JPWO2002021619A1 - Solid polymer electrolyte fuel cell - Google Patents

Abstract

The present invention provides an electrode, an electrode diffusion layer for introducing gas, and a gas mixture on both surfaces of an electrolyte membrane containing a matrix and a proton donor serving as a membrane base material. A solid polymer electrolyte fuel cell, in which the separators forming the outer shell of the unit cell are sequentially arranged, wherein the solid polymer electrolyte fuel cell uses an amorphous polyolefin for the electrolyte membrane matrix. Related to fuel cells.

Description

［式中、ｍ及びｎは、それぞれ独立して１以上の整数（好ましくは１〜１０００００）を表し；Ｒは水素原子、ハロゲン原子又は炭素数１〜２０の置換もしくは非置換の炭化水素基（例えば、アルキル基、アルコキシアルキル基、ハロゲン化アルキル基、アルケニル基、アリール基、アルコキシアリール基、ハロゲン化アリール基、アラルキル基、アルコキシアラルキル基）を表し；Ａはシクロペンタジエンもしくはその誘導体とノルボルナジエンもしくはその誘導体との付加反応物又はその水素添加物、又はジシクロペンタジエンもしくはその誘導体とエチレンとの付加反応物を表す。］
で示される重合体が挙げられる。
シクロペンタジエンもしくはその誘導体とノルボルナジエンもしくはその誘導体との付加反応物の水素添加物、又はジシクロペンタジエンもしくはその誘導体とエチレンとの付加反応物は、次式：

［式中、ｎは１以上の整数（好ましくは１〜１００００）であり；Ｒ^１〜Ｒ^１２は、それぞれ独立して水素原子、ハロゲン原子又は炭素数１〜２０の炭化水素基（例えば、アルキル基、アルケニル基、アリール基、アラルキル基）を表し、Ｒ^１とＲ^２、Ｒ^５とＲ^６、Ｒ^９とＲ^１０、Ｒ^１１とＲ^１２は、それぞれ共同して炭素数１〜２０のアルキリデン基を表してもよく、Ｒ^９〜Ｒ^１２は、互いに結合して単環又は多環を形成してもよい。］
で示すことができる。
前記、シクロペンタジエンもしくはその誘導体とノルボルナジエンもしくはその誘導体との付加反応物の水素添加物、又はジシクロペンタジエンもしくはその誘導体とエチレンとの付加反応物としては、例えばテトラシクロ−３−ドデセン、８−メチルテトラシクロ−３−ドデセン、８−エチルテトラシクロ−３−ドデセン、８−プロピルテトラシクロ−３−ドデセン、８−ブチルテトラシクロ−３−ドデセン、８−イソブチルテトラシクロ−３−ドデセン、８−ヘキシルテトラシクロ−３−ドデセン、８−ステアリルテトラシクロ−３−ドデセン、５，１０−ジメチルテトラシクロ−３−ドデセン、２，１０−ジメチルテトラシクロ−３−ドデセン、８，９−ジメチルテトラシクロ−３−ドデセン、８−エチル−９−メチルテトラシクロ−３−ドデセン、１１，１２−ジメチルテトラシクロ−３−ドデセン、２，７，９−トリメチルテトラシクロ−３−ドデセン、９−エチル−２，７−ジメチルテトラシクロ−３−ドデセン、９−イソブチル−２，７−ジメチルテトラシクロ−３−ドデセン、９，１１，１２−トリメチルテトラシクロ−３−ドデセン、９−エチル−１１，１２−ジメチルテトラシクロ−３−ドデセン、９−イソブチル−１１，１２−ジメチルテトラシクロ−３−ドデセン、５，８，９，１０−テトラメチルテトラシクロ−３−ドデセン、８−エチリデンテトラシクロ−３−ドデセン、８−エチリデン−９−メチルテトラシクロ−３−ドデセン、８−エチリデン−９−エチルテトラシクロ−３−ドデセン、８−エチリデン−９−イソプロピルテトラシクロ−３−ドデセン、８−エチリデン−９−ブチルテトラシクロ−３−ドデセン、８−ｎ−プロピリデンテトラシクロ−３−ドデセン、８−ｎ−プロピリデン−９−メチルテトラシクロ−３−ドデセン、８−ｎ−プロピリデン−９−エチルテトラシクロ−３−ドデセン、８−ｎ−プロピリデン−９−イソプロピルテトラシクロ−３−ドデセン、８−ｎ−プロピリデン−９−ブチルテトラシクロ−３−ドデセン、８−イソプロピリデンテトラシクロ−３−ドデセン、８−イソプロピリデン−９−メチルテトラシクロ−３−ドデセン、８−イソプロピリデン−９−エチルテトラシクロ−３−ドデセン、８−イソプロピリデン−９−イソプロピルテトラシクロ−３−ドデセン、８−イソプロピリデン−９−ブチルテトラシクロ−３−ドデセン、８−クロロテトラシクロ−３−ドデセン、８−ブロモテトラシクロ−３−ドデセン、８−フルオロテトラシクロ−３−ドデセン、８，９−ジクロロテトラシクロ−３−ドデセン、ヘキサシクロ−４−ヘプタデセン、１２−メチルヘキサシクロ−４−ヘプタデセン、１２−エチルヘキサシクロ−４−ヘプタデセン、１２−イソブチルヘキサシクロ−４−ヘプタデセン、１，６，１０−トリメチル−１２−イソブチルヘキサシクロ−４−ヘプタデセン、オクタシクロ−５−ドコセン、１５−メチルオクタシクロ−５−ドコセン、１５−エチルオクタシクロ−５−ドコセン、ペンタシクロ−４−ヘキサデセン、１，３−ジメチルペンタシクロ−４−ヘキサデセン、１，６−ジメチルペンタシクロ−４−ヘキサデセン、１５，１６−ジメチルペンタシクロ−４−ヘキサデセン、ヘプタシクロ−５−エイコセン、ヘプタシクロ−５−ヘンエイコセン、ペンタシクロ−４−ペンタデセン、１，３−ジメチルペンタシクロ−４−ペンタデセン、１，６−ジメチルペンタシクロ−４−ペンタデセン、１４，１５−ジメチルペンタシクロ−４−ペンタデセン、ペンタシクロ−４，１０−ペンタデカジエン等が挙げられる。
非晶性ポリオレフィンの他の例としては、シクロペンタジエンもしくはその誘導体とノルボルナジエンもしくはその誘導体との付加反応物と、エチレン、ブタジエン及びスチレン誘導体から選ばれる少なくとも１種の不飽和単量体との共重合体が挙げられる。前記スチレン誘導体としては、例えばスチレン、ｏ−メチルスチレン、ｍ−メチルスチレン、ｐ−メチルスチレン、α−メチルスチレン、ｏ−クロロスチレン、ｍ−クロロスチレン、ｐ−クロロスチレン、ｏ−エチルスチレン、ｍ−エチルスチレン、ｐ−エチルスチレン、ｐ−メトキシスチレン、ｐ−クロロエチルスチレン、ｐ−メチル−α−メチルスチレンなどが挙げられる。これらは２種以上を組み合わせて用いることもできる。
また、環状構造を有する非晶性ポリオレフィンの他の例としては、次式：

［式中、ｎは０又は１以上の整数（好ましくは１〜１００００）を表し、ｍは１以上の整数（好ましくは１〜１００００）を表し、Ｒ^１〜Ｒ^４は、それぞれ独立して水素原子又は炭素数１〜２０の炭化水素基（例えば、アルキル基、アルケニル基、アリール基、アラルキル基）を表す。］
で示される、テトラシクロ−３−ドデセン又はその誘導体とビシクロヘプト−２−エン又はその誘導体とからなる開環重合体の水素添加物が挙げられる。
前記テトラシクロ−３−ドデセン又はその誘導体としては、例えばテトラシクロ−３−ドデセン、５，１０−ジメチルテトラシクロ−３−ドデセン、２，１０−ジメチルテトラシクロ−３−ドデセン、１１，１２−ジメチルテトラシクロ−３−ドデセン、２，７，９−トリメチルテトラシクロ−３−ドデセン、９−エチル−２，７−ジメチルテトラシクロ−３−ドデセン、９−イソブチル−２，７−ジメチルテトラシクロ−３−ドデセン、９，１１，１２−トリメチルテトラシクロ−３−ドデセン、９−エチル−１１，１２−ジメチルテトラシクロ−３−ドデセン、９−イソブチル−１１，１２−ジメチルテトラシクロ−３−ドデセン、５，８，９，１０−テトラメチルテトラシクロ−３−ドデセン、８−メチルテトラシクロ−３−ドデセン、８−エチルテトラシクロ−３−ドデセン、８−プロピルテトラシクロ−３−ドデセン、８−ヘキシルテトラシクロ−３−ドデセン、８−ステアリルテトラシクロ−３−ドデセン、８，９−ジメチルテトラシクロ−３−ドデセン、８−メチル−９−エチルテトラシクロ−３−ドデセン、８−シクロヘキシルテトラシクロ−３−ドデセン、８−イソブチルテトラシクロ−３−ドデセン、８−ブチルテトラシクロ−３−ドデセン、８−エチリデンテトラシクロ−３−ドデセン、８−エチリデン−９−メチルテトラシクロ−３−ドデセン、８−エチリデン−９−エチルテトラシクロ−３−ドデセン、８−エチリデン−９−イソプロピルテトラシクロ−３−ドデセン、８−エチリデン−９−ブチルテトラシクロ−３−ドデセン、８−ｎ−プロピリデンテトラシクロ−３−ドデセン、８−ｎ−プロピリデン−９−メチルテトラシクロ−３−ドデセン、８−ｎ−プロピリデン−９−エチルテトラシクロ−３−ドデセン、８−ｎ−プロピリデン−９−イソプロピルテトラシクロ−３−ドデセン、８−ｎ−プロピリデン−９−ブチルテトラシクロ−３−ドデセン、８−イソプロピリデンテトラシクロ−３−ドデセン、８−イソプロピリデン−９−メチルテトラシクロ−３−ドデセン、８−イソプロピリデン−９−エチルテトラシクロ−３−ドデセン、８−イソプロピリデン−９−イソプロピルテトラシクロ−３−ドデセン、８−イソプロピリデン−９−ブチルテトラシクロ−３−ドデセン等が挙げられる。
前記ビシクロヘプト−２−エン又はその誘導体としては、例えばビシクロヘプト−２−エン、６−メチルビシクロヘプト−２−エン、５，６−ジメチルビシクロヘプト−２−エン、１−メチルビシクロヘプト−２−エン、６−エチルビシクロヘプト−２−エン、６−ｎ−ブチルビシクロヘプト−２−エン、６−イソブチルビシクロヘプト−２−エン、７−メチルビシクロヘプト−２−エン等が挙げられる。
非晶性ポリオレフィンとしては、例えば、特開平７−３１６２２２号公報に記載の環状構造を有しない重合体を用いることもできる。このような非晶性ポリオレフィンとしては、例えばポリプロピレン、プロピレン・エチレン共重合体、プロピレン・ブテン−１共重合体、プロピレン・ブテン−１・エチレン三元共重合体、プロピレン・ヘキセン−１・オクテン−１三元共重合体、プロピレン・ヘキセン−１・４−メチルペンテン−１三元共重合体、ポリブテン−１が挙げられる。
前述した非晶性ポリオレフィンのうち、ノルボルネン又はノルボルネン誘導体を用いて重合したポリマーは、非晶性オレフィンの中でも特に耐熱性、耐酸性及び加工性に優れた材料であり、また低コスト膜を作製するための経済性も合わせ持っている。
本発明に用いる非晶性ポリオレフィンとしては、ＧＰＣ測定法による平均分子量５万以上３０万以下、比重１．１以下、ガラス転移点温度（Ｔｇ）１６５℃以上のものが好ましい。
非晶性ポリオレフィンとしては、例えばアートン^ＴＭ（ＪＳＲ社）、ＡＰＯＡＰＬ^ＴＭ−６５０９Ｔ（三井化学（株））、ウベタック^ＴＭＵＴ２７８０（宇部レキセン（株））等種々の製品が市販されているので、これらを用いることができる。
本発明の固体高分子電解質型燃料電池の構造としては、特に制限はなく、例えば、膜ベース材料となるマトリックス及びプロトン供与体を含む電解質膜の両面に、電極と、ガスを導く電極拡散層と、ガスの混合を防ぎ、電極面内の集電及び電池厚さ方向の導通を確保し、単電池の外殼を形成するセパレータとを順次配置してなる構造が挙げられる。
電解質膜のイオン伝導抵抗を高温下で長期間低く維持するためには電解質の散逸を防ぐ必要がある。このような点から、電解質膜のプロトン供与体と前記マトリックスとが少なくとも酸素原子とＳｉ、Ｔｉ及びＺｒから選ばれる一つの原子、好ましくはＳｉとが結合している原子団を介して結合している電解質膜を用いることが好ましい。これによりイオン交換基がマトリックスに強固に固定されるため、イオン交換基が時間とともに膜外に離脱して膜の抵抗が上昇する現象を大幅に抑制でき、長寿命化を実現することができる。
前記のように無機物と有機物を化学結合により結合させる場合、シランカップリング剤の利用は合成の簡便性と試薬の経済性から有効である。特に３−イソシアネートプロピルトリエトキシシランを用いた場合、電解質膜の耐熱性、電池環境下における安定性、イオン導電体の散逸抑制に効果的であるが、これに限定されるものではない。
電解質膜にイオン伝導性を付与するプロトン供与体についてもマトリックスと同様に、耐熱性が要求される。更に、水は常圧で沸点が１００℃であるため、膜をそれ以上の温度で湿潤状態に保つためには全体を加圧雰囲気にする必要がある。このような点から、プロトン供与体としては、プロトン伝導性を有する金属酸化物を用いることが好ましく、良好なプロトン伝導性を示し、高温でもイオン伝導性が劣化しない材料としてポリ酸を用いることが更に好ましい。
ポリ酸としては、中心イオンとして、Ｗ、Ｓｉ、Ｓｎ、Ｚｎ、Ｐ及びＭｏからなる群から選ばれる少なくとも１つを含むものが好ましい。
ポリ酸としては、イソポリ酸のみならず、２種以上の中心イオンを含むヘテロポリ酸を用いることができる。イソポリ酸としては、例えばイソポリタングステン酸水和物、イソポリモリブデン酸水和物、酸化スズ水和物（ＳｎＯ_２・ｎＨ_２Ｏ）が挙げられ、ヘテロポリ酸としては、例えばケイタングステン酸水和物が挙げられる。
これらのポリ酸は材料自身に水分子を水和水の形で保持、あるいは材料表面などに吸着させているため、高温条件で相対湿度が低くても十分なイオン伝導性を確保することができる。即ち、１００℃以上の運転温度においても電池環境をその温度における飽和水蒸気圧まで昇圧する必要がないため、従来よりもコンプレッサー等の捕機に消費されるエネルギーが少なく、その分のシステム効率向上が見込める。
これらのプロトン伝導材料の使用により高温条件でも抵抗が低く、かつ電解質膜を湿潤させるための水蒸気量を低く抑えることができる。なぜなら材料自身に水分子を水和水の形で保持、あるいは材料表面などに吸着させているために相対湿度が低い環境においてもプロトンの伝導パスを確保できるためである。このことにより電池の運転圧力を低く設定できることからシステム構成の簡略化に有効である。
プロトン供与体として用いるプロトン伝導性を有する金属酸化物としては、少なくともＰを含む酸化ケイ素を用いることもできる。特に、耐熱性が高いリン酸系ガラス（例えば、ｘＰ_２Ｏ_５・ｙＳｉＯ_２、ｘＰ_２Ｏ_５・ｙＺｒＯ_２・ｚＳｉＯ_２（ここで、ｘ、ｙ及びｚは任意の数を表す。）、より具体的には５Ｐ_２Ｏ_５・５ＺｒＯ_２・９０ＳｉＯ_２のような組成が挙げられる。）を用いることにより電解質膜としての高温安定性が更に向上できる。このとき、リン酸系ガラスはプロトン伝導パスとなる吸着水や吸着水酸基、内部包含水量を多くするために多孔質構造とすることが好ましい。
本発明の固体高分子電解質型燃料電池を構成する電解質膜の典型的な構造を図１に示す。非晶性ポリオレフィン主鎖に置換基Ｒ_１、Ｒ_２が結合した構造となっている。ここで、Ｒ_１、Ｒ_２はそれぞれ
−Ｒ_１１−ＳｉＲ_１２−Ｏ−Ｒ_１３−Ｐ_１
−Ｒ_２１−ＳｉＲ_２２−Ｏ−Ｒ_２３−Ｐ_２
で示される構成又は水素原子を表す。但し、Ｒ_１及びＲ_２がともに水素原子の場合はない。Ｒ_１Ｘ、Ｒ_２Ｘは有機材料からなる原子団、Ｐ_Ｘはプロトン供与体である。Ｒ_１Ｘ、Ｒ_２Ｘは省略される場合もありうる。
発明を実施するための最良の形態
以下、本発明を実施例及び比較例により説明する。
（実施例１）
電解質膜マトリックス材料としてＪＳＲ社製のアートン^ＴＭ（比重１．０８、ガラス転移点温度１７１℃、熱伝導率０．１６ｋｃａｌ／ｍ・ｈｒ・℃）粉末８０ｇとトルエン２２０ｍｌをガラス製４つ口フラスコに添加し、窒素雰囲気下で攪拌し電解質膜マトリックス溶液ａを得た。溶液ａに３−イソシアネートプロピルトリエトキシシラン８ｇを添加し７５℃で窒素雰囲気下２４時間還流攪拌混合し溶液ｂを作製した。
ケイタングステン酸水和物（関東化学社製）１６ｇをメタノール３０ｍｌに溶解した溶液ｃを溶液ｂに加え攪拌して電解質溶液ｃ’を作製した後、テープキャスティング法により厚さ５０μｍのフィルムに展開し、大気中７５℃で１０時間乾燥させ電解質膜ｄを得た。本電解質膜は沸騰水溶液に放置しても溶液のプロトン濃度に変化は見られなかった。これはイオン交換基であるケイタングステン酸がカップリングにより化学的にマトリックスに固定されているためである。
白金微細粒子をカーボン粉体に析出させた触媒２．５ｇと電解質溶液ｃ’９０ｇを混合し触媒ペーストｅを作製した。電解質膜ｄの表面に触媒ペーストｅをスクリーン印刷により、一辺が１０ｃｍの正方形薄膜状に展開し、触媒層を形成した。このとき白金の使用量は塗布触媒面積１ｃｍ^２当たり０．３ｍｇとなるように展開量つまり触媒層厚さを調節した。触媒層塗布は電解質膜ｄの両面に行い、塗布後は窒素雰囲気下７５℃で１０時間乾燥処理を行った。この処理は触媒層中の溶媒を飛散させるとともに、触媒層中の電解質膜基材のゲル化反応を促進させる意味を持つ。前記方法により面積１００ｃｍ^２の触媒層がその表裏面に形成された電解質膜、いわゆる一体化電極ｆを得た。
この一体化電極ｆの触媒面両面に、集電機能を兼ねる電極拡散層（ジャパンゴアテックス社製、ＣＡＲＢＥＬ−ＣＬ）を配置し、ガス流路を形成したカーボン製セパレータと組み合わせ試験用単セルとした。本セルを実施例１とする。この単セルを恒温槽に入れ、アノードガスとして水素を、カソードガスとして空気を供給し、発電試験を行った。なお、アノードガス、カソードガスは温度調節可能なバブラーを通過させることで加湿し、電解質膜が乾燥することによるイオン伝導抵抗増加を防いだ。アノード及びカソードのガスライン出口にはそれぞれ圧力調整弁を設け、１００℃以上のセル温度にもガス加湿が行える構造とした。発電試験はセル温度１３０℃とし、アノードガス及びカソードガスの加湿温度も１３０℃に設定した。
（実施例２）
電解質膜マトリックス材料としてＪＳＲ社製のアートン^ＴＭ（比重１．０８、ガラス転移点温度１７１℃、熱伝導率０．１６ｋｃａｌ／ｍ・ｈｒ・℃）粉末８０ｇとトルエン２２０ｍｌをガラス製４つ口フラスコに添加し、窒素雰囲気下で攪拌し電解質膜マトリックス溶液ａを得た。溶液ａに３−イソシアネートプロピルトリエトキシシラン８ｇを添加し７５℃で窒素雰囲気下２４時間還流攪拌混合し溶液ｂを作製した。
ＰＯ［ＯＣＨ（ＣＨ_３）_２］_３−ｘ（ＯＨ）_ｘ１００ｇにイソプロパノール２００ｇ及びオルトケイ酸エチル（Ｓｉ（ＯＣ_２Ｈ_５）_４）５８ｇを加え、７０℃で窒素雰囲気下５時間攪拌し溶液ｇを作製した。溶液ｇに酸触媒として０．１Ｎ塩酸を添加し、溶液ｈとした。溶液ｈを１００℃で１０時間加熱した後、５００℃で２４時間更に熱処理を行い、リン酸系ガラスｉを得た。
ボールミルで５時間粉砕処理したリン酸系ガラスｉ２５ｇに溶液ｂ５０ｇ添加し、０．１Ｎ塩酸を加えて電解質溶液ｊを作製した。溶液ｊをテープキャスティング法により厚さ５０μｍのフィルムに展開し、大気中７５℃で１０時間乾燥させ電解質膜ｋを得た。
以降は実施例１と同様にして一体化電極ｌを作製し、小型セルに組み込み発電試験を行った。本セルを実施例２とした。
（比較例）
実施例１と同様に白金微細粒子をカーボン粒子に析出させた触媒２０ｇとナフィオン^ＴＭ５ｗｔ％溶液４００ｇを混練し触媒ペーストを作製した。メタノールを粘度調整用に添加しペースト粘度を５０ｃＰとした後、ナフィオン^ＴＭ１１７（デュポン社製）表面上にスクリーン印刷法で厚さ薄膜状に展開し触媒層を形成した。このとき、白金の使用量は塗布触媒面積１ｃｍ^２当たり０．３ｍｇとなるように展開量を調節した。窒素雰囲気下７５℃で１０時間乾燥させた後、反対面にも同様の手法で触媒層を作製し、一体化電極ｍとした。この一体化電極ｍに電極拡散層（ジャパンゴアテックス社製、ＣＡＲＢＥＬ−ＣＬ）、カーボン製セパレータを配置し単セルとした。本セルを比較例とした。比較例セルに加湿水素及び加湿空気を供給し、セル温度１３０℃にて発電試験を行った。
図２に実施例１、２及び比較例について電極面積１ｃｍ^２当たり０．５Ａの電流を流した時のセル電圧経時変化を示す。比較例１は、１３０℃の運転条件において数百時間経過後に電池電圧が減少した。これは高温条件下でかつ相対湿度が低いため電解質膜の水含有率が低下してプロトン伝導率が増加したためと考えられる。更に、パーフルオロカーボンスルホン酸系電解質膜は親水基がクラスター構造を形成してプロトンチャネルを確保する構造をとるが、高温条件下ではクラスター構造が維持できなくなるためにイオン伝導抵抗が増加したことも起因している。
これに対し、実施例１及び２では、発電試験を行った３０００時間において電池電圧の低下はほとんどみられなかった。実施例１及び２の電解質膜は膜基材及びイオン伝導体の耐熱性が優れるとともに材料相互が強固に結合されているためと考えられる。
図３は、１３０℃において供給ガスの相対湿度を変化させたときの実施例１、２及び比較例の伝導率を測定した結果を示す。伝導率は交流１ｋＨｚの４端子法で評価した。比較例の電解質膜は相対湿度が低い条件では伝導率が急激に低下した。これは、この膜が膜中に存在するプロトン供与基であるスルホン酸基に水分子が水和してはじめてプロトン伝導性を示すためである。よって、膜の含水率が下がる低相対湿度時はイオン伝導抵抗が増加するため、高温作動型電池の電解質膜としては不適といえる。
一方、実施例１は相対湿度４０％においても、そのイオン伝導抵抗は相対湿度１００％時とほとんど変化がなく、最も低い抵抗値からの増加割合は１０％以内であった。これはプロトン伝導体として用いたケイタングステン酸に水和の形で水分子が安定に存在するため、水和水を移動チャネルとしてプロトンが伝導することに起因している。
この傾向は実施例２についても同様であり、むしろ実施例１よりも伝導率の相対湿度依存性は小さくなった。これは、実施例２で用いたプロトン伝導体であるリン酸系ガラスがその表面及び内部に水や水酸基を吸着、包含しているためである。
本明細書中で引用した全ての刊行物、特許及び特許出願をそのまま参考として本明細書中にとり入れるものとする。
産業上の利用の可能性
本発明によれば、燃料電池の高温作動化が可能になり、電極触媒の耐ＣＯ被毒性向上、カソード反応の反応抵抗減少による性能向上、電池排熱を燃料改質部の熱源の一部に回収することによるシステム効率向上が可能となる。
【図面の簡単な説明】
図１は、本発明の固体高分子電解質型燃料電池を構成する電解質膜の構造概略図である。図２は、実施例１、２と比較例のセル電圧経時変化を示す図である。図３は、実施例１、２と比較例の供給ガスの相対湿度と抵抗を示す図である。Technical field
The present invention relates to a solid polymer electrolyte fuel cell capable of extracting energy from a fuel and an oxidant by utilizing an electrochemical reaction.
Background art
One of the features of a polymer electrolyte fuel cell (PEFC) is low-temperature operation.
As a realistic power supply system, a system in which hydrogen is produced by refining fossil fuel and power is generated by PEFC using the hydrogen is conceivable. However, in this system, by-products mainly composed of CO are contained in the reformed gas from hundreds of ppm to several%, and this CO is selected on the surface of the platinum catalyst, which is a reaction field of the electrochemical reaction of PEFC. Since the reaction is inhibited by adsorption (catalyst poisoning), there is a problem that the battery performance is reduced.
In order to reduce CO in the reformed gas, it is possible to reduce CO from a few ppm to several tens of ppm by providing a CO removing device for the purpose of performing selective oxidation or the like. There is a problem that hydrogen reacts during the selective oxidation and the efficiency is reduced.
The main component of the catalyst used in PEFC is platinum, but attempts have been made to improve the poisoning of CO by alloying with other metals. However, when power is continuously generated from a battery, performance degradation is currently unavoidable.
In particular, PEFC has a large polarization of the reduction reaction at the cathode. In order to improve the performance of PEFC, reduction of reaction polarization is a research topic.
As a means for solving these problems, it is effective to operate the battery at a high temperature. At about 80 ° C., which is the current operating temperature of PEFC, the CO tolerance is at the level of tens of ppm. For example, in a phosphoric acid fuel cell operating at about 200 ° C., the CO tolerance increases to a level of several percent.
In addition, as the temperature rises, the reaction rate of the chemical reaction also increases, so that the cathode reaction polarization is reduced and the battery voltage is expected to be improved.
Furthermore, since the exhaust heat temperature recovered from the PEFC body also rises with an increase in the operating temperature, the means of utilizing heat, which currently only has a hot water supply of 40 to 70 ° C., is replaced by an absorption refrigerator, which has high added value. It can be adapted to produce cold heat or to produce steam for use in fuel reforming. This makes it possible to improve overall system efficiency.
However, with the current configuration of PEFC, high-temperature operation was almost impossible. Currently used electrolyte membrane is Nafion of DuPont^TMHowever, the glass transition point was about 130 ° C., and continuous operation at high temperatures was difficult due to the material characteristics. In addition, in the currently used electrolyte membrane, the ionic conduction resistance increases as the water content decreases. Therefore, at 100 ° C. or higher where water boils, the internal resistance increases and the cell performance deteriorates. When the inside of the battery and the gas supply system are in a pressurized state, the water content of the electrolyte membrane is improved, but an auxiliary power to be supplied to a compressor or the like for pressurization is required, which also causes a problem of complicating the system. .
Further, the production process of the fluorine-based film is complicated, and the production equipment requires a large-scale one. Therefore, an inevitably manufactured electrolyte membrane is also expensive. Also, there is a problem that it cannot be easily incinerated because it contains fluorine even when discarded.
As an electrolyte membrane having heat resistance, for example, a phosphoric acid-impregnated polybenzimidazole (PBI) membrane is known (JT Wang, et al., Electrochim. Acta., 41, 193 (1996)). This film has a heat resistance of 150 ° C. or higher, and the material cost is relatively low as compared with Nafion. However, since phosphoric acid, which is a proton donor, is not fixed to the PBI substrate by a chemical bond, there is a problem that phosphoric acid is dissipated during long-term operation to increase ionic resistance.
Development of a proton conductive material by partially sulfonating polyetheretherketone (PEEK), which is a heat-resistant plastic, has also been conducted (USP 5,362,836). However, there are problems in that the material swells under operating conditions and has poor dimensional stability, and that the mechanical strength is weak.
Disclosure of the invention
The present invention includes the following inventions.
(1) A solid polymer electrolyte fuel cell using an amorphous polyolefin for the electrolyte membrane matrix.
(2) An electrode, an electrode diffusion layer for introducing gas, and a gas mixture are prevented from being mixed on both surfaces of an electrolyte membrane containing a matrix and a proton donor serving as a membrane base material. A solid polymer electrolyte fuel cell in which continuity is ensured and separators forming an outer shell of a unit cell are sequentially arranged, wherein the amorphous polyolefin is used for the electrolyte membrane matrix according to the above (1). Solid polymer electrolyte fuel cell.
(3) The above (2), wherein the proton donor of the electrolyte membrane and the matrix are bonded via an atomic group in which at least an oxygen atom is bonded to one atom selected from Si, Ti and Zr. Solid polymer electrolyte fuel cell.
(4) The solid polymer electrolyte fuel cell according to (3), wherein the proton donor is a polyacid.
(5) The solid polymer electrolyte fuel cell according to (4), wherein the polyacid contains at least one selected from the group consisting of W, Si, Sn, Zn, P, and Mo as a central ion.
(6) The solid polymer electrolyte fuel cell according to (3), wherein silicon oxide containing at least P is used as the proton donor.
The solid polymer electrolyte fuel cell of the present invention is characterized in that an amorphous polyolefin is used for a matrix serving as a base material of an electrolyte membrane. Here, the matrix is a main component of the electrolyte membrane, and a portion which is not included in proton conduction is collectively represented.
The material serving as the matrix of the electrolyte membrane is required to have acid resistance from the operating conditions of the battery in addition to heat resistance, and is also required to have stability of the material for a long operating time. In addition, when the electrolyte membrane is broken or cracked, hydrogen and oxygen present in the reaction gas directly react with each other, so that the base material has a certain degree of mechanical strength and flexibility even in a thinned state. There must be. As a material satisfying such conditions, an amorphous polyolefin is particularly suitable.
Here, the amorphous polyolefin refers to a polyolefin having a crystallinity C (%) of 0 or more and 7 or less. Here, C = dc · (d−dc) / (d · (dc−da)) (dc: density of crystal part, da: density of non-crystal part, d: density of sample). The amorphous polyolefin itself is a known material.
Examples of the amorphous polyolefin include a polymer having a cyclic structure described in JP-A-7-258504.
As the amorphous polyolefin having a cyclic structure, for example, the following formula:

[Wherein, m and n each independently represent an integer of 1 or more (preferably 1 to 100,000); R represents a hydrogen atom, a halogen atom or a substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms ( A represents, for example, an alkyl group, an alkoxyalkyl group, a halogenated alkyl group, an alkenyl group, an aryl group, an alkoxyaryl group, a halogenated aryl group, an aralkyl group, an alkoxyaralkyl group); A represents cyclopentadiene or a derivative thereof and norbornadiene or a derivative thereof; It represents an addition reaction product with a derivative or a hydrogenated product thereof, or an addition reaction product of dicyclopentadiene or a derivative thereof with ethylene. ]
The polymer shown by these is mentioned.
The hydrogenated product of the addition product of cyclopentadiene or its derivative and norbornadiene or its derivative, or the addition product of dicyclopentadiene or its derivative and ethylene is represented by the following formula:

[Wherein, n is an integer of 1 or more (preferably 1 to 10,000);¹~ R¹²Each independently represents a hydrogen atom, a halogen atom, or a hydrocarbon group having 1 to 20 carbon atoms (eg, an alkyl group, an alkenyl group, an aryl group, and an aralkyl group);¹And R², R⁵And R⁶, R⁹And R¹⁰, R¹¹And R¹²May jointly represent an alkylidene group having 1 to 20 carbon atoms,⁹~ R¹²May combine with each other to form a monocyclic or polycyclic ring. ]
Can be indicated by
Examples of the hydrogenated product of the addition product of cyclopentadiene or its derivative with norbornadiene or its derivative, or the addition product of dicyclopentadiene or its derivative with ethylene are, for example, tetracyclo-3-dodecene, 8-methyltetra Cyclo-3-dodecene, 8-ethyltetracyclo-3-dodecene, 8-propyltetracyclo-3-dodecene, 8-butyltetracyclo-3-dodecene, 8-isobutyltetracyclo-3-dodecene, 8-hexyltetra Cyclo-3-dodecene, 8-stearyltetracyclo-3-dodecene, 5,10-dimethyltetracyclo-3-dodecene, 2,10-dimethyltetracyclo-3-dodecene, 8,9-dimethyltetracyclo-3- Dodecene, 8-ethyl-9-methyltetracyclo- -Dodecene, 11,12-dimethyltetracyclo-3-dodecene, 2,7,9-trimethyltetracyclo-3-dodecene, 9-ethyl-2,7-dimethyltetracyclo-3-dodecene, 9-isobutyl-2 , 7-Dimethyltetracyclo-3-dodecene, 9,11,12-trimethyltetracyclo-3-dodecene, 9-ethyl-11,12-dimethyltetracyclo-3-dodecene, 9-isobutyl-11,12-dimethyl Tetracyclo-3-dodecene, 5,8,9,10-tetramethyltetracyclo-3-dodecene, 8-ethylidenetetracyclo-3-dodecene, 8-ethylidene-9-methyltetracyclo-3-dodecene, 8- Ethylidene-9-ethyltetracyclo-3-dodecene, 8-ethylidene-9-isopropyltetracyclo-3-do Sen, 8-ethylidene-9-butyltetracyclo-3-dodecene, 8-n-propylidenetetracyclo-3-dodecene, 8-n-propylidene-9-methyltetracyclo-3-dodecene, 8-n-propylidene -9-ethyltetracyclo-3-dodecene, 8-n-propylidene-9-isopropyltetracyclo-3-dodecene, 8-n-propylidene-9-butyltetracyclo-3-dodecene, 8-isopropylidenetetracyclo- 3-dodecene, 8-isopropylidene-9-methyltetracyclo-3-dodecene, 8-isopropylidene-9-ethyltetracyclo-3-dodecene, 8-isopropylidene-9-isopropyltetracyclo-3-dodecene, 8 -Isopropylidene-9-butyltetracyclo-3-dodecene, 8-chlorotetracy Clo-3-dodecene, 8-bromotetracyclo-3-dodecene, 8-fluorotetracyclo-3-dodecene, 8,9-dichlorotetracyclo-3-dodecene, hexacyclo-4-heptadecene, 12-methylhexacyclo- 4-heptadecene, 12-ethylhexacyclo-4-heptadecene, 12-isobutylhexacyclo-4-heptadecene, 1,6,10-trimethyl-12-isobutylhexacyclo-4-heptadecene, octacyclo-5-docosene, 15- Methyloctacyclo-5-docosene, 15-ethyloctacyclo-5-docosene, pentacyclo-4-hexadecene, 1,3-dimethylpentacyclo-4-hexadecene, 1,6-dimethylpentacyclo-4-hexadecene, 15, 16-dimethylpentacyclo-4-hexade Heptacyclo-5-eicosene, heptacyclo-5-heneicosene, pentacyclo-4-pentadecene, 1,3-dimethylpentacyclo-4-pentadecene, 1,6-dimethylpentacyclo-4-pentadecene, 14,15-dimethylpentane Cyclo-4-pentadecene, pentacyclo-4,10-pentadecadiene and the like can be mentioned.
Another example of the amorphous polyolefin is a copolymer of an addition reaction product of cyclopentadiene or a derivative thereof with norbornadiene or a derivative thereof, and at least one unsaturated monomer selected from ethylene, butadiene, and a styrene derivative. Coalescence. Examples of the styrene derivative include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, o-ethylstyrene, m -Ethylstyrene, p-ethylstyrene, p-methoxystyrene, p-chloroethylstyrene, p-methyl-α-methylstyrene and the like. These can be used in combination of two or more.
Further, as another example of the amorphous polyolefin having a cyclic structure, the following formula:

[Wherein, n represents 0 or an integer of 1 or more (preferably 1 to 10000), m represents an integer of 1 or more (preferably 1 to 10000), and R¹~ R⁴Each independently represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms (eg, an alkyl group, an alkenyl group, an aryl group, and an aralkyl group). ]
And a hydrogenated product of a ring-opened polymer composed of tetracyclo-3-dodecene or a derivative thereof and bicyclohept-2-ene or a derivative thereof.
Examples of the tetracyclo-3-dodecene or a derivative thereof include tetracyclo-3-dodecene, 5,10-dimethyltetracyclo-3-dodecene, 2,10-dimethyltetracyclo-3-dodecene, and 11,12-dimethyltetracyclo. -3-dodecene, 2,7,9-trimethyltetracyclo-3-dodecene, 9-ethyl-2,7-dimethyltetracyclo-3-dodecene, 9-isobutyl-2,7-dimethyltetracyclo-3-dodecene , 9,11,12-trimethyltetracyclo-3-dodecene, 9-ethyl-11,12-dimethyltetracyclo-3-dodecene, 9-isobutyl-11,12-dimethyltetracyclo-3-dodecene, 5,8 , 9,10-Tetramethyltetracyclo-3-dodecene, 8-methyltetracyclo-3-dodecene 8-ethyltetracyclo-3-dodecene, 8-propyltetracyclo-3-dodecene, 8-hexyltetracyclo-3-dodecene, 8-stearyltetracyclo-3-dodecene, 8,9-dimethyltetracyclo-3- Dodecene, 8-methyl-9-ethyltetracyclo-3-dodecene, 8-cyclohexyltetracyclo-3-dodecene, 8-isobutyltetracyclo-3-dodecene, 8-butyltetracyclo-3-dodecene, 8-ethylidenetetra Cyclo-3-dodecene, 8-ethylidene-9-methyltetracyclo-3-dodecene, 8-ethylidene-9-ethyltetracyclo-3-dodecene, 8-ethylidene-9-isopropyltetracyclo-3-dodecene, 8- Ethylidene-9-butyltetracyclo-3-dodecene, 8-n-propylidene Toracyclo-3-dodecene, 8-n-propylidene-9-methyltetracyclo-3-dodecene, 8-n-propylidene-9-ethyltetracyclo-3-dodecene, 8-n-propylidene-9-isopropyltetracyclo- 3-dodecene, 8-n-propylidene-9-butyltetracyclo-3-dodecene, 8-isopropylidenetetracyclo-3-dodecene, 8-isopropylidene-9-methyltetracyclo-3-dodecene, 8-isopropylidene -9-ethyltetracyclo-3-dodecene, 8-isopropylidene-9-isopropyltetracyclo-3-dodecene, 8-isopropylidene-9-butyltetracyclo-3-dodecene and the like.
Examples of the bicyclohept-2-ene or a derivative thereof include bicyclohept-2-ene, 6-methylbicyclohept-2-ene, 5,6-dimethylbicyclohept-2-ene, and 1-methylbicyclohept- 2-ene, 6-ethylbicyclohept-2-ene, 6-n-butylbicyclohept-2-ene, 6-isobutylbicyclohept-2-ene, 7-methylbicyclohept-2-ene and the like Is mentioned.
As the amorphous polyolefin, for example, a polymer having no cyclic structure described in JP-A-7-316222 can be used. Examples of such an amorphous polyolefin include polypropylene, propylene / ethylene copolymer, propylene / butene-1 copolymer, propylene / butene-1 / ethylene terpolymer, and propylene / hexene-1-octene- Terpolymer, propylene / hexene-1,4-methylpentene-1 terpolymer, and polybutene-1.
Among the above-mentioned amorphous polyolefins, a polymer polymerized using norbornene or a norbornene derivative is a material excellent in heat resistance, acid resistance, and workability especially among amorphous olefins, and also produces a low-cost film. It also has economical efficiency.
As the amorphous polyolefin used in the present invention, those having an average molecular weight of 50,000 to 300,000 by GPC measurement, a specific gravity of 1.1 or less, and a glass transition temperature (Tg) of 165 ° C. or more are preferable.
Examples of amorphous polyolefins include ARTON^TM(JSR), APOAPL^TM-6509T (Mitsui Chemicals), Ubetac^TMVarious products such as UT2780 (Ube Lexen Co., Ltd.) are commercially available, and these can be used.
The structure of the solid polymer electrolyte fuel cell of the present invention is not particularly limited, and for example, an electrode and an electrode diffusion layer for guiding gas are provided on both surfaces of a matrix serving as a membrane base material and an electrolyte membrane containing a proton donor. And a structure in which gas is prevented from being mixed, current collection in the electrode surface and conduction in the battery thickness direction are ensured, and separators forming the outer shell of the unit cell are sequentially arranged.
In order to keep the ionic conduction resistance of the electrolyte membrane low at a high temperature for a long period of time, it is necessary to prevent the dissipation of the electrolyte. From such a point, the proton donor of the electrolyte membrane and the matrix are bonded via at least an oxygen atom and one atom selected from Si, Ti and Zr, preferably via an atomic group bonded to Si. It is preferable to use a solid electrolyte membrane. As a result, the ion-exchange groups are firmly fixed to the matrix, so that the phenomenon in which the ion-exchange groups are released from the membrane over time and the resistance of the membrane increases can be significantly suppressed, and a longer life can be realized.
When an inorganic substance and an organic substance are bound by a chemical bond as described above, the use of a silane coupling agent is effective from the viewpoint of simplicity of synthesis and economy of reagents. In particular, when 3-isocyanatopropyltriethoxysilane is used, it is effective in heat resistance of the electrolyte membrane, stability in a battery environment, and suppression of ionic conductor dissipation, but is not limited thereto.
A proton donor that imparts ionic conductivity to an electrolyte membrane is also required to have heat resistance, like the matrix. Furthermore, since water has a boiling point of 100 ° C. at normal pressure, the entire atmosphere must be in a pressurized atmosphere in order to keep the membrane moist at a higher temperature. From such a point, as the proton donor, it is preferable to use a metal oxide having proton conductivity, and it is preferable to use a polyacid as a material that shows good proton conductivity and does not deteriorate in ionic conductivity even at a high temperature. More preferred.
The polyacid preferably contains at least one selected from the group consisting of W, Si, Sn, Zn, P and Mo as a central ion.
As the polyacid, not only an isopolyacid but also a heteropolyacid containing two or more kinds of central ions can be used. Examples of the isopolyacid include isopolytungstic acid hydrate, isopolymolybdic acid hydrate, tin oxide hydrate (SnO₂・ NH₂O), and examples of the heteropolyacid include silicotungstic acid hydrate.
Since these polyacids retain water molecules in the form of water of hydration on the material itself or adsorb it on the surface of the material, sufficient ionic conductivity can be ensured even at low relative humidity under high temperature conditions. . That is, even at an operating temperature of 100 ° C. or higher, it is not necessary to raise the battery environment to the saturated steam pressure at that temperature, so that less energy is consumed by a trap such as a compressor than in the past, and the system efficiency is improved accordingly. I can expect.
By using these proton conductive materials, the resistance is low even under high temperature conditions, and the amount of water vapor for wetting the electrolyte membrane can be kept low. This is because a proton conduction path can be secured even in an environment where the relative humidity is low because water molecules are held in the form of water of hydration in the material itself or adsorbed on the surface of the material. As a result, the operating pressure of the battery can be set low, which is effective for simplifying the system configuration.
As the metal oxide having proton conductivity used as a proton donor, silicon oxide containing at least P can also be used. In particular, phosphate-based glass having high heat resistance (for example, xP₂O₅・ YSiO₂, XP₂O₅・ YZrO₂・ ZSiO₂(Where x, y and z represent arbitrary numbers), more specifically 5P₂O₅・ 5ZrO₂・ 90SiO₂And the like. ) Can further improve the high-temperature stability as an electrolyte membrane. At this time, the phosphate glass preferably has a porous structure in order to increase the amount of adsorbed water and adsorbed hydroxyl groups serving as proton conduction paths and the amount of water contained therein.
FIG. 1 shows a typical structure of an electrolyte membrane constituting the solid polymer electrolyte fuel cell of the present invention. Substituent R in amorphous polyolefin main chain₁, R₂Are combined. Where R₁, R₂Are each
-R₁₁-SiR₁₂-OR_Thirteen-P₁
-R₂₁-SiR₂₂-OR₂₃-P₂
Or a hydrogen atom. Where R₁And R₂Are not hydrogen atoms. R_1X, R_2XIs an atomic group composed of organic material, P_XIs a proton donor. R_1X, R_2XMay be omitted.
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described with reference to Examples and Comparative Examples.
(Example 1)
Arton manufactured by JSR as an electrolyte membrane matrix material^TM(Specific gravity: 1.08, glass transition temperature: 171 ° C., thermal conductivity: 0.16 kcal / m · hr · ° C.) 80 g of powder and 220 ml of toluene are added to a glass four-necked flask, and the mixture is stirred under a nitrogen atmosphere and the electrolyte membrane is stirred. A matrix solution a was obtained. 8 g of 3-isocyanatopropyltriethoxysilane was added to solution a, and the mixture was refluxed and mixed at 75 ° C. under a nitrogen atmosphere for 24 hours to prepare solution b.
A solution c prepared by dissolving 16 g of silicotungstic acid hydrate (manufactured by Kanto Kagaku Co., Ltd.) in 30 ml of methanol was added to the solution b and stirred to prepare an electrolyte solution c ′. And dried in air at 75 ° C. for 10 hours to obtain an electrolyte membrane d. Even when the present electrolyte membrane was left in a boiling aqueous solution, no change was observed in the proton concentration of the solution. This is because silicotungstic acid, which is an ion exchange group, is chemically fixed to the matrix by coupling.
A catalyst paste e was prepared by mixing 2.5 g of a catalyst in which platinum fine particles were precipitated on carbon powder and 90 g of an electrolyte solution c '. The catalyst paste e was spread on the surface of the electrolyte membrane d in a square thin film having a side of 10 cm by screen printing to form a catalyst layer. At this time, the amount of platinum used was 1 cm of the coated catalyst area.²The amount of development, that is, the thickness of the catalyst layer, was adjusted so as to be 0.3 mg per unit. The catalyst layer was applied on both sides of the electrolyte membrane d, and after the application, a drying treatment was performed at 75 ° C. for 10 hours in a nitrogen atmosphere. This treatment has the meaning of dispersing the solvent in the catalyst layer and promoting the gelling reaction of the electrolyte membrane substrate in the catalyst layer. 100cm area by the above method²An electrolyte membrane having a catalyst layer formed on the front and back surfaces, that is, a so-called integrated electrode f was obtained.
An electrode diffusion layer (CARBEL-CL, manufactured by Japan Gore-Tex Co.) is also disposed on both sides of the catalyst surface of the integrated electrode f, and a single cell for a combination test is formed with a carbon separator having a gas flow path. did. This cell is referred to as a first embodiment. This single cell was placed in a thermostat, and hydrogen was supplied as an anode gas and air was supplied as a cathode gas, and a power generation test was performed. The anode gas and the cathode gas were humidified by passing through a temperature-adjustable bubbler to prevent an increase in ion conduction resistance due to drying of the electrolyte membrane. Pressure adjusting valves were provided at the gas line outlets of the anode and the cathode, respectively, so that gas humidification was possible even at a cell temperature of 100 ° C. or more. In the power generation test, the cell temperature was set to 130 ° C., and the humidifying temperatures of the anode gas and the cathode gas were also set to 130 ° C.
(Example 2)
Arton manufactured by JSR as an electrolyte membrane matrix material^TM(Specific gravity: 1.08, glass transition temperature: 171 ° C., thermal conductivity: 0.16 kcal / m · hr · ° C.) 80 g of powder and 220 ml of toluene are added to a glass four-necked flask, and the mixture is stirred under a nitrogen atmosphere and the electrolyte membrane is stirred. A matrix solution a was obtained. 8 g of 3-isocyanatopropyltriethoxysilane was added to solution a, and the mixture was refluxed and mixed at 75 ° C. under a nitrogen atmosphere for 24 hours to prepare solution b.
PO [OCH (CH₃)₂]_3-x(OH)_x100 g of isopropanol and ethyl orthosilicate (Si (OC₂H₅)₄) 58 g was added, and the mixture was stirred at 70 ° C under a nitrogen atmosphere for 5 hours to prepare a solution g. To the solution g, 0.1N hydrochloric acid was added as an acid catalyst to obtain a solution h. After the solution h was heated at 100 ° C. for 10 hours, it was further heat-treated at 500 ° C. for 24 hours to obtain a phosphate glass i.
50 g of solution b was added to 25 g of phosphoric acid-based glass i which had been pulverized by a ball mill for 5 hours, and 0.1 N hydrochloric acid was added to prepare an electrolyte solution j. The solution j was spread on a film having a thickness of 50 μm by a tape casting method, and dried at 75 ° C. in the air for 10 hours to obtain an electrolyte membrane k.
Thereafter, an integrated electrode 1 was prepared in the same manner as in Example 1, and was assembled in a small cell to perform a power generation test. This cell was designated as Example 2.
(Comparative example)
20 g of a catalyst in which fine platinum particles were deposited on carbon particles in the same manner as in Example 1 and Nafion^TM400 g of a 5 wt% solution was kneaded to prepare a catalyst paste. After adding methanol for viscosity adjustment to make the paste viscosity 50 cP, Nafion^TM117 (manufactured by DuPont) was developed into a thin film by screen printing to form a catalyst layer. At this time, the amount of platinum used was 1 cm²The amount of development was adjusted to 0.3 mg per unit. After drying at 75 ° C. for 10 hours in a nitrogen atmosphere, a catalyst layer was formed on the opposite surface in the same manner as above to obtain an integrated electrode m. An electrode diffusion layer (CARBEL-CL, manufactured by Japan Gore-Tex Corporation) and a carbon separator were arranged on the integrated electrode m to form a single cell. This cell was used as a comparative example. Humidified hydrogen and humidified air were supplied to the comparative example cell, and a power generation test was performed at a cell temperature of 130 ° C.
FIG. 2 shows an electrode area of 1 cm for Examples 1 and 2 and Comparative Example.²5 shows the change over time in the cell voltage when a current of 0.5 A flows per unit cell. In Comparative Example 1, the battery voltage decreased after several hundred hours under the operating condition of 130 ° C. This is presumably because the water content of the electrolyte membrane was reduced due to the low relative humidity under high temperature conditions and the proton conductivity was increased. Furthermore, the perfluorocarbon sulfonic acid-based electrolyte membrane has a structure in which the hydrophilic group forms a cluster structure to secure the proton channel. However, the ion conduction resistance increases because the cluster structure cannot be maintained under high temperature conditions. are doing.
On the other hand, in Examples 1 and 2, there was almost no decrease in the battery voltage at 3000 hours when the power generation test was performed. It is considered that the electrolyte membranes of Examples 1 and 2 have excellent heat resistance of the membrane substrate and the ionic conductor, and that the materials are firmly bonded to each other.
FIG. 3 shows the results of measuring the conductivity of Examples 1, 2 and Comparative Example when the relative humidity of the supply gas was changed at 130 ° C. The conductivity was evaluated by an AC 1 kHz four-terminal method. The conductivity of the electrolyte membrane of the comparative example sharply decreased under the condition of low relative humidity. This is because this membrane shows proton conductivity only when water molecules are hydrated to sulfonic acid groups which are proton donating groups present in the membrane. Therefore, at low relative humidity where the water content of the membrane decreases, the ionic conduction resistance increases, and it can be said that the membrane is not suitable as an electrolyte membrane for a high-temperature operated battery.
On the other hand, in Example 1, even at a relative humidity of 40%, the ionic conduction resistance hardly changed from that at a relative humidity of 100%, and the rate of increase from the lowest resistance value was within 10%. This is due to the fact that water molecules are stably present in the form of hydration in the silicotungstic acid used as the proton conductor, so that protons are conducted using the water of hydration as a transfer channel.
This tendency was the same for Example 2, and the relative humidity dependency of the conductivity was smaller than that of Example 1. This is because the phosphate glass used as the proton conductor used in Example 2 adsorbs and contains water and hydroxyl groups on its surface and inside.
All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety.
Industrial potential
According to the present invention, it is possible to operate a fuel cell at a high temperature, improve resistance to CO poisoning of an electrode catalyst, improve performance by reducing a reaction resistance of a cathode reaction, and use exhaust heat of a cell as a part of a heat source of a fuel reformer. The system efficiency can be improved by collection.
[Brief description of the drawings]
FIG. 1 is a schematic structural diagram of an electrolyte membrane constituting a solid polymer electrolyte fuel cell of the present invention. FIG. 2 is a diagram showing changes over time in cell voltages of Examples 1 and 2 and Comparative Example. FIG. 3 is a diagram showing relative humidity and resistance of supply gas of Examples 1 and 2 and Comparative Example.

Claims (6)

A polymer electrolyte fuel cell using an amorphous polyolefin as the electrolyte membrane matrix. Electrodes, an electrode diffusion layer for conducting gas, and gas mixing are prevented on both sides of the electrolyte membrane containing the matrix and proton donor serving as the membrane base material, thereby ensuring current collection in the electrode surface and conduction in the battery thickness direction. A solid polymer electrolyte fuel cell in which separators forming an outer shell of a unit cell are sequentially arranged, wherein the amorphous polyolefin is used for the electrolyte membrane matrix. Polymer electrolyte fuel cell. 3. The solid according to claim 2, wherein the proton donor of the electrolyte membrane and the matrix are bonded via an atomic group in which at least an oxygen atom and one atom selected from Si, Ti and Zr are bonded. Polymer electrolyte fuel cell. 4. The solid polymer electrolyte fuel cell according to claim 3, wherein said proton donor is a polyacid. 5. The solid polymer electrolyte fuel cell according to claim 4, wherein the polyacid contains at least one selected from the group consisting of W, Si, Sn, Zn, P and Mo as a central ion. 4. The solid polymer electrolyte fuel cell according to claim 3, wherein silicon oxide containing at least P is used as said proton donor.

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