Electro-Deposition Pt Catalysts Supported on Carbon-Nanotubes for Methanol Oxidation

Journal of Harbin Institute of Technology ( New Series)，Vol.22, No.5, 2015doi:10.11916/j.issn. 1005-91 13.2015.05.013Electro-Deposition Pt Catalysts Supported on Carbon- Nanotubesfor Methanol OxidationHaili Song, Peixia Yang *，Xiaoyu Wen, Maozhong An and Jinqiuu Zhang( Chemical Engineering Instiute, Harbin Instiute of Technology, Harbin 150001, China)A bstract: In order to study the properties of supporting Pt catalysts for methanol oxidation, carbon-nanotubesare used by electrochemical deposition method. Different deposition turns, different cyclic voltammetry scanningspeeds and processing time with ascorbic acid are investigated in this paper. The micrographs of PV/CNTscatalysts are characterized by scanning electron microscopy，the electro-catalytic properties of PV/CNTs catalystsfor methanol oxidation are investigated by cycle voltammetry and chronoamperometry. The results show that thesize of platinum will be greater with the faster scanning speed. After dissolution in ascorbic acid, Pt nano-particles disperse uniformly. The obtained Pv/ CNTs catalysts show a high electro-catalytic activity and stability.Keywords: Carbon nanotube; Pt catalyst ; Cyclic voltammetry; Ascorbic acidCLC number: TM911.46Document code: AArticle ID: 1005-9113(2015)05-0085-04area of common concerm and has made great progress”。1 IntroductionThis paper studies the use of CNTs as Pt catalystsupport by voltammetry method and processes theDirect methanol fuel cells ( DMFCs ) haveobtained Pt particles with ascorbic acid， furtherattracted increasing attention in portable power andreducingnano-particles size. The impact ofmobile applications because of the high energy density ,experimental factors affecting the performance ofrapid start-up, and low temperature[ 1-3].However, thecatalysts have been investigated. Additionally， theconversion from chemical to electrical energy still facesbetter conditions of process preparation is chosen, andseveral critical challenges，including the durability andthe physical properties of obtained catalysts aretheir low electro-catalytic activity4. Pt is the mostanalyzed. The catalysts show a high durability anceffective single metal catalyst for methanol oxidation.electro-catalytic activity for methanol oxidation.Because of the high cost of Pt catalysts, reducing theamount of Pt and enhancing its electro-catalytic activity2 Experimentaland stability are still the hot spots of DMFC research5l.Variety of catalyst support has been studied in last2.1 Reagents and Apparatusesdecades ranging from vulcan carbon， carbon black,Chloroplatinic acid ( H,PtCl。●6H2O ) wascarbon nano-fiber and graphene. Among them, carbonobtained from Shenyang Kedachem co. Ltd. Ascorbicnanotubes ( CNTs) as catalyst support material haveacid was purchased from Tianjin Kemiouchemco. Ltd.drawn great interest because of their large accessibleAll other chemicals were analytical grade. All solutionssurface areas， high stability， and high electronwere prepared with pure water. The pristine CNTs wereconductivity6-. Recently, many methods have beenpurchased from Shenzhen Nanotechnologies Port Coreported such as Liquid-phase chemical reductionLtd. All electrochemical measurements were performedmethod8J，Sol-gel method 9，Hydrothermal method ,with an electrochemical workstation( CHI630B,Solid state reaction method, Electro-reduction. 10- 12]Shanghai，Chenhua ) through a conventional three-Electro-depositionhasadvantages)f simpleelectrode cell.technology，low cost and high purity coating. B2.2 Pt/ CNTs Catalysts Preparationcontrolling the current,electrolyte components andrnde_( GCE) was polishedprocess parameters， one can control the coatingcarel中国煤化工n dry it with high puritycomponents, grains， grain size. It has been a researchnitroC NM H G 0.1% Nafion solutionReceived 2014-04- 16.Sponsored by the Fundamental Research Funds for the Central Universities ( Grant No. HTT. ICRST.2010005 ).* Corresponding author. E-mail: yangpeixia@ hit.edu.cn.Journal of Harbin Institute of Technology ( New Series)，Vol.22, No.5, 2015diluted by ethanol was dispersed ultrasonically. Then,demonstrated by chronoamperometry test at a fixed.5 μL of the ink obtained was pipetted and spread on apotental of 0.5 V in 0.5 M CH3OH+0.5 M H2SO4polished glassy carbon electrode (GCE, 0 4 mm) asmixed solutions. High-purity argon was purged throughthe working electrode. Pt/ CNTs catalysts were preparedthe solution for 10 min before the tests were performed.by cycle voltammetry method with three-electrodeAll electrochemical experiments were performed atsystem. GCE was used as the working electrode， aambient temperature (25+1 C).saturated calomel electrode ( SCE ) used as thereference electrode and the counter electrode was aResults and Discussionbright Pt plate. The voltammetric activation behaviorwas characterized in 0.5 M H2 SO.+5 mM H, PtCl。3.1Effect of Deposition Circles on Catalystmixed solutions. The prepared catalysts took squarePt/CNTs catalysts prepared by electrochemicalwave method when it was treated by ascorbic acid ondeposition method can control the deposit amount bythe Electrochemical Tester M273, in a 30 mM ascorbiccontrolling the cycle turns. So appropriate cycle turnsacid+0.1 M H,SO, mixed solutions.are essential to guarantee the grain size and the deposit2.3Electrochemical Measurementamount. SEM image of Pt/CNTs catalysts prepared byThe catalytic activities of catalysts loaded ondifferent cycle turns is shown in Fig. 1 with scanningcarbon nano-materials were measured by cyclepotential ranging from -0.3 to 1.3 V，scanning speedvoltammetry method. The durabilty of Pt/CNTs wasat 50 mV/s.(a) 60 eircles(b) 130 eircles(c) 160 circlesFig.1 SEM images of PV/CNTs prepared by different deposition turnsAs can be seen in Fig.1， Pt particles dispersedown, which is consistent with the SEM images.uniformly on the surface of CNTs and the grain size is3.2Effect of Cyclic Voltammetry Scanning Speedsabout 150 nm. When added to 130 circles, Pt particleson Catalystbegan to reunite. When added to 160 eircles， PtSEM images of Pt/CNTs at different scanningparticles size is about 250 nm，and covers the wholespeeds of 25 mV/s, 50 mV/s, 75 mV/s, respectively,CNTs. Pt nano-particles grow up with cycle turnsscanning potential ranging from -0.3- 1.3 V are shownaddition because the original nucleus begin to form atin Fig.3.low cycle turns. And nucleating is slow and dispersesAs can be seen in Fig. 3，Pt nano-particlesevenly. Then Pt particles quickly grow up on the basisdisperse uniformly on the walls of CNTs. Pt grain sizeof the original nucleus until a reunion at high cycleincreases with scanning speeds addition. At 25mV/s,turms-14. In this paper, deposition circles at 60 arePt particle reaches about 30 nm. At 50 mV/s，Pttaken.particle reaches about 40 nm. At 75 mV/s, Pt particleAs can be seen in Fig.2， the peak current forreaches about 90 nm.methanol oxidation increases with deposition circlesAs can be seen in Fig.4， with the increase oaddition, reaching maximum at 1 30 circles. The reasonscanning speed， the peak currents for methanolis that when the deposition circles were small， Ptoxidation reaction get smaller and smaller. So both forparticles dispersed evenly on the surface. With cyclePt particles morphology and the catalytic properties，turms addition， the effective surface of catalystcyclic voltammetrv sranning sneed in electro-depositionincreases，and the peak current for methanol oxidationis t中国煤化工this article, 25 mV/salso increases. When the scanning laps reach a certainscan|Y片C N M H Gpare the catalysts- 5amount, the active position provided by CNTs will be .3.3 Effect of' Ascorbic Acid Treatment on Catalystoccupied by Pt particles deposited before. Then, thePropertiescatalysts will grow up， and the active surface willPv/ CNTs catalysts prepared by cyclie voltammnetry, .decrease，creating the catalytic properties cuttingscanning potential ranging from -0.3-1.3 V, scanningJournal of Harbin Institute of Technology ( New Series)，Vol.22, No.5, 2015speed at 25 mV/s， and running 60 circles have aparticle size in 30 mM ascorbic acid +0.1 M H2 SO4relatively smaller grain size ( 30 nm). But comparingmixed solutions using pulse potential. SEM images ofwith the commercial catalysts, its grain size is too big.catalysts are treated and untreated by ascorbic acidThe obtained Pt particles prepared by above method isrespectively, as shown in Fig.5.treated with ascorbic acid, further reducing the catalyst4.44.5-4.2-4.0 t3.5t刁3.82.5-3.4-2.0f3.2 t占3.0个1.5-2.8 t.0_2.6 t20304050607080100 12(140 160 180Cycle number(r)(a) Scanning circle is from 20 to 80 turns( b) Scanning eircle is from 90 to 170 turnsFig.2 Curves of peak current for methanol oxidation varying with cycle turn(a)25 mV/s(b) 50 mV/s(c) 75 mV/sFig.3 SEM images of Pt/ CNTs catalyst in different eyclic voltammetry scanning speedsSEM images in Fig.5 reveal some differencesamount of Pt particles is cutting down，as well as thebetween the two images. In Fig.5( a)，there are muchgrain size. Consequently, it is also improved that themore Pt particles on the surface, but some particlesgrain size of Pt particles can be reduced by cyclicreunite. And after dissolving in the ascorbic acid, thevoltammetry method dissolution in ascorbic acid.-6r 25 mV/s.50 mV/s,? -20|75 mV/s-0.40.4Potential(V)(a)Undissolved(b)Dissolved for 10 minFig.4 CV curves of Pt/CNTs catalysts preparedat different scanning speeds inFig.5 Efects of ascorbic acid dissolved0.5 M methanol+ 0.5 M HSO, .As can be seen in Fig.6，the electro-activitycatalytic stability of the electro-catalyst in Fig.7. It isdecreases a little after dissolution in ascorbic acidthe measurement of its oxidation current with time ，because the amount of Pt particles is lower. But Pdon中国煤化工M H2SO4 at 0.5 V forparticles disperse much evenly than before. And the7 00remaining solutions can be reused again, which can出CNMHG.rent value is due to thesave the amount of Pt.formation of intermediates during methanol oxidation.3.4 Catalyst Stability TestThe current of Pt/CNTs is higher compared to otherChronoamperometry is performed to measureelectro-catalysts during the whole testing time ，Journal of Harbin Institute of Technology ( New Series)，Vol.22, No.5, 2015indicating higher stability of the catalysts. Hence one[ 2] Tang Yawen, Bao Jianchun, Zhou Yiming, et al. Preparationcan conclude that the CNTs are a better alternative forof Pt/Carbon-nanotubes catalysts and their electrocatalyticanode catalyst support' 16].activities for oxidation of methanol. Chinese Journal 0Inorganic Chemistry, 2003, 19 (8) :905-908.12[ 3] Chen Weixiang, Lee Jimyang, Liu Zhaolin. Carbon supportedPt nano-particles prepared by microwave heating and theirUndissolvedelectrocatalytic activities for methanol oxidation. ActaChimicaSimica, 2004, 62 (1):42-46.[4]Niu Yulian, Xiao Xueqing, Gu Zhiguo, et al. Synthesis and)telectrochemical property of the graphene/Pt composites.Chinese Jourmal of Inorganic Chemistry, 2012, 28 (4):Dissolved751-756. .[5] Zhou Yang, Chu Youqun, Liu Weiming, et al. Nano-WO3modified Carbon nanotube supported Pt catalysts and their-12electrocatalytic activity for methanol electro- oxidation. Acta-0.40.0.81.2Physico-Chimica Sinica, 2013, 29 (2) :287-292.Potential(V)[6] Wu Gang， Bo Qingxu. Carbon nanotube supported PtFig.6 CV curves of Pt/CNTS catalyst before and afterelectrodes for methanol oxidation :A comparison betweentreatment in ascorbic acid in the methanol solutionmulti-and single-walled carbon nanotubes. Journal of PowerSources, 2007, 174 (1):148- 158.[7]Jha N, Jafri R I, Rajalakshmi N, et al. Graphene- muliwalled carbon nanotube hybrid electrocatalyst supportmaterial for direct methanol fuel cell. International Journalof Hydrogen Energy, 2011, 36 (12) :7284-7290.[8] Qin Zuzeng, Liu Zili， Wang Yanhua. Promotion effect of. P/CNTsMo in amorphous NiP catalysts for the liquid- phasecatalytic hydrogenation of nitrobenzene to aniline. Chemical言Engineering Communications, 2014, 201 (3) :338-351.t Pt catalysts[9] Agarwal G, Reddy G B. Study of surface morphology andoptical properties of Nb2O。 thin films with annealing.Journal of Materials Science: Materials in Electronics ,2005, 16 (1):21-24.Time(s)Fig.7 Chronoamperometry curve of Pt/ CNTs catalyst in[ 10]Park K w, Choi J H,Ahn K s, et al. PtRu alloy and0.5 M H2 SO, +0.5 M CH,OH solutionsPtRu-WO，nanocompositeelectrodesor methanolelectrooxidation fabricated by a sputtering depositionmethod. The Journal of Physical Chemistry B, 2004, 108( 19) :5989-5994.4 Conclusions[ 11]Zhang Qinyi, Tang Shuihua, Zhang Jie, et al. Researchprogress of Ni ( OH ) 2/ graphene composites as electrodePU/CNTs catalysts are prepared by electro-material for supercapacitors. Electronic Components anddeposition using cyclic voltammetry method. ControlMaterials, 2013, 32 (12):1-7.the amount of deposition turns to decide the amount of[ 12]Jia Jianbo, Cao Linyuan, W ang Zhenhui. Platinum-coatedPt particles, and decide the scanning speeds to controlgold nanoporous film surface: electrodeposition andthe deposition speeds of Pt nano-particles, the grainenhanced electrocatalytic activity for methanol oxidation.Langmuir, 2008, 24 (11) :5932-5936.size of Pt nano-particles and the degree of its[13] Cao Lixin， Tu Zhenmi， Li Ning, et al. Progress indispersion. The obtained catalysts reach about 30 nmpreparation of single metal electrodeposited nanocrystallineby choosing the scanning speeds at 25 mV/s, cycling .materials. Materials Protection, 2009, 42 (6) :47-50.60 turns. After dissolution treatment in ascorbic acid,[14]Li Huaixiang， Zhao Jing, Wang Ruihua. Study of Zinesmaller size catalysts have a better catalytic activity andoxide films by a square wave current wave currentstability. The direct methanol fuel cell performance ofelictrolysis. Journal of Shandong Normal Universitythe anode and cathode electrodes using these catalysts( Natural Science), 2005, 20 (2) :48-50.[15]Ji K, Chang G, Oyama M，et al. Eficient and cleanwill be presented in future work.synthesis of graphene supported platinum nanoclusters andReferencesits application in direct methanol fuel cell. Electrochimica中国煤化工[1] Hu Chuangang, Guo Yuming， Cao Yanxia, et al. A facile-quan， Yue Ruirui, et al.method for preparation of high performance Pt catalystMHCNMH(long-term stable Pt-loadedsupported on multi-wall carbon nanotubes for methanolPEDOT/ graphene composites for ethanol electrooxidation.electrooxidation. 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