Microporous and Mesoporous Materials 134 (2010) 1–7

Contents lists available at ScienceDirect

Microporous and Mesoporous Materials

journal homepage: www.elsevier .com/locate /micromeso

Synthesis of nano-sized Pt/C via zeolite-templating method and its applicationto the cathode catalyst in PEMFC

J.Y. Lee a, Y.H. Yun a, S.W. Park a, S.D. Kim a, S.C. Yi b, W.J. Kim a,*

a Department of Materials Chemistry and Engineering, College of Engineering, Konkuk University, 1-Hwa yang dong, Kwang Jin Gu, Seoul 143-701, Republic of Koreab Department of Chemical Engineering, College of Engineering, Han Yang University, 17-Haeng dang dong, Seong dong gu, Seoul 133-791, Republic of Korea

a r t i c l e i n f o

Article history:Received 15 January 2010Received in revised form 12 April 2010Accepted 25 April 2010Available online 29 April 2010

Keywords:Zeolite templatingRamping rateDecompositionAgglomerationCell performance

1387-1811/$ - see front matter � 2010 Elsevier Inc. Adoi:10.1016/j.micromeso.2010.04.022

* Corresponding author. Tel.: +82 2 450 3502; fax:E-mail address: whajungk@konkuk.ac.kr (W.J. Kim

a b s t r a c t

Well-dispersed nano-sized Pt/C with less agglomeration was successfully synthesized via zeolite-tem-plating method. Depending on the ramping rate such as 0.1 �C/min, 0.2 �C/min and 2.0 �C/min for thedecomposition of PtðNH3Þþ4 within zeolite pore channel, the degree of agglomeration of Pt particleswas significantly affected. The Pt content of various nano-sized Pt/C synthesized via zeolite-templatingmethod using different ramping rate is in the range of 37–49% based on Pt/C only excluding water con-tent. The TEM images clearly show that the size of Pt/C formed within zeolite pore channel is highly uni-form throughout pore channels indicating the steric effect exerted by zeolite pore channel with therestriction of agglomeration of Pt particles. For zeolite-eliminated Pt/C, however, the TEM images showthat the degree of agglomeration of Pt particles was significantly increased with the ramping rate, result-ing in the formation of larger Pt particles. The BET surface areas of Pt/C are inversely proportional to theramping rate. Finally, the results show that the MEA fabricated with Pt/C obtained at low ramping ratewould lead to much better cell performance compared to that fabricated with commercial Pt/C. Itstrongly suggests that the cathode fabricated with well-dispersed Pt particles would provide more elec-trochemical active sites, thus leading to the enhancement of cell performance.

� 2010 Elsevier Inc. All rights reserved.

1. Introduction

It is well known that the physico-chemical properties of nano-particles are quite different from that of bulk particles due to thepartially coordinated surface atoms exposed to reactants. In fuelcell applications, especially, the particle size of Pt over carbon af-fects the dispersion and thus the limited availability in electro-chemical reaction has been a significant barrier against fuel cellperformance in spite of high Pt loading [1–6]. In conventional fab-rication methods, unfortunately, inactive catalyst sites are alwayspresent in catalyst layer, which are not available for electrochem-ical reaction in fuel cell because the electrochemical reaction islimited only at the interface between the polymer electrolyte andthe Pt catalyst exposed to reactant known as three phase reactionzone [7]. Recent researches also suggest that the reduction of Ptloadings in electrocatalyst can be achieved through an enhance-ment of Pt utilization by increasing the active Pt sites, reducingthe active layer thickness (625 lm) and introducing smaller, car-bon-supported nano-sized Pt particles (<10 nm) [8–10]. Accordingto Tsuchiya and Kobayashi [11], total cost of PEMFCs is contributedby electrode up to 40% including 1.7% from Pt itself. Reducing Pt

ll rights reserved.

+82 2 447 5469.).

loading upon increasing dispersion of Pt on support through reduc-tion in Pt particle size is one of most critical factors. As an effort toreduce Pt particle size, several reports have been published. It iswell known that the reduction of PtðNH3Þ2þ4 -exchanged zeolitewith hydrogen results in very low platinum dispersion [12]. Rea-gan [13] claimed that the metal dispersion can be remarkably en-hanced by either decomposition or calcination prior to reduction.Graaf et al. [14] suggested that nano-sized Pt particles with narrowsize distribution smaller than 1 nm could be obtained under pre-cisely controlled heating rate: that is, low heating rate is preferredbecause it allows the slow desorption of water and ammonia frommicroporous zeolite in connection with the stabilization of mobilePt species by the cavity walls of zeolite. Recently, Coker et al. [15]reported that the size-controlled Pt clusters on nanostructured car-bon using zeolite as template have been successfully synthesized.They also studied the effect of zeolite types such as zeolites A, X,USY, ZSM-5 and SBA-15 and found that zeolite structure, Pt loadingand calcinations condition should have affected Pt cluster size andparticle dispersion [16]. As of now, the cell performance of the MEAfabricated with electrocatalyst using zeolite-templating methodfor PEMFC has not been reported.

In this study, the synthesis of the nano-sized Pt cluster sup-ported on carbon mesostructure using zeolite as a template is dis-cussed and the cell performance MEA fabricated with nano-sizedPt/C synthesized through zeolite Y also discussed.

20 40 60 80

0.1°C/min

0.2°C/min

Inte

nsity

2Theta

2.0°C/min

(111)

(200)(220) (311)

Fig. 1. XRD patterns of Pt/C synthesized using zeolite Y as a template at differentramping rates for decomposition of PtðNH3Þ2þ4 : (a) 0.1 �C/min, (b) 0.2 �C/min and (c)2 �C/min.

2 J.Y. Lee et al. / Microporous and Mesoporous Materials 134 (2010) 1–7

2. Experimental

2.1. Preparation of nano-sized Pt/C powder

Zeolite Y with Si/Al ratio of 2.19 was synthesized following theprocedures reported by Kim et al. [17]. For ion-exchange, 1.161 g oftetraammineplatinum(II) nitrate (50 wt.% Pt, Alfa Aesar) wasdissolved in 300 ml of deionized water for 30 min at room temper-ature and 3 g of zeolite Y was added to this solution for ion-exchange at 60 �C for 24 h under stirring. Upon completion ofion-exchange, so obtained PtðNH3Þþ2

4 —Y was washed thoroughlyusing deionized water and dried at 55 �C in vacuum oven for 4 h.PtðNH3Þþ2

4 —Y zeolite was heated up to 150 �C under 100 cc of Arflow at 5 �C of ramping rate and maintained at this temperaturefor 2 h. The sample was then decomposed by heating up to350 �C at different ramping rates of 0.1 �C/min, 0.2 �C/min and2.0 �C/min under air flow of 50 ml/min as reported in Graaf et al.[14], followed by cooling down to room temperature in air flow.The obtained Pt–zeolite Y was kept in vacuum oven at 120 �C for1 h to degas. The mixture of furfuryl alcohol (FFA, 99% Acros) andethanol with equal mass ratios was prepared and stirred for30 min. The corresponding amount of Pt–zeolite Y to the mass ratioof 1:2:2 in Pt–Y, FFA and ethanol was then added to this solutionkept in chilling ice water and maintained at room temperaturefor 1 h under vacuum. The solution was heated up to 120 �C at5 �C of ramping rate, followed by polymerization at this tempera-ture for 5 h. Pt–Y/polymeric FFA composite material was put in aquartz glass tube furnace and heated up to 400 �C at 5 �C of ramp-ing rate for 1 h under argon flow of 100 ml/min. The sample washeated up to 800 �C at ramping rate of 5 �C/min under 0.75% pro-pylene in N2 at 100 ml/min and kept at 800 �C for 2 h. Followingthe cooling to 300 �C at 4 �C/min of cooling rate under 100 ml/min of N2 flow, the sample was kept at 300 �C for another 2 h under10 % H2 in N2 flow with 100 ml/min to reduce Pt oxide forms tometallic state. Finally, the samples were cooled down under100 ml/min of N2 flow and Pt/C/zeolite Y was sonicated in HF solu-tion to dissolve zeolite part for 4 h.

2.2. Preparation of electrode using nano-sized Pt/C

Cathode was fabricated in following manner. The catalyst inkwas prepared to fabricate Pt/C electrode as follows. Pt/C synthe-sized via zeolite-templating method was first added to isopropylalcohol (IPA, 99.5%, Samchun Chemicals) as a solvent to which Naf-ion dispersion (5 wt.%, Dupont Chem. Co.) was sequentially added.To ensure the sufficient mixing, this ink was subject to 30 min ofsonication. After preparing catalyst ink, it was sprayed on commer-cial gas diffusion layer (GDL, SEAL SCCG 5N PLHOS MPL) of3 � 3 cm2 up to gain Pt loading of 0.3 mg/cm2. Anode was fabri-cated following exactly the same procedures adopted for cathodeexcept commercial Pt/C (40% Pt in C, Alfa Aesar) and Pt loadingof 0.2 mg/cm2.

Upon fabricating electrodes for both cathode and anode, then,the membrane electrode assembly (MEA) with 3 � 3 cm2 was fab-ricated as follows. Commercial Nafion 115 (Dupont) for the mem-brane of MEA was pretreated with hydrogen peroxide (5 wt.%) andthen sulfuric acid (0.5 M) boiled at 353 K for at least 1 h and kept in

Table 1Summary of elemental analysis and % ion-exchange of zeolite Y.

Sample no. Si/Al Si Al Na Pt % Ion-exchange

Zeolite Y 2.190 0.776 0.355 0.343 – –PtY0.1 2.303 0.790 0.334 0.135 0.084 60.6PtY0.2 2.437 0.785 0.321 0.131 0.084 61.8PtY2.0 2.486 0.788 0.317 0.130 0.085 62.1

DI water. Finally MEA was assembled by hot pressing under800 psig for 3 min at 135 �C.

Fig. 2. EDS spectroscopy of different Pt/C catalysts obtained after eliminatingzeolite template by HF solution: (a) 0.1 �C/min, (b) 0.2 �C/min, (c) 2 �C/min and (d)commercial Pt/C.

J.Y. Lee et al. / Microporous and Mesoporous Materials 134 (2010) 1–7 3

2.3. Characterization

The as-synthesized nano-sized Pt/C powder was characterizedusing various analytical instruments. Powder X-ray diffractionanalyses (XRD, Rigaku Model D/Max 2200) were performed usingCu Ka radiation to identify the product phase for Pt. The Si/Al ratioof zeolite Y and % ion-exchange was identified by inductivelycoupled plasma atomic emission spectrometry (ICP-AES, SpectroModular). Scanning electron micrograph (SEM, JEOL JSM 6380)and transmission electron micrograph (TEM, JEOL JEM2000EX)analyses were conducted for surface composition and particle size.Energy dispersive spectroscope (EDS) was used to confirm theresidual of Si and Al in zeolite after eliminating zeolite templatefrom PtCYs samples. Thermal analysis (Model TA2050 TA instru-ments) was conducted to confirm the Pt content in Pt/C. The BETsurface area for as-made Pt/C and Pt/C/zeolite Y was identified byN2 adsorption (Micrometrics, Tristar™ II 3020).

Cyclic voltammetry was conducted in a conventional three elec-trode electrochemical cell using a glassy carbon electrode with6 mm in diameter as a working electrode, Pt wire as a counter elec-trode and a saturated calomel electrode (SCE) as a reference elec-trode [18]. Electrochemical measurements were recorded andreported vs. normal hydrogen electrode (NHE). The glassy carbon(GC) electrode was polished with 1 lm Al2O3 slurry and washedultrasonically with deionized water before each use. The ink slurrywas prepared by mixing various Pt/C samples obtained, DI water,5 wt.% Nafion dispersion and 2-propanol. The same amount ofink slurry was dropped on the GC electrode with a micropipetteand the GC electrode was then dried in a vacuum oven.

100 200 300 400 500 600

-6

-4

-2

0

2

4

6

DTA

/K

Temperature / °C

2.0 0.1 0.2 commercial

b

100 200 300 400 500 600

40

50

60

70

80

90

100

% W

eigh

t Los

s

Temperature [ °C]

a

Fig. 3. TG curves (a) and DTA curves (b) of different PtCn synthesized at differentramping rates: (h) PtC0.1, (}) PtC0.2, (4) PtC2.0 and (q) commercial Pt/C.

3. Results and discussion

Through this study, nano-sized Pt/C was successfully synthe-sized via zeolite-templating method at various conditions. Uponcompletion of ion-exchange, Pt(NH3)4–Y was decomposed at dif-ferent ramping rate and the elemental analysis for Pt–Y was con-ducted using ICP-AES and the results are summarized in Table 1.

Pt–salt–Y zeolites were then decomposed to eliminate ammo-nia complex up to 350 �C at different ramping rates such as0.1 �C/min, 0.2 �C/min and 2 �C/min, respectively. The XRD analysisfor so-obtained samples was conducted and shown in Fig. 1.

As can be seen in Fig. 1, four characteristic peaks indexed on(1 1 1), (2 0 0), (2 2 0) and (3 1 1) are clearly seen, indicating suc-cessful formation of Pt particles on carbon through zeolite-tem-plating method.

In order to confirm if zeolite was completely eliminated, the en-ergy dispersive spectroscope (EDS) analysis was conducted andshown in Fig. 2. As shown in Fig. 2, no Si or Al was detected, indi-cating complete elimination of zeolite residual.

Fig. 4. TEM images of various PtCYn synthesized via template method at differentramping rates for decomposition of PtðNH3Þ2þ4 : (a) PtCY0.1, (b) PtCY0.2 and (c)PtCY2.0.

4 J.Y. Lee et al. / Microporous and Mesoporous Materials 134 (2010) 1–7

After eliminating zeolite by dissolving in HF solution, TG/DTAanalysis was conducted to measure the Pt content and shown inFig. 3. It is interesting to notice that a slight weight loss starts at300 �C followed by a majority of weight loss at highest tempera-ture of about 412 �C for the sample decomposed at a ramping rateof 0.1 �C/min. This result suggests that the oxidation of carbonstacked around well-dispersed small Pt particles has occurred earlycompared to other cases due to easier access of oxygen to thosecarbon particles for the oxidation. The TG curves for the rampingrate of 0.2 �C/min shows the rapid weight loss at 380 �C and410 �C, respectively. This stepwise weight loss at lower tempera-ture might be attributed to the rapid oxidation of carbon surround-ing less agglomerated Pt particles due to easy access of oxygen tothem while the weight loss at higher temperature corresponds tothe oxidation of carbon particles inside the agglomerates. On theother hand, commercial Pt/C shows the oxidation of carbon at420 �C and 432 �C, respectively. The oxidation at higher tempera-ture suggests higher agglomeration of Pt particles which makesthe access of oxygen to carbon difficult. As seen in this figure, thePt contents of various Pt/C samples obtained at different rampingrates of 0.1 �C/min, 0.2 �C/min and 2 �C/min for the decompositionof PtðNH3Þ2þ4 (hereinafter, PtCn, n indicates ramping rate) wasdetermined to be 49.0%, 37.0% and 48.7%, respectively, while thatof commercial Pt/C is 40%, based on Pt/C only excluding watercontent.

In order to manifest the effect of ramping rate on the Pt disper-sion over carbon, TEM was taken for both Pt/C/Ys and Pt/Cs beforeand after eliminating zeolite by dissolving zeolite Y in HF solutionand shown in Figs. 4 and 5, respectively. As can be seen in Fig. 4, Pt/Cs existing within zeolite Y (hereinafter, PtCYn, Pt/C in zeolite Yand n indicates ramping rate) obtained at different ramping ratefor decomposition of ion-exchanged PtðNH3Þ2þ4 within the porechannels of zeolite Y do not exhibit any significant difference in

Fig. 5. TEM images of various PtCn after eliminating zeolite Y in HF solution synthesized vPtC0.1, (b) PtC0.2, (c) PtC2.0 and (d) commercial.

particle size and distribution. It is noticeable in Fig. 4(c), however,that a few larger agglomerated particles indicated by arrows havebeen formed for PtC2.0 although the particle size of most of Pt par-ticles within zeolite channel seems highly uniform throughoutpore channels regardless of ramping rate. It strongly indicates thatthe steric effect exerted by the pore channel of zeolite Y shouldhave restricted the agglomeration of Pt cluster. On the other hand,upon eliminating zeolite Y by dissolution in HF solution, it moreclearly shows a significant effect of ramping rate on particle sizeand dispersion of Pt cluster as seen in Fig. 5. PtC0.1 in Fig. 5(a)shows the best dispersion comprising �3 nm of Pt particles whilePtC2.0 in Fig. 5(c) shows significant agglomeration. According toGraaf et al. [14], too fast ramping rate would lead to the incompleteoxidation of ammonia, resulting in less well dispersed platinumthrough autoreduction of the Pt precursor. Another reason for poordispersion of Pt particles is due to the presence of water vapor inthe pores of zeolite which will coordinate to the Pt cations andframework oxygen. It enhances the mobility of cations in zeolite,thus leading to higher degree of agglomeration and thus poor dis-persion. It is consistent with TG curve where the weight loss due towater shows the largest for PtC2.0.

The particle size and size distribution was determined by col-lecting the data from 200 particles based on TEM and shown inFig. 6. It is seen that the average particle size increases with ramp-ing rate for the decomposition of PtðNH3Þ2þ4 after ion-exchangewithin zeolite Y.

The BET surface area and pore size distribution of differentPtCYn were measured from N2 adsorption isotherm and shown inFigs. 7 and 8, and summarized in Table 2. For PtCYn at differentramping rate for the decomposition of PtðNH3Þ2þ4 , Fig. 7 showsthe hysteresis, indicating the characteristics of carbon mesopore.It is interesting to notice that the PtCY0.1 shows the least hystere-sis curve. It is attributed to the less agglomeration due to the low-

ia templating method at different ramping rates for decomposition of PtðNH3Þ2þ4 : (a)

05

101520253035404550556065

(C) Ave.Size= 2.744 nm

Freq

uenc

y

Particle size (nm)

05

10152025303540455055606570

(A) Ave.Size=2.243 nmFr

eque

ncy

Particle size (nm)

05

101520253035404550556065

(B) Ave.Size=2.32 nm

Freq

uenc

y

Particle size (nm)

0 1 2 53 4 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 805

101520253035404550556065

(D) Ave.Size= 3.43 nm

Freq

uenc

y

Particle size (nm)

Fig. 6. Particle size distribution of various PtC samples obtained at different ramping rate for the decomposition of PtðNH3Þ2þ4 : (a) 0.1 �C/min,(b) 0.2 �C/min, (c) 2.0 �C/min and(d) commercial.

0.0 0.2 0.4 0.6 0.8 1.040

60

80

100

120

140

Qua

ntity

Ads

orbe

d (c

m3/g

STP

)

Relative Pressure (P/Po)

Fig. 7. N2 adsorption isotherms of different PtCYn measured at 77 K: (j, h)PtCY0.1, (�, }) PtCY0.2 and (N, 4) PtCY2.0 where filled symbol representsadsorption and open symbol, desorption, respectively.

2 4 6 8 100.00

0.02

0.04

0.06

Pore

Vol

ume

(cm

3 /g)

Pore Diameter (nm)

Fig. 8. BJH Pore size distribution of different PtCYn: (j) PtCY0.1 and (�) PtCY0.2and (N) PtCY2.0, respectively.

J.Y. Lee et al. / Microporous and Mesoporous Materials 134 (2010) 1–7 5

est ramping rate, indicating more regular pore structure made bysmaller Pt particles. It is clearly seen in Fig. 8 that the pore size dis-tribution of PtCY2.0 is broader with significant population of largepores than other two cases while PtCY0.1 shows the lowestpopulation of large pores. It was reported that the formation ofmicropores around 1.2 nm and 1.5 nm may be attributed to thecarbonization of furfuryl alcohol during which the emission of

small gaseous molecules such as CO2, H2 and H2O has led to thegeneration of a large number of micropores [19,20]. In addition,there are two other reasons to form the pores of which pore sizeis determined by heating rate. As mentioned previously [14], theincomplete oxidation of ammonia due to rapid heating would leadto poor dispersed platinum through autoreduction of the Pt precur-sor. Another reason due to the presence of water vapor in the poresof zeolite would also lead to poor dispersion because it coordinates

Table 2Summary of physical properties for various samples.

Sample no. BET surfacearea (m2)

BJH pore diameter(nm)

Micropore volume(cm3)

PtCY0.1 218 2.95 0.066PtCY0.2 230 3.19 0.065PtCY2.0 263 4.23 0.077PtC0.1 527 5.03 0.181PtC0.2 460 5.30 0.101PtC2.0 268 5.74 0.046Commercial 151 9.01 0.016

0 2 4 6 8 10 12 140.00

0.02

0.04

0.06

0.08

Pore

Vol

ume

(cm

3 /g)

Pore Diameter (nm)

Fig. 10. BJH pore size distribution of different PtC: (h) PtC0.1 and (�) PtC0.2, (4)PtC2.0 and (I) commercial, respectively.

6 J.Y. Lee et al. / Microporous and Mesoporous Materials 134 (2010) 1–7

to the Pt cations and framework oxygen. It enhances the mobilityof cations in zeolite, thus leading to higher degree of agglomerationand thus poor dispersion. Fig. 8 clearly shows that as the rampingrate was decreased, the population of pore with 15–20 nm was in-creased. The pore size definitely depends on the formation of car-bon micropores and mesopores because it is directly related to thedegree of infiltration of carbon precursor. As the zeolite pore chan-nels are filled with carbon precursor, the pore channels or cages arethen formed after the removal of the zeolite framework [21].Therefore, the resulting BET surface area is determined, dependingon the degree of infiltration of carbon precursor.

In Fig. 8, the BET surface area of these three solid samples are inthe order of PtCY2.0 > PtCY0.2 > PtCY0.1, strongly suggesting thatthe formation of small Pt particles within zeolite Y pore channelsshould have restricted the accessibility of N2 molecules to adsorp-tion sites.

N2 adsorption experiment was also conducted for the obtainedsolid PtC samples and shown in Fig. 9. Unlike previous case, theBET surface areas of various PtCn are in the order of PtC0.1 >PtC0.2 > PtC2.0 > commercial Pt/C with 527 m2/g, 460 m2/g,268 m2/g and 151 m2/g, respectively. The pore size and pore vol-ume of these samples is summarized in Table 2. It is seen in Table2 that the average pore size of PtCn samples is in the order of com-mercial Pt/C > PtC2.0 > PtC0.2 > PtC0.1, indicating the smallest Ptparticle size of PtC0.1 with less agglomeration. As seen in Fig. 10,the commercial Pt/C possesses the least population of small pore.BET surface area by N2 adsorption directly depends on the adsorb-able sites for N2. In case of PtCY, the pore diameter (2.95–4.23 nm)is smaller than of Pt/C (5.03–5.74 nm) and the resulting microporevolume of PtCY increases from 0.066 cm3 to 0.73 cm3 while that ofPtCs decreases from 0.181 cm3 to 0.046 cm3. The decrease ofmicropore volume leads to the decrease in adsorbable site and thusBET surface area.

0.0 0.2 0.4 0.6 0.8 1.00

40

80

120

160

200

240

Qua

ntity

Ads

orbe

d (c

m3

/g S

TP)

Relative Pressure (P/Po)

Fig. 9. N2 adsorption isotherms of different Pt/C/Z measured at 77 K: (j, h) PtC0.1and (�, }) PtC0.2 and (N, 4) PtC2.0 where filled symbol represents adsorption andopen symbol, desorption, respectively.

Using those samples, the MEAs were fabricated following theprocedures mentioned in experimental section. In order to investi-gate the effect of ramping rate on cell performance, various PtCnobtained at different ramping rates were incorporated into cathodeelectrode at the fixed total Pt loading of 0.3 mg/cm2. MEAs werethen assembled with cathodes made by PtCn obtained with zeoliteas a template for cathode, commercial electrode for anode at totalPt loading of 0.2 g/cm2 and Nafion 115. As can be seen in Fig. 11, itclearly shows that the cell performances of MEAs assembled withcathodes made by PtCn obtained from zeolite template methodare much better than of commercial Pt/C-containing MEA. As seenin Fig. 11, the MEAs assembled with cathodes using PtC2.0, PtC0.1and PtC0.2 were enhanced in cell performance by about 100%,280% and 320% at 0.6 V with 200 mA, 380 mA and 420 mA of cur-rent density compared to about 100 mA for that of commercial Pt/Cunder the conditions of 80 �C and 1 atm using H2/O2, respectively.It is believed that the cathode fabricated with well-dispersed Ptparticles with less agglomeration would provide more electro-chemical active sites, thus leading to the enhancement of cell per-formance. This result strongly indicates that the effect of rampingrate for the decomposition of Pt(NH3)4 on the cell performance isdistinct. The MEA fabricated with electrodes using PtC obtainedat lower than or equal to 0.2 �C/min shows the much better masstransfer at high current density. It is attributed to the less agglom-eration of Pt particles as shown in Fig. 5, thus leading to better

0 200 400 600 800 1000 12000.0

0.2

0.4

0.6

0.8

1.0

Current Density(mA/cm2)

Po

ten

tial

(V)

0

50

100

150

200

250

300

350

Po

wer D

ensity(m

W/cm

2)

Fig. 11. Cell performance of various MEAs fabricated with different PtCs: (j, h)PtC0.1, (�, }) PtC0.2, (N, 4) PtC2.0 and (I, .) commercial, respectively.

0.0 0.2 0.4 0.6 0.8 1.0 1.2-4.0x10-4

-3.0x10-4

-2.0x10-4

-1.0x10-4

0.0

1.0x10-4

2.0x10-4

3.0x10-4

Cu

rren

t/A

Potential/V

Fig. 12. Cyclic voltammograms of different Pt/C synthesized from zeolite-templat-ing method obtained in 0.5 M H2SO4 with scan rate of 20 mV s�1: (}) 0.1 �C/min,(j) 0.2 �C/min, (N) 2.0 �C/min and (.) commercial Pt/C.

J.Y. Lee et al. / Microporous and Mesoporous Materials 134 (2010) 1–7 7

mass transfer while the mass transfer resistance was increased forthe case of 2.0 �C/min. It is concluded, therefore, that the optimumramping rate for the decomposition of PtðNH3Þþ4 should be requiredto provide well-dispersed nano-sized Pt particles on carbon havinga larger portion of small pores with restricted agglomeration, final-ly leading to the enhanced cell performance.

Cyclic voltammetry was applied to measure the electrochemicalactive surface area (ECSA) of various Pt/C catalysts synthesized viazeolite-templating method and the results are shown in Fig. 12. Asseen in Fig. 12, the peaks at 0–0.3 V represents the hydrogendesorption and the double layer region at 0.3–0.8 V which corre-sponds to the region free of adsorbed species represents the char-acteristic of the carbon support [21]. Electrochemical active surfacearea was calculated by the following equation. The electrochemicalactive surface areas for Pt/Cs obtained at different ramping rate of0.1 �C/min, 0.2 �C/min, 2.0 �C/min and commercial Pt/C are23.5 m2/g, 28.1 m2/g, 15.9 m2/g and 13.8 m2/g, respectively. It isseen that the cell performance is highly consistent with ECSA.The results suggest that the ramping rate should have affectedthe dispersity of Pt particles, enhancing the cell performance.

ECSA ðm2Pt=QPtÞ ¼

Charge ðQ H C=m2Þ210 ðlC=m2

PtÞ � Pt wt: ðgPt=m2Þ

4. Conclusions

Several conclusions have been drawn through this study as fol-lows. First of all, the results show that the BET surface area ofPtCYn before eliminating zeolite Y was increased with the rampingrate due to higher agglomeration. It is attributed to the fact that asthe PtðNH3Þþ4 is decomposed at higher ramping rate such as 2.0 �C/

min, it would not to allow sufficient time to reduce: that is, leadingto easier access of N2 to adsorbable sites due to more loose stackingof larger Pt particles within the pore channels of zeolite Y. On theother hand, low ramping rate such as 0.1 �C/min should allow suf-ficient time to reduce for PtðNH3Þþ4 and thus leading to low BET sur-face area.

When eliminating zeolite Y through the dissolution in HF solu-tion, the Pt particles with incomplete decomposition of NHþ4 athigher ramping rate would lead to further growth of Pt particles,finally resulting in lower BET surface area. The TEM images clearlysupport the significant agglomeration of Pt particles as the ramp-ing rate for the decomposition of PtðNH3Þþ4 is increased.

Finally, the results show that the MEA fabricated with PtCn ob-tained at low ramping rate would lead to much better cell perfor-mance than of the MEA fabricated with commercial Pt/C. It isattributed to more electrochemical active sites provided by well-dispersed Pt particles with less agglomeration. It is concluded thatthe optimum ramping rate for the decomposition of PtðNH3Þþ4should be critical with regard to cell performance.

Acknowledgement

This research was supported by Basic Science Research Programthrough the National Research Foundation of Korea (NRF) fundedby the Ministry of Education, Science and Technology (Grant Num-ber 2009-0083705).

References

[1] S. Lister, G. McLean, J. Power Sources 130 (2004) 61–76.[2] G.J.K. Acres, J.C. Frost, G.A. Hards, R.J. Potter, T.R. Ralph, D. Thompsett, G.T.

Burstein, G.J. Hutchings, Catal. Today 38 (1997) 393–400.[3] M.S. Wilson, S. Gottesfeld, J. Appl. Electrochem. 22 (1992) 1–7.[4] C.H. Hsu, C.C. Wan, J. Power Sources 115 (2003) 268–273.[5] G. Sasikumar, M. Raja, S. Parthasarathy, Electrochim. Acta 40 (1995) 285–290.[6] G. Sasikumar, J.W. Ihm, H. Ryu, J. Power Sources 132 (2004) 11–17.[7] A. Loselevich, A.A. Kornyshev, W. Lehnert, Solid State Ionics 124 (1999) 221–

237.[8] K.L. Huang, Y.C. Lai, C.H. Tsai, J. Power Sources 156 (2006) 224–231.[9] S. Gamburzev, A.J. Appleby, J. Power Sources 107 (2002) 5–12.

[10] S. Mukerjee, S. Srinivasan, A.J. Appleby, Electrochim. Acta 40 (1995) 285–290.[11] H. Tsuchiya, O. Kobayashi, Int. J. Hydrogen Energy 29 (2004) 985–990.[12] R.A. Dalla Betta, M. Boudart, in: J.W. Hightower (Ed.), Proceedings, Fifth

International Congress on Catalysis, Palm Beach 1972, North Holland,Amsterdam, 1973, p. 96.

[13] W.J. Reagan, J. Catal. 69 (1981) 89–90.[14] J. de Graaf, A.J. van Dillen, K.P. de Jong, D.C. Koningsberger, J. Catal. 203 (2001)

307–321.[15] E.N. Coker, W.A. Steen, J.E. Miller, Micropor. Mesopor. Mater. 101 (2007) 440–

444.[16] E.N. Coker, W.A. Steen, J.E. Miller, Micropor. Mesopor. Mater. 104 (2007) 236–

247.[17] Y.C. Kim, J.Y. Jeong, J.Y. Hwang, S.D. Kim, W.J. Kim, J. Porous Mater. 16 (2009)

299–306.[18] K.S. Lee, H.Y. Park, Y.H. Cho, I.S. Park, S.J. Yoo, Y.E. Sung, J. Power Sources 195

(2010) 1031–1037.[19] S.A. Johnson, E.S. Brigham, P.J. Olliver, T.E. Mallouk, Chem. Mater. 9 (1997)

2448–2458.[20] E. Fitzer, W. Schafer, Carbon 32 (1970) 353–364.[21] S. Vengatesan, H.J. Kim, S.K. Kim, I.H. Oh, S.Y. Lee, E.A. Cho, H.Y. Ha, T.H. Lim,

Electrochim. Acta 54 (2008) 856–861.