化学镀制备高性能直接乙醇燃料电池(DEFC)阳极催化剂PtRu/C和PtRuSn/C

第14卷第2期电化学2008年5月ELECTROCHEMISTRYMay 2008文章编号:1006-3471(2008)02015005化学镀制备高性能直接乙醇燃料电池(DEFC)阳极催化剂PtRu/C和 PtRusn/C朱静,苏怡,马华,程方益,陶占良,梁静,陈军(南开大学化学学院新能源材料化学研究所和能源材料化学天津市重点实验室,天津30001)摘要:应用化学镀方法以活化敏化处理的活性炭作载体制备高分散催化剂PRu/C和 PtRuSn/C.XRDTEM及电化学测试表明,该催化剂P、Ru、Sn形成合金金属颗粒的平均粒径约为3m.PRu/C和 PRusn/C二者对乙醇的阳极氧化都具有良好的催化活性和稳定性关键词:化学镀;直接乙醇燃料电池;PRu/C催化剂;PRSn/C催化剂中图分类号:TM9114文献标识码:A直接醇燃料电池直接以液醇作燃料,其能量转明,以活化敏化处理的炭作载体再由化学镀方法换密度高、环境污染小,而且燃料来源丰富、价格低合成的催化剂将有利于提高催化剂纳米颗粒在炭廉、贮存和运输方便,适用于便携式和家用电子设表面的分散性减小粒径尺寸,进而提高催化剂的备.近年来直接甲醇燃料电池(DMFC)的研究性能.本文进一步应用该化学镀方法合成了P已取得了显著的成就但甲醇的毒性大,广泛应用 Rw/C PtRusn/C催化剂,同时研究了上述两种催受到诸多限制.与甲醇相比,乙醇毒性较小,是一化剂对乙醇阳极氧化的催化活性.结果表明化学种可再生、有前途的甲醇替代燃料但至今,可用镀方法制备的催化剂具有较高的活性而且三元催于乙醇电化学氧化的催化剂活性较低,其抗CO中化剂 PtRuSn/C对乙醇的氧化催化表现出更优越毒能力也较差,这是制约直接乙醇燃料电池的性能(DEFC)商业化的主要问题2.因此开发新型高1实验部分效抗CO中毒能力强的阳极催化剂乃是当前乙醇1.1催化剂的制备燃料电池领域研究的热点之一.虽然众多的文献活性炭 Vulcan XC-72( Cabot,比表面积250指出炭载PRu对甲醇的氧化表现出优越的催化m2/3),H2PC4·6H2ORuC3SnC2·2H20、PdCl2性能,但就乙醇而言其彻底氧化是一个12电等试剂均分析纯子转移的过程,不仅包括醇的吸附脱氢、中间产物化学镀方法制备炭载PRu/C(P:Ru=0.5CO等氧化还包括CC键的断裂,这就使得乙0.5)、 PtRuSn/C(P:Ru:Sn=0.5:0.15:0.35)催醇的氧化更加复杂近年来的研究表明如在PR化剂:将活性炭XC72在含有SnC2·2H12O催化剂中添加适量的Sn,将有利于降低CC键断PdCl2,Na2SnO3·4H20和乙二醇的胶体钯溶液中裂的反应活化能,从而提高乙醇氧化的反应速超声波振荡(活化敏化)10min,水洗去除残留的SnCl2和PCl2,然后将活化敏化后的活性炭转移提高催化剂金属颗粒的分散性,控制粒径是提到化学镀溶液中,镀液组成为H2PCL4(1.93mmol高催化剂性能有效方法.本课题组近期的研究表L)和RC4(3.63mmo/L)或H2PC4(1.93mmb中国煤化工收稿日期:2007-1225,修订日期200801-15*通讯作者,Tel:(862CN MH Gkai ed国家863项目(No.2007AA05z124、No.2006AO5Zl30)和天津国际科技合作项目(No.07 ZCGHHZ00700)资助第2期朱静等:化学镀制备高性能直接乙醇燃料电池(DEFC)阳极催化剂PhRu/C和 PtRusn/C151L)、RuCl2(3.63mmo/L)和SnCl2·2H2O(4.43峰均有明显的宽化现象这和金属颗粒粒径较小或mmol/L),搅拌1h,使活性炭和化学镀液混合均金属颗粒结晶存在缺陷有关,根据 Scherrer公匀.滴人适量的Na2CO2溶液调pH值到10,再逐式2计算活性炭活化处理前后以化学镀方法制滴滴入20mg/L的硼氢化钠溶液,强搅拌2h,使金备的 PtRuSn颗粒的平均粒径分别约为42m和属盐充分还原.沉淀经离心分离、多次水洗后在3.2nm60°C真空干燥4h直接还原法制备催化剂:将未经活化敏化前(111)处理的活性炭XC-72直接分散到上述化学镀液中使金属盐还原(2001.2研究电极的制备取上述5mg催化剂分散在05mL5%Na-fon0.5mL乙醇溶液中,超声分散Ih成糊,然后b取5μL催化剂糊滴在抛光后的玻碳电极表面(=3mm),60℃干燥2h13产物表征2e(°)用 Rigaku D/max2500型粉末X射线行射仪(CuKa,A=0.15405m)作物相分析,透射电子图1以化学镀方法制备的RRuC(a,b)和 PtRuSny/c(e,显微镜( Philips Tecnai-F20)观察产物的形貌d)催化剂的XRD谱图活性炭经活化敏化处理(a,c);未经前处理(b,d)1.4电化学测试Fig 1 XRD pattems of the PtRw/ C (a, b)and PtRuSn/c电化学测试使用 PARSTAT2273电化学工作(c, d)prepared by electroless-deposition with(a, c)站(美国 AMETEK)三电极体系.以载有活性物质or without(b, d)sensitization-activation pretreatment的玻碳电极作研究电极,Ag/AgCl-KCl作参比电极面积为1cm2的铂片作对电极.电解液是052.2样品的TEM分析l/LH2SO4和0.5mo/L乙醇混合溶液,循环伏图2示出 Pt Rusn/C催化剂的TEM照片及其安测试的扫描速率50mv/s,电位区间-0.2-0.8粒径分布.如图所见活性炭未经活化敏化处理Ⅴ极化曲线测试扫速05mV/s.计时电流法在0.5制备的催化剂(A,B)颗粒有团聚现象而且颗粒较V电位下测试1500s.大,平均粒径约为4.2mm.而经过活化-敏化处理2结果和讨论制备的催化剂(C,D),其金属颗粒大多均匀地分散2.1样品的XRD分析在炭载体的表面没有明显的团聚现象,且颗粒粒图1分别为经活化敏化处理(a,c)和未经处径分布较窄,在1.2~5mm之间,平均粒径约为24C催化剂的xRD衍射谱.如图,两种方法制备的2.3催化剂的电化学性能测试二元 PtRu/c催化剂(a,b)和三元 PtRuSn/C催化图3给出乙醇在0.5mo/LH2SO4溶液中,于剂(c,d)的谱线基本一致,其特征峰分别归属为炭两种不同方法制备的PRuC(a,b)和 PtRuSn/C载体的(002),铂的(111)、(200)、(220)晶面.对(c,d)催化剂上氧化的循环伏安曲线(A)和计时比P的标准卡片( JCPDS No.4802),PRu/C催化电流曲线(B).从图3A见,不论是二元或三元体剂的2θ有所正移,说明Ru扩散进入Pt的晶格形系V凵中国煤化工化剂(a,),其成PRu合金与文献报道的结果一致而三元伏安CNMHG制备的炭载催化PtRuSn/c催化剂的26相对PRuC发生负移,这剂(b,uJ,Ⅺ凡乜龀叫负移和峰电流密是由于部分Sn进入PRu的晶格导致晶格常数增度的增大.图中,曲线a和b在0.75V处显示的大田,并形成PRSn合金.图中4种样品的衍射峰电流分别为15.5mA/cm2和11.6mA/cm2,可152电化学2008年8305202.53.03.540455.05.56.06.5Particle size/rm88目30252015101.52.02.53.03.5404.55.05.5Particle size/ nm图2活性炭未经活化敏化处理(A,B)和经活化敏化处理(C,D)以化学镀方法制备的三元 PRusn/C催化剂的TEM照片及其粒径分布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图3活性炭经活化敏化处理(,)和未经前处理b,d)以化学方V凵中国煤化工c(,d催化剂在0.5mo/L乙醇0.5mlL硫酸溶液中的循环伏安曲线(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期朱静等:化学镀制备高性能直接乙醇燃料电池(DEFC)阳极催化剂PRu/C和 PtRuSn/C153见前者比后者提高了近33.6%,这与本课题组此流增大更明显,说明该催化剂的反应活性更高.据前报道的PRu/C对甲醇氧化催化的结果基本一图,乙醇在两种催化剂表面氧化的Tael斜率,均约致9,对三元 PtRuSn/C催化剂,经前处理制备的为135mV/de,与文献报道的结果一致,说明炭载催化剂其峰电流密度为31.2mA/cm2,较之未乙醇在这两种催化剂表面氧化的速控步骤没有发经前处理的炭载催化剂(峰电流24.6mMcm2)也生变化,Sn的添加没有改变乙醇氧化反应的速控提高了近26.5%.另外,对比曲线a和c还可看步骤而是提高了它的反应速率出,于PRuC加入适量的Sn有利于提高催化剂的3结论性能,这是因为Sn的加入不仅有利于CC键和以化学镀方法制备用于乙醇阳极氧化的PC-H键的断裂加速了乙醇的氧化,而且能够R/C和 PtRusn/C催化剂活性炭经活化敏化处在较低电位下提供活性氧,从而提高催化剂的抗理有利于提高催化剂颗粒的分散性,减小粒径,从CO中毒的能力,使催化剂保持较高的活性而提高催化剂的反应活性,Sn的加入更为明显提计时电流曲线(图3B)示明,经过活化敏化处高该催化剂催化活性和稳定性理制备的炭载催化剂(曲线a,c),其电流密度均大于未经前处理制备的炭载催化剂(曲线b,d同样证明了前者具有较高的催化活性和较好的稳参考文献( References):定性.再如,图中曲线c在测试过程中始终保持着[1] Song Shuqin(宋树芹), Wang Yi(王毅), Shen pej.较高的电流密度,而且衰减缓慢,说明Sn的添加使kang(沈培康). 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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中国煤化工CNMHG