化學(xué)鍍制備高性能直接乙醇燃料電池(DEFC)陽(yáng)極催化劑PtRu/C和PtRuSn/C

第14卷第2期電化學(xué)2008年5月ELECTROCHEMISTRYMay 2008文章編號:1006-3471(2008)02015005化學(xué)鍍制備高性能直接乙醇燃料電池(DEFC)陽(yáng)極催化劑PtRu/C和 PtRusn/C朱靜,蘇怡,馬華,程方益,陶占良,梁靜,陳軍(南開(kāi)大學(xué)化學(xué)學(xué)院新能源材料化學(xué)研究所和能源材料化學(xué)天津市重點(diǎn)實(shí)驗室,天津30001)摘要:應用化學(xué)鍍方法以活化敏化處理的活性炭作載體制備高分散催化劑PRu/C和 PtRuSn/C.XRDTEM及電化學(xué)測試表明,該催化劑P、Ru、Sn形成合金金屬顆粒的平均粒徑約為3m.PRu/C和 PRusn/C二者對乙醇的陽(yáng)極氧化都具有良好的催化活性和穩定性關(guān)鍵詞:化學(xué)鍍;直接乙醇燃料電池;PRu/C催化劑;PRSn/C催化劑中圖分類(lèi)號:TM9114文獻標識碼:A直接醇燃料電池直接以液醇作燃料,其能量轉明,以活化敏化處理的炭作載體再由化學(xué)鍍方法換密度高、環(huán)境污染小,而且燃料來(lái)源豐富、價(jià)格低合成的催化劑將有利于提高催化劑納米顆粒在炭廉、貯存和運輸方便,適用于便攜式和家用電子設表面的分散性減小粒徑尺寸,進(jìn)而提高催化劑的備.近年來(lái)直接甲醇燃料電池(DMFC)的研究性能.本文進(jìn)一步應用該化學(xué)鍍方法合成了P已取得了顯著(zhù)的成就但甲醇的毒性大,廣泛應用 Rw/C PtRusn/C催化劑,同時(shí)研究了上述兩種催受到諸多限制.與甲醇相比,乙醇毒性較小,是一化劑對乙醇陽(yáng)極氧化的催化活性.結果表明化學(xué)種可再生、有前途的甲醇替代燃料但至今,可用鍍方法制備的催化劑具有較高的活性而且三元催于乙醇電化學(xué)氧化的催化劑活性較低,其抗CO中化劑 PtRuSn/C對乙醇的氧化催化表現出更優(yōu)越毒能力也較差,這是制約直接乙醇燃料電池的性能(DEFC)商業(yè)化的主要問(wèn)題2.因此開(kāi)發(fā)新型高1實(shí)驗部分效抗CO中毒能力強的陽(yáng)極催化劑乃是當前乙醇1.1催化劑的制備燃料電池領(lǐng)域研究的熱點(diǎn)之一.雖然眾多的文獻活性炭 Vulcan XC-72( Cabot,比表面積250指出炭載PRu對甲醇的氧化表現出優(yōu)越的催化m2/3),H2PC4·6H2ORuC3SnC2·2H20、PdCl2性能,但就乙醇而言其徹底氧化是一個(gè)12電等試劑均分析純子轉移的過(guò)程,不僅包括醇的吸附脫氫、中間產(chǎn)物化學(xué)鍍方法制備炭載PRu/C(P:Ru=0.5CO等氧化還包括CC鍵的斷裂,這就使得乙0.5)、 PtRuSn/C(P:Ru:Sn=0.5:0.15:0.35)催醇的氧化更加復雜近年來(lái)的研究表明如在PR化劑:將活性炭XC72在含有SnC2·2H12O催化劑中添加適量的Sn,將有利于降低CC鍵斷PdCl2,Na2SnO3·4H20和乙二醇的膠體鈀溶液中裂的反應活化能,從而提高乙醇氧化的反應速超聲波振蕩(活化敏化)10min,水洗去除殘留的SnCl2和PCl2,然后將活化敏化后的活性炭轉移提高催化劑金屬顆粒的分散性,控制粒徑是提到化學(xué)鍍溶液中,鍍液組成為H2PCL4(1.93mmol高催化劑性能有效方法.本課題組近期的研究表L)和RC4(3.63mmo/L)或H2PC4(1.93mmb中國煤化工收稿日期:2007-1225,修訂日期200801-15*通訊作者,Tel:(862CN MH Gkai ed國家863項目(No.2007AA05z124、No.2006AO5Zl30)和天津國際科技合作項目(No.07 ZCGHHZ00700)資助第2期朱靜等:化學(xué)鍍制備高性能直接乙醇燃料電池(DEFC)陽(yáng)極催化劑PhRu/C和 PtRusn/C151L)、RuCl2(3.63mmo/L)和SnCl2·2H2O(4.43峰均有明顯的寬化現象這和金屬顆粒粒徑較小或mmol/L),攪拌1h,使活性炭和化學(xué)鍍液混合均金屬顆粒結晶存在缺陷有關(guān),根據 Scherrer公勻.滴人適量的Na2CO2溶液調pH值到10,再逐式2計算活性炭活化處理前后以化學(xué)鍍方法制滴滴入20mg/L的硼氫化鈉溶液,強攪拌2h,使金備的 PtRuSn顆粒的平均粒徑分別約為42m和屬鹽充分還原.沉淀經(jīng)離心分離、多次水洗后在3.2nm60°C真空干燥4h直接還原法制備催化劑:將未經(jīng)活化敏化前(111)處理的活性炭XC-72直接分散到上述化學(xué)鍍液中使金屬鹽還原(2001.2研究電極的制備取上述5mg催化劑分散在05mL5%Na-fon0.5mL乙醇溶液中,超聲分散Ih成糊,然后b取5μL催化劑糊滴在拋光后的玻碳電極表面(=3mm),60℃干燥2h13產(chǎn)物表征2e(°)用 Rigaku D/max2500型粉末X射線(xiàn)行射儀(CuKa,A=0.15405m)作物相分析,透射電子圖1以化學(xué)鍍方法制備的RRuC(a,b)和 PtRuSny/c(e,顯微鏡( Philips Tecnai-F20)觀(guān)察產(chǎn)物的形貌d)催化劑的XRD譜圖活性炭經(jīng)活化敏化處理(a,c);未經(jīng)前處理(b,d)1.4電化學(xué)測試Fig 1 XRD pattems of the PtRw/ C (a, b)and PtRuSn/c電化學(xué)測試使用 PARSTAT2273電化學(xué)工作(c, d)prepared by electroless-deposition with(a, c)站(美國 AMETEK)三電極體系.以載有活性物質(zhì)or without(b, d)sensitization-activation pretreatment的玻碳電極作研究電極,Ag/AgCl-KCl作參比電極面積為1cm2的鉑片作對電極.電解液是052.2樣品的TEM分析l/LH2SO4和0.5mo/L乙醇混合溶液,循環(huán)伏圖2示出 Pt Rusn/C催化劑的TEM照片及其安測試的掃描速率50mv/s,電位區間-0.2-0.8粒徑分布.如圖所見(jiàn)活性炭未經(jīng)活化敏化處理Ⅴ極化曲線(xiàn)測試掃速05mV/s.計時(shí)電流法在0.5制備的催化劑(A,B)顆粒有團聚現象而且顆粒較V電位下測試1500s.大,平均粒徑約為4.2mm.而經(jīng)過(guò)活化-敏化處理2結果和討論制備的催化劑(C,D),其金屬顆粒大多均勻地分散2.1樣品的XRD分析在炭載體的表面沒(méi)有明顯的團聚現象,且顆粒粒圖1分別為經(jīng)活化敏化處理(a,c)和未經(jīng)處徑分布較窄,在1.2~5mm之間,平均粒徑約為24C催化劑的xRD衍射譜.如圖,兩種方法制備的2.3催化劑的電化學(xué)性能測試二元 PtRu/c催化劑(a,b)和三元 PtRuSn/C催化圖3給出乙醇在0.5mo/LH2SO4溶液中,于劑(c,d)的譜線(xiàn)基本一致,其特征峰分別歸屬為炭?jì)煞N不同方法制備的PRuC(a,b)和 PtRuSn/C載體的(002),鉑的(111)、(200)、(220)晶面.對(c,d)催化劑上氧化的循環(huán)伏安曲線(xiàn)(A)和計時(shí)比P的標準卡片( JCPDS No.4802),PRu/C催化電流曲線(xiàn)(B).從圖3A見(jiàn),不論是二元或三元體劑的2θ有所正移,說(shuō)明Ru擴散進(jìn)入Pt的晶格形系V凵中國煤化工化劑(a,),其成PRu合金與文獻報道的結果一致而三元伏安CNMHG制備的炭載催化PtRuSn/c催化劑的26相對PRuC發(fā)生負移,這劑(b,uJ,Ⅺ凡乜齔叫負移和峰電流密是由于部分Sn進(jìn)入PRu的晶格導致晶格常數增度的增大.圖中,曲線(xiàn)a和b在0.75V處顯示的大田,并形成PRSn合金.圖中4種樣品的衍射峰電流分別為15.5mA/cm2和11.6mA/cm2,可152電化學(xué)2008年8305202.53.03.540455.05.56.06.5Particle size/rm88目30252015101.52.02.53.03.5404.55.05.5Particle size/ nm圖2活性炭未經(jīng)活化敏化處理(A,B)和經(jīng)活化敏化處理(C,D)以化學(xué)鍍方法制備的三元 PRusn/C催化劑的TEM照片及其粒徑分布Fig. 2 TEM images and particle size distribution of the PtRuSn/C catalysts synthesized by electroless-deposition without(A, B)orth (C, D)sensitization-activation pretreatme16] B250.150.000.150.300450600.750250500750100012501500圖3活性炭經(jīng)活化敏化處理(,)和未經(jīng)前處理b,d)以化學(xué)方V凵中國煤化工c(,d催化劑在0.5mo/L乙醇0.5mlL硫酸溶液中的循環(huán)伏安曲線(xiàn)(A)和CNMHGFig-3 Cyclic voltammograms(A)and chronoamperometry curves(B)of the PRw/C(a, b)and PtRuSn/C(c, d)synthesizedby electroless-deposition with(a, c)or without(b, d) sensitization-activation pretreatment, 0.5 mol/L ethanol-0 5 molL H,SO, in solution at scan rate 50 mv/, room temperature第2期朱靜等:化學(xué)鍍制備高性能直接乙醇燃料電池(DEFC)陽(yáng)極催化劑PRu/C和 PtRuSn/C153見(jiàn)前者比后者提高了近33.6%,這與本課題組此流增大更明顯,說(shuō)明該催化劑的反應活性更高.據前報道的PRu/C對甲醇氧化催化的結果基本一圖,乙醇在兩種催化劑表面氧化的Tael斜率,均約致9,對三元 PtRuSn/C催化劑,經(jīng)前處理制備的為135mV/de,與文獻報道的結果一致,說(shuō)明炭載催化劑其峰電流密度為31.2mA/cm2,較之未乙醇在這兩種催化劑表面氧化的速控步驟沒(méi)有發(fā)經(jīng)前處理的炭載催化劑(峰電流24.6mMcm2)也生變化,Sn的添加沒(méi)有改變乙醇氧化反應的速控提高了近26.5%.另外,對比曲線(xiàn)a和c還可看步驟而是提高了它的反應速率出,于PRuC加入適量的Sn有利于提高催化劑的3結論性能,這是因為Sn的加入不僅有利于CC鍵和以化學(xué)鍍方法制備用于乙醇陽(yáng)極氧化的PC-H鍵的斷裂加速了乙醇的氧化,而且能夠R/C和 PtRusn/C催化劑活性炭經(jīng)活化敏化處在較低電位下提供活性氧,從而提高催化劑的抗理有利于提高催化劑顆粒的分散性,減小粒徑,從CO中毒的能力,使催化劑保持較高的活性而提高催化劑的反應活性,Sn的加入更為明顯提計時(shí)電流曲線(xiàn)(圖3B)示明,經(jīng)過(guò)活化敏化處高該催化劑催化活性和穩定性理制備的炭載催化劑(曲線(xiàn)a,c),其電流密度均大于未經(jīng)前處理制備的炭載催化劑(曲線(xiàn)b,d同樣證明了前者具有較高的催化活性和較好的穩參考文獻( References):定性.再如,圖中曲線(xiàn)c在測試過(guò)程中始終保持著(zhù)[1] Song Shuqin(宋樹(shù)芹), Wang Yi(王毅), Shen pej.較高的電流密度,而且衰減緩慢,說(shuō)明Sn的添加使kang(沈培康). Thermodynamic and kinetic considera-三元 Pt Rusn/C催化劑的反應活性和穩定性都明tions for ethanol electrooxidation in direct ethanol fuel顯提高cells [J]. Chinese Joumal of Catalysis, 2007, 28(9)圖4分別示出室溫下測試的兩種催化劑電極752754在乙醇H2SO4溶液中的極化曲線(xiàn)及其對應的 Tafel[2] Song Shuqing(宋樹(shù)芹), Chen Likang(陳利康),Li曲線(xiàn).如圖可見(jiàn),在低過(guò)電位區兩條極化曲線(xiàn)非常Jianguo(劉建國),etal. Preliminary study on directethanol fuel cell [J]. Electrochemistry( in Chinese)接近,電流隨電位緩慢增加,當電位超過(guò)0.35V時(shí)2002,8(1):105-110電流開(kāi)始迅速增大,而且三元 PtRuSn/C催化劑電[3] Xue Xinzhong, Lu tianhong'R/C catalyst using imiu Changpeng, et al.Novel preparation method of P-Rwdazolium ionic liquid as solvent [J]. Electrochim Acta2005,50(16-17):34703478[4] Wei Zhaobin(魏昭彬), Liu Jianguo(劉建國),QiaoYaguang(喬亞光),etl. Performance of a direct“高0methanol fuel cell [J]. Electrochemistry(in Chinese)15124090603000306092001,7(2):228-233Pt. RuuIsSneson of different promotion effect of PRw/C and PtRuSn-0.10.00.l020.3040.50607[6]Bai Yuxia, Li Jinfeng, Qiu Xinping, et al. MesocarbonE/ V(vs Ag/AgCl)microbeads supported PSn catalysts for electrochemical圖4化學(xué)鍍方法合成的PRuC(●)和 PRuSn/c(▲)催化oxidation of ethanol [J]. J Mater Sci, 2007, 42:4508劑在0.5moM/L乙醇0.5mo/LH2SO4溶液中的極4512.化曲線(xiàn)和Tael曲線(xiàn)[7]Antolini F. Gonalex E.R. Ethanol oxidationFig 4 Polarization plots of the PRw/C(.)and PtRuSn/C中國煤化工 atalysts prepared by(A)in 0. 5 mol/L ethanol and 0. 5 mol/L H2soCNMHGJ Electrochem Soscan rate 0. 5 mV/s, room temperature, inset is the2007,154(1):B39B47[8] Zhou Weijiang, Song Shuqing, Li Wenzhen, et al. Ptbased anode catalysts for direct ethanol fuel cells [J]154電化學(xué)2008年Solid State Ionics, 2004, 175: 797-803[12] Lu Qingye, Yang Bo, Zhuang Lin, et al. Pattem rec-[9] Zhu Jing, Su Yi, Cheng Fangyi, et al. Improving theognition on the structure-activity relationship of nanoperformance of PRw/C catalysts for methanol oxidationPt-Ru catalysts: methodology and preliminary demonby sensitization and activation treatment [J].J PowerSources,2007,166:331-336879[10] Guo J W, Zhao T S, Prabhuram J, et al. Preparation [13] Colmati F, Antolini E, Gonzalez E R. Effect of tem-and characterization of a PRw/C nanocatalyst for directperature on the mechanism of ethanol oxidation onmethanol fuel cells [J]. Electrochim Acta, 2005, 51bon supported Pt, PtRu and Pt, Sn electrocatalysts754-763.[J]. J Power Sources, 2006, 157:98-103.[11] Neto A 0, Dias R R, Tusi MM, et al. Electro-oxida- [14] Suffredini H B, Tricoli V, Vatistas N, et al.Electro-tion of methanol and ethanol using PRw/C, PSn/Coxidation of methanol and ethanol using a P-RuO,/Celectrocatalysts prepared by an alcohol-composite prepared by the sol-gel technique and sup-J Power Sources, 2001, 166ported on boron-doped diamond [J]. J Power Sources87912006,158:124-128.Electroless-deposition Synthesis of Highly Active PtRwc andPtRuSn/c as anode Catalysts for DEFCZHU Jing, SU Yi, MA Hua, CHENG Fang-yi, TAO Zhan-liang, LIANG Jing, Chen JunInstitute of New Energy Material Chemistry and Key Laboratory of Energy Meterial ChemistryNankai University, Tianyin 300071, ChinaAbstract In this paper, the preparation, characterization, and ethanol electrocatalytic oxidation of Pt. s RuoC and Pto. s Ruo 1s Sno. 3/C electrocatalysts were reported. The electroless-deposition with sensitization-activationpretreatment was applied to prepare Pto. Ruo. s/C and Pto. s Ruo 1s Sn,3/C electrocatalysts. The XRD and TEManalyses showed that the as-prepared catalysts were composed of well-dispersed PtRu or PtRuSn nanoparticleswith an average particle size of about 3 nm. The electrochemical measurements demonstrated that the as-prepared/ c catalysts exhibited much enhanced peak current density for ethanol electro-oxidation as compared to that synthesized without pretreatment. This result revealed that the pretreatment is favor-ole to the dispersion, size distribution and alloy degree of the nanocatalysts on the carbon support. In particu-lar, the peak current density of ethanol oxidation on Pto. s Ruo. isSn, 3s/C was nearly twice larger than that of Pt.sRuo.s/C, indicating their potentialKey words: electroless-deposition; DEFC; PtRw/C catalyst; PtRuSn/ C cataly中國煤化工CNMHG