JP4087651B2 - Electrocatalyst for solid polymer electrolyte fuel cell - Google Patents
Electrocatalyst for solid polymer electrolyte fuel cell Download PDFInfo
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- JP4087651B2 JP4087651B2 JP2002206216A JP2002206216A JP4087651B2 JP 4087651 B2 JP4087651 B2 JP 4087651B2 JP 2002206216 A JP2002206216 A JP 2002206216A JP 2002206216 A JP2002206216 A JP 2002206216A JP 4087651 B2 JP4087651 B2 JP 4087651B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description
【０００１】
【発明の属する技術分野】
本発明は、固体高分子電解質型燃料電池に用いられる電極触媒に関する。
【０００２】
【従来の技術】
固体高分子電解質型燃料電池は、低温で高い電流密度が取り出せることから、ポータブル電源、電気自動車の駆動電源、また、コージェネレーションの電源として開発が進められている。
【０００３】
固体高分子電解質型燃料電池の基本構造は、燃料極（アノード）、空気極（カソード）及び両電極間に配された固体高分子電解質であるイオン交換膜から構成されている。通常、燃料極と空気極の両電極は貴金属が担持された触媒と高分子電解質の混合体から構成される。
【０００４】
固体高分子電解質型燃料電池において、水素を燃料とした場合、燃料極では、水素ガスが電極中の細孔を通過して電解質と電極の界面に達し、触媒表面で電子を放出して水素イオンとなる。水素イオンは電極中の電解質および両電極間の固体高分子電解質膜を通じ空気極に達する。放出された電子は電極中の触媒担体を通って外部回路に流れ、外部回路から空気極に達する。一方、酸素を酸化剤とした空気極では、酸素が電極中の細孔を通過して触媒に達し、燃料極から到達した水素イオン、および外部回路により移動した電子と反応して水を生成する。
【０００５】
一般的に燃料電池の出力を向上させるには両電極反応を促進させることが必要である。その為には、電極触媒の活性物質である白金や白金合金が両電極反応に対して高活性を有し、さらに、電極内において白金や白金合金が効率的かつ有効に両電極反応に利用されることが必要である。即ち、触媒には高活性な貴金属、特に白金または白金合金をカーボンブラック上に担持した触媒が用いられ、導電性電解質としてはイオン伝導性の高い高分子電解質であるパーフルオロカーボンスルホン酸等が使用され、両者が十分に接触することが求められる。
【０００６】
電極の製造方法としてはこれまでに種々の方法が提案されている。
例えば、「電気化学」５３、Ｎｏ．１０、ｐ．８１２〜８１７（１９８５）には、固体高分子電解質としてパーフルオロカーボンスルホン酸樹脂であるＮａｆｉｏｎ１１７溶液（商品名、Ａｌｄｒｉｃｈ Ｃｈｅｍｉｃａｌ社製、Ｈ型、脂肪族アルコールと水の混合溶媒中５％の溶液）を用い、触媒粉末と混合する方法が報告されている。
【０００７】
特開平４−１６２３６５号公報には、白金触媒担持のカーボンブラックと触媒無担持のカーボンブラックとを、固体高分子電解質であるＮａｆｉｏｎのブタノール溶液で浸漬処理し、ついでポリテトラフルオロエチレンのディスパージョンで処理することが記載されている。
【０００８】
特開平８−４１８１５３号公報においては、▲１▼まず触媒粒子として、例えば白金ブラックや白金を担持させたカーボンブラック粒子を製造し、▲２▼この粒子と固体高分子電解質溶液とを、さらに溶媒を加えて均一にすることにより懸濁液を調製し、▲３▼次いで、必要に応じて結合剤としてのポリテトラフルオロエチレン等を混合する方法が記載されている。この方法においては、▲２▼の混合による懸濁液調製工程と、その懸濁液から含まれている溶媒を除去する工程とが特に重要であることが説明されている。
【０００９】
特開平８−２２７７１６号公報には、電極触媒と固体高分子電解質の混合工程において遊星ボールミルにて物理的に混合する方法を開示されている。
【００１０】
【発明が解決しようとする課題】
しかし上記いずれの方法によって得られる電極触媒も、白金を担持させたカーボンブラックの表面はグラファイトの構造と官能基をあわせもつために、親水性部と疎水性部を共有する結果、凝集粒子を生成し易く、高分散を達成することができない。また、Ｎａｆｉｏｎ１１７溶液のようなパーフルオロスルホン酸樹脂が凝集を起こし易かったり、電極触媒とこれらの樹脂との接触が不十分であるという問題を有している。
【００１１】
本発明は上記従来の課題を解決するもので、触媒の活性金属がカーボンブラック上に高分散しており、しかも固体高分子電解質、特にパーフルオロカーボンスルホン酸樹脂と親和性の高い電極触媒を提供するものである。
【００１２】
【課題を解決するための手段】
上記課題を解決するため、本発明者らは、触媒の担体として用いられるカーボンブラックを酸処理することにより、その表面構造を改質し、パーフルオロカーボンスルホン酸樹脂の凝集抑制と触媒表面への高分散状態での付着を実現し得ることを見出した。
【００１３】
すなわち、本発明は、カーボンブラックと、該カーボンブラックに担持された白金または白金合金とからなり、ＪＩＳ Ｋ１４７４に記載の方法により測定されたｐＨが２〜７であることを特徴とする、固体高分子型燃料電池用電極触媒を提供する。
【００１４】
【発明の実施の形態】
本発明の電極触媒には担体としてカーボンブラックが使用される。
【００１５】
本発明の電極触媒には活性金属として白金または白金合金が使用される。白金合金としては、例えば白金−ルテニウム合金、白金−モリブデン合金等があがられ、中でも好ましいのは白金−ルテニウム合金である。白金または白金合金の好ましい担持量は、５〜７０質量％、さらに好ましくは１０〜６０質量％である。
【００１６】
本発明の電極触媒は、ＪＩＳ Ｋ１４７４に記載の方法により測定されたｐＨが２〜７である点に特徴を有する。ｐＨは、好ましくはｐＨ３〜６の範囲であり、より好ましくは３．５〜５．５の範囲である。ｐＨが低すぎると白金や白金合金が溶出しやすくなる。
【００１７】
触媒のｐＨを調整するのに使用される酸としては、無機酸、有機酸のいずれも使用することができ、無機酸としては、例えば塩酸、硝酸、硫酸などが挙げられ、有機酸としては、例えばギ酸、酢酸、しゅう酸、マロン酸等の脂肪族カルボン酸が挙げられる。なかでも好ましいものは脂肪族有機酸、特にカルボン酸である。
【００１８】
本発明の電極触媒の製造方法としては、担体であるカーボンブラックを酸で処理した後に白金または白金合金を担持させる方法でも、カーボンブラックに白金または白金合金を担持させた後に酸で処理する方法でもよい。
このような酸処理により、カーボンブラックの表面状態が疎水性から親水性に変換され、さらに酸との親和状態も良好になる結果、パーフルオロカーボンスルホン酸の良好な接触が得られる。
【００１９】
【実施例】
以下に実施例を挙げて本発明を具体的に説明する。
なお、触媒のｐＨはＪＩＳ Ｋ１４７４ ５．１０の活性炭試験方法のｐＨ値測定方法に従い測定した。具体的には、電極触媒の乾燥カーボン質量で１．０ｇを秤量し、水１００ｍｌを加えて静かに５分間の沸騰後、室温まで冷却後水を加えて１００ｍｌにメスアップし、よく攪拌しながら懸濁液のｐＨを測定した。
【００２０】
〔実施例１〕
市販の電極触媒ＳＡ５０ＢＫ（エヌ・イー ケムキャット製 ５０％Ｐｔカーボンブラック ＢＥＴ比表面積 ３４７ｍ２／ｇ、Ｘ線回折によるＰｔ粒子径 ２．５ｎｍ、ｐＨ ６．５）を１０．０ｇを秤量し１．５Ｌの水に懸濁させスラリーとした。次に濃度１モル／Ｌの硝酸溶液を調製し、これを１０ｍｌスラリーに加えた後、スラリー温度を上昇させ、沸騰状態にて３時間還流をおこなった。次に、この触媒を濾別、洗浄、乾燥、粉砕した。このように処理した後の触媒粉末を測定したところ、Ｐｔ分析値５０％、ＢＥＴ比表面積３３８ｍ２／ｇ、Ｐｔの結晶子径は２．６ｎｍ、ｐＨ ４．０であった。
【００２１】
〔実施例２〕
実施例１において加える酸を１モル／Ｌの硝酸溶液に変えて蟻酸（和光純薬製純度99%）１０ｍｌに変更してＰｔ５０％の電極触媒の粉末を調製した。該粉末は、ＢＥＴ比表面積３４５ｍ２／ｇ、Ｐｔの結晶子径は２．５ｎｍ、ｐＨ ５．８であった。
【００２２】
〔実施例３〕
実施例１において加える酸を硝酸に変えて酢酸（和光純薬製 特級 純度９９．７％以上）１０ｍｌに変更してＰｔ５０％の電極触媒の粉末を調製した。 該粉末はＢＥＴ比表面積３４６ｍ２／ｇ、Ｐｔの結晶子径は２．５ｎｍ、ｐＨ ４．８であった。
【００２３】
〔実施例４〕 実施例１において加える酸を硝酸に変えてしゅう酸２水和物（和光純薬製 特級）１０ｇに変更してＰｔ５０％の電極触媒の粉末を調製した。該粉末はＢＥＴ比表面積３４５ｍ２／ｇ、Ｐｔの結晶子径は２．６ｎｍ、ｐＨ ５．０であった。
【００２４】
〔実施例５〕
市販の電極触媒ＳＡ２７−１３ＲＣ（エヌ・イー ケムキャット製 ２７％Ｐｔ１３％Ｒｕカーボンブラック ＢＥＴ比表面積 １３０ｍ２／ｇ、Ｘ線回折によるＰｔ粒子径 ６．２ｎｍ、ｐＨ ７．５）を１０．０ｇを秤量し１．５Ｌの水に懸濁させスラリーとした。次に１モル／Ｌの硝酸溶液を調製し、１０ｍｌを加えた後、スラリー温度を上昇させ、沸騰状態にて３時間還流をおこなった。この触媒を濾別、洗浄、乾燥、粉砕した。該粉末は、Ｐｔ分析値２７％、Ｒｕ１３％、ＢＥＴ比表面積１３０ｍ２／ｇ、Ｐｔの結晶子径は６．２ｎｍ、ｐＨ ４．０であった。
【００２５】
〔比較例１〕
実施例１で使用した市販の電極触媒ＳＡ５０ＢＫ（エヌ・イー ケムキャット製 ５０％Ｐｔカーボンブラック ＢＥＴ比表面積 ３４７ｍ２／ｇ、Ｘ線回折によるＰｔ粒子径 ２．５ｎｍ、ｐＨ ６．５）を使用した。
【００２６】
〔比較例２〕
実施例１で添加した硝酸とその添加量を濃硝酸（和光純薬製 特級）５０ｍｌとした。該粉末は、Ｐｔ分析値４７．３％、ＢＥＴ比表面積３３５ｍ２／ｇ、Ｐｔの結晶子径 ２．６ｎｍ、ｐＨ ２．４であった。
【００２７】
〔比較例３〕
実施例５で使用した市販の電極触媒ＳＡ２７−１３ＲＣ（エヌ・イー ケムキャット製 ２７％Ｐｔ１３％Ｒｕカーボンブラック ＢＥＴ比表面積 １３０ｍ２／ｇ、Ｘ線回折によるＰｔ粒子径 ６．２ｎｍ、ｐＨ ７．５）を使用した。
【００２８】
〔電池性能評価の為の電極調製〕
ＰＴＦＥ(ポリテトラフルオロエチレン、三井フルオロケミカル製：テフロン３０Ｊ)で撥水処理した５０×５０ｍｍ、厚さ１２０μｍの多孔質カーボンペーパー(東レ製：ＴＧＰ−Ｈ−１２０)を電極基質として準備した。次に、実施例１〜５および比較例１〜３で得られた白金担持カーボン粉末および白金−ルテニウム担持カーボン粉末触媒それぞれと水、５重量％ナフィオン溶液(アルドリッチ社製)を所定量混ぜ合わせペーストとした。このようにペースト状にしたものを上記電極基質の片面全面に均一に塗布してから乾燥し、触媒層を形成した。こうして、各実施例及び各比較例の白金担持カーボン粉末又は白金−ルテニウム担持カーボン粉末を用いた電極を作成した。
【００２９】
次に、実施例1の白金担持カーボン粉末を用いて得た電極二枚を、パーフルオロスルフォン酸電解質膜(デュポン社製、商品名：ナフィオン１１２)の両面に、それぞれの電極の触媒層側が電解質に接するように重ね合わせ、ホットプレス機で熱圧着して電解質膜−電極接合体ＭＥＡ−１を得た。
【００３０】
次に、実施例２の白金担持カーボン粉末を用いて得た電極二枚を用いた以外は、上記ＭＥＡ−１の作製と同様の方法で電解質膜−電極接合体ＭＥＡ−２を作製した。
【００３１】
次に、実施例３の白金担持カーボン粉末を用いて得た電極二枚を用いた以外は、上記ＭＥＡ−１の作製と同様の方法で電解質膜−電極接合体ＭＥＡ−３を作製した。
【００３２】
次に、実施例４の白金担持カーボン粉末を用いて得た電極二枚を用いた以外は、上記ＭＥＡ−１の作製と同様の方法で電解質膜−電極接合体ＭＥＡ−４を作製した。
【００３３】
次に、比較例１の白金担持カーボン粉末を用いて得た電極二枚を用いた以外は、上記ＭＥＡ−１の作製と同様の方法で電解質膜−電極接合体ＭＥＡ−５を作製した。
【００３４】
次に、比較例２の白金担持カーボン粉末を用いて得た電極二枚を用いた以外は、上記ＭＥＡ−１の作製と同様の方法で電解質膜−電極接合体ＭＥＡ−６を作製した。
【００３５】
次に、アノードとなる実施例５の白金−ルテニウム担持カーボン粉末による電極と、カソードとして比較例１の白金担持カーボン粉末による電極を用いた以外は、上記ＭＥＡ−１の作製と同様の方法で電解質膜−電極接合体ＭＥＡ−７を作製した。
【００３６】
次に、アノードとなる比較例３の白金−ルテニウム担持カーボン粉末による電極と、カソードとして比較例１の白金担持カーボン粉末による電極を用いた以外は、上記ＭＥＡ−１の作製と同様の方法で電解質膜−電極接合体ＭＥＡ−８を作製した。
【００３７】
上記のように作製した各ＭＥＡを燃料電池単セル評価装置(Ｓｃｒｉｂｅｒ Ａｓｓｏｃｉａｔｅｓ製：ｍｏｄｅｌ８９０)に組み込み、セル温度を８０℃とし、アノードに９０℃にて飽和水蒸気で加湿した１気圧の純水素もしくは１００ｐｐｍＣＯを含む水素を、カソードには同様に５０℃で加湿した1気圧の酸素を、それぞれのガスの利用率が常に５０％となるように流量を増加させ単セルを運転した。
【００３８】
図１に、電極幾何面積あたりの白金使用量を０．３０ｍｇ／ｃｍ２とした実施例１によるＭＥＡ−１および比較例１によるＭＥＡ−5を用い、アノードガスとして純水素を供給したた場合の電流密度−電圧曲線を示す。硝酸洗浄を行うことにより、特に低電流密度領域において性能の向上が見られる。このような領域における電極性能は、反応界面への反応ガスの拡散や反応生成水の系外への移動といった物質拡散の影響を受けにくく、触媒本来の活性が電極反応を支配する領域であり、触媒粒子とパーフルオロカーボンスルホン酸の接触が良好に保たれることにより得られる。ここで、このような領域に帰属するセル電圧０．８５VにおけるＩＲフリー電流密度を測定し、得られた値を電極幾何面積あたりの白金使用量で割り返したものを触媒の質量活性と規定し計算を行ったところ、比較例１によるＭＥＡ−5では３０５Ａ／ｇ−Ｐｔであるのに対して、実施例１によるＭＥＡ−１では３４５Ａ／ｇ−Ｐｔとなり、活性が大幅に向上していることが分かる。
【００３９】
図２に、電極幾何面積あたりの白金使用量を０．３０ｍｇ／ｃｍ２とした実施例２によるＭＥＡ−２および比較例１によるＭＥＡ−5を用い、アノードガスとして純水素を供給した場合の電流密度−電圧曲線を示す。蟻酸洗浄を行うことでも、全ての電流密度領域において性能の向上が見られる。セル電圧０．８５VにおけるＩＲフリー電流密度を測定し、質量活性の計算を行ったところ、比較例１によるＭＥＡ−5の３０５Ａ／ｇ−Ｐｔに対して、実施例２によるＭＥＡ−２では３２５Ａ／ｇ−Ｐｔとなり、活性が向上していることが分かる。
【００４０】
図３に、電極幾何面積あたりの白金使用量を０．３０ｍｇ／ｃｍ２とした実施例３によるＭＥＡ−３および比較例１によるＭＥＡ−5を用い、アノードガスとして純水素を供給した場合の電流密度−電圧曲線を示す。酢酸酸洗浄を行うことでも、全ての電流密度領域において性能の向上が見られる。セル電圧０．８５VにおけるＩＲフリー電流密度を測定し、質量活性の計算を行ったところ、比較例１によるＭＥＡ−5の３０５Ａ／ｇ−Ｐｔに対して、実施例３によるＭＥＡ−３では３８６Ａ／ｇ−Ｐｔとなり、活性が大幅に向上していることが分かる。
【００４１】
図４に、電極幾何面積あたりの白金使用量を０．３０ｍｇ／ｃｍ２とした実施例４によるＭＥＡ−４および比較例１によるＭＥＡ−5を用い、アノードガスとして純水素を供給した場合の電流密度−電圧曲線を示す。しゅう酸洗浄を行うことでも、全ての電流密度領域において性能の向上が見られる。セル電圧０．８５VにおけるＩＲフリー電流密度を測定し、質量活性の計算を行ったところ、比較例１によるＭＥＡ−5の３０５Ａ／ｇ−Ｐｔに対して、実施例４によるＭＥＡ−４では４１５Ａ／ｇ−Ｐｔとなり、活性が大幅に向上していることが分かる。
【００４２】
図５に、電極幾何面積あたりの白金使用量を０．３０ｍｇ／ｃｍ２とした比較例２によるＭＥＡ−６および比較例１によるＭＥＡ−5を用い、アノードガスとして純水素を供給した場合の電流密度−電圧曲線を示す。実施例１と同じ硝酸洗浄でも比較例２のように酸濃度が高いと、触媒中の白金が溶出するため、全ての電流密度領域において性能の低下が見られた。セル電圧０．８５VにおけるＩＲフリー電流密度を測定し、質量活性の計算を行ったところ、比較例１によるＭＥＡ−5の３０５Ａ／ｇ−Ｐｔに対して、比較例２によるＭＥＡ−６では２６６Ａ／ｇ−Ｐｔとなり、活性が大きく低下していることが分かる。
【００４３】
以上の性能試験の結果をまとめたものについて表１に示す。ここから、ｐＨ３．５−５．５の範囲において良好な質量活性が得られていることがわかる。
【表１】
図６に、電極幾何面積あたりの白金使用量を０．３０ｍｇ／ｃｍ２とした実施例5によるＭＥＡ−７および比較例３によるＭＥＡ−８を用い、アノードガスとして１００ｐｐｍＣＯを含む水素を供給した場合の電流密度−電圧曲線を示す。硝酸洗浄を行うことにより、全ての電流密度領域においてCO耐性の向上が見られる。電流密度０．５Ａ／ｃｍ２におけるセル電圧を比較したところ、比較例３によるＭＥＡ−８の０．６４２Ｖに対して、実施例５によるＭＥＡ−７では０．７２８Ｖとなった。
【００４５】
以上の性能試験の結果をまとめたものについて表２に示す。
【表２】
【発明の効果】
本発明の固体高分子電解質型燃料電池用電極触媒は、活性金属である白金または白金合金がカーボンブラック上に高分散しており、しかも固体高分子電解質、特にパーフルオロカーボンスルホン酸樹脂と親和性に優れている。そのため、このような樹脂と高い接触を実現できるので燃料電池の出力向上に大いに寄与するものである。
【図面の簡単な説明】
【図１】 電極幾何面積あたりの白金使用量を０．３０ｍｇ／ｃｍ２とした実施例１によるＭＥＡ−１および比較例１によるＭＥＡ−5を用い、アノードガスとして純水素を供給したた場合の電流密度−電圧曲線を示す。
【図２】 電極幾何面積あたりの白金使用量を０．３０ｍｇ／ｃｍ２とした実施例２によるＭＥＡ−２および比較例１によるＭＥＡ−5を用い、アノードガスとして純水素を供給した場合の電流密度−電圧曲線を示す。
【図３】 電極幾何面積あたりの白金使用量を０．３０ｍｇ／ｃｍ２とした実施例３によるＭＥＡ−３および比較例１によるＭＥＡ−5を用い、アノードガスとして純水素を供給した場合の電流密度−電圧曲線を示す。
【図４】 電極幾何面積あたりの白金使用量を０．３０ｍｇ／ｃｍ２とした実施例４によるＭＥＡ−４および比較例１によるＭＥＡ−5を用い、アノードガスとして純水素を供給した場合の電流密度−電圧曲線を示す。
【図５】 電極幾何面積あたりの白金使用量を０．３０ｍｇ／ｃｍ２とした比較例２によるＭＥＡ−６および比較例１によるＭＥＡ−5を用い、アノードガスとして純水素を供給した場合の電流密度−電圧曲線を示す。
【図６】 電極幾何面積あたりの白金使用量を０．３０ｍｇ／ｃｍ２とした実施例5によるＭＥＡ−７および比較例３によるＭＥＡ−８を用い、アノードガスとして１００ｐｐｍＣＯを含む水素を供給した場合の電流密度−電圧曲線を示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrode catalyst used for a solid polymer electrolyte fuel cell.
[0002]
[Prior art]
Solid polymer electrolyte fuel cells are being developed as portable power supplies, electric vehicle drive power supplies, and cogeneration power supplies because high current density can be obtained at low temperatures.
[0003]
The basic structure of a solid polymer electrolyte fuel cell is composed of a fuel electrode (anode), an air electrode (cathode), and an ion exchange membrane that is a solid polymer electrolyte disposed between both electrodes. Usually, both the fuel electrode and the air electrode are composed of a mixture of a catalyst carrying a noble metal and a polymer electrolyte.
[0004]
In a solid polymer electrolyte fuel cell, when hydrogen is used as the fuel, hydrogen gas passes through the pores in the electrode and reaches the interface between the electrolyte and the electrode at the fuel electrode. It becomes. Hydrogen ions reach the air electrode through the electrolyte in the electrode and the solid polymer electrolyte membrane between the electrodes. The emitted electrons flow through the catalyst carrier in the electrode to the external circuit, and reach the air electrode from the external circuit. On the other hand, in an air electrode using oxygen as an oxidizing agent, oxygen passes through the pores in the electrode and reaches the catalyst, and reacts with hydrogen ions that have reached from the fuel electrode and electrons that have moved by an external circuit to produce water. .
[0005]
In general, in order to improve the output of the fuel cell, it is necessary to promote the double electrode reaction. To that end, platinum and platinum alloys, which are active substances for electrode catalysts, have high activity for both electrode reactions, and platinum and platinum alloys are efficiently and effectively used for both electrode reactions in the electrodes. It is necessary to That is, a catalyst having a highly active noble metal, especially platinum or a platinum alloy supported on carbon black, is used as the catalyst, and perfluorocarbon sulfonic acid, which is a polymer electrolyte with high ion conductivity, is used as the conductive electrolyte. , Both are required to be in full contact.
[0006]
Various methods for producing electrodes have been proposed so far.
For example, “electrochemistry” 53, no. 10, p. 812-817 (1985) includes a Nafion 117 solution (trade name, manufactured by Aldrich Chemical Co., H-type, 5% solution in a mixed solvent of aliphatic alcohol and water), which is a perfluorocarbon sulfonic acid resin, as a solid polymer electrolyte. A method of using and mixing with catalyst powder has been reported.
[0007]
In JP-A-4-162365, platinum catalyst-supported carbon black and catalyst-free carbon black are immersed in a butanol solution of Nafion, which is a solid polymer electrolyte, and then a polytetrafluoroethylene dispersion is used. Processing is described.
[0008]
In JP-A-8-418153, (1) first, for example, platinum black or carbon black particles carrying platinum are produced as catalyst particles, and (2) the particles and the solid polymer electrolyte solution are further mixed with a solvent. (3) A method of mixing a polytetrafluoroethylene or the like as a binder as required is described. In this method, it is explained that the suspension preparation step by mixing (2) and the step of removing the solvent contained in the suspension are particularly important.
[0009]
Japanese Patent Application Laid-Open No. 8-227716 discloses a method of physical mixing in a planetary ball mill in the step of mixing an electrode catalyst and a solid polymer electrolyte.
[0010]
[Problems to be solved by the invention]
However, the electrocatalyst obtained by any of the above methods produces aggregated particles as a result of sharing the hydrophilic part and the hydrophobic part because the surface of the carbon black carrying platinum has both the structure and functional group of graphite. It is easy to do and high dispersion cannot be achieved. In addition, perfluorosulfonic acid resins such as Nafion 117 solution are prone to agglomeration, and there is a problem that contact between the electrode catalyst and these resins is insufficient.
[0011]
The present invention solves the above-described conventional problems, and provides an electrode catalyst in which an active metal of a catalyst is highly dispersed on carbon black and has a high affinity for a solid polymer electrolyte, particularly perfluorocarbon sulfonic acid resin. Is.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors modified the surface structure of the carbon black used as the catalyst carrier by acid treatment, thereby suppressing the aggregation of the perfluorocarbon sulfonic acid resin and increasing the surface of the catalyst. It has been found that adhesion in a dispersed state can be realized.
[0013]
That is, the present invention comprises carbon black and platinum or a platinum alloy supported on the carbon black, and has a pH of 2 to 7 measured by the method described in JIS K1474. An electrode catalyst for a molecular fuel cell is provided.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Carbon black is used as a support in the electrode catalyst of the present invention.
[0015]
In the electrode catalyst of the present invention, platinum or a platinum alloy is used as an active metal. Examples of the platinum alloy include a platinum-ruthenium alloy and a platinum-molybdenum alloy. Among these, a platinum-ruthenium alloy is preferable. The preferable carrying amount of platinum or platinum alloy is 5 to 70% by mass, more preferably 10 to 60% by mass.
[0016]
The electrode catalyst of the present invention is characterized in that the pH measured by the method described in JIS K1474 is 2-7. The pH is preferably in the range of pH 3-6, more preferably in the range of 3.5-5.5. If the pH is too low, platinum and platinum alloys are likely to elute.
[0017]
As the acid used to adjust the pH of the catalyst, either an inorganic acid or an organic acid can be used. Examples of the inorganic acid include hydrochloric acid, nitric acid, sulfuric acid, and the like. Examples thereof include aliphatic carboxylic acids such as formic acid, acetic acid, oxalic acid, and malonic acid. Of these, preferred are aliphatic organic acids, particularly carboxylic acids.
[0018]
The method for producing the electrode catalyst of the present invention includes a method in which platinum or a platinum alloy is supported after treating carbon black as a support with an acid, or a method in which platinum or a platinum alloy is supported on carbon black and then treated with an acid. Good.
By such an acid treatment, the surface state of the carbon black is converted from hydrophobic to hydrophilic, and the affinity state with the acid is also improved. As a result, good contact with the perfluorocarbon sulfonic acid is obtained.
[0019]
【Example】
The present invention will be specifically described below with reference to examples.
The pH of the catalyst was measured according to the pH value measurement method of the activated carbon test method of JIS K1474 5.10. Specifically, 1.0 g of the dry carbon mass of the electrode catalyst was weighed, 100 ml of water was added and gently boiled for 5 minutes, then cooled to room temperature, water was added to make up to 100 ml, and stirred well. The pH of the suspension was measured.
[0020]
[Example 1]
10.0 g of commercially available electrocatalyst SA50BK (50% Pt carbon black BET specific surface area 347 m 2 / g, Pt particle size 2.5 nm, pH 6.5 by X-ray diffraction) manufactured by N.E. The slurry was suspended in water. Next, a nitric acid solution having a concentration of 1 mol / L was prepared and added to a 10 ml slurry, and then the slurry temperature was raised and refluxed in a boiling state for 3 hours. Next, the catalyst was filtered off, washed, dried and pulverized. The catalyst powder after the treatment was measured. As a result, the Pt analysis value was 50%, the BET specific surface area was 338 m 2 / g, the crystallite size of Pt was 2.6 nm, and the pH was 4.0.
[0021]
[Example 2]
The acid added in Example 1 was changed to a 1 mol / L nitric acid solution and changed to 10 ml of formic acid (99% purity manufactured by Wako Pure Chemical Industries) to prepare a Pt 50% electrocatalyst powder. The powder had a BET specific surface area of 345 m 2 / g, a Pt crystallite size of 2.5 nm, and a pH of 5.8.
[0022]
Example 3
The acid added in Example 1 was changed to nitric acid and changed to 10 ml of acetic acid (special grade purity 99.7% or more manufactured by Wako Pure Chemical Industries) to prepare an electrode catalyst powder of 50% Pt. The powder had a BET specific surface area of 346 m 2 / g, a Pt crystallite size of 2.5 nm, and a pH of 4.8.
[0023]
[Example 4] The acid added in Example 1 was changed to nitric acid and changed to 10 g of oxalic acid dihydrate (special grade manufactured by Wako Pure Chemical Industries) to prepare an electrode catalyst powder of 50% Pt. The powder had a BET specific surface area of 345 m 2 / g, a Pt crystallite size of 2.6 nm, and a pH of 5.0.
[0024]
Example 5
10.0 g of commercially available electrocatalyst SA27-13RC (27% Pt 13% Ru carbon black, BET specific surface area 130 m 2 / g, Xt diffraction Pt particle diameter 6.2 nm, pH 7.5, manufactured by N.E. Chemcat) was weighed. And suspended in 1.5 L of water to form a slurry. Next, a 1 mol / L nitric acid solution was prepared, 10 ml was added, the slurry temperature was raised, and the mixture was refluxed for 3 hours in a boiling state. The catalyst was filtered off, washed, dried and ground. The powder had a Pt analysis value of 27%, Ru of 13%, a BET specific surface area of 130 m 2 / g, a Pt crystallite size of 6.2 nm, and a pH of 4.0.
[0025]
[Comparative Example 1]
The commercially available electrocatalyst SA50BK used in Example 1 (50% Pt carbon black BET specific surface area 347 m 2 / g, manufactured by N.E. Chemcat, Pt particle diameter 2.5 nm, pH 6.5 by X-ray diffraction) was used.
[0026]
[Comparative Example 2]
The nitric acid added in Example 1 and the amount added were 50 ml of concentrated nitric acid (special grade manufactured by Wako Pure Chemical Industries). The powder had a Pt analysis value of 47.3%, a BET specific surface area of 335 m 2 / g, a Pt crystallite diameter of 2.6 nm, and a pH of 2.4.
[0027]
[Comparative Example 3]
Commercially available electrocatalyst SA27-13RC used in Example 5 (27% Pt 13% Ru carbon black, BET specific surface area 130 m 2 / g, manufactured by N.E. Chemcat, Pt particle diameter 6.2 nm, pH 7.5 by X-ray diffraction) It was used.
[0028]
[Electrode preparation for battery performance evaluation]
A porous carbon paper (made by Toray: TGP-H-120) having a water repellent treatment of 50 × 50 mm and a thickness of 120 μm treated with PTFE (polytetrafluoroethylene, manufactured by Mitsui Fluorochemicals: Teflon 30J) was prepared as an electrode substrate. Next, a predetermined amount of each of the platinum-supported carbon powder and the platinum-ruthenium-supported carbon powder catalyst obtained in Examples 1 to 5 and Comparative Examples 1 to 3, water, and a 5 wt% Nafion solution (manufactured by Aldrich) were mixed in a predetermined amount. It was. The paste in this way was uniformly applied to the entire surface of one side of the electrode substrate and then dried to form a catalyst layer. Thus, an electrode using the platinum-supported carbon powder or platinum-ruthenium-supported carbon powder of each Example and each Comparative Example was prepared.
[0029]
Next, two electrodes obtained by using the platinum-supported carbon powder of Example 1 were placed on both sides of a perfluorosulfonic acid electrolyte membrane (manufactured by DuPont, product name: Nafion 112), and the catalyst layer side of each electrode was an electrolyte. The membranes were stacked so as to be in contact with each other and thermocompression bonded with a hot press machine to obtain an electrolyte membrane-electrode assembly MEA-1.
[0030]
Next, an electrolyte membrane-electrode assembly MEA-2 was produced in the same manner as in the production of MEA-1, except that two electrodes obtained using the platinum-supported carbon powder of Example 2 were used.
[0031]
Next, an electrolyte membrane-electrode assembly MEA-3 was produced in the same manner as in the production of MEA-1, except that two electrodes obtained using the platinum-supported carbon powder of Example 3 were used.
[0032]
Next, an electrolyte membrane-electrode assembly MEA-4 was produced in the same manner as in the production of MEA-1, except that two electrodes obtained using the platinum-supported carbon powder of Example 4 were used.
[0033]
Next, an electrolyte membrane-electrode assembly MEA-5 was produced in the same manner as in the production of MEA-1, except that two electrodes obtained using the platinum-supported carbon powder of Comparative Example 1 were used.
[0034]
Next, an electrolyte membrane-electrode assembly MEA-6 was produced in the same manner as in the production of MEA-1, except that two electrodes obtained using the platinum-supported carbon powder of Comparative Example 2 were used.
[0035]
Next, an electrolyte was prepared in the same manner as in the preparation of MEA-1, except that the electrode made of platinum-ruthenium-supported carbon powder of Example 5 serving as the anode and the electrode made of platinum-supported carbon powder of Comparative Example 1 were used as the cathode. Membrane-electrode assembly MEA-7 was produced.
[0036]
Next, an electrolyte was prepared in the same manner as in the preparation of MEA-1, except that the electrode made of platinum-ruthenium-supported carbon powder of Comparative Example 3 to be the anode and the electrode made of platinum-supported carbon powder of Comparative Example 1 were used as the cathode. Membrane-electrode assembly MEA-8 was produced.
[0037]
Each MEA produced as described above was incorporated into a fuel cell single cell evaluation apparatus (manufactured by Scriber Associates: model 890), the cell temperature was set to 80 ° C., and the anode was heated to 90 ° C. with 1 atmosphere of pure hydrogen or 100 ppm CO A single cell was operated by increasing the flow rate of hydrogen containing 1 and oxygen at 1 atm humidified at 50 ° C. to the cathode in such a manner that the utilization rate of each gas was always 50%.
[0038]
FIG. 1 shows a case where pure hydrogen was supplied as anode gas using MEA-1 according to Example 1 and MEA-5 according to Comparative Example 1 in which the amount of platinum used per electrode geometric area was 0.30 mg / cm 2 . A current density-voltage curve is shown. By performing nitric acid cleaning, performance is improved particularly in a low current density region. The electrode performance in such a region is less affected by material diffusion such as diffusion of reaction gas to the reaction interface and movement of reaction product water out of the system, and the original activity of the catalyst dominates the electrode reaction. It is obtained by maintaining good contact between the catalyst particles and perfluorocarbon sulfonic acid. Here, the IR free current density at a cell voltage of 0.85 V belonging to such a region was measured, and the value obtained by dividing the obtained value by the amount of platinum used per electrode geometric area was defined as the mass activity of the catalyst. As a result of calculation, the MEA-5 according to Comparative Example 1 shows 305 A / g-Pt, whereas the MEA-1 according to Example 1 shows 345 A / g-Pt, and the activity is greatly improved. I understand.
[0039]
FIG. 2 shows the current when MEA-2 according to Example 2 and MEA-5 according to Comparative Example 1 in which the amount of platinum used per electrode geometric area was 0.30 mg / cm 2 was supplied as pure anode gas. A density-voltage curve is shown. By performing formic acid cleaning, performance is improved in all current density regions. When the IR free current density at a cell voltage of 0.85 V was measured and the mass activity was calculated, 305 A / g-Pt of MEA-5 according to Comparative Example 1 was 325 A / g with MEA-2 according to Example 2. It turns out that it is g-Pt and the activity is improved.
[0040]
FIG. 3 shows the current when pure hydrogen was supplied as anode gas using MEA-3 according to Example 3 and MEA-5 according to Comparative Example 1 in which the platinum usage per electrode geometric area was 0.30 mg / cm 2. A density-voltage curve is shown. Even with acetic acid cleaning, performance is improved in all current density regions. When the IR free current density at a cell voltage of 0.85 V was measured and the mass activity was calculated, the MEA-5 according to Comparative Example 1 was 305 A / g-Pt, whereas the MEA-3 according to Example 3 was 386 A / It turns out that it becomes g-Pt and activity is improving significantly.
[0041]
FIG. 4 shows the current when MEA-4 according to Example 4 and MEA-5 according to Comparative Example 1 in which the amount of platinum used per electrode geometric area was 0.30 mg / cm 2 and pure hydrogen was supplied as the anode gas. A density-voltage curve is shown. Even with oxalic acid cleaning, performance is improved in all current density regions. When the IR free current density at a cell voltage of 0.85 V was measured and the mass activity was calculated, the MEA-5 according to Comparative Example 1 was 305 A / g-Pt, whereas the MEA-4 according to Example 4 was 415 A / It turns out that it becomes g-Pt and activity is improving significantly.
[0042]
FIG. 5 shows the current when pure hydrogen is supplied as anode gas using MEA-6 according to Comparative Example 2 and MEA-5 according to Comparative Example 1 in which the amount of platinum used per electrode geometric area is 0.30 mg / cm 2. A density-voltage curve is shown. Even in the same nitric acid cleaning as in Example 1, when the acid concentration was high as in Comparative Example 2, platinum in the catalyst was eluted, so that a decrease in performance was observed in all current density regions. When the IR free current density at a cell voltage of 0.85 V was measured and the mass activity was calculated, the MEA-5 according to Comparative Example 1 was 305 A / g-Pt, whereas the MEA-6 according to Comparative Example 2 was 266 A / It turns out that it becomes g-Pt and activity has fallen large.
[0043]
Table 1 summarizes the results of the above performance tests. From this, it can be seen that good mass activity is obtained in the range of pH 3.5-5.5.
[Table 1]
FIG. 6 shows a case where MEA-7 according to Example 5 and MEA-8 according to Comparative Example 3 in which the amount of platinum used per electrode geometric area is 0.30 mg / cm 2 and hydrogen containing 100 ppm CO as an anode gas is supplied. The current density-voltage curve of is shown. By performing nitric acid cleaning, CO resistance is improved in all current density regions. When the cell voltage at a current density of 0.5 A / cm 2 was compared, it was 0.728 V for MEA-7 according to Example 5 compared to 0.642 V for MEA-8 according to Comparative Example 3.
[0045]
The results of the above performance tests are summarized in Table 2.
[Table 2]
【The invention's effect】
In the solid polymer electrolyte fuel cell electrode catalyst of the present invention, platinum or platinum alloy, which is an active metal, is highly dispersed on carbon black, and has an affinity for solid polymer electrolytes, particularly perfluorocarbon sulfonic acid resins. Are better. Therefore, since high contact with such a resin can be realized, it greatly contributes to the improvement of the output of the fuel cell.
[Brief description of the drawings]
FIG. 1 shows the case where MEA-1 according to Example 1 and MEA-5 according to Comparative Example 1 in which the amount of platinum used per electrode geometric area is 0.30 mg / cm 2 and pure hydrogen is supplied as an anode gas. A current density-voltage curve is shown.
FIG. 2 shows the current when MEA-2 according to Example 2 and MEA-5 according to Comparative Example 1 in which the amount of platinum used per electrode geometric area is 0.30 mg / cm 2 and when pure hydrogen is supplied as an anode gas. A density-voltage curve is shown.
FIG. 3 shows the current when MEA-3 according to Example 3 and MEA-5 according to Comparative Example 1 in which the amount of platinum used per electrode geometric area was 0.30 mg / cm 2 and pure hydrogen was supplied as anode gas. A density-voltage curve is shown.
FIG. 4 shows the current when MEA-4 according to Example 4 and MEA-5 according to Comparative Example 1 in which the amount of platinum used per electrode geometric area was 0.30 mg / cm 2 and pure hydrogen was supplied as the anode gas. A density-voltage curve is shown.
FIG. 5 shows the electric current when pure hydrogen is supplied as anode gas using MEA-6 according to Comparative Example 2 and MEA-5 according to Comparative Example 1 in which the amount of platinum used per electrode geometric area is 0.30 mg / cm 2. A density-voltage curve is shown.
FIG. 6 shows a case where MEA-7 according to Example 5 and MEA-8 according to Comparative Example 3 in which the amount of platinum used per electrode geometric area is 0.30 mg / cm 2 is used and hydrogen containing 100 ppm CO is supplied as an anode gas. The current density-voltage curve of is shown.
Claims (4)
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| JP2002206216A JP4087651B2 (en) | 2002-07-15 | 2002-07-15 | Electrocatalyst for solid polymer electrolyte fuel cell |
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| JP2002206216A JP4087651B2 (en) | 2002-07-15 | 2002-07-15 | Electrocatalyst for solid polymer electrolyte fuel cell |
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Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006179427A (en) * | 2004-12-24 | 2006-07-06 | Toyota Motor Corp | Electrode catalyst for fuel cell, and the fuel cell |
| KR100738062B1 (en) * | 2006-05-16 | 2007-07-10 | 삼성에스디아이 주식회사 | Membrane and electrode assembly, and fuel cell using the same |
| KR100846478B1 (en) | 2006-05-16 | 2008-07-17 | 삼성에스디아이 주식회사 | Supported Catalyst, manufacturing method thereof, and fuel cell using the same |
| JP5270468B2 (en) * | 2009-06-22 | 2013-08-21 | トヨタ自動車株式会社 | ELECTRODE CATALYST FOR FUEL CELL, ITS MANUFACTURING METHOD, AND SOLID POLYMER TYPE FUEL CELL USING THE SAME |
| JP5821330B2 (en) * | 2011-02-21 | 2015-11-24 | 株式会社エクォス・リサーチ | Fuel cell catalyst manufacturing equipment |
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