高潔,朱玉嬋,任占冬,李文陽(yáng),全姍姍,劉曄,王又容,柴波
?
Ir0.5Pt0.5O2陽(yáng)極的電催化活性及氧化電解水制備
高潔,朱玉嬋,任占冬,李文陽(yáng),全姍姍,劉曄,王又容,柴波
(武漢輕工大學(xué)化學(xué)與環(huán)境工程學(xué)院,湖北武漢430023)
氧化電解水作為一種新型、高效、環(huán)保的殺菌劑,具有廣闊的應(yīng)用前景。但目前在氧化電解水制備過(guò)程中,其陽(yáng)極電催化材料存在效率低和使用壽命短等問(wèn)題。采用亞當(dāng)斯融合法制備了Ir0.5Pt0.5O2復(fù)合氧化物電極。通過(guò)XRD表征,其晶型為典型的金紅石型結(jié)構(gòu)。SEM結(jié)果表明雖然顆粒之間存在團(tuán)聚現(xiàn)象,但是可以明顯觀察到大量蜂窩狀結(jié)構(gòu)存在,提高了催化劑的比表面積和電化學(xué)面積。進(jìn)一步的CV表征證明了這一點(diǎn),同時(shí)在CV圖中表現(xiàn)出明顯的鉑銥復(fù)合氧化物結(jié)構(gòu)的特征。利用LSV技術(shù)分別考察了Ir0.5Pt0.5O2的析氯和析氧極化曲線(xiàn),發(fā)現(xiàn)其單位表觀面積上析氯活性明顯提高,而析氧活性明顯降低。計(jì)算表明Ir0.5Pt0.5O2的析氯反應(yīng)Tafel斜率為56.3 mV·dec-1,反應(yīng)機(jī)理為Volmer-Heyrovsky機(jī)理,速控步驟為電化學(xué)脫附步驟;其析氧反應(yīng)Tafel斜率為126.6 mV·dec-1,控速步驟為催化劑表面氫氧化物的形成。進(jìn)一步電化學(xué)阻抗實(shí)驗(yàn)表明在1 g·L-1NaCl溶液中, Ir0.5Pt0.5O2析氯電催化活性?xún)?yōu)于IrO2,這與前面研究結(jié)果一致。在此基礎(chǔ)上,以Ir0.5Pt0.5O2/Ti為陽(yáng)極制備氧化電解水,在相同條件下,其有效氯含量明顯優(yōu)于IrO2/Ti,同時(shí)電解效率也明顯提高,強(qiáng)化試驗(yàn)壽命是IrO2/Ti的3.14倍,大大提高了電極性能,有利于其商品化使用。
Ir0.5Pt0.5O2復(fù)合材料;電解;析氯;析氧;反應(yīng)動(dòng)力學(xué)
引 言
氧化電解水作為一種新型無(wú)毒環(huán)保的殺菌劑,具有殺菌廣譜、迅速、強(qiáng)力、持續(xù)等特點(diǎn)。近年來(lái),隨著對(duì)氧化電解水研究的不斷深入,其應(yīng)用范圍也不斷拓寬,其在醫(yī)療衛(wèi)生[1-8]、食品安全、農(nóng)作物生長(zhǎng)[9-20]等多個(gè)領(lǐng)域均有應(yīng)用研究。氧化電解水的制備是通過(guò)電解濃度極稀的氯化鈉溶液得到的,與之相類(lèi)似的體系有氯堿工業(yè)和海水電解,但是三者之間有著明顯的區(qū)別,即氯化鈉在各電解液中的濃度不同。在氯堿工業(yè)中經(jīng)常使用的是飽和氯化鈉溶液,而海水電解中氯化鈉的質(zhì)量分?jǐn)?shù)也達(dá)到2%,但在氧化電解水制備中氯化鈉的質(zhì)量分?jǐn)?shù)僅為0.05%。如此大的電解質(zhì)濃度差異,造成了電催化反應(yīng)類(lèi)型和電解效率的不同。在氯堿工業(yè)中,主要的陽(yáng)極反應(yīng)為析氯反應(yīng);而在氧化電解水制備過(guò)程中,除了析氯反應(yīng)外,還有大量的析氧反應(yīng)發(fā)生,如何調(diào)配兩者之間的反應(yīng)選擇性,提高電解效率,這些都取決于對(duì)電極材料的研究。如果仍采用氯堿工業(yè)中常用的Ru基金屬氧化物電催化材料(析氯和析氧電位僅相差100 mV)[21-24],勢(shì)必影響其電解效率和電極使用壽命,因?yàn)殛?yáng)極析氧電流較大時(shí)會(huì)破壞電極表面金屬氧化物涂層的缺氧固溶體結(jié)構(gòu),在涂層和鈦基體界面產(chǎn)生不導(dǎo)電的TiO2鈍化膜,從而導(dǎo)致了電解效率和電極壽命大大降低。與Ru基等金屬氧化物電極相比,Ir基金屬氧化物的析氯和析氧活性略低,但其電極的使用壽命會(huì)大幅度增加[25-28],但仍然很難滿(mǎn)足這種特殊條件下實(shí)際使用的需要。而PtO2電極具有較高的析氧過(guò)電位[29-30],如果將PtO2引入IrO2中,這樣可以進(jìn)一步降低電極材料析氧活性,從而提高析氯選擇性,提高電極使用壽命。本文旨在制備鉑銥復(fù)合氧化物催化劑,考察其析氯、析氧反應(yīng)電催化活性,并考察其制備氧化電解水的性能和電極使用壽命。
1 實(shí)驗(yàn)材料和方法
1.1 Ir0.5Pt0.5O2粉體催化劑的制備
本文采用改進(jìn)亞當(dāng)斯融合法[31-32]制備Ir0.5Pt0.5O2粉體催化劑,即在燒杯里加入10 ml等量的H2IrCl6·6H2O和H2PtCl6·6H2O溶液,控制溶液中金屬離子總濃度為0.1 mol·L-1,加入過(guò)量30%的硝酸鈉及10 ml異丙醇。將所得溶液在60℃下持續(xù)攪拌直到異丙醇揮發(fā)完全,然后再將混合物在 80℃烘干。將其冷卻后,經(jīng)充分研磨,并在管式爐中500℃下燒結(jié)30 min。將混合物冷卻至室溫后,用大量蒸餾水洗滌多次,以便除去所有的氯離子,并用AgNO3溶液檢測(cè)洗滌液中無(wú)Cl-為止,并在 80℃下干燥完全,得到催化劑粉體。
1.2 Ir0.5Pt0.5O2/Ti的制備
本文通過(guò)熱分解法制備鈦基氧化物薄膜電極。即將預(yù)處理好的鈦板浸入預(yù)先配制好的涂液(0.2 mol·L-1H2PtCl6·6H2O+H2IrCl6·6H2O乙醇異丙醇混合溶液)之中,然后以1 mm·s-1的速度將鈦板平穩(wěn)地從涂液中提拉出來(lái),在黏度和重力作用下基板表面形成一層均勻的液膜,并于80~90℃烘干10 min至表面溶劑全部揮發(fā),然后放入馬弗爐在500℃條件下熱氧化10 min,冷卻至室溫后再次涂膜,此過(guò)程重復(fù)15次,最后一次熱氧化時(shí)間為1 h,并退火至室溫。
1.3 催化劑表征及電化學(xué)測(cè)試
涂層表面形貌、組成和結(jié)構(gòu)用掃描電鏡(SEM),X射線(xiàn)衍射(XRD)技術(shù)分析。X射線(xiàn)衍射型號(hào)為Shimadzu XRD-600,Cu-Kα射線(xiàn)源,管電流30 mA,管電壓40 kV,掃描范圍10°~90°,掃描速率4(°)·min-1。掃描電鏡型號(hào)為S-3000N,日本HITACHI公司。BET比表面積是在-196℃下的氮?dú)夥罩型ㄟ^(guò)物理吸附測(cè)定,儀器型號(hào)為Micromeritics ASAP2020。電化學(xué)性能的測(cè)定在CHI700D電化學(xué)工作站上進(jìn)行,電解池采用三電極體系,輔助電極為碳紙電極,參比電極為可逆氫參比電極或飽和甘汞電極,工作電極為載有Ir0.5Pt0.5O2/GC(表觀面積為0.196 cm2)。在25℃,0.5 mol·L-1H2SO4溶液中測(cè)定電極的循環(huán)伏安曲線(xiàn)和析氧極化曲線(xiàn),在飽和NaCl溶液(6 mol·L-1)中測(cè)定電極的析氯極化曲線(xiàn),在1 g·L-1NaCl溶液中進(jìn)行電化學(xué)阻抗測(cè)試,測(cè)試的頻率范圍為100 kHz~0.1 Hz, 擾動(dòng)幅值10 mV,測(cè)試電勢(shì)為1.3 V(SCE)。
1.4 氧化電解水的制備、性能測(cè)試及壽命實(shí)驗(yàn)
在自制離子膜電解槽中,陽(yáng)極是Ir0.5Pt0.5O2/Ti電極(有效面積1 cm2),陰極為鈦板。中間用陽(yáng)離子交換膜將電解槽分成陽(yáng)極區(qū)和陰極區(qū),體積分別為100 ml。電解過(guò)程中。添加濃度為1g·L-1的 NaCl溶液作為電解質(zhì),電流密度為100 mA·cm-2,電極間距為4 cm,電解30 min,在陽(yáng)極區(qū)得到EOW。氧化電解水物性測(cè)定,其中有效氯含量采用碘量法滴定;pH和ORP值采用pH酸度計(jì)和ORP儀直接測(cè)定,美國(guó)熱電-奧立龍。氯離子含量測(cè)定采用電位滴定法,美國(guó)熱電-奧立龍,工作電極為Ag電極,參比電極雙鹽橋飽和甘汞電極。強(qiáng)化實(shí)驗(yàn)壽命測(cè)試采用2 cm×2 cm Ti板作為陰極,1 cm×1 cm Ir0.5Pt0.5O2/Ti作為陽(yáng)極,電解液是0.5 mol·L-1H2SO4,溫度40℃,電流密度200 mA·cm-2。
2 實(shí)驗(yàn)結(jié)果與討論
2.1 XRD譜圖分析
由于IrO2和PtO2都是金紅石型晶體,具有相同的對(duì)稱(chēng)性和相近的晶格常數(shù),所以?xún)烧吣茉趶V泛配比范圍內(nèi)形成混晶。圖1是Ir0.5Pt0.5O2和IrO2的XRD譜圖,從圖中可以看出IrO2是典型的金紅石相晶體結(jié)構(gòu),對(duì)比JCPDS15-0870標(biāo)準(zhǔn)卡片,其在27.8°、34.7°、53.9°和66.6°的衍射峰分別是IrO2的(110)、(101)、(211)、(112)晶面的特征峰。而當(dāng)IrO2中摻入PtO2,形成Ir0.5Pt0.5O2固溶體后,其在34.1°處是明顯(101)晶面衍射峰,這是金紅石型晶體典型特征。另外,在60.6°和71.8°處是其(002)、(301)晶面特征峰。通過(guò)Scherrer公式,對(duì)它們的(101)晶面進(jìn)行擬合計(jì)算其粒徑,其中IrO2為4.18 nm,而Ir0.5Pt0.5O2的粒徑為3.89 nm,粒徑明顯變小,這將有助于提高電極表面的比表面積,從而提高電催化活性。
圖1 Ir0.5Pt0.5O2和IrO2催化劑的XRD譜圖
2.2 SEM圖分析
圖2是Ir0.5Pt0.5O2和IrO2催化劑的SEM圖,從圖中可以看出兩種催化劑都出現(xiàn)不同程度的團(tuán)聚現(xiàn)象,這可能是由于在制備過(guò)程中,需要高溫退火氧化,所以出現(xiàn)大量顆粒聚集現(xiàn)象。在圖2 (a)中可以看出,排除個(gè)別少數(shù)大的顆粒外,IrO2的粒徑大小還是比較均勻,在100~200 nm之間。圖2 (b)是Ir0.5Pt0.5O2的SEM圖,仍然可以觀察到粒徑很大的顆粒,但在圖中方框所標(biāo)注區(qū)域內(nèi),可以觀察到明顯細(xì)小的網(wǎng)狀結(jié)構(gòu),其晶粒尺寸遠(yuǎn)遠(yuǎn)小于IrO2粒徑,這將大大有助于提高其比表面積,其BET比表面積達(dá)到255.4 m3·g-1,是IrO2的3.1倍。但比表面積是催化劑本身的物理性質(zhì),雖然其提高會(huì)有助于提高電催化活性,但其電化學(xué)面積才最能真正反映其電催化活性位點(diǎn)數(shù)目多少,所以以下將利用電化學(xué)循環(huán)伏安法來(lái)表征其電化學(xué)面積。
圖2 Ir0.5Pt0.5O2和IrO2催化劑的SEM圖
2.3 循環(huán)伏安(CV)表征
圖3是Ir0.5Pt0.5O2和IrO2的CV曲線(xiàn),其表面電量值能夠代表活性位點(diǎn)的多少。圖3 (a)是IrO2的CV曲線(xiàn),這是典型IrO2循環(huán)伏安曲線(xiàn),其中電勢(shì)在0.9 V是Ir3+/Ir4+的氧化還原;電勢(shì)在1.25 V是Ir4+/Ir5+的氧化還原,對(duì)其CV曲線(xiàn)進(jìn)行積分,得到其氧化物表面電量為0.151 mC。當(dāng)將PtO2摻入IrO2后,其CV特征發(fā)生明顯的變化,結(jié)果如圖3 (b)所示。從圖中可以看出在1.0 V出現(xiàn)了明顯氧化峰,其起始電勢(shì)為0.75 V,這個(gè)氧化峰在純IrO2的CV中沒(méi)有觀察到,這代表Pt表面氧化形成Pt-OH,而在0.85 V處是其還原峰。另外,在氫區(qū)(0.03~0.3 V),陰極電流明顯增加,這是由于PtO2在電勢(shì)較低情況下很容易被還原得到Pt,而Pt表面的HUPD電流會(huì)使陰極電流增加。對(duì)其表面電量進(jìn)行積分,電量為0.4 mC,是純IrO2的2.65倍,說(shuō)明其表面電化學(xué)活性位點(diǎn)增多,這將有利于電催化反應(yīng)活性的提高。此外,觀察到Ir0.5Pt0.5O2的表面氧化起始電勢(shì)比IrO2正移150 mV,說(shuō)明其表面更難以發(fā)生氧化,這正是PtO2加入的結(jié)果,因?yàn)镻tO2比IrO2析氧活性更差。
圖3 Ir0.5Pt0.5O2和IrO2催化劑的CV曲線(xiàn)
2.4 氯析出(CER)電催化活性
氧化電解水中主要?dú)⒕钚砸蜃邮荋ClO,而其產(chǎn)生是通過(guò)陽(yáng)極析氯反應(yīng)得到的,所以研究電極材料析氯反應(yīng)活性是十分重要的,其析氯反應(yīng)活性越高,產(chǎn)生的HClO含量越高,預(yù)示著殺菌活性越好[15]。圖4是Ir0.5Pt0.5O2和IrO2在6 mol·L-1氯化鈉溶液中的極化曲線(xiàn)。從圖4 (a)中可以看出,Ir0.5Pt0.5O2和IrO2兩者的析氯起始電勢(shì)很接近,均在1.05 V(SCE)。但隨著極化電勢(shì)增加,它們?cè)趩挝幻娣e上氯析出反應(yīng)活性有著明顯不同,其中IrO2的析氯活性較差,析氯電流(@1.4 V)僅為40.3 mA·cm-2;但當(dāng)形成鉑銥復(fù)合氧化物后,其析氯活性明顯增大,析氯電流(@1.4 V)達(dá)到了86.9 mA·cm-2,是IrO2的2.16倍。這一方面是因?yàn)楫?dāng)鉑銥之間形成復(fù)合氧化物后,其電化學(xué)面積有所增加(見(jiàn)CV表征),從而帶來(lái)了電催化活性的提高;另一方面則可能是由于PtO2本身析氧活性較差,所以其加入有利于抑制析氧反應(yīng)的發(fā)生,從而提高析氯反應(yīng)的選擇性,提高析氯反應(yīng)活性。為了明確電極材料組成對(duì)析氯反應(yīng)電催化活性的影響,就必須排除電化學(xué)活性面積變化對(duì)催化反應(yīng)活性的影響,所以將它們對(duì)其表面電量進(jìn)行歸一化。圖4 (b)則是Ir0.5Pt0.5O2和IrO2對(duì)其表面電量進(jìn)行歸一化后的析氯活性,從圖中可以看出,兩者析氯反應(yīng)活性比較接近,說(shuō)明兩者在每個(gè)表面活性位點(diǎn)上的析氯反應(yīng)活性一樣,并不會(huì)因?yàn)樾纬蓮?fù)合氧化物而發(fā)生改變。對(duì)比IrO2電極,Ir0.5Pt0.5O2電極在單位表觀面積上析氯反應(yīng)活性的提高很大程度上是因?yàn)槠浔砻婊钚苑磻?yīng)位點(diǎn)的增加。
圖4 Ir0.5Pt0.5O2和IrO2析氯反應(yīng)的線(xiàn)性伏安曲線(xiàn)
從前面的研究得知Ir0.5Pt0.5O2具有較好的析氯反應(yīng)活性,下面進(jìn)一步分析其析氯反應(yīng)機(jī)理。從圖5中可以看出Ir0.5Pt0.5O2的Tafel斜率為56.3 mV·dec-1,其析氯反應(yīng)機(jī)理應(yīng)為Volmer-Heyrovsky機(jī)理[33-36],其反應(yīng)過(guò)程分兩步,其中第2步是其反
應(yīng)的速控步驟,S代表活性位點(diǎn)。
所以,其析氯反應(yīng)電流可以寫(xiě)成
將式(4)代入式(3)中,可以得到式(5),再經(jīng)簡(jiǎn)單數(shù)學(xué)變換得到式(6)
2.5 氧析出(OER)電催化活性
前面考察了Ir0.5Pt0.5O2的氯析出反應(yīng)活性,但在制備氧化電解水過(guò)程中,除了析氯反應(yīng)之外,還會(huì)伴隨著大量析氧反應(yīng)的發(fā)生。析氧反應(yīng)的存在一方面會(huì)降低析氯反應(yīng)效率,另一方面會(huì)使電極表面金屬氧化物涂層的缺氧固溶體結(jié)構(gòu)發(fā)生破壞,涂層和鈦基體界面產(chǎn)生不導(dǎo)電的TiO2鈍化膜,從而大大降低電解效率和電極壽命,所以盡量避免析氧反應(yīng)的發(fā)生。圖7 (a)是單位表觀面積上的析氧極化曲線(xiàn),從圖中可以看出,與析氯活性不同,Ir0.5Pt0.5O2的析氧活性與其本身的電化學(xué)面積并不呈正比。其中IrO2電化學(xué)面積小于Ir0.5Pt0.5O2,但其氧析出電流卻大于后者。如再將它們的析氧活性對(duì)表面電量進(jìn)行歸一化,排除電化學(xué)面積的影響,如圖7 (b)所示,它們析氧活性之間差別則進(jìn)一步增大。以上研究結(jié)果說(shuō)明析氧反應(yīng)活性主要受電極組成的影響。由于PtO2本身的析氧活性較差,所以形成復(fù)合氧化物后,會(huì)使析氧活性減小,而析氧活性的減小正好可以提高析氯反應(yīng)選擇性以及電極壽命。
圖7 Ir0.5Pt0.5O2和IrO2析氧反應(yīng)的線(xiàn)性伏安曲線(xiàn)
為了進(jìn)一步分析析氧反應(yīng)活性變化的機(jī)理,首先做了兩者的Tafel曲線(xiàn),從圖8中可以看出,IrO2和Ir0.5Pt0.5O2的析氧反應(yīng)Tafel曲線(xiàn)斜率有很大不同,預(yù)示著其析氧反應(yīng)機(jī)理的不同。在酸性體系中,文獻(xiàn)中一般認(rèn)為析氧反應(yīng)過(guò)程如下[37-39]
為了更清晰地表達(dá)析氯和析氧選擇性的變化,選擇在電流密度為20 mA·cm-2下對(duì)比兩者的析氯和析氧電勢(shì),結(jié)果表明IrO2分別為1.239 V和1.392 V,氯氧電勢(shì)差為153 mV;而Ir0.5Pt0.5O2分別為1.154 V和1.432 V,氯氧電勢(shì)差為278 mV。Ir0.5Pt0.5O2的氯氧電勢(shì)差明顯大于IrO2,意味著析氯反應(yīng)選擇性增加,電流效率提高。
2.6 電化學(xué)阻抗
由于氧化電解水制備時(shí),氯化鈉濃度為1 g·L-1,所以Ir0.5Pt0.5O2和IrO2的電化學(xué)阻抗測(cè)試在該濃度下進(jìn)行,設(shè)定電極電勢(shì)為1.3 V(SCE),其阻抗復(fù)平面圖如圖9所示。
圖9 Ir0.5Pt0.5O2和IrO2在1 g·L-1NaCl溶液中阻抗復(fù)平面圖
電極電勢(shì)為1.3 V(SCE)時(shí),析氯反應(yīng)已經(jīng)明顯發(fā)生,采用Zview軟件進(jìn)行擬合,其等效電路設(shè)計(jì)為s(ff)(ctdl),其中s代表溶液電阻,f代表電極材料膜電阻,ct代表析氯反應(yīng)時(shí)電荷轉(zhuǎn)移電阻;f代表電極材料膜電容,dl代表電極表面的雙電層電容。從表1中可以看出在1.3 V時(shí),Ir0.5Pt0.5O2的f小于IrO2,說(shuō)明其導(dǎo)電性更好;而ct明顯變小及dl明顯變大,則說(shuō)明其析氯反應(yīng)電催化活性高,這與前面析氯極化曲線(xiàn)等研究結(jié)果一致。
表1 Ir0.5Pt0.5O2和IrO2在1g·L-1 NaCl溶液中等效電路擬合阻抗參數(shù)
2.7 氧化電解水制備和電極使用壽命
前面的研究表明形成鉑銥復(fù)合氧化物后,其析氯和析氧活性發(fā)生明顯變化。下面考察氧化電解水實(shí)際制備中Ir0.5Pt0.5O2電極的性能。表2是分別以Ir0.5Pt0.5O2/Ti、IrO2/Ti作為陽(yáng)極材料,在自制離子膜電解槽中通過(guò)電解1 g·L-1NaCl溶液制備得到氧化電解水,并考察其pH、ORP和有效氯值等性能參數(shù),以及電解后溶液中的氯離子含量及電解效率。如表2中所示,兩種電極制備得到EOW的pH和ORP值相近,但有效氯含量和電解效率上相差較大,說(shuō)明兩者析氯反應(yīng)活性有很大差別。其中Ir0.5Pt0.5O2電解得到的EOW中含有較多有效氯,而在前期研究中發(fā)現(xiàn)有效氯越高,氧化電解水的殺菌效率越高[15,40-41]。另外,從電解后溶液中氯離子含量以及電解效率來(lái)看,Ir0.5Pt0.5O2也要好于IrO2電極,這些說(shuō)明Ir0.5Pt0.5O2更適合作為制備EOW的陽(yáng)極電催化材料。
表2 Ir0.5Pt0.5O2/Ti和IrO2/Ti制備電解水的指標(biāo)參數(shù)和電解效率
Note:Initial content of chloride ion in solution is 607 mg·L-1, volume of solution is 120 ml, current density is 100 mA·cm-2, electrode area is 1 cm2, electrolytic time is 0.5 h.
前面的研究中Ir0.5Pt0.5O2表現(xiàn)出很好的析氯反應(yīng)活性和較高的電解效率,下面進(jìn)一步考察其電極使用壽命,因?yàn)槭褂脡勖鼘?duì)于電極實(shí)際應(yīng)用是十分重要的。采用在0.5 mol·L-1H2SO4溶液中,電流密度200 mA·cm-2,溫度40℃下進(jìn)行強(qiáng)化壽命實(shí)驗(yàn),結(jié)果如圖10所示。從圖10中可以看出,IrO2電極強(qiáng)化壽命為100 h,而Ir0.5Pt0.5O2電極強(qiáng)化壽命為341 h,提高了3.41倍,說(shuō)明當(dāng)鉑銥形成復(fù)合氧化物后由于析氧活性的下降,減少了電極表面金屬氧化物涂層的缺氧固溶體結(jié)構(gòu)發(fā)生破壞,較好地防止不導(dǎo)電的TiO2鈍化膜的形成,所以其使用壽命大幅度增加。
圖10 Ir0.5Pt0.5O2/Ti和IrO2/Ti催化劑的強(qiáng)化壽命實(shí)驗(yàn)
3 結(jié) 論
針對(duì)目前氧化電解水制備過(guò)程中,其陽(yáng)極電催化材料析氯反應(yīng)選擇性低和使用壽命短等問(wèn)題,制備了鉑銥復(fù)合氧化物電極。結(jié)果表明Ir0.5Pt0.5O2具有典型的金紅石型結(jié)構(gòu),呈蜂窩狀分布,具有較大比表面積和電化學(xué)面積,具有較好的析氯反應(yīng)活性和較差的析氧反應(yīng)活性。Ir0.5Pt0.5O2的析氯反應(yīng)Tafel斜率為56.3 mV·dec-1,反應(yīng)機(jī)理為Volmer-Heyrovsky機(jī)理;其析氧反應(yīng)Tafel斜率為126.6 mV·dec-1,控速步驟為催化劑表面氫氧化物的形成。以上研究表明,Ir0.5Pt0.5O2電催化劑作為陽(yáng)極材料來(lái)制備氧化電解水是十分適宜的。實(shí)驗(yàn)結(jié)果表明,以Ir0.5Pt0.5O2/Ti電極制備的氧化電解水中有效氯含量明顯優(yōu)于IrO2/Ti,同時(shí)電解效率也明顯提高,強(qiáng)化實(shí)驗(yàn)壽命是IrO2/Ti的3.14倍,大大提高了電極性能,有利于其商品化使用。
References
[1] Thorn R M S, Lee S W H, Robinson G M, Greenman J, Reynolds D M. Electrochemically activated solutions: evidence for antimicrobial efficacy and applications in health care environments [J]......., 2012, 31 (5): 641-653
[2] Gulabivala K, Stock C J R, Lewsey J D, Ghori S, Ng Y L, Spratt D A. Effectiveness of electrochemically activated water as an irrigant in an infected tooth model [J]...., 2004, 37 (9): 624-631
[3] Chittoria R K, Yootla M, Sampatrao L M, Raman S V. The role of super oxidized solution in the management of diabetic foot ulcer: our experience [J]....., 2007, 9: 125-128
[4] Vorobjeva N V, Vorobjeva L I, Khodjaev E Y. The bactericidal effects of electrolyzed oxidizing water on bacterial strains involved in hospital infections [J]..., 2004, 28 (6): 590-592
[5] Fenner D C, Bürge B, Kayser H P, Wittenbrink M M. The anti-microbial activity of electrolysed oxidizing water against microorganisms relevant in veterinary medicine [J]......., 2006, 53 (3): 133-137
[6] Robinson G M, Lee S W H, Greenman J, Salisbury V C, Reynolds D M. Evaluation of the efficacy of electrochemically activated solutions against nosocomial pathogens and bacterial endospores [J]...., 2010, 50 (3): 289-294
[7] Morita C, Nishida T, Ito K. Biological toxicity of acid electrolyzed functional water: effect of oral administration on mouse digestive tractand changes in body weight [J]...., 2011, 56 (4): 359-366
[8] Park G W, Boston D M, Kase J A, Sampson M N, Sobsey M D. Evaluation of liquid- and fog-based application of Sterilox hypochlorous acid solution for surface inactivation of human norovirus [J]...., 2007, 73 (14): 4463-4468
[9] Keskinen L A, Burke A, Annous B A. Efficacy of chlorine, acidic electrolyzed water and aqueous chlorine dioxide solutions to decontaminateO157:H7 from lettuce leaves [J]...., 2009, 132 (2/3): 134-140
[10] Koide S, Shitanda D, Note M, Cao W. Effects of mildly heated, slightly acidic electrolyzed water on the disinfection and physicochemical properties of sliced carrot [J]., 2011, 22 (2/3): 452-456
[11] McCarthy S, Burkhardt III W. Efficacy of electrolyzed oxidizing water againstandon conveyor belt and raw fish surfaces [J]., 2012, 24 (1/2): 214-219
[12] Xie J, Sun X H, Pan Y J, Zhao Y. Combining basic electrolyzed water pretreatment and mild heat greatly enhanced the efficacy of acidic electrolyzed water againston shrimp [J]., 2012, 23 (2): 320-324
[13] Rahman S M E, Wang J, Oh D H. Synergistic effect of low concentration electrolyzed water and calcium lactate to ensure microbial safety, shelf life and sensory quality of fresh pork [J]., 2013, 30 (1): 176-183
[14] Ren Zhandong (任占冬), Zhu Yuchan (朱玉嬋), Liu Ye (劉曄), Zhang Zhiyong (張智勇), Zhang Qi (張奇). Electrolyzed potential water sterilizing technics and mechanism on pork stuffing [J].(農(nóng)業(yè)機(jī)械學(xué)報(bào)), 2009, 40 (12): 139-143
[15] Zhu Yuchan (朱玉嬋), Ren Zhandong (任占冬), Liu Ye (劉曄), Zhang Zhiyong (張智勇). Sterilization characteristics of electrolyzed-oxidizing water and its sterilizing effect for meat [J].(化工學(xué)報(bào)), 2009, 60 (10): 2583-2589
[16] Cao W, Zhu Z W, Shi Z X, Wang C Y, Li B M. Efficiency of slightly acidic electrolyzed water for inactivation ofand its contaminated shell eggs [J]...., 2009, 130 (2): 88-93
[17] Graca A, Abadias M, Salazar M, Nunes C. The use of electrolyzed water as a disinfectant for minimally processed apples [J]..., 2011, 61 (2/3): 172-177
[18] Xiong K, Liu H J, Li L T. Product identification and safety evaluation of aflatoxin B1 decontaminated by lectrolyzed oxidizing water [J]...., 2012, 60 (38): 9770-9778
[19] Zhang Houcheng (張后成), Zhu Yuchan (朱玉嬋), Ren Zhandong (任占冬), Pan Deng (潘登), Liu Ye (劉曄), Wang Yourong (王又容), Chai Bo (柴波). Sterilizing effect and mechanism of neutral electrolyzed oxidizing water on cabbage [J].(農(nóng)業(yè)工程學(xué)報(bào)), 2013, 29 (22): 277-283
[20] Huang Y R, Hung Y C, Hsu S Y, Huang Y W, Hwang D F. Application of electrolyzed water in the food industry [J]., 2008, 19 (4): 329-345
[21] Trieu V, Schley B, Nattera H, Kintrup J, Bulan A, Hempelmann R. RuO2-based anodes with tailored surface morphology for improved chlorine electro-activity [J].., 2012, 78: 188-194
[22] Cao H Z, Lu D H, Lin J P, Ye Q, Wu J J, Zheng G Q. Novel Sb-doped ruthenium oxide electrode with ordered nanotube structure and its electrocatalytic activity toward chlorine evolution [J].., 2013, 91: 234-239
[23] Petrykin V, Macounová K, Okubea M, Mukerjeec S, Krtil P. Local structure of Co doped RuO2nano crystalline electrocatalytic materials for chlorine and oxygen evolution [J]., 2013, 202: 63-69
[24] Neodoa S, Rosestolato D, Ferro S, Battisti A D. On the electrolysis of dilute chloride solutions: influence of the electrode material on Faradaic efficiency for active chlorine, chlorate and perchlorate [J].., 2012, 78: 282-291
[25] Hu W, Chen S L, Xia Q H. IrO2/Nb-TiO2electrocatalyst for oxygen evolution reaction in acidic medium [J]..., 2014, 39 (13): 6967-6976
[26] Xu J Y, Liu G Y, Li J L, Wang X D. The electrocatalytic properties of an IrO2/SnO2catalyst using SnO2as a support and an assisting reagent for the oxygen evolution reaction [J].., 2012, 59: 105-112
[27] HuW, Wang Y Q, Hu X H, Zhou Y Q, Chen S L. Three-dimensional ordered macroporous IrO2as electrocatalyst for oxygen evolution reaction in acidic medium [J]...., 2012, 22: 6010-6016
[28] Ye Z G, Meng H M, Sun D B. New degradation mechanism of Ti/IrO2+MnO2anode for oxygen evolution in 0.5M H2SO4solution [J].., 2008, 53: 5639-5643
[29] Stoyanova A, Borisov G, Lefterova E, Slavcheva E. Oxygen evolution on Ebonex-supported Pt-based binary compounds in PEM water electrolysis [J]..., 2012, 37 (21): 16515-16521
[30] Reier T, Oezaslan M, Strasser P. Electrocatalytic oxygen evolution reaction (OER) on Ru, Ir, and Pt catalysts: a comparative study of nanoparticles and bulk materials [J].., 2012, 2 (8): 1765-1772
[31] Adams R, Shriner R L. Platinum oxide as a catalyst in the reduction of organic compoundsⅢpreparation and properties of the oxide of platinum obtained by the fusion of chloroplatinic acid with sodium nitrate [J]....., 1923, 45: 2171-2179
[32] Song S D, Zhang H M, Ma X P, Shao Z G, Zhang Y N, Yi B L. Bifunctional oxygen electrode with corrosion-resistive gas diffusion layer for unitized regenerative fuel cell [J]..., 2006, 8: 399-405
[33] Santana M H P, Faria A D L. Oxygen and chlorine evolution on RuO2+TiO2+CeO2+Nb2O5mixed oxide electrodes [J].., 2006, 51: 3578-3585
[34] Hansen H A, Man I C, Studt F, Abild-Pedersen F, Bligaard T, Rossmeisl J. Electrochemical chlorine evolution at rutile oxide (110) surfaces [J]....., 2010, 12: 283-290
[35] Guerrini E, Consonni V, Trasatti S. Surface and electrocatalytic properties of well-defined and vicinal RuO2single crystal faces [J]..., 2005, 9: 320-329
[36] Ferro S, Battisti A D. Electrocatalysis and chlorine evolution reaction at ruthenium dioxide deposited on conductive diamond [J]...., 2002, 106: 2249-2254
[37] Ye Z G, Meng H M, Chen D, Yu H Y, Huan Z S, Wang X D, Sun D B. Structure and characteristics of Ti/IrO2()+MnO2(1-) anode for oxygen evolution [J]., 2008, 10: 346-354
[38] Macounova K, Makarova M, Krtil P. Oxygen evolution on nanocrystalline RuO2and Ru0.9Ni0.1O2-δelectrodes-DEMS approach to reaction mechanism determination [J]..., 2009, 11: 1865-1868
[39] Tsuji E, Imanishi A, Fukui K, Nakato Y. Electrocatalytic activity of amorphous RuO2electrode for oxygen evolution in an aqueous solution [J].., 2011, 56: 2009-2016
[40] Zhu Yuchan (朱玉嬋), Ren Zhandong (任占冬), Liu Ye (劉曄), Chen Hongmei (陳紅梅). Sterilizing effect and neutral electrolyzed oxidizing water [J]....(中國(guó)公共衛(wèi)生), 2011, 27 (6): 805-806
[41] Ren Zhandong (任占冬), Zhu Yuchan (朱玉嬋), Liu Ye (劉曄), Zhou Xiaorong (周曉榮), Zhang Zhiyong (張智勇). Sterilizing effect and mechanism of electrolyzed water [J]..... (中華預(yù)防醫(yī)學(xué)), 2008, 8: 578-581
Electrocatalytic performance of Ir0.5Pt0.5O2anode and preparation of electrolyzed oxidizing water
GAO Jie, ZHU Yuchan, REN Zhandong, LI Wenyang, QUAN Shanshan, LIU Ye, WANG Yourong, CHAI Bo
School of Chemical and Environmental EngineeringWuhan Polytechnic UniversityWuhanHubeiChina
Electrolyzed oxidizing water (EOW), as an innovative disinfectant characterized by its high efficiency, broad antimicrobial spectrum, and non-toxic residues, has been broadly used in health care industry, medicines, agriculture, and food processing. EOW is usually generated by electrolysis of a dilute NaCl solution in a chamber with two cells separated by membrane, and is obtained from the anode side. But low current efficiency and short service life of the anode in EOW generators restrict the application of EOW. Ir0.5Pt0.5O2anode was prepared by the improved Adams fusion method. The properties of Ir0.5Pt0.5O2anode was investigated with X-ray diffraction (XRD), scanning electron microscope (SEM) and electrochemistry cyclic voltammetry (CV). The crystal type is rutile with (101), (002) and (301) crystal planes. A large number of cellular structures were observed on the surface of the anode, which greatly increased specific surface area of the anode. With increasing specific surface area, electric charge was enhanced to 0.4 mC, which was 2.65 times of pure IrO2. Electrochemical characteristics of the anode surface, such as oxidation peaks at 1.0 V(Pt-OH) and 0.9 V(Ir3+/Ir4+) proved the formation of platinum iridium oxide. The activities of chlorine evolution and oxygen evolution were also studied through linear sweep voltammetry (LSV). Compared with IrO2, chlorine evolution activity in unit apparent surface area increased significantly, but oxygen evolution activity decreased obviously. The slope of Tafel was 56.3 mV·dec-1for chlorine evolution reaction (CER), and the mechanism was Volmer-Heyrovsky in which the rate controlling step was electrochemical desorption. The slope of Tafel was 126.6 mV·dec-1for oxygen evolution reaction (OER), and the rate controlling step was formation of surface hydroxide on the catalyst surface. Electrochemical surface structure and electrochemical performance of Ir0.5Pt0.5O2oxide coatings in 1 g·L-1NaCl solution were investigated with electrochemical impedance spectroscopy (EIS). CER activity of Ir0.5Pt0.5O2was better than IrO2, which was in agreement with previous research. In the actual EOW preparation, electrolysis efficiency and available chlorine content (ACC) of EOW on the Ir0.5Pt0.5O2anode were much greater than IrO2anode under the same condition. The accelerated life of Ir0.5Pt0.5O2anode was 3.14 times of the IrO2anode and the performance of the anode was greatly improved, which favored its commercial use.
Ir0.5Pt0.5O2composites; electrolysis; chlorine evolution; oxygen evolution; reaction kinetics
2014-08-05.
Prof. ZHU Yuchan, zhuyuchan@163.com; Prof. REN Zhandong, renzhandong@163.com
10.11949/j.issn.0438-1157.20141176
TQ 151.2
A
0438—1157(2015)03—0992—09
國(guó)家自然科學(xué)基金項(xiàng)目(31101370);湖北省自然科學(xué)基金項(xiàng)目(2012FFB04803);武漢輕工大學(xué)校立科研計(jì)劃項(xiàng)目(2015d8)。
2014-08-05收到初稿,2014-12-08收到修改稿。
聯(lián)系人:朱玉嬋,任占冬。第一作者:高潔(1990—),女,碩士研究生。
supported by the National Natural Science Foundation of China (31101370) and the Natural Science Foundation of Hubei Province (2012FFB04803).