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JP3906923B2 - Method for activating gas diffusion electrode - Google Patents

Method for activating gas diffusion electrode Download PDF

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JP3906923B2
JP3906923B2 JP2003283979A JP2003283979A JP3906923B2 JP 3906923 B2 JP3906923 B2 JP 3906923B2 JP 2003283979 A JP2003283979 A JP 2003283979A JP 2003283979 A JP2003283979 A JP 2003283979A JP 3906923 B2 JP3906923 B2 JP 3906923B2
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gas diffusion
electrode
electrolysis
diffusion electrode
voltage
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JP2005048266A (en
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健二 野々村
幸治 斎木
洋明 相川
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Mitsui Chemicals Inc
Toagosei Co Ltd
Kaneka Corp
Osaka Soda Co Ltd
Asahi Kasei Chemicals Corp
Tokuyama Corp
Tosoh Corp
AGC Inc
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Asahi Glass Co Ltd
Mitsui Chemicals Inc
Daiso Co Ltd
Toagosei Co Ltd
Kaneka Corp
Asahi Kasei Chemicals Corp
Tokuyama Corp
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Description

本発明は、ガス拡散電極の電極性能を向上させる活性化方法に関する。   The present invention relates to an activation method for improving electrode performance of a gas diffusion electrode.

ガス拡散陰極を陰極に使用し、陰極に酸素ガスを供給して行う酸素陰極食塩電解法は、通常のイオン交換膜法食塩電解に較べて省エネルギー効果が大きく、現在実用化を目指して開発中である。この技術においては、上記のように陰極にはガス拡散電極が使用され、このガス拡散電極に酸素が供給される。多くのガス拡散電極は、液体の存在下に気体の反応物を電解反応させるための反応層と、気体は透過するが電解液は透過しないガス供給層とから構成される。反応層は、一般に触媒が担持された親水性カーボンブラック、疎水性カーボンブラック及びポリテトラフルオロエチレン(PTFE)から構成され、これらの材料からそれらの配合比率を変化させて、電解液が浸入する親水部とガスか供給される疎水部から成るように分散、自己組織化されることにより製造されている。そして、製造後そのままセルに装着して使用していた。   The oxygen cathodic salt electrolysis method, which uses a gas diffusion cathode as the cathode and supplies oxygen gas to the cathode, has a greater energy saving effect than ordinary ion exchange membrane salt electrolysis, and is currently being developed for practical application. is there. In this technique, a gas diffusion electrode is used as the cathode as described above, and oxygen is supplied to the gas diffusion electrode. Many gas diffusion electrodes are composed of a reaction layer for electrolytically reacting a gaseous reactant in the presence of a liquid, and a gas supply layer that transmits gas but does not transmit electrolyte. The reaction layer is generally composed of hydrophilic carbon black, hydrophobic carbon black and polytetrafluoroethylene (PTFE) on which a catalyst is supported, and the mixing ratio of these materials is changed to allow the electrolyte to enter. It is manufactured by being dispersed and self-assembled so as to consist of a part and a hydrophobic part supplied with gas. And after manufacture, it mounted | worn and used for the cell as it was.

この状態で電解を開始すると、当初は電圧が高く、その後電圧は徐々に低下してゆく。その期間は電極により異なり、数週間から数ヶ月に及ぶ。このような現象が長期に及ぶことは、電力エネルギーの損失を意昧する。高電圧の原因は、反応過電圧であることが測定により分かっている。   When electrolysis is started in this state, the voltage is initially high and then the voltage gradually decreases. The duration varies from electrode to electrode and ranges from weeks to months. Such a long-term phenomenon implies a loss of power energy. Measurements have shown that the cause of the high voltage is a reaction overvoltage.

このような現象が起こる理由は、次のように理解されている。製造直後のガス拡散電極の反応層は撥水性が高く、反応成分である水が電極内へなかなか浸入できない。反応成分供給の困難さが過電圧の上昇として現れる。PTFE量、疎水性カーボンの使用割合を低下し、水の浸入を容易にすることによって、運転初期から低電圧を維持することは可能であるが、このような電極の寿命は概して非常に短い。   The reason why such a phenomenon occurs is understood as follows. The reaction layer of the gas diffusion electrode immediately after production has high water repellency, and water as a reaction component cannot easily enter the electrode. The difficulty in supplying reaction components appears as an increase in overvoltage. Although it is possible to maintain a low voltage from the beginning of operation by reducing the amount of PTFE, the proportion of hydrophobic carbon used, and facilitating water ingress, the life of such electrodes is generally very short.

一方、疎水性の高い電極においても、当該電極において水素発生反応を行うことにより、運転当初より低電圧を実現できることが知られている(例えば特許文献1参照)。このことは、水素発生を行うことによって反応層内の濡れが進行し、反応成分である水の供給が容易になるためと推測されている。測定をすると、水素発生反応を行った電極の過電圧は低くなっている。   On the other hand, it is known that even a highly hydrophobic electrode can realize a low voltage from the beginning of operation by performing a hydrogen generation reaction at the electrode (see, for example, Patent Document 1). This is presumed to be because the wetting in the reaction layer proceeds by generating hydrogen, and the supply of water as a reaction component is facilitated. When measured, the overvoltage of the electrode that has undergone the hydrogen generation reaction is low.

初期活性化のための水素発生は、陰極室への酸素供給を停止し、さらに窒素を供給し酸素を無くした状態で、定電流電解を行うことによって水素発生が可能となる。その際の電流密度は通常、食塩電解と同じ電流密度で行われている。例えば300mA/cm2(3kA/m2)前後の電流密度である。 Hydrogen generation for initial activation can be performed by performing constant-current electrolysis in a state where oxygen supply to the cathode chamber is stopped and nitrogen is further supplied to eliminate oxygen. The current density at that time is usually performed at the same current density as that of the salt electrolysis. For example, the current density is around 300 mA / cm 2 (3 kA / m 2 ).

特許第2990512号公報Japanese Patent No. 2990512

しかしながら、従来の水素発生方法には、電解条件によっては電極が破壊される場合があるという致命的な問題があった。従来の活性化方法における電解時間は、1分程度と極めて短い時間であった。この時間を越えると電極は破壊されてしまう。電極によっては1分以内から破壊が始まった。電極の内部で水素発生が起り、組織がガス発生圧力に耐えられないため、破壊が起こると理解される。このように破壊に至る時間が極めて短いため、親水化の効果が出る前に電極が破壊されてしまうという問題があった。   However, the conventional hydrogen generation method has a fatal problem that the electrode may be destroyed depending on electrolysis conditions. The electrolysis time in the conventional activation method was as short as about 1 minute. If this time is exceeded, the electrode will be destroyed. Depending on the electrode, destruction started within 1 minute. It is understood that hydrogen breakdown occurs inside the electrode and the breakdown occurs because the tissue cannot withstand the gas generation pressure. As described above, since the time to break is extremely short, there is a problem that the electrode is broken before the effect of hydrophilization.

本発明は、このような従来の課題に鑑みてなされたものであり、確実に反応層内部を親水化し、かつ電極の破壊が起こらない、ガス拡散電極の初期活性化法を提供することを目的とする。   The present invention has been made in view of such conventional problems, and it is an object of the present invention to provide an initial activation method for a gas diffusion electrode that reliably hydrophilizes the inside of a reaction layer and does not cause electrode destruction. And

本発明者等は、これらの問題について鋭意研究した結果、極めて微少な電流密度で水素発生を行うことによって、電極の破壊が起こることなく、初期過電圧を低減できることを発見し、このような知見に基づいて本発明は完成するに至ったものである。   As a result of diligent research on these problems, the present inventors have found that by generating hydrogen at an extremely small current density, the initial overvoltage can be reduced without causing electrode destruction. Based on this, the present invention has been completed.

すなわち、本発明は、次の構成によって上記の課題を解決した。
(1)ガス拡散電極を電解液中で陰極として電解を行い、水素を発生させることにより、ガス拡散電極の活性化を行う方法において、0.4mA/cm2ないし100mA/cm2の低電流密度で電解することを特徴とするガス拡散電極の活性化方法。
(2)電解液が苛性ソーダ水溶液であることを特徴とする請求項1記載のガス拡散電極の活性化方法。
That is, the present invention solves the above-described problems by the following configuration.
(1) a gas diffusion electrode performs electrolysis as the cathode in the electrolytic solution, by generating hydrogen, lower current density in the method of activating the gas diffusion electrode, 0.4 mA / cm 2 to 100 mA / cm 2 A method for activating a gas diffusion electrode, characterized by electrolyzing with a gas.
(2) The method for activating a gas diffusion electrode according to claim 1, wherein the electrolytic solution is an aqueous caustic soda solution.

本発明によれば、低電流密度で水素発生処理を行うことで、ガス拡散電極を破壊することなく、本来の電極性能をはじめから発揮させることができる。   According to the present invention, by performing the hydrogen generation treatment at a low current density, the original electrode performance can be exhibited from the beginning without destroying the gas diffusion electrode.

本発明を具体的に塩化アルカリ電解の酸素陰極として実施するための条件について説明する。まず、製造したガス拡散電極を電解槽にセットする。電解槽は陽極部、イオン交換膜、陰極部を順に重ねて構成される。陽極部は陽極を収容する陽極室から構成される。陽極としては、通常酸化ルテニウムをコーティングしたチタン製電極(DSA(登録商標))を使用することができる。
イオン交換膜としてはパーフルオロスルフォン酸/パーフルオロカルボン酸積層膜(商品名例;ナフィオン、フレミオン、アシプレックス)が使用できる。
陰極部はガス拡散陰極と、隣接するガス室を収容する陰極枠から構成される。イオン交換膜とガス拡散電極の間隙は、苛性ソーダ液で満たされる。
ガス拡散電極の裏面はガス室となる。ガス室には金属製の充填物が充填され、充填物はガス拡散電極裏面と接触し、隔壁→金属製ガス室充填物→ガス拡散電極と電気が供給される。
陽極室には塩水を流し、中間室(陰極液室)には苛性ソーダ液を流し、ガス室には酸素含有ガスを流し、陽極陰極間に通電することによって電解反応を行うことができる。
The conditions for specifically implementing the present invention as an oxygen cathode for alkaline chloride electrolysis will be described. First, the manufactured gas diffusion electrode is set in an electrolytic cell. The electrolytic cell is constructed by sequentially stacking an anode part, an ion exchange membrane, and a cathode part. The anode part is composed of an anode chamber that houses the anode. As the anode, a titanium electrode (DSA (registered trademark)) coated with ruthenium oxide can be used.
As the ion exchange membrane, a perfluorosulfonic acid / perfluorocarboxylic acid laminated membrane (trade name examples; Nafion, Flemion, Aciplex) can be used.
The cathode portion is composed of a gas diffusion cathode and a cathode frame that accommodates an adjacent gas chamber. The gap between the ion exchange membrane and the gas diffusion electrode is filled with a caustic soda solution.
The back surface of the gas diffusion electrode is a gas chamber. The gas chamber is filled with a metal filling, and the filling is in contact with the back surface of the gas diffusion electrode, and electricity is supplied to the partition → the metal gas chamber filling → the gas diffusion electrode.
An electrolytic reaction can be performed by flowing salt water in the anode chamber, flowing caustic soda solution in the intermediate chamber (catholyte chamber), flowing an oxygen-containing gas in the gas chamber, and energizing between the anode and cathode.

水素発生活性化は、ガス室への酸素供給を停止し、好ましくは窒素等の不活性ガスにより酸素置換を行った後、電解することによって行われる。活性化すべきガス拡散電極は、陰極となるように通電する必要がある。温度は、室温から電解操業温度の範囲内で特に問題なく行うことができる。活性化は、電解操業前に行うのが通常であるから、所定の温度まで加温されていない場合が多いが、特に問題はない。最も重要なことは、水素発生の電流密度を0.4mA/cm2ないし100mA/cm2とすることである。これ以下の電流密度では活性化効果が不十分である。一方、これ以上の電流密度では電極が破壊される恐れがある。好ましくは1mA/cm2ないし100mA/cm2である。通電時間は10分程度が好ましい。好ましい電流密度範囲内においても、比較的高い電流密度では水素発生時間は短くても構わない。 The hydrogen generation activation is performed by electrolysis after stopping the oxygen supply to the gas chamber and preferably performing oxygen substitution with an inert gas such as nitrogen. The gas diffusion electrode to be activated needs to be energized so as to become a cathode. The temperature can be carried out without any particular problem within the range from room temperature to the electrolysis operating temperature. Since the activation is usually performed before the electrolytic operation, it is often not heated to a predetermined temperature, but there is no particular problem. Most importantly, the current density for hydrogen generation is set to 0.4 mA / cm 2 to 100 mA / cm 2 . If the current density is less than this, the activation effect is insufficient. On the other hand, at a current density higher than this, the electrode may be destroyed. It is preferably 1 mA / cm 2 to 100 mA / cm 2 . The energization time is preferably about 10 minutes. Even within a preferable current density range, the hydrogen generation time may be short at a relatively high current density.

水素発生反応が起こっていることを確認することは重要である。ガス室を窒素置換しても、ガス拡散電極内には酸素が大量に吸着されており、水素発生反応よりも酸素還元反応が優先するため、吸着された酸素が消費されるまで水素発生は起こらない。ガス拡散電極は通常大気中で製造され、またたとえ窒素のような不活性ガス中で製造されても、電解槽に装着されるまでには大気開放されるのが通例であり、大量の酸素を吸着しているわけである。水素発生反応が起こっていても電流が微少であるため、苛性ソーダ液中への気泡発生が必ず起るわけではないので気泡発生により水素発生反応を確認するのは困難である。水素発生反応を確認するためには電圧を監視するのがよい。酸素還元反応が起こっている間は、電解槽電圧は1Vないし1.5Vである。一方、水素発生反応が起っている場合は、電圧は2.0Vないし2.5Vとなる。従って、電圧が2V以上を示してから10分程度電解を続けるのがよい。   It is important to confirm that a hydrogen evolution reaction is taking place. Even if the gas chamber is replaced with nitrogen, a large amount of oxygen is adsorbed in the gas diffusion electrode, and the oxygen reduction reaction has priority over the hydrogen generation reaction, so hydrogen generation does not occur until the adsorbed oxygen is consumed. Absent. Gas diffusion electrodes are usually manufactured in the atmosphere, and even if they are manufactured in an inert gas such as nitrogen, they are usually opened to the atmosphere before being installed in the electrolytic cell, and a large amount of oxygen is released. It is adsorbed. Even if a hydrogen generation reaction occurs, since the current is very small, bubbles are not necessarily generated in the caustic soda solution, so it is difficult to confirm the hydrogen generation reaction by the generation of bubbles. The voltage should be monitored to confirm the hydrogen generation reaction. While the oxygen reduction reaction is taking place, the electrolytic cell voltage is 1V to 1.5V. On the other hand, when the hydrogen generation reaction occurs, the voltage is 2.0V to 2.5V. Therefore, it is preferable to continue electrolysis for about 10 minutes after the voltage shows 2 V or more.

上記の例は、電解と初期活性化を同一の電解槽にて行った例である。活性化は、電解とは異なる予備活性化電解槽において行うことも可能である。例えば、苛性ソーダ水溶液の中にニッケルメッシュからなる陽極とガス拡散電極を対向させて配置し、ガス拡散電極が陰極となるように通電することによっても可能である。この場合電解槽とは別の設備を用意する必要があるが、設備は非常に簡単なものである。電解槽に装着する前に活性化できるという利点があり、この場合電解槽では当初から通常の電解条件で電解を行なうことができるので、電解槽の電解操作が簡単となる。   In the above example, electrolysis and initial activation are performed in the same electrolytic cell. Activation can also be performed in a pre-activated electrolytic cell different from electrolysis. For example, an anode made of nickel mesh and a gas diffusion electrode are arranged in a caustic soda solution so as to face each other, and energization is performed so that the gas diffusion electrode becomes a cathode. In this case, it is necessary to prepare a facility separate from the electrolytic cell, but the facility is very simple. There is an advantage that it can be activated before being attached to the electrolytic cell. In this case, the electrolytic cell can be electrolyzed under normal electrolysis conditions from the beginning, so that the electrolytic operation of the electrolytic cell is simplified.

活性化に使用する直流電源は、電解用電源をそのまま使用することもできるが、別途小型の直流電源を使用する方が好ましい。活性化に使用する電流は電解電流に較べて逢かに微少であり、電解用電源では、このような微少電流を制御することは困難な場合が多いからである。工業用電解槽は、運転前は回路から切り離されている場合が通常であり、別途小型の直流電源を当該電解槽へ結線することは容易である。   As the DC power source used for activation, an electrolysis power source can be used as it is, but it is preferable to use a separate small DC power source. This is because the current used for activation is much smaller than the electrolysis current, and it is often difficult to control such a microcurrent with an electrolysis power supply. An industrial electrolytic cell is usually disconnected from a circuit before operation, and it is easy to connect a small DC power source to the electrolytic cell.

活性化の効果は、工業用電解槽においては、活性化前後の槽電圧で判断するしかない。一方小型の実験室用電解槽であれば、カレントインターラプト法により、過電圧の変化として確認することができる。槽電圧をオシロスコープ等で監視しながら電解電流を瞬断すれば、瞬断直後の電圧は理論分解電圧に過電圧を加えた電圧を示すから、理論分解電圧を差し引いた値から過電圧を知ることができる。なお、この過電圧は陽極の過電圧も含むが、活性化処理で陽極が変化を受けることはないので、陰極の活性化効果を知ることができる。電解槽内に第3の参照電極を挿入して陰極の電位を測定すれば、陰極の電位変化を直接知ることができる。   The effect of activation can only be judged by the cell voltage before and after activation in an industrial electrolytic cell. On the other hand, a small laboratory electrolytic cell can be confirmed as a change in overvoltage by a current interrupt method. If the electrolytic current is momentarily interrupted while monitoring the cell voltage with an oscilloscope, etc., the voltage immediately after the instantaneous interruption indicates the voltage obtained by adding the overvoltage to the theoretical decomposition voltage, so the overvoltage can be known from the value obtained by subtracting the theoretical decomposition voltage. . Although this overvoltage includes the overvoltage of the anode, since the anode is not changed by the activation process, the activation effect of the cathode can be known. If the potential of the cathode is measured by inserting the third reference electrode into the electrolytic cell, the potential change of the cathode can be directly known.

以下実施例により本発明を具体的に説明する。ただし、本発明は、これらの実施例のみに限定されるものではない。なお、全実施例を通じて、部は全て重量部を、%は全て重量%を意味する。
(実施例1)
The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples. Throughout all the examples, all parts are by weight and all% are by weight.
(Example 1)

銀を10%担持した親水性カーボンブラック(AB−12、平均粒径400オングストローム、試作品、電気化学工業社製)2.5部に、界面活性剤8%トライトンを200部と、PTFEディスパージョンD−1(ダイキン工業社製)を1部分散させた。この分散液にイソプロピルアルコールを300部加え、自己組織化させ、親水部とした。別に、疎水性カーボンブラック(No.6、平均粒径500オングストローム、試作品、電気化学工業社製)2部に、界面活性剤8%トライトンを200部とPTFEディスパージョンD−1(ダイキン工業社製)を1.4部分散させ、イソプロピルアルコールを300部加え、自己組織化させ疎水部とした。親水部と疎水部を7:3の割合で混合撹拌、ろ過、乾燥して反応層原料粉末を作った。   PTFE dispersion with 2.5 parts of hydrophilic carbon black carrying 10% silver (AB-12, average particle size 400 angstrom, prototype, manufactured by Denki Kagaku Kogyo), 200 parts of surfactant 8% triton One part of D-1 (manufactured by Daikin Industries) was dispersed. To this dispersion, 300 parts of isopropyl alcohol was added and self-assembled to form a hydrophilic part. Separately, 2 parts of hydrophobic carbon black (No. 6, average particle size 500 angstrom, prototype, manufactured by Denki Kagaku Kogyo Co., Ltd.), 200 parts of surfactant 8% Triton and PTFE dispersion D-1 (Daikin Kogyo Co., Ltd.) 1.4 parts) was dispersed, and 300 parts of isopropyl alcohol was added to self-assemble to form a hydrophobic part. The hydrophilic portion and the hydrophobic portion were mixed and stirred at a ratio of 7: 3, filtered and dried to prepare a reaction layer raw material powder.

疎水性カーボンブラック(No.6、平均粒径500オングストローム、試作品、電気化学工業製)2部と、PTFEディパージョン(D−1、ダイキン工業社製)1.4部から製造したガス供給層分散液を、イソプロピルアルコールで自己組織化させ、ろ過、乾燥してガス供給層原料粉末を得た。ロール法でガス拡散電極シートを製造し、80℃で3時間乾燥し、界面活性剤をエタノール抽出装置で除去した。乾燥後、銀網と共に50kg/cm2で380℃、60秒間プレスして電極を得た。できあがったガス拡散電極の厚みは1.0mm、その内反応層の厚みは0.10mmであった。 Gas supply layer manufactured from 2 parts of hydrophobic carbon black (No. 6, average particle size 500 angstrom, prototype, manufactured by Denki Kagaku Kogyo) and 1.4 parts of PTFE dispersion (D-1, manufactured by Daikin Industries, Ltd.) The dispersion was self-assembled with isopropyl alcohol, filtered and dried to obtain a gas supply layer raw material powder. A gas diffusion electrode sheet was produced by a roll method, dried at 80 ° C. for 3 hours, and the surfactant was removed by an ethanol extraction apparatus. After drying, an electrode was obtained by pressing at 380 ° C. for 60 seconds at 50 kg / cm 2 with a silver net. The resulting gas diffusion electrode had a thickness of 1.0 mm, and the thickness of the reaction layer was 0.10 mm.

この電極を使用して、有効電極面積が幅10cm高さ60cmである酸素陰極電解槽を組み立てた。陽極にはDSA(登録商標)(チタン製電極)、イオン交換膜にはフレミオン893(登録商標)を使用した。陽極室には飽和食塩水を、陰極液室には31%苛性ソーダ水溶液を、ガス室にはPSAより93%酸素を必要量の1.5倍供給し、電解槽の温度を87℃に維持しながら電解を行った。極間距離は1mm、電流密度は3kA/m2とした。 Using this electrode, an oxygen cathode electrolytic cell having an effective electrode area of 10 cm in width and 60 cm in height was assembled. DSA (registered trademark) (titanium electrode) was used for the anode, and Flemion 893 (registered trademark) was used for the ion exchange membrane. Saturated saline solution is supplied to the anode chamber, 31% sodium hydroxide aqueous solution is supplied to the catholyte chamber, and 93% oxygen is supplied to the gas chamber 1.5 times the required amount from PSA, and the temperature of the electrolytic cell is maintained at 87 ° C. Electrolysis was performed. The distance between the electrodes was 1 mm, and the current density was 3 kA / m 2 .

初期電解電圧は2.06Vであった。カレントインターラプト法により過電圧を測定したところ0.47Vであった。48時間後も電圧、過電圧は初期と全く同じであった。48時間後に酸素の供給を停止し、電流500mA(電流密度0.83mA/cm2)で10分間電解を行った。そのときの指示電圧は2.55Vであり、水素発生を行っていることがわかった。再び酸素を以前と同様に供給し、電流密度3kA/m2で電解を行った。電解電圧は2.01V、過電圧は0.42Vであった。その後電圧は2.01Vで安定に推移した。また電解槽を解体し、電極を観測したところ異常はまったく認められなかった。
なお、電解を開始して48時間後に電極の活性化を行なったのは、この種の電極は活性化処理をしなくとも長時間電解すると活性化されるものであって、その時間は電極の種類によって異なり、短時間の運転で活性化するものもあるので、今回の試験で用いた電極が短時間で活性化されるものではないことを確認するために、2日間の運転を行なってその間に電圧低下が起こらなかったことを示したものであり、以下の例でも同様にした。
(比較例1)
The initial electrolysis voltage was 2.06V. The overvoltage measured by the current interrupt method was 0.47V. Even after 48 hours, the voltage and overvoltage were exactly the same as in the initial stage. After 48 hours, the supply of oxygen was stopped, and electrolysis was performed for 10 minutes at a current of 500 mA (current density of 0.83 mA / cm 2 ). The indicated voltage at that time was 2.55 V, and it was found that hydrogen was generated. Again, oxygen was supplied as before, and electrolysis was performed at a current density of 3 kA / m 2 . The electrolytic voltage was 2.01V, and the overvoltage was 0.42V. After that, the voltage was stable at 2.01V. When the electrolytic cell was disassembled and the electrodes were observed, no abnormality was observed.
The reason why the electrode was activated 48 hours after the start of electrolysis was that this type of electrode was activated when electrolysis was performed for a long time without any activation treatment, Depending on the type, there are some that are activated in a short time operation, so in order to confirm that the electrode used in this test is not activated in a short time, the operation was performed for 2 days. This shows that no voltage drop occurred, and the same applies to the following examples.
(Comparative Example 1)

実施例1と同一の電極を使用して、実施例1と同様な条件で電解を開始した。電圧、過電圧も実施例1と同様であった。48時間後、酸素の供給を停止し、180A(電流密度3kA/m2)で1分間電解を行った。その間、30秒後ぐらいから出口の苛性ソーダ液が黒く濁り、電極の破壊が始まっていることがわかった。再び酸素を供給し、電解を行ったところ電圧は2.15Vと上昇していた。
(比較例2)
Using the same electrode as in Example 1, electrolysis was started under the same conditions as in Example 1. The voltage and overvoltage were the same as in Example 1. After 48 hours, the supply of oxygen was stopped, and electrolysis was performed at 180 A (current density: 3 kA / m 2 ) for 1 minute. In the meantime, it was found that the caustic soda solution at the outlet became black and cloudy after about 30 seconds, and the destruction of the electrode started. When oxygen was supplied again and electrolysis was performed, the voltage increased to 2.15V.
(Comparative Example 2)

実施例1と同一の電極を使用して、実施例1と同様な条件で電解を開始した。電圧、過電圧も実施例1と同様であった。48時間後、酸素の供給を停止し、200mA(電流密度0.34mA/cm2)で10分間電解を行った。再び酸素を以前と同様に供給し、電流密度3kA/m2で電解を行った。電解電圧は2.06V、過電圧は0.47Vであり、電圧の低下は全く認められなかった。
(実施例2)
Using the same electrode as in Example 1, electrolysis was started under the same conditions as in Example 1. The voltage and overvoltage were the same as in Example 1. After 48 hours, the supply of oxygen was stopped, and electrolysis was performed at 200 mA (current density: 0.34 mA / cm 2 ) for 10 minutes. Again, oxygen was supplied as before, and electrolysis was performed at a current density of 3 kA / m 2 . The electrolytic voltage was 2.06 V, the overvoltage was 0.47 V, and no voltage drop was observed.
(Example 2)

実施例1と同一の電極を使用して、実施例1と同様な条件で電解を開始した。電圧、過電圧も実施例1と同様であった。48時間後、酸素の供給を停止し、300mA(電流密度0.50mA/cm2)で10分間電解を行った。再び酸素を以前と同様に供給し、電流密度3kA/m2で電解を行った。電解電圧は2.03V、過電圧は0.44Vであり、電圧の低下は0.03Vであった。 Using the same electrode as in Example 1, electrolysis was started under the same conditions as in Example 1. The voltage and overvoltage were the same as in Example 1. After 48 hours, the supply of oxygen was stopped, and electrolysis was performed at 300 mA (current density: 0.50 mA / cm 2 ) for 10 minutes. Again, oxygen was supplied as before, and electrolysis was performed at a current density of 3 kA / m 2 . The electrolytic voltage was 2.03 V, the overvoltage was 0.44 V, and the voltage drop was 0.03 V.

本発明によれば、極めて微少な電流密度で水素発生処理を行うことによって、ガス拡散電極を破壊することなく、ガス拡散電極の反応槽内部の親水性細孔に電解液を浸入しやすくすることができ、初期過電圧を低減でき、本来の電極性能をはじめから発揮させることができる。   According to the present invention, by performing the hydrogen generation treatment at an extremely small current density, the electrolyte can easily enter the hydrophilic pores inside the reaction tank of the gas diffusion electrode without destroying the gas diffusion electrode. The initial overvoltage can be reduced and the original electrode performance can be exhibited from the beginning.

Claims (2)

ガス拡散電極を電解液中で陰極として電解を行い、水素を発生させることにより、ガス拡散電極の活性化を行う方法において、0.4mA/cm2ないし100mA/cm2の低電流密度で電解することを特徴とするガス拡散電極の活性化方法。 The gas diffusion electrodes perform electrolysis as the cathode in the electrolytic solution, by generating the hydrogen, in the method to activate the gas diffusion electrode, to 0.4 mA / cm 2 not to electrolysis at a low current density of 100 mA / cm 2 A method for activating a gas diffusion electrode. 電解液が苛性ソーダ水溶液であることを特徴とする請求項1記載のガス拡散電極の活性化方法。   2. The method of activating a gas diffusion electrode according to claim 1, wherein the electrolytic solution is an aqueous caustic soda solution.
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