Influence of the support on the physicochemical properties of Pt electrocatalysts: Comparison of catalysts supported on different carbon materials

Trang 1

Contents lists available atScienceDirect

Materials Chemistry and Physics

j o u r n a l h o m e p a g e :w w w e l s e v i e r c o m / l o c a t e / m a t c h e m p h y s

Inﬂuence of the support on the physicochemical properties of Pt electrocatalysts: Comparison of catalysts supported on different carbon materials

L Calvillo, V Celorrio, R Moliner, M.J Lázaro∗

Instituto de Carboquímica (CSIC), Miguel Luesma Castán 4, 50018 Zaragoza, Spain

a r t i c l e i n f o

Article history:

Received 11 March 2010

Received in revised form

15 December 2010

Accepted 8 February 2011

Keywords:

Mesoporous materials

Electrocatalyst

Physicochemical characterization

a b s t r a c t

Pt nanoparticles have been supported on different carbon materials for their use as electrocatalysts in polymeric electrolyte fuel cells Carbon nanofibers (CNF) and ordered mesoporous carbon (CMK-3) have been studied as supports that could replace carbon black in the preparation of commercial electrocata-lysts The use of these non-conventional carbon materials allowed the determination of the influence of the support on the physicochemical properties of catalysts Additionally, Pt catalyst supported on Vul-can XC-72R (commercial electrocatalyst support) has been prepared in order to establish a comparison Catalysts were prepared by the incipient wetness impregnation method, and subsequently, they were reduced in a H2flow Supports and catalysts were characterized by different analytical techniques in order to determine the effect of the support Results proved that the support has a strong influence on the physicochemical properties of catalysts These properties depended on the nature of the support and are associated with the metal–support interaction

1 Introduction

In recent years, fuel cells have attracted considerable attention

due to their high energy efﬁciency with zero emissions Among the

different types of fuel cells, polymer electrolyte fuel cells (PEMFCs

and DMFCs) are the most promising for both portable and

station-ary applications due to their advantageous features[1,2] However,

at present, there are some aspects that make fuel cells not

compet-itive with respect to other current power sources One of them is

that the electrochemical processes need noble metal-based

elec-trocatalysts to occur at signiﬁcant rate[3–5]

Nowadays, the most effective low-temperature fuel cell

cat-alysts are highly dispersed platinum nanoparticles supported on

carbon materials[6,7] Carbon has been used for many years as a

support for industrial precious metal catalysts[8] However, studies

comparing different forms of carbon supports for fuel cell

electro-catalysts are quite sparse For fuel cell applications, in addition to

a high surface area for a good metal dispersion and a mesoporous

structure for facilitating the reactants and products diffusion, the

carbon support must have sufﬁcient electrical conductivity to allow

the ﬂow of electrons[7,9,10] Carbon support plays a vital role in the

preparation and performance of catalysts because it enhances the

dispersion of the active phase and provides a framework that allows

electron conduction and gas diffusion It has been shown that

car-∗ Corresponding author Tel.: +34 976 733977; fax: +34 976 733318.

E-mail address: mlazaro@icb.csic.es (M.J Lázaro).

bon support has a strong inﬂuence on the properties of supported noble metal catalysts, including metal particle size, morphology, size distribution, stability, and dispersion[4,11] On the other hand, carbon supports can also affect the performance of fuel cell cata-lysts by altering mass transport, catalyst layer electric conductivity, active electrochemical area, and metal nanoparticle stability during the operation[12–14] Hence, the optimization of carbon supports

is very important in PEFC development

At present, carbon blacks are the most commonly used support due to their high mesoporous distribution and their graphitic char-acteristics Among them, Vulcan XC-72(R) is the most used material because of its high electrical conductivity and speciﬁc surface area [15,16] However, new carbon materials, such as carbon nanoﬁbers and nanotubes, carbon xerogels and aerogels, or ordered carbons, are being studied in order to improve the electrochemical perfor-mance of the catalysts in the fuel cell[17–21]

In this work, carbon materials with different morphological and textural properties have been proposed as an alternative that could replace carbon blacks (Vulcan XC-72) as supports in the preparation

of electrocatalysts The use of these non-conventional carbon mate-rials as support allows studying the inﬂuence of carbon properties

on the preparation of catalysts Carbon nanoﬁbers and ordered mesoporous carbon have been used for preparing platinum elec-trocatalysts In addition, the effect of the support functionalization was studied Supports and electrocatalysts were characterised by scanning and transmission electron microscopy (SEM and TEM),

N2-physisorption, temperature programmed desorption (TPD), and X-ray diffraction (XRD)

Trang 2

2 Experimental

2.1 Preparation of carbon supports and Pt electrocatalysts

Carbon nanoﬁbers (CNF) were synthesized via the thermocatalytic

decomposi-tion of methane, as described in [22] Brieﬂy, CNF were grown over a Ni:Cu:Al 2 O 3

(mass ratio 78:6:16) catalyst in a pure methane ﬂow at 700◦C for 10 h Prior to the

synthesis, the catalyst was reduced in a pure H 2 ﬂow at 550 ◦ C for 3 h.

Ordered mesoporous carbon (CMK-3) was prepared by incipient

wet-ness impregnation of SBA-15 silica with a carbon precursor (furan resin,

Hüttenes–Albertus), as detailed elsewhere [23,24] Subsequently, impregnated

sil-ica was cured and carbonized at 700 ◦ C for 2 h in N 2 atmosphere, and a silica–carbon

composite was obtained Finally, silica–carbon composite was washed with HF (40%,

Fluka) at room temperature overnight to remove the silica.

Vulcan XC-72R was supplied by Cabot, and was used to establish a comparison

with the other carbon materials.

In order to study the effect of the support surface chemistry on the properties

of catalysts, carbon materials were subjected to different oxidation treatments to

modify their surface chemistry Different oxidation conditions (oxidizing agent and

temperature) were selected for each material depending on their nature Carbon

nanoﬁbers and Vulcan XC-72R were treated with concentrated HNO 3 (Nc) and a

mixture of HNO 3 –H 2 SO 4 (1:1, v/v) (NS) at either room (Ta) or boiling (Tb)

tempera-ture for 0.5 h and 2 h [22,25] In the case of CMK-3 carbon, due to their non-graphitic

nature, milder oxidation conditions were used to maintain the ordered structure.

Treatments were carried out with diluted (2 M) and concentrated HNO 3 (65%) at

room temperature for 0.5 h and 2 h [23] Complete studies about the

functionaliza-tion of the carbon materials can be found in [22,23,25] From these functionalization

studies, some samples with different textural properties and surface chemistry were

selected as supports in order to study their effect on the catalyst properties A list of

the studied supports is presented in Table 1.

The platinum supported catalysts with a 20 wt.% loading were prepared by the

incipient wetness impregnation method using H 2 PtCl 6 ·6H 2 O (Sigma–Aldrich) as

Table 1

Nomenclature and description of the supports studied in this work.

Support Oxidation treatment

Oxidizing agent Temperature ( ◦ C) Time (h) CNF

CNF NSTa0.5 HNO 3 –H 2 SO 4 1:1 (v/v) 25 0.5 CNF NcTb0.5 Concentrated HNO 3 (65%) 115 0.5 CNF NSTb0.5 HNO 3 –H 2 SO 4 1:1 (v/v) 115 0.5 CNF NcTb2 Concentrated HNO 3 (65%) 115 2 CNF NSTb2 HNO 3 –H 2 SO 4 1:1 (v/v) 115 2 CMK-3

CMK-3 NdTa0.5 Diluted HNO 3 (2M) 25 0.5 CMK-3 NcTa0.5 Concentrated HNO 3 (65%) 25 0.5 CMK-3 NdTa2 Diluted HNO 3 (2M) 25 2 CMK-3 NcTa2 Concentrated HNO 3 (65%) 25 2 Vulcan

Vulcan NSTa0.5 HNO 3 –H 2 SO 4 1:1 (v/v) 25 0.5 Vulcan NcTb0.5 Concentrated HNO 3 (65%) 115 0.5 Vulcan NcTb2 Concentrated HNO 3 (65%) 115 2

metal precursor Subsequently, platinum precursor was reduced in H 2 atmosphere

at 300 ◦ C for 2 h.

2.2 Characterization techniques SEM micrographs were obtained using a JEOL JSM 6400 operating

at 20 kV TEM studies were made on a TEM 200 kV JEOL JEM 2010F Both techniques were used to study the morphology of the carbon

sup-Fig 1 Study of the morphology of the original (non-oxidized) carbon supports: (a) SEM image of CNF; (b) TEM image of CNF; (c) TEM image of CMK-3; and (d) SEM image

Trang 3

Table 2

Textural parameters of the original (non-oxidized) carbon supports and their

cor-responding Pt catalysts.

Sample S BET (m 2 g−1) V Total (cm 3 g−1) S Mesopore

(m 2 g−1)

S Micropore (m 2 g−1)

ports TEM was also used to determine the platinum particle size and

dispersion.

X-ray diffraction (XRD) patterns were recorded using a Bruker AXS B8 Advance

diffractometer with Â–Â conﬁguration and using Cu K␣ radiation XRD was used to

study the morphology of both the carbon supports and metal particles.

N 2 adsorption–desorption isotherms were measured at 77 K using a

Micromerit-ics ASAP 2020 Total surface area and pore volume were determined using the

BET (Brunauer–Emmett–Teller) equation and the single point method, respectively.

Pore size distribution (PSD) curves were calculated by BJH (Barrett–Joyner–Halenda)

method The position of the maximum of the PSD was used as the average pore

diam-eter The textural properties of both the supports and catalysts were determined by

this technique.

The surface chemistry of the carbon supports (amount of surface oxygen groups)

was analyzed by temperature programmed desorption experiments The

exper-iments were carried out from room temperature up to 1050◦C using a rate of

10◦C/min The amounts of CO and CO 2 desorbed from the carbon samples were

ana-lyzed by gas chromatography The determination of deconvolutions was calculated

by using Origin software.

3 Results and discussion

3.1 Characterization of carbon supports

Carbon materials proposed as catalyst supports showed

mor-phological and textural differences as well as different surface

chemistry The effect of the differences on the catalyst properties

was investigated

The morphology of CNF was studied by scanning and

transmis-sion electron microscopy (SEM and TEM)[22] SEM images showed

that the carbon deposited during the decomposition of methane

appeared as long ﬁlaments that grew from the catalyst particles

(Fig 1a), whereas TEM images showed that carbon nanoﬁbers had

herringbone morphology (Fig 1b) CMK-3 carbon had a highly

ordered structure that consisted of periodic arrays of hexagonal

nanorods with uniform mesopores between them, as observed by

TEM (Fig 1c) This structure was an inverse replica of the structure

of the SBA-15 silica used as template (see Refs.[23,24]) Finally,

Vulcan XC-72R, supplied by Cabot, consisted of spherically shaped

carbon nanoparticles, called primary particles, with sizes in the

range of 30–60 nm These particles form aggregates in the form

of chains or clusters, as shown inFig 1d

The nature of the carbon materials before the oxidation

treat-ments was studied by X-ray diffraction (XRD) CNF was the most

crystalline material, as seen inFig 2 They showed a sharp peak of

great intensity at 2Â = 26.24◦, which is assigned to the basal planes

of graphite (0 0 2) Vulcan XC-72R also showed one peak at around

2Â = 24.8◦, which was broader and less intense than the peak for

CNF This peak is attributed to the turbostratic structure of the

pri-mary particles, which consist of “crystalline” regions of 1.5–2.0 nm

in length and 1.2–1.5 nm in height with a random disposition

However, CMK-3 carbon showed a broad peak of low intensity,

characteristic of amorphous carbon materials

Textural properties of the different carbon materials were

deter-mined by N2-physisorption Results for the non-oxidized materials

are summarized inTable 2 Vulcan XC-72R had a speciﬁc surface

area of 218 m2g−1and a pore volume of 0.41 cm3g−1 It had a

meso-porous structure, but contained a large number of micropores of

80 70 60 50 40 30 20 10

Ni (200)

Ni (111) Graphite (002)

CMK-3 Vulcan

2-Theta (degree)

CNF

Fig 2 XRD diffractograms of the original (non-oxidized) carbon materials used as

supports: nature of the support.

less than 1 nm (30% of the total surface area) Therefore, it is possi-ble that an important portion of nanoparticles may be sunken into these micropores, resulting in little or no electrochemical activity because of the difﬁculty of reactant accessibility[7,10] On the other hand, micropores could effectively block the sinking of the metal nanoparticles CNF had a relatively large accessible surface area of

96 m2g−1 and a pore volume of 0.23 cm3g−1 They had a meso-porous structure with an average pore diameter of approximately

4 nm (micropore volume was negligible) CMK-3 had a high speciﬁc surface area (1163 m2g−1) and a large pore volume (0.81 cm3g−1)

It was mainly a mesoporous material with narrow pore size dis-tribution around 3 nm, although it contained a small amount of micropores (less than 3% of the total surface area) that resulted from the carbonization of the carbon precursor itself

The surface chemistry of carbon materials was studied using temperature programmed desorption (TPD) experiments These experiments give information about the amount, nature and ther-mal stability of the oxygen groups contained on the carbon surface and the oxygen groups created during the oxidation treatments Acidic groups are decomposed into CO2at lower temperatures and basic and neutral groups are decomposed into CO at higher tem-peratures[26–28] It is expected that these surface oxygen groups have two functions during the catalyst preparation by the incipi-ent wetness impregnation method On one hand, it is expected that they increase the wettability of the carbon support, thereby facil-itating the access of the aqueous solution of the metal precursor

to the internal pore structure during the impregnation stage And

on the other hand, it is expected that they act as metal anchoring sites, preventing the mobility and, in consequence, the agglomer-ation of platinum particles during the metal precursor reduction stage.Fig 3shows an estimation of the number of surface oxygen groups of the original carbon materials (before the oxidation treat-ments) CNF had a very small amount of oxygen groups due to their inert nature, and Vulcan XC-72R only had oxygen groups desorbed

as CO However, CMK-3 showed a high content of oxygen groups, compared with the other materials

The oxidation treatments affected the different properties of the carbon materials and the effects depended on the severity of the oxidation conditions

Trang 4

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

2

Vulcan CMK-3

CNF

CO CO2

Fig 3 Estimation of the number of surface oxygen groups of the original

(non-oxidized) carbon materials as CO and CO 2 amounts desorbed during the TPD

experiments.

Oxidation treatments affected the morphology of the carbon

materials For CNF and Vulcan, similar results were obtained The

less severe treatments did not modify their structure However, it

was observed that the most severe treatments resulted in the

short-ening of CNFs (see Ref.[22]) and modiﬁed the original structure of

the primary particles of Vulcan and their aggregates (see Ref.[25])

In the case of CMK-3, the ordered structure was not altered

dur-ing the oxidation treatments (see Ref.[23]), since milder oxidation

conditions were selected for this material

In all cases, the oxidation treatments resulted in a decrease of

both the speciﬁc surface area and the pore volume of the carbon

materials, which depended on the oxidation conditions[22,23,25]

More severe oxidation conditions resulted in a more signiﬁcant

decrease of the textural properties However, the pore size

distri-bution was not modiﬁed

Regarding the surface chemistry, an increase in the number of

surface oxygen groups after the oxidation treatments was observed

in all cases This result can be observed inFig 7, where the total

amount of oxygen groups is represented as CO + CO2 amounts

During these treatments, carboxylic groups, phenols and quinones

were mainly created [22,23,25] It is expected that carboxylic

groups will increase the wettability of carbon materials, and

phe-nols and quinones, which are stable at high temperatures, will act

as anchoring sites for the metal precursor

3.2 Physicochemical characterization of electrocatalysts

3.2.1 Effect of the nature of the support

Firstly, the effect of the use of different carbon materials as

cat-alyst support was studied For this study, only the original carbon

materials (before the oxidation treatments) will be used Fig 4

shows the XRD patterns of the catalysts supported on the

non-oxidized carbon materials All samples showed the characteristic

peaks of the fcc structure of platinum However, the intensity and

width of the peaks, which are related to the Pt crystallite size,

depended on the carbon material used as support The average Pt

crystallite size was determined from the XRD diffractograms using

the Scherrer’s equation and the values obtained are summarized in

Table 3

Average Pt crystallite size obtained from the XRD diffractograms using the Scherrer’s

equation for catalysts supported on the non-oxidized carbon materials.

80 70 60 50 40 30 20 10

Pt(220) Pt(200)

Pt(111)

Pt/CMK-3

Pt/Vulcan

2-Theta (degree) Pt/CNF

Fig 4 XRD diffractograms of Pt catalysts supported on the non-oxidized carbon

materials.

Table 3 The size of Pt crystallites supported on carbon nanoﬁbers was about 3 nm, whereas Pt crystallites supported on CMK-3 were approximately 7.6 nm Taking into account that all catalysts were prepared by the same method and with the same metal loading,

it can be deduced that the support has an important effect on the size of supported Pt crystallites In this case, a relationship between the Pt crystallite size and the crystalline grade of the support can

be established The higher the crystalline grade of the support, the smaller the Pt crystallite size In addition, Pt crystallites supported

on Vulcan had an average size of about 5.6 nm This value was intermediate between those obtained for carbon nanoﬁbers and CMK-3, which conﬁrms the relationship between the crystalline grade of the support and the metal crystallite size In the literature, this effect is attributed to the type of metal–support interaction [29,30], which is related to the nature of the support and has been considered to affect the growth, the structure and the dispersion of metal particles[4,31] This is due to the electronic interaction at the platinum–carbon interface, which modify the electronic structure

of the metal

The metal–support interaction also affects the crystalline struc-ture of the metal Metal particles supported on CNF presented a highly crystalline structure (Fig 5a), which can be associated with

a strong metal–support interaction[29] In contrast, Pt particles supported on Vulcan and CMK-3 adopted a more dense globular morphology (Fig 5b and c), which can be associated to a weak metal–support interaction

From these results, it can be deduced that more crystalline car-bon supports result in smaller and more crystalline Pt particles, and that this effect is attributed to the metal–support interaction The size and distribution of platinum particles were also stud-ied by transmission electron microscopy TEM images of the

Pt catalysts showed that a uniform distribution of Pt particles was achieved for all carbon materials by the incipient wetness impregnation method, as observed in Fig 6 A narrow particle size distribution was obtained in catalysts supported on carbon nanoﬁbers and Vulcan Moreover, the particle size calculated by TEM was in concert with XRD results However, catalysts supported

on CMK-3 showed a broad particle size distribution In this case, although the TEM and XRD results were not in agreement, the par-ticle size calculated by XRD corresponded to the size of the metal aggregates observed by TEM

Trang 5

Fig 5 TEM images of the Pt catalysts supported on non-oxidized (a) CNF; (b) CMK-3;

and (c) Vulcan: crystallinity of Pt nanoparticles.

Fig 6 TEM images of platinum catalysts supported on non-oxidized (a) CNF; (b)

CMK-3; and (c) Vulcan: dispersion of Pt nanoparticles.

Trang 6

1

2

3

4

5

6

7

CNF CNF

NSTa0,5

CNF NcTb0,5

CNF NSTb0,5

CNF NcTb2

CNF NSTb2

0 5 10 15 20 25

Oxygen groups

Pt crystallite size

0

1

2

3

4

5

6

7

CMK-3 CMK-3

NdTa0.5

CMK-3 NdTa2

CMK-3 NcTa0.5

CMK-3 NcTa2

0 5 10 15 20 25

Oxygen groups

Pt crystallite size

0

1

2

3

4

5

6

7

Vulcan Vulcan

NSTa0.5

Vulcan NcTb0.5

Vulcan NcTb2

0 5 10 15 20 25

Oxygen groups

Pt crystallite size

(a)

(b)

(c)

Fig 7 Effect of the surface chemistry of the support on catalyst properties:

relation-ship between the total number of surface oxygen groups of the support (CO + CO 2

desorbed amounts during TPD experiments) and the average Pt crystallite size

(obtained by XRD) for oxidized and non-oxidized (a) CNF; (b) CMK-3; and (c) Vulcan.

Textural properties of catalysts were also studied by N2

-physisorption, and the results are summarized inTable 2 Catalysts

exhibited a lower surface area and total pore volume than the

corresponding carbon supports In particular, the decrease of the

mesoporosity was more signiﬁcant after catalyst loading when

car-bon nanoﬁbers and CMK-3 were used as supports This strongly

indicates that platinum was mainly distributed in the mesoporous

structure of the supports However, a more signiﬁcant decrease of

microporosity was observed in the case of Pt/Vulcan, indicating

that platinum was mainly distributed in the micropore structure

The portion of particles inside the micropores will likely have

lit-tle or no electrochemical activity due to the difﬁculty of reactant

accessibility

3.2.2 Effect of the surface chemistry of the support

The size and the aggregation grade of platinum particles are also

related to the surface chemistry of the carbon supports[32,33]

Fig 8 TEM images of the Pt catalysts supported on the oxidized materials (a) Pt/CNF

NSTa0.5; (b) Pt/CMK-3 NcTa2; and (c) Pt/Vulcan NcTb2: formation of Pt agglomer-ates.

However, it must be taken into account that the effect of the sur-face chemistry of the support on the catalyst properties depends

on the catalyst synthesis method and the nature of the metal pre-cursor Therefore, it is necessary to carry out an exhaustive study

to determine the effect that the surface chemistry of the support

Trang 7

has on catalyst preparation Conclusions extracted from this study

are only valid for this catalyst synthesis method.Fig 7shows, for

each carbon material, the relationship between the total number of

surface oxygen groups of the support (calculated as CO + CO2

des-orbed amount during the TPD experiments) and the Pt crystallite

size obtained from the XRD diffractograms The same effect of the

surface chemistry of the support was observed for all carbon

mate-rials: An increase in the platinum crystallite size was observed as

the number of surface oxygen groups increased[32]

In order to study further the effect of the oxygenated groups

of the support, catalysts supported on the oxidized supports were

analyzed by TEM (Fig 8) The formation of Pt particles

agglomer-ates on the oxidized supports was detected It was observed that

platinum particles deposited on oxidized carbons had a similar

size to particles deposited on the non-oxidized carbons Hence,

the increase of crystallite size detected by XRD was due to the

formation of agglomerates, and it was not due to the formation

of larger crystallites According to these results, for the incipient

wetness impregnation method, the agglomeration of the metal

par-ticles as the number of oxygen groups increases can be attributed to

the decomposition of less stable oxygen groups during the

reduc-tion stage of the metal precursor[33–35] The decomposition of

these groups facilitates the mobility of platinum on the support

surface favouring in consequence the agglomeration of platinum

particles This effect was more signiﬁcant in catalysts supported

on oxidized CMK-3 carbons due to their higher content of oxygen

groups (Fig 8c)

4 Conclusions

Carbon nanoﬁbers and ordered mesoporous carbons have

been proposed as alternative supports that could replace carbon

blacks in the preparation of commercial electrocatalysts for

low-temperature fuel cells The use of these non-conventional carbon

materials as support allowed studying the inﬂuence of support

properties on the physicochemical properties of catalysts Thus, the

main conclusions obtained from this study are:

- The size and morphology of platinum particles depend on

the nature of the support Higher crystalline grades of the

support are conductive to smaller platinum particle size and

higher crystalline structures, which are associated with a strong

metal–carbon interaction However, the more amorphous the

carbon support, the higher the platinum size and the more dense

the globular morphology These features are associated with a

weak metal–carbon interaction

- The dispersion of metal particles also depends on the

sur-face chemistry of carbon supports For the incipient wetness

impregnation method, the agglomeration of platinum particles

increases as the number of the surface oxygen groups of the

support increases This is attributed to the decomposition of the

less stable surface oxygen groups during the catalyst reduction

stage, which facilitates the mobility of platinum on the

sup-port surface and, thereby favours the agglomeration of platinum

particles

In future work, the electrochemical characterization of

these catalysts will be carried out in order to determine the

effect of the support on the electrochemical performance of catalysts

Acknowledgements

The authors gratefully acknowledge ﬁnancial support given by the Aragón Government under the project PM042/2007 L Calvillo and V Celorrio also acknowledge the Spanish National Research Council and CSIC for their FPI and JAE grants, respectively

References

[1] P.P Edwards, V.L Kuznetsov, W.I.F David, N.P Brandon, Energy Policy 36 (2008) 4356.

[2] B.D McNicol, D.A.J Rand, K.R Williams, J Power Sources 83 (1999) 15 [3] G.J.K Acres, J.C Frost, G.A Hards, R.J Potter, T.R Ralph, Catal Today 38 (1997) 393.

[4] X Yu, S Ye, J Power Sources 172 (2007) 133.

[5] J.-H Wee, K.-Y Lee, S.H Kim, J Power Sources 165 (2007) 667.

[6] A Antolini, Mater Chem Phys 78 (2003) 563.

[7] H Liu, C Song, L Zhang, J Zhang, H Wang, D.P Wilkinson, J Power Sources 155 (2006) 95.

[8] E Auer, A Freund, J Pietsch, T Tacke, Appl Catal A: Gen 173 (1998) 259 [9] G.S Chai, S.B Yoon, J.-S Yu, J.-H Choi, Y.-E Sung, J Phys Chem B 108 (2004) 7074.

[10] E Antolini, Appl Catal B: Environ 88 (2009) 1.

[11] M Kim, J.-N Park, H Kim, S Song, W.-H Lee, J Power Sources 163 (2006) 93.

[12] S.C Hall, V Subramanian, G Teeter, B Rambabu, Solid State Ionics 175 (2004) 809.

[13] M Inoue, S Akamaru, A Taguchi, T Abe, Vacuum 83 (2009) 658.

[14] J.R.C Salgado, F Alcaide, G Álvarez, L Calvillo, M.J Lázaro, E Pastor, J Power Sources 195 (2010) 4022.

[15] Y Shao, G Yin, J Zhang, Y Gao, Electrochim Acta 51 (2006) 5853.

[16] K Wikander, H Ekström, A.E.C Palmqvist, A Lundblad, K Holmberg, G Lind-bergh, Fuel Cells 6 (2006) 21.

[17] D Sebastián, J.C Calderón, J.A González-Expósito, E Pastor, M.V Martínez-Huerta, I Suelves, R Moliner, M.J Lázaro, Int J Hydrogen Energy 35 (2010) 9934.

[18] J.B Joo, P Kim, W Kim, J Yi, J Electroceram 17 (2006) 713.

[19] Ch.-Ch Chien, K.-T Jeng, Mater Chem Phys 99 (2006) 80.

[20] J.R.C Salgado, J.J Quintana, L Calvillo, M.J Lázaro, P.L Cabot, I Esparbé, E Pastor, Phys Chem Chem Phys 10 (2008) 6796.

[21] J Marie, S Berthon-Fabry, P Achard, M Chatenet, A Pradourat, E Chainet, J Non-Cryst Solids 350 (2004) 88.

[22] L Calvillo, M.J Lázaro, I Suelves, Y Echegoyen, E.G Bordejé, R Moliner, J Nanosci Nanotechnol 9 (2009) 4164.

[23] M.J Lázaro, L Calvillo, E.G Bordejé, R Moliner, R Juan, C.R Ruiz, Microporous Mesoporous Mater 103 (2007) 158.

[24] L Calvillo, V Celorrio, R Moliner, P.L Cabot, I Esparbé, M.J Lázaro, Microporous Mesoporous Mater 116 (2008) 292.

[25] M.J Lázaro, L Calvillo, V Celorrio, J.I Pardo, S Perathoner, R Moliner, in: J Sanders Ian, L Peeten Thomas (Eds.), Carbon Black: Production, Properties and Uses, Nova Science Publishers, 2011, p 2.

[26] J.L Figueiredo, M.F.R Pereira, M.M.A Freitas, J.J.M Orfao, Carbon 37 (1999) 1379.

[27] A.E Aksoylu, M Madalena, A Freitas, M.F.R Pereira, J.L Figueiredo, Carbon 39 (2001) 175.

[28] P.V Samant, F Gonc¸alves, M.M.A Freitas, M.F.R Pereira, J.L Figueiredo, Carbon

42 (2004) 1321.

[29] C.A Bessel, K Laubernds, N.M Rodríguez, R.T.K Baker, J Phys Chem B 105 (2001) 1115.

[30] P Serp, M Corrias, P Kalck, Appl Catal A: Gen 253 (2003) 337.

[31] C Prado-Burguete, A Linares-Solano, F Rodríguez-Reinoso, C Salinas-Martínez

de Lecea, J Catal 115 (1989) 98.

[32] L Calvillo, M Gangeri, S Perathoner, G Centi, R Moliner, M.J Lázaro, J Power Sources 192 (2009) 144.

[33] A Sepúlveda-Escribano, F Coloma, F Rodríguez-Reinoso, Appl Catal A: Gen.

173 (1998) 247.

[34] M.C Román-Martínez, D Cazorla-Amorós, A Linares-Solano, C Salinas-Martínez de Lecea, Carbon 33 (1995) 3.

[35] S Litster, G McLean, J Power Sources 130 (2004) 61.

Định dạng
Số trang	7
Dung lượng	1,92 MB