JPH11219715A - Operation control method for fuel cell - Google Patents
Operation control method for fuel cellInfo
- Publication number
- JPH11219715A JPH11219715A JP10034126A JP3412698A JPH11219715A JP H11219715 A JPH11219715 A JP H11219715A JP 10034126 A JP10034126 A JP 10034126A JP 3412698 A JP3412698 A JP 3412698A JP H11219715 A JPH11219715 A JP H11219715A
- Authority
- JP
- Japan
- Prior art keywords
- electrode
- fuel
- potential
- fuel cell
- fuel electrode
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
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- Fuel Cell (AREA)
- Inert Electrodes (AREA)
Abstract
Description
【0001】[0001]
【発明の属する技術分野】本発明は、燃料電池の運転制
御方法に関し、さらに詳しくは、固体高分子型燃料電池
などにおいて燃料極に用いられる燃料極触媒(Ptある
いはPt−Ru等の貴金属触媒)が燃料ガス中に含まれ
る一酸化炭素(CO)ガス等により被毒・失活しないよ
うにする運転制御方法に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell operation control method, and more particularly, to a fuel electrode catalyst (a noble metal catalyst such as Pt or Pt-Ru) used for a fuel electrode in a polymer electrolyte fuel cell or the like. The present invention relates to an operation control method for preventing poisoning and deactivation by carbon monoxide (CO) gas or the like contained in fuel gas.
【0002】[0002]
【従来の技術】従来、この種の燃料電池として、例え
ば、固体高分子型燃料電池は、図5に示すような基本構
造を有する。すなわち、この固体高分子型燃料電池は、
水素イオン導電性の高分子固体電解質膜12の片側面に
燃料極(負極)14が、また反対側面に空気極(正極)
16がそれぞれ一体的に設けられ、それぞれの電極面に
は集電体(セパレータ)18が配設される。2. Description of the Related Art Conventionally, as a fuel cell of this type, for example, a polymer electrolyte fuel cell has a basic structure as shown in FIG. That is, this polymer electrolyte fuel cell
A fuel electrode (negative electrode) 14 is provided on one side of the hydrogen ion conductive polymer solid electrolyte membrane 12, and an air electrode (positive electrode) is provided on the other side.
16 are provided integrally, and a current collector (separator) 18 is provided on each electrode surface.
【0003】そして集電体18の燃料極14との対向面
には燃料ガス(主に水素ガス)の貫流路が形成され、空
気極16との対向面には酸化剤ガス(主に空気)の貫流
路が形成される。電解質膜12の材料としては、一般に
フッ素系陽イオン交換膜、例えば、デュポン社の「ナフ
ィオン(Nafion)」(商品名)が用いられ、電極基材に
は、カーボンブラック、カーボンペーパ、カーボンクロ
ス等のカーボン材料が、また集電体(セパレータ)には
グラファイト等が用いられる。A flow path for a fuel gas (mainly hydrogen gas) is formed on the surface of the current collector 18 facing the fuel electrode 14, and an oxidizing gas (mainly air) is formed on the surface facing the air electrode 16. Are formed. As a material of the electrolyte membrane 12, a fluorine-based cation exchange membrane, for example, "Nafion" (trade name) of DuPont is generally used, and carbon black, carbon paper, carbon cloth, or the like is used as an electrode substrate. And a current collector (separator) such as graphite.
【0004】この電池の基本原理は、図6に示すよう
に、燃料極に水素、空気極に酸素を供給すると、次の反
応式に示すように、燃料極では酸化反応、空気極では還
元反応が起こり、電解質膜中を水素イオンが移動するこ
とにより起電力が生じるものである。 燃料極:H2 → 2H+ + 2e- 空気極:1/2O2 + 2H+ + 2e- → H2OThe basic principle of this battery is that, as shown in FIG. 6, when hydrogen is supplied to the fuel electrode and oxygen is supplied to the air electrode, an oxidation reaction is performed at the fuel electrode and a reduction reaction is performed at the air electrode as shown in the following reaction formula. Occurs, and hydrogen ions move through the electrolyte membrane to generate an electromotive force. Fuel electrode: H 2 → 2H + + 2e - cathode: 1 / 2O 2 + 2H + + 2e - → H 2 O
【0005】ところでこの種の燃料電池では、十分に大
きな反応速度が得られるように両電極に電極触媒が用い
られる。この反応速度は発電電流として表れるので、こ
れにより高い発電出力が得られる。通常、固体高分子型
燃料電池では、燃料極、空気極とも、Pt触媒あるい
は、Ptを含む多元系触媒(例えば、Pt−Ru触媒)
が用いられる。これらの触媒は通常カーボン電極に担持
されている。In this type of fuel cell, an electrode catalyst is used for both electrodes so that a sufficiently high reaction rate can be obtained. Since this reaction speed appears as a generated current, a high power output can be obtained. Generally, in a polymer electrolyte fuel cell, both a fuel electrode and an air electrode are a Pt catalyst or a multi-component catalyst containing Pt (for example, a Pt-Ru catalyst).
Is used. These catalysts are usually supported on carbon electrodes.
【0006】一方、使用される燃料ガスも、メタン等の
低分子量の炭化水素やメタノール等のアルコール類を改
質して発生させた水素リッチなガスを燃料として用いる
場合がある。図7にそのプラントの概略構成を示した
が、燃料であるメタノールは、改質部において、例えば
Cu−Zn系触媒上で水と反応し、下式のように水素と
二酸化炭素の混合ガスとなり、燃料電池の燃料極に送ら
れる。 CH3OH + H2O → 3H2 + CO2 On the other hand, as a fuel gas to be used, a hydrogen-rich gas generated by reforming a low molecular weight hydrocarbon such as methane or an alcohol such as methanol may be used as a fuel. FIG. 7 shows a schematic configuration of the plant. Methanol as a fuel reacts with water on, for example, a Cu—Zn-based catalyst in a reforming section, and becomes a mixed gas of hydrogen and carbon dioxide as in the following equation. Is sent to the fuel electrode of the fuel cell. CH 3 OH + H 2 O → 3H 2 + CO 2
【0007】ところがこのとき、必ずしも完全に上記反
応が進行するわけではなく、例えば、 CH3OH → 2H2 + CO CO2 + H2 → CO + H2O 等の経路で数%のCOが副生される。この副生されたC
Oは、燃料極の電極触媒であるPt系電極触媒の触媒毒
として作用する。COは、この電極触媒上に強く吸着さ
れ、本来の燃料極の反応である水素酸化の反応を阻害す
る。However, at this time, the above-mentioned reaction does not always proceed completely. For example, several% of CO is added by a route such as CH 3 OH → 2H 2 + CO CO 2 + H 2 → CO + H 2 O. Be born. This by-product C
O acts as a catalyst poison for the Pt-based electrode catalyst, which is the electrode catalyst for the fuel electrode. CO is strongly adsorbed on the electrode catalyst and inhibits a hydrogen oxidation reaction which is an original reaction of the fuel electrode.
【0008】そこで通常、燃料ガス中に含まれるCO濃
度を低減すべく、CO除去部を改質部の後段に置いてい
る。ここでは、下式のようなシフト反応およびCO選択
酸化反応を利用してCO濃度が低減される。 シフト反応:CO + H2O → CO2 + H2 CO選択酸化反応:2CO + O2 → 2CO2 [0008] Therefore, in order to reduce the concentration of CO contained in the fuel gas, a CO removing section is usually provided after the reforming section. Here, the CO concentration is reduced by utilizing a shift reaction and a CO selective oxidation reaction as shown in the following equation. Shift reaction: CO + H 2 O → CO 2 + H 2 CO selective oxidation reaction: 2CO + O 2 → 2CO 2
【0009】上述のように、改質部の後段にCO除去部
を設けることにより改質器出口(燃料電池入り口)のC
O濃度を数10ppmまで低減することが可能となる。
尚、電池の作動温度は比較的低く(200℃以下)、通
常100℃以下の温度で運転される。As described above, by providing the CO removing section at the subsequent stage of the reforming section, the C at the reformer outlet (fuel cell inlet) is provided.
O concentration can be reduced to several tens of ppm.
The operating temperature of the battery is relatively low (200 ° C. or less), and the battery is usually operated at a temperature of 100 ° C. or less.
【0010】[0010]
【発明が解決しようとする課題】しかしながら、この程
度のCO濃度でも、燃料極に純Pt触媒を用いると被毒
を受け、電池性能は低下する。Pt−Ru二元系触媒な
ど通常知られている耐CO性の触媒を用いれば、電池温
度約80℃以上では、数十ppmのCO濃度なら殆どそ
の性能低下は問題にならないことが知られているが、立
ち上がり時など電池温度が十分に上がっていない場合に
は、数十ppmでも性能低下が著しい。However, even with such a CO concentration, if a pure Pt catalyst is used for the fuel electrode, the fuel electrode is poisoned and the cell performance is reduced. It is known that if a generally known CO-resistant catalyst such as a Pt-Ru binary catalyst is used, at a battery temperature of about 80 ° C. or higher, if the CO concentration is several tens of ppm, the performance degradation hardly causes a problem. However, when the battery temperature is not sufficiently raised, such as at the time of startup, the performance is significantly reduced even at several tens of ppm.
【0011】また、負荷変動があり、経時的に改質器で
のガス処理量が変化する場合には、一時的に熱バランス
が崩れて多量のCOが燃料電池に送られることがある。
この場合、耐CO性触媒といえども被毒し、性能が低下
する。したがって燃料極の耐CO対策としては、CO除
去部によるCO濃度の低減とPt−Ru等の耐CO性触
媒の使用に依っても必ずしも十分な対策とは言い難い。Further, when there is a load fluctuation and the gas processing amount in the reformer changes over time, the heat balance may be temporarily lost and a large amount of CO may be sent to the fuel cell.
In this case, even the CO-resistant catalyst is poisoned and its performance is reduced. Therefore, as a countermeasure against CO in the fuel electrode, it is not always sufficient to use a CO-resistant catalyst such as Pt-Ru to reduce the CO concentration by the CO removing section and use a CO-resistant catalyst.
【0012】そこでさらに進歩したCO被毒回避のため
の技術としては、燃料ガスに2%程度の酸素を混入し、
電極触媒上に吸着したCO分子を酸化除去する方法が提
案されている[S.Gottesfeld and J.Pafford, J.Electro
chem. Soc.135, 2651(1988);S.Gottesfeld, US Patent
4910099(Mar.20,1990);D.P.Wilkinson, H.H.Voss, J.Du
dley, G.J.Lamont and V.Basura, US Patent 5432021(1
995), US patent 5482680(1996)参照]。この方法を用い
ると従来よりも低い温度(〜室温)、高いCO濃度(1
00ppm以上)でも性能低下が問題にならなくなると
言われている。Therefore, as a further advanced technique for avoiding CO poisoning, about 2% of oxygen is mixed into fuel gas.
A method for oxidizing and removing CO molecules adsorbed on an electrode catalyst has been proposed [S. Gottesfeld and J. Pafford, J. Electro
chem. Soc. 135 , 2651 (1988); S. Gottesfeld, US Patent
4910099 (Mar. 20, 1990); DP Wilkinson, HHVoss, J. Du
dley, GJ Lamont and V. Basura, US Patent 5432021 (1
995), US patent 5482680 (1996)]. When this method is used, a lower temperature (up to room temperature) and a higher CO concentration (1
(00 ppm or more), it is said that performance degradation does not become a problem.
【0013】しかし、燃料や吹き込む空気の流量の制御
を誤ると電池内での発火や爆発を引き起こす危険を否定
できない。自動車の動力源など、一般民生用の発電装置
としての安全性を確保するためには、少なくとも吹き込
むO2 濃度を1%以下に抑えなければならないが、現状
技術では、O2 濃度を下げると効果が十分得られないと
いう問題がある。However, if the fuel and the flow rate of the blown air are incorrectly controlled, the danger of causing ignition or explosion in the battery cannot be denied. Including a power source for an automobile, in order to ensure the safety of the power generation device for general consumer is must be kept at least blowing O 2 concentration of 1% or less, in the state of the art, lowering the O 2 concentration effect Is not obtained.
【0014】本発明の解決しようとする課題は、燃料ガ
スとして主にメタンやメタノールなどの炭化水素やアル
コール類を水蒸気改質して得られる改質ガスを用いる燃
料電池において、Pt系やPt−Ru系等の活性触媒が
担持される燃料電極の電極表面に吸着されるCO等を酸
化除去し、燃料ガス(水素)中に含まれるCO等の不純
物による電池性能の低下を回避回復することのできる運
転制御方法を提供することにある。An object of the present invention is to provide a fuel cell using a reformed gas obtained by steam reforming hydrocarbons such as methane and methanol or alcohols as a fuel gas. It is intended to oxidize and remove CO and the like adsorbed on the electrode surface of a fuel electrode on which an active catalyst such as a Ru-based catalyst is carried, thereby avoiding and recovering a decrease in battery performance due to impurities such as CO contained in a fuel gas (hydrogen). It is an object of the present invention to provide an operation control method which can be performed.
【0015】[0015]
【課題を解決するための手段】この課題を解決するため
本第一発明に係る燃料電池の運転制御方法は、白金系な
どの電極触媒が担持される燃料極に一酸化炭素などの被
毒ガスを含む燃料ガスを供給すると共に空気極に酸化剤
ガスを供給し、燃料極の酸化及び空気極の還元反応によ
り発電起電力を生じさせる燃料電池において、その発電
中に燃料極の電極電位を一時的に標準水素電極電位に対
して+0.3V 以上貴なる電位とする過程を含むことを
要旨とするものである。According to a first aspect of the present invention, there is provided a method of controlling operation of a fuel cell, wherein a poisonous gas such as carbon monoxide is deposited on a fuel electrode carrying an electrode catalyst such as a platinum-based catalyst. In a fuel cell that supplies fuel gas containing oxidant gas to the cathode while supplying oxidizing gas to the cathode, and generates an electromotive force by oxidation of the anode and reduction reaction of the cathode, the electrode potential of the anode is temporarily changed during the power generation. In addition, the gist of the present invention is to include a step of setting the potential to be +0.3 V or more to the standard hydrogen electrode potential.
【0016】上記構成を有する本発明の運転制御方法で
は、燃料極の電極触媒に蓄積するCO等の不純物を燃料
電池の運転を継続したまま一時的に燃料極の電位を標準
水素電極電位に対して+0.3V よりも貴なる電位にす
ることにより、燃料極を失活させたCO等を酸化除去す
る。そのためCO等による被毒・失活した燃料極表面の
電極触媒はその表面が清浄化され、水素酸化活性が回復
する。In the operation control method of the present invention having the above configuration, the potential of the fuel electrode is temporarily reduced with respect to the standard hydrogen electrode potential while the operation of the fuel cell is continued while impurities such as CO accumulated in the electrode catalyst of the fuel electrode are maintained. By setting the potential to be more noble than +0.3 V, CO and the like that have deactivated the fuel electrode are oxidized and removed. Therefore, the surface of the electrode catalyst on the surface of the fuel electrode that has been poisoned or deactivated by CO or the like is cleaned, and the hydrogen oxidation activity is restored.
【0017】また本第二発明は、燃料極の電極電位を一
時的に標準水素電極電位に対して+0.3V 以上貴なる
電位とする過程として、空気極への酸化剤ガスの供給を
続けたまま燃料ガスの供給量もしくは濃度を減少させる
か、或いは燃料ガスの供給を停止することを要旨とする
ものである。According to the second aspect of the present invention, the supply of the oxidizing gas to the air electrode is continued as a process of temporarily setting the electrode potential of the fuel electrode to a potential nobler than +0.3 V with respect to the standard hydrogen electrode potential. The gist of the present invention is to reduce the supply amount or concentration of the fuel gas as it is or to stop the supply of the fuel gas.
【0018】通常燃料極触媒に吸着されたCO等を電気
化学的に酸化除去できる反応は、+0.3V (標準水素
電極基準)以上の電位域である。また燃料電池が作動し
ている時の燃料極の電位は、+0.1V (標準水素電極
基準)以下であるが、対極の酸素極は酸素等の酸化剤が
供給される限り、十分高い貴な電位を有しているので、
燃料ガスの供給もしくは濃度を一旦減少あるいは停止す
ることにより、燃料極電位を標準水素電極に対し0.3
V 以上貴な電位にすることができる。燃料極電位が上
昇して+0.3V 以上のある電位に達したときに燃料ガ
スの供給を再開するというような運転を行うとよい。燃
料極の電位は理論的には空気極と同電位(+1.0V 標
準水素電極基準くらい)までの上昇は可能であり、CO
を電気化学的に酸化除去する電位は十分に得られる。Usually, a reaction capable of electrochemically oxidizing and removing CO and the like adsorbed on the fuel electrode catalyst is in a potential range of +0.3 V (standard hydrogen electrode standard) or higher. The potential of the fuel electrode when the fuel cell is operating is +0.1 V (standard hydrogen electrode standard) or lower, but the oxygen electrode of the counter electrode is sufficiently high as long as an oxidizing agent such as oxygen is supplied. Because it has a potential,
By temporarily reducing or stopping the supply or concentration of the fuel gas, the fuel electrode potential is set to 0.3 with respect to the standard hydrogen electrode.
It can be set to a noble potential of V or more. It is preferable to perform an operation such as restarting the supply of the fuel gas when the fuel electrode potential rises and reaches a certain potential of +0.3 V or more. The potential of the fuel electrode can theoretically rise to the same potential as the air electrode (+1.0 V, about the standard hydrogen electrode standard).
Is sufficiently obtained to electrochemically oxidize and remove.
【0019】したがって燃料極への燃料ガスの供給量も
しくは濃度を減少あるいは停止する電位をあらかじめ設
定しておき(例えば、0.1V)、その電位を越えると燃
料ガスの供給を減少あるいは停止し、また燃料ガスの供
給を再開する電位もあらかじめ設定しておき(例えば、
0.6V)、その電位に達すると燃料ガスの供給を再開
するように運転制御の自動化を図ることが望ましい。Therefore, a potential for reducing or stopping the supply amount or concentration of the fuel gas to the fuel electrode is set in advance (for example, 0.1 V), and when the potential is exceeded, the supply of the fuel gas is reduced or stopped. In addition, the potential for restarting the supply of the fuel gas is also set in advance (for example,
0.6V), it is desirable to automate the operation control so that the supply of the fuel gas is restarted when the potential is reached.
【0020】[0020]
【発明の実施の形態】以下、本発明の実施例を詳細に説
明する。 (第1の実施例)初めに図1に、この実施例のために製
作した小型の試験用固体高分子型燃料電池(単電池)の
構造を示す。この実施例では、燃料極触媒にPt−Ru
(原子比で1:1)合金触媒をカーボンブラック上に担
持したもの、空気極触媒に純Pt触媒をカーボンブラッ
ク上に担持したもの、電解質膜にナフィオン(デュポン
社の商標名)を用いた。電極の面積は10cm2 とした。DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. (First Embodiment) First, FIG. 1 shows a structure of a small test polymer electrolyte fuel cell (unit cell) manufactured for this embodiment. In this embodiment, Pt-Ru is used as the fuel electrode catalyst.
(1: 1 atomic ratio) An alloy catalyst supported on carbon black, an air electrode catalyst supported on a pure Pt catalyst on carbon black, and Nafion (trade name of DuPont) used as an electrolyte membrane. The area of the electrode was 10 cm 2 .
【0021】実験方法としては、初めに燃料極に純水
素、空気極に空気を供給し、電池の作動温度を60℃と
し、5Aの一定電流で起電力を生じさせた。これにより
端子間の電圧が0.7V で安定作動した。この状態で、
燃料極に供給している水素にCO100ppmを加える
と、端子間電圧は経時的に低下し、最終的には端子間電
圧はおよそ0.3V 程度まで低下した。これは、燃料極
のPt−Ru触媒にCOが化学吸着し、水素の酸化反応
を阻害したためである。As an experimental method, first, pure hydrogen was supplied to the fuel electrode and air was supplied to the air electrode, the operating temperature of the battery was set to 60 ° C., and an electromotive force was generated at a constant current of 5 A. As a result, the voltage between terminals became stable at 0.7 V. In this state,
When 100 ppm of CO was added to the hydrogen supplied to the fuel electrode, the inter-terminal voltage decreased over time, and finally the inter-terminal voltage decreased to about 0.3 V. This is because CO was chemically adsorbed on the Pt-Ru catalyst of the fuel electrode and inhibited the oxidation reaction of hydrogen.
【0022】ここで一旦電流を停止し、まず、空気極に
供給されるガスを空気から純水素に切り替えた。次に燃
料極の電位を、この純水素に切り替えた空気極に対して
+0.05V となるように保持しながら、燃料極に流通
するガスをCOを含む水素から純粋な窒素へと切り替え
た。その後、燃料極の電位を純水素を供給している空気
極(以下「水素参照電極」と呼ぶ)に対して+0.05
V から貴なる方向(+方向、酸化反応がより進みやす
くなる方向)に走査していき、電流の応答性を調べた。Here, the current was temporarily stopped, and first, the gas supplied to the air electrode was switched from air to pure hydrogen. Next, the gas flowing through the fuel electrode was switched from hydrogen containing CO to pure nitrogen while maintaining the potential of the fuel electrode at +0.05 V with respect to the air electrode switched to pure hydrogen. Thereafter, the potential of the fuel electrode is increased by +0.05 with respect to the air electrode supplying pure hydrogen (hereinafter referred to as “hydrogen reference electrode”).
Scanning was performed in a noble direction from V 1 (+ direction, a direction in which the oxidation reaction proceeds more easily), and the response of the current was examined.
【0023】図2は、水素参照電極に対する燃料極の電
位(V)と電流密度(mA/cm2)との関係を示したも
のである。この図2のデータに示されるように、実線で
示した一回目の走査では、水素参照電極に対して +0.
3Vあたりから酸化方向の電流が流れはじめ、表面に吸
着したCOが電気化学的に酸化されているのがわかる。
COの酸化は水素参照電極に対して+0.5V 程度で完
了した。水素参照電極に対し+1.0Vまで電位走査し
た後、再び+0.05Vまで戻し、しばらく保持した
後、二回目の電位走査(破線で示す)を行った。FIG. 2 shows the relationship between the potential (V) of the fuel electrode with respect to the hydrogen reference electrode and the current density (mA / cm 2 ). As shown in the data of FIG. 2, in the first scan shown by the solid line, +0.
A current in the oxidation direction began to flow at around 3 V, indicating that the CO adsorbed on the surface was electrochemically oxidized.
The oxidation of CO was completed at about +0.5 V with respect to the hydrogen reference electrode. After scanning the potential of the hydrogen reference electrode to +1.0 V, the potential was returned to +0.05 V again, and after holding for a while, the second potential scanning (shown by a broken line) was performed.
【0024】二回目の走査では、+0.35V 以下の電
位領域に一回目の走査では認められなかった吸着水素の
酸化に起因する電流が認められ、水素酸化反応に対する
活性が回復していることが示され、さらにCOの酸化に
起因する酸化電流は消失した。 この結果より、電極触
媒上に吸着したCOは、水素電極基準で+0.3V より
も高い電位で酸化が始まり、+0.5V 以上で完全に酸
化除去されることと、一旦酸化除去された後は、触媒の
本来の機能である水素酸化の活性は回復されることがわ
かる。In the second scan, a current due to the oxidation of adsorbed hydrogen, which was not observed in the first scan, was observed in the potential region of +0.35 V or less, indicating that the activity for the hydrogen oxidation reaction was restored. In addition, the oxidation current caused by the oxidation of CO disappeared. From this result, it is found that the CO adsorbed on the electrode catalyst starts to oxidize at a potential higher than +0.3 V on the basis of the hydrogen electrode, and is completely oxidized and removed at +0.5 V or higher. It can be seen that the activity of hydrogen oxidation, which is the original function of the catalyst, is restored.
【0025】(第2の実施例)次に上記した試験用燃料
電池を用いて、燃料ガスとして水素75%、CO100
ppmを含むメタノール改質ガスを供給し、0.5A/c
m2 一定電流での放電を、作動温度60℃、電池内圧
1.5atmの条件で行った。(Second embodiment) Next, using the test fuel cell described above, 75% hydrogen and CO100
Supplying methanol reformed gas containing 0.5 ppm, 0.5 A / c
Discharge at a constant current of m 2 was performed under the conditions of an operating temperature of 60 ° C. and a battery internal pressure of 1.5 atm.
【0026】この実験では一定電流の放電状態の下、放
電時間の経過とともに電池電圧は低下するが、その電池
電圧が0.6V を割り込んだところで、燃料の供給を停
止し、電池電圧が 0.1Vとなったところで速やかに燃
料供給を再開するようにした。そして燃料の供給再開後
には電極活性は初期状態まで回復し、元の電圧 (0.6
V)まで戻るのでその電圧が再び 0.6Vを割り込んだ
ところで燃料の供給を停止し、この操作を繰り返すよう
にした。In this experiment, under a constant current discharge state, the battery voltage decreases with the passage of discharge time. When the battery voltage falls below 0.6 V, the supply of fuel is stopped, and the battery voltage is reduced to 0.6. When the voltage reached 1 V, the fuel supply was immediately restarted. After the fuel supply is resumed, the electrode activity is restored to the initial state, and the original voltage (0.6) is restored.
V), the supply of fuel was stopped when the voltage fell below 0.6 V again, and this operation was repeated.
【0027】図3は、その一定電流の放電状態における
燃料極の電位(水素電極基準)を示したものである。比
較として継続的に運転する場合(従来技術)の電位の変
化を細線あるいは破線で示している。通常、燃料電池が
作動している時の燃料極の電位は、+0.1V(標準水素
電極基準)以下であり、燃料極触媒上に吸着されたCO
は除去されず蓄積されていく。FIG. 3 shows the potential of the fuel electrode (with reference to the hydrogen electrode) in the discharge state at the constant current. As a comparison, a change in potential in the case of continuous operation (prior art) is shown by a thin line or a broken line. Normally, when the fuel cell is operating, the potential of the fuel electrode is +0.1 V (standard hydrogen electrode standard) or less, and the CO adsorbed on the fuel electrode catalyst is
Are accumulated without being removed.
【0028】そして燃料極触媒の活性点がCOで占めら
れてくると、通常の燃料電池反応である水素酸化反応が
阻害され、一定電流や一定負荷の条件で発電すると、過
電圧が増大するため、燃料極の電位は経時的に上昇す
る。燃料極触媒上に吸着されたCOは、電気化学的に酸
化除去することができるが、この反応が起きるのは、通
常+0.3V(標準水素電極基準)以上の電位域である。When the active point of the fuel electrode catalyst is occupied by CO, the hydrogen oxidation reaction, which is a normal fuel cell reaction, is hindered. When power is generated under a constant current or a constant load, the overvoltage increases. The potential of the fuel electrode increases with time. The CO adsorbed on the fuel electrode catalyst can be electrochemically oxidized and removed, but this reaction usually occurs in a potential range of +0.3 V or more (based on a standard hydrogen electrode).
【0029】そのためやがて、COが酸化されうる電位
まで電極電位が上昇すると、一部のCOが酸化され、こ
れによって触媒活性サイトが開放されるので過電圧が減
少して電極電位は下降する。そして0.3V 以下に下が
ると再び燃料極触媒へのCOの吸着が起こって電極電位
が上昇し、0.3V を挟んでCOの吸着と酸化が繰り返
されるため図3に細線で示したようなジグザグ状に電位
の昇降動力を繰り返す。あるいは同図に破線で示したよ
うに0.3V 近辺の一定の電位で推移することとなる。As a result, when the electrode potential rises to a potential at which CO can be oxidized, a portion of CO is oxidized, thereby opening the catalytically active site, thereby reducing the overvoltage and lowering the electrode potential. When the voltage falls below 0.3 V, CO adsorption to the fuel electrode catalyst occurs again, and the electrode potential rises. CO adsorption and oxidation are repeated across 0.3 V, so that a thin line as shown in FIG. The power of raising and lowering the potential is repeated in a zigzag manner. Alternatively, as shown by a broken line in the figure, the potential changes at a constant potential near 0.3 V.
【0030】これに対して本発明の運転方法では、太い
実線で示したように、燃料の供給を停止した時点で燃料
極の電位が急激に上昇し、燃料供給の再開によって元の
電位まで急激に低下する。そしてこれの繰り返しによっ
て燃料極の電位は平均電位+0.1V 以下を維持しつつ
発電できることが明らかとなった。このように本発明方
法の運転制御によれば、燃料の一時停止により燃料極の
触媒表面が一旦完全に清浄化されるので、燃料極におけ
る水素酸化活性は完全に回復されることになる。On the other hand, in the operation method of the present invention, as shown by the thick solid line, the potential of the fuel electrode rapidly rises when the fuel supply is stopped, and suddenly returns to the original potential when the fuel supply is restarted. To decline. By repeating this, it became clear that power generation was possible while maintaining the potential of the fuel electrode at an average potential of +0.1 V or less. As described above, according to the operation control of the method of the present invention, the catalyst surface of the fuel electrode is once completely cleaned by temporarily stopping the fuel, so that the hydrogen oxidation activity at the fuel electrode is completely recovered.
【0031】一方図4は、その一定電流の放電状態にお
ける燃料電池の電圧変化を示したものである。比較とし
て継続的に運転する場合(従来技術)の電圧変化を破線
で示している。このデータよりわかるように、破線で示
した従来技術の電圧変化は、時間の経過によって電池電
圧が低下し、0.3V 当たりまで低下した後もなだらか
な低下傾向を示すことがわかる。FIG. 4 shows a change in voltage of the fuel cell in the discharge state at a constant current. For comparison, the voltage change in the case of continuous operation (prior art) is indicated by a broken line. As can be seen from this data, the voltage change of the prior art shown by the broken line shows that the battery voltage decreases with the passage of time and shows a gradual decrease tendency even after decreasing to about 0.3 V.
【0032】これに対して本発明の場合は、実線で示し
たように、燃料の供給を停止した時点で電池電圧が急激
に低下し、燃料供給の再開によって元の電圧まで急激に
回復する。そしてこれの繰り返しによって電池電位は燃
料の停止・再開の時間を除いて0.6V 以上に保たれた
状態が得られる。本発明によれば、この過程を繰り返す
ことによって高い平均電圧を維持しつつ発電できること
になる。On the other hand, in the case of the present invention, as shown by the solid line, the battery voltage suddenly drops when the supply of fuel is stopped, and rapidly recovers to the original voltage when the fuel supply is restarted. By repeating this, a state is obtained in which the cell potential is maintained at 0.6 V or more except for the time for stopping and restarting the fuel. According to the present invention, power generation can be performed while maintaining a high average voltage by repeating this process.
【0033】燃料極電極電位をCOが酸化除去されるほ
ど高く、水素電極基準の電位で+0.5V 以上とするそ
の他の方法としては、発電の電流を大きくする方法があ
げられる。As another method for increasing the fuel electrode electrode potential so that CO is oxidized and removed and increasing the potential on the basis of the hydrogen electrode to +0.5 V or more, there is a method of increasing the power generation current.
【0034】本発明は上記した実施例に何等限定される
ものではなく、本発明の趣旨を逸脱しない範囲で種々の
改変が可能である。例えば、上記実施例では説明しなか
ったが、燃料極に水素電極基準電位センサを設け、その
電位センサからの検知信号により燃料極の電位があるレ
ベル(例えば、+ 0.1V)より貴になると燃料極への
燃料の供給を停止し、あるレベル(例えば、+ 0.6
V)より貴になると燃料の供給を再開するように制御す
るとよい。またあるいは、その燃料電池に電圧センサを
設け、その電圧センサからの検知信号により同様の制御
(例えば、電圧が0.6V以下になったら燃料の供給を
停止し、0.1V以下になると燃料の供給を再開する)
を行なうようにしてもよく、このようにすれば、燃料電
池の運転が自動的に(オートマチックに)制御されるこ
とになる。The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. For example, although not described in the above embodiment, a hydrogen electrode reference potential sensor is provided in the fuel electrode, and when the potential of the fuel electrode becomes higher than a certain level (for example, +0.1 V) by a detection signal from the potential sensor, The supply of fuel to the anode is stopped, and a certain level (for example, +0.6)
V) It is better to control so that the supply of fuel is restarted when it becomes more noble. Alternatively, a voltage sensor is provided in the fuel cell, and the same control is performed based on a detection signal from the voltage sensor (for example, the supply of fuel is stopped when the voltage becomes 0.6 V or less, and the fuel supply is stopped when the voltage becomes 0.1 V or less). Resume supply)
In this case, the operation of the fuel cell is automatically (automatically) controlled.
【0035】[0035]
【発明の効果】本発明に係る燃料電池の運転制御方法に
よれば、運転中に燃料電極の表面に吸着されるCO等の
不純物を運転途中においてその電極への燃料の供給を一
時的に停止することにより酸化除去し、その燃料電極に
担持される電極触媒の活性が維持されるようにしたもの
であるから、その燃料電池は高い起電力の発生を持続す
ることができ、結果として発電エネルギー効率を向上さ
せることができるものである。また燃料電極はその電極
触媒のCOによる被毒・失活が継続的に回復されるため
に恒久的使用が可能となり、メインテナンスフリーの状
態が得られる等の経済的メリットも大きく、産業上極め
て有益な運転方法と言える。According to the fuel cell operation control method of the present invention, the supply of fuel to the electrode is temporarily stopped during operation due to impurities such as CO adsorbed on the surface of the fuel electrode during operation. By doing so, the activity of the electrocatalyst supported on the fuel electrode is maintained by oxidation, so that the fuel cell can continue to generate high electromotive force, and as a result, The efficiency can be improved. In addition, since the fuel electrode is continuously recovered from the poisoning and deactivation of the electrode catalyst by CO, the fuel electrode can be used permanently and has a great economical advantage such as a maintenance-free state. It can be said that it is a driving method.
【図1】本発明の実施に用いられた試験用固体高分子型
燃料電池の構造を示した図である。FIG. 1 is a diagram showing the structure of a test polymer electrolyte fuel cell used in the practice of the present invention.
【図2】図1に示した試験用燃料電池を用いた実験とし
て、燃料極の対水素参照電極電位(V)と電流密度(m
A/cm2 )との関係を示した図である。FIG. 2 shows an experiment using the test fuel cell shown in FIG. 1 in which the potential of a fuel electrode with respect to hydrogen reference electrode (V) and the current density (m) were measured.
A / cm 2 ).
【図3】別の実験としてCOを含む水素を燃料として燃
料極に供給した時の電位変化を本発明方法と従来技術と
で比較して示した図である。FIG. 3 is a diagram showing, as another experiment, a potential change when hydrogen containing CO is supplied to a fuel electrode as a fuel, by comparing the method of the present invention with a conventional technique.
【図4】図3の実験において燃料電池の電圧変化を本発
明方法と従来技術とで比較して示した図である。FIG. 4 is a graph showing a change in voltage of the fuel cell in the experiment of FIG.
【図5】従来一般に知られる固体高分子型燃料電池の基
本構造を示した図である。FIG. 5 is a diagram showing a basic structure of a conventional polymer electrolyte fuel cell generally known.
【図6】図5に示した燃料電池の基本原理を説明するた
めに示した図である。FIG. 6 is a view for explaining a basic principle of the fuel cell shown in FIG. 5;
【図7】図5及び図6に示した燃料電池において燃料と
して改質ガスを用いる場合のプラントの概略構成を示し
た図である。FIG. 7 is a diagram showing a schematic configuration of a plant when a reformed gas is used as fuel in the fuel cells shown in FIGS. 5 and 6.
10 固体高分子型燃料電池 12 高分子固体電解質膜 14 燃料極 16 空気極 Reference Signs List 10 polymer electrolyte fuel cell 12 polymer solid electrolyte membrane 14 fuel electrode 16 air electrode
Claims (2)
を含む燃料ガスを供給すると共に空気極に酸化剤ガスを
供給し、燃料極の酸化及び空気極の還元反応により発電
起電力を生じさせる燃料電池において、その発電中に、
燃料極の電極電位を一時的に標準水素電極電位に対して
+0.3V 以上貴なる電位とする過程を含むことを特徴
とする燃料電池の運転制御方法。A fuel gas containing a poisoning component is supplied to a fuel electrode on which an electrode catalyst is carried, and an oxidizing gas is supplied to an air electrode to generate an electromotive force by oxidation of the fuel electrode and a reduction reaction of the air electrode. In the resulting fuel cell, during its power generation,
A method for controlling operation of a fuel cell, comprising a step of temporarily setting the electrode potential of a fuel electrode to a potential nobler than +0.3 V with respect to a standard hydrogen electrode potential.
素電極電位に対して+0.3V 以上貴なる電位とする過
程が、空気極への酸化剤ガスの供給を続けたまま燃料ガ
スの供給量もしくは濃度を減少させる過程あるいは燃料
ガスの供給を停止する過程であることを特徴とする前記
請求項1に記載する燃料電池の運転制御方法。2. The step of temporarily setting the electrode potential of the fuel electrode to a potential nobler than +0.3 V with respect to the standard hydrogen electrode potential is performed by continuously supplying the oxidizing gas to the air electrode. 2. The method for controlling operation of a fuel cell according to claim 1, wherein the step is a step of decreasing the supply amount or concentration or a step of stopping the supply of the fuel gas.
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JP03412698A JP3536645B2 (en) | 1998-01-30 | 1998-01-30 | Fuel cell operation control method |
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JP2016527387A (en) * | 2013-05-31 | 2016-09-08 | サステイナブル イノベーションズ エルエルシーSustainable Innovations,Llc | Hydrogen recycling apparatus and operation method |
WO2023217720A1 (en) * | 2022-05-09 | 2023-11-16 | Robert Bosch Gmbh | Method for operating a fuel cell system, and control device |
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