Pt/onion-like fullerenes as catalyst for direct methanol fuel cell

RARE METALS .Vol. 25 ,Spec. Issue , Oct 2006 ,p. 305Pt/ onion-like fullerenes as catalyst for direct methanol fuel cellGUO Jumjie2) ,YANG Xiaowei'2) , YAO Yanlit 2) ,WANG Xiaomin' 2) ,LIU Xuguang) ,and XU Bingshe' 2)1 ) College of Materials Science and Engineering , Taiyuan University of Technology ,Taiyuan 0300242 ) Key Laboratory of Interface Science and Engineering in Advanced Materials , Ministry of Education ,Taiyuan University of Technolo-gy ,Taiyuan 030024 , China( Received 2006-06-25 )Abstract : Onion-like fullerenes synthesized by are discharge in water were used as support of Pt nanoparticles as electro-catalytic materials for direct methanol fuel cell. Uniform platinum nanoparticles with the average diameter of about 4.3 nmwere well dispersed on the surface of onion-like fullerenes by impregnation-reduction method. The morphologies and micro-structures of the as-prepared composites were studied by means of XRD and TEM. Electrochemical analysis shows that thiskind of nano material may be an excellent candidate to be used as the support of catalyst for methanol electrochemical oxi-dation.Key words : DMFC iarc discharge ; onion-like fullerenes ; electrochemical properties[ This work was financially supported by National Basic Research Program of China ( No. 2004CB217808 ) ,National .Natural Science Foundation of China ( No. 20471041 ) , Key Project of National Natural Science Foundation of Chi-na( No. 90306014 ) , Natural Science Foundation of Shanxi Province ( No. 20051018 ) and Shanxi Research Fundfor Returned Scholars ( No. 200428 200523 ). ]that Pt , Ru and PtRu deposited on CNTs have better1. Introductionperformance than other carbon-supported catalyst[ 9-Noble metal nanoparticles , such as Pt and Ru，10 ]are unique materials and have a broad application asRecently , the appearance of novel carbon materi-electrocatalysts in the direct methanol fuel cell ( DM-als provides new choices of carbon supports[ 10 ]. YetFC [ 1-3 ] To improve the performance of the directthe synthesis of Pt nanoparticles with uniform size andmethanol fuel cell( DMFC ) , intense efforts have beengood dispersion over the carbon supports as an electro-devoted towards the development of the electrocatalystscatalytic materials remains to be a challenging work.[4 ] It has been shown that nanometer-sized Pt parti-Onion-like fullerenes( OLFs )[ 11-12 ] have atcles with a high density of active sites usually exhibittracted great attention from both a fundamental and anfavorable catalytic properties. In addition to catalystapplied point of view since their discovery[ 13 ]preparation , the choice of a suitable carbon support isIn this paper , OLFs prepared by arc discharge ina factor that may affect the performance of supportedwate中国煤化Isupport of Pt nanoparti-catalysts. It has been proved that the structure of thecl:IYHCN M H Gpaticles were preparedcarbon support[ 5-8 ] can influence the structure of theby the method of impregnation reduction with formal-catalyst layer and , as a result , the electrochemical .dehyde as reducing agent. The morphologies and mi-properties of the catalyst. For instance , it was found .crostructure of Pt/ OLFs composite nanoparticles wereCorresponding aJ BingsheE-mail : xubs@ public. ty. sx. cn306RARE METALS , Vol. 25 ,Spec. Issue , Oct 2006observed on a high-resolution transmission electron mi-High-resolution transmission electron microscopycroscope( HRTEM ) and X-ray diffraction( XRD ).( HRTEM ) images were obtained on a JEOL JEM-The object of the present work was to study the proba-2010. X-ray diffraction ( XRD ) measurements werebility of PvVOLFs as the catalyst of DMFC.carried out on a D/ max-3C X-ray diffractometer usinga Cu Ka source operating at 30 kV and 200 mA to2. Experimentalcharacterize the structure of the Pt/OLFs.2.1. Synthesis and characterization of Pt/OLFs .2.2. Preparation and characterization of elec-catalyststrodesHigh-quality OLFs were synthesized by arc dis-Electrochemical experiments of the as-preparedcharge in water. Our apparatus consisted of two graph-20wt. % Pv/C catalysts were carried out on an electro-ite electrodes submerged to a depth of 8 cm below wa-chemical interface ( Autolab PGSTAT302 ). A stand-ter surface in a glass container. The arc current andard three-electrode cell was used with saturated calo-voltage could be altered between 50 A and 22-28 V ,respectively. The synthesis details of OLFs may bemel electrode ( SCE ) as the reference electrode andplatinum foil as the counter electrode. Working elec-found elsewhere[ 14 ] For the better anchoring of thetrode was made of a paste on a glassy carbon platePt nanoparticles , as-produced OLFs were oxidized inwith a diameter of4 mm , which was mixed with a so-concentrated HNO, for4 h.lution of perfluorosulfonic acid( 5wt. % , Nafion , DuA typical impregnation-reduction method was em-Pont )( Acros Inc. ) and electrocatalyst. The Pt load-ployed to prepare OLFs- supported Pt catalyst withing on the electrodes was ca. 0.12 mg° cm-All theformaldehyde as reducing agent. For synthesizing Pv/OLFs with the Pt loading of 20wt. % ,a 0. 060 g ofpotentials in this study are reported with respect tcSCE. The electrolyte solution was 2. 0 mol. IOLFs were uniformly dispersed in 2.1 ml of an aque-CH20H/1.0 mol. L-1 H2SO4 , which was preparedous solution of H2PtCl。( 7.4 g° L-' ) by ultrasound.from high-purity sulfuric , methanol and distilled wa-Then 20 ml of the formaldehyde was dropped slowlyter.into the H2PtCl。solution at 333 K and0.8 ml of H2O2( 30v/o ) was added to stabilize the Pt particles undercontinuous stirring for 5 h. The solid product was3. Results and discussionrinsed with deionized water repeatedly and filtered.3.1. Morphology and structure of PV/OLFs cata-Finally , the product was dried at 343 K for 12 h in alystsvacum oven. The final P/OLFs catalyst with a metalFig.1 shows TEM images of synthesizedloading of 20wt. % was obtained.Pt / OLFs catalysts ，It can be found that the(田)，(b中国煤化工fHCNMHG50 nm10 nmFig.1. TEM images of Pt/OLFs at low( a ) and high ( b ) magnification.Guo J.J. et al. , Pt/ onion-like fullerenes as catalyst for direct methanol fuel cell307spherical platinum particles are uniform in size and .long-term stability of Pt/OLFs electrode was evaluatednearly monodispersed on the surface of OLFs. Fig. 1by cyclic voltammetry in 1 mol. L 1 H2SO。 + 2 mol.( b ) shows a high magnification image of Pv/ OLFs cat-L-1 CH,OH solution. The corresponding results arealysts , in which concentric graphitic layers of the par-presented in Fig.4. In Fig. 4 ,the peak current densi-ticle are resolved clearly , related to the so-called on-ty of the forward scan decreases gradually with the in-ion-like fullerenes.crease of cycle number. When the cyclic number isThe powder XRD pattern of Pv/OLFs catalysts is .500 , 65% loss of the electrocatalytic activity of the e-shown in Fig.2. The acute peak at about 26° is corre-lectrode can be observed. This may result from threesponding to diffraction of graphitic OLFs for supportingreasons : accumulation of poisonous specious ( such asmetals. The synthesized Pt nanoparticles supported on( CO )ads ) on the surface of the Pt particles , metha-OLFs forms a face-centered cubic( f. c. c. ) structureand the peaks at ca.39. 7° ,46. 2° and 67. 6° belongol consumption during the successive scans andto Pt( 111 ),( 200 ) and ( 220 ) , respectively. Thechange of the surface structure of the Pt particlesmean size of Pt particles was estimated to be 4. 3 nm .[ 15]by the Scherrer equation.It can be concluded from the results above thatOLFs may be an excellent candidate to be used as the3.2. Electrochemical characterization of Pt/ OLFssupport of catalyst for DMFC. Theelectrodes14FFig. 3 shows the cyclic voltammograms of the12methanol electrooxidation over the PtVOLFs catalyst ,10in the electrolyte of 2. 0 mol. L-1 CH3OH and 1.0mol. L-' H2SO4 at room temperature. The scanningrate used here is 50 mV. s-'. The voltammetric fea-tures are in good agreement with most published works[7 ,9] The curent peak at about 0.7 V versus SCE0.4in the forward scan is attributed to methanol electrooxi-E/V (vs. SCE)dation on the catalysts. In the backward scan , the re-Fig.3. Cyclic voltammogram curve of Pt/OLFs electrodesoxidation of methanol is clearly observed due to the re-in 1.0 mol. L1 H,SO。 +2.0 mol. L -1 CH, OH solutionsduction of oxide of platinum.at room temperature at scan rate of 50 mV，s -1In the practical opinion , the long-term stabilty of20-electrocatalysts is very important. The8-614-包12-10-中国煤化工MHCNMHG400 500 600jr umber2050 67890Fig. 4. Long-term stability of Pt/OLFs electrode in 1. 020(°)mol. L- H,SO, +2.0 mol: L-1 CH, OH aqueous solutionsFig. 2.、XRD patterns of Pt/OLFs catalyst.at scan rate of 50 mV. s-' .308RARE METALS , Vol.25 ,Spec. 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