JP2004068127A

JP2004068127A - Electrode for electrolysis, method for manufacturing the same, and electrolytic cell having this electrode for electrolysis

Info

Publication number: JP2004068127A
Application number: JP2002232389A
Authority: JP
Inventors: Chiaki Iwakura; 岩倉　千秋; Hiroshi Inoue; 井上　博史; Naoharu Furukawa; 古川　直治; Shinji Nohara; 野原　愼士; Tsuneto Furuta; 古田　常人; Yoshinori Nishiki; 錦　善則; Megumi Koizumi; 小泉　恵
Original assignee: Permelec Electrode Ltd
Current assignee: De Nora Permelec Ltd
Priority date: 2002-08-09
Filing date: 2002-08-09
Publication date: 2004-03-04

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode which can drastically improve current efficiency and can rapidly perform a desired reaction, a method for manufacturing the same, and an electrolytic cell using this electrode. <P>SOLUTION: The electrode 5 for electrolysis is obtained by three-dimensionally forming a hydrogen occlusion material 3 which is an electrode active material on the surface of an electrode base material 1. Atomic hydrogen which is occluded into the hydrogen occlusion material and has high activity is usable as a hydrogenation source and the hydrogen occlusion material has a three-dimensional structure and has an immense increase of its surface area. The current efficiency of the target hydrogenation reaction etc., is improved by the synergistic effects of both. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、水素化反応に適した電解用電極、その製造方法、該電解用電極を有する電解セルに関する。
【０００２】
【従来の技術】
水素吸蔵材料からなる電極を有する電解セルで、電極から到達した原子状水素を用いて被処理物質の還元や水素化を行う電解方法が提案されている（特開平９−１８４０８６号公報）。またこの方法は還元や水素化反応以外に脱水素反応にも適用され、該脱水素反応には、天然物の合成に用いられるケトン類の脱水素による不飽和ケトンの生成や芳香族炭化水素の生成などが含まれる。
通常の水素吸蔵材である箔を使用する電極反応では、二次元表面で反応が進行するため、電解処理に時間を要し、工業的な応用が困難である。反応速度を向上させるためには、触媒を最適化すること、及び被処理物質との接触面積を大きくすることが望ましい。
【０００３】
このための触媒としてパラジウム黒や白金黒を担持させたもの（特開平１１−６１４７４号公報）が提案され、又電解室内に多孔性材料を充填して反応面積を増加させること（特開平１０−１９５６８６号公報）が提案されている。還元体の製造方法として、水素吸蔵金属から脱着する活性な原子状水素によるもの（特開平１１−６１４２３号公報）が提示され、一方で箔のコストと耐久性の観点から隔膜を支持体とする電極構造体（特開２０００−２３４１９３公報）が開示されている。
【０００４】
【発明が解決しようとする課題】
これらの従来技術により著しく電解性能は向上したが、反応効率の向上の面では、より以上の改良が求められている。
本発明は、水素化、還元、脱水素あるいは酸化等の反応における電流効率の低さを大幅に改善し、所望の反応を短時間で行うことのできる電極、その製造方法、前記電極を使用する電解セルを提供することを目的とする。
【０００５】
【課題を解決するための手段】
本発明は、第１に、電極基材表面に、電極活性物質である水素吸蔵材料を三次元的に形成したことを特徴とする電解用電極であり、この水素吸蔵材料表面に、水素吸蔵材料以外の触媒を担持しても良く、本発明は、第２に、電極基材表面にテンプレートを三次元的に形成し、このテンプレートを水素吸蔵材料で被覆した後、前記テンプレートを溶出させて、前記電極基材表面に電極活性物質である水素吸蔵材料を三次元的に形成することを特徴とする電解用電極の製造方法であり、本発明は、第３に、前記電解用電極の電極基材を該電極基材が隔膜として陽極室及び陰極室を区画するように配置したことを特徴とする電解セルである。
【０００６】
以下本発明を詳細に説明する。
本発明では、電極基材表面に、水素吸蔵材料を電極物質として三次元的に担持して電解用電極を構成する。この電解用電極を電解に使用すると、陰極での水電解で生成する水素ガスは発生機の原子状水素のまま水素吸蔵材料に吸蔵される。そしてこの電極物質である水素吸蔵材料は莫大な表面積を有するため、電解液と十分に接触し、該電解液中に水素添加反応を受ける反応対象が存在すると、吸蔵された水素が反応性の高い原子状水素として反応対象と反応して水素化反応が行われる。なおこの反応は水素化反応に限定されず、原子状水素により進行する任意の反応、例えば還元、脱水素あるいは酸化等の反応が含まれる。
【０００７】
このときの原子状水素と反応対象との接触効率が非常に良いため、反応対象の水素化反応の電流効率が従来の二次元的な電極物質を有する電解用電極より遥かに良好になる。
又効率の水素化反応に加えて他の反応が必要な場合には、前記水素吸蔵材料以外の適宜の触媒を更に担持すれば良い。
【０００８】
本発明の電極物質として、パラジウム、パラジウム合金、ニッケル、チタン、ジルコニウム、ジルコニウム合金、ミッシュメタル（Ｍｍ）に代表される希土類金属を含む水素吸蔵金属又は合金等があり、これらを薄膜や板として使用する。その厚さは反応を速やかに進行させる観点（電極内の水素吸蔵を経て反応室で水素置換反応が進行するための充電時間を考慮する）と機械的強度を維持する観点を考慮して決定され、通常は０．０５ｍｍから１ｍｍが好適である。
【０００９】
この電極物質を三次元的に担持して使用する電極基材は、電解セル内を陽極室と陰極室に区画する隔膜として使用しても良く、この場合の電極基体はイオン交換膜又は多孔性膜としても良いが、この膜材料は膜を介した液の移動を防止する機能が必要とされ、例えばパラジウム黒又は金属パラジウム又はパラジウム合金よりなる液不透過物質が使用できる。使用可能なイオン交換膜は特に限定されないが例えば旭硝子株式会社製アニオン交換膜のセレミオンＡＭＴ、カチオン交換膜のセレミオンＣＭＶ，株式会社トクヤマ製のアニオン交換膜のネオセプタＡＭＨやカチオン交換膜のネオセプタＣＭＨなどが挙げられる。多孔性膜としては例えば湯浅株式会社のユミクロン膜、住友電工株式会社製のポアフロン膜が挙げられる。液不透過性膜は、蒸着法、スパッタ法、イオンプレーティング法のような物理的成膜法や、電気めっき、無電解めっき、及びこれらの組み合わせにより形成できる。多孔性膜の空孔部をパラジウム黒又は金属パラジウム又はパラジウム合金で埋めることにより、電解室の溶液が反応室に透過することを防止し、電解により生成した原子状水素のみが透過できるようになる。パラジウム黒又は金属パラジウム又はパラジウム合金の膜厚は０．５μｍから３０μｍが望ましい。
【００１０】
テンプレートとして用いる物質は、電極基材表面に比較的容易に層状に積層でき、その後に被覆される電極物質を溶解させることなく除去できれば特に限定されないが、ポリスチレンや二酸化珪素の使用が望ましい。これらの物質はコロイド粒子の形態であること、特に球状コロイド粒子の形態であることが好ましい。溶媒に懸濁させた球状コロイド粒子を塗布や含浸により電極基材表面に被覆（担持）する。電極基材上のコロイド粒子は溶媒蒸発に伴う自己集合により三次元的に規則正しく配列する。コロイド粒子はそのサイズが数十ｎｍ〜数百μｍの高分子コロイドが適しており、各粒子径は０．１μｍ〜１０μｍの範囲が好適である。前記テンプレートは、これらのコロイド粒子を１μｍ〜１００μｍとなるように塗布又は浸漬し、溶媒を蒸発させて作製できる。
このテンプレート上に担持する電極物質は前述の通りであるが、例えば光沢の出ないパラジウム黒は大面積を有し、金属パラジウムと比べて数百から数千倍の水素吸蔵能を示し、更に有機化合物の水素化反応触媒や選択的水素化反応触媒として非常に優れた特性を有する材料といえる。
【００１１】
この電極物質及び後述する触媒物質の担持法は、特に限定されず、前述の塗布や浸漬の他に、電気化学的還元、無電解めっき、水素吸蔵合金から脱着する活性な原子状水素による還元による析出、あるいは蒸着法、スパッタ法、イオンプレーティング法のような物理的析出法が挙げられる。
一例としてパラジウム材料を用いた三次元触媒構造体を電気化学的還元（電気めっき）で得るためには、溶媒に懸濁した球状ポリスチレン粒子を塗布し、溶媒を蒸発させた後のパラジウム箔を陰極とし、白金を陽極とし、更にめっき液として塩酸又は塩酸とエタノールの混合液に塩化パラジウムを溶解した液を用い、電流密度０．１Ａ／ｄｍ^２〜１Ａ／ｄｍ^２の範囲で電解を行えば良い。パラジウム析出量はめっき時間の長短により調節でき、０．１μｍ〜１００μｍの厚さとすることが好適である。
【００１２】
このように水素吸蔵材料をコロイド粒子等のテンプレート上に析出させた後、あるいは更に触媒物質の析出後に、前記コロイド粒子等の除去を行う。この除去は通常、コロイド粒子のみを溶解し水素吸蔵材料を溶解しない溶媒にパラジウム箔等の電極基材全体を浸漬することにより行う。コロイド粒子がポリスチレン粒子の場合は、酢酸エチルに約１日浸漬することにより水素吸蔵材料をそのままの形で残してポリスチレン粒子のみを溶出させることができる。
ポリスチレン溶出後の電極基材表面は、連通孔を有するハニカム構造又はそれに類似する三次元構造となり、物理的強度に優れた電極基材が得られる。この三次元構造を有する電極基材の電極物質の表面積は、二次元電極物質と比べて飛躍的に増大し、反応物との接触面積が大きくなって電流効率が向上する。
【００１３】
電極物質としてこれまで述べた水素吸蔵材料の他に、水素化、還元、脱水素、酸化等の各種用途の触媒を担持することもできる。これらの触媒の材質は、白金族金属、銅、亜鉛、スズ、金、銀などの金属や、それらの合金あるいは酸化物等である。これらの材質は、化学的還元、電気化学的還元、水素吸蔵金属から脱着する原子状水素による還元のいずれかの方法により析出させることが好ましい。析出後に、更に触媒成分を電気化学的に又は焼成により酸化物に変換することも可能かつ有効である。しかしながら触媒成分の担持量が多過ぎると、水素の反応室への供給が阻害されることがあるため、厚さは５μｍ以下が好ましい。
【００１４】
通常前記水素吸蔵材料を析出させた電極基材は陰極として使用され、その対極となる陽極は、酸性中での酸素発生反応である場合は、白金、イリジウム等の金属あるいはそれらの酸化物、又はホウ素をドープした導電性ダイヤモンド等が使用できる。これらの触媒は、そのまま板状として用いても、チタン、ニオブ、タンタルなどの耐食性を有する板、金網、粉末焼結体、金属繊維焼結体上に、熱分解法、樹脂による固着法、複合めっき、高圧法、ＣＶＤ法などにより１〜５００ｇ／ｍ^２となるように担持しても良い。アルカリ溶液を使用する場合には、ニッケルやステンレス材料が使用できる。
【００１５】
電解室の隔膜は、前述した通り電極基体が兼用するように電極を配置しても良いが、別個の中性隔膜やイオン交換膜の使用が可能である。イオン交換膜はフッ素樹脂系及び炭化水素樹脂系のいずでも良いが、耐食性の面で前者が好ましく、陽極及び陰極で生成する各イオンが対極で消費されるのを防止するとともに、液の伝導性が低い場合にも電解を速やかに進行させる機能を有する。
電解条件は、温度は５℃から６０℃が好ましく、電流密度は１〜１００Ａ／ｄｍ^２が好ましい。
【００１６】
電解室の厚さは抵抗損失を低下させるためになるべく薄くすべきであるが、電解液を供給する際のポンプの圧力損失を小さくし、圧力分布を均一に保つために１〜１０ｍｍとすることが好ましい。
電解セルの材料は、耐久性の観点から、ガラス、カーボン、耐食性の優れたチタンやステンレス、ＰＴＦＥ樹脂等が好ましい。
本発明の電解用電極は、有機合成特に炭素−炭素二重又は三重結合の水素化、又は無機合成、廃水処理等の用途に使用できる。該電解用電極を設置した電解セルは、非常に反応性の高い原子状水素で反応を行うことができ、かつ電気化学的制御により反応速度をほぼ任意に変えることができる特徴を有し、処理対象は溶液でも気体でも良い。
【００１７】
【発明の実施の形態】
次に添付図面に基づいて本発明の電解用電極及び該電極を設置した電解セルの実施態様を説明するが、本発明はこれに限定されるものではない。
【００１８】
図１ａから図１ｃは本発明に係る電解用電極の一連の製造工程を示す縦断面図である。
パラジウム箔等の電極基材１に、溶媒に懸濁させた多数のポリスチレン粒子２を塗布し、溶媒を蒸発除去すると、図１ａに示すようにその表面に規則正しく配列された複数層のポリスチレン粒子２を有する電極基材１が得られる。
【００１９】
次いで図１ｂに示すように、このポリスチレン粒子２をテンプレートとして使用し、このポリスチレン粒子２全体を隙間が生じないように、パラジウム黒等の水素吸蔵材料３で被覆する。この水素吸蔵材料３による被覆は、対応する金属イオンを含む水溶液中で電解還元して行うことが望ましい。
このポリスチレン粒子２及び水素吸蔵材料３を担持した電極基材１をポリスチレン粒子２を溶出させられる溶媒、例えば酢酸エチル中に浸漬する。これにより図１ｃに示すようにポリスチレン粒子が溶出して、互いに連通するポリスチレン粒子と同数及び同形状の球状空間４が形成され、前記水素吸蔵材料３はこの球状空間４に面するため、莫大な表面積が得られることになる。このようにして莫大な電解面積を有する電解用電極５が得られる。
【００２０】
図２は図１ｃで得られた電解用電極を電極セルに設置した状態を示す縦断面図である。
電解セル６は、隔膜としても機能する電解用電極５の電極基材１により、該電極基材１上に担持された水素吸蔵材料（陰極として機能）３が位置する反応室（陰極室）７と、多孔性陽極８が収容された電解室（陽極室）９に区画されている。前記反応室７には水素化される反応基質自体又は陰極液１０に溶解した反応基質が供給され、電解室９には導電性物質例えば水酸化カリウム等が溶解した陽極液１１が供給される。
この状態で両極３及び８間に通電すると、反応室７で水電解による水素ガス発生が起こるが、陰極物質が水素吸蔵材料から成るため、発生機の原子状水素が該水素吸蔵材料３に吸蔵される。この吸蔵された原子状水素は水素化反応等を受ける成分が陰極液１０中に含まれていると、直ちに水素吸蔵材料３表面から放出されて対象成分の水素化を行う。このときに水素供給物質が非常に反応性の高い原子状水素であること、及びこの原子状水素が放出する水素吸蔵材料３が莫大な表面積で反応対象物と接触するため、水素化反応の電流効率が上昇し、効果的な水素化反応が実施できる。
【００２１】
［実施例］
次に本発明に係る電解用電極に関する実施例及び比較例を記載するが、これらは本発明を限定するものではない。
【００２２】
実施例１
厚さ５０μｍのパラジウム箔表面に、溶媒である水に懸濁させた多数の平均粒径約１μｍの球状ポリスチレン粒子を塗布し、更に乾燥して前記溶媒を除去した。このパラジウム箔表面の多数球状ポリスチレン粒子間の空間や前記粒子表面に次の条件でパラジウム黒を電気化学的に析出させた。
陽極：白金
陰極：球状ポリスチレン粒子を担持したパラジウム箔
電解液：０．０２８Ｍ塩化パラジウム＋１Ｍ塩酸水溶液
電流密度：０．１Ａ／ｄｍ^２
電解時間：３０分
【００２３】
このようにして作製したパラジウム黒を析出させた球状ポリスチレン粒子担持パラジウム箔を２４時間酢酸エチルに浸漬し、ポリスチレン粒子を溶解して、三次元構造を有するパラジウム黒層を電極基材であるパラジウム箔上に形成して電解用電極とした。
又電解時間を増減させて、析出量が０〜０．３ｍｇ／ｃｍ^２である計４種類の電解用電極を作製した。
【００２４】
比較例１
厚さ５０μｍのパラジウム箔表面に、球状ポリスチレン粒子を塗布しなかったこと以外は実施例１と同じ析出条件でパラジウム黒を析出させて電極基材に二次元パラジウム黒を担持した電解用電極とし、更に電解時間を増減させて、析出量が０〜１．８ｍｇ／ｃｍ^２である計４種類の電解用電極を作製した。
実施例１の電極と比較例１の電極のそれぞれについて、各析出量でのＲｏｕｇｈｎｅｓｓ　Ｆａｃｔｏｒ　（粗面化因子）を測定したところ図３のグラフに示す通りであった。図から同じ析出量での実施例１の電極基材の表面積は比較例１の電極基材の表面積は１０倍以上で大きな面積拡大効果があったことが分かる。
【００２５】
実施例２
実施例１で作製した電解用電極を陰極として使用し、陽極として多孔性ニッケル電極を使用して図２に示す電解セルを組み立て、電解室は１Ｍ水酸化カリウム水溶液で満たし、反応室には反応基質として４−メチルスチレンを加えた。
室温下で電流密度が１Ａ／ｄｍ^２となるように電流を流して４−メチルスチレンの水素化を行ったところ、７０％の電流効率で▲１▼式に示すように、４−エチルトルエンが生成した。
析出量のみ異なる他の２個の電解用電極を同様にして作製し、▲１▼式で示す反応に使用し、その電流効率を測定した。その結果を図４のグラフに示した。
【００２６】
【化１】

【００２７】
比較例２
陰極兼隔膜としてパラジウム箔のみを用いたこと以外は実施例２と同様にして４−メチルスチレンの水素化を試みた。その結果、４−メチルスチレンの水素化に関する電流効率は図４のグラフに示す通り、０％であった。これはパラジウム黒が担持されていないため、反応室側への原子状水素の供給量が殆どないことが原因であると考えられる。
【００２８】
比較例３
陰極兼隔膜として、実施例２と同量のパラジウム黒をテンプレートを使用せずに担持したパラジウム箔を用いたこと以外は実施例２と同様にして４−メチルスチレンの水素化を試みた。パラジウム黒の担持量はそれぞれ０．７ｍｇ／ｃｍ^２、１．５ｍｇ／ｃｍ^２及び３．１ｍｇ／ｃｍ^２とした。各担持量における電流効率は図４のグラフに示す通り、順に３７％、７２％及び８５％であった。
低析出量の領域で電流効率が低いのは、パラジウム黒触媒層が三次元化していないため、実質上の反応面積が小さいことが原因であると推定される。
【００２９】
実施例３
実施例１で作製した電解用電極の上に、電気めっきにより０．１μｍの厚さでスズを担持して本実施例の電解用電極とした。
この電解用電極を陰極として使用し、陽極として多孔性ニッケル電極を使用して図２に示す電解セルを組み立て、電解室は１Ｍ水酸化カリウム水溶液で満たし、反応室には反応基質として０．０３Ｍ硝酸水溶液３０ｍｌを加えた。
室温下で電流密度が１０Ａ／ｄｍ^２となるように電流を流して硝酸イオンの還元を行ったところ、図５のグラフに示す通り、５０％の電流効率で硝酸イオンが還元されて約４０分後に硝酸イオン濃度が約２０ｍｇ／リットルとなり、約１時間２０分後には実質的に零になった。
【００３０】
比較例４
比較例３の電解用電極の上に、電気めっきにより０．１μｍの厚さでスズを担持して本比較例の電解用電極とした。
この電解用電極を使用して実施例３と同様の条件で硝酸イオンの還元を試みた。その結果、硝酸イオンは図５のグラフに示すように約２０％の電流効率で還元された。
【００３１】
【発明の効果】
本発明は、電極基材表面に、電極活性物質である水素吸蔵材料を三次元的に形成したことを特徴とする電解用電極である。
この電解用電極は水素化源として水素吸蔵材料中に吸蔵された活性の高い原子状水素を使用できること、及び水素吸蔵材料が三次元的構造を有し莫大な表面積の増大があり、両者の相乗効果により、対象の水素化反応等の電流効率が上昇する。
又本発明の電解用電極では、水素吸蔵材料以外に他の触媒を担持しても良く、これにより有用性の高い電解用電極が提供できる。
【００３２】
本発明の三次元的構造は、電極基材表面にテンプレートを三次元的に形成し、このテンプレートを水素吸蔵材料で被覆した後、前記テンプレートを溶出させて、前記電極基材表面に電極活性物質である水素吸蔵材料を三次元的に形成することにより得られ、これにより連通孔を有するハニカム構造又はそれに類似する三次元構造となり、物理的強度に優れた電極基材が得られる。この三次元構造を有する電極基材の電極物質の表面積は、二次元電極物質と比べて飛躍的に増大し、反応物との接触面積が大きくなって電流効率が向上する。
前記電解用電極を電解セルに収容する際には、電極基材を隔膜と兼用でき、電解セルの小型化等に寄与できる。
【図面の簡単な説明】
【図１】図１ａから図１ｃは本発明に係る電解用電極の一連の製造工程を示す縦断面図である。
【図２】図１ｃで得られた電解用電極を電極セルに設置した状態を示す縦断面図である。
【図３】実施例１と比較例１における電解用電極のパラジウム黒析出量と粗面化因子の関係を示すグラフである。
【図４】実施例２と比較例２及び３における電解用電極のパラジウム黒析出量と電流効率の関係を示すグラフである。
【図５】実施例３と比較例４における反応時間と硝酸イオン濃度の関係を示すグラフである。
【符号の説明】
１　電極基材
２　ポリスチレン粒子
３　水素吸蔵材料
４　球状空間
５　電解用電極
６　電解セル[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrode for electrolysis suitable for a hydrogenation reaction, a method for producing the same, and an electrolysis cell having the electrode for electrolysis.
[0002]
[Prior art]
An electrolysis method has been proposed in which an object cell is reduced or hydrogenated using atomic hydrogen that has reached from the electrode in an electrolysis cell having an electrode made of a hydrogen storage material (Japanese Patent Application Laid-Open No. 9-184086). This method is also applied to dehydrogenation reactions other than reduction and hydrogenation reactions, including the generation of unsaturated ketones by dehydrogenation of ketones used in the synthesis of natural products and the production of aromatic hydrocarbons. Generation etc. are included.
In an electrode reaction using a foil that is a normal hydrogen storage material, the reaction proceeds on a two-dimensional surface, so that time is required for electrolytic treatment, and industrial application is difficult. In order to improve the reaction rate, it is desirable to optimize the catalyst and to increase the contact area with the substance to be treated.
[0003]
A catalyst supporting palladium black or platinum black has been proposed for this purpose (Japanese Patent Application Laid-Open No. H11-61474), and the reaction area is increased by filling a porous material in the electrolysis chamber (Japanese Patent Application Laid-Open No. 195686). As a method for producing a reductant, a method using active atomic hydrogen desorbing from a hydrogen storage metal (Japanese Patent Application Laid-Open No. 11-61423) is proposed. On the other hand, a diaphragm is used as a support from the viewpoint of foil cost and durability. An electrode structure (JP-A-2000-234193) is disclosed.
[0004]
[Problems to be solved by the invention]
Although the electrolysis performance has been remarkably improved by these conventional techniques, further improvement is required in terms of improving the reaction efficiency.
The present invention significantly improves the low current efficiency in reactions such as hydrogenation, reduction, dehydrogenation, and oxidation, and enables an electrode capable of performing a desired reaction in a short time, a method for producing the electrode, and the use of the electrode. It is an object to provide an electrolytic cell.
[0005]
[Means for Solving the Problems]
The first aspect of the present invention is an electrode for electrolysis, characterized in that a hydrogen storage material as an electrode active substance is three-dimensionally formed on the surface of an electrode substrate, and the hydrogen storage material is provided on the surface of the hydrogen storage material. Other than this, the present invention may, secondly, form a template three-dimensionally on the surface of the electrode substrate, coat the template with a hydrogen storage material, and elute the template, A method for producing an electrode for electrolysis, characterized in that a hydrogen storage material, which is an electrode active substance, is formed three-dimensionally on the surface of the electrode base material. An electrolytic cell, wherein the material is arranged so that the electrode substrate separates an anode chamber and a cathode chamber as a diaphragm.
[0006]
Hereinafter, the present invention will be described in detail.
In the present invention, an electrode for electrolysis is formed by three-dimensionally supporting a hydrogen storage material as an electrode substance on the surface of an electrode substrate. When this electrode for electrolysis is used for electrolysis, hydrogen gas generated by water electrolysis at the cathode is occluded in the hydrogen storage material as atomic hydrogen of the generator. Since the hydrogen storage material, which is an electrode material, has an enormous surface area, when the hydrogen storage material is sufficiently in contact with the electrolyte and there is a reaction target that undergoes a hydrogenation reaction in the electrolyte, the stored hydrogen has high reactivity. The hydrogenation reaction is performed by reacting with the reaction target as atomic hydrogen. Note that this reaction is not limited to a hydrogenation reaction, and includes any reaction that proceeds with atomic hydrogen, for example, a reaction such as reduction, dehydrogenation, or oxidation.
[0007]
At this time, since the contact efficiency between the atomic hydrogen and the reaction target is very good, the current efficiency of the hydrogenation reaction of the reaction target is much better than the conventional electrode for electrolysis having a two-dimensional electrode material.
When another reaction is required in addition to the efficient hydrogenation reaction, an appropriate catalyst other than the hydrogen storage material may be further supported.
[0008]
Examples of the electrode material of the present invention include palladium, a palladium alloy, nickel, titanium, zirconium, a zirconium alloy, and a hydrogen storage metal or alloy containing a rare earth metal represented by a misch metal (Mm). These are used as a thin film or a plate. I do. The thickness is determined in consideration of the viewpoint of promptly proceeding the reaction (considering the charging time for the hydrogen replacement reaction to proceed in the reaction chamber via the hydrogen absorption in the electrode) and the viewpoint of maintaining the mechanical strength. Usually, 0.05 mm to 1 mm is suitable.
[0009]
The electrode substrate that supports and uses the electrode substance three-dimensionally may be used as a diaphragm that partitions the inside of the electrolytic cell into an anode chamber and a cathode chamber. In this case, the electrode substrate is an ion exchange membrane or a porous membrane. Although a membrane may be used, this membrane material needs to have a function of preventing liquid from moving through the membrane. For example, a liquid impermeable substance made of palladium black, metallic palladium, or a palladium alloy can be used. There are no particular limitations on the ion exchange membranes that can be used. No. Examples of the porous membrane include a Yumicron membrane manufactured by Yuasa Corporation and a Poreflon membrane manufactured by Sumitomo Electric Industries, Ltd. The liquid impermeable film can be formed by a physical film forming method such as an evaporation method, a sputtering method, or an ion plating method, electroplating, electroless plating, and a combination thereof. Filling the pores of the porous membrane with palladium black or metal palladium or a palladium alloy prevents the solution in the electrolytic chamber from permeating into the reaction chamber and allows only atomic hydrogen generated by electrolysis to permeate . The thickness of the palladium black, metallic palladium or palladium alloy is preferably 0.5 μm to 30 μm.
[0010]
The substance used as the template is not particularly limited as long as it can be relatively easily laminated on the surface of the electrode substrate and can be removed without dissolving the electrode substance to be subsequently coated, but the use of polystyrene or silicon dioxide is preferable. These substances are preferably in the form of colloidal particles, especially in the form of spherical colloidal particles. Spherical colloid particles suspended in a solvent are coated (supported) on the electrode substrate surface by coating or impregnation. The colloid particles on the electrode substrate are regularly arranged three-dimensionally by self-assembly accompanying the evaporation of the solvent. As the colloid particles, a polymer colloid having a size of several tens nm to several hundreds of μm is suitable, and each particle diameter is preferably in a range of 0.1 μm to 10 μm. The template can be prepared by applying or dipping these colloidal particles to a thickness of 1 μm to 100 μm and evaporating the solvent.
The electrode material supported on this template is as described above, but for example, non-glossy palladium black has a large area, shows hundreds to thousands times the hydrogen storage capacity as compared with metal palladium, and further has an organic property. It can be said that the material has very excellent properties as a catalyst for the hydrogenation reaction of a compound or a selective hydrogenation reaction catalyst.
[0011]
The method of supporting the electrode material and the catalyst material described below is not particularly limited. In addition to the above-described coating and dipping, electrochemical reduction, electroless plating, reduction by active atomic hydrogen desorbing from the hydrogen storage alloy is performed. Precipitation or a physical deposition method such as an evaporation method, a sputtering method, or an ion plating method may be used.
As an example, in order to obtain a three-dimensional catalyst structure using a palladium material by electrochemical reduction (electroplating), spherical polystyrene particles suspended in a solvent are applied, and the palladium foil after evaporating the solvent is used as a cathode. and then, platinum as an anode and using a further solution prepared by dissolving palladium chloride in a mixture of hydrochloric acid or hydrochloric acid and ethanol as the plating solution, it may be performed electrolysis in a range of current density of 0.1A ^/ dm ² ~1A / dm 2 . The amount of palladium deposited can be adjusted by adjusting the plating time, and the thickness is preferably 0.1 μm to 100 μm.
[0012]
After the hydrogen storage material is deposited on the template such as colloidal particles, or after the catalytic substance is further deposited, the colloidal particles are removed. This removal is usually performed by immersing the entire electrode substrate such as a palladium foil in a solvent in which only the colloid particles are dissolved and the hydrogen storage material is not dissolved. When the colloidal particles are polystyrene particles, only the polystyrene particles can be eluted by immersing the colloidal particles in ethyl acetate for about one day while leaving the hydrogen storage material as it is.
The surface of the electrode substrate after elution of polystyrene has a honeycomb structure having communication holes or a three-dimensional structure similar thereto, and an electrode substrate having excellent physical strength can be obtained. The surface area of the electrode material of the electrode substrate having the three-dimensional structure is dramatically increased as compared with the two-dimensional electrode material, and the contact area with the reactant is increased, thereby improving the current efficiency.
[0013]
In addition to the hydrogen storage materials described above, catalysts for various uses such as hydrogenation, reduction, dehydrogenation, and oxidation can be supported as electrode materials. The materials of these catalysts include metals such as platinum group metals, copper, zinc, tin, gold, silver, and alloys and oxides thereof. These materials are preferably deposited by any of the following methods: chemical reduction, electrochemical reduction, and reduction with atomic hydrogen desorbed from a hydrogen storage metal. After the precipitation, it is also possible and effective to convert the catalyst component into an oxide electrochemically or by calcination. However, if the supported amount of the catalyst component is too large, the supply of hydrogen to the reaction chamber may be hindered. Therefore, the thickness is preferably 5 μm or less.
[0014]
Usually, the electrode substrate on which the hydrogen storage material is deposited is used as a cathode, and the anode serving as the counter electrode is a metal such as platinum or iridium or an oxide thereof, if the reaction is an oxygen generation reaction in an acid, or Conductive diamond doped with boron can be used. These catalysts can be used in the form of a plate as they are, but they can be applied to a corrosion-resistant plate such as titanium, niobium, or tantalum, a wire mesh, a powder sintered body, or a metal fiber sintered body by a thermal decomposition method, a resin fixing method, or a composite method. It may be supported by plating, a high-pressure method, a CVD method, or the like so as to be 1 to 500 g / m ² . When an alkaline solution is used, nickel or stainless steel material can be used.
[0015]
As described above, the electrodes of the electrolytic chamber may be arranged so that the electrode substrate also serves as the diaphragm, but a separate neutral diaphragm or an ion exchange membrane may be used. The ion exchange membrane may be either a fluororesin type or a hydrocarbon resin type, but the former is preferable in terms of corrosion resistance. In addition to preventing each ion generated at the anode and cathode from being consumed at the counter electrode, the conductivity of the liquid is reduced. It has the function of promptly proceeding electrolysis even when the property is low.
Regarding the electrolysis conditions, the temperature is preferably 5 ° C. to 60 ° C., and the current density is preferably 1 to 100 A / dm ² .
[0016]
The thickness of the electrolytic chamber should be as small as possible to reduce the resistance loss, but should be 1 to 10 mm to reduce the pressure loss of the pump when supplying the electrolyte and keep the pressure distribution uniform. Is preferred.
The material of the electrolytic cell is preferably glass, carbon, titanium, stainless steel, PTFE resin, or the like having excellent corrosion resistance, from the viewpoint of durability.
The electrode for electrolysis of the present invention can be used for organic synthesis, particularly for hydrogenation of carbon-carbon double or triple bonds, or for inorganic synthesis, wastewater treatment and the like. The electrolysis cell in which the electrode for electrolysis is installed has a feature that the reaction can be performed with extremely reactive atomic hydrogen and that the reaction rate can be almost arbitrarily changed by electrochemical control. The target may be a solution or a gas.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the electrode for electrolysis of the present invention and an electrolytic cell provided with the electrode will be described with reference to the accompanying drawings, but the present invention is not limited thereto.
[0018]
1a to 1c are longitudinal sectional views showing a series of manufacturing steps of the electrode for electrolysis according to the present invention.
A large number of polystyrene particles 2 suspended in a solvent are applied to an electrode substrate 1 such as a palladium foil, and the solvent is removed by evaporation. As shown in FIG. Is obtained.
[0019]
Next, as shown in FIG. 1B, the polystyrene particles 2 are used as a template, and the whole of the polystyrene particles 2 is coated with a hydrogen storage material 3 such as palladium black or the like so that no gap is formed. The coating with the hydrogen storage material 3 is preferably performed by electrolytic reduction in an aqueous solution containing the corresponding metal ions.
The electrode substrate 1 supporting the polystyrene particles 2 and the hydrogen storage material 3 is immersed in a solvent capable of eluting the polystyrene particles 2, for example, ethyl acetate. As a result, as shown in FIG. 1 c, the polystyrene particles elute and form spherical spaces 4 having the same number and the same shape as the polystyrene particles communicating with each other, and the hydrogen storage material 3 faces the spherical spaces 4, so that it is enormous. Surface area will be obtained. Thus, the electrode for electrolysis 5 having a huge electrolysis area is obtained.
[0020]
FIG. 2 is a longitudinal sectional view showing a state where the electrode for electrolysis obtained in FIG. 1c is installed in an electrode cell.
The electrolytic cell 6 includes a reaction chamber (cathode chamber) 7 in which the hydrogen storage material (functioning as a cathode) 3 supported on the electrode substrate 1 is located by the electrode substrate 1 of the electrode for electrolysis 5 which also functions as a diaphragm. And an electrolytic chamber (anode chamber) 9 in which a porous anode 8 is accommodated. The reaction chamber 7 is supplied with the reaction substrate itself to be hydrogenated or the reaction substrate dissolved in the catholyte 10, and the electrolysis chamber 9 is supplied with the anolyte 11 in which a conductive substance such as potassium hydroxide or the like is dissolved.
When electricity is supplied between the

electrodes

3 and 8 in this state, hydrogen gas is generated by water electrolysis in the reaction chamber 7. However, since the cathode material is made of a hydrogen storage material, the atomic hydrogen of the generator is stored in the hydrogen storage material 3. Is done. When the occluded atomic hydrogen contains a component that undergoes a hydrogenation reaction or the like in the catholyte 10, it is immediately released from the surface of the hydrogen storage material 3 and hydrogenates the target component. At this time, the hydrogen supply material is very reactive atomic hydrogen, and the hydrogen storage material 3 released by the atomic hydrogen comes into contact with the reaction target with a huge surface area, so that the current of the hydrogenation reaction is increased. The efficiency is increased, and an effective hydrogenation reaction can be performed.
[0021]
[Example]
Next, Examples and Comparative Examples relating to the electrode for electrolysis according to the present invention will be described, but these do not limit the present invention.
[0022]
Example 1
A large number of spherical polystyrene particles having an average particle diameter of about 1 μm suspended in water as a solvent were applied to the surface of a 50 μm-thick palladium foil, and the solvent was removed by drying. Palladium black was electrochemically deposited on the surface of the palladium foil between the many spherical polystyrene particles and on the surface of the particles under the following conditions.
Anode: Platinum Cathode: Palladium foil electrolyte carrying spherical polystyrene particles: 0.028 M palladium chloride + 1 M hydrochloric acid aqueous solution Current density: 0.1 A / dm ²
Electrolysis time: 30 minutes
The thus prepared palladium foil carrying spherical polystyrene particles on which palladium black is deposited is immersed in ethyl acetate for 24 hours to dissolve the polystyrene particles, and a palladium black layer having a three-dimensional structure is formed on the palladium foil serving as an electrode substrate. An electrode for electrolysis was formed thereon.
The electrolysis time was increased or decreased to produce a total of four types of electrolysis electrodes having a deposition amount of 0 to 0.3 mg / cm ² .
[0024]
Comparative Example 1
On the surface of a 50 μm-thick palladium foil, palladium black was deposited under the same deposition conditions as in Example 1, except that spherical polystyrene particles were not applied, to provide an electrode for electrolysis carrying two-dimensional palladium black on an electrode substrate, By further increasing or decreasing the electrolysis time, a total of four types of electrolysis electrodes having a deposition amount of 0 to 1.8 mg / cm ² were produced.
For each of the electrode of Example 1 and the electrode of Comparative Example 1, the Roughness Factor (roughening factor) at each deposition amount was measured, and the results were as shown in the graph of FIG. It can be seen from the figure that the surface area of the electrode substrate of Example 1 was 10 times or more the surface area of the electrode substrate of Comparative Example 1 at the same deposition amount, and that there was a large area expansion effect.
[0025]
Example 2
The electrolytic cell shown in FIG. 2 was assembled using the electrode for electrolysis prepared in Example 1 as a cathode and a porous nickel electrode as an anode. The electrolytic chamber was filled with a 1M aqueous solution of potassium hydroxide, and the reaction chamber was filled with a reaction solution. 4-methylstyrene was added as a substrate.
Hydrogenation of 4-methylstyrene was carried out at room temperature by passing a current so that the current density became 1 A / dm ^{2. As} shown in the equation (1) at a current efficiency of 70%, 4-ethyltoluene was Generated.
Two other electrolysis electrodes differing only in the amount of deposition were prepared in the same manner, and used for the reaction represented by the formula (1), and the current efficiency was measured. The results are shown in the graph of FIG.
[0026]
Embedded image

[0027]
Comparative Example 2
The hydrogenation of 4-methylstyrene was attempted in the same manner as in Example 2 except that only the palladium foil was used as the cathode and diaphragm. As a result, the current efficiency regarding the hydrogenation of 4-methylstyrene was 0% as shown in the graph of FIG. It is considered that this is because palladium black is not supported, and there is almost no supply of atomic hydrogen to the reaction chamber.
[0028]
Comparative Example 3
Hydrogenation of 4-methylstyrene was attempted in the same manner as in Example 2 except that a palladium foil carrying the same amount of palladium black as in Example 2 without using a template was used as the cathode and diaphragm. Each supported amount of palladium black 0.7 mg ^/ cm 2, was 1.5 mg / cm ² and 3.1 mg / cm ^2. As shown in the graph of FIG. 4, the current efficiencies at each load were 37%, 72%, and 85%, respectively.
It is presumed that the reason why the current efficiency is low in the region where the amount of deposition is low is that the palladium black catalyst layer is not three-dimensionally formed and, therefore, has a substantially small reaction area.
[0029]
Example 3
On the electrode for electrolysis prepared in Example 1, tin was supported at a thickness of 0.1 μm by electroplating to obtain an electrode for electrolysis of this example.
The electrolytic cell shown in FIG. 2 was assembled using the electrode for electrolysis as a cathode and a porous nickel electrode as an anode. The electrolytic chamber was filled with a 1 M aqueous potassium hydroxide solution, and the reaction chamber was filled with 0.03 M as a reaction substrate. 30 ml of aqueous nitric acid solution were added.
When a current was passed at room temperature so that the current density became 10 A / dm ² , the nitrate ion was reduced. As shown in the graph of FIG. 5, the nitrate ion was reduced at a current efficiency of 50% and about 40 minutes. Later, the nitrate ion concentration became about 20 mg / liter, and became substantially zero after about 1 hour and 20 minutes.
[0030]
Comparative Example 4
On the electrode for electrolysis of Comparative Example 3, tin was supported at a thickness of 0.1 μm by electroplating to obtain an electrode for electrolysis of this Comparative Example.
Using this electrode for electrolysis, reduction of nitrate ions was attempted under the same conditions as in Example 3. As a result, nitrate ions were reduced at a current efficiency of about 20% as shown in the graph of FIG.
[0031]
【The invention's effect】
The present invention is an electrode for electrolysis, wherein a hydrogen storage material, which is an electrode active substance, is formed three-dimensionally on the surface of an electrode substrate.
This electrode for electrolysis can use highly active atomic hydrogen stored in the hydrogen storage material as a hydrogenation source, and the hydrogen storage material has a three-dimensional structure and a huge increase in surface area. The effect increases the current efficiency of the target hydrogenation reaction and the like.
Further, the electrode for electrolysis of the present invention may support another catalyst in addition to the hydrogen storage material, thereby providing a highly useful electrode for electrolysis.
[0032]
In the three-dimensional structure of the present invention, a template is three-dimensionally formed on the surface of the electrode substrate, and after covering the template with a hydrogen absorbing material, the template is eluted to form an electrode active material on the surface of the electrode substrate. Is obtained by three-dimensionally forming the hydrogen storage material as described above, whereby a honeycomb structure having communication holes or a three-dimensional structure similar to the honeycomb structure is obtained, and an electrode substrate having excellent physical strength can be obtained. The surface area of the electrode material of the electrode substrate having the three-dimensional structure is dramatically increased as compared with the two-dimensional electrode material, and the contact area with the reactant is increased, thereby improving the current efficiency.
When accommodating the electrode for electrolysis in an electrolytic cell, the electrode substrate can also be used as a diaphragm, which can contribute to downsizing of the electrolytic cell and the like.
[Brief description of the drawings]
FIGS. 1a to 1c are longitudinal sectional views showing a series of manufacturing steps of an electrode for electrolysis according to the present invention.
FIG. 2 is a longitudinal sectional view showing a state where the electrode for electrolysis obtained in FIG. 1c is installed in an electrode cell.
FIG. 3 is a graph showing the relationship between the amount of deposited palladium black on the electrode for electrolysis and the surface roughening factor in Example 1 and Comparative Example 1.
FIG. 4 is a graph showing the relationship between the amount of black palladium deposited on the electrode for electrolysis and the current efficiency in Example 2 and Comparative Examples 2 and 3.
FIG. 5 is a graph showing the relationship between reaction time and nitrate ion concentration in Example 3 and Comparative Example 4.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electrode base material 2 Polystyrene particles 3 Hydrogen storage material 4 Spherical space 5 Electrolysis electrode 6 Electrolysis cell

Claims

An electrode for electrolysis, wherein a hydrogen storage material, which is an electrode active substance, is formed three-dimensionally on the surface of an electrode substrate.

On the surface of the electrode substrate, three-dimensionally form a hydrogen storage material that is an electrode active substance, and further include gold, platinum group metal, platinum group metal black, copper, tin, and alloys and oxides thereof on the surface An electrode for electrolysis, wherein a catalyst layer containing at least one selected from the group is formed.

3. The electrode for electrolysis according to claim 1, wherein the hydrogen storage material is at least one selected from the group consisting of palladium, palladium alloys, nickel, titanium, zirconium, zirconium alloys, aluminum, carbon, and rare earth metals.

A template is three-dimensionally formed on the surface of the electrode substrate, and after the template is coated with a hydrogen storage material, the template is eluted, and the hydrogen storage material as an electrode active substance is three-dimensionally coated on the surface of the electrode substrate. A method for producing an electrode for electrolysis, characterized in that the electrode for electrolysis is formed.

The method according to claim 4, wherein the template is a colloid particle selected from polystyrene and silicon dioxide.

An electrolytic cell, wherein the electrode for electrolysis according to any one of claims 1 to 3 is arranged so that an electrode substrate of the electrode for electrolysis functions as a diaphragm.