JP2004281072A - Fuel cell power generation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell power generation device having high volume efficiency and capable of providing high output. <P>SOLUTION: This fuel cell power generation device is equipped with a plurality of cells. Each cell is characterized by including: a unit stack part 16 composed by stacking a plurality of unit power generation parts each including an anode electrode 4, a cathode electrode 7 and an electrolyte film 8; and a heat insulation layer 39 used for covering a surface of the stack part 16 and having heat conductivity ≤ 0.1 (W/m/K); and by satisfying the following formula (1): 20≤P/S≤31 (1), wherein P is the output (mW) of each cell; and S is the surface area (cm<SP>2</SP>) of the unit stack part 16 of each cell. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３３】
例えば、直接型メタノール燃料電池によってパソコンを駆動する場合には、必要な出力２０〜３０Ｗの電力に対して６０〜９０Ｗの発熱量が生じてしまうことになり、これらの熱を外部に放熱する必要がでてくる。図８に、放熱量とそれに必要な放熱フィン及びファンの容積の関係を表す図を示す。２０〜３０Ｗの発電を行なった際の放熱量は、前述した（５）式から６０〜９０Ｗ程度であるため、２０〜３０Ｗの発電を行なった際には、１５０〜２５０ｍＬの容積をもつ放熱機構が必要となることが図８から理解できる。その結果、直接型メタノール燃料電池発電装置全体の容積が著しく大きくなるため、応用上問題を生じてしまう。特に、放熱機構の容積を小さくすることは、直接型メタノール燃料電池の小型化を行なう上で重要である。
【００３４】
以上述べた様に、直接型メタノール燃料電池の高出力化を行なうと、スタック部から生じる発熱量も増大し、単位発電部の発電に最適な６０℃〜８０℃の間に、スタック部の温度を維持することができなくなるという問題を生じてしまう。そのため、スタック部の作製には、出力的観点からだけでなく熱的観点にも立った設計を行なう必要がある。
【００３５】
本発明に係る第１の燃料電池発電装置は、複数の単位電池を備えた燃料電池発電装置であって、
各単位電池は、
アノード電極と、カソード電極と、前記アノード電極及び前記カソード電極の間に配置される電解質膜とを含む複数の単位発電部を積層した単位スタック部と、
前記単位スタック部の表面を被覆する熱伝導率が０．１（Ｗ／ｍ／Ｋ）以下の断熱層とを含み、かつ下記（１）式を満足することを特徴とする。
【００３６】
２０≦Ｐ／Ｓ≦３１ （１）
但し、Ｐは各単位電池の出力（ｍＷ）で、Ｓは各単位電池の単位スタック部の表面積（ｃｍ^２）である。
【００３７】
ここで、単位スタック部は、複数の単位発電部を縦もしくは横に積層したものであることが望ましく、図１及び図２に示す構造を有するものが例示される。単位発電部を縦に積層すると、単位発電部が直列に接続され、また、単位発電部を横に積層すると、単位発電部が並列に接続される。本発明においては、このような構成を有する複数の単位電池を直列接続、並列接続、あるいは直列接続と並列接続とを組合わせて組電池として使用することができる。
【００３８】
（Ｐ／Ｓ）を前述した（１）式に限定する理由について説明する。Ｐは、各単位電池の定格出力密度と電極面積（アノード電極とカソード電極との反応面積）との積である。また、Ｓは、各単位スタック部の占有体積と等しい大きさの直方体の表面積である。（Ｐ／Ｓ）を２０ｍＷ／ｃｍ^２未満にすると、発電に伴う自己発熱量が不足するため、自己発熱により単位スタック部の温度を６０℃以上に維持することが困難になる。一方、（Ｐ／Ｓ）が３１ｍＷ／ｃｍ^２を超えると、発電時の発熱量が多くなるため、単位スタック部の温度が８０℃を超え、高起電力を得られない恐れがある。
【００３９】
熱伝導率が０．１（Ｗ／ｍ／Ｋ）以下の断熱層は、例えば、空気のような１０^−１〜１０^−２（Ｗ／ｍ／Ｋ）程度の熱伝導率を有する気泡分散材、マイクロサーモのような１０^−２〜１０^−４（Ｗ／ｍ／Ｋ）程度の熱伝導率を有する粉末質断熱材等から形成することができる。また、この断熱層は、真空断熱により形成することも可能である。さらに、断熱層の熱伝導率が低いほど、断熱層の厚さを薄くすることができるため、燃料電池発電装置の小型化を促進することができる。
【００４０】
熱伝導率が０．１（Ｗ／ｍ／Ｋ）以下の断熱層の厚さは、例えば空気の場合には、０．１〜２ｍｍの範囲内にすることが望ましい。これは以下に説明する理由によるものである。断熱層の厚さを０．１ｍｍ未満にすると、他の単位電池から受ける熱的影響が大きくなるため、単位スタック部の温度むらが大きくなる恐れがある。断熱層の厚さが２ｍｍを超えると、燃料電池発電装置の体積効率が低くなる恐れがある。
【００４１】
本発明において、単位スタック部を断熱層で被覆する第１の理由は、単位スタック部における温度分布を一様にするためである。特に、直接型メタノール燃料電池のセパレータ材料としては、金属やカーボンなど熱伝導率の高い材料を用いるので、熱伝導率が低い断熱層で表面を薄く覆うだけで、十分な効果があると考えられる。また、単位電池間の熱的影響を小さくする点、さらには、直接型メタノール燃料電池の立ち上げ時に、すみやかに単位発電部の温度を６０℃〜８０℃の範囲に上昇させるという観点からも有効である。
【００４２】
本発明に関わる燃料電池発電装置における式（１）を導出するための原理を説明する。
【００４３】
単位電池からの発熱量は、前述した（５）式で与えられる。それに対して、単位スタック部表面からの放熱量Ｑ′は、単位スタック部の表面積をＳとすると、下記（６）式で表される。
【００４４】
【数２】

【００４５】
ここで、ａは熱伝導率（＝１０Ｗ／Ｋ／ｍ^２）で、σはシュテファン・ボルツマン係数（５．６７×１０^−８Ｗ／ｍ^２／Ｋ^４）で、εは輻射率（＝０．７）で、Ｔ_０ は室温（＝３００Ｋ）である。熱伝導率としては、通常、５〜１０（Ｗ／Ｋ／ｍ^２）の値を用いるが、直接型メタノール燃料電池のセパレータに金属やカーボンなど熱伝導率の高い材料を用いる点と本発明の計算では輻射熱を考慮している点という２点から、熱伝導率ａ＝１０（Ｗ／Ｋ／ｍ^２）を用いた。また、セパレータにカーボン材料を用いると、輻射率は０．９程度、金属を用いると０．５程度になると考えられるが、計算結果を大きく変更しないので、平均値である０．７を用いた。これらの値を代入すると、単位電池の到達する温度６０℃〜８０℃の範囲で、αは６．０×１０〜９．２×１０ｍＷ／ｃｍ^２ と計算される。よって、単位電池が自己発熱により６０℃〜８０℃の範囲に到達するための条件は、式（５）及び式（６）より以下の（７）式で与えられる。
【００４６】
２０ｍＷ／ｃｍ^２≦Ｐ／Ｓ≦３１ｍＷ／ｃｍ^２ （７）
すなわち、前述した（１）式が得られた。式（１）に従い、単位電池の設計を行なえば、自己発熱により単位スタック部の温度を６０℃〜８０℃の範囲内に維持することができ、スタック部の放熱や断熱を行なうための機構を少なくすることができ、直接型メタノール電池全体の容積の小型化が可能となる。即ち、直接型メタノール燃料電池発電装置の携帯機器用途応用上、非常に有用である。
【００４７】
式（１）及び式（７）の正当性を確めるために、１Ｗの直接型メタノール燃料電池発電装置に関して、単位スタック部の放熱や断熱に必要な機構の容積を見積もった計算結果を示す。図９に示すように、単位スタック部における単位発電部１の積層数を４とし、シール幅Ｌを５ｍｍ、セパレータ９の高さ（電極部込み）Ｈを２．５ｍｍとした。例えば、電極から得られる出力密度を５０ｍＷ／ｃｍ^２ とすれば電極幅Ｘは２．２４ｃｍとなり、単位スタック部の表面積Ｓは３４ｃｍ^２ となる。この単位スタック部が７０℃になるために必要な断熱・放熱機構の容積を見積もった。図９に示すように、単位スタック部の表面には、断熱機構として空気層３９を形成し、この空気層３９の容積を断熱機構の容積とした。なお、空気の熱伝導率は、２．６×１０^−２（Ｗ／ｍ／Ｋ）である。一方、単位スタック部の放熱機構に関しては、前述した図８から、単位スタック部を７０℃まで冷却するのに必要な放熱フィン及びファンの容積を見積もった。図１０に、縦軸に断熱機構と放熱機構に必要な合計容積、横軸にＰ／Ｓをとってプロットした結果を示す。各線は、単位発電部から得られる出力密度を変化させた時の計算結果である。この図からも分かる様に、単位発電部の出力密度に関わらず、Ｐ／Ｓ＝２３．８４において、断熱及び放熱に必要な補器系が最も小型化することが分かる。次に、単位発電部における出力密度が５０ｍＷ／ｃｍ^２ の時に、６０℃〜８０℃の範囲において、断熱及び放熱に必要な補器の容積がどの様に変化するか計算した結果を、図１１に示す。６０℃〜８０℃の温度範囲において、容積が最小となるＰ／Ｓが式（７）の範囲で変化していることが示された。よって、前述した（１）式の正当性が確認された。
【００４８】
ここで、本発明の計算では、単位スタック部の温度が一様に上昇するという仮定の下で計算を行なっている。しかしながら、金属やカーボンなど熱伝導率の高い材料をセパレータを用いたとしても、実際には、単位スタック部の表面よりも内部の方が温度が高くなる傾向がある。そこで、本発明にある様に、単位スタック部の表面を断熱層で被覆すれば、単位スタック部の温度を一様にする上で効果的である。また、上記計算からも示された様に、（Ｐ／Ｓ）が本発明の範囲にあれば、スタック部を６０℃〜８０℃へ上昇させるために、断熱層以外の他の断熱機構を必要としない。よって、本発明において、単位スタック部表面を覆う断熱層は、電池全体の小型化という観点からも、できる限り熱伝導率の低い材料を薄く覆った方が良い。例えば、最も熱伝導率の低い空気を、０．５ｍｍ程度の厚みで覆う場合が挙げられる。この程度の断熱を行なった場合でも、セパレータとの熱伝導率が大きく異なるために、スタック内部の温度を一様にするという観点では効果的である。一方、熱伝導率としては、セパレータに対して十分無視できるので、熱伝導率としてａ＝１０（Ｗ／Ｋ／ｍ^２）を用いたとしても、計算結果を変更させることはない。
【００４９】
以上説明した本発明に係る第１の燃料電池発電装置によれば、前述した（１）式を満足する単位スタック部の表面を熱伝導率が０．１（Ｗ／ｍ／Ｋ）以下の断熱層で被覆しているため、発電時の発熱により単位スタック部の温度を６０℃〜８０℃の範囲内に維持することができる。その結果、前述した図１０、図１１に示すように、断熱・放熱に要する機構の容積を小さくすることができるため、燃料電池発電装置の小型化を図ることができる。
【００５０】
また、単位電池間の熱的干渉を少なくすることができるため、単位電池の温度分布を均一にすることができる。その結果、単位電池を構成する単位発電部間の出力特性のばらつきを小さくすることができるため、一部の単位発電部に転極が生じるのを回避することができ、高電圧を得ることができる。
【００５１】
従って、本発明によれば、体積効率に優れ、かつ高出力な燃料電池発電装置を実現することができる。
【００５２】
また、本発明に係る第２の燃料電池発電装置は、複数の単位電池を備えた燃料電池発電装置であって、
各単位電池は、
アノード電極と、カソード電極と、前記アノード電極及び前記カソード電極の間に配置される電解質膜とを含む複数の単位発電部を積層した単位スタック部と、
前記単位スタック部の表面を前記表面との間に隙間を開けて囲む断熱板とを含み、かつ前述した（１）式を満足することを特徴とするものである。
【００５３】
断熱板としては、例えば、アクリル板を挙げることができる。また、単位スタック部を断熱板で囲む手法としては、例えば、断熱板で形成された容器内に単位スタック部を収納する、断熱板で形成された容器内を断熱板で仕切り、仕切られた空間内に単位スタック部を収納する等を挙げることができる。
【００５４】
断熱板と単位スタック部との間に形成された隙間（空気層）は、断熱層として機能することができる。この隙間の大きさは、前述した第１の燃料電池発電装置で説明したのと同様な理由により０．１〜２ｍｍの範囲内にすることが望ましい。
【００５５】
以上説明した本発明に係る第２の燃料電池発電装置によれば、前述した（１）式を満足する単位スタック部を単位スタック部との間に隙間を開けて断熱板で囲んでいるため、発電時の発熱により単位スタック部の温度を６０℃〜８０℃の範囲内に維持することができる。その結果、前述した図１０、図１１に示すように、断熱・放熱に要する機構の容積を小さくすることができるため、燃料電池発電装置の小型化を図ることができる。
【００５６】
また、単位電池間の熱的干渉を少なくすることができるため、単位電池の温度分布を均一にすることができる。その結果、単位電池を構成する単位発電部間の出力特性のばらつきを小さくすることができるため、一部の単位発電部に転極が生じるのを回避することができ、高電圧を得ることができる。
【００５７】
【実施例】
以下、本発明の実施例を図面を参照して詳細に説明する。
【００５８】
（実施例１）
＜５Ｗ直接型メタノール燃料電池スタック部の設計＞
まず最初に単位発電部を作成し、電流電圧特性の測定を行なった。そして、次に、この実験結果に基づき、５Ｗ直接型メタノール燃料電池スタック部の設計を行なった。
【００５９】
＜直接型メタノール燃料電池の触媒層・電解質接合体の作製＞
公知のプロセス（Ｒ．Ｒａｍａｋｕｍａｒ ｅｔ ａｌ．Ｊ．Ｐｏｗｅｒ Ｓｏｕｒｃｅｓ ６９（１９９７）７５）により、アノード用触媒（Ｐｔ：Ｒｕ＝１：１）担持カーボンブラックとカソード用触媒（Ｐｔ）担持カーボンブラックを作製した。触媒担持量は、カーボン１００に対して重量比でアノードは３０、カソードは１５とした。前記プロセスにおいて作製したアノード用触媒担持カーボンブラックにパーフルオロカーボンスルホン酸溶液（Ｄｕｐｏｎｔ社Ｎａｆｉｏｎ溶液ＳＥ−２００９２）とイオン交換水を添加し、前記触媒担持カーボンブラックを分散させてペーストを調製した。アノード拡散層としての撥水処理済カーボンペーパー（Ｅ−ＴＥＫ社製の商品名がＴＧＰＨ−１２０）の上にペーストを５５０μｍ塗布し、乾燥させ、アノード触媒層を形成することによりアノード電極を得た。前記プロセスにおいて作製したカソード用触媒担持カーボンブラックにパーフルオロカーボンスルホン酸溶液（Ｄｕｐｏｎｔ社Ｎａｆｉｏｎ溶液ＳＥ−２００９２）とイオン交換水を加え、前記触媒担持カーボンブラックを分散させてペーストを調製した。カソード集電体としての撥水処理済カーボンペーパー（Ｅ−ＴＥＫ社製の商品名がＴＧＰＨ−０９０）の上にペーストを２２５μｍ塗布した後、乾燥させ、カソード触媒層を形成することにより、カソード電極を得た。アノード電極のアノード触媒層とカソード電極のカソード触媒層の間に、電解質膜としての市販のパーフルオロカーボンスルホン酸膜（Ｄｕｐｏｎｔ社Ｎａｆｉｏｎ１１７）を配置し、これらにホットプレス（１２５℃、５分間、５０ｋｇ／ｃｍ^２）を施すことにより、アノード電極、電解質膜及びカソード電極を接合し、触媒層・電解質接合体を得た。接合体中のアノード触媒層の断面積は、１０ｃｍ^２ であった。また、接合体を切断し、断面積を電子顕微鏡で観察したところ、アノード触媒層の厚さは１０５μｍで、カソード触媒層の厚さは５０μｍであった。また、この電子顕微鏡観察により、アノード電極と電解質膜とカソード電極との接合状態が良好であることを確認することができた。
【００６０】
＜単位発電部評価用セルの作製＞
作製した触媒層・電解質接合体をカーボン製のセパレータに装着し、ネジで締め付けることにより密閉した。セパレータにはシリコンラバーヒーターが装着されており、市販の温度コントローラーを用いて、ホルダー内部の温度制御が可能となる様にした。ところで、アノード電極側に位置するセパレータには、前述した図４に示すような形状のアノード流路が形成されている。アノード流路のメタノール供給口に供給チューブを接続すると共に、アノード流路のメタノール排出口に排出チューブを接続した。メタノール水溶液容器（容積１０ｍＬ）にメタノール水溶液を収容し、市販の送液ポンプを用いて送液し、供給チューブ及び供給口を通してアノード流路に供給した。アノード拡散層であるアノードカーボンペーパーに浸み込まなかったメタノール水溶液をメタノール排出口を通して排出チューブから排出した。
【００６１】
一方、カソード電極側に位置するセパレータにも、アノード流路と同様な形状のカソード流路が形成されている。カソード流路の酸化剤供給口に供給チューブを接続すると共に、カソード流路の酸化剤排出口に排出チューブを接続した。市販のエアーポンプを用いて空気を送気し、供給チューブ及び供給口を通してカソード流路に供給した。空気の流量は、市販のマスフローコントローラーを用いて調整した。送液は０．６ｍＬ／ｍｉｎ〜６ｍＬ／ｍｉｎまでの範囲で調整可能であり、送気は２０ｍＬ／ｍｉｎ〜５Ｌ／ｍｉｎの範囲で調整可能であることを確認した。また、市販の電子負荷機を用いて、負荷を調整した。さらに、電圧検出手段には、市販のデジタルマルチメーターを用いた。
【００６２】
＜電流電圧特性の測定＞
前記メタノール水溶液容器中のメタノール水溶液として、メタノール濃度２Ｍのものを用意し、０．６ｍＬ／ｍｉｎで送液を行った。また、送気量は１００ｍＬ／ｍｉｎとし、温度は５０℃、７０℃、９０℃に関して実験を行なった。測定した電流電圧特性の結果を図１２に示す。図１２からも分かる様に、７０℃の場合が最も高い出力密度が得られ、負荷電流密度１７０（ｍＡ／ｃｍ^２）において、最大出力密度５０（ｍＡ／ｃｍ^２）が得られることが分かった。しかし、それよりも電流密度を増大させると急激な電圧降下が起きるために出力密度の低下が起き、安定した出力が得られないことが分かった。これは、負荷電流に対してメタノール水溶液の供給量が追いつかず、燃料不足の状態になるためと推察される。そこで、安定して出力の得られる１００（ｍＡ／ｃｍ^２）、０．４１Ｖを単位発電部の定格出力として、５Ｗ直接型メタノール燃料電池スタック部の設計を行なうこととした。
【００６３】
＜５Ｗ直接型メタノール燃料電池の単位スタック部の設計＞
まず、シール幅Ｌが５ｍｍで、セパレータの高さＨ（電極部込み）が２．５ｍｍの単位発電部を用いて、単位発電部の積層数が４で、出力Ｐが１Ｗの断熱層未形成の単位電池（実施例１）と、単位発電部の積層数が２０で、出力Ｐが５Ｗの断熱層未形成の単位電池（比較例１）とを用意した。図１３に、実施例１の単位電池と比較例１の単位電池について、Ｐ／Ｓ（ｍＷ／ｃｍ^２）と単位スタック部を構成する単位発電部の出力密度ｐ（ｍＷ／ｃｍ^２）との関係を示す。なお、図１３では、単位発電部の電極面積を変更することにより単位スタック部の表面積Ｓを変え、（Ｐ／Ｓ）を変更した。
【００６４】
また、（Ｐ／Ｓ）が２０〜３１（ｍＷ／ｃｍ^２）の範囲を一点鎖線に囲まれた範囲として示した。実施例１の単位電池によれば、（Ｐ／Ｓ）が２０〜３１（ｍＷ／ｃｍ^２）の範囲において、単位発電部からの出力密度が４０（ｍＷ／ｃｍ^２）となる。一方、比較例１の単位電池によると、（Ｐ／Ｓ）が２０〜３１（ｍＷ／ｃｍ^２）の範囲における単位発電部での出力密度が２０（ｍＷ／ｃｍ^２）より小さくなるばかりか、単位発電部において出力密度４０（ｍＷ／ｃｍ^２）の発電を行なえば、発熱量が過剰となり、スタック部の温度が８０℃を超えてしまうことが予想される。
【００６５】
そこで、単位発電部１を縦方向に４個スタックしたスタック部を単位スタック部１６とし、それを５個直列に接続することによって５Ｗスタックを作製した。そして、単位スタック部１６それぞれの全体を厚さが０．３ｍｍのアクリル板４０で囲み、単位スタック部１６とアクリル板４０の間に断熱層３９として厚さが０．２ｍｍの空気層（熱伝導率が２．６×１０^−２（Ｗ／ｍ／Ｋ））を形成し、単位スタック部１６の断熱を行ない、５個の単位電池を得た。単位電池の模式的な断面図を図１４に示す。以後、この作製した１Ｗの単位電池を、実施例１の単位電池と称することにする。
【００６６】
一方、単位発電部を２０個縦方向に積層した５Ｗスタック部を比較例１の単位電池とした。
【００６７】
（実施例２）
＜５Ｗ直接型メタノール燃料電池スタック部の作製＞
まず、実施例１で説明したのと同様な１Ｗの単位電池の作製を行なった。実施例１と同様の方法により、電極面積（反応面積）が６．１ｃｍ^２ の単位発電部を２０枚作製した。そして、それぞれについて上記測定を行い、どの単位発電部からも１００ｍＡ／ｃｍ^２ の電流密度において０．４Ｖ以上の電圧が得られることを確認した。そこで、セパレータ（流路板）で挟んで、４枚の単位発電部を直列に並べた。流路板には、１枚の板の一方の面に前述した図４に示す構造を有するアノード流路が形成され、かつ他方の面に前述した図４に示すような蛇行形状のカソード流路が形成されたものを使用した。また、単位発電部のアノード電極とカソード電極の端部には、燃料や空気の漏れがない様に、フッ素樹脂によるシール材を取り付けた。最後に、ネジで締め付け、４枚の単位発電部を、電気的に直列に接続した。
【００６８】
さらに、各単位発電部に対して、並列に送液、送気が行える様に配管の接続を行った。最後に、作製した単位スタック部を厚さが０．３ｍｍのアクリル板で囲み、単位スタック部とアクリル板の間に断熱層として厚さが０．２ｍｍの空気層を形成し、断熱を行ない、単位電池を得た。但し、セパレータにはシリコンラバーヒーターが装着されており、市販の温度コントローラーを用いて、ホルダー内部の温度制御が可能となる様にした。そして、アノード電極側にメタノール濃度２Ｍのメタノール水溶液を１．４５ｍＬ／ｍｉｎで送液すると共に、カソード電極側に２４０ｍＬ／ｍｉｎで空気を供給し、単位スタック部を７０℃に維持しながら、負荷電流６００ｍＡをひいたところ、電圧１．６２Ｖが得られることが分かった。このことにより、単位発電部の定格出力から予想される出力が、単位電池から得られていることが確認され、単位電池の構成に問題がないことを確認した。また、この単位スタック部の表面積Ｓは３７．９６ｃｍ^２であり、（Ｐ／Ｓ）は２６．３４ｍＷ／ｃｍ^２となる。即ち、（Ｐ／Ｓ）が前述した（１）式で規定される範囲を満足していることを確認することができた。そして、同様の方法により単位電池を５個用意し、これらを直列に接続した。また、各単位電池に対しても、並列に送液、送気が行える様に配管の接続を行った。単位電池間を直列接続した状態を模式的に図１５に示す。また、図１５に、単位電池にメタノール水溶液を並列に送液する送液経路を４１とし、単位電池に空気を並列に送気する送気経路を４２として示す。
【００６９】
さらに、この様にして構成した複数の単位電池からなるスタック部に対して、アノード電極にメタノール濃度２Ｍのメタノール水溶液を７．５ｍＬ／ｍｉｎで送液し、かつカソード電極に空気を１．３Ｌ／ｍｉｎで送気し、単位スタック部を７０℃に維持しながら、負荷電流６００ｍＡをひいたところ、８Ｖ以上の電圧が得られることが確認された。即ち、各単位電池に対するメタノール水溶液及び空気の配流に問題がないことが示されたことになる。こうして、実施例２のスタック部を完成した。
【００７０】
次に、実施例１と同様の方法により作製した電極面積６．１ｃｍ^２ の単位発電部を２０枚用意し、単位発電部それぞれをセパレータ（流路板）で挟みながら、２０枚の単位発電部を縦方向に積層することにより直列に接続し、比較例２のスタック部を作製した。実施例２の単位電池作製と同様、流路板には、１枚の板の一方の面に前述した図４に示す構造を有するアノード流路が形成され、かつ他方の面に前述した図４に示すような蛇行形状のカソード流路が形成されたものを使用した。また、単位発電部のアノード電極とカソード電極の端部には、燃料や空気の漏れがない様に、フッ素樹脂によるシール材を取り付けた。最後に、ネジで締め付け、２０枚の単位発電部を、電気的に直列に接続した。セパレータには、シリコンラバーヒーターが装着されており、市販の温度コントローラーを用いて、ホルダー内部の温度制御が可能となる様にしてある。但し、比較例２のスタック部は、実施例１における設計から、スタック部の温度が７０℃以上になることが予想されるので、断熱層で囲まなかった。実施例２の燃料電池と同様、アノード電極にメタノール濃度２Ｍのメタノール水溶液を７．５ｍＬ／ｍｉｎで送液し、かつカソード電極に空気を１．３Ｌ／ｍｉｎで送気し、スタック部を７０℃に維持しながら、負荷電流６００ｍＡをひいたところ、８Ｖ以上の電圧が得られることが確認された。即ち、各単位発電部に対して、メタノール水溶液及び空気の配流に問題がないことが確認されたことになる。こうして、比較例２のスタック部を完成させた。
【００７１】
＜５Ｗ直接型メタノール燃料電池システムの作製及び特性評価＞
次に、実施例２及び比較例２のスタック部を用いて前述した図６、図７に示した直接型メタノール燃料電池システムを構成し、実施例２及び比較例２の５Ｗ直接型メタノール燃料電池スタック部の特性を評価した。メタノール水溶液容器には２Ｍのメタノール水溶液を１０ｍＬ、補充用第２のメタノール水溶液容器にはＣｏｎｃのメタノールを１０ｍＬを入れた。メタノールの燃料利用効率を７０％として計算すると、理論上はスタック部を４５時間連続駆動可能であることが予想される。なお、メタノール水溶液容器は、実施例２においては共通燃料タンクとして使用され、比較例２においては単位電池の数が１組であるため、この単位電池の燃料タンクとして使用される。さらに、カソード回収容器には、３０ｍＬの容器を用意した。Ｃｏｎｃのメタノールが反応によりすべて水に変わることを想定すれば、９ｍＬの水が生成され、さらに、メタノール水溶液容器中の水９．２ｍＬがカソード電極側よりすべて排出されたとしても、溢れることがない様にした。また、カソード回収容器には、水を１０ｍＬ入れ、カソード電極及びアノード電極から排出される気体をバブリングすることが可能な構成とした。第１の送液ポンプからは７．５ｍＬ／ｍｉｎの流量でメタノール水溶液を、送気用ポンプからは１．３Ｌ／ｍｉｎの流量で空気を、単位電池に供給できる様に調整を行なった。ところで、アノード電極側で、流路板から排出されるメタノール水溶液をメタノール水溶液容器中に回収はしているものの、アノード触媒層中での反応によりメタノールを消費するため、メタノール水溶液容器中のメタノール濃度が徐々に薄くなって行くことが予想される。通常、０．５Ｍよりメタノール濃度が薄くなると出力がとれないと考えられている。計算により、燃料利用効率を７０％とすると、約５分３６秒でメタノール水溶液容器中のメタノール濃度が１Ｍ以下になることが予想される。そこで、５分３６秒毎に、第２の送液ポンプより第２のメタノール水溶液容器からＣｏｎｃ．メタノール０．４ｍＬの送液を行なうこととした。また、アノード触媒層中の反応では、水とメタノールをモル比１対１で消費するので、第３の送液ポンプによりカソード回収容器から同時に、５分３６秒毎に水０．１８ｍＬの送液も行なうこととした。
【００７２】
次に、実際に行なったスタック部の評価方法及び実験結果に関して説明を行なう。まず、実施例２及び比較例２の単位電池に装着されているラバーヒーターによりスタック部が７０℃まで上昇させ、７０℃になったことが確認された後、第１の送液ポンプ及び送気ポンプを駆動させた。そして、５分間、前記操作を行ないながら、負荷電流６００ｍＡを引いた時の電圧を観測した。その結果、８．１Ｖの電圧が５分間得られることが確認された。そこで、ラバーヒーターのスイッチを切り、さらに１時間、負荷電流６００ｍＡに対する電圧の変化を観測した。
【００７３】
実施例２の燃料電池発電装置に関しては、ラバーヒーターのスイッチを切った後、５分経過後から電圧の低下が見られ、約１０分後に８Ｖまで低下したものの、その後は電圧はほぼ一定となることが分かった。この実験より、実施例２の燃料電池発電装置は安定した出力が得られることが確認された。一方、比較例２の燃料電池発電装置に関しても同様の実験を行なったところ、約１８分後より著しい電圧降下が観測されただけでなく、カソード回収容器から水が蒸発していることも確認された。その後１０分後、メタノール水溶液容器中のメタノール水溶液がすべてなくなったため実験を中止した。これはスタック部からの発熱量が過剰であったため、スタック部の温度が上がりすぎ、生成した水が異常に気化したものと考えられる。そのため、カソード回収容器中の温度が上昇し、内部の水がすべて蒸発したものと考えられる。即ち、計算から予想された様に、比較例２の燃料電池発電装置を用いた場合には、放熱器が必要であることが分かった。そこで、発生する熱量から予想される放熱器（容積２０ｍＬ）を比較例２の単位電池に装着し、放熱を行なうことにより再度実験を行なった。しかしながら、比較例２の燃料電池発電装置では、放熱器を設ける前と同様に著しい電圧降下が観測され、６００ｍＡ、８．１Ｖでの連続駆動時間が１時間に満たなかった。これは、スタック部を構成する単位発電部の温度のばらつきが大きく、６００ｍＡの負荷電流で引いた際に転極を生じ、これにより電流集中が生じたためである。
【００７４】
実験終了後、スタック部の大きさの比較を行なった。実施例２のスタック部は断熱層を含めて７０ｍＬ、比較例２のスタック部は６０ｍＬであった。しかしながら、比較例２の発電装置は、２０ｍＬの放熱器を必要とするため、直接メタノール燃料電池の小型化という面で、実施例２の発電装置が有効であることが分かった。実施例２の発電装置と比較例２の発電装置について、スタック部の容積と出力密度との関係を図１６に示す。図１６からも、実施例２の発電装置の方が比較例２の発電装置に比較して小容積で高い出力密度を得られることが理解できる。
【００７５】
（実施例３）
２Ｗの単位電池２個と３Ｗの単位電池１個より、７Ｗの組電池の作製を行った。
【００７６】
＜２Ｗの単位電池の作製＞
実施例１で説明したのと同様な方法により、電極面積１６．７ｃｍ^２の単位発電部を３枚作製した。そして、それぞれについて上記測定を行い、どの単位発電部からも１００ｍＡ／ｃｍ^２の電流密度において０．４Ｖ以上の電圧が得られることを確認した。そこで、セパレータ（流路板）で挟んで、３枚の単位発電部を直列に並べた。流路板には、１枚の板の一方の面に前述した図４に示す構造を有するアノード流路が形成され、かつ他方の面に前述した図４に示すような蛇行形状のカソード流路が形成されたものを使用した。また、単位発電部のアノード電極とカソード電極の端部には、燃料や空気の漏れがない様に、フッ素樹脂によるシール材を取り付けた。最後に、ネジで締め付け、３枚の単位発電部を、電気的に直列に接続した。さらに、各単位発電部に対して、並列に送液、送気が行える様に配管の接続を行った。最後に、作製した単位スタック部を厚さが０．３ｍｍのアクリル板で囲み、単位スタック部とアクリル板の間に断熱層として厚さが０．２ｍｍの空気層を形成し、断熱を行ない、単位電池を得た。但し、セパレータにはシリコンラバーヒーターが装着されており、市販の温度コントローラーを用いて、ホルダー内部の温度制御が可能となる様にした。そして、アノード電極側にメタノール濃度２Ｍのメタノール水溶液を２．９８ｍＬ／ｍｉｎで送液すると共に、カソード電極側に５００ｍＬ／ｍｉｎで空気を供給し、単位スタック部を７０℃に維持しながら、負荷電流１６７０ｍＡをひいたところ、電圧１．２１Ｖが得られることが分かった。このことにより、単位発電部の定格出力から予想される出力が、単位電池から得られていることが確認され、単位電池の構成に問題がないことを確認した。また、この単位スタック部の表面積Ｓは６６．９１ｃｍ^２であり、（Ｐ／Ｓ）は２９．８９ｍＷ／ｃｍ^２となる。即ち、（Ｐ／Ｓ）が前述した（１）式で規定される範囲を満足していることを確認することができた。さらに、同様の作製方法により、出力Ｐが２Ｗの単位電池を、もう一個用意した。
【００７７】
＜３Ｗの単位電池の作製＞
前述した実施例１で説明したのと同様な方法により、電極面積３７．５ｃｍ^２の単位発電部を２枚作製した。そして、それぞれについて上記測定を行い、どの単位発電部からも１００ｍＡ／ｃｍ^２の電流密度において０．４Ｖ以上の電圧が得られることを確認した。そこで、セパレータ（流路板）で挟んで、２枚の単位発電部を直列に並べた。流路板には、１枚の板の一方の面に前述した図４に示す構造を有するアノード流路が形成され、かつ他方の面に前述した図４に示すような蛇行形状のカソード流路が形成されたものを使用した。また、単位発電部のアノード電極とカソード電極の端部には、燃料や空気の漏れがない様に、フッ素樹脂によるシール材を取り付けた。最後に、ネジで締め付け、２枚の単位発電部を、電気的に直列に接続した。さらに、各単位発電部に対して、並列に送液、送気が行える様に配管の接続を行った。最後に、作製した単位スタック部を厚さが０．３ｍｍのアクリル板で囲み、単位スタック部とアクリル板の間に断熱層として厚さが０．２ｍｍの空気層を形成し、断熱を行ない、単位電池を得た。但し、セパレータにはシリコンラバーヒーターが装着されており、市販の温度コントローラーを用いて、ホルダー内部の温度制御が可能となる様にした。そして、アノード電極側にメタノール濃度２Ｍのメタノール水溶液を４．４６ｍＬ／ｍｉｎで送液すると共に、カソード電極側に７５０ｍＬ／ｍｉｎで空気を供給し、単位スタック部を７０℃に維持しながら、負荷電流３７５０ｍＡをひいたところ、電圧０．８Ｖが得られることが分かった。このことにより、単位発電部の定格出力から予想される出力が、単位電池から得られていることが確認され、単位電池の構成に問題がないことを確認した。また、この単位スタック部の表面積Ｓは１１３．４９ｃｍ^２であり、（Ｐ／Ｓ）は２６．４３ｍＷ／ｃｍ^２となる。即ち、（Ｐ／Ｓ）が前述した（１）式で規定される範囲を満足していることを確認することができた。
【００７８】
＜７Ｗ直接型メタノール燃料電池システムの作製＞
並列に接続した２個の２Ｗ単位電池と３Ｗ単位電池１個を直列に接続した。また、各単位電池に対して、並列に送液、送気が行える様に配管の接続を行った。さらに、この様にして構成した組電池に対して、アノード電極にメタノール濃度２Ｍのメタノール水溶液を１０．４２ｍＬ／ｍｉｎで送液し、かつカソード電極に空気を１．７５Ｌ／ｍｉｎで供給し、単位スタック部を７０℃に維持しながら、負荷電流３５００ｍＡをひいたところ、約２Ｖの電圧が得られ、７Ｗの出力を確認することができた。即ち、各単位電池に対するメタノール水溶液及び空気の配流に問題がないことが示されたことになる。こうして、実施例３のスタック部を完成した。
【００７９】
この様にして完成した７Ｗ直接型メタノール燃料電池システムでは、単位電池３個より構成されているため、スタック部内部における配流の分岐が少なくて済む。そのため、実施例２で説明したのと同様な方法により１Ｗの単位電池を７個直列に接続することによって作製したスタック部に比較して、配管部分の占める体積を小さくすることが可能となり、直接型メタノール燃料電池システムの小型化に有効であることが分かった。
【００８０】
なお、前述した実施例では、単位電池のアノード極に供給する燃料を一つにまとめて貯蔵する共通燃料タンクを使用する例を説明したが、単位電池それぞれが燃料タンクを備える構成にしても良い。
【００８１】
前述した実施例では、メタノール流量制御装置と電流経時変化記録評価装置とを用いる例を説明したが、本発明に係る燃料電池発電装置は、メタノール流量制御装置と電流経時変化記録評価装置を持たない発電システムに適用することができる。
【００８２】
また、前述した実施例では、カソード回収容器を用いる例を説明したが、カソード回収容器を用いず、カソード流路から排出される液体を直接、第１のメタノール水溶液容器に戻すことも可能である。
【００８３】
さらに、前述した実施例では、第１のメタノール水溶液容器にメタノールを補充する手段として第２のメタノール水溶液容器を用いる例を説明したが、メタノール補充手段を持たない構成にすることも可能である。
【００８４】
なお、本発明は上記実施形態そのままに限定されるものではなく、実施段階ではその要旨を逸脱しない範囲で構成要素を変形して具体化できる。また、上記実施形態に開示されている複数の構成要素の適宜な組み合わせにより、種々の発明を形成できる。例えば、実施形態に示される全構成要素から幾つかの構成要素を削除してもよい。さらに、異なる実施形態にわたる構成要素を適宜組み合わせてもよい。
【００８５】
【発明の効果】
以上詳述したように本発明によれば、小型で、かつ高出力が得られる燃料電池発電装置を提供することができる。
【図面の簡単な説明】
【図１】断熱層未形成の単位スタック部の一例を示す断面図。
【図２】断熱層未形成の単位スタック部の別な例を示す断面図。
【図３】図１、図２の単位スタック部に組込まれる単位発電部を示す模式図。
【図４】図１、図２の単位スタック部に組込まれるセパレータを示す模式図。
【図５】直接型メタノール燃料電池における電流電圧特性の濃度依存性を示す特性図。
【図６】直接型メタノール燃料電池発電装置の一例を示す模式図。
【図７】図６の直接型メタノール燃料電池発電装置の電気回路の一例を示す回路図。
【図８】直接型メタノール燃料電池発電装置における放熱量とそれに必要な放熱器の容積との関係を示す特性図。
【図９】本発明に係る燃料電池発電装置に組込まれる単位電池の一例を示す断面図。
【図１０】直接型メタノール燃料電池発電装置における（Ｐ／Ｓ）と断熱・放熱機構の容積との関係を出力密度別に示した特性図。
【図１１】直接型メタノール燃料電池発電装置における（Ｐ／Ｓ）と断熱・放熱機構の容積との関係を単位スタック部の温度別に示した特性図。
【図１２】実施例１の直接型メタノール燃料電池発電装置における電流電圧特性の温度依存性を示す特性図。
【図１３】実施例１及び比較例１の直接型メタノール燃料電池発電装置における（Ｐ／Ｓ）と出力密度との関係を示す特性図。
【図１４】実施例１の直接型メタノール燃料電池発電装置に組込まれる単位電池の一例を示す断面図。
【図１５】実施例１の直接型メタノール燃料電池発電装置における複数の単位電池からなるユニットの要部を示す模式図。
【図１６】実施例２及び比較例２の直接型メタノール燃料電池発電装置における電池容積と出力密度との関係を示す特性図。
【符号の説明】
１…単位発電部、２…アノード拡散層、３…アノード触媒層、４…アノード電極、５…カソード拡散層、６…カソード触媒層、７…カソード電極、８…電解質膜、９…セパレータ、１０…アノード流路、１１…カソード流路、１５…シール材、１６…単位スタック部、１７…締め付けネジ、２０…スタック部、２１…メタノール水溶液、２２…第１のメタノール水溶液容器、２７…カソード回収容器、２８…液体、３０…第２のメタノール水溶液容器、３９…断熱層、４０…アクリル板。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel cell power generator.
[0002]
[Prior art]
Expectations for high-performance secondary batteries and fuel cells are increasing as power sources for portable electronic devices that support the information society and as key elements for electric vehicles and power storage systems to combat air pollution and global warming. . In particular, as an application to electric vehicles, PEM (PEFC, solid electrolyte fuel cell) using hydrogen and oxygen as fuel has been promising. It is considered to be suitable for electric vehicles in that two points are obtained in that high output can be obtained by using clean energy such as hydrogen and oxygen and output can be restored by replenishing fuel. However, the fuel cell has a drawback that the output decreases with a large change in load current, so that it is difficult to generate power at the time of rapid acceleration. On the other hand, electric vehicles that run on lithium-ion secondary batteries alone have already been realized, but lithium-ion secondary batteries alone can be used from the viewpoints of safety issues and the inability to recover output even if non-aqueous electrolyte is replenished. It is considered difficult to apply it to electric vehicles. Therefore, hybrid batteries (assembled batteries) that take advantage of both features of a lithium ion secondary battery and a fuel cell are becoming important in application to electric vehicles. Furthermore, in order to solve the problem of reducing the fuel volume used for PEM, a method of using compressed hydrogen (250 atm), liquid hydrogen, a hydrogen storage alloy, or the like as a fuel is being studied. Under such circumstances, a direct methanol fuel cell (DMFC) that generates power by directly extracting protons from methanol (for example, described in JP-A-2001-93551) has a smaller output than PEM. Although it has the drawback, attention has been paid from this viewpoint. Further, due to the feature that the fuel volume can be reduced, the direct methanol fuel cell is considered to be applied to portable electronic devices, and expectations for application to various fields are increasing.
[0003]
The direct methanol fuel cell includes a membrane-electrode assembly including an anode electrode, a cathode electrode, and an electrolyte membrane, and a separator that supplies a fuel containing methanol to the anode electrode and supplies an oxidizing gas to the cathode electrode. It has a unit power generation unit. In order to improve the output of the direct methanol fuel cell, it is necessary to increase the number of stacks of the unit power generation units. However, since the amount of heat generated during power generation increases, the stack cells (stacks of unit power generation units) However, there arises a problem that the temperature of the object increases and the electromotive force decreases.
[0004]
In order to maintain the temperature of the stack cell at an appropriate value, it is conceivable to provide a heat radiator such as a radiation fin in the stack cell. However, even if a radiator is used, thermal interference between adjacent unit power generation units is unavoidable, so the temperature difference between the inside and the surface of the stack cell increases, and the output characteristics of the unit power generation unit that constitutes the stack cell are reduced. The problems of electromotive force drop, such as variation and the occurrence of inversion in some unitary power generation units during output, were not solved. In addition, the installation of the radiator also causes a new problem that the volume efficiency of the fuel cell is reduced.
[0005]
[Patent Document 1]
JP 2001-93551 A
[0006]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel cell power generator having high volumetric efficiency and high output.
[0007]
[Means for Solving the Problems]
A first fuel cell power generator according to the present invention is a fuel cell power generator including a plurality of unit cells,
Each unit battery is
An anode electrode, a cathode electrode, and a unit stack unit in which a plurality of unit power generation units including an electrolyte membrane disposed between the anode electrode and the cathode electrode are stacked;
A heat insulating layer covering the surface of the unit stack portion and having a thermal conductivity of 0.1 (W / m / K) or less, and satisfies the following expression (1).
[0008]
20 ≦ P / S ≦ 31 (1)
Here, P is the output (mW) of each unit battery, and S is the surface area (cm) of the unit stack portion of each unit battery. ² ).
[0009]
A second fuel cell power generator according to the present invention is a fuel cell power generator having a plurality of unit cells,
Each unit battery is
An anode electrode, a cathode electrode, and a unit stack unit in which a plurality of unit power generation units including an electrolyte membrane disposed between the anode electrode and the cathode electrode are stacked;
A heat insulating plate surrounding the surface of the unit stack portion with a gap between the unit stack portion and the surface, and satisfying the following expression (1).
[0010]
20 ≦ P / S ≦ 31 (1)
Here, P is the output (mW) of each unit battery, and S is the surface area (cm) of the unit stack portion of each unit battery. ² ).
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a fuel cell power generator according to the present invention will be described by taking a direct methanol fuel cell power generator as an example.
[0012]
FIG. 1 and FIG. 2 show an example of the unit stack portion where the heat insulating layer is not formed. FIG. 1 shows a case where the unit power generation units are stacked in the vertical direction, and FIG. 2 shows a case where the unit power generation units are stacked in the horizontal direction. As shown in FIG. 3, the unit power generation unit 1 includes a porous anode diffusion layer 2, an anode electrode 4 including an anode catalyst layer 3 formed on the diffusion layer 2, a porous cathode diffusion layer 5, and a porous cathode diffusion layer 5. A catalyst layer-electrolyte assembly comprising a cathode electrode 7 including a cathode catalyst layer 6 formed on a layer 5 and an electrolyte membrane 8 disposed between the anode catalyst layer 3 and the cathode catalyst layer 6; A separator 9 is provided for supplying and discharging a fuel such as an aqueous methanol solution to the layer 2 and for supplying and discharging an oxidizing gas to the cathode catalyst layer 6. As the separator 9, one having only the anode flow channel 10 or the cathode flow channel 11 formed on one surface, the other having the anode flow channel 10 formed on one surface and the cathode flow channel 11 formed on the other surface. There are things. FIG. 4 shows an example of the pattern of the anode channel 10 of the separator 9. The anode flow path 10 has a meandering shape. One end is a fuel supply port 12 and the other end is a fuel discharge port 13. A screw hole 14 into which a fastening screw for fixing the unit power generation unit is inserted is formed at an end of the separator 9. The cathode flow path also has a meandering shape similar to that described with reference to FIG. 4, and one end is an oxidant supply port and the other end is an oxidant discharge port. A seal member 15 for preventing leakage of fuel and oxidant is attached to the ends of the anode electrode 4 and the cathode electrode 7.
[0013]
The unit stack section 16 in which the unit power generation sections 1 shown in FIG. 1 are vertically stacked is fixed with a tightening screw 17. On the other hand, in a stack unit 16 in which the unitary power generation units 1 shown in FIG. 2 are stacked horizontally, two unitary power generation units are arranged side by side, and one set of the unitary power generation units is stacked vertically and fixed with a fastening screw 17. Have been.
[0014]
As the electrolyte membrane, for example, a Nafion membrane having high proton conductivity is used. On the other hand, the catalyst used for the anode catalyst layer is, for example, PtRu which is less poisoned, and the catalyst used for the cathode catalyst layer is, for example, Pt.
[0015]
In such a direct methanol fuel cell, as shown in FIG. 3 described above, a methanol aqueous solution (CH ₃ OH and H ₂ O) and the catalytic reaction (CH ₃ OH + H ₂ O → 6H ⁺ + 6e ⁻ + CO ₂ ) By the proton (H ⁺ ). The generated protons pass through the electrolyte membrane 8 and are supplied to the cathode catalyst layer 6 with oxygen (O 2). ₂ ) On the catalyst to produce water (6H ⁺ + 6e ⁻ + 3 / 2O ₂ → 3H ₂ Power generation is performed based on the principle O). Further, FIG. 5 shows an experimental result regarding a typical current-voltage characteristic of the direct methanol fuel cell. Each line represents a difference in current-voltage characteristics with respect to the methanol concentration of the supplied aqueous methanol solution. The output density of the direct methanol fuel cell is defined by the product of the current density and the voltage, and as shown in FIG. 5, it can be seen that the output density varies greatly depending on the methanol concentration of the methanol aqueous solution to be sent.
[0016]
Here, the improvement of the output density of the direct methanol fuel cell is achieved by maintaining a high voltage up to a high load current. First, in order to obtain a high load current, it is necessary to increase the amount of methanol supplied to the anode catalyst layer per unit time. However, since the Nafion membrane also permeates the aqueous methanol solution, the aqueous methanol solution not used for the reaction in the anode catalyst layer reaches the cathode catalyst layer, and the same reaction occurs in the cathode catalyst layer as in the anode catalyst layer. An electromotive force is generated. This is a crossover overvoltage, which causes a problem of reducing the electromotive force of the direct methanol fuel cell. The crossover overvoltage is more serious as the methanol concentration is higher. If a 5 M or more aqueous methanol solution is supplied to the anode catalyst layer, the output may be significantly reduced. Further, from the viewpoint of suppressing deterioration of an electrolyte membrane such as a Nafion membrane, the concentration of the methanol aqueous solution is preferably set to 5M or less. Therefore, in order to operate the direct methanol fuel cell, it is preferable that the concentration of the methanol aqueous solution as the fuel be 5 M or less.
[0017]
As another method of reducing the crossover overvoltage, a method is considered in which all the methanol supplied to the anode catalyst layer is consumed in the anode catalyst layer and is not permeated to the cathode catalyst layer. That is, a method of improving the catalytic activity in the anode catalyst layer or increasing the amount of supported catalyst can be considered, but cannot be realized with the current catalyst. In addition, electrolyte membranes have been developed to prevent the aqueous methanol solution that was not used in the anode catalyst layer from permeating the cathode catalyst layer.However, in practice, many electrolyte membranes have poor proton conductivity. In many cases. Therefore, in order to reduce the crossover overvoltage, it is desirable to lower the methanol concentration of the aqueous methanol solution used as the fuel. However, when a low-concentration fuel is used, the size of the fuel container needs to be increased, so that the characteristics of the direct methanol fuel cell may not be fully utilized.
[0018]
As described above, it is desirable to use a methanol aqueous solution having a methanol concentration of 5M or less as a fuel. For example, when a thin methanol aqueous solution of about 1M is used as a fuel, not only the capacity of the methanol aqueous solution container becomes large, but also the inside of the battery is increased. Therefore, methanol shortage tends to occur in the reaction, so that it becomes necessary to send the methanol aqueous solution from the methanol aqueous solution container quickly. By performing such an operation, the crossover overvoltage can be reduced, and the output as a battery increases, but the pump output for supplying the aqueous methanol solution also increases, so that the output of the entire power generator decreases. There is a risk of doing it.
[0019]
As described above, from the viewpoint of fuel supply, it is desirable to send a concentrated methanol aqueous solution at a small flow rate, but from the viewpoint of output, it is desirable to send a thin methanol aqueous solution at a large flow rate. That is, in order to reduce the fuel volume and obtain a high output, it is necessary to send an aqueous methanol solution having an optimum concentration at an optimum flow rate.
[0020]
Then, FIG. 6 shows a schematic configuration diagram of an example of a power generation system using a direct methanol fuel cell, which can solve the above problem.
[0021]
This power generation system includes a stack unit 20 including a unit stack unit 16 in which a heat insulating layer is not formed as illustrated in FIGS. 1 and 2 described above. A methanol aqueous solution container 22 containing a methanol aqueous solution 21 is connected to a fuel supply port of an anode flow path via a first liquid sending pump 23. The fuel outlet of the anode flow path is connected to a methanol aqueous solution container 22 via a discharge pipe 24, and the discharged methanol aqueous solution is returned to the methanol aqueous solution container 22 for reuse. As an oxidant supply unit for supplying an oxidant such as air, a pump (or a blower fan) 25 is connected to an oxidant supply port of the cathode channel. The outlet of the cathode flow path is connected to a cathode recovery container 27 via a check valve 26, and the water and excess oxidant discharged from the cathode electrode are recovered in the cathode recovery container 27. Has become. Further, water 28 is stored in the cathode recovery container 27 before the start of power generation, and a pipe 29 is connected below the liquid level, so that gas discharged from the cathode electrode can be bubbled in the water. It has a possible structure. Methanol, formaldehyde, and formic acid discharged from the cathode electrode are more than two orders of magnitude more soluble in water than air and carbon dioxide, so if bubbling in water, these substances will dissolve into the liquid and be recovered. Only air and carbon dioxide are discharged into the gas in the container 27. In particular, the higher the internal pressure of the collection container 27 is, the more effective it can be realized by adjusting the elastic body used for the check valve 26. Further, the check valve 26 also has a function of preventing the liquid inside the cathode recovery container 27 from flowing back. Further, in accordance with the concentration of the aqueous methanol solution 21 in the aqueous methanol solution container 22 evaluated from the change over time of the load current, the second aqueous methanol solution container 30 is And a second liquid feed pump 31. Further, the upper surface of the methanol aqueous solution container 22 is connected to a portion below the liquid level of the cathode recovery container 27 via a check valve 32, and the gas discharged from the methanol aqueous solution container 22 is supplied to the inside of the cathode recovery container 27. Is configured to perform bubbling with the water 28. As a result, of the gas discharged from the methanol aqueous solution container 22, methanol gas and formaldehyde dissolve in the water 28 in the cathode recovery container 27, and only carbon dioxide is discharged into the gas in the cathode recovery container 27. become. Further, in order to send the liquid (including water 28) in the cathode recovery container 27 to the first methanol aqueous solution container 22, the cathode recovery container 27 and the first methanol The aqueous solution container 22 is connected. As a result, methanol, formaldehyde and formic acid dissolved in the liquid in the cathode recovery container 27 can be reused as fuel for performing the reaction of the anode electrode, and also these substances harmful to the environment and the human body. Can be completely decomposed. Further, in order to discharge the gas accumulated in the cathode recovery container 27 to the outside, a discharge pipe 35 exits from the cathode recovery container 27 through a check valve 34 to the outside.
[0022]
Next, an example of a circuit for implementing the power generation system is shown in FIG. According to the concentration of the aqueous methanol solution 21 in the aqueous methanol solution container 22 evaluated from the load current recorded as a change with time corresponding to the operation time, the flow rate J of the aqueous methanol solution flowing through the anode flow path is determined. _m The flow rate control means for controlling (mL / min) includes a methanol flow rate control device 36 and a current temporal change record evaluation device 37. A first liquid feed pump 23 is provided as a means for sending liquid from the first methanol aqueous solution container 22 to the stack section 20, and a second methanol aqueous solution container 30 and a second liquid feed pump 31 are provided as methanol replenishing means. A third liquid feed pump 33 is provided as means for sending water from the cathode recovery container 27 to the first methanol aqueous solution container 22. In addition, the first, second, and third liquid feed pumps 23, 31, and 33 share the methanol flow rate control device 36 and the current temporal change record evaluation device 37. The external circuit 38 is connected to the stack unit 20. The current temporal change record evaluation device 37 is connected to the methanol flow control device 36 and the external circuit 38. A liquid supply pump (including first, second, and third liquid supply pumps 23, 31, and 33), an auxiliary device 39 including a blower fan 25 and a heater (not shown) are driven by the output of the direct methanol fuel cell. Therefore, the power supply of the auxiliary device is directly connected to the direct methanol fuel cell.
[0023]
For example, the flow rate control means records the temporal change of the current output from the direct methanol fuel cell to the external circuit 38 by the current temporal change recording / evaluating device 37 and evaluates the methanol in the methanol aqueous solution container 22 based on the data. The control is performed by controlling the amount of liquid supplied from the first liquid supply pump 23 by the methanol flow controller 36 according to the concentration of the aqueous solution.
[0024]
Further, the methanol replenishing means sends a command to the second liquid sending pump 31 in accordance with the methanol concentration evaluated by the methanol flow rate control device 36 to send the liquid from the second methanol aqueous solution container 30 to the methanol aqueous solution container 22. It is performed by:
[0025]
When the concentration of the aqueous methanol solution 21 in the aqueous methanol solution container 22 decreases (for example, becomes 0.5 M or less), the output may decrease sharply due to the lack of methanol in the unit power generation unit 1. Therefore, when the concentration of the aqueous methanol solution 21 in the first aqueous methanol solution container 22 becomes low (for example, 0.5 M or less), it is necessary to replace the aqueous methanol solution container 22 while leaving the aqueous methanol solution inside. Come. Thus, as in the power generation system shown in FIG. 6 described above, a concentrated methanol aqueous solution is sent from the second methanol aqueous solution container 30 to the methanol aqueous solution container 22 so that the methanol concentration in the methanol aqueous solution container 22 is equal to or more than a predetermined value ( If it is set to, for example, 0.5 M or more, the methanol aqueous solution in the methanol aqueous solution container 22 can be reused, and all the methanol aqueous solution in the container 22 can be used up. Further, since the second aqueous methanol solution container 30 is exclusively used for replenishment, it is possible to replace the second aqueous methanol solution container 30 when all the aqueous methanol solution in the second aqueous methanol solution container 30 is used up. Become. At the same time, water is also sent from the cathode recovery container 27 to the methanol aqueous solution container 22, so that the shortage of water in the anode electrode can be eliminated. Further, the output can be restored by returning the methanol concentration in the methanol aqueous solution container 22 to the initial concentration.
[0026]
In addition, direct methanol fuel cells have very sensitive output characteristics to temperature. The operating temperature at which the maximum output is obtained in the direct methanol fuel cell is around 70 ° C., and when the temperature drops by about 20 ° C., the diffusion rate of methanol in the anode catalyst layer decreases, so that the critical load current decreases, The power density decreases. On the other hand, when the temperature is higher than 70 ° C. by about 20 ° C., the diffusion rate of methanol in the anode catalyst layer becomes too high, so that the influence of the crossover phenomenon is strengthened and the electromotive force is significantly reduced. Therefore, in order to obtain a sufficient output from the direct methanol fuel cell, it is necessary to maintain the operating temperature at about 70 ° C. ± 10 ° C. However, if any heat insulating structure or heat radiating structure is provided in the stack portion in order to maintain the temperature of the stack portion at around 70 ° C., the entire direct methanol fuel cell power generation device becomes large, and the size of the portable device becomes large. This is an application problem. The calorific value generated by the direct methanol fuel cell can be divided into two types: calorific value generated by power generation and calorific value generated by combustion of methanol permeated (crossed over) through the cathode catalyst layer in the cathode catalyst layer. it can. Heat value Q per unit time generated by power generation ₁ (W) is given by the following equation (2).
[0027]
Q ₁ = NS _e (1.21-V) J (2)
Here, (1.21-V) is a voltage drop with respect to an electromotive force of 1.21 V determined from the Gibbs free energy of the power generation reaction, V is the voltage (V) of the unit power generation unit, and J is the unit power generation unit. Current density (mA / cm ² ) And S _e Is the electrode area of the unit power generation unit (cm ² ), And n is the number of stacked unit power generation units in the stack unit.
[0028]
Further, the calorific value Q generated by the combustion of methanol crossed over the cathode catalyst layer ₂ (W) is given by the following equation (3).
[0029]
Q ₂ = 7.27 × 10 ⁵ nS _e J _m (3)
However, 7.27 is a value derived from the enthalpy change 727 (kJ / mol) of the combustion reaction of methanol. _m Is the methanol flow rate per unit area crossing over the cathode catalyst layer (mol / cm ² / Sec).
[0030]
Therefore, the heat value Q (W) of the entire stack is expressed by the following equation (4).
[0031]
Q = Q ₁ + Q ₂ (4)
By the way, the flow rate of methanol crossing over the cathode catalyst layer depends on the flow rate of the aqueous methanol solution supplied to the anode flow channel, and cannot be directly linked to the output density obtained by power generation. However, when the flow rate of methanol consumed by the crossover increases, not only does the amount of methanol used for power generation (fuel use efficiency) decrease, but also the consumption of the first liquid sending pump used for sending the methanol aqueous solution increases. This causes an increase in power, that is, a decrease in output that can be effectively taken out of the direct methanol fuel cell. Therefore, if only the methanol flow rate (J / 6F) (F: Faraday constant, 96487 C / mol) necessary for extracting the current density J is supplied to the anode catalyst layer, it is possible to suppress the decrease in overvoltage due to crossover. Instead, it is possible to increase the fuel use efficiency and reduce the power consumption by the liquid feed pump. However, the diffusion time of methanol in the anode catalyst layer is actually finite, and it is not possible to stably generate power only by supplying a flow rate of methanol necessary for power generation, (1.6). It has been experimentally found that it is necessary to feed a fuel of about × J / 6 × F). Therefore, even when the optimum methanol flow rate required for power generation is supplied, the crossover methanol flow rate is considered to be about (0.6 × J / 6 × F). That is, at 0.4 V, which is generally used as the electromotive force of the unitary power generation unit of the direct methanol fuel cell, considering these factors, the output obtained from the fuel cell (including the output to the auxiliary device) P (W ), The heat value Q (W) of the stack portion is expressed by the following equation (5).
[0032]
(Equation 1)

[0033]
For example, when a personal computer is driven by a direct methanol fuel cell, a required amount of power of 20 to 30 W generates 60 to 90 W of heat, and these heats need to be radiated to the outside. Comes out. FIG. 8 is a diagram showing the relationship between the amount of heat radiation and the necessary volume of the heat radiation fins and the fan. The amount of heat radiation at the time of power generation of 20 to 30 W is about 60 to 90 W according to the above-mentioned formula (5), and therefore, at the time of power generation of 20 to 30 W, a heat radiation mechanism having a volume of 150 to 250 mL. 8 can be understood from FIG. As a result, the volume of the whole direct methanol fuel cell power generator becomes extremely large, which causes a problem in application. In particular, reducing the volume of the heat radiating mechanism is important for reducing the size of the direct methanol fuel cell.
[0034]
As described above, when the output of the direct methanol fuel cell is increased, the calorific value generated from the stack unit also increases, and the temperature of the stack unit is set to 60 ° C. to 80 ° C., which is optimal for power generation in the unit power generation unit. Cannot be maintained. Therefore, it is necessary to design the stack portion not only from the viewpoint of output but also from the viewpoint of heat.
[0035]
A first fuel cell power generator according to the present invention is a fuel cell power generator including a plurality of unit cells,
Each unit battery is
An anode electrode, a cathode electrode, and a unit stack unit in which a plurality of unit power generation units including an electrolyte membrane disposed between the anode electrode and the cathode electrode are stacked;
A heat insulating layer covering the surface of the unit stack portion and having a thermal conductivity of 0.1 (W / m / K) or less, and satisfying the following expression (1).
[0036]
20 ≦ P / S ≦ 31 (1)
Here, P is the output (mW) of each unit battery, and S is the surface area (cm) of the unit stack portion of each unit battery. ² ).
[0037]
Here, it is desirable that the unit stack section is formed by stacking a plurality of unit power generation sections vertically or horizontally, and one having the structure shown in FIGS. 1 and 2 is exemplified. When the unit power generation units are stacked vertically, the unit power generation units are connected in series, and when the unit power generation units are stacked horizontally, the unit power generation units are connected in parallel. In the present invention, a plurality of unit batteries having such a configuration can be used as an assembled battery by connecting them in series, in parallel, or in a combination of series and parallel connections.
[0038]
The reason why (P / S) is limited to the above equation (1) will be described. P is the product of the rated output density of each unit cell and the electrode area (the reaction area between the anode electrode and the cathode electrode). S is the surface area of a rectangular parallelepiped having a size equal to the volume occupied by each unit stack. (P / S) is 20 mW / cm ² If the value is less than the above, the self-heating amount due to the power generation is insufficient, so that it becomes difficult to maintain the temperature of the unit stack portion at 60 ° C. or more due to the self-heating. On the other hand, (P / S) is 31 mW / cm ² If the temperature exceeds the limit, the amount of heat generated at the time of power generation increases, so that the temperature of the unit stack portion exceeds 80 ° C., and a high electromotive force may not be obtained.
[0039]
The heat insulating layer having a thermal conductivity of 0.1 (W / m / K) or less is, for example, 10 ^-1 -10 ^-2 (W / m / K) A bubble dispersing material having a thermal conductivity of about 10 ^-2 -10 ^-4 (W / m / K) can be formed from a powder heat insulating material having a thermal conductivity of about (W / m / K). This heat insulating layer can also be formed by vacuum heat insulation. Furthermore, the lower the thermal conductivity of the heat insulating layer, the smaller the thickness of the heat insulating layer, so that the size reduction of the fuel cell power generator can be promoted.
[0040]
The thickness of the heat insulating layer having a thermal conductivity of 0.1 (W / m / K) or less is desirably in the range of 0.1 to 2 mm in the case of air, for example. This is for the reason described below. If the thickness of the heat insulating layer is less than 0.1 mm, the thermal influence from other unit cells increases, and the temperature unevenness of the unit stack may increase. If the thickness of the heat insulating layer exceeds 2 mm, the volume efficiency of the fuel cell power generator may be reduced.
[0041]
In the present invention, the first reason for covering the unit stack portion with the heat insulating layer is to make the temperature distribution in the unit stack portion uniform. In particular, since a material having high thermal conductivity such as metal or carbon is used as a separator material of the direct methanol fuel cell, it is considered that a sufficient effect can be obtained by merely covering the surface with a heat insulating layer having low thermal conductivity. . It is also effective from the viewpoint of reducing the thermal effect between the unit cells, and from the viewpoint of immediately raising the temperature of the unit power generation unit to the range of 60 ° C. to 80 ° C. when starting up the direct methanol fuel cell. It is.
[0042]
The principle for deriving the equation (1) in the fuel cell power generator according to the present invention will be described.
[0043]
The amount of heat generated from the unit battery is given by the above-described equation (5). On the other hand, the amount of heat radiation Q 'from the surface of the unit stack portion is represented by the following equation (6), where S is the surface area of the unit stack portion.
[0044]
(Equation 2)

[0045]
Here, a is the thermal conductivity (= 10 W / K / m ² ) And σ is the Stephan Boltzmann coefficient (5.67 × 10 ^-8 W / m ² / K ⁴ Is the emissivity (= 0.7) and T ₀ Is room temperature (= 300K). The thermal conductivity is usually 5 to 10 (W / K / m ² ) Is used. The heat conductivity a is determined from two points, that is, a material having high heat conductivity such as metal or carbon is used for the separator of the direct methanol fuel cell, and that the radiation heat is considered in the calculation of the present invention. = 10 (W / K / m ² ) Was used. Further, when a carbon material is used for the separator, the emissivity is considered to be about 0.9, and when a metal is used, the emissivity is considered to be about 0.5. However, since the calculation result is not significantly changed, an average value of 0.7 is used. . When these values are substituted, α is 6.0 × 10 to 9.2 × 10 mW / cm in the temperature range of 60 ° C. to 80 ° C. at which the unit battery reaches. ² Is calculated. Therefore, the condition for the unit battery to reach the range of 60 ° C. to 80 ° C. by self-heating is given by the following equation (7) from equations (5) and (6).
[0046]
20mW / cm ² ≦ P / S ≦ 31 mW / cm ² (7)
That is, the above-mentioned equation (1) was obtained. If the unit battery is designed according to the formula (1), the temperature of the unit stack can be maintained within the range of 60 ° C. to 80 ° C. by self-heating, and a mechanism for radiating heat and insulating the stack is provided. Therefore, the volume of the direct methanol battery as a whole can be reduced. That is, the direct methanol fuel cell power generation device is very useful in application to portable equipment.
[0047]
In order to confirm the validity of the equations (1) and (7), a calculation result of estimating the capacity of a mechanism required for heat radiation and heat insulation of a unit stack portion for a 1 W direct type methanol fuel cell power generator is shown. . As shown in FIG. 9, the number of stacked unit power generation units 1 in the unit stack unit was 4, the seal width L was 5 mm, and the height (including the electrode unit) H of the separator 9 was 2.5 mm. For example, the power density obtained from the electrode is 50 mW / cm ² Then, the electrode width X is 2.24 cm, and the surface area S of the unit stack portion is 34 cm. ² It becomes. The volume of the heat insulating / radiating mechanism required for the unit stack to reach 70 ° C. was estimated. As shown in FIG. 9, an air layer 39 was formed on the surface of the unit stack portion as a heat insulating mechanism, and the volume of the air layer 39 was used as the volume of the heat insulating mechanism. The thermal conductivity of air is 2.6 × 10 ^-2 (W / m / K). On the other hand, regarding the heat radiation mechanism of the unit stack portion, the volumes of the radiation fins and the fan required to cool the unit stack portion to 70 ° C. were estimated from FIG. FIG. 10 shows the results of plotting the total volume required for the heat insulating mechanism and the heat radiation mechanism on the vertical axis and P / S on the horizontal axis. Each line is a calculation result when the output density obtained from the unit power generation unit is changed. As can be seen from this figure, regardless of the output density of the unitary power generation unit, the auxiliary system required for heat insulation and heat radiation is smallest when P / S = 23.84. Next, the output density in the unit power generation unit is 50 mW / cm. ² FIG. 11 shows a calculation result of how the volume of the auxiliary device necessary for heat insulation and heat radiation changes in the range of 60 ° C. to 80 ° C. It was shown that in the temperature range of 60 ° C. to 80 ° C., the P / S at which the volume became minimum changed within the range of Expression (7). Therefore, the validity of the above equation (1) was confirmed.
[0048]
Here, in the calculation of the present invention, the calculation is performed on the assumption that the temperature of the unit stack unit rises uniformly. However, even if a material having high thermal conductivity such as metal or carbon is used for the separator, actually, the temperature tends to be higher inside the unit stack portion than on the surface thereof. Therefore, as in the present invention, covering the surface of the unit stack section with a heat insulating layer is effective in making the temperature of the unit stack section uniform. Further, as shown from the above calculations, if (P / S) is within the range of the present invention, other heat insulating mechanisms other than the heat insulating layer are required to raise the stack portion to 60 ° C to 80 ° C. And not. Therefore, in the present invention, it is preferable that the heat insulating layer covering the surface of the unit stack portion cover a material having low thermal conductivity as thinly as possible from the viewpoint of miniaturization of the whole battery. For example, there is a case where air having the lowest thermal conductivity is covered with a thickness of about 0.5 mm. Even when this degree of heat insulation is performed, the thermal conductivity between the separator and the separator is greatly different, so that it is effective from the viewpoint of making the temperature inside the stack uniform. On the other hand, since the thermal conductivity is sufficiently negligible for the separator, a = 10 (W / K / m ² ) Does not change the calculation result.
[0049]
According to the first fuel cell power generator according to the present invention described above, the surface of the unit stack portion satisfying the above-described expression (1) is thermally insulated with a thermal conductivity of 0.1 (W / m / K) or less. Since the layers are covered, the temperature of the unit stack portion can be maintained in the range of 60 ° C. to 80 ° C. due to heat generated during power generation. As a result, as shown in FIGS. 10 and 11 described above, the volume of the mechanism required for heat insulation and heat radiation can be reduced, so that the fuel cell power generator can be downsized.
[0050]
Further, since thermal interference between the unit cells can be reduced, the temperature distribution of the unit cells can be made uniform. As a result, variation in output characteristics between the unit power generation units constituting the unit battery can be reduced, so that it is possible to avoid inversion of some unit power generation units and obtain a high voltage. it can.
[0051]
Therefore, according to the present invention, it is possible to realize a fuel cell power generation device that is excellent in volume efficiency and high in output.
[0052]
A second fuel cell power generator according to the present invention is a fuel cell power generator having a plurality of unit cells,
Each unit battery is
An anode electrode, a cathode electrode, and a unit stack unit in which a plurality of unit power generation units including an electrolyte membrane disposed between the anode electrode and the cathode electrode are stacked;
A heat insulating plate surrounding the surface of the unit stack portion with a gap between the unit stack portion and the surface, and satisfying the above-mentioned expression (1).
[0053]
An example of the heat insulating plate is an acrylic plate. As a method of enclosing the unit stack portion with a heat insulating plate, for example, storing the unit stack portion in a container formed of a heat insulating plate, partitioning the inside of the container formed of a heat insulating plate with a heat insulating plate, and partitioning the space And the like, in which a unit stack portion is housed.
[0054]
The gap (air layer) formed between the heat insulating plate and the unit stack portion can function as a heat insulating layer. The size of the gap is desirably within the range of 0.1 to 2 mm for the same reason as described in the first fuel cell power generator described above.
[0055]
According to the above-described second fuel cell power generator according to the present invention, the unit stack portion satisfying the above-mentioned expression (1) is surrounded by the heat insulating plate with a gap provided between the unit stack portion and the unit stack portion. The temperature of the unit stack portion can be maintained in the range of 60 ° C. to 80 ° C. due to heat generated during power generation. As a result, as shown in FIGS. 10 and 11 described above, the volume of the mechanism required for heat insulation and heat radiation can be reduced, so that the fuel cell power generator can be downsized.
[0056]
Further, since thermal interference between the unit cells can be reduced, the temperature distribution of the unit cells can be made uniform. As a result, variation in output characteristics between the unit power generation units constituting the unit battery can be reduced, so that it is possible to avoid inversion of some unit power generation units and obtain a high voltage. it can.
[0057]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0058]
(Example 1)
<Design of 5W direct methanol fuel cell stack>
First, a unit power generation unit was created, and current-voltage characteristics were measured. Then, based on the experimental results, a 5W direct methanol fuel cell stack was designed.
[0059]
<Production of catalyst layer / electrolyte assembly for direct methanol fuel cell>
By a known process (R. Ramakumar et al. J. Power Sources 69 (1997) 75), a carbon black supported on an anode catalyst (Pt: Ru = 1: 1) and a carbon black supported on a cathode catalyst (Pt) were produced. . The catalyst carrying amount was 30 for the anode and 15 for the cathode in a weight ratio to 100 carbon. A perfluorocarbon sulfonic acid solution (Dupont's Nafion solution SE-20092) and ion-exchanged water were added to the anode catalyst-supporting carbon black produced in the above process, and the catalyst-supporting carbon black was dispersed to prepare a paste. An anode electrode was obtained by applying a paste of 550 μm on a water-repellent carbon paper (trade name: TGPH-120, manufactured by E-TEK) as an anode diffusion layer, drying the paste, and forming an anode catalyst layer. . A perfluorocarbon sulfonic acid solution (Dupont's Nafion solution SE-20092) and ion-exchanged water were added to the cathode catalyst-supporting carbon black produced in the above process, and the catalyst-supporting carbon black was dispersed to prepare a paste. A 225 μm paste was applied on a water-repellent carbon paper (trade name: TGPH-090, manufactured by E-TEK) as a cathode current collector, followed by drying to form a cathode catalyst layer. Got. A commercially available perfluorocarbon sulfonic acid membrane (Napion 117 manufactured by Dupont) as an electrolyte membrane was arranged between the anode catalyst layer of the anode electrode and the cathode catalyst layer of the cathode electrode, and hot pressed (125 ° C., 5 minutes, 50 kg / m). cm ² ), The anode electrode, the electrolyte membrane and the cathode electrode were joined to obtain a catalyst layer / electrolyte assembly. The cross-sectional area of the anode catalyst layer in the joined body is 10 cm ² Met. Further, when the joined body was cut and the cross-sectional area was observed with an electron microscope, the thickness of the anode catalyst layer was 105 μm, and the thickness of the cathode catalyst layer was 50 μm. In addition, the electron microscope observation confirmed that the bonding state between the anode electrode, the electrolyte membrane, and the cathode electrode was good.
[0060]
<Preparation of unit power generation unit evaluation cell>
The prepared catalyst layer / electrolyte assembly was mounted on a carbon separator, and sealed with screws. A silicon rubber heater was attached to the separator, and the temperature inside the holder could be controlled using a commercially available temperature controller. By the way, the separator located on the anode electrode side is provided with an anode flow channel having a shape as shown in FIG. 4 described above. A supply tube was connected to the methanol supply port of the anode flow path, and a discharge tube was connected to the methanol discharge port of the anode flow path. An aqueous methanol solution was accommodated in a methanol aqueous solution container (volume: 10 mL), sent using a commercially available liquid sending pump, and supplied to the anode channel through a supply tube and a supply port. The aqueous methanol solution that did not permeate the anode carbon paper as the anode diffusion layer was discharged from the discharge tube through the methanol discharge port.
[0061]
On the other hand, a cathode channel having the same shape as the anode channel is also formed on the separator located on the cathode electrode side. A supply tube was connected to the oxidant supply port of the cathode flow path, and a discharge tube was connected to the oxidant discharge port of the cathode flow path. Air was supplied using a commercially available air pump, and was supplied to the cathode channel through a supply tube and a supply port. The air flow rate was adjusted using a commercially available mass flow controller. It was confirmed that the liquid sending was adjustable in the range of 0.6 mL / min to 6 mL / min, and the gas sending was adjustable in the range of 20 mL / min to 5 L / min. The load was adjusted using a commercially available electronic load machine. Further, a commercially available digital multimeter was used as the voltage detecting means.
[0062]
<Measurement of current-voltage characteristics>
A methanol aqueous solution having a concentration of 2 M was prepared as the aqueous methanol solution in the aqueous methanol solution container, and the solution was fed at a flow rate of 0.6 mL / min. In addition, the experiment was performed with an air supply rate of 100 mL / min and temperatures of 50 ° C, 70 ° C, and 90 ° C. FIG. 12 shows the results of the measured current-voltage characteristics. As can be seen from FIG. 12, the highest output density was obtained at 70 ° C., and the load current density was 170 (mA / cm). ² ) At a maximum power density of 50 (mA / cm ² ) Was obtained. However, it was found that when the current density was increased more than that, a sharp voltage drop occurred, so that the output density was lowered and a stable output could not be obtained. This is presumably because the supply amount of the aqueous methanol solution could not keep up with the load current, resulting in a shortage of fuel. Therefore, a stable output of 100 (mA / cm ² ), 0.41 V was set as the rated output of the unit power generation unit, and a 5 W direct methanol fuel cell stack unit was designed.
[0063]
<Design of unit stack of 5W direct methanol fuel cell>
First, using a unit power generation unit having a seal width L of 5 mm and a separator height H (including the electrode unit) of 2.5 mm, a heat generation layer having a number of stacked unit power generation units of 4 and an output P of 1 W was not formed. And a unit battery (Comparative Example 1) in which the number of stacked unit power generation units is 20 and the output P is 5 W and the heat insulating layer is not formed is prepared. FIG. 13 shows the P / S (mW / cm) of the unit battery of Example 1 and the unit battery of Comparative Example 1. ² ) And the output density p (mW / cm) of the unit power generation section constituting the unit stack section. ² ). In FIG. 13, (P / S) was changed by changing the electrode area of the unit power generation unit to change the surface area S of the unit stack unit.
[0064]
(P / S) is 20 to 31 (mW / cm). ² ) Is shown as a range surrounded by a chain line. According to the unit battery of Example 1, (P / S) is 20 to 31 (mW / cm). ² ), The output density from the unit power generation unit is 40 (mW / cm). ² ). On the other hand, according to the unit battery of Comparative Example 1, (P / S) was 20 to 31 (mW / cm). ² ), The output density at the unit power generation unit is 20 (mW / cm). ² ), The output density is 40 (mW / cm) in the unit power generation section. ² If the power generation is performed in (2), it is expected that the calorific value will be excessive and the temperature of the stack portion will exceed 80 ° C.
[0065]
Therefore, a stack unit in which four unit power generation units 1 were stacked in the vertical direction was set as a unit stack unit 16, and five of them were connected in series to produce a 5W stack. Then, the entire unit stack section 16 is entirely surrounded by an acrylic plate 40 having a thickness of 0.3 mm, and an air layer (heat conduction layer) having a thickness of 0.2 mm is formed between the unit stack section 16 and the acrylic plate 40 as a heat insulating layer 39. 2.6 × 10 ^-2 (W / m / K)), and the unit stack 16 was insulated to obtain five unit batteries. FIG. 14 shows a schematic cross-sectional view of the unit battery. Hereinafter, the produced 1 W unit battery is referred to as a unit battery of Example 1.
[0066]
On the other hand, a 5 W stack unit in which 20 unit power generation units were vertically stacked was defined as a unit battery of Comparative Example 1.
[0067]
(Example 2)
<Preparation of 5W direct methanol fuel cell stack>
First, a 1 W unit battery similar to that described in Example 1 was manufactured. By the same method as in Example 1, the electrode area (reaction area) was 6.1 cm. ² 20 unit power generation units were manufactured. Then, the above measurement was performed for each unit, and 100 mA / cm ² It was confirmed that a voltage of 0.4 V or more was obtained at a current density of. Therefore, four unit power generation units were arranged in series with a separator (flow path plate) interposed therebetween. In the flow channel plate, an anode flow channel having the structure shown in FIG. 4 is formed on one surface of one plate, and a meandering cathode flow channel as shown in FIG. 4 is formed on the other surface. Was used. In addition, a sealing material made of a fluororesin was attached to the ends of the anode electrode and the cathode electrode of the unit power generation unit so that fuel and air did not leak. Finally, four unit power generation units were electrically connected in series by screwing.
[0068]
Further, piping was connected to each unit power generation unit so that liquid supply and air supply could be performed in parallel. Finally, the produced unit stack portion is surrounded by an acrylic plate having a thickness of 0.3 mm, an air layer having a thickness of 0.2 mm is formed as a heat insulating layer between the unit stack portion and the acrylic plate, and heat insulation is performed. Got. However, a silicon rubber heater was attached to the separator, and the temperature inside the holder could be controlled using a commercially available temperature controller. Then, a methanol aqueous solution having a methanol concentration of 2M is supplied to the anode electrode side at a rate of 1.45 mL / min, and air is supplied to the cathode electrode side at a rate of 240 mL / min. It was found that a voltage of 1.62 V was obtained when 600 mA was applied. Thereby, it was confirmed that the output expected from the rated output of the unit power generation unit was obtained from the unit battery, and that there was no problem in the configuration of the unit battery. The surface area S of the unit stack portion is 37.96 cm. ² And (P / S) is 26.34 mW / cm ² It becomes. That is, it was confirmed that (P / S) satisfied the range defined by the above-described equation (1). Then, five unit batteries were prepared in the same manner and connected in series. Also, piping was connected to each unit battery so that liquid supply and air supply could be performed in parallel. FIG. 15 schematically shows a state in which the unit batteries are connected in series. Further, FIG. 15 shows a liquid supply path 41 for supplying an aqueous methanol solution to the unit cells in parallel, and an air supply path 42 for supplying air to the unit cells in parallel.
[0069]
Further, a methanol aqueous solution having a methanol concentration of 2M is sent to the anode electrode at a flow rate of 7.5 mL / min to the stack section composed of a plurality of unit cells configured as described above, and air is supplied to the cathode electrode at a rate of 1.3 L / min. When the air was supplied in min. and the load current was 600 mA while maintaining the unit stack portion at 70 ° C., it was confirmed that a voltage of 8 V or more was obtained. That is, it was shown that there was no problem in the distribution of the aqueous methanol solution and air to each unit battery. Thus, the stack of Example 2 was completed.
[0070]
Next, an electrode area of 6.1 cm produced in the same manner as in Example 1. ² 20 unit power generation sections are prepared, and the 20 unit power generation sections are vertically stacked and connected in series while sandwiching each of the unit power generation sections with a separator (flow path plate). Was prepared. As in the production of the unit battery of Example 2, the flow channel plate has an anode flow channel having the structure shown in FIG. 4 on one surface of one plate, and the anode flow channel shown in FIG. The one having a meandering cathode flow path as shown in FIG. In addition, a sealing material made of a fluororesin was attached to the ends of the anode electrode and the cathode electrode of the unit power generation unit so that fuel and air did not leak. Finally, it was fastened with a screw, and the 20 unit power generation units were electrically connected in series. A silicon rubber heater is mounted on the separator, and the temperature inside the holder can be controlled using a commercially available temperature controller. However, the stack portion of Comparative Example 2 was not surrounded by a heat insulating layer because the temperature of the stack portion was expected to be 70 ° C. or higher from the design in Example 1. As in the fuel cell of Example 2, an aqueous methanol solution having a methanol concentration of 2M was sent to the anode electrode at 7.5 mL / min, and air was sent to the cathode electrode at 1.3 L / min. It was confirmed that a voltage of 8 V or more was obtained when a load current of 600 mA was applied while maintaining the load current. That is, it was confirmed that there was no problem in the distribution of the aqueous methanol solution and the air to each unit power generation unit. Thus, the stack portion of Comparative Example 2 was completed.
[0071]
<Production of 5W direct methanol fuel cell system and evaluation of characteristics>
Next, the direct methanol fuel cell system shown in FIGS. 6 and 7 was configured using the stack units of the embodiment 2 and the comparative example 2, and the 5W direct methanol fuel cell of the embodiment 2 and the comparative example 2 was formed. The characteristics of the stack were evaluated. The methanol aqueous solution container contained 10 mL of a 2M aqueous methanol solution, and the supplemental second methanol aqueous solution container contained 10 mL of Conc methanol. If the fuel utilization efficiency of methanol is calculated as 70%, it is theoretically expected that the stack portion can be continuously driven for 45 hours. The methanol aqueous solution container is used as a common fuel tank in Example 2, and in Comparative Example 2, since the number of unit cells is one set, it is used as a fuel tank for this unit cell. Further, a 30 mL container was prepared as a cathode recovery container. Assuming that all the methanol in the Conc is converted to water by the reaction, 9 mL of water is generated, and even if 9.2 mL of water in the methanol aqueous solution container is entirely discharged from the cathode electrode side, there is no overflow. I did it. Further, the cathode recovery container was configured so that 10 mL of water was put therein, and gas discharged from the cathode electrode and the anode electrode could be bubbled. Adjustments were made so that a methanol aqueous solution could be supplied to the unit battery from the first liquid supply pump at a flow rate of 7.5 mL / min, and air could be supplied from the air supply pump at a flow rate of 1.3 L / min. By the way, although the aqueous methanol solution discharged from the flow path plate is collected in the aqueous methanol solution container on the anode electrode side, since the methanol is consumed by the reaction in the anode catalyst layer, the methanol concentration in the aqueous methanol solution container is increased. Is expected to gradually fade. It is generally considered that no output can be obtained when the methanol concentration is lower than 0.5 M. By calculation, assuming that the fuel use efficiency is 70%, it is expected that the methanol concentration in the methanol aqueous solution container will be 1 M or less in about 5 minutes and 36 seconds. Therefore, every 5 minutes and 36 seconds, the Conc. It was decided to send 0.4 mL of methanol. In addition, since the reaction in the anode catalyst layer consumes water and methanol in a molar ratio of 1 to 1, 0.18 mL of water is simultaneously supplied from the cathode recovery container by the third liquid supply pump every 5 minutes and 36 seconds. Also decided to do it.
[0072]
Next, an evaluation method and an experimental result of the stack portion actually performed will be described. First, the stack portion was raised to 70 ° C. by the rubber heater mounted on the unit batteries of Example 2 and Comparative Example 2, and after it was confirmed that the temperature reached 70 ° C., the first liquid supply pump and the air supply The pump was driven. Then, while performing the above operation for 5 minutes, the voltage when the load current was reduced to 600 mA was observed. As a result, it was confirmed that a voltage of 8.1 V was obtained for 5 minutes. Therefore, the rubber heater was turned off, and a change in voltage with respect to a load current of 600 mA was observed for another hour.
[0073]
Regarding the fuel cell power generation device of Example 2, after the rubber heater was turned off, the voltage dropped after 5 minutes, and dropped to 8 V after about 10 minutes, but thereafter the voltage became almost constant. I found out. From this experiment, it was confirmed that the fuel cell power generator of Example 2 could obtain a stable output. On the other hand, when a similar experiment was performed on the fuel cell power generation device of Comparative Example 2, not only a significant voltage drop was observed after about 18 minutes, but also it was confirmed that water had evaporated from the cathode recovery container. Was. Ten minutes later, the experiment was stopped because the methanol aqueous solution in the methanol aqueous solution container was completely exhausted. This is considered to be because the amount of heat generated from the stack portion was excessive, the temperature of the stack portion was too high, and the generated water was abnormally vaporized. Therefore, it is considered that the temperature in the cathode recovery container rose and all the water inside evaporated. That is, as expected from the calculation, it was found that a radiator was required when the fuel cell power generation device of Comparative Example 2 was used. Therefore, a radiator (capacity: 20 mL) expected from the amount of heat generated was mounted on the unit battery of Comparative Example 2, and the experiment was performed again by radiating heat. However, in the fuel cell power generation device of Comparative Example 2, a remarkable voltage drop was observed as before the radiator was provided, and the continuous driving time at 600 mA and 8.1 V was less than 1 hour. This is because the temperature variation of the unit power generation units constituting the stack unit is large, and when the load is drawn with a load current of 600 mA, reversal occurs, which causes current concentration.
[0074]
After the experiment was completed, the sizes of the stack portions were compared. The stack portion of Example 2 including the heat insulating layer was 70 mL, and the stack portion of Comparative Example 2 was 60 mL. However, since the power generation device of Comparative Example 2 requires a radiator of 20 mL, the power generation device of Example 2 was found to be effective in reducing the size of the direct methanol fuel cell. FIG. 16 shows the relationship between the volume of the stack portion and the output density for the power generation device of Example 2 and the power generation device of Comparative Example 2. From FIG. 16, it can be understood that the power generation device of Example 2 can obtain a higher output density with a smaller volume than the power generation device of Comparative Example 2.
[0075]
(Example 3)
A 7 W assembled battery was produced from two 2 W unit batteries and one 3 W unit battery.
[0076]
<Preparation of 2W unit battery>
According to the same method as described in Example 1, the electrode area was 16.7 cm. ² Three unit power generation units were manufactured. Then, the above measurement was performed for each unit, and 100 mA / cm ² It was confirmed that a voltage of 0.4 V or more was obtained at a current density of. Therefore, three unit power generation units were arranged in series with a separator (flow path plate) interposed therebetween. In the flow channel plate, an anode flow channel having the structure shown in FIG. 4 is formed on one surface of one plate, and a meandering cathode flow channel as shown in FIG. 4 is formed on the other surface. Was used. In addition, a sealing material made of a fluororesin was attached to the ends of the anode electrode and the cathode electrode of the unit power generation unit so that fuel and air did not leak. Finally, the three power generating units were electrically connected in series by screwing. Further, piping was connected to each unit power generation unit so that liquid supply and air supply could be performed in parallel. Finally, the produced unit stack portion is surrounded by an acrylic plate having a thickness of 0.3 mm, an air layer having a thickness of 0.2 mm is formed as a heat insulating layer between the unit stack portion and the acrylic plate, and heat insulation is performed. Got. However, a silicon rubber heater was attached to the separator, and the temperature inside the holder could be controlled using a commercially available temperature controller. Then, a methanol aqueous solution having a methanol concentration of 2M is supplied to the anode electrode side at a rate of 2.98 mL / min, and air is supplied to the cathode electrode side at a rate of 500 mL / min. When 1670 mA was applied, it was found that a voltage of 1.21 V was obtained. Thereby, it was confirmed that the output expected from the rated output of the unit power generation unit was obtained from the unit battery, and that there was no problem in the configuration of the unit battery. The surface area S of the unit stack portion is 66.91 cm. ² And (P / S) is 29.89 mW / cm. ² It becomes. That is, it was confirmed that (P / S) satisfied the range defined by the above-described equation (1). Further, another unit battery having an output P of 2 W was prepared by the same manufacturing method.
[0077]
<Preparation of 3W unit battery>
An electrode area of 37.5 cm was obtained in the same manner as described in the first embodiment. ² Two unit power generation units were manufactured. Then, the above measurement was performed for each unit, and 100 mA / cm ² It was confirmed that a voltage of 0.4 V or more was obtained at a current density of. Therefore, two unit power generation units were arranged in series with a separator (flow path plate) interposed therebetween. In the flow channel plate, an anode flow channel having the structure shown in FIG. 4 is formed on one surface of one plate, and a meandering cathode flow channel as shown in FIG. 4 is formed on the other surface. Was used. In addition, a sealing material made of a fluororesin was attached to the ends of the anode electrode and the cathode electrode of the unit power generation unit so that fuel and air did not leak. Finally, the two unit power generation units were electrically connected in series by screwing. Further, piping was connected to each unit power generation unit so that liquid supply and air supply could be performed in parallel. Finally, the produced unit stack portion is surrounded by an acrylic plate having a thickness of 0.3 mm, an air layer having a thickness of 0.2 mm is formed as a heat insulating layer between the unit stack portion and the acrylic plate, and heat insulation is performed. Got. However, a silicon rubber heater was attached to the separator, and the temperature inside the holder could be controlled using a commercially available temperature controller. Then, a methanol aqueous solution having a methanol concentration of 2M is supplied to the anode electrode side at 4.46 mL / min, and air is supplied to the cathode electrode side at 750 mL / min. When 3750 mA was applied, it was found that a voltage of 0.8 V was obtained. Thereby, it was confirmed that the output expected from the rated output of the unit power generation unit was obtained from the unit battery, and that there was no problem in the configuration of the unit battery. The surface area S of this unit stack portion is 113.49 cm. ² And (P / S) is 26.43 mW / cm. ² It becomes. That is, it was confirmed that (P / S) satisfied the range defined by the above-described equation (1).
[0078]
<Production of 7W direct methanol fuel cell system>
Two 2W unit batteries and one 3W unit battery connected in parallel were connected in series. Further, piping was connected to each unit battery so that liquid supply and air supply could be performed in parallel. Further, a 10.2 mL / min methanol aqueous solution having a methanol concentration of 2 M was sent to the anode electrode at a rate of 10.42 mL / min, and air was fed to the cathode electrode at 1.75 L / min. When a load current of 3500 mA was applied while maintaining the stack portion at 70 ° C., a voltage of about 2 V was obtained, and an output of 7 W was confirmed. That is, it was shown that there was no problem in the distribution of the aqueous methanol solution and air to each unit battery. Thus, the stack of Example 3 was completed.
[0079]
In the 7W direct methanol fuel cell system completed in this way, since the unit is constituted by three unit cells, the distribution branch in the stack portion can be reduced. Therefore, the volume occupied by the pipe portion can be reduced as compared with the stack portion manufactured by connecting seven 1W unit batteries in series in the same manner as described in Example 2, and directly. It was found to be effective for downsizing of the methanol fuel cell system.
[0080]
In the above-described embodiment, an example is described in which a common fuel tank that collectively stores fuel supplied to the anode electrode of the unit cells is used, but each unit cell may include a fuel tank. .
[0081]
In the above-described embodiment, an example is described in which the methanol flow rate control device and the current temporal change record evaluation device are used. However, the fuel cell power generation device according to the present invention does not include the methanol flow rate control device and the current temporal change record evaluation device. It can be applied to power generation systems.
[0082]
Further, in the above-described embodiment, an example in which the cathode recovery container is used has been described. However, the liquid discharged from the cathode flow path can be directly returned to the first methanol aqueous solution container without using the cathode recovery container. .
[0083]
Further, in the above-described embodiment, an example is described in which the second methanol aqueous solution container is used as a means for replenishing the first methanol aqueous solution container with methanol. However, a configuration without the methanol replenishing means may be employed.
[0084]
Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements in an implementation stage without departing from the scope of the invention. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Further, components of different embodiments may be appropriately combined.
[0085]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide a fuel cell power generation device that is small in size and high in output.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a unit stack portion where a heat insulating layer is not formed.
FIG. 2 is a cross-sectional view showing another example of a unit stack portion where a heat insulating layer is not formed.
FIG. 3 is a schematic diagram showing a unit power generation unit incorporated in the unit stack unit of FIGS. 1 and 2;
FIG. 4 is a schematic view showing a separator incorporated in the unit stack section of FIGS. 1 and 2;
FIG. 5 is a characteristic diagram showing concentration dependence of current-voltage characteristics in a direct methanol fuel cell.
FIG. 6 is a schematic diagram showing an example of a direct methanol fuel cell power generator.
7 is a circuit diagram showing an example of an electric circuit of the direct methanol fuel cell power generator of FIG.
FIG. 8 is a characteristic diagram showing a relationship between a heat release amount and a required radiator volume in the direct methanol fuel cell power generator.
FIG. 9 is a sectional view showing an example of a unit cell incorporated in the fuel cell power generator according to the present invention.
FIG. 10 is a characteristic diagram showing the relationship between (P / S) and the volume of the heat insulating / radiating mechanism in the direct methanol fuel cell power generator for each output density.
FIG. 11 is a characteristic diagram showing the relationship between (P / S) and the volume of the heat insulation / radiation mechanism in the direct methanol fuel cell power generation device for each temperature of the unit stack portion.
FIG. 12 is a characteristic diagram showing temperature dependence of current-voltage characteristics in the direct methanol fuel cell power generator of the first embodiment.
FIG. 13 is a characteristic diagram showing a relationship between (P / S) and power density in the direct methanol fuel cell power generation devices of Example 1 and Comparative Example 1.
FIG. 14 is a cross-sectional view illustrating an example of a unit cell incorporated in the direct methanol fuel cell power generator according to Embodiment 1.
FIG. 15 is a schematic diagram showing a main part of a unit including a plurality of unit cells in the direct methanol fuel cell power generator according to Embodiment 1.
FIG. 16 is a characteristic diagram showing a relationship between a battery capacity and an output density in the direct methanol fuel cell power generators of Example 2 and Comparative Example 2.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Unit power generation part, 2 ... Anode diffusion layer, 3 ... Anode catalyst layer, 4 ... Anode electrode, 5 ... Cathode diffusion layer, 6 ... Cathode catalyst layer, 7 ... Cathode electrode, 8 ... Electrolyte membrane, 9 ... Separator, 10 ... Anode channel, 11 ... Cathode channel, 15 ... Seal material, 16 ... Unit stack part, 17 ... Tightening screw, 20 ... Stack part, 21 ... Methanol aqueous solution, 22 ... First methanol aqueous solution container, 27 ... Cathode recovery Container, 28: liquid, 30: second aqueous methanol solution container, 39: heat insulating layer, 40: acrylic plate.

Claims (4)

A fuel cell power generator including a plurality of unit cells,
Each unit battery is
An anode electrode, a cathode electrode, and a unit stack unit in which a plurality of unit power generation units including an electrolyte membrane disposed between the anode electrode and the cathode electrode are stacked;
A fuel cell power generator comprising: a heat insulating layer covering the surface of the unit stack portion and having a thermal conductivity of 0.1 (W / m / K) or less, and satisfying the following expression (1).
20 ≦ P / S ≦ 31 (1)
Here, P is the output (mW) of each unit battery, and S is the surface area (cm ² ) of the unit stack portion of each unit battery. A fuel cell power generator including a plurality of unit cells,
Each unit battery is
An anode electrode, a cathode electrode, and a unit stack unit in which a plurality of unit power generation units including an electrolyte membrane disposed between the anode electrode and the cathode electrode are stacked;
A fuel cell power generator, comprising: a heat insulating plate surrounding a surface of the unit stack portion with a gap between the unit stack portion and the surface, and satisfying the following expression (1).
20 ≦ P / S ≦ 31 (1)
Here, P is the output (mW) of each unit battery, and S is the surface area (cm ² ) of the unit stack portion of each unit battery. 3. The fuel cell power generator according to claim 1, wherein each unit cell further includes a fuel tank in which fuel is stored. 3. The fuel cell power generator according to claim 1, further comprising a common fuel tank that collectively stores fuel supplied to each unit cell.

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