium(4+);sulfate Chemical compound [O-2].[Ti+4].[O-]S([O-])(=O)=O DCKVFVYPWDKYDN-UHFFFAOYSA-L 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 238000010992 reflux Methods 0.000 description 1
- 239000010948 rhodium Substances 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
- 229910052707 ruthenium Inorganic materials 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000007784 solid electrolyte Substances 0.000 description 1
- FAKFSJNVVCGEEI-UHFFFAOYSA-J tin(4+);disulfate Chemical compound [Sn+4].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O FAKFSJNVVCGEEI-UHFFFAOYSA-J 0.000 description 1
- QHGNHLZPVBIIPX-UHFFFAOYSA-N tin(ii) oxide Chemical class [Sn]=O QHGNHLZPVBIIPX-UHFFFAOYSA-N 0.000 description 1
- 229910000348 titanium sulfate Inorganic materials 0.000 description 1
- NXHILIPIEUBEPD-UHFFFAOYSA-H tungsten hexafluoride Chemical compound F[W](F)(F)(F)(F)F NXHILIPIEUBEPD-UHFFFAOYSA-H 0.000 description 1
- CMPGARWFYBADJI-UHFFFAOYSA-L tungstic acid Chemical compound O[W](O)(=O)=O CMPGARWFYBADJI-UHFFFAOYSA-L 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- GPPXJZIENCGNKB-UHFFFAOYSA-N vanadium Chemical compound [V]#[V] GPPXJZIENCGNKB-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Landscapes
- Fuel Cell (AREA)
- Inert Electrodes (AREA)
Description
本発明は電極触媒に関する。また本発明は、この電極触媒を含む膜電極接合体に関する。更に本発明は、この膜電極接合体を有する固体高分子形燃料電池に関する。 The present invention relates to an electrode catalyst. The present invention also relates to a membrane electrode assembly containing this electrode catalyst. Furthermore, the present invention relates to a polymer electrolyte fuel cell having this membrane electrode assembly.
固体高分子形燃料電池は、パーフルオロアルキルスルホン酸型高分子などのプロトン伝導性を有する高分子膜を固体電解質とし、該固体高分子膜の各面に電極触媒が施されてなる酸素極及び燃料極が形成された膜電極接合体を備えている。 In a polymer electrolyte fuel cell, a polymer membrane having proton conductivity such as a perfluoroalkyl sulfonic acid type polymer is used as a solid electrolyte, and an oxygen electrode formed by applying an electrode catalyst to each surface of the solid polymer membrane and an oxygen electrode. It includes a membrane electrode assembly on which a fuel electrode is formed.
電極触媒は、一般に担体となるカーボンブラックなどの導電性炭素材料の表面に、白金を始めとする各種貴金属含有触媒が担持されてなる。電極触媒は、燃料電池の運転時の電位変化により、カーボンが酸化腐食し、担持されている金属触媒の凝集や脱落が起こることが知られている。その結果、運転時間の経過とともに燃料電池の性能が低下してくる。そこで、燃料電池の製造においては、実際に必要な量よりも多量の貴金属含有触媒を担体に担持させておくことで性能にゆとりを持たせて、高寿命化を図っている。しかし、このことは経済性の観点から有利とは言えない。 The electrode catalyst generally has various noble metal-containing catalysts such as platinum supported on the surface of a conductive carbon material such as carbon black which is a carrier. It is known that in the electrode catalyst, carbon is oxidatively corroded due to a change in potential during operation of the fuel cell, and the metal catalyst supported is aggregated or dropped. As a result, the performance of the fuel cell deteriorates with the lapse of operating time. Therefore, in the manufacture of fuel cells, the carrier is supported with a amount of a noble metal-containing catalyst that is larger than the amount actually required to provide a margin in performance and to extend the service life. However, this is not advantageous from an economic point of view.
そこで、固体高分子形燃料電池の高寿命化や経済性の改善などを図ることを目的として、電極触媒に関する種々の検討がなされている。例えば、これまで担体として用いられてきた導電性炭素に代えて、非炭素系の材料である導電性酸化物担体を用いることが提案されている（特許文献１）。この文献においては、電極触媒の担体として酸化スズが用いられている。この文献には、この酸化スズにアンチモンをドープすることが記載されている。 Therefore, various studies on electrode catalysts have been made for the purpose of extending the life of polymer electrolyte fuel cells and improving economic efficiency. For example, it has been proposed to use a conductive oxide carrier, which is a non-carbon material, instead of the conductive carbon that has been used as a carrier (Patent Document 1). In this document, tin oxide is used as a carrier for the electrode catalyst. This document describes doping this tin oxide with antimony.
しかし、上述した特許文献１に記載の酸化スズを電極触媒の担体として用いた場合であっても、酸化スズにドープされたアンチモンにより貴金属含有触媒が被毒することにより、貴金属含有触媒が本来的に有する触媒活性などの性能を十分に発揮させることは容易ではなかった。 However, even when the tin oxide described in Patent Document 1 described above is used as a carrier for the electrode catalyst, the noble metal-containing catalyst is inherently poisoned by the antimony doped with tin oxide. It was not easy to fully exert the performance such as the catalytic activity of the.
したがって本発明の課題は、前述した従来技術が有する欠点を解消し得る電極触媒を提供することにある。 Therefore, an object of the present invention is to provide an electrode catalyst capable of eliminating the above-mentioned drawbacks of the prior art.
本発明は、所定の元素である第１添加元素を含む酸化スズの担体と、
酸化スズ及び酸化チタンから選択される少なくとも１種の粒子が多数集合してなり、前記担体の表面の少なくとも一部を被覆する被覆層と、
前記被覆層に担持された貴金属含有触媒と、
を有し、
前記被覆層における前記第１添加元素の含有率が、前記担体における前記第１添加元素の含有率より低い電極触媒を提供するものである。
The present invention comprises a tin oxide carrier containing a first additive element, which is a predetermined element, and
A coating layer in which a large number of particles of at least one selected from tin oxide and titanium oxide are aggregated to cover at least a part of the surface of the carrier.
The noble metal-containing catalyst supported on the coating layer and
Have,
It provides an electrode catalyst in which the content of the first additive element in the coating layer is lower than the content of the first additive element in the carrier.
また本発明は、前記の電極触媒を含む触媒層が、固体高分子電解質膜の少なくとも一面に設けられた膜電極接合体を提供するものである。 The present invention also provides a membrane electrode assembly in which the catalyst layer containing the electrode catalyst is provided on at least one surface of the solid polymer electrolyte membrane.
更に本発明は、前記の膜電極接合体を有する固体高分子形燃料電池を提供するものである。 Further, the present invention provides a polymer electrolyte fuel cell having the membrane electrode assembly.
本発明によれば、第１添加元素の含有率が担体よりも低い被覆層を貴金属含有触媒と担体との間に設けることによって、担体の酸化スズに含まれる第１添加元素による貴金属含有触媒の被毒が防止されるため、貴金属含有触媒が本来的に有する性能が十分に発揮される電極触媒が提供される。 According to the present invention, by providing a coating layer having a lower content of the first additive element than that of the carrier between the noble metal-containing catalyst and the carrier, the noble metal-containing catalyst due to the first additive element contained in the tin oxide of the carrier can be used. Since poisoning is prevented, an electrode catalyst is provided in which the inherent performance of the noble metal-containing catalyst is sufficiently exhibited.
以下本発明を、その好ましい実施形態に基づき説明する。本発明の電極触媒は、担体と、担体の表面の少なくとも一部を覆う被覆層と、被覆層に担持された貴金属含有触媒とを有する。 Hereinafter, the present invention will be described based on its preferred embodiment. The electrode catalyst of the present invention has a carrier, a coating layer covering at least a part of the surface of the carrier, and a noble metal-containing catalyst supported on the coating layer.
本発明の電極触媒においては、担体の表面、すなわち担体と貴金属含有触媒との間に、酸化スズ及び酸化チタンから選択される少なくとも１種の粒子が多数集合して形成される被覆層が介在する。そして、被覆層における第１添加元素の含有率は、担体における第１添加元素の含有率よりも低くなっている。この状態は、被覆層における第１添加元素の含有率が０である場合、すなわち被覆層に第１添加元素が含まれない場合も含んでいる。第１添加元素の詳細については後述する。 In the electrode catalyst of the present invention, a coating layer formed by a large number of particles of at least one selected from tin oxide and titanium oxide is interposed on the surface of the carrier, that is, between the carrier and the noble metal-containing catalyst. .. The content of the first additive element in the coating layer is lower than the content of the first additive element in the carrier. This state also includes the case where the content of the first additive element in the coating layer is 0, that is, the case where the coating layer does not contain the first additive element. Details of the first additive element will be described later.
このように、上述した被覆層が、担体と貴金属含有触媒との間に介在することで、担体に含まれる第１添加元素が貴金属含有触媒に向けて拡散することが効果的に防止され、貴金属含有触媒が本来的に有する性能が十分に発揮されることが判明した。つまり、貴金属含有触媒が、第１添加元素によって被毒されにくくなることが判明した。 As described above, by interposing the above-mentioned coating layer between the carrier and the noble metal-containing catalyst, it is possible to effectively prevent the first additive element contained in the carrier from diffusing toward the noble metal-containing catalyst, and the noble metal. It was found that the inherent performance of the contained catalyst was fully exhibited. That is, it was found that the noble metal-containing catalyst is less likely to be poisoned by the first additive element.
担体は酸化スズから構成されている。担体を構成する酸化スズは、スズの酸化物から構成される。スズの酸化物には、例えば四価のスズの酸化物であるＳｎＯ２や、二価のスズの酸化物であるＳｎＯなどがある。スズの酸化物の結晶構造の同定には例えば粉末Ｘ線回折測定を用いることができる。特にスズの酸化物はＳｎＯ２を主体とすることが、耐酸性を高める観点から好ましい。「ＳｎＯ２を主体とする」とは、スズの酸化物に含まれるスズのうちの５０モル％以上がＳｎＯ２からなることを言う。 The carrier is composed of tin oxide. The tin oxide constituting the carrier is composed of an oxide of tin. Examples of the tin oxide include SnO 2 , which is a tetravalent tin oxide, and SnO, which is a divalent tin oxide. For example, powder X-ray diffraction measurement can be used to identify the crystal structure of the tin oxide. In particular, it is preferable that the tin oxide is mainly SnO 2 from the viewpoint of enhancing acid resistance. " Mainly SnO 2 " means that 50 mol% or more of tin contained in tin oxide is composed of SnO 2 .
担体を構成する酸化スズの導電性を高める目的で、酸化スズ中には、酸化スズの導電性を向上させ得る元素が含まれている。そのような元素としては、例えばタンタル、ニオブ、リン、アンチモン、タングステン、モリブデン、インジウム、バナジウム、フッ素及び塩素からなる群より選択される少なくとも１種が挙げられる。これらの添加元素のうち、酸化スズの導電性の一層の向上の観点からは、タンタル、リン、アンチモン、タングステン、フッ素からなる群より選択される少なくとも１種を用いることが好ましく、特にアンチモン及びタンタルから選択される少なくとも１種を用いることが更に好ましい。なお、本明細書において、酸化スズの導電性を高める目的で酸化スズに添加される前記元素のことを「第１添加元素」と言う。 For the purpose of increasing the conductivity of tin oxide constituting the carrier, tin oxide contains an element that can improve the conductivity of tin oxide. Such elements include, for example, at least one selected from the group consisting of tantalum, niobium, phosphorus, antimony, tungsten, molybdenum, indium, vanadium, fluorine and chlorine. Among these additive elements, from the viewpoint of further improving the conductivity of tin oxide, it is preferable to use at least one selected from the group consisting of tantalum, phosphorus, antimony, tungsten and fluorine, particularly antimony and tantalum. It is more preferable to use at least one selected from. In the present specification, the element added to tin oxide for the purpose of increasing the conductivity of tin oxide is referred to as "first added element".
第１添加元素が添加された酸化スズに含まれる第１添加元素の含有率は、第１添加元素をＭ１で表すとＭ１（ｍｏｌ）／（Ｓｎ（ｍｏｌ）＋Ｍ１（ｍｏｌ））×１００で表して、好ましくは１ｍｏｌ％以上３０ｍｏｌ％以下である。以下、この値を担体における「第１添加元素含有率」と言う。第１添加元素含有率を１ｍｏｌ％以上に設定することで、第１添加元素を含有する酸化スズの導電性を十分に高くすることができる。第１添加元素含有率が３０ｍｏｌ％を超えても、担体としての導電率は大きく向上しない。第１添加元素を含有する酸化スズの導電性を一層高め、かつ比表面積を十分に高くする観点から、第１添加元素含有率は更に好ましくは１ｍｏｌ％以上１５ｍｏｌ％以下、一層好ましくは１ｍｏｌ％以上１０ｍｏｌ％以下である。また、第１添加元素がアンチモン及びタンタルの場合には、５ｍｏｌ％以下であることが好ましい。第１添加元素として２種以上の元素を併用した場合には、前記のＭ１のモル数は、使用したすべての第１添加元素の合計モル数を意味する。 The content of the first additive element contained in tin oxide to which the first additive element is added is represented by M1 (mol) / (Sn (mol) + M1 (mol)) × 100 when the first additive element is represented by M1. It is preferably 1 mol% or more and 30 mol% or less. Hereinafter, this value is referred to as "first additive element content" in the carrier. By setting the content of the first additive element to 1 mol% or more, the conductivity of tin oxide containing the first additive element can be sufficiently increased. Even if the content of the first additive element exceeds 30 mol%, the conductivity as a carrier is not significantly improved. From the viewpoint of further increasing the conductivity of tin oxide containing the first additive element and sufficiently increasing the specific surface area, the content of the first additive element is more preferably 1 mol% or more and 15 mol% or less, still more preferably 1 mol% or more. It is 10 mol% or less. When the first additive element is antimony or tantalum, it is preferably 5 mol% or less. When two or more kinds of elements are used in combination as the first additive element, the number of moles of M1 mentioned above means the total number of moles of all the first additive elements used.
第１添加元素含有率は、第１添加元素がハロゲン以外の元素である場合には、ＩＣＰ質量分析装置（ＩＣＰ−ＭＳ）によって測定される。あるいは、ＩＣＰ質量分析に代えて、蛍光Ｘ線（ＸＲＦ）分析を用いることもできる。これらの測定方法を採用する場合、酸化スズの質量は、測定されたスズの質量をＳｎＯ２に換算して算出される。一方、第１添加元素がハロゲンである場合、ハロゲンの質量は、例えば三菱化学アナリテック社製自動試料燃焼装置（ＡＱＦ−２１００Ｈ）によって測定される。 The content of the first additive element is measured by an ICP mass spectrometer (ICP-MS) when the first additive element is an element other than halogen. Alternatively, fluorescent X-ray (XRF) analysis can be used instead of ICP mass spectrometry. When these measuring methods are adopted, the mass of tin oxide is calculated by converting the measured mass of tin into SnO 2. On the other hand, when the first additive element is halogen, the mass of halogen is measured by, for example, an automatic sample combustion device (AQF-2100H) manufactured by Mitsubishi Chemical Analytech.
第１添加元素は、酸化スズ中に固溶しているか、又は酸化スズ中に添加元素の化合物（例えば添加元素の酸化物）の状態で存在している。第１添加元素が酸化スズ中に固溶しているとは、酸化スズにおけるスズのサイトが添加元素の原子で置換されていること、又は添加元素の原子が酸化スズの結晶格子の原子間の隙間に侵入したことを指す。添加元素が酸化スズ中に固溶していると、担体である添加元素を含有する酸化スズの導電性が高くなるので好ましい。 The first additive element is either dissolved in tin oxide or exists in tin oxide in the form of a compound of the additive element (for example, an oxide of the additive element). The fact that the first additive element is dissolved in tin oxide means that the tin site in tin oxide is replaced by the atom of the additive element, or the atom of the additive element is between the atoms of the tin oxide crystal lattice. It means that it has entered the gap. It is preferable that the additive element is dissolved in tin oxide because the conductivity of tin oxide containing the additive element as a carrier is increased.
第１添加元素を含む酸化スズから構成される担体は粒子状の形態をしている。粒子状の場合、個々の粒子の平均粒子径は、好ましくは５ｎｍ以上１００ｎｍ以下、更に好ましくは１０ｎｍ以上６０ｎｍ以下であることが、電極触媒の担体の比表面積を大きくし得る点から好ましい。粒子の形状に特に制限はなく、例えば球状、多面体状、板状若しくは紡錘状、又はこれらの混合など、種々の形状を採用することができる。担体の平均粒子径は、電子顕微鏡で観察することによって測定する。電子顕微鏡観察によって１００個以上の担体のフェレ径を測定し、その平均値をもって平均粒子径とする。 The carrier composed of tin oxide containing the first additive element is in the form of particles. In the case of particles, the average particle size of each particle is preferably 5 nm or more and 100 nm or less, more preferably 10 nm or more and 60 nm or less, from the viewpoint of increasing the specific surface area of the carrier of the electrode catalyst. The shape of the particles is not particularly limited, and various shapes such as a spherical shape, a polyhedral shape, a plate shape or a spindle shape, or a mixture thereof can be adopted. The average particle size of the carrier is measured by observing with an electron microscope. The ferret diameters of 100 or more carriers are measured by electron microscope observation, and the average value thereof is taken as the average particle diameter.
担体の粒子は、個々に独立した分散状態になっていてもよい。あるいは複数の該粒子が凝集した凝集体になっていてもよい。凝集体になっている場合、該粒子はその不定数が不規則に集合した不定形の形状をしていてもよい。あるいは、複数個の該粒子が数珠状に連なった鎖状構造部位を有していてもよい。 The particles of the carrier may be individually dispersed. Alternatively, a plurality of the particles may be aggregated into an agglomerate. When agglomerates, the particles may have an amorphous shape in which the indefinite numbers are irregularly assembled. Alternatively, the plurality of the particles may have a chain structure portion in which the particles are connected in a bead shape.
本発明の電極触媒においては、後述する被覆層の表面、又は担体の表面と被覆層の表面に、貴金属含有触媒が担持されている。貴金属含有触媒としては、貴金属そのもの、及び貴金属と貴金属以外の元素とを含む合金などが用いられる。貴金属としては、例えば白金、ロジウム、ルテニウム、イリジウム、パラジウム、オスミウム、金及び銀などが挙げられる。これらの貴金属は１種を単独で、又は２種以上を組み合わせて用いることができる。貴金属含有触媒に含まれる貴金属以外の元素としては、例えばコバルト、鉄、ニッケル、タングステン、モリブデン、タンタル、ニオブ及びスズなどが挙げられる。これらの元素は１種を単独で、又は２種以上を組み合わせて用いることができる。これらの貴金属含有触媒のうち、白金及び白金基合金（例えば白金ニッケル合金や白金コバルト合金）は、固体高分子形燃料電池の作動温度である８０℃付近の温度域において、酸素の還元及び水素の酸化に対する電気化学的触媒活性が高いので、特に好適に用いられる。 In the electrode catalyst of the present invention, the noble metal-containing catalyst is supported on the surface of the coating layer described later, or the surface of the carrier and the surface of the coating layer. As the noble metal-containing catalyst, a noble metal itself, an alloy containing the noble metal and an element other than the noble metal, or the like is used. Examples of precious metals include platinum, rhodium, ruthenium, iridium, palladium, osmium, gold and silver. These precious metals may be used alone or in combination of two or more. Examples of elements other than the noble metal contained in the noble metal-containing catalyst include cobalt, iron, nickel, tungsten, molybdenum, tantalum, niobium and tin. These elements may be used alone or in combination of two or more. Of these noble metal-containing catalysts, platinum and platinum-based alloys (for example, platinum nickel alloys and platinum cobalt alloys) are used to reduce oxygen and hydrogen in the temperature range of around 80 ° C, which is the operating temperature of polymer electrolyte fuel cells. It is particularly preferably used because of its high electrochemical catalytic activity for oxidation.
貴金属含有触媒は、微粒子の形態で被覆層に担持されていることが有利である。貴金属含有触媒の微粒子の平均粒子径は、担体の平均粒子径よりも小さいことを条件として、例えば１ｎｍ以上２０ｎｍ以下とすることが好ましい。この範囲の平均粒子径を有する貴金属含有触媒の微粒子を担持させることで、触媒活性を向上させることができる。貴金属含有触媒の微粒子の平均粒子径は、電子顕微鏡像から測定される貴金属含有触媒の粒径（フェレ径）の平均値により得ることができる。 It is advantageous that the noble metal-containing catalyst is supported on the coating layer in the form of fine particles. The average particle size of the fine particles of the noble metal-containing catalyst is preferably 1 nm or more and 20 nm or less, provided that it is smaller than the average particle size of the carrier. Catalytic activity can be improved by supporting fine particles of a noble metal-containing catalyst having an average particle size in this range. The average particle size of the fine particles of the noble metal-containing catalyst can be obtained from the average value of the particle size (ferret diameter) of the noble metal-containing catalyst measured from the electron microscope image.
貴金属含有触媒に含まれる貴金属に着目したとき、貴金属の担持量は、電極触媒の全質量、つまり担体の質量と、貴金属含有触媒の質量と、後述する被覆層の総和に対して１質量％以上３０質量％以下とすることが好ましく、１質量％以上２０質量％以下とすることが更に好ましい。この範囲の担持量に設定することで、電極反応を十分に円滑に行うことが可能になる。貴金属の担持量は、電極触媒を適当な方法で溶解して溶液となし、ＩＣＰ発光分析によりこの溶液を分析することで求めることができる。 When focusing on the noble metal contained in the noble metal-containing catalyst, the amount of the noble metal supported is 1% by mass or more based on the total mass of the electrode catalyst, that is, the mass of the carrier, the mass of the noble metal-containing catalyst, and the total of the coating layers described later. It is preferably 30% by mass or less, and more preferably 1% by mass or more and 20% by mass or less. By setting the loading amount within this range, the electrode reaction can be sufficiently smoothly performed. The amount of the noble metal supported can be determined by dissolving the electrode catalyst by an appropriate method to form a solution, and analyzing this solution by ICP emission spectrometry.
被覆層を構成する酸化スズ及び／又は酸化チタンは、担体よりも微粒のものである。酸化スズ及び／又は酸化チタンの平均粒子径は、担体の粒径よりも小さいことを条件として、１ｎｍ以上２０ｎｍ以下であることが好ましく、１ｎｍ以上１０ｎｍ以下であることが更に好ましい。酸化スズ又は酸化チタンの平均粒子径は、担体の平均粒子径の測定方法に準じて測定される。 The tin oxide and / or titanium oxide constituting the coating layer is finer than the carrier. The average particle size of tin oxide and / or titanium oxide is preferably 1 nm or more and 20 nm or less, and more preferably 1 nm or more and 10 nm or less, provided that the particle size is smaller than the particle size of the carrier. The average particle size of tin oxide or titanium oxide is measured according to the method for measuring the average particle size of the carrier.
被覆層は、酸化スズ及び／又は酸化チタンの微粒子の集合体から構成されている。被覆層は、所定の厚みを有して、担体と貴金属含有触媒とを隔てていることが好ましい。これによって、担体と被覆層とからなる部位に導電性を付与させつつ、担体に含まれる第１添加元素が貴金属含有触媒に向けて拡散することが効果的に防止される。この観点から、被覆層はその厚みが１ｎｍ以上２０ｎｍ以下であることが好ましく、１ｎｍ以上１０ｎｍ以下であることが更に好ましい。被覆層の厚みは、透過型電子顕微鏡（ＴＥＭ）観察によって測定することができる。 The coating layer is composed of an aggregate of fine particles of tin oxide and / or titanium oxide. The coating layer preferably has a predetermined thickness and separates the carrier and the noble metal-containing catalyst. This effectively prevents the first additive element contained in the carrier from diffusing toward the noble metal-containing catalyst while imparting conductivity to the portion composed of the carrier and the coating layer. From this viewpoint, the thickness of the coating layer is preferably 1 nm or more and 20 nm or less, and more preferably 1 nm or more and 10 nm or less. The thickness of the coating layer can be measured by transmission electron microscopy (TEM) observation.
被覆層を構成する酸化スズは、担体を構成する酸化スズと同様に、スズの酸化物から構成される。スズの酸化物には、例えばＳｎＯ２やＳｎＯなどがある。スズの酸化物の結晶構造の同定には例えば粉末Ｘ線回折測定を用いることができる。特にスズの酸化物はＳｎＯ２を主体とすることが、第１添加元素の拡散を効果的に抑制し得る観点から好ましい。「ＳｎＯ２を主体とする」とは、スズの酸化物に含まれるスズのうちの５０モル％以上がＳｎＯ２からなることを言う。 The tin oxide constituting the coating layer is composed of an oxide of tin, similarly to the tin oxide constituting the carrier. Examples of tin oxides include SnO 2 and SnO. For example, powder X-ray diffraction measurement can be used to identify the crystal structure of the tin oxide. In particular, it is preferable that the tin oxide is mainly SnO 2 from the viewpoint of effectively suppressing the diffusion of the first additive element. " Mainly SnO 2 " means that 50 mol% or more of tin contained in tin oxide is composed of SnO 2 .
一方、被覆層を構成する酸化チタンは、チタンの酸化物からなる。チタンの酸化物としては例えばＴｉＯ２などが挙げられるが、これに限られない。チタンの酸化物がＴｉＯ２である場合、このＴｉＯ２はルチル型の結晶構造であってもよく、あるいはアナターゼ型、ブルカイト型の結晶構造であってもよい。 On the other hand, the titanium oxide constituting the coating layer is made of an oxide of titanium. Examples of titanium oxides include, but are not limited to, TIO 2. When the oxide of titanium is TiO 2 , the TiO 2 may have a rutile-type crystal structure, or may have an anatase-type or brookite-type crystal structure.
被覆層を構成する微粒子は、酸化スズのみであってもよく、酸化チタンのみであってもよい。あるいは酸化スズと酸化チタンとを混合して用いてもよい。いずれの場合であっても、電極触媒の全体に占める被覆層の割合は、１質量％以上５０質量％以下であることが好ましく、１質量％以上２５質量％以下であることが更に好ましい。この範囲の割合で被覆層を設けることで、担体と被覆層とからなる部位に導電性を付与させつつ、第１添加元素の拡散を一層効果的に防止することができる。電極触媒の全体に占める被覆層の割合は、次の方法で測定される。すなわち、担体に被覆層を形成した後の重量から担体に被覆層を形成する前の重量を差し引くことにより、算出される。 The fine particles constituting the coating layer may be only tin oxide or only titanium oxide. Alternatively, tin oxide and titanium oxide may be mixed and used. In any case, the proportion of the coating layer in the entire electrode catalyst is preferably 1% by mass or more and 50% by mass or less, and more preferably 1% by mass or more and 25% by mass or less. By providing the coating layer at a ratio within this range, it is possible to more effectively prevent the diffusion of the first additive element while imparting conductivity to the portion composed of the carrier and the coating layer. The ratio of the coating layer to the entire electrode catalyst is measured by the following method. That is, it is calculated by subtracting the weight before forming the coating layer on the carrier from the weight after forming the coating layer on the carrier.
被覆層は、担体の表面に直接に配置されていることが好ましい。また被覆層の表面に貴金属含有触媒が直接配置されていることが好ましい。つまり被覆層は、担体と直接に接しており、且つ貴金属含有触媒とも直接に接していることが好ましい。尤も、被覆層と担体との間に別の部位が介在していることは許容される。同様に、被覆層と貴金属含有触媒との間に別の部位が存在していることも許容される。 The coating layer is preferably placed directly on the surface of the carrier. Further, it is preferable that the noble metal-containing catalyst is directly arranged on the surface of the coating layer. That is, it is preferable that the coating layer is in direct contact with the carrier and also with the noble metal-containing catalyst. However, it is permissible for another site to intervene between the coating layer and the carrier. Similarly, it is permissible for another site to be present between the coating layer and the noble metal-containing catalyst.
被覆層は、（１−１）担体の表面全域を満遍なく被覆していてもよく、あるいは（１−２）複数の被覆層が適切な距離を保ち担体の表面が露出するように部分的に被覆していてもよい。（１−１）の場合、貴金属含有触媒は、被覆層の表面全域を満遍なく被覆していてもよく、あるいは複数の貴金属含有触媒が適切な距離を保ち被覆層の表面が露出するように部分的に被覆していてもよい。一方、（１−２）の場合、担体の表面のうち、被覆層が存在しておらず露出している領域には、貴金属含有触媒が直接に配置されていてもよい。したがって（１−２）の場合には、貴金属含有触媒は、被覆層上に配置されているか、あるいは、本発明の効果が失われないことを条件として、被覆層上及び担体の表面に直接配置されている。 The coating layer may (1-1) cover the entire surface of the carrier evenly, or (1-2) partially cover the surface of the carrier so that the plurality of coating layers maintain an appropriate distance and the surface of the carrier is exposed. You may be doing it. In the case of (1-1), the noble metal-containing catalyst may evenly cover the entire surface of the coating layer, or a plurality of noble metal-containing catalysts may partially cover the entire surface of the coating layer so as to maintain an appropriate distance and expose the surface of the coating layer. May be covered with. On the other hand, in the case of (1-2), the noble metal-containing catalyst may be directly arranged on the surface of the carrier where the coating layer does not exist and is exposed. Therefore, in the case of (1-2), the noble metal-containing catalyst is placed on the coating layer or directly on the coating layer and on the surface of the carrier, provided that the effect of the present invention is not lost. Has been done.
被覆層を構成する酸化スズ及び／又は酸化チタンには、（２−１）スズやチタン以外の元素を含有しなくてもよく、（２−２）第１添加元素とは異なる元素を含有してもよく、（２−３）第１添加元素を含有してもよく、あるいは（２−４）第１添加元素と第１添加元素とは異なる元素の両方を含有してもよい。なお、第１添加元素の貴金属含有触媒への拡散をより一層防止するためには、（２−１）及び（２−２）の場合が好ましい。また、（２−３）及び（２−４）の場合には、被覆層における第１添加元素の含有率は、担体における第１添加元素の含有率より低くしなければならない。なお、（２−３）及び（２−４）の場合には、酸化スズ及び／又は酸化チタンに第１添加元素を予め添加する場合や、電極触媒を使用している際に、担体の酸化スズに含まれる第１添加元素が移行することにより、被覆層の酸化スズ及び／又は酸化チタンに含まれる場合も含む。 The tin oxide and / or titanium oxide constituting the coating layer does not have to contain an element other than (2-1) tin and titanium, and contains an element different from (2-2) the first additive element. It may contain (2-3) the first additive element, or (2-4) both the first additive element and an element different from the first additive element may be contained. The cases (2-1) and (2-2) are preferable in order to further prevent the diffusion of the first additive element into the noble metal-containing catalyst. Further, in the cases of (2-3) and (2-4), the content of the first additive element in the coating layer must be lower than the content of the first additive element in the carrier. In the cases of (2-3) and (2-4), the carrier is oxidized when the first additive element is added in advance to tin oxide and / or titanium oxide, or when the electrode catalyst is used. The case where the first additive element contained in tin is transferred to tin oxide and / or titanium oxide in the coating layer is also included.
被覆層を構成する酸化スズ及び／又は酸化チタンに含まれる添加元素は、酸化スズや酸化チタン中に固溶しているか、又は酸化スズや酸化チタン中に添加元素の化合物（例えば添加元素の酸化物）の状態で存在している。添加元素が酸化スズや酸化チタン中に固溶しているとは、酸化スズや酸化チタンにおけるスズやチタンのサイトが添加元素の原子で置換されていること、又は添加元素の原子が酸化スズや酸化チタンの結晶格子の原子間の隙間に侵入したことを指す。 The additive elements contained in tin oxide and / or titanium oxide constituting the coating layer are either dissolved in tin oxide or titanium oxide, or a compound of the additive element in tin oxide or titanium oxide (for example, oxidation of the additive element). It exists in the state of (thing). The fact that the additive element is dissolved in tin oxide or titanium oxide means that the tin or titanium site in tin oxide or titanium oxide is replaced by the atom of the additive element, or the atom of the additive element is tin oxide or It means that it has invaded the gap between atoms in the crystal lattice of titanium oxide.
（２−３）及び（２−４）の場合、酸化スズ及び／又は酸化チタンに含まれる第１添加元素の含有率は、第１添加元素をＭ１で表すとＭ１（ｍｏｌ）／（Ｓｎ（ｍｏｌ）＋Ｔｉ（ｍｏｌ）＋Ｍ１（ｍｏｌ））×１００で表される。そして、被覆層における第１添加元素の含有率は、担体における「第１添加元素含有率」より低く、且つ本発明の効果を失われないことを条件として、０ｍｏｌ％以上３０ｍｏｌ％以下であることが好ましい。以下、この値を被覆層における「第１添加元素含有率」と言う。第１添加元素として２種以上の元素を併用した場合には、前記のＭ１のモル数は、使用したすべての第１添加元素の合計モル数を意味する。被覆層における第１添加元素含有率は、担体における第１添加元素含有率と同様の方法で測定できる。 In the case of (2-3) and (2-4), the content of the first additive element contained in tin oxide and / or titanium oxide is M1 (mol) / (Sn (Sn) when the first additive element is represented by M1. It is represented by (mol) + Ti (mol) + M1 (mol)) × 100. The content of the first additive element in the coating layer is 0 mol% or more and 30 mol% or less, provided that the content of the first additive element is lower than the "first additive element content" in the carrier and the effect of the present invention is not lost. Is preferable. Hereinafter, this value is referred to as "first additive element content" in the coating layer. When two or more kinds of elements are used in combination as the first additive element, the number of moles of M1 mentioned above means the total number of moles of all the first additive elements used. The content of the first additive element in the coating layer can be measured in the same manner as the content of the first additive element in the carrier.
（２−２）の場合、被覆層を構成する酸化スズ及び／又は酸化チタンの微粒子には、担体と被覆層とからなる部位に導電性を付与させつつ、第１添加元素の貴金属含有触媒への拡散を防止するために、第１添加元素とは異なる元素である第２添加元素を含有することが好ましい。そして、第２添加元素は、第１添加元素と異なることを条件として、タングステン、モリブデン、ニオブ、リン、塩素及びフッ素からなる群より選択される少なくとも１種の元素である。 In the case of (2-2), the fine particles of tin oxide and / or titanium oxide constituting the coating layer are imparted to the noble metal-containing catalyst of the first additive element while imparting conductivity to the portion composed of the carrier and the coating layer. It is preferable to contain a second additive element, which is an element different from the first additive element, in order to prevent the diffusion of the compound. The second additive element is at least one element selected from the group consisting of tungsten, molybdenum, niobium, phosphorus, chlorine and fluorine, provided that it is different from the first additive element.
第２添加元素を含有する酸化スズ及び／又は酸化チタンに含まれる第２添加元素の含有率は、第２添加元素をＭ２で表すとＭ２（ｍｏｌ）／（Ｓｎ（ｍｏｌ）＋Ｔｉ（ｍｏｌ）＋Ｍ２（ｍｏｌ））×１００で表される。そして、好ましくは０．０１ｍｏｌ％以上３０ｍｏｌ％以下、更に好ましくは０．０１ｍｏｌ％以上１５ｍｏｌ％以下である。以下、この値を「第２添加元素含有率」と言う。第２添加元素含有率を１ｍｏｌ％以上に設定することで、担体に含まれる第１添加元素の貴金属含有触媒への拡散が、更に一層効果的に防止される。第２添加元素として２種以上の元素を併用した場合には、前記のＭ２のモル数は、使用したすべての第２添加元素の合計モル数を意味する。第２添加元素含有率は、第１添加元素含有率と同様の方法で測定できる。 The content of the second additive element contained in tin oxide and / or titanium oxide containing the second additive element is M2 (mol) / (Sn (mol) + Ti (mol) + M2 when the second additive element is represented by M2. It is represented by (mol)) × 100. Then, it is preferably 0.01 mol% or more and 30 mol% or less, and more preferably 0.01 mol% or more and 15 mol% or less. Hereinafter, this value is referred to as "second additive element content". By setting the content of the second additive element to 1 mol% or more, the diffusion of the first additive element contained in the carrier into the noble metal-containing catalyst can be prevented even more effectively. When two or more kinds of elements are used in combination as the second additive element, the number of moles of M2 mentioned above means the total number of moles of all the second additive elements used. The content of the second additive element can be measured by the same method as the content of the first additive element.
以上のとおり、本発明の電極触媒は、担体と貴金属含有触媒とが被覆層によって隔てられている部位を有するので、このことに起因して、担体に含まれる第１添加元素が貴金属含有触媒へ拡散することが防止されている。 As described above, the electrode catalyst of the present invention has a portion where the carrier and the noble metal-containing catalyst are separated by a coating layer, and due to this, the first additive element contained in the carrier becomes a noble metal-containing catalyst. It is prevented from spreading.
次に、本発明の電極触媒の好適な製造方法について説明する。まず担体の製造方法を説明する。担体は公知の方法、例えば湿式合成法や、プラズマ合成法によって好適に製造することができる。湿式合成法においては、スズ源及び第１添加元素源を含む溶液から、スズ及び第１添加元素を含む共沈物を生成させ、次いで該共沈物を焼成することで、目的とする担体を得ることができる。 Next, a suitable manufacturing method of the electrode catalyst of the present invention will be described. First, a method for producing a carrier will be described. The carrier can be suitably produced by a known method, for example, a wet synthesis method or a plasma synthesis method. In the wet synthesis method, a co-precipitate containing tin and the first additive element is generated from a solution containing the tin source and the first additive element source, and then the co-precipitate is calcined to obtain a target carrier. Obtainable.
得られた担体の表面には被覆層を形成する。被覆層の形成は、例えば次の方法で行うことができる。すなわち、スズ源及び／又はチタン源となる水溶性化合物を水溶液に添加して溶解させた後、担体を添加し、撹拌することで分散液を得る。スズ源の化合物としては、例えば、塩化スズ、フッ化スズ、硫酸スズ、スズ酸ナトリウム、スズ酸カリウムなどが挙げられる。チタン源の化合物としては、例えば、塩化チタン、硫酸チタンなどが挙げられる。 A coating layer is formed on the surface of the obtained carrier. The coating layer can be formed by, for example, the following method. That is, a water-soluble compound serving as a tin source and / or a titanium source is added to an aqueous solution to dissolve it, and then a carrier is added and stirred to obtain a dispersion liquid. Examples of the tin source compound include tin chloride, tin fluoride, tin sulfate, sodium tinate, potassium tinate and the like. Examples of the titanium source compound include titanium chloride and titanium sulfate.
得られた分散液を所定温度に加熱、撹拌させた後、固形分を分離、乾燥して、スズ源及び／又はチタン源の化合物から酸化スズ又は酸化チタンの微粒子を担体の表面に生成させる。加熱温度はスズ源及び／又はチタン源の化合物の種類に応じて適切な温度が選択されるが、一般に５℃以上１００℃以下の加熱によって満足すべき大きさの微細な粒子が首尾よく得られる。加熱の雰囲気は、大気などの酸素含有雰囲気とすることができる。加熱時における担体表面に付着しているスズ源及び／又はチタン源の化合物の量に応じて、加熱後に形成される被覆層の担体表面の被覆の程度が決まる。加熱時における担体表面に付着しているスズ源及び／又はチタン源の化合物の量が相対的に少ない場合には、被覆層は、担体の表面を部分的に被覆する傾向が高くなる。一方、加熱時における担体表面に付着しているスズ源及び／又はチタン源の化合物の量が相対的に多い場合には、被覆層は、担体の表面を満遍に被覆する傾向が高くなる。 The obtained dispersion is heated to a predetermined temperature and stirred, and then the solid content is separated and dried to generate fine particles of tin oxide or titanium oxide from the compound of the tin source and / or the titanium source on the surface of the carrier. The heating temperature is selected according to the type of tin source and / or titanium source compound, but in general, heating at 5 ° C. or higher and 100 ° C. or lower successfully obtains fine particles of a satisfactory size. .. The heating atmosphere can be an oxygen-containing atmosphere such as the atmosphere. The degree of coating on the carrier surface of the coating layer formed after heating is determined by the amount of tin source and / or titanium source compounds adhering to the carrier surface during heating. When the amount of tin source and / or titanium source compounds adhering to the surface of the carrier during heating is relatively small, the coating layer tends to partially cover the surface of the carrier. On the other hand, when the amount of the tin source and / or titanium source compound adhering to the surface of the carrier during heating is relatively large, the coating layer tends to cover the surface of the carrier evenly.
酸化スズ及び／又は酸化チタンの微粒子中に第１添加元素や第２添加元素を含有させるためには、例えばスズ源及び／又はチタン源の化合物として、第１添加元素や第２添加元素を含む水溶性化合物を用いればよい。例えばスズ源の化合物として塩化スズやフッ化スズを用いることで、塩素及びフッ素含有の酸化スズの微粒子を得ることができる。また、チタン源の化合物として塩化チタンを用いることで、塩素含有の酸化チタンの微粒子を得ることができる。また、スズ源及び／又はチタン源と、第１添加元素や第２添加元素源とを含む溶液から、スズ源及び／又はチタン源と、第１添加元素や第２添加元素とを含む共沈物を担体表面に生成させることで、第１添加元素や第２添加元素含有の酸化スズ又は酸化チタンを得ることができる。 In order to contain the first additive element and the second additive element in the fine particles of tin oxide and / or titanium oxide, for example, the compound of the tin source and / or the titanium source includes the first additive element and the second additive element. A water-soluble compound may be used. For example, by using tin chloride or tin fluoride as the compound of the tin source, fine particles of tin oxide containing chlorine and fluorine can be obtained. Further, by using titanium chloride as the compound of the titanium source, fine particles of titanium oxide containing chlorine can be obtained. Further, a co-precipitation containing a tin source and / or a titanium source and a first additive element or a second additive element from a solution containing a tin source and / or a titanium source and a first additive element or a second additive element source. By forming a substance on the surface of the carrier, tin oxide or titanium oxide containing the first additive element or the second additive element can be obtained.
このようにして、担体の表面に被覆層を形成したら、次に貴金属含有触媒を担持させる。貴金属含有触媒の担持には、公知の方法、例えばエタノール法や、コロイド法を採用することができる。例えば貴金属含有触媒として白金を担持させる場合には、エタノール法においては、ジニトロジアミン白金硝酸溶液を純水で希釈して水溶液とし、これに担体を加えて混合、分散し、次にエタノールを加えて混合し、還流しながら加熱して数時間保持して白金微粒子を生成させればよい。還元温度は８０℃以上１００℃以下とすることが好ましく、還元時間は３〜６時間とすることが好ましい。コロイド法によって白金を担持させる場合には、白金を含有するコロイドを含む液に担体を分散し、該コロイドを該担体に担持する。詳細には、白金を含有する、コロイドの前駆体を含む液に、還元剤を添加して該前駆体を還元し、白金を含有するコロイドを生成させる。そして、生成した白金を含有するコロイドを含む液に担体を分散し、該コロイドを該担体に、白金を含有する微粒子として担持させる。エタノール法の詳細は、例えば特開平９−４７６５９号に記載されている。コロイド法の詳細は、例えばＷＯ２００９／０６０５８２に記載されている。 After the coating layer is formed on the surface of the carrier in this way, the noble metal-containing catalyst is then supported. A known method such as an ethanol method or a colloidal method can be adopted for supporting the noble metal-containing catalyst. For example, when platinum is supported as a noble metal-containing catalyst, in the ethanol method, a dinitrodiamine platinum nitric acid solution is diluted with pure water to form an aqueous solution, a carrier is added thereto, mixed and dispersed, and then ethanol is added. Platinum fine particles may be produced by mixing and heating while refluxing and holding for several hours. The reduction temperature is preferably 80 ° C. or higher and 100 ° C. or lower, and the reduction time is preferably 3 to 6 hours. When platinum is supported by the colloid method, the carrier is dispersed in a solution containing a colloid containing platinum, and the colloid is supported on the carrier. Specifically, a reducing agent is added to a solution containing a platinum-containing colloidal precursor to reduce the precursor to produce a platinum-containing colloid. Then, the carrier is dispersed in the produced liquid containing the platinum-containing colloid, and the colloid is supported on the carrier as platinum-containing fine particles. Details of the ethanol method are described in, for example, Japanese Patent Application Laid-Open No. 9-47659. Details of the colloidal method are described, for example, in WO2009 / 060582.
このようにして、担体の表面に貴金属含有触媒の微粒子を付着させたら、次に熱処理を行う。この熱処理は、貴金属含有触媒を活性化させる目的で行われる。熱処理は、還元性雰囲気下に行うことが好適である。還元性雰囲気としては、水素や一酸化炭素などが挙げられる。貴金属含有触媒の微粒子の触媒被毒などの問題がなく、入手が容易であるという点では水素が好ましい。水素を用いる場合には、これを濃度１００％で用いてもよく、あるいは不活性気体、例えば窒素、ヘリウム、アルゴンなどで好ましくは０．１〜５０体積％、更に好ましくは１〜１０体積％に希釈して用いてもよい。熱処理の温度は、貴金属含有触媒の活性化を首尾よく行う観点から、８０℃以上２５０℃以下に設定することが好ましく、８０℃以上２００℃以下に設定することが更に好ましい。 After the fine particles of the noble metal-containing catalyst are attached to the surface of the carrier in this way, heat treatment is then performed. This heat treatment is performed for the purpose of activating the noble metal-containing catalyst. The heat treatment is preferably performed in a reducing atmosphere. Examples of the reducing atmosphere include hydrogen and carbon monoxide. Hydrogen is preferable in that it does not cause problems such as catalyst poisoning of fine particles of a noble metal-containing catalyst and is easily available. When hydrogen is used, it may be used at a concentration of 100%, or an inert gas such as nitrogen, helium, argon or the like is preferably used in an amount of 0.1 to 50% by volume, more preferably 1 to 10% by volume. It may be diluted and used. The temperature of the heat treatment is preferably set to 80 ° C. or higher and 250 ° C. or lower, and more preferably 80 ° C. or higher and 200 ° C. or lower, from the viewpoint of successfully activating the noble metal-containing catalyst.
以上のようにして、目的とする電極触媒が得られる。この電極触媒は、固体高分子電解質膜の一方の面に配置された酸素極及び他方の面に配置された燃料極を有する膜電極接合体における酸素極又は燃料極の少なくとも一方に含有させて用いることができる。電極触媒は、好適には酸素極及び燃料極の双方に含有させることができる。 As described above, the desired electrode catalyst can be obtained. This electrode catalyst is used by being contained in at least one of an oxygen electrode or a fuel electrode in a membrane electrode assembly having an oxygen electrode arranged on one surface of a solid polymer electrolyte membrane and a fuel electrode arranged on the other surface. be able to. The electrode catalyst can preferably be contained in both the oxygen electrode and the fuel electrode.
酸素極及び燃料極は、本発明の電極触媒を含む触媒層と、ガス拡散層とを含んでいることが好ましい。電極反応を円滑に進行させるために、電極触媒は固体高分子電解質膜に接していることが好ましい。ガス拡散層は、集電機能を有する支持集電体として機能するものである。更に、電極触媒にガスを十分に供給する機能を有するものである。ガス拡散層としては、この種の技術分野において従来用いられてきたものと同様のものを用いることができる。例えば多孔質材料であるカーボンペーパー、カーボンクロスを用いることができる。具体的には、例えば表面をポリ四フッ化エチレンでコーティングした炭素繊維と、当該コーティングがなされていない炭素繊維とを所定の割合とした糸で織成したカーボンクロスにより形成することができる。 The oxygen electrode and the fuel electrode preferably include a catalyst layer containing the electrode catalyst of the present invention and a gas diffusion layer. In order for the electrode reaction to proceed smoothly, it is preferable that the electrode catalyst is in contact with the solid polymer electrolyte membrane. The gas diffusion layer functions as a support current collector having a current collector function. Further, it has a function of sufficiently supplying gas to the electrode catalyst. As the gas diffusion layer, a gas diffusion layer similar to that conventionally used in this kind of technical field can be used. For example, carbon paper and carbon cloth, which are porous materials, can be used. Specifically, for example, it can be formed by a carbon cloth woven from a carbon fiber whose surface is coated with polytetrafluoroethylene and a carbon fiber whose surface is not coated with a yarn having a predetermined ratio.
固体高分子電解質としては、この種の技術分野において従来用いられてきたものと同様のものを用いることができる。例えばパーフルオロスルホン酸ポリマー系のプロトン伝導体膜、リン酸などの無機酸を炭化水素系高分子化合物にドープさせたもの、一部がプロトン伝導体の官能基で置換された有機／無機ハイブリッドポリマー、高分子マトリックスにリン酸溶液や硫酸溶液を含浸させたプロトン伝導体などが挙げられる。 As the solid polymer electrolyte, the same ones conventionally used in this kind of technical field can be used. For example, a perfluorosulfonic acid polymer-based proton conductor film, a hydrocarbon-based polymer compound doped with an inorganic acid such as phosphoric acid, or an organic / inorganic hybrid polymer in which a part is substituted with a functional group of the proton conductor. , Proton conductor in which a polymer matrix is impregnated with a phosphoric acid solution or a sulfuric acid solution.
前記膜電極接合体は、その各面にセパレータが配されて固体高分子形燃料電池となされる。セパレータとしては、例えばガス拡散層との対向面に、一方向に延びる複数個の凸部（リブ）が所定間隔をおいて形成されているものを用いることができる。隣り合う凸部間は、断面が矩形の溝部となっている。この溝部は、燃料ガス及び空気などの酸化剤ガスの供給排出用流路として用いられる。燃料ガス及び酸化剤ガスは、燃料ガス供給手段及び酸化剤ガス供給手段からそれぞれ供給される。膜電極接合体の各面に配されるそれぞれのセパレータは、それに形成されている溝部が互いに直交するように配置されることが好ましい。以上の構成が燃料電池の最小単位を構成しており、この構成を数十個〜数百個並設してなるセルスタックから燃料電池を構成することができる。 The membrane electrode assembly is made into a polymer electrolyte fuel cell in which separators are arranged on each surface thereof. As the separator, for example, a separator having a plurality of protrusions (ribs) extending in one direction formed at predetermined intervals on a surface facing the gas diffusion layer can be used. A groove having a rectangular cross section is formed between adjacent convex portions. This groove is used as a flow path for supplying and discharging an oxidizing agent gas such as fuel gas and air. The fuel gas and the oxidant gas are supplied from the fuel gas supply means and the oxidant gas supply means, respectively. Each separator arranged on each surface of the membrane electrode assembly is preferably arranged so that the grooves formed therein are orthogonal to each other. The above configuration constitutes the minimum unit of the fuel cell, and the fuel cell can be configured from a cell stack in which dozens to hundreds of these configurations are arranged side by side.
以上、本発明をその好ましい実施形態に基づき説明したが、本発明は前記実施形態に制限されない。例えば前記実施形態においては、本発明の電極触媒を、固体高分子電解質形燃料電池の電極触媒として用いた例を中心に説明したが、本発明の電極触媒を、固体高分子電解質形燃料電池以外の燃料電池、例えばアルカリ形燃料電池、リン酸形燃料電池、直接メタノール形燃料電池などの各種燃料電池における電極触媒として用いることができる。 Although the present invention has been described above based on the preferred embodiment, the present invention is not limited to the above embodiment. For example, in the above-described embodiment, the example in which the electrode catalyst of the present invention is used as the electrode catalyst of the solid polymer electrolyte fuel cell has been mainly described, but the electrode catalyst of the present invention is other than the solid polymer electrolyte fuel cell. It can be used as an electrode catalyst in various fuel cells such as an alkaline fuel cell, a phosphoric acid fuel cell, and a direct methanol fuel cell.
以下、実施例により本発明を更に詳細に説明する。しかしながら本発明の範囲は、かかる実施例に制限されない。特に断らない限り、「％」は「質量％」を意味する。 Hereinafter, the present invention will be described in more detail with reference to Examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "mass%".
〔実施例１〕
（１）担体の製造
アンチモン及びタンタルを含有する酸化スズ粒子を湿式合成法によって製造した。５０ｍＬのエタノール中に、１．５６０ｇのＳｂＣｌ３及び１．２２５ｇのＴａＣｌ５を添加して、これを溶解させたアンチモン及びタンタル含有溶液を得た。これとは別に、８８．４９３ｇのＮａ２ＳｎＯ３・３Ｈ２Ｏを純水に溶解させて、１０００ｍＬのスズ含有水溶液を得た。アンチモン及びタンタル含有溶液に０．５ｍｏｌ／Ｌの硝酸水溶液を１２９４ｍＬ添加した後、この溶液にスズ含有水溶液を１０００ｍＬ添加した。この添加によって液中に沈殿物が生成した。液を２５℃で１時間静置して沈殿物の熟成を行った後、濾過によって沈殿物を回収し、更にリパルプ洗浄した。次いで１２０℃で１５時間乾燥させて固形物を得た。この固形物を乳鉢で粉砕後、大気雰囲気下、７３０℃で５時間の焼成を行った。焼成後、微粒化を目的に、更にボールミルで１６時間の解砕を行い、１μｍのメンブレンフィルターで濾過した後、乾燥させて目的とするアンチモン及びタンタル含有酸化スズ粒子を得た。ＩＣＰ質量分析装置によって測定された第１添加元素（アンチモン及びタンタル）含有率は、３．０ｍｏｌ％（Ｓｂ：２．０ｍｏｌ％、Ｔａ：１．０ｍｏｌ％）であった。また担体の平均粒子径は２０ｎｍであった。
（２）被覆層の形成
次に、１．５ｇのフッ化スズを２００ｇのイオン交換水に溶解した後、（１）で得られた１．５ｇの担体を添加して、大気雰囲気下で８０℃で１時間の加熱、撹拌を行い、懸濁液を得た。次いで懸濁液を固液分離し、大気雰囲気下で固形分を１２０℃で乾燥した。このようにして、担体の表面に、フッ素含有酸化スズの微粒子集合体からなる被覆層を形成した。電子顕微鏡（ＴＥＭ）観察の結果、被覆層は、担体の表面を部分的に被覆していることが確認された。被覆層の厚みは５ｎｍであった。フッ素含有酸化スズの微粒子の平均粒子径は、３ｎｍであった。フッ素含有酸化スズにおける第２添加元素（フッ素）含有率は１２ｍｏｌ％であった。
[Example 1]
(1) Production of carrier Tin oxide particles containing antimony and tantalum were produced by a wet synthesis method. 1.560 g of SbCl 3 and 1.225 g of TaCl 5 were added to 50 mL of ethanol to obtain an antimony and tantalum-containing solution in which they were dissolved. Separately, Na 2 SnO 3 · 3H 2 O in 88.493g dissolved in pure water to give a tin-containing aqueous solution of 1000 mL. After adding 1294 mL of a 0.5 mol / L nitric acid aqueous solution to the antimony and tantalum-containing solution, 1000 mL of the tin-containing aqueous solution was added to this solution. This addition produced a precipitate in the liquid. The liquid was allowed to stand at 25 ° C. for 1 hour to mature the precipitate, and then the precipitate was recovered by filtration and further washed with repulp. Then, it was dried at 120 ° C. for 15 hours to obtain a solid substance. After crushing this solid matter in a mortar, it was calcined at 730 ° C. for 5 hours in an air atmosphere. After firing, the particles were further crushed with a ball mill for 16 hours for the purpose of atomization, filtered through a 1 μm membrane filter, and then dried to obtain the desired antimony and tantalum-containing tin oxide particles. The content of the first additive element (antimony and tantalum) measured by the ICP mass spectrometer was 3.0 mol% (Sb: 2.0 mol%, Ta: 1.0 mol%). The average particle size of the carrier was 20 nm.
(2) Formation of coating layer Next, after dissolving 1.5 g of tin fluoride in 200 g of ion-exchanged water, 1.5 g of the carrier obtained in (1) was added, and 80 in an air atmosphere. The mixture was heated and stirred at ° C. for 1 hour to obtain a suspension. The suspension was then solid-liquid separated and the solids were dried at 120 ° C. in the atmosphere. In this way, a coating layer made of a fine particle aggregate of fluorine-containing tin oxide was formed on the surface of the carrier. As a result of electron microscope (TEM) observation, it was confirmed that the coating layer partially covered the surface of the carrier. The thickness of the coating layer was 5 nm. The average particle size of the fine particles of fluorine-containing tin oxide was 3 nm. The content of the second additive element (fluorine) in the fluorine-containing tin oxide was 12 mol%.
（３）貴金属含有触媒の担持
（２）複数回実施して得られた３．０ｇの被覆層を形成した担体を用いて、公知の方法により白金ニッケル合金を担持させた電極触媒を得た。貴金属含有触媒中の白金の担持量は、電極触媒の質量に対して１２．７％であった。
(3) Supporting a Noble Metal-Containing Catalyst (2) Using a carrier on which a 3.0 g coating layer was formed obtained by carrying out a plurality of times, an electrode catalyst in which a platinum-nickel alloy was supported was obtained by a known method. The amount of platinum supported in the noble metal-containing catalyst was 12.7% with respect to the mass of the electrode catalyst.
〔実施例２〕
２．６ｇのフッ化スズを２００ｇのイオン交換水に溶解した液と、０．１０６ｇのタングステン酸を５０％フッ化水素酸溶液で溶解させた後２１．３ｍＬに希釈した液とを混合して、タングステンとスズの混合溶液を作成した。上記混合溶液に実施例１で得られた担体１０ｇを加えて、８０℃で１時間の加熱、撹拌を行い、懸濁液を得た。次いで懸濁液を固液分離し、大気雰囲気下にて１２０℃で乾燥した。電子顕微鏡観察の結果、担体の表面を全体的に連続に被覆していることが確認された。被覆層の厚みは２ｎｍであった。フッ素タングステン含有酸化スズの微粒子の平均粒子径は１ｎｍであった。フッ素タングステン含有酸化スズにおける第２添加元素（フッ素及びタングステン）含有率は０．６ｍｏｌ％であった。
得られた被覆層を持つ担体に実施例１と同様の方法で貴金属含有触媒を担持し、電極触媒を得た。貴金属含有触媒中の白金の担持量は、電極触媒の質量に対して１３．２％であった。
[Example 2]
A solution prepared by dissolving 2.6 g of tin fluoride in 200 g of ion-exchanged water and a solution prepared by dissolving 0.106 g of tungstic acid in a 50% hydrofluoric acid solution and then diluting it to 21.3 mL are mixed. , A mixed solution of tungsten and tin was prepared. 10 g of the carrier obtained in Example 1 was added to the above mixed solution, and the mixture was heated and stirred at 80 ° C. for 1 hour to obtain a suspension. The suspension was then solid-liquid separated and dried at 120 ° C. in an air atmosphere. As a result of electron microscope observation, it was confirmed that the surface of the carrier was continuously covered as a whole. The thickness of the coating layer was 2 nm. The average particle size of the fine particles of tin oxide containing tungsten fluoride was 1 nm. The content of the second additive element (fluorine and tungsten) in the fluorine-tungsten-containing tin oxide was 0.6 mol%.
A noble metal-containing catalyst was supported on the obtained carrier having a coating layer in the same manner as in Example 1 to obtain an electrode catalyst. The amount of platinum supported in the noble metal-containing catalyst was 13.2% with respect to the mass of the electrode catalyst.
〔比較例１〕
実施例１において、被覆層を形成しなかった以外は、実施例１と同様にして電極触媒を得た。貴金属含有触媒中の白金の担持量は、電極触媒の質量に対して１２．１％であった。
[Comparative Example 1]
An electrode catalyst was obtained in the same manner as in Example 1 except that the coating layer was not formed in Example 1. The amount of platinum supported in the noble metal-containing catalyst was 12.1% with respect to the mass of the electrode catalyst.
次に、実施例１で得られた電極触媒を用い、以下の手順で燃料電池を製造した。
（１）カソード用の電極触媒層の形成
実施例１で得られた電極触媒０．８０ｇを容器に入れ、更に純水、エタノール及び２−プロパノールを３５：４５：２０の質量比（混合液として０．８０ｇ）で順に加えた。このようにして得られたインクを、超音波で３分間にわたり分散した。次いで、直径１０ｍｍのイットリウム安定化ジルコニア製ボールを容器内に入れ、遊星ボールミル（シンキーＡＲＥ３１０）で８００ｒｐｍで２０分間撹拌した。更にインクに５％ナフィオン（登録商標）（２７４７０４−１００ＭＬ、Ａｌｄｒｉｃｈ社製）を加え、超音波分散と遊星ボールミルにより前記と同様な撹拌を行った。ナフィオンの添加量は、ナフィオン／被覆層が形成された担体の質量比が７．４％となるような量とした。このようにして得られたインクを、ポリ四フッ化エチレンのシート上にバーコーターを用いて塗工し、塗膜を６０℃で乾燥させた。
Next, using the electrode catalyst obtained in Example 1, a fuel cell was manufactured by the following procedure.
(1) Formation of Electrode Catalyst Layer for Cathode 0.80 g of the electrode catalyst obtained in Example 1 is placed in a container, and pure water, ethanol and 2-propanol are further added in a mass ratio of 35:45:20 (as a mixed solution). 0.80 g) was added in order. The ink thus obtained was ultrasonically dispersed over 3 minutes. Next, yttria-stabilized zirconia balls having a diameter of 10 mm were placed in a container, and the mixture was stirred with a planetary ball mill (Sinky ARE310) at 800 rpm for 20 minutes. Further, 5% Nafion (registered trademark) (274704-100ML, manufactured by Aldrich) was added to the ink, and the same stirring as described above was carried out by ultrasonic dispersion and a planetary ball mill. The amount of Nafion added was such that the mass ratio of the carrier on which the Nafion / coating layer was formed was 7.4%. The ink thus obtained was applied onto a sheet of polytetrafluoroethylene using a bar coater, and the coating film was dried at 60 ° C.
（２）アノード用の電極触媒層の形成
田中貴金属工業社製の白金担持カーボンブラック（ＴＥＣ１０Ｅ５０Ｅ）１．００ｇを容器に入れ、更に純水、エタノール及び２−プロパノールを４５：３５：２０の質量比（混合液として１２．８ｇ）で順に加えた。このようにして得られたインクを、超音波で３分間にわたり分散した。次いで、直径１０ｍｍのイットリウム安定化ジルコニア製ボールを容器内に入れ、遊星ボールミル（シンキーＡＲＥ３１０）によって８００ｒｐｍで２０分間撹拌した。更にインクに５％ナフィオン（登録商標）（２７４７０４−１００ＭＬ、Ａｌｄｒｉｃｈ社製）を加え、超音波分散と遊星ボールミルにより前記と同様な撹拌を引き続き行った。ナフィオンの添加量は、ナフィオン／カーボンブラックの質量比が０．７０となるような量とした。このようにして得られたインクを、ポリ四フッ化エチレンのシート上にバーコーターを用いて塗工し、塗膜を６０℃で乾燥させた。
(2) Formation of electrode catalyst layer for anode Put 1.00 g of platinum-supported carbon black (TEC10E50E) manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. in a container, and further add pure water, ethanol and 2-propanol in a mass ratio of 45:35:20. (12.8 g as a mixed solution) was added in order. The ink thus obtained was ultrasonically dispersed over 3 minutes. Next, yttria-stabilized zirconia balls having a diameter of 10 mm were placed in a container and stirred at 800 rpm for 20 minutes by a planetary ball mill (Sinky ARE310). Further, 5% Nafion (registered trademark) (274704-100ML, manufactured by Aldrich) was added to the ink, and the same stirring as described above was continued by ultrasonic dispersion and a planetary ball mill. The amount of Nafion added was such that the mass ratio of Nafion / carbon black was 0.70. The ink thus obtained was applied onto a sheet of polytetrafluoroethylene using a bar coater, and the coating film was dried at 60 ° C.
（３）ＣＣＭ（膜電極接合体）の製造
得られたカソード用及びアノード用電極触媒層付ポリ四フッ化エチレンのシートを５４ｍｍ四方の正方形状に切り出し、ナフィオン（登録商標）（ＮＲＥ−２１２、Ｄｕ−Ｐｏｎｔ社製）の電解質膜と重ね合わせ、１４０℃、２５ｋｇｆ／ｃｍ２の条件下に２分間大気中で熱プレスし、転写を行った。このようにして、ナフィオンからなる固体高分子電解質膜の各面にカソード及びアノード触媒層を形成した。電極触媒層における白金の量は、カソード触媒層では０．１６３ｍｇ−Ｐｔ／ｃｍ２でアノード触媒層では０．０６６ｍｇ−Ｐｔ／ｃｍ２であった。
(3) Manufacture of CCM (Membrane Electrode Assembly) The obtained sheet of polytetrafluoroethylene with electrode catalyst layer for cathode and anode was cut into a square shape of 54 mm square, and Nafion (registered trademark) (NRE-212, It was superposed on an electrolyte membrane manufactured by Du-Pont) and heat-pressed in the air for 2 minutes under the conditions of 140 ° C. and 25 kgf / cm 2, and transfer was performed. In this way, a cathode and an anode catalyst layer were formed on each surface of the solid polymer electrolyte membrane made of Nafion. The amount of the platinum in the electrode catalyst layer, the cathode catalyst layer in the anode catalyst layer at 0.163mg -Pt / cm 2 was 0.066mg -Pt / cm 2.
（４）燃料電池の組み立て
前記（３）で得られたＣＣＭ及びＪＡＲＩ標準セルを用いて燃料電池を組み立てた。ガス拡散層としてＳＩＧＲＡＣＥＴ（登録商標）２５ＢＣＨ（ＳＧＬ社製）を用いた。また、ガスケットとして、Ｓi／ＰＥＮ／Ｓｉ（１８０μｍ）を用いた。
(4) Assembly of fuel cell A fuel cell was assembled using the CCM and JARI standard cells obtained in (3) above. SIGRACET® 25BCH (manufactured by SGL) was used as the gas diffusion layer. Further, Si / PEN / Si (180 μm) was used as the gasket.
実施例２及び比較例１で得られた電極触媒についても、実施例１と同様の方法により、燃料電池を組み立てた。 For the electrode catalysts obtained in Example 2 and Comparative Example 1, a fuel cell was assembled by the same method as in Example 1.
〔質量比活性〕
実施例１と実施例２及び比較例１で得られた電極触媒を用いて作製した燃料電池について、膜電極接合体（ＭＥＡ）の発電特性を評価した。燃料電池のアノード及びカソードに、８０℃に加熱し、１００％ＲＨに加湿した窒素を流通させて安定化した後、加湿した水素をアノードに供給するとともに、加湿した酸素をカソードに供給した。この条件下で発電特性（電流−電圧特性）を測定した。そして測定結果から０．８５ＶにおけるＩＲフリーでの質量比活性、すなわち燃料電池セルの内部抵抗による電圧低下を差し引くことで補正した質量比活性を算出した。その結果を表１に示す。
[Mass ratio activity]
The power generation characteristics of the membrane electrode assembly (MEA) were evaluated for the fuel cells produced using the electrode catalysts obtained in Example 1, Example 2, and Comparative Example 1. The anode and cathode of the fuel cell were heated to 80 ° C., and nitrogen humidified to 100% RH was circulated to stabilize the anode, and then humidified hydrogen was supplied to the anode and humidified oxygen was supplied to the cathode. The power generation characteristics (current-voltage characteristics) were measured under these conditions. Then, the mass ratio activity at 0.85 V in IR-free, that is, the mass ratio activity corrected by subtracting the voltage drop due to the internal resistance of the fuel cell was calculated from the measurement result. The results are shown in Table 1.
表１に示す結果から明らかなとおり、被覆層が存在している実施例の電極触媒を用いると、該被覆層を設けていない比較例の電極触媒に比べて、触媒活性が高くなることが判る。また、実施例の電極触媒は発電特性測定後に貴金属含有触媒中にアンチモン及びタンタルの存在が確認できなかったのに対し、比較例の電極触媒は発電特性測定後に貴金属含有触媒中にアンチモン及びタンタルが存在していることが確認された。 As is clear from the results shown in Table 1, it can be seen that when the electrode catalyst of the example in which the coating layer is present is used, the catalytic activity is higher than that of the electrode catalyst of the comparative example in which the coating layer is not provided. .. Further, in the electrode catalyst of the example, the presence of antimony and tantalum could not be confirmed in the noble metal-containing catalyst after the power generation characteristic measurement, whereas in the electrode catalyst of the comparative example, antimony and tantalum were contained in the noble metal-containing catalyst after the power generation characteristic measurement. It was confirmed that it existed.
Claims (10)
酸化スズ及び酸化チタンから選択される少なくとも１種の粒子が多数集合してなり、前記担体の表面の少なくとも一部を被覆する被覆層と、
前記被覆層に担持された貴金属含有触媒と、
を有し、
前記被覆層における前記第１添加元素の含有率が、前記担体における前記第１添加元素の含有率より低い電極触媒。 Electrically conductive, it viewed including the first additional element is a predetermined element, and carrier particulate tin oxide,
A coating layer in which a large number of particles of at least one selected from tin oxide and titanium oxide are aggregated to cover at least a part of the surface of the carrier.
The noble metal-containing catalyst supported on the coating layer and
Have,
An electrode catalyst in which the content of the first additive element in the coating layer is lower than the content of the first additive element in the carrier.
A polymer electrolyte fuel cell having the membrane electrode assembly according to claim 9.
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