A Highly Stable Catalyst for PEM Fuel Cell Based on Durable Titanium Diboride Support and Polymer...

This article appeared in a journal published by Elsevier. The attached

copy is furnished to the author for internal non-commercial research

and education use, including for instruction at the authors institution

and sharing with colleagues.

Other uses, including reproduction and distribution, or selling or

licensing copies, or posting to personal, institutional or third party

websites are prohibited.

In most cases authors are permitted to post their version of the

article (e.g. in Word or Tex form) to their personal website or

institutional repository. Authors requiring further information

regarding Elsevier’s archiving and manuscript policies are

encouraged to visit:

http://www.elsevier.com/copyright

http://www.elsevier.com/copyright

Author's personal copy

A highly stable catalyst for PEM fuel cell based on durable titanium diboridesupport and polymer stabilization

Shibin Yin a, Shichun Mu a,b,*, Haifeng Lv a, Niancai Cheng a, Mu Pan a, Zhengyi Fu a

a State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, ChinabDepartment of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, OX1 3QR, UK

1. Introduction

Proton exchange membrane (PEM) fuel cells have drawn a great

deal of attention from the aspects of both fundamental studies and

applications as powerful energy converting devices. However, the

commercializationofPEMfuel cellshasbeenseriouslyobstructedby

their poor durability [1]. The catalyst degradation is one of themost

important reasons for fuel cell performance deterioration. Com-

monly, the catalystsused inPEMfuel cells are carbonsupportedPtor

Pt-based catalysts. The catalyst degradation is mainly caused by

carbon corrosion, which leads to the agglomeration of Pt nano-

particles under extremely harsh working environments [2–5].

Carbon can be oxidized in the event of fuel starvation [4] or partial

hydrogen coverage [6], and this process will be even promoted by

the catalysis of Pt [7]. Therefore, highly stable catalyst supports are

urgently desired to enhance catalyst lifetime.

Carbon nanotubes (CNTs) have been employed to improve

catalyst durability. It has been reported that Pt/CNTs catalysts have

a lower electrochemical surface area loss, and a higher oxygen

reduction reaction activity and corrosion resistance in comparison

with Pt/C [8–10]. Usually, a pre-oxidation of the CNTs surface is

necessary to facilitate the Pt precursor distribution throughout the

inert CNTs’ surface. However, this pre-oxidation treatment

decreases the surface stability of CNTs [11,12]. In addition, CNTs

readily tend to tangle together, resulting in a non-uniformly

dispersion of CNTs in solutions.

Graphite intercalation compounds (GICs) are also used as PEM

fuel cells catalyst supports due to their unusual properties [13].

According to Shioyama et al. [14], an improved oxygen reduction

activity (ORR) has been obtained in the application of GICs as

catalyst supports, but the relatively large particle size of GICs could

limit the catalyst activity. Meanwhile, the inert surface of GICs

needs to be pre-treated to obtain uniformly dispersed Pt catalysts.

Carbon aerogel can increase the contact area between Pt and

electrolyte because of the high pore size distributions [15], and

accordingly, the catalytic surface area of Pt on carbon aerogel

increased with respect to that on Vulcan XC-72. However, the

chemical stability of the catalyst is considered due to the

amorphous property of carbon aerogel.

Tungsten carbide (WC) has also attracted attention for this

purpose. Meng and Shen [16] have studied the synergistic effect of

WC/CandPt catalysts on theORR inalkalinemedia. Chhinaet al. [17]

have investigated the thermal and electrochemical stability of WC

catalyst supports, and found WC was more thermally and

electrochemically stable thancarbonsupports.However, its stability

inacidelectrolyte isnot ideal becauseWCcanbecorroded in sulfuric

acid, which decreases the catalyst’s stability [18,19].

Both conducting oxides and semiconductor ceramics have been

investigated as oxidation resistant catalyst supports. Magneli phase

titanium–oxygen (TinO2n�1, where n is between 4 and 10) has been

Applied Catalysis B: Environmental 93 (2010) 233–240

A R T I C L E I N F O

Article history:

Received 24 June 2009

Received in revised form 3 September 2009

Accepted 26 September 2009

Available online 11 November 2009

Keywords:

Catalyst

Conducting ceramic

Titanium diboride

Stability

Proton exchange membrane fuel cells

A B S T R A C T

Titanium diboride (TiB2) is an electrically conducting ceramic with good conductivity, excellent thermal

stability and corrosion resistance in acid medium. Here we report for the first time its application as a

new catalyst support in proton exchange membrane (PEM) fuel cells. This novel catalyst (Pt/TiB2) was

formed by a colloid route, in which the highly dispersed Pt nanoparticles were stabilized by Nafion

functional polymers. This significantly facilitates the dispersion of Pt nanoparticles on TiB2. The

electrochemical stability of TiB2 was investigated and showed almost no changes in redox region after

oxidation during 48 h at 1.20 V. Further, it was found that the electrochemical stability of Pt/TiB2 catalyst

is about four times higher than that of the commercial Pt/C under electrochemical oxidation cycles in the

potential range of 0.6–1.2 V. The excellent stability of Pt/TiB2 could be attributed to the stability of TiB2

support as well as the introduction of Nafion as stabilizer, which enhance both the metal–support

interaction and the steric hindrance effect of the surface of Pt nanoparticles.

� 2009 Elsevier B.V. All rights reserved.

* Corresponding author at: State Key Laboratory of Advanced Technology for

Materials Synthesis and Processing, Wuhan University of Technology, Wuhan

430070, China. Tel.: +86 27 87651837; fax: +86 27 87879468.

E-mail addresses: [email protected], [email protected] (S. Mu).

Contents lists available at ScienceDirect

Applied Catalysis B: Environmental

journa l homepage: www.e lsev ier .com/ locate /apcatb

0926-3373/$ – see front matter � 2009 Elsevier B.V. All rights reserved.

doi:10.1016/j.apcatb.2009.09.034


attempted for this application. In particular, Ti4O7 exhibits a high

electrical conductivity of 1000 S cm�1 at room temperature, which

is considerably higher than the graphitized carbon (conductivity of

727 S cm�1) [20]. Chhina et al. [21] have found that indium tin oxide

(ITO) shows better electrochemical and thermodynamic stabilities

than carbon black for Pt/C catalysts. However, most of transition

metal oxides are unstable in acidic environments of PEM fuel cells.

Reeve et al. [22] indeed observed that the oxygen reduction activity

of the oxides declines substantially in acidic solutions. The slow

dissolution of metal components in oxides and their re-deposition

would cause severe cumulative poisoning problems.

Recently, it was also reported that titanium nitride (TiN)

supported Pt for PEM fuel cells showed higher catalytic perfor-

mance than conventional Pt/C catalysts [23], but the durability of

TiN as the support material is not clear yet. Further studies are

necessary to understand TiN as a catalyst support and especially

evaluate its durability properties.

Compared with all these candidates discussed above for PEM

fuel cells catalyst supports, titanium diboride (TiB2) ceramic

obtains many superior properties, including high melting point,

great hardness, good electrical, high thermal conductivity,

excellent thermal stability and corrosion resistance in acidic

medium [24,25], which makes it a promising solution as a support

material in PEM fuel cells. Surprisingly, it is very hard to find any

published results on its application in fuel cells. Here,we report our

study of Pt/TiB2 as PEM fuel cells catalysts, and demonstrate that

this novel catalyst has an excellent electrochemical stability.

2. Experimental

2.1. Preparation of stable Pt colloids and Pt/TiB2 catalysts

The preparation mechanism of Pt/TiB2 catalysts is shown in

Fig. 1A, where the highly dispersed Pt nanoparticles can be

supported on TiB2 using a colloidal route indicative of a strong

metal–polymer–support interaction. The mixture of 300.0 ml

ethanol, 300.0 ml deionized water, 360.0 mg H2PtCl6�6H2O and

5.0 ml 5.0 wt.% perfluorosulfonic acid (PSFA) Nafion1 (Du Pont Co.)

were used as received, and then vigorously stirred for 10 min at

80 8C in awater bath. The Pt colloidwas obtained after the pH value

of the mixture was adjusted to 9.0 by using 2.0 M NaOH solution,

and refluxed for 1–2 h until the solution turned from light yellow

to dark. TEM image (shown in Fig. 1B) shows a very narrow size

distribution of Pt colloid with the average size of about 1.5 nm.

TiB2 powders were prepared by self-propagating high-tem-

perature synthesis (SHS) [24]. TiB2 particles are uniform, and have

a narrow size distribution within about 1.8 mm (see Fig. 1C). Then

490.0 mg TiB2 was added into 20.0 ml ethanol and ultrasonic

stirring for 10 min. The above prepared Pt colloid was then added

drop-wise. Subsequently, the 18.6 wt.% Pt loaded TiB2 catalysts

were obtained after filtering, washing and drying.

2.2. Physicochemical characterization of Pt/TiB2

Lattice phases of Pt crystals and supports were characterized

using powder X-ray diffraction (XRD) with Cu Ka source

(l = 0.15406 nm, 35 mA). The (1 1 1) peak of the Pt diffraction

patterns was fitted to Gaussian line shapes on a linear background.

The average size of Pt nano-particles (D) was calculated according

to the Debye–Scherrer formula [26]. Infrared spectra of the

prepared Pt/TiB2 catalyst was carried out to detect the presence of

Nafion (as protecting agent of Pt) in Pt/TiB2 catalysts by Fourier

transform infrared spectroscopy (Nicolet MAGNA-IR 560, FTIR,

USA). The reference Nafion was prepared by evaporating 5.0 wt.%

Nafion liquid. The structure of the as-prepared TiB2 support, Pt

colloid, and Pt/TiB2 was characterized by a scanning electron

microscopy (SEM, JSM-5610LV) and a high-resolution transmis-

sion electron microscopy (HRTEM, JEM-2010FEF). The presence of

Fig. 1. Schematic of the Pt colloid particles and the Pt/TiB2 catalystswith perfluorosulfonic acidNafion as a stabilizer of Pt particles (A); TEM image of the Pt colloid particles (B)

and SEM micrograph of TiB2 powders (C).

S. Yin et al. / Applied Catalysis B: Environmental 93 (2010) 233–240234


Nafion for Pt/TiB2 catalysts was evaluated by the energy dispersive

X-ray spectrometry (EDX) attached to HRTEM combined with FTIR

analysis.

Thermogravimetric analysis (TGA7, PerkinElmer, Norwalk, CT,

USA) was used to characterize the thermal stability of the Pt/TiB2

catalyst in comparison with the commercially available Pt/C

catalyst (20 wt.% Pt on Vulcan XC-72, JM) under air flowing at

10 ml min�1. The temperature ranged from room temperature to

1000 8C at a heating rate of 5 8C min�1.

2.3. Electrochemical characterization of Pt/TiB2

The electrochemical accelerated durability test (ADT) was

employed to evaluate the long-term performance of catalyst. The

ADT is an inexpensive and time-effective method for screening

catalysts in terms of stability and performance [27].

A glass carbon (GC) electrode was prepared before ADT. The

supported catalysts (or supports) were added to 500.0 ml

deionized water with 21.0ml 5.0 wt.% Nafion solution, and then

dispersed onto the flat surface of a polished GC disk electrode

(Ø = 4.0 mm) using Finnpipette Digital Micropipette (Thermo

electron corp.) with a catalyst loading 0.4 mg cm�2. The solvent

on the surface of the electrode was removed by infrared

irradiation.

The prepared GC electrode was tested electrochemically in

0.5 M H2SO4 solution at 25 8C. The scan rate was controlled to

20 mV s�1 using a computer-controlled Autolab PGSTAT 30

potentiostat (Eco Chemie B.V., Holand). Platinum electrode was

used as the counter electrode, and Hg/Hg2SO4 electrode as the

reference electrode. It should be noted that all the potential

measured is referred to the reversible hydrogen electrode (RHE)

without specification. Ultra-pure N2 was passed through H2SO4

solution for 30 min prior to electrochemical experiments. In the

chronoamperometric, a constant potential of 1.20 V in 150 ml

solution was applied for electrochemical oxidation. The ADT was

conducted by cyclic voltammograms (CVs) between 0.6 and 1.20 V.

All the CV curves were recorded from 0 to 1.20 V at a scan rate of

20 mV s�1 before and after chronoamperometric and ADT [28]. The

electrochemical surface area (ESA) of catalysts was calculated with

the charge of hydrogen desorption region as follows:

EAS ¼QH

½Pt� � 0:21(1)

where QH is the charge for hydrogen desorption (mC cm�2), 0.21 is

the charge required to oxidize a monolayer of H2 on bright Pt, and

[Pt] the Pt loading (mg cm�2) on the electrode [29].

In addition, the oxygen reduction reaction (ORR) performance

of the as-prepared catalysts was evaluated by rotating disk

electrode (RDE) technique in 0.5 M H2SO4 electrolyte at a sweep

rate of 10 mV s�1 and a speed of 1600 rpm at room temperature.

3. Results and discussion

3.1. Physicochemcial properties of Pt/TiB2

As shown in Fig. 2A, the (1 0 2) peak of TiB2 overlaps with

Pt(2 2 0), and the (1 0 1) peak of TiB2 is very close to Pt(2 0 0).

Therefore, only the peak of Pt(1 1 1) can be used to calculate the

average particle size of Pt nano-crystals using Debye–Scherrer

Fig. 2. XRD pattern of (a) as prepared TiB2 powders and (b) the prepared Pt/TiB2 (A); FTIR spectra of the prepared Pt/TiB2 with the perfluorosulfonic acid Nafion as the

protecting agent of Pt nano-particles and the reference perfluorosulfonic acid Nafion (B), the bands at b1, b2, b3, b4 and b5 are assigned to S55O asymmetric stretching (–SO2OH

group), CF2 asymmetric stretching, CF2 symmetric stretching, S–O symmetric stretching (�SO3� ion) and C–O–C symmetric stretching of Nafion respectively; TGA data of Pt/

TiB2 and commercial 20 wt.% Pt/C (C): (a) TG of Pt/C, (b) DSC of Pt/C, (c) TG of Pt/TiB2 and (d) DSC of Pt/TiB2.

S. Yin et al. / Applied Catalysis B: Environmental 93 (2010) 233–240 235


formula [26]. The average size of Pt nano-crystals is 3.4 nm, which

is comparable to that of the commercial Pt/C [21].

FTIR spectra of the Nafion and Pt/TiB2 catalysts are given in

Fig. 2B. For the Pt/TiB2 catalyst, the strong characteristic band at

1279 cm�1 can be assigned to CF2 stretching vibration correspond-

ing to the bands at 1234 cm�1 in Nafion. The other relatively weak

band at 991 cm�1 is associated with the C–O–C symmetric

stretching vibration related to the band at 983 cm-�1 in Nafion.

These results verify the presence of Nafion in the as-prepared

Pt/TiB2 catalysts.

As shown in Fig. 2C, the weight loss of Pt/C catalysts begins at

low temperature (�120 8C) due to the evaporation of moisture.

When temperature rises to about 200 8C, the carbon support is

oxidized and a peak at 397.2 8C appears. A minor-peak occurs as

the temperature further ramps to 450 8C, which could be

attributed to the oxidization of the relatively stable carbon. The

loss of Pt/TiB2 is only 2.18% up to 500 8C, in contrast to 80.41% loss

for Pt/C. The low loss can be mainly attributed to the oxidation of

Nafion in Pt/TiB2. TiB2 starts to be oxidized as the temperature

increases to 532.2 8C accompanying a weak exothermic peak. A

maximum exothermic peak appears at 685.8 8C, which could be

attributed to the partial evaporation of B2O3. When the tempera-

ture further ramps to 1000 8C, Pt/C loses 82.49% of its total weight,

but Pt/TiB2 increases to 62.70% of total weight due to the partial

Fig. 3. CV curves of TiB2 (A) and carbon supports (Vulcan XC-72) (B) by held at1.20 V (versus RHE) for different durations (0.5 M H2SO4, scan rate: 20 mV s�1, temperature:

25 8C).

Fig. 4. CV curves of Pt/TiB2 (A) and the commercial 20 wt.% Pt/C (B) by accelerated durability tests (0.5 MH2SO4, scan rate: 20 mV s�1, temperature: 25 8C); oxygen reduction

reaction on the as-prepared Pt/TiB2 and the commercial 20 wt.% Pt/C (C). Changes of electrochemical surface area (ESA) of catalysts related to Pt catalytic surface areawith the

increased potential cycles (D).



oxidation of TiB2. These results clearly indicate that Pt/TiB2 has a

higher thermal stability than the commercial Pt/C because of the

high thermal stability of TiB2.

3.2. Electrochemical performance of TiB2 and Pt/TiB2

As seen from Fig. 3A, TiB2 ceramic has almost no change in

redox region after oxidation treatment for different durations,

which implies that almost no oxide was produced on TiB2 surface

during 48 h hold at 1.20 V. In contrast, a visible current peak occurs

in the redox region for XC-72 carbon black (Fig. 3B), which results

from the surface oxide formation due to the hydroquinone-

quinone (HQ-Q) redox couple on the carbon black surface [28]. The

current peak at about 0.60 V in XC-72 electrode indicates a higher

oxidation degree of carbon with potential-holding time. These

results suggest that TiB2 is more resistant to electrochemical

oxidation than carbon black. Meanwhile, the concentration of Ti

ion in solution was ca. 0.07mg ml�1 at 1.20 V for 48 h identified by

inductively coupled plasma atomic emission spectrometry (ICP-

AES, PE). And the corrosion rate of Ti in TiB2 is only ca. 0.2 mg h�1.

The initial and final CVs of Pt/TiB2 during the ADT are shown in

Fig. 4. The initial ESA of Pt/TiB2 is 34.7 m2 g�1, which is lower than

that of Pt/C (61.4 m2 g�1) as shown in Fig. 4A and B. This ESA

decrease can be attributed to the large particle size and density of

Fig. 5. TEM images of the as-prepared Pt/TiB2 before accelerated durability tests (ADT) (A) and EDX patterns of the Pt/TiB2 for the selected spot as shown in (A) before ADT (B);

after 6000 potential cycles (C); EDX patterns of the Pt/TiB2 for a selected spot as shown in (C) after ADT (D); particle size distribution of Pt before and after ADT (E).



TiB2 compared with that of carbon support and also the possibility

of the surface of Pt is partially occupied by Nafion. However, an

improvement of ORR activity of Pt/TiB2 is observed in terms of

onset potential. The Pt/TiB2 shows a higher reduced current of

0.29 mA cm�2 at 0.9 V as compared to Pt/C (0.11 mA cm�2 at

0.9 V) with the same Pt loading (see in Fig. 4C). Similar to TiB2

supports, Avasarala et al. [23] have demonstrated that TiN-

supported Pt catalysts have an excellent activity of oxygen

reduction in comparison with carbon-supported catalyst. This

further validates that the improved activity of Pt can be attributed

to the influence of support materials [30,31]. That is, the

conductive ceramics, as the supports of Pt catalysts, are helpful

to enhance the electrocatalytic activity of Pt catalysts. In addition,

our experimental results indicate a negligible effect of Nafion

layers of the outer Pt surfaces on the catalytic activity of the

supportedparticles. In fact, Tian [32] andour previous studies [33]

have shown that SO3� end groups in the polyelectrolyte chain

structure of Nafion can facilitate the reaction species transfer

process for ORR.

Fig. 4D shows the ESA loss of Pt versus the electrochemical

oxidation cycle number. The ESA of Pt/C decreases rapidly with the

cycle numbers increment. However, there is no obvious ESA loss in

thefirst 600cycles forPt/TiB2, andonlya slowdecrease in the further

cycles. The ESA loss rate of the Pt/C reaches 1.56� 10�2 m2 g�1

cycle�1, whereas the Pt/TiB2 has only 4.08� 10�3 m2 g�1 cycle�1,

which is 3.8 times lower than the Pt/C. This indicates Pt/TiB2 has

approximately four times longer lifetime than Pt/C under the

condition of an electrochemical acceleration.

Fig. 5A shows Pt particles are highly dispersed on the TiB2

before ADT. It is surprising that after 6000 potential cycles there

are still large number of Pt particles remaining on the surface of

TiB2 (see Fig. 5B) with the increase in Pt particle size. The

occurrence of elements F and S shown in Fig. 5C indicates the

existence of Nafion polymer as a stabilizer on the Pt particles. The

strong peak of Ti in the substrate (TiB2) compared to that of Pt can

be observed before ADT. After ADT, the relative intensity of Ti is

weakened as compared to that of Pt (Fig. 5D), which indicates that

a rather slow corrosion of TiB2 supports as mentioned previously

occurs during ADT despite the fact that the TiB2 supports show a

higher electrochemical stability than carbon black. In addition, the

average particle size of Pt particles increases from 3.2 to 5.7 nm,

Fig. 5E. Thus, the agglomerated Pt particles may partially prevent

the electron beam from penetrating the Pt metals and possibly

weaken the intensity of Ti.

After 5100 potential cycles, Pt particles agglomerate on carbon

supports into larger ones, leading to a massive decrease of Pt

particles and leaving behind more bare carbon surfaces as shown

in Fig. 6A and B. The average particle size before and after ADT is

about 2.9 and 6.5 nm respectively (see Fig. 6C). The Pt particles

in Pt/C display a faster agglomeration rate compared to the case

of Pt/TiB2. This further demonstrate that Pt/TiB2 has a higher

electrochemical stability than Pt/C catalysts.

Fig. 6. TEM images of the commercial 20 wt.% Pt/C catalyst before ADT (A) and after 5100 potential cycles (B); particle size distribution of Pt before and after ADT (C).



3.3. Stable mechanism of Pt/TiB2

It has been reported that smaller particle size leads to easier

agglomeration of particles due to higher specific surface energy

[34–36]. The Pt particle size in both commercial Pt/C and Pt/TiB2

catalysts is in the range of 2–5 nm, which endows Pt particles with

a strong tendency to agglomeration, and leads to ESA loss. On the

other hand, it is well known that carbon support can be corroded

during a long-term operation [37,38] and this corrosion can be

promoted especially in the presence of Pt [2,39]. This weakens the

interaction between carbon and Pt particles, and then Pt particles

would collapse into the carbon-deficient XC-72 support thus

accelerating the agglomeration of Pt particles. Meanwhile, the

decrease of Pt particle number could be also attributed to the

Ostwald ripening [40]. In contrast, the TiB2 supports have very high

electrochemical and thermal stabilities with respect to carbon

supports, which endow Pt particles on TiB2 supports with a higher

stability and less reduction than that on carbon supports.

The migration of Pt particles on support is regarded to be very

dependant on the Pt–support interaction as well as the steric

effects of Pt particles. It has been reported that Nafion molecules

can be self-assembled onto inorganic nanoparticles through

electrostatic interaction, preventing further growth of inorganic

nanoparticles [41]. In our previous studies, we have reported a

novel approach to significantly increase lifetime of Pt/C catalysts

through Nafion stabilization and given rise to three times higher

durability than conventional Pt/C that commonly used in PEM fuel

cell [33]. Therefore, the Pt particles stabilized with Nafion in Pt/

TiB2 with both electron rich �SO3� groups in Nafion and highly

electron deficient surface of TiB2 can offer a strong adhesion to

Nafion modified Pt and support surface, which may increases the

interaction between Pt particles and conductive supports. There-

fore, the Pt particles can be anchored tightly on the TiB2 surface. At

the same time, the electrostatic repulsion between self-assembled

Nafion layer on different Pt surfaces may supplymore strong steric

hindrance than that of pure Pt particles that probably enhances the

resistance to Pt particle migration.

Fig. 7 shows two simple migration models of Pt particles

stabilized with Nation on support surfaces. We propose that Pt

particles are mainly driven by a changeable electric field force (f1)

during electrochemical acceleration tests, and Pt particles only

moves when the electric field force (f1) applied to the particles is

greater than the friction resistance (f2) of Pt particles. Pt colloid

particles should have a high resistance to migration because of the

strong Pt–supports interaction. Therefore, the gathering of

particles is relatively difficult. When f1 is sufficient magnitude

as compared to f2, as shown in Fig. 7A, the migration and gathering

of Pt colloid particles take place, but the aggregation is possibly

hindered by Nafion polymer layer distributed on Pt surfaces, and

can occur when Nafion is decomposed by a long-term electro-

chemical oxidation. When the electric field force (f1) is not

sufficient magnitude, as shown in Fig. 7B, the migration of Pt

colloid particles will not take place. However, Nafion can be

decomposed with the time, leading to the decrease of resistance to

particle migration. Once the critical force to drive particles is

achieved, the Pt particles may move onto the support surface and

Fig. 7. Schematic of the migration model of Pt particles movement on support surfaces. Pt colloid particles migration driven by an electric field force (A) and Pt particles

migration companying with Nafion polymer oxidization (B).



gather each other. In this case, Pt particles may aggregate due to

the absence of the protection role from the integrated Nafion

polymers.

In fact, we have observed no significant change for the catalytic

surface area in the first 600 cycles for Pt/TiB2 followed by a slow

electrochemical surface area loss after 600 cycles. This phenom-

enon may be well explained by the Pt particle migration model

with Nafion polymer layer oxidization (see Fig. 7B). In the first 600

cycles, Pt particles are fixed on the support surfaces. With the

electrochemical oxidation cycle increment, the oxidation of Nafion

occurs, resulting in the decline of both the metal-support

interaction and the steric effect of the surface of Pt particles. As

a result, after 600 cycles, the critical force to drive particles

migration is obtained, which promotes the migration and

agglomeration of Pt particles.

4. Conclusions

Pt/TiB2 catalysts as a potential stable catalyst for PEM fuel cells

have been obtained and evaluated. The Pt/TiB2 prepared byNafion-

stabilized Pt particles shows an improved oxygen reduction

reaction activity and remarkably high electrochemical stability.

The stability of Pt/TiB2 is approximately 4 times better than that of

the commercial Pt/C, endowing this novel catalyst with an

excellent stability resulting from the TiB2 supports and also

possibly from polymer stabilization effect. It should be noted that

TiB2 powders used in the present investigation is of relatively big

particle size and heavy density that will reduce the Pt utilization

efficiency. In this sense, there is still much room to improve Pt/TiB2

activity. Given its desirable activity and excellent stability Pt/TiB2

exhibits very good potential as a stable catalyst for PEM fuel cells.

Acknowledgments

This work was supported by the New Century Excellent Talent

Program of Ministry of Education of China (No. NCET-07-0652), the

National Natural Science Foundation of China (NSFC) (No.

50632050), and theMinistry ofEducationofChina (No. PCSIRT0644).

Wewould like to thank Prof. P.P. Edward F.R.S., Prof. S.C.E. Tsang, Dr.

M.O. Jones and Dr. A. Sartbaeva in the Inorganic Chemistry

Laboratory, University of Oxford, for their helpful discussion.

References

[1] J.R. Yu, T. Matsuura, Y. Yoshikawa, M.N. Islam, M. Hori, Electrochem. Solid-StateLett. 8 (2005) A156–A158.

[2] Y.Y. Shao, G.P. Yin, Y.Z. Gao, P.F. Shi, J. Electrochem. Soc. 153 (2006) A1093–A1097.[3] L.M. Roen, C.H. Paik, T.D. Jarvic, Electrochem. Solid-State Lett. 7 (2004) A19–A22.[4] S.D. Knights, K.M. Colbow, J. St-Pierre, D.P. Wilkinson, J. Power Sources 127 (2004)

127–134.[5] H.A. Gasteiger, S.S. Kocha, B. Sompalli, F.T. Wagner, Appl. Catal. B 56 (2005) 9–35.[6] C.A. Reiser, L. Bregoli, T.W. Patterson, J.S. Yi, J.D. Yang, M.L. Perry, T.D. Jarvi,

Electrochem. Solid-State Lett. 8 (2005) A273–A276.[7] M.H. Shao, P. Liu, R.R. Adzic, J. Am. Chem. Soc. 128 (2006) 7408–7409.[8] C. Kim, Y.J. Kim, Y.A. Kim, T. Yanagisawa, K.C. Park, M. Endo, M.S. Dresselhaus, J.

Appl. Phys. 96 (2004) 5903–5905.[9] K.P. Gong, F. Du, Z.H. Xia, M. Durstock, L.M. Dai, Science 323 (2009) 760–764.[10] X. Wang, W.Z. Li, Z.W. Chen, M. Waje, Y.S. Yan, J. Power Sources 158 (2006) 154–

159.[11] V. Georgkilas, K. Kordatos, M. Prato, D.M. Guldi, M. Holzinger, A. Hirsch, J. Am.

Chem. Soc. 124 (2002) 760–761.[12] S.C. Mu, H.L. Tang, S.H. Qian, M. Pan, R.Z. Yuan, Carbon 44 (2006) 762–767.[13] R. Setton, Adv. Mater. 1 (1989) 348–349.[14] H. Shioyama, Y. Yamada, A. Ueda, T. Kobayashi, Carbon 43 (2005) 2374–2378.[15] A. Smirnova, X. Dong, H. Hara, A. Vasiliev, N. Sammes, Int. J. Hydrogen Energy 30

(2005) 149–158.[16] H. Meng, K.P. Shen, Chem. Commun. 35 (2005) 4408–4410.[17] H. Chhina, S. Campbel, O. Kesler, J. Power Sources 164 (2007) 431–440.[18] H. Scholl, B. Hofman, A. Rauscher, Electrochim. Acta 37 (1992) 447–452.[19] H. Scholl, B. Hofman, J. Kupis, K. Polaski, Electrochim. Acta 39 (1994) 115–117.[20] T. Ioroi, Z. Siroma, N. Fujiwara, S. Yamazaki, K. Yasuda, Electrochem. Commun. 7

(2005) 183–188.[21] H. Chhina, S. Campbell, O. Kesler, J. Power Sources 161 (2006) 893–900.[22] R.W. Reeve, P.A. Christensen, A.J. Dickinson, A. Hamnett, K. Scott, Electrochim.

Acta 45 (2000) 4237–4250.[23] B. Avasarala, T. Murray, W.Z. Li, P. Haldar, J. Mater. Chem. 19 (2009) 1803–1805.[24] J.Y. Zhang, Z.Y. Fu, W.M. Wang, J. Mater. Sci. Technol. 21 (2005) 841–844.[25] B. Basu, G.B. Raju, A.K. Suri, Int. Mater. Rev. 51 (2006) 352–374.[26] V. Radmilovic, H.A. Gasteiger, P.N. Ross, J. Catal. 154 (1995) 98–106.[27] H.R. Colon-Mercado, H.S. Kim, B.N. Popov, Electrochem. Commun. 6 (2004) 795–

799.[28] J.J. Wang, G.P. Yin, Y.Y. Shao, S. Zhang, Z.B. Wang, Y.Z. Gao, J. Power Sources 171

(2007) 331–339.[29] F. Maillard, M. Martin, F. Gloaguen, J.M. Leger, Electrochim. Acta 47 (2002) 3431–

3440.[30] J. Nicole, D. Tsiplakides, C. Pliangos, X.E. Verykios, C. Comninellis, C.G. Vayenas, J.

Catal. 204 (2001) 23–34.[31] Y.H. Zhang, M.L. Toebes, A. van der Eerden, W.E. O’Grady, K.P. de Jong, D.C.

Koningsberger, J. Phys. Chem. B108 (2004) 18509–18519.[32] Z.Q. Tian, S.P. Jiang, Z.C. Liu, L. Li, Electrochem. Commun. 9 (2007) 1613–1618.[33] N.C. Cheng, S.C. Mu, M. Pan, P.P. Edwards, Electrochem. Commun. 11 (2009)

1610–1614.[34] J. Xie, D.L. Wood, K.L. More, P. Atanassov, R.L. Borup, J. Electrochem. Soc. 152

(2005) A1011–A1020.[35] E. Guilminot, A. Corcella, F. Charlot, F. Maillard, M. Chatenet, J. Electrochem. Soc.

154 (2007) B96–B105.[36] G.X. Wang, L. Yang, J.Z. Wang, H.K. Liu, S.X. Dou, J. Nanosci. Nanotechnol. 5 (2005)

1135–1140.[37] R.L. Bourp, J.R. Davey, F.H. Garzon, D.L. Wood, M.A. Inbody, J. Power Sources 163

(2006) 76–81.[38] S.C. Ball, S.L. Hudson, D. Thompsett, B. Theobald, J. Power Sources 171 (2007) 18–

25.[39] L.M. Roen, C.T. Paik, D.H. Jarvi, Electrochem. Solid State Lett. 7 (2004) A19–A22.[40] A.V. Virkar, Y.K. Zhou, J. Electrochem. Soc. 154 (2007) B540–B547.[41] J.J. Pan, H.L. Zhang, M. Pan, J. Colloid Interface SCI 326 (2008) 55–60.


A Highly Stable Catalyst for PEM Fuel Cell Based on Durable Titanium Diboride Support and Polymer...

Documents

Transcript of A Highly Stable Catalyst for PEM Fuel Cell Based on Durable Titanium Diboride Support and Polymer...