Electrodeposited Pt and Pt-Sn nanoparticles on Ti as anodes for direct methanol fuel cells

第37卷第3期燃料化学学报Vol.37 No.32009年6月Joumal of Fuel Chemistry and TechnologyJun. 2009文章编号: 02533 2409(2009 )03 0346-09Electrodeposited Pt and Pt-Snnanoparticles on Ti as anodes for direct methanol fuel cellsHanaa B HASSAN(Deparment of Chemistry, Faculy of Science，University of Cairo, Giza, Egypt)Abstract: Electro-oxidation of methanol was studied on titanium supported nancrytallile Pl and Pr,-Sn, catalysts prepared byelectmodeposition techniques. Their electro-catalytic activities were studied in 0.5 mol/L H,SO2 and compared to those of a smooh PI,PVPr and Pr-Sn/Pt electrodes. Platinum was deposited on TI by galvanostatic and potentiostatic techniques. X-ray difractomeler( XRD) and energy dispersive X -ray ( EDX) techniques were applied in order to investigate the chemical composition and the phasestructure of the modifed electrodes. Seanning eton microscopy (SEM) was used to characterize the surface momphology and tocorrelate the results obtained from the two electrochemical deposition methods. Results show that modified PVTi electrodes prepared bythe two methods have comparable performance and enhanced catalytic activity towards methanol eletro oxidation compared to P/Pt andsmooth Pt electrodes. Steady state Tafel plots experiments show a higher rate of methanol oxidation on a PV/Ti catalyst than that on awith time as indicated from the eyelic votlammetry and the chronoamperometric experiments. The efeet of variations in the compositionfor binary catalysts of the type Pr, -Sn,/Ti towards the methanol oxidation reaction is reported. Consequenly, the Pr.-Sn,/Ti (xy (8:1), molar ratio) catalyst is a very promising one for methanol oxidation.Key words: eetrdeposition; methanol; electro-oxidation; fuel cells; elcero-catalysis.sCLC number: 0646 Document code: AIn recent years, Ti and TiO2 electrodes have beenthan that of a bulk Pt electrodel9].During theused as anodes or cathodes for some electrochemicalinteraction of HCO0H with powdered TiO2 and PVTiO2reactions of technological interest such as oxygen andcatalysts，formaldehyde can be detected， On thechlorine evolution reactions, the reduction of oxygenother side，highly dispersed Pt deposition over the Tiand the methanol oxidation reaction[1-51. It has beenmesh showed higher electro-catalytic activity towardsreported that, the electro-catalytic properties of Tivmethanol oxidation with a stable performance comparedTiO2 electrodes can be improved by doping the oxideto the conventional hot pressed carbon supported Ptfilm with noble metals like Pr[6-12]. The PVTiO2catalysts[l5]. In addition， Pt nanophases and acomposite can be synthesized in various ways such astitanium oxide matrix Pt-TiO, that was fabricated byelectrochemical'3) , electroless deposition4i ，thermalmeans of the co-sputteing deposition method showed adecomposition'etc. The deposition of P1 on Tiremarkably enhanced performance for methanolcan be realized either by direct deposition on the oxideoxidation under UV ilumination. The compositefilm or on the oxide free surface. It was reported thatcatalyst Ti02 nanoubes/PVC ( TNT/PvC ) showedTi would be an ideal substrate for metals depositionenhanced catalytic activity towards ethanol oxidation inbecaure of its low cost， mechanical strength andacid solution. The P/TiO2 molar ratio was alsoresistance to acid16 .optimized and a 1:1 ratio was found to be the best(2) .Electro-oxidation of methanol was studied on PtOn the other hand, addition of Sn into the Ptfinely dispersed on TiO2 and Ti metal7l. Thecatalyst promotes the electro-catalytic activity for thedeposition of Pt on Ti at open circuit was studied onelectro-oxidations of C，C2 and C3 alcohols. Thefreshly polished Ti and on Ti covered by a thin oxidevariation of Sn content by forming PiSn alloys causesfilml4]. Besides, the electrochemical activities of Tisignificant structural and electronic modifcations of Ptsupported nanostructure Pt were much higher than thaterytallites' 231. The PtSn bimetallic nanoparticlesof the bulk Pt electrode. The nanostructure Pt electrodeprepared by a hydrothermal method with average sizeswithunpolished Ti supportshowed higherof 2 nm showed enhanced electro-catalytic activity andelectrochemical activity thanthe polished Tilifetime for the electro-oxidation of methanol comparedsupport8. Also, the electro-catalytic activity of thisUV-visibleelectrode for the oxidation of HCOOH was much higherspectr中国煤化工Si copenaepeMYHCNMHGReeived date: 2008 10-07; Received in revised form; 2009-0204.Corresponding author: Hana B Hassan, Tel; + 20235676563, + 20103871963; Fax: + 2025727556. +2025728843;E-mail: hana20055@ hotmail. com.第3期Hanaa B Hassan: Electrodeposited Pt and Pr-Sn nanoparticles on Ti as anodes for direct methanol fuel cells347formed when the precursors of Pt and Sn were mixedsuface). Real surface areas of the prepared electrodestogether. The results suggest that Pt and multivalent Snwere estimated using Nova 2000 series based on theare the active species for the oxidation process'BET theory.The aim of the present investigation is to study theThe phase structure and the crystal size of theeffect of deposition Pt and/or Pt, -Sn, nanoparicles onelectrodeposited particles on the surface of electrodesTi and Pt suhstrates by potentiostatic and/orwere studied by X-ray diffractometry ( BRUKER axc-galvanostatic lechniques at different ratios and examineD8) using CuKx radiation with λ= 0. 1542 nm. Thetheir performance and stablities with time towardsgrain size of Pt paricles deposited on Ti surfaces canmethanol electro-oxidation in H2SO, solution.be estimated by the Scherrer equation!27:0.9A1 Experimental“Beos(02)(1)1.1 MaterialsMeasurements were performed on aWhere λ is CuKa wave length, B is the broadening ofPt sheet electrode of apparent surface area ofthe full width at half maximum (F. W. H. M). The0.125 cm2 and a purity of 99. 99% and on a Ti discscanning electron microscope ( SEM) ( JEOL-JSM-metal electrode of 99. 9% purity and apparent surface5410) and the energy dispersive X-ray (EDX) ( EDX-area of 0. 125 cm2 modified by electrodeposited PtOxford) tool were used to determine the averageand/or P1-Sn. Chemicals were obtained from BDHcomposition ratio of Pt and Pl-Sn on the Ti surfaces and(SnCl2, H,PtCl, H2S0。and methanol, AR). 'Theto examine the Pt and Pt-Sn surface morphology. Inwere used without further purification and solutionseach measurement an area of 10 μm in diameter waswere prepared using triply ditilled water.examined to a depth of about 2 μm.1.2 Electrodeposition proceduresBefore the.3 Electrochemical measurements Electrochemicaleleetrodeposition process, Ti and Pt were mechanicallymeasurements were performed on Pt and Ti electrodespolished using metallurgical papers of various grades,of the same apparent surface area of 0. 125 cm2then they were subsequently degreased with acetone ,modifed by electrodeposited Pt and/or Pt-Sn and therinsed with dilll water and dried with a soft tissuecurrent density was referred to this area. Thepaper. The surface area of each electrode waselectrochemical cell was described elsewherel28. Thecalculated from the apparent area and the currentreference electrode to which all potentials are referreddensity was referred to it.is the Hg/ Hg2S02/ 1. 0 mol/L H,SO,(MMS) (E° =The eetrodepositin of Pt on Ti and Pt electrodes0.680V vs NHE), and a Pt sheet was used as thewas performed from 8. 0 mmo/L K, PtC1。in 0.5 mol/Lcounter electrode. The electrochemical measurementsH2SO。by using the potentiostatic deposition atwere performed by using Amel 5000 ( supplied by- 530 mV vs Hg/ Hg2SO2/ 1. 0mol/L H2SO,( MMS)Amel Instrument, Italy). The PC was interfaced withfor 15 min and the charge consumed was calculated.the instrument through a serial RS-232 card. AmelFor a set of experiments, the time of the Pt depositioneasy scan soft ware was used in connection with PC toon Ti was changed from 1 min up to 20 min. Anothercontrol the Amel 5000 system. All the reportedmethod for Pl deposition on Ti was the galvanostaticpotentials were corected by the positive feedbacktechnique at a constant current of - 1 mA for differenttechnique. All the measurements were carried out attime intervals. The amount of Pt deposited on Tiroom temperature of about (30土2) C.electrodes was evaluated from the charge consumedduring the electrodeposition; assuming100%2 Results and discussioneffciency for the following faradie reaction(26] : PrtCI。22.1Characterization of the prepared anodes+4e→Pl+6Cl-.Generally, the structure and properties of PVTi and Pt-The electrodeposition of Pl and Sn on Ti and PrSn/Ti depend mainly on the method of preparation.electrodes was performed from K,PtCl。 and SnCl2 inEDX analysis resuls Pt and PI-Sn deposited on the Ti0.5 mol/L H2SO, solution by using different molarsurface in each case are shown in Figure 1. Theratio of Pt:Sn (8:1 and 1:1)， with the potentiostaticchemical content of the electrodeposits PI and Pt-Sn ondeposition at -850 mV vs Hg/ Hg2S0,/ 1. 0 mol/LTi are given in Table I. It is noted that the position ofH2S04 (MMS) for 15 min. Also， the time of thePt pand the positiondeposition of Pt-Sn on Ti was varied from 1 up toofS中国煤化工ev, while 1 peak25 min. ( After the preparation of the modified Ti andis4.:TYHCNMHGPi electrodes, no further pretrealment of the electrodeSEM patterms of the Ti， PVTi and Pt-Sn/Tiwas necessary to avoid any changes in the substratesurfaces are shown in Figure 2.348燃料化学学报第37卷(ab)|PhriPtTi T101S201Energy E/keV(d)PTi TiT515201CFigureI EDX analyisof(a) Ti, (b) PVTi (galvanoslatic depositin), (c) P/Ti (potentiostatie deposition) and (d) Pr-Sn/Ti30kVX3.500Sum 0000 I 30kVX3S00Syum 0000000 I 30kVX 3.5005um 000000 30kVX3,5005 um 00000Figure2 SEM pttemsof (a) Ti, (b) P/Ti (alvanostatic deposition), (c) PVTi (potentiosatic deposition) and (d) PI-Sn/TiTable1 EDX analysis of the modified electrodesthe percent composition of Pt on the Ti surface is aboutSampleP1% Ti% Sn %93. 4% and the true surface area is 262 cm/mg of Pt.P/'Ti galvanostatic8614The Pt loading of this electrode is about 5 mg/cm'. ItPVTi potentiostatic93.46.6is noticed that the galvanostatic technique can preparePrt-Sn/Ti (8: 1) potentiostatic 88. 10.9a higher surface area and a smaller particle size P/Tielectrode than the potentiostatic technique.It can be seen that the average composition ratioOn the other hand, the presence of Sn with PtofPt: Ti for the PVTi electrode that was prepared bychange the morphology of the electrode surface asthe galvanostatic method for 15 min (Figure2(b)) isappears in SEM pattem ( Figure 2(d)). The surfaceabout 86: 14 and the average particles size is aboutof Pi particles is covered with shiny Sn particles and5.3 nm ( calculated from XRD patterm by usingthe percent composition of Sn deposited is illustrated inScherrer equation)，also this method gave a Pt loadingTable I. The average particles size is about 7. 1 nm,of about 3. 65 mg/cm2 on the Ti surface, The trueand the presence of Sn slighuly increases the Pi particlesurface area of this electrode is calculated and it wassize.中国煤化工_his eletrode isfound to be 296 cm2/mg of Pt. While, the PV/Ti288 cmelectrode that was prepared by potentiostatic technique:YHCNMHGmsofthePV/Tifor 15 min ( Figure 2(c)) shows the average particleselectrodes preparedby the two electrodepositionsize of 5.8 nm, and the particles are almost uniformlymethods and Pt-Sn/Ti respectively. Diffraction patternspread in condensed layers form on the Ti surface, andof PI shows five sharp peaks with different intensities第3期Hanaa B Hassan: Eletodeposited PI and Pt-Sn nanoparticles on Ti as anodes for direct methanol fuel cells349and another few small peaks corresponding to TiO2.a)|(6)0)|iiinie20300040080100201“)201(° )20/(° )Figure3 XRD pattemns of (a) PV/Ti ( galvanostatie deposited), (b) PVTi ( potentostatic deposited) and (c) Pr-Sn/Tio: Pr;●: TiO22.2 Electro-oxidation of methanol Methanol+ 270 mV of relatively small current density probablyelectro-oxidation on a smooth Pt electrode itdue to the oxidation of methanol or one of intermediate0.5 moVL H2SO。 occurs at a relatively lowerproducts of its oxidation. The main problem here is theoverpotential with relatively small oxidation currentpoor stability of Pt electrode over repeated cyclizationdensity and poor stability with time. Figure 4 showswhich reaches 16% after 50 cycles. Adsorbed CO iseyelic voltammograms of Pt electrode in 0. 5 mol/Lone of the most known intermediate products ofH2SO. in absence and in presence of 2. 0 mol/Lmethanol oxidation which causes deactivation andmethanol at a scan rate of 50 mV/s.blocking of the active sites of the electrode surfaceduring the oxidation process with the timel29!. In orderto enhance the performance of the Pt electrode, onepossibility is to increase the active surface area bydispersing the catalyst on a substrate. Methanoloxidation on Ti modified with Pt shows a highert/catalytic activity as shown in Figure 5.From Figure5(a), it is found that, as the time ofPt deposition increases up to 15 min, the oxidationPr in 0.5 mol/L H,SO,peak current density of methanol increase. After that2 mol/L MeOH.... afer 50 cyclestime a further slightly increase of the oxidation currentdensity is probably because of the saturation level of Pt20.505 1.0deposition on Ti surface with such long time ofE1 V(MMS)deposition. Also, there is a certain ratio between PtFigure 4 Cyelic volammugram of Pt eletrode in 0.5 molV/Land Ti on the electrode surface at which the highestH2SO,( the dashed line) and in presence of 2.0 moVLcatalytic activity is achieved. In Figure 5(b)，inMeOH ( the solid line) and afer 50 cycles ( the dotted line)addition to the hydrogen and oxygen evolution， twoata scan rale of 50 mV/ssmall peaks are observed in the blank voltammogram.One in the anodic direction at about + 500 mV ofFor the blank ceyclic voltammogram of Pt inrelatively small current density is probably due to the0.5 mol/L H2SO, the polarzation starts at - 600 mVPt oxides formation， and the other in the cathodicupto +1 400 mV ( MMS) in the anodic direction,direction al about - 40 mV (MMS) is probably due tothen the scan reverses to - 600 mV in the cathodicthe Pt oxides reduction. In presence of 2. 0 mol/Ldirection. The hydrogen evolution takes place at themethanol, an oxidation peak appears at + 523 mVstarting potential characterized by a high cathodie( MMS ) of oxidation current density of aboutcurrent density and the oxygen evolution takes place at220 mA/cm2 in the anodic direction, and a reoxidationrelatively high positive potential , in addition to anotherpeak appears in the reverse scan at about +50 mV ofreduction peak in the cathodie direction near to 0 mVrelatively smaller oxidation current density due to the(MMS) due to the Pt oxides reduction. In presence ofoxidat中国煤化工its intermediale2. 0 mol/L Me0H, there is an oxidation peak at aboutepeated potential+ 392 mV ( MMS) of 2.7 mA/cm2 oxidation currentcyelizYHC N M H Gation peak curentdensity in the forward direction and another reoxidationdensity is 67% of the current density of the first eycle.peak appears in the reverse direction at aboutThis indicates that not only the oxidation of methanol350燃料化学学报第37卷occurs at higher current density, but also the stabilitythe poisoning efect is less compared to the smooth Pt.of the electrode over repeated cyelization is improved as250|(a(b)200 -- 0.5 mol/L H.SO,200- 2 mol/L MeOH... after 50 cycles150 t100直50卜15200.01.5Time t/minE/ V(MMS)Figure5 (a) Effect of changing the amount of Pl deposied gavanosatically at - 1 mA on a Ti electrode on the etcroiation ofmethanol;(b) Cyelic volammograms of PVTi electrode ( prepared hy galvanostatie deposition for 15 min) in 0.5 mo/L H,SO, inabsence ( the dashed line) and in presence of 2. 0 mol/L methanol ( the solid line) and after 50 cycles(the dotted line) at a scan rate of 50 mV/sOn the other side, the performance of PVTireverse scan at about + 50 mV of relatively smallelectrode that was prepared poteniostatically atoxidation current density due to the oxidation of-530 mV ( MMS) for different time intervals towardsmethanol or one of its intermediate products that formedelectro-oxidation of methanol is represented in Figureduring the oxidation process. The stability of this6. Also, it is found that as the time of Pt depositionelctrode after 50 cycles is about 57%. By comparingincreases ( the percent composition of Pi increases),the performance of PVTi electrodes towards methanolthe oxidation current density of methanol increases upoxidation, it is found that the P/'Ti electrode preparedto15 min. In Figure 6(b), the shape of the blankby the galvanostatic technique has slightly highercyclie voltammogram is almost the same as that of PV/oxidation current density and larger stability than theTi prepared by the galvanoslatic. method， but inPVTi electrode prepared by the potentiostatic onepresence of 2. 0 mol/L methanol, the oxidation peakThis is due to the smaller particles size of Pr and thecurent density occurs at about + 500 mV ( MMS) oflarger surface area of this electrode cormpared with the :204 mA/cm2 and the reoxidation peak appears in thePt deposited potentiostatically as reported above.200 (间)-- 0.5 mol/L H.SO,(b- 2.0 mol/L MeOH180 .... afer S0 cycles150身120100 F60504- 8-0.4 0.0.8 12Figure6 (a) Efect of changing the amount of Pt deposited potentistatically at - 530 mV (MMS) on a Ti electrode on theelecrooxidation of methanol;( b) Cyclic voltammograms of PVTi electrode ( prepared by potentiostatir deposition for 15 min) in0.5 mol/L H2S0, in absence ( the dashed line) and in presence of 2. 0 mol/L methanol ( the solid line) andufter 50 cycles (the doted line) al a中国煤化工Table 2 shows the performances of a smooth Pt (of super;YHC N M H G towards methanol45 cm2 real surface area) and the modified PVTieleetro-oxidation with respect to the oxidation currentelectrodes. It is found that, PVTi electrodes aredensity and the stability of the electrodes over repeated第3期Hanaa B Hassan: Electrodeposited Pt and Pr-Sn nanoparticles on Ti as anodes for direct methanol fuel cells 351cyclization. The enhancement is atributed to thsmaller particles size, and the mode of its distributionincrease of the surface area of Pt deposited on Ti, theas shown in Figure 2.Table 2 Electrochemical parameters of methanol oxidation at difTerent modified electrodesI, mAE./ mVEfficiency afterSample/ mA.cm-2_ / real surface area( MMS)50 cyclesPt2.70.0639316%PVPI potentiostatie300.1731043% .P/Ti ( galvanostatic)2200.7453267%P/Ti (putentiostatic2040.7850057%P-Sn/Pl (8: I) potentiostatic1040.5479%P-Sn/'Ti (8: 1) potentiostatic3641. 2660098%Figure 7 shows the cyclic voltammograms of PVPton the substrate. P4 can adsorb and dehydrogenateelectrode prepared by potentiostatic deposition of Pt atmethanol at relatively low potentials but it cannot-530 mV(MMS) for 15 minutes on a Pr electrode ofadsorb OH. It is therefore the objective of research onthe same apparent surface area as a Ti with a similarbimetallic catalysts is to find a metal that can adsorbprepare manner as PVTi.OH radical or any other oxygen containing species arelatively lower potentials'x , . Alloying element( metal) facilitates the adsorption of oxygen containing3tspecies such as OHdaand Pt-OH reacts withorganic poison. Also, the. enhancement may occur by2tpreventing the formation of a strongly adsorbedpoisoning species such as CO either by blocking thesites necessary for its adsorption'or by oxidizing0tcompletely CO in solution into CO20, Ti metal canP/Ptin 0.5 mol/L H,SO,perhaps achieve these goals. Also， an extended2 mol/L MeOHHuckel caleulation of the Pt-Ti bonding' 35) ilustratedafer 50 cyclesflling of the d-band by donation of d-electrons from Ti0.50.0to unfilled Pt d-orbital that makes decrease in bindingE1 V(MMS)of CO to Pt ( this donation occurs even with an oxygenFigure 7 Cyelic voltammograms of PVPr eletrode ( preparedbound to the Ti site). The donation should make Tiby potentioslatic deposition for 15 min) in 0.5 mo/L H2SO,even more electropositive, binding oxygen even morein absence ( the dashed line) and in presence of 2. 0 moVLstrongly than the pure metal. Every CO moleculemethanol ( the solid line) and after 50 cycles (theadsorbing on Ti atom is dissociated. On the bases ofdotted line) at a scan rale of 50 mV/sthese discussions, it is suggested that the high catalyticIt is found that the PV/Ti electrode has higheractivity of Pv/Ti electrode relative to that of P/Pt oneoxidation curent density and large stability with timecan be atributed to one of each of the fllowing:towards methanol oxidation than the PVPt ( Table 2)the surface nature of Ti can facilitate thebecause of the higher surface area of the PVTdeposition of more Pt particles on its surface resulting(262 cm2 ) compared with the PV/Pt (180 cm2 ).in increasing the real surface area of the electrode.Taking into consideration the real surface area of each- Ti can increase the catalytic activity of Pt by itselectrode，it is found that, the oxidation currentelectrons donation to unfilled Pt d-orbital.density of methanol at the P/Ti electrode is about 4.5Anodic Tafel lines for methanol electro-oxidationtimes greater than that at the PV/Pt electrode and 13ona Pt and on a PVTi electrode in 0. 5 mol/L H2SO,times greater than that at the smooth PI electrode. Theat 1 mV/s were studied and represented in Figure 8.greater stability of PvTi electrodes over repeatedAnodic Tafel slopes of 92 mV/decade anccyeclization compared to Pv Pt and smooth Pl electrodes71 mV/decade were estimated on a Pt and PVTiis atributed to the efect of the bimetallic catalysts. Itrespectively. This indicates a facile mechanism and ais known that, oxidation of methanol on a Pi occurshigheriation on a PVTidue to the presence of oxygenated species ( Pt0 orelectro中国煤化工me peee ofTTPr0H), which help the oxidation of CO to CO2. ThewithMYHCNM H Gf CO where itmethanol oxidation reaction requires the adsorption ofdissociates on Pt-Ti alloys much easier than on a purethe methanol and O2 containing species (e.g. OH)P+{4J.352燃料化学学报第37卷at molar ratio of (8: 1) respectively at - 850 mVPr( MMS) for different time intervals and the cyclicePVTi0.09 tvoltammogram of the methanol oxidation was traced ineach case in Figure 9(a). It is found that as the timeof the deposition increase the oxidation current densityof methanol oxidation increases up to 20 min. The; 0.06cyclic votammetric behavior of Pt-Sn/Ti electrode( prepared for I5 min deposition) in 0. 5 mol/L, H2S04in absence and in presence of 2. 0 mol/L MeOH is0.03represented in Figuer 9(b). Addition of 2. 0 mol/L10methanol to the electrolyte shows the presence of anIn 1/mA cm2anodic peak at about + 600 mV due to methanolFigure 8 Anodic Tafel lines for methanol electro oxidationoxidation， the current density of which is aboutona Pr and PVTi electrode in 0.5 mol/L H2SO,364 mA/ cm'，and another reoxidation peak appears inat 1 mV/sthe reverse scan at + 36 mV ( MMS) of relatively smallIn another trial to increase the catalytic activitycurrent densily probably due to the reoxidation 0and the stability of P/Ti electrode, a small amount ofmethanol or one of intermediate product of itsin was electrodeposited with Pt. The electrode wasoxidation. The peak current density value of methanolprepared by potentiostatic deposition of Pt and Sn on Tiafer 50 cycles is 98% of the first cycle.(ab)600|夏 0450 -- 0.5 mol/L H.SO,1 15- 2.0 mol/L MeOil.... after 50 cycles 1号400Time t/min300I5020000.0.5.0.51E/ V(MMS)Figure9 (a) Efeet of changing the amount of Pt-Sn (8: 1) deposited ptentiostically at - 830 mV ( MMS) on a Ti eletrode onthe etrooxidation of methanol;(b) Cycie volammorams of Pr-Sn/Ti (8: 1) leetrodle ( prepared by polentiostatic deposionfor 15 min) in 0.5 mol/L H2S04 in absence ( the dashed line) and in presence of 2. 0 mol/L methanol(the solid line) and after 50 cyles (the doted line) al a scan rate of 50 mV/sFigure 10 shows that Ti modified with Pt and Snhas a much higher catalytic activity towards methanol120- -- 0.5 mo/L H.SO,一20 mol/L MeOHoxidation than P1-Sn/Pl ( prepared in a similar manner9... afer 50 cyclesas a P1-Sn/Ti electrode).Taking into consideraion the real surface area of60the two electrodes, it is found that the oxidation currentdensity of methanol at a Pt-Sn/Ti electrode is 2. 3.30lytimes greater than that at a P1-Sn/Pt electrode.Stabilities of both electrodes over repeated cyclizationvas improved in the presence of Sn deposits, but it is.30-0.higher in case of P-Sn/Ti electrode (Table 2), as thepoisoning effect is less. Stability here means theFigure 10 Cyelic volammograms of Pl-Sn/Pl eletrodepreservation of the catalytic activity of the electrode中国煤化工on for15 min) inover repeated cyelization.F ashed line) and inThe efet of variations in the composition of theMHC N M H Golid line) and aherbinary catalyst of the type Pt,Sn,/ Ti on the methanol50 cycles (the dotted line) at a scan rate of 50 mV/soxidation reaction in acid medium was also studied.第3期Hanaa B Hassan: Electrodeposited Pt and PI-Sn nanoparticles on Ti as anodes for diret methanol fuel cells353A 1:1, (Pt:Sn) was prepared and Pr-Sn wereoxygenated species required for the oxidationdeposited on the Ti electrode surface for various timeprocesso especially -CHO type compounds and CO tointervals. The performance of this electrode is shown in02 facilitating the methanol oxidation'33. UsingFigure 11. It is found that the oxidation current ofthernal desorption spectra ( TDS) Mehandru et almethanol increases as the time of the depositionfound that CO was much easier to be dissociated on Pt-increases up to 20 min. But methanol oxidation currentTi alloys than on pure Pt and clean Ti surfaces at roomat that electrode is less than that obtained on Pt-Sn/Titemperature, so the behavior of Pr-Sn llys should beelectrode prepared in 8:1 molar ratio Pl:Sn, so onequalitatively similar to the P-Ti alloys'3s. Also, theexpects that there is a certain ratio between the twoaddition of Sn promotes the electro-catalytic activitiesmetals that achieves the highest catalytie activity, andfor the electro-oxidations of methanol, as the variationthis ratio must contain more Pt than Sn, otherwise thof Sn content by forming PtSn alloys causes significantcatalytic activity decreasesstructural and ectronic modifications of Pterstallites, resulting in increase of lttice parameterand decrease of the Pt 5d band vacancies with Sn300 Fcontent"150号200●-。PUTi- A Pt-Sn/Ti(8:12。- * PI-Sn/Pr100 ta。600510152025Time t/minFigure 11 Oxidation peak current density of 2.0 mol/LMeOH in 0.5 mol/L H2SO, at Pt-Sn/Ti (1:1) electrode2([ prepared by potentiostatie deposition at - 850 mV ( MMS)]at diferent time inlevalsFigure 12 Chronoamperometrie data of the PV/Pr,PVTi, Pr-Sn/Pt and PI-Sn/Ti.By comparing the performance and the stabilitiesof the various prepared electrodes in Table 2, it is3 Conclusionsclear that the Pt-Sn/Ti (8: 1) electrode shows the bestThe electro-oxidation of methanol occurs on aperformance. The chronoamperometric experiment forsmooth Pt and a P/Pt electrode with relatively smallthe PV/Pt， P/Ti, Pt-Sn/Pt and Pt-Sn/Ti electrodesoxidationcurrent density and poor stability.was recorded at + 300 mV for the PVPt electrode andModification of Ti with Pt and/or PtSn (i.e. PVTi andat + 500 mV ( MMS) for the other electrodes andPl-Sn/Ti electrodes) has many advantages compared torepresented in Figure 12. It shows that, the stability ofPVPt and Pt-Sn/Pt electrodes. The combination effectPl-Sn/Ti electrodes is much higher than otherof Pr, Sn and Ti improves the catalytic activity and theelectrodes.stability of the prepared electrode through completeThe role of Sn in enhancing the catalytic oxidationoxidation of the intermediate product of methanolof methanol was attributed to its ability to adsorb theoxidation.References[1] ABDEL AAL A. HASSAN H B, ABDEL RAHIM M A, Nanostructured Ni-P-TIO2 composile coating for eltrocatalytie oxidaion of small organicmolecules[J]. J Electroanal Chem, 2008 , 619/620: 17-25.[2] ABDEL AAL A, HASSAN H B. Electrodeposited nanocomposie catings for fuel cell eplication[J]. 」Alys Comp, 2009, 477(1/2): 652-3] ABDEL RAHIM M A, HASSAN H B. Titanium and plainum modified titanium electrodes as catalysts for methanol leclcooxidation[J]. ThinSolid Films, 2009, 517(11): 3362-3369.4] TAMMEVESKI K, TENNO T, ROSENTAL A, TALONEN P, JOIANSSON L中国煤化工en on P-:TOr2 coled Tiectndes in alkal: slulin[J]. Elertrochem Soc, 1999 146(2): 669676.[5] ROJAS MI, ESPLANDIL M J, AVAILIEI. B, LEIVA E P M, MACAGINO VYHC N M H Gactions at tianiumn oxideelectrodes mdifed with plainum[ J]. Electrochim Acta, 1998, 43(12/13):6] SMOTKIN E, BARD A J, CAMPION A, F0X M A, MALLOUK T M. WEBBER s E, WHITE J M. Bipolar titanium dioxide/ platinumsemiconducor poeletrodes and muleletrode arays for unsisted photolytie waler sliting[J]. Phys Chem, 1986. 90( I9): 46044607.7] WEBER MF, DICNAM MJ, PARKS M, VENTER R D. Kinetics of oxygen reduction on spullered platinum[J]. Electrochem Soe, 1986, 133354燃料化学学报第37卷(4): 734-738.8] CIIO1Y K, SsEOSS, CIUIO K H, CHO1 Q w, PARK s M. Thin liunium dioxide flm cectode pepared by thermal dooptio[J].nlectvechem Soe, 1992, 139(6): 1803-1807.[9] AVALLE: I. SANTOS E, LEIVA K PM. MACACNO v A. hacdceriztion of Tio2 flms molied by plaium doping[J]. Thin Solid Flms,1992, 219(1/2): 7-17.[10] AVAIJE L. SANTOS E, MACACNO V A. ETR on TIO2 films modifed by Pr doping[J]. Elertnochim Acta, 1994, 39(8/9): 1291-1295.[川] TAMMEVESKI K, ARULEPP M, TENNO T, FERRATER C, CLARET J Oxygen ecrordctio on liunium spponted thin Pr fime inalkaline slution[J. Fletrochim Acta, 1997, 42( 19): 2961-2967.[12] SCIMICKI.ER w, STIMMING u. Redox ractions at tianium letrode covered with doped pasive films[ J]. Thin Solid Films, 1981, 75(4):331-340.[13] MENTUS V s. Eectrohermial response of a composite P/TiO2 layer formed peonidoamially on tianium surfaces[ J]. letrchim Aelta,2005 , 50( 18): 3609 -3615.[14] KOKKINIDIS G, PAPOUTSIS A, STOYCIIEV D, MILCHEV A. Eectroles depositin of Pr on Ti calytie activity for the hyrogen erolutionreacin[小. J Eletranal Chem, 2000 486(1): 48-5.[15] YUE H, SCOTT K, Diret methanol alaline fuel cell with calyed metal mesh anodes[ J]. Eletrochem Comun, 2004, 6(4): 361-365.[16] MUSIANI M, FURLANELTO F, BERTANCELLO R. Eleendeposied PbO2 + Ru02 : A composite anode for oaxyen evolution from suphurieeacid solution[J]. J Electroanal Chem, 1999, 465(2); 160-167.[17] FREITAS R C, SANTOS M C, OLIVEIRA R TS, BUI.HOFS LO s, PEREIRA E C. Methanol and chanol ecroidation using PI etodesprepared ly the polymerie precursor mehodf J]. Power Sources, 2006, 158(1): 164-168.[18] LAIL B, CHEN D-H. HUANG TC. Preparation and chreterzation of Tspported nanosnoctured P eletndles by letroporerie depoition[小. Mater Res Bull, 2001 , 36(5/6) : 1049-1055.[19] LAIL B, CHEN D-H, HUANG T-C. Preparaion and lecerocatalytie acivity of P/TI nanostuctured eletrodes[J]. Mater Chem, 200, 11(5): 1491-1494.[20] RASKO J, KECSKES T, KISS J. Foraleyde frmation in the iteractio of HCOOH with P sppoted on TiO2[J]. JCatal, 2004, 224(2):261 268.[21] PARK K.W, HIAN S-B, 1E. J-M. Photo ( Uv )-enhanced perormance of P-T02 nostrueture letrde for methanol oridation [J].Electrochem Commun, 200, 9(7): 1578-1581.[22] SONC H, QIU x, IF, zHU w, CIIEN L. Ehanol eleto oxidation on catalysls with TiO2 cated carbon nanotubes us spor[J].Elertrechem Commun, 2007, 9(6): 1416-1421.[23] KIMJII, CHOILSM, NAMSH, SEO M H, CHOIS H, KIM W B. Influence of Sn content on PSn/C calalysts for lectroidaion of CiCjalerhols: Synthesis, chararerizaion, and elcrocatalytie aetivity[J]. Appl Catal B, 2008, 82( 1/2): 89-102.[24] ZHIENG l, XIONC L, SUNJ, U」, YANG s, XIA J. Capping ugent free synthesis of PSn bnmalie naopartiele with enhancedelectrocatalytic activily and lifetime over methanol oxidution[ J]. Catal Commun, 2008, 9(5): 624-629.[25] JIANG l., SUN C, ZII0U z, ZHOU w. XIN Q. Preparation and characerization of PISn/C anode eroeatalysts for direet ethanol fuel ell(J].Catal Today .2004, 93-95: 665-670.[26] POURNCHI-AZAR M H, HABIBI A B. Preparaion of a platinumlayer-modifed aluminum electrode by electrochemiceal and elecrolesscementations and is use for the ectroxidation of methanol[J]. J Elertoanal Chem, 2005 , 580(1): 23-34.[27] CULLITY B D. Elements of X-ray dffaction[l M].2nd ed. London: Addison Wesley Publishing, 1978.[28] ABDEL. RAHIM M A, IASSANS H B, KHALIL M w. Platinum tin llay etrodes for dret methanol fuel ells[J]J. Appl Eectrocem, 20030: 151-11555[29] MORAILON E, CASES JF, VA7QUEZJ L, ALDAZ A. Ireresible adoption of methanol on P(110) in carbonale slution[J]. ElenchimActa, 1992, 37( 10): 1883.1886.[30] BACOTSKY vs, ASSIEV YU B, KIIAZOVA 0 A. Cenerlied scheme of ceminpion, ecetridaio and lectredution of simpleorganir compounds on platinum group metals[J]. Electroanal (Chrm, 1977. 81(2): 229-238.[31] VASSILIEV Y B, BAGOTZKY V s, 0OSETROVA V, MIKHAILOVA A A. The mechanism of tin promoted letnecemical oidation of orgniesulstanres on platinum[J小J Eletroanal Chem, 1979, 97(1): 63-76.[32] SIIBATA M, MOTOO s. Eletroealysis by ad-atoms: Part Xx. Rate-delermining step in methanol oridation enhanced by oyenadortinguduloms[ J]. J Elertmanal Chem, 1986. 209(1): 151-158.[33] HIM.NETT A, KENNEDY BJ. Bintalie carbon sported anodes for the diret methanl-air fuel ell[J]. Elctrochim Actu, 1988, 3(11):;1613-1618.[34] GASTEIGER H A, MARKOVIC MN. ROSS P N. Sincturul efete in eceotatalysis cecnoxidationo of carbon monoxide on PgSn single eytalalloy surfaces[J]. Catal Lett, 1996, 36(1/2): 18.[35] MEHANDRU s P, ANDRESSON A B. ROSS P N. co usoption on 111) and (10) suface of the P3Ti aloy: Evidence for pallel bindingand strong arivation of CO[J J Catal, 1986, 100(1): 210-218.[36] JIANG L, ZANG H, SUN C, XIN Q. Inluence of preparation method on the performance of PISn/C anode letroatalyt for diret ethanol fuelells[J. Chin J Catal, 2006, 27(1); 15-19.中国煤化工MYHCNMHG