Optimizacion de Cantidad de Nafion

8/10/2019 Optimizacion de Cantidad de Nafion

1/10

Optimization of the amount of Nafion in multi-walled carbon

nanotube/Nafion composites as Pt supports in gas diffusion

electrodes for proton exchange membrane fuel cells

Hussein Gharibi a,*, Masoumeh Javaheri a, Mehdi Kheirmand b, Rasol Abdullah Mirzaie c

a Department of Chemistry, Faculty of Science, Tarbiat Modares University, P.O. Box 14115-175 Tehran, IranbDepartment of Chemistry, Faculty of Science, Yasouj University, Yasouj, Iranc Department of Chemistry, Faculty of Science, Shahid Rajaee University, Tehran, Iran

a r t i c l e i n f o

Article history:

Received 20 June 2010

Received in revised form

11 August 2010

Accepted 2 September 2010

Available online 8 October 2010

Keywords:

Catalyst layer (CL)

Gas diffusion electrode (GDE)Oxygen reduction reaction (ORR)

Proton exchange membrane fuel cell

(PEMFC)

Pt support

a b s t r a c t

The Nafion loading in multi-walled carbon nanotube (MWCNT) composites with Nafion

used as Pt support in the oxygen reduction reaction (ORR) has been studied. We varied the

amount of Nafion in these composites and added a Pt loading of 0.3 mg cm2 to the catalyst

layer. The performance of these electrodes in the ORR was measured with linear sweep

voltammetry (LSV), electrochemical impedance spectroscopy (EIS), chronoamperometry,

inductive coupled plasma (ICP), X-ray diffraction (XRD), transmission electron microscopy

(TEM), and scanning electron microscopy (SEM). In addition, we compared the performance

of the MWCNTs as Pt supports with those of the composites. Our results indicate that the

composites are better Pt supports in comparison with MWCNT.

Copyright 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rightsreserved.

1. Introduction

Carbon nanotubes possess a wide variety of remarkable

properties, most notably high electrical and thermal conduc-

tivities, mechanical strength, and large catalytic surface areas,and thus have potential uses in a variety of power generation

and storage devices, including proton exchange membrane

fuel cells (PEMFCs)[1].

Composite electrodes consisting of Pt nanoparticles sup-

ported on multi-walled carbon nanotubes grown directly on

carbon paper (Pt/MWCNTs/carbon paper) have previously

been synthesized by using glacial acetic acid as a reducing

agent [2]. Leeand Hu have successfully developed a simple but

effective method for grafting various chemical reagents onto

the opposite tube-ends of individual carbon nanotubes, as

confirmed with X-ray photoelectron spectroscopy measure-

ments. This approach could be used in the site-selective self-

assembly of both MWCNTs and single-walled carbon nano-tubes (SWCNTs) into a large variety of novel functional

systems with highly controllable structures and various

applications [3,4]. Tang and Wu presented a detailed

comparison of MWCNTs and SWCNTs in an effort to identify

the better supporting carbon material for electrocatalysts in

direct methanol fuel cells (DMFCs)[5,6]. Salvetat et al. found

that the mechanical properties of nanotubes are strongly

dependent on their structures; various types of nanotubes

* Corresponding author.E-mail addresses:[email protected],[email protected](H. Gharibi).

A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m

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 / h e

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 6 ( 2 0 1 1 ) 1 3 3 2 5 e1 3 3 3 4

0360-3199/$ e see front matter Copyright 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

doi:10.1016/j.ijhydene.2010.09.008
mailto:[email protected]:[email protected]://www.sciencedirect.com/http://www.elsevier.com/locate/hehttp://dx.doi.org/10.1016/j.ijhydene.2010.09.008http://dx.doi.org/10.1016/j.ijhydene.2010.09.008http://dx.doi.org/10.1016/j.ijhydene.2010.09.008http://dx.doi.org/10.1016/j.ijhydene.2010.09.008http://dx.doi.org/10.1016/j.ijhydene.2010.09.008http://dx.doi.org/10.1016/j.ijhydene.2010.09.008http://www.elsevier.com/locate/hehttp://www.sciencedirect.com/mailto:[email protected]:[email protected]


2/10


3/10

ionomer increases the size of the three-dimensional zone of

catalytic activity and the platinum utilization in the electrode,

and also helps to retain moisture and prevent membrane

dehydration, especially at high current densities. The Nafioncontent in the electrode must be optimized to achieve high

performance. As the platinum loading increases, the electrode

thickness and the Nafion thickness increase, and hence the

optimum Nafion content can depend on the platinum loading

[23e27]. Electrodes with Pt/CNT catalysts sulfonated through

the in situ radical polymerization of 4-styrenesulfonate have

been found to exhibit better performance than their unsulfo-

nated counterparts, mainly because of the easier access for

protons and the well-dispersed distribution of the sulfonated

Pt/CNT catalysts; thus sulfonation improves performance and

reduces the cost of Pt/CNT-based PEMFCs. A half-MEA with an

active area of 1.0 cm 1.0 cm was fabricated by employing

a Nafion 115 membrane and an in-house CNT-based gasdiffusion electrode (GDE) with a platinum loading of approx.

0.05 mg cm2; Nafion electrolytes were not used [28]. In

a previous study [29,30], we prepared a catalyst layer con-

taining a PANIeNafion composite.

In this paper, we introduce a new method for the prepa-

ration of MWCNT/Nafion composites, and our results with

this method are compared with those of other methods. The

main distinguishing feature of this method is in the timing of

the addition of the Nafion solution to the MWCNTs. The

effects of varying the Nafion loading in the catalyst layer on

the electrode performance and the Pt surface area were

investigated; for this purpose we fabricated four electrodes

with different amounts of Nafion (0.5, 0.75, 1, and1.25mgcm2). The performance of these electrodes in the ORR

was compared with that of an electrode with MWCNTs as a Pt

support and a Nafion loading of 1 mg cm2. Furthermore, the

electrodes were characterized with cyclic voltammetry (CV),

linear sweep voltammetry (LSV), electrochemical impedance

spectroscopy (EIS), chronoamperometry, scanning electron

microscopy (SEM), transmission electron microscopy (TEM),

and X-ray diffraction (XRD). The new method was found to

result in better performance and lower resistance.

2. Experimental

2.1. Composite preparation

In this research, we fabricated four composites with various

amounts of Nafion. Since MWCNTs are chemically inert, the

MWCNTs (20e30 nm Aldrich) were functionalized by pre-

treatment with 70% nitric acid in order to introduce surface

oxides before preparation of the composites[3,4,15,18]. In our

Fig. 4 e XRD patterns of GDE1, GDE2, GDE3, GDE4, and GDE5.

Fig. 5e Cyclic voltammetry curves for the GDEs for a scan

rate of 50 mV sL1.

Fig. 6 e IeVcurves of the GDEs in the ORR for a scan rate of

1 mV sL1 at 25 C.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 6 ( 2 0 1 1 ) 1 3 3 2 5 e1 3 3 3 4 13327
http://dx.doi.org/10.1016/j.ijhydene.2010.09.008http://dx.doi.org/10.1016/j.ijhydene.2010.09.008http://dx.doi.org/10.1016/j.ijhydene.2010.09.008http://dx.doi.org/10.1016/j.ijhydene.2010.09.008


4/10

study, the MWCNTs were refluxed under constant agitation at

120 C in concentrated nitric acid for 12 h. The solid phase was

removed by filtration and washed with distilled water, and the

recovered functionalized MWCNTs were then dried at 80 C

for 12 h.

The composites were prepared from the dried samples and

Nafion solution (5% from Aldrich). Mixtures of functionalized

MWCNTs and various amounts of Nafion solution in 2-prop-anol (Merck), water, and glycerol (Merck) were sonicated for

20 min with a sonicator (Misonix model S-3000) to prepare

homogeneous suspensions; these suspensions were dried at

70 C.

Four MWCN/Nafion composites were prepared, each con-

taining a different amount of Nafion. The resulting electrodes

contained 0.5, 0.75, 1, and 1.25 mg cm2 of Nafion in the

catalyst layer and were named GDE1, GDE2, GDE3, and GDE4,

respectively.

2.2. Preparation of Pt/MWCNT and Pt/composite

(Nafione

MWCNT)

In this step, Pt was deposited on the MWCNT/Nafion

composites. One additional electrode named GDE5 in which Pt

was deposited on functionalized MWCNTs was prepared.

The MWCNT/Nafion composites for GDE1eGDE4 and the

functionalized MWCNTs for GDE5 were vigorously mixed with

H2PtCl6 solution in a 2-propanol (Merck) and water (1:3 v/v)

solvent mixture at 50 C for 6 h. These suspensions were then

heated to 80 C, and the pH of each suspension was adjusted

to 8.5 with a 0.5 M Na2CO3solution. An abundant amount of

sodium formate (HCOONa) [Merck] was added to perform

a chemical reduction for 2 h. Each suspension was then

filtered, washed, and dried at 90 C for 4 h. Our ICP results

indicated that the samples contained 6.7 wt.% Pt, and so GDEs

could be prepared from the Pt/functionalized MWCNTs and

the Pt/MWCNT/Nafion composites.

2.3. Fabrication of the GDEs

For the diffusion layer, a mixture of 30 wt.% PTFE and 70 wt.%

Vulcan in 2-propanol (Merck), water, and glycerol (Merck) was

sonicated for 20 min with a sonicator (Misonix model S-3000)

to produce a homogeneous suspension. The suspension was

rolled onto the carbon paper (TGPH-0120T) (Toray), and the

electrode was dried in air at 120 C for 1 h and then finally

sintered at 340 C for 30 min. The loading of Nafion in the

diffusion layer was fixed at 1 mg cm2 [31,32].

To prepare the catalyst layers in GDE1eGDE4, a homoge-

neous suspension containing the desired amounts of the

Pt-MWCNT/Nafion composite (6.7 wt.%), glycerol (Merck),2-propanol (Merck), and water was sonicated for 20 min. This

suspension was rolled onto the diffusion layer; the electrode

was then dried at 40 C for 30 min and then at 80 C for 30 min.

The Pt loading was 0.3 mg cm2.

To prepare the catalyst layer of GDE5, a homogeneous

suspension containing the desired amounts of Pt/MWCNT

(6.7 wt.%), Nafion solution (5% from Aldrich) in glycerol,

2-propanol, water, and glycerol was sonicated for 20 min. This

suspension was rolled onto the diffusion layer; the electrode

was dried at 40 C for 30 min and then at 80 C for 30 min. The

Pt loading was 0.3 mg cm2.

2.4. Electrochemical measurements

An EG&G Princeton Applied Research Model 273A instrument

was used to determine the electrochemical properties of the

electrodes. The performances of the porous GDEs (geometric

exposed area 1 cm2) in the reduction of oxygen were investi-

gatedin2MH2SO4. All measurements were performed at 25 C

in a conventional three-electrode cell, with O2 flowing at

50 mL min1. The GDEs were mounted into a Teflon holder

that contains a pyrolytic graphite disk as a current collector

and has provision for feeding oxygen from the back of the

Fig. 7 e Graphical representation of the Nafion ionomer

position in catalyst layer.

Fig. 8 e Chronoamperograms of the GDEs in the presence

of O2, E [0.4 V vs. Ag/AgCl, at 25 C, not stirred the

solution.



5/10

electrode. A large area platinum flat electrode was used as

the counter electrode. An Ag/AgCl reference electrode was

placed close to the working electrode surface. A rotating disk

electrode immersed in 2 M H2SO4 with a rotation rate of

1500 rpm was used to perform cyclic voltammetry. The elec-

trochemical cell was connected to a potentiostategalvanostat

(EG&G Model 273A) for IeV polarization measurements and

chronoamperometry, and to a frequency response detector(model 1025) for electrochemical impedance spectroscopy. In

order to perform a quantitative evaluation of resistance

against the ORR, the AC impedance method was used. In the

Nyquist plot of the semicircle diameter,Rpis the polarization

resistance and the sum of the electrode and electrolyte

resistance that was subtracted for these GDEs. The polariza-

tion resistance is the sum of two terms: the charge transfer

and diffusion resistances. Impedance measurement was

investigated in 0.4 V vs. Ag/AgCl potential for obtaining Rp.

This potential is in ohmic resistance region. The AC potential

amplitude was 5 mV, and the frequency range was

10 kHze0.1 Hz. We used impedance measurements to char-

acterize the ionic resistances of the electrodes. At lowfrequencies, a Warburg-like response (45 slope) is observed,

which indicates the occurrence of ion migration through the

Nafion membrane and catalyst layer. The ionic resistance Rioncan be obtained from the length of the Warburg-like region

projected onto the real impedance (Zreal) axis [33,34,35]. For

obtainingRion, the impedance measurement has been inves-

tigated in OCV potential and experimental complex-plane

impedance plots (10 kHze0.1 Hz) for Argon-bathed are shown

inFig. 3.

2.5. Measurements of the physical properties of the

electrodes

A scanning electron microscope (Model XL30, Philips co.) was

used after coating the electrodes surfaces with gold, a trans-

mission electron microscope (TEM/STEM CM Philips 200) was

used to produce the TEM images, and XRD analysis was

carried out for the catalysts by using an XPERT MPD Philips

diffractometer with a Cu X-ray source operating at 40 kV and

40 mA. The XRD patterns were obtained at a scanning rate of

1/min with a step size in the 2q scan of 0.02 in the range

20e100.

The amount of Pt reduced on each support was determined

by using the inductive coupled plasma (ICP) technique (ICP-

OES, Varian Vista-PRO, Australia); for these measurements we

dissolved 5 mg of each sample (synthesized Pt on the

supports) and standard samples (Pt/C 10% and 20% wt) ina mixture of hydrochloric acid and nitric acid (3/1). These

solutions were refluxed at 70 C and then used in the ICP

measurements.

3. Results and discussion

The GDEs (1e5) were prepared with different amounts of

Nafion, as explained inExperimental sectionandTable 1. The

results are shown inFigs. 1e16and inTable 2.

The ICP results indicate that the Pt loading in these GDEs is

0.3 mg cm2 (Fig. 1).

As mentioned above, there are three participants in elec-

trochemical reactions: gases, electrons, and protons. The

reactions can only take place on portions of the catalyst

surface to which all three participants have access. The elec-

trons travel through the electrically conductive solids,

including the catalyst itself, so it is important that the catalyst

particles are electrically connected in some way to the

substrate. Protons travel through the ionomer, so the catalyst

mustalso be in intimate contact with the ionomer. Finally, the

reactant gases travel only through voids, so the electrode

must be sufficiently porous to allow gases to travel to the

reaction sites. At the same time, product water must be

effectively removed or the electrode will flood and prevent

oxygen access. The reactions take place at a three-phase

boundary between ionomer, solid, and empty space[32].

3.1. AC impedance spectroscopy

To gain more information about the GDEs (GDE1eGDE5), the

a.c. impedance spectrum of each electrode was obtained. The

Fig. 9e SEM image of the catalyst layer of GDE1

(0.5 mg cmL2 Nafion in a MWCNT/Nafion composite) at

a magnification of 15,0003.






6/10

resulting data were obtained at 400 mV vs. Ag/AgCl saturated

with KCl, and were plotted in the Nyquist representation. The

polarization resistance Rp was found to be lower for GDE3,

which contains 1 mg cm2 Nafion in the catalyst layer, than

for the other GDEs. Although the impedance spectra have

similar semi-circularshapes, the diameters of the semi-circles

differ significantly. As shown in Fig. 2, theresistancesof GDE1,

GDE2, and GDE4 are too high in comparison with those of theother electrodes. When the amount of Nafion in the GDEs is

increased from 0.5 to 0.75, the resistance of the electrode

decreases. However, upon an additional increase in the

amount of Nafion, a high resistance is observed, i.e., in GDE4.

The high resistance of this electrode is due to an excess of

Nafion in the catalyst layer. Therefore, we should optimize the

amount of Nafion in the GDEs. One approach is to suggest that

the optimum value of the amount of Nafion arises for the GDE

with the lowest resistance, so GDE3 is then the best electrode.

In the case of GDE5, the ionomer blocks the catalyst sites, so

the resistance of electrode GDE5 is higher than that of GDE3.

The ionic resistance or proton transport of each GDE was

determined by using a half-cell assembly in a conventionalthree-electrode system; the working electrode contained

carbon paper, MPL, catalyst layer, and a Nafion 112

membrane. The results are shown inFig. 3andTable 2: GDE3

has the lowest ionic resistance, which is attributed to its

optimum three-phase zone.

3.2. XRD pattern of platinum

Fig. 4 shows the XRD patterns of the Pt/MWCNT and Pt-

MWCNT/Nafion composite nanocatalysts. The peak at

2q 26.5 corresponds to the (002) planes of the graphitized

MWCNTs and the peaks at 2q 39.8

, 67.5

, and 46.2

areassociated with the (111), (220), and (200) planes of fcc (face

centered cubic) Pt, respectively. These results indicate that Pt

has been successfully reduced. The average sizes of the Pt

particles were calculated from the line broadening of the (111)

peak by using the Scherrer equation after background

subtraction and found to be 0.76, 3.57, 3.59, 1.64, and 0.75 nm

for the five samples, respectively (Table 2).

d 0:9lB2qcosq

(1)

wheredis the average particle size, lis the wavelength of the

X-ray (1.54056 A), q is the angle at the maximum of the peak,

andB2qis the width of the peak at half-height. This variation

in the crystal size of Pt arises because the support of Pt in each

sample is different.These results show that Nafion plays an important role

during the synthesis and that varying the concentration of

Nafion has someinfluence on the formation of the Pt particles,

i.e., the concentration of Nafion influences the reduction of

platinum on the surface of the MWCNTs. In the preparation of

GDE5, the Pt nuclei grew as soon as the reducing agents,

sodium formate (HCOONa), was added to the mixture, i.e.,

before they were covered with Nafion. This growth resulted in

the inferior performance of GDE5 in comparison with those of

GDE2 and GDE3 since some of its Pt particles were masked by

Nafion, which was added to this mixture after the coating of

Pt onto the MWCNT support. Since the Pt particles are covered

with Nafion, the concentration of exposed Pt on the surfaceof the MWCNT support is reduced; therefore, the performance

of GDE5 decreases. This conclusion is verified by the XRD

pattern for GDE3 (seeFig. 4).

3.3. Electroactive surface area (EAS)

The cyclic voltammograms for GDEl, GDE2, GDE3, GDE4, and

GDE5 are shown inFig. 5. The coulombic charge for hydrogen

desorption was used to calculate the electroactive surface

area (EAS) of each electrode (Table 2)[36]:

EAS Qh0:21 Pt (2)

where Qh is the charge forhydrogen desorption (mC cm2)and

[Pt] is the platinum loading (mg cm2) and 0.21 (mC cm2) is

the charge required to oxidize a monolayer of H2on bright Pt.

The roughness factor (Rf) can then be calculated by using the

following equation:


(1 mg cmL2 Nafion in a MWCNT/Nafion composite) at







7/10


8/10

3.5. Chronoamperometry

The diffusion coefficients of O2in the GDEs were determined

with chronoamperometry. For large electrodes, the informa-

tion obtained was limited by the Cottrellian decay with time.

According to Winlove et al. [38], the time window for these

experiments follows the relation 1 > s1/2 > 0.5, where s isa dimensionless parameter equal to 4Dt/r2. The Cottrell [39]

equation is:

i nFAD=pt1=2C) (6)

where i is the limiting current (mA), n the number of electrons,

Fis the Faraday constant (96485 C mol1),Ais the surface area

of the electrode (cm2),Dis the diffusion coefficient (cm2 s1),t

is the time (s), and C*is the concentration of the reactant.

The highest value of the permeability (D1/2 C*) was

obtained for GDE3 (Fig. 8andTable 2). This result is consistent

with the enhancement of the diffusion of oxygen in the

reaction layer of this MWCNT/Nafion composite due to its

optimum level of Nafion.

3.6. SEM and TEM results

The electrode layer is composed of Pt agglomerates and

a Nafion film. The catalytic layer usually has a dual pore

distribution: micro pores are present in the agglomerates,

and macro pores are located between the agglomerates. The

Nafion is likely to be localized in the macro pores in contact

with the Pt agglomerates. A further complication arises

because reactant diffusion does not often occur in the

gaseous phase through the electrode; instead, the reactant

dissolves in the electrolyte and then diffuses into the solu-

tion. In this model, we expect that the reaction of oxygen

(electro-reduction) is controlled by the following transport

processes: (1) oxygen diffusion into the pore space of the

electrode and dissolution into Nafion; (2) oxygen diffusion

through the Nafion layer; and (3) proton transfer in the

Nafion layer. We carefully controlled the fabrication process

to prevent the effect of fabrication process on the Pt

morphology. We emphasize that the loading of Nafion varies

in the GDEs (GDE1eGDE4), which means that the

morphology of the reduced Pt particles will vary from

support to support, as shown by the XRD results ( Fig. 4).

Fig. 15e TEM image of the catalyst layer of GDE3

(1 mg cmL2 Nafion in a MWCNT/Nafion composite).

Fig. 16e TEM image of the catalyst layer of GDE5

(1 mg cmL2 Nafion).

Table 2 e Tafel slopes, current densities, permeabilities, charge transfer resistances, ionic resistances, electroactive surfaceareas, and roughness factors of the GDEs.

GDE b(mV dec1)

i 104

at 0.9 V (A cm2)(D1/2 C*) 109

(mol cm2 s1/2)EAS

(m2 g1)Rf Rp( ohm) Rion/3 (ohm) d(nm)

1 71 11.3 11.9 15.4 51 1.4 66.7 0.76

2 73 15.1 28.0 39.7 132 1.2 10.9 3.57

3 70 16.8 32.1 44.1 147 0.8 5.3 3.59

4 86 10.4 11.5 22.4 74 1.3 64.6 1.64

5 75 13.7 24.0 36.6 122 1.3 31.0 0.75



9/10

Therefore, a low Nafion content (less than 0.75 mg cm2) is

not desirable since good contact between the catalyst, elec-

trolyte, and reagents is reduced; without such contact the

integrity of the catalyst layer and the membrane, and the

proton conductivity are insufficient. At high ionomer load-

ings (1.25 mg cm2, GDE4), the proton conductivity is

enhanced, but the catalyst active area is then expected to be

limited (Table 2) by the formation of a thick Nafion layer onthe catalyst surface, which then reduces the electro-

conductivity of the Pt layer. We also note that the mechan-

ical integrity of the catalyst layer is insufficient for Nafion

contents below 0.75 mg cm2, which means that the incor-

porated Nafion cannot properly bind the catalyst particles.

At a Nafion content of 1.25 mg cm2, as in GDE4 which

exhibits reduced performance, the thick Nafion layer

reduces the catalyst active area in spite of the enhanced

proton conductivity in the catalyst layer. On the basis of our

results, a Nafion content of 1 mg cm2 (GDE3) optimizes

proton transfer within the catalyst layer without limiting

oxygen diffusion.Figs. 9e13show that the number and size

of the pores are different in each catalyst. Thus the numberand the size of the pores in GDE3 have optimum values,

which improve its performance in the ORR. As we expected,

Fig. 13shows that the Pt/MWCNT surface is covered by the

Nafion ionomer; this means that some active sites are

blocked and the performance of GDE5 in the ORR is inferior

to that of GDE3.

TEM images of GDE2, GDE3, and GDE5 are shown in Figs.

14e16; these images confirm the details of the above

discussion.

4. Conclusion

The influence of the Nafion loading in the catalyst layer

on electrode performance was studied; four different

GDEs were prepared by using MWCNT-Nafion composites

(with varying amounts of Nafion) as Pt supports, and the

performances of these GDEs and of Pt/MWCNT were

compared.

A simple, fast, and energy-efficient method for the prepa-

ration of Pt/MWCNTeNafion composites and Pt/MWCNT

catalysts with high electrocatalytic activity was developed.

We have shown that thetiming of the addition of Nafion to the

catalyst layer is very important and prepared an electrode

(GDE3) that exhibits excellent performance in the ORR. Our

XRD results indicate that the Pt particles were reducedsuccessfully onto the MWCNT-Nafion composites and onto

the MWCNTs, and that the particle sizes were in the range

0.75e3.59 nm. The results for the electrochemical parameters,

such as the current density at 0.9 V, the polarization resis-

tance, and the permeability, indicate that the coating of Pt

with the optimized content of Nafion (namely the GDE3

MWCNT-Nafion composite) exhibits better performance in

the ORR than Pt on MWCNTs and the other electrodes (GDE1,

GDE2, GDE4). The superior performance of this electrode can

be attributedto better reactant accessibility to the three-phase

zone. The present technique can be used as a general method

for the preparation of supported metal particles from metal

precursors.

Appendix. Nomenclature

A geometricarea of electrode

b Tafel slope

B2q width of the peak at half-height

C* concentration of the reactantd average particle size

D diffusion coefficient

D1/2 C*permeability

EAS electroactive surface area

Eeq open-circuit voltage

F Faraday constant

i current density

io exchange current density

MEA membrane electrode assembly

MPL micro pore layer

n number of electrons

OCV open-circuit voltage

Rp polarization resistanceRf roughness factor

S catalyst surface area

t time

h over-potential

q angle at the maximum of the peak

l wavelength of the X-ray

r density

r e f e r e n c e s

[1] Landi BJ, Raffaellea RP, Heben MJ, Alleman JL, VanDerveer W,Gennett T. Development and characterization of single wallcarbon nanotubeeNafion composite actuators. Mater Sci EngB 2005;116:359.

[2] Saha MS, Li R, Sun X. High loading and monodispersed Ptnanoparticles on multiwalled carbon nanotubes for highperformance proton exchange membrane fuel cells. J PowerSources 2008;177:314.

[3] Hu CG, Wang WL, Liao KJ, Liu GB, Wang YT. Systematicinvestigation on the properties of carbon nanotubeelectrodes with different chemical treatments. J Phys ChemSolids 2004;65:1731.

[4] Lee KM, Li L, Dai L. Asymmetric end-functionalization ofmulti-walled carbon nanotubes. J Am Chem Soc 2005;127:4122.

[5] Tang H, Chen J, Yao S, Nie L, Kuang Y, Huang Z, et al.Deposition and electrocatalytic properties of platinum onwell-aligned carbon nanotube (CNT) arrays for methanoloxidation. Mater Chem Phys 2005;92:548.

[6] Wu G, Xu BQ. Carbon nanotube supported Pt electrodes formethanol oxidation: a comparison between multi- andsingle-walled carbon nanotubes. J Power Sources 2007;174:148.

[7] Salvetat J, Bonard P, Thomson MJ, Kulik AJ, Forro L, Benoit W,et al. Mechanical properties of carbon nanotubes. Appl PhysA 1999;69:255.

[8] Wang C, Waje M, Wang X, Tang JM, Haddon RC, Yan Y.Proton exchange membrane fuel cells with carbon nanotubebased electrodes. Nano Lett 2004;4(2):345.

[9] Shao Y, Yin G, Wang J, Gao Y, Shi P. Multi-walled carbon

nanotubes based Pt electrodes prepared with in situ ion



10/10

exchange method for oxygen reduction. J Power Sources2006;161:47.

[10] Wang JJ, Yin GP, Zhang J, Wang ZB, Gao YZ. High utilizationplatinum deposition on single-walled carbon nanotubes ascatalysts for direct methanol fuel cell. Electrochim Acta 2007;52:7042.

[11] Kim H, Jeong NJ, Lee SJ, Song KS. Electrochemical depositionof Pt nanoparticles on CNTs for fuel cell electrode. Korean

J Chem Eng 2008;25(3):443.[12] Rajalakshmi N, Ryu H, Shaijumon MM, Ramaprabhu S.

Performance of polymer electrolyte membrane fuel cellswith carbon nanotubes as oxygen reduction catalyst supportmaterial. J Power Sources 2005;140:250.

[13] Wang M, Woo KD, Kim DK. Preparation of Pt nanoparticleson carbon nanotubes by hydrothermal method. EnergConvers Manage 2006;47:3235.

[14] Liu JM, Meng H, Li J, Liao SJ, Bu JH. Preparation of highperformance Pt/CNT catalysts stabilized byethylenediaminetetraacetic acid disodium salt. Fuel Cells2007;07(5):402.

[15] Hu CG, Wang WL, Wang SX, Zhu W, Li Y. Investigation onelectrochemical properties of carbon nanotubes. Diam RelatMater 2003;12:1295.

[16] Tsai MC, Yeh TqK, Tsai CH. Electrodeposition ofplatinumeruthenium nanoparticles on carbon nanotubesdirectly grown on carbon cloths for methanol oxidation.Mater Chem Phys 2008;109:422.

[17] Weissmann M, Coutanceau C, Brault P, Leger JM. Directchemical deposition of platinum on ionic conductivemembranes and evaluation of the electrocatalytic activity.Electrochem Commun 2007;9:1097.

[18] Guo DJ, Li HL. Electrochemical synthesis of Pdnanoparticles on functional MWNT surfaces. ElectrochemCommun 2004;6:999.

[19] Guo Z, Dong S. Electrogenerated chemiluminescence fromRu(Bpy)3 2ion-exchanged in carbon nanotube/perfluorosulfonated ionomer composite films. Anal Chem2004;76:2683.

[20] Ambrosio EP, Francia C, Manzoli M, Penazzi N, Spinelli P.Platinum catalyst supported on mesoporous carbon forPEMFC. Int J Hydrogen Energy 2008;33:3142.

[21] Passalacqua E, Lufrano F, Squadrito G, Patti A, Giorgi L.Nafion content in the catalyst layer of polymer electrolytefuel cells: effects on structure and performance. ElectrochimActa 2001;46:799.

[22] Kim KH, Lee KY, Kim HJ, Cho EA, Lee SY, Lim TH, et al. Theeffects of Nafion ionomer content in PEMFC MEAs preparedby a catalyst-coated membrane (CCM) spraying method. Int

J Hydrogen Energy 2010;35:2119.[23] Cheng CH, Lin HH, Lai GJ. Numerical prediction of the effect

of catalyst layer Nafion loading on the performance of PEMfuel cells. J Power Sources 2007;164:730.

[24] Qi Z, Kaufman A. Low Pt loading high performance cathodesfor PEM fuel cells. J Power Sources 2003;113:37.

[25] Antolini E, Giorgi L, Pozio A, Passalacqua E. Influence ofNafion loading in the catalyst layer of gas-diffusionelectrodes for PEFC. J Power Sources 1999;77:136.

[26] Boyer C, Gamburzev S, Velev O, Srinivasan S, Appleby AJ.Measurements of proton conductivity in the active layer ofPEM fuel cell gas diffusion electrodes. Electrochim Acta 1998;

43(24):3703.[27] Sasikumar G, Ihm JW, Ryu H. Optimum Nafion content in

PEM fuel cell electrodes. Electrochim Acta 2004;50:601.[28] Du CY, Zhao TS, Liang ZX. Sulfonation of carbon-nanotube

supported platinum catalysts for polymer electrolyte fuelcells. J Power Sources 2008;176:9.

[29] Gharibi H, Zhiani M, Mirzaie AR, Kheirmand M, Entezami AA,Kakaei K, et al. Investigation of polyaniline impregnation onthe performance of gas diffusion electrode (GDE) in PEMFCusing binary of Nafion and polyaniline nanofiber. J PowerSources 2006;157:703.

[30] Gharibi H, Zhiani M, Entezami AA, Mirzaie RA, Kheirmand M,Kakaei K. Study of polyaniline doped with trifluoromethanesulfonic acid in gas-diffusion electrodes for proton-exchangemembrane fuel cells. J Power Sources 2006;155:138.

[31] KheirmandM, Gharibi H, Mirzaie RA,Faraji M,Zhiani M. Studyof the synergism effect of a binary carbon system in thenanostructure of the gas diffusion electrode (GDE) of a protonexchange membrane fuel cell. J Power Sources 2007;169:327.

[32] Barbir F. PEM fuel cells: theory and practice. Elsevier Inc;2005. p 93.

[33] Lefebvre MC, Martin RB, Pickup PG. Characterization of ionicconductivity profiles within proton exchange membrane fuelcell gas diffusion electrodes by impedance spectroscopy.Electrochem Solid-State Lett 1999;2(6):259.

[34] Qi Z, Lefebvre MC, Pickup PG. Electron and proton transportin gas diffusion electrodes containing electronicallyconductive proton-exchange polymers. J Electroanal Chem1998;459:9.

[35] Saab AP, Garzon FH, Zawodzinski TA. Determination of

ionic and electronic resistivities in carbon/polyelectrolytefuel-cell composite electrodes. J Electrochem Soc 2002;149(12):1541.

[36] Pozio A, Francesco MD, Cemmi A, Cardellini F, Giorgi L.Comparison of high surface Pt/C catalysts by cyclicvoltammetry. J Power Sources 2002;105:13.

[37] Bockris JOM. Modern electrochemistry. 2nd ed. Plenum;2000. p. 1054.

[38] Winlove CP, Parker KH, Oxenham RKC. The measurement ofoxygen diffusivity and concentration bychronoamperometry using microelectrodes. J ElectroanalChem 1984;170:293.

[39] Wang J. Analytical electrochemistry. 2nd ed. Wiley;2000. p 60.


Optimizacion de Cantidad de Nafion

Documents

Transcript of Optimizacion de Cantidad de Nafion