gas diffusion layer electrode for PEM fuel cell

gas diffusion layer electrode for PEM fuel cell

Applied Surface Science 257 (2011) 10408–10413 Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/...

664KB Sizes 0 Downloads 24 Views

Applied Surface Science 257 (2011) 10408–10413

Contents lists available at ScienceDirect

Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc

Electrocatalysis of oxygen reduction reaction on Nafion/platinum/gas diffusion layer electrode for PEM fuel cell Sekineh Chabi a,∗ , Mehdi Kheirmand b a b

Fuel Cell and Surfactant Lab., Dep. of Chemistry, School of Science, Tarbiat Modares University, Tehran, Iran Department of Chemistry, School of Science, Yasouj University, Yasouj, Iran

a r t i c l e

i n f o

Article history: Received 16 November 2010 Received in revised form 3 June 2011 Accepted 20 June 2011 Available online 23 July 2011 Keywords: Platinum Electroless plating Oxygen reduction reaction Nafion membrane Gas diffusion electrode Proton exchange membrane fuel cell

a b s t r a c t In this work a new membrane electrode based on Pt-coated Nafion membrane was fabricated. Chemical deposition process was used to coat platinum on Nafion 117 membrane and then Pt-coated Nafion membrane was hot pressed on gas diffusion layer (GDL) to make new membrane electrode. The electrochemical and chemical studies of the Pt-coated Nafions were investigated by electrochemical techniques, X-ray diffraction and scanning electron microscopy. The electrochemical results indicated that as the concentration of H2 PtCl6 increased, the oxygen reduction reaction rate increased until the concentration was reached where the reduction reaction was limited by the problem of mass transport. The electrochemical results for oxygen reduction reaction showed that the new electrode which prepared by plating Nafion membrane with 0.06 M H2 PtCl6 in electroless plating solution, has a higher performance than other electrodes. The XRD results showed that the average platinum particle size of the best sample was about 3 nm. The loading of platinum for this electrode was 0.153 mg cm−2 . © 2011 Elsevier B.V. All rights reserved.

1. Introduction Proton exchange membrane fuel cells (PEMFCs) have attracted strong attention as next-generation power sources for portable and residential applications. The most important advantages of PEMFCs are zero or low noxious emission of environmental pollutant, quick start up, high power density, low operation temperature, and low noise [1–4]. However, PEMFCs must overcome economics obstacles to become commercially viable [5]. For the PEMFCs, the cost of platinum catalyst has always hindered their commercialization. The kinetic of oxygen reduction reaction in the PEMFC requires the precious platinum catalyst due to its lower activity [6,7]. Since platinum is a very rare and expensive metal, it is necessary to have low platinum in the electrode [8,9]. In addition to the high cost of platinum, the problem related to the thick catalyst layer was another reason to fabricate new MEA with low loading of platinum. It was found that high loading of platinum causes increment in the resistance of the membrane [10]. Catalyst layer with shorter thickness produce better performance due to lower diffusion barriers and better catalyst addition [11]. To minimize the loading of expensive catalytic metal, one general approach has been to use smaller catalyst particles. However, long operational lifetimes are particularly difficult to achieve with lower catalyst loadings. Also, catalyst

∗ Corresponding author. E-mail address: s [email protected] (S. Chabi). 0169-4332/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2011.06.104

particle size may be unstable and increases by agglomeration or sintering [12,13]. To alleviate these impediments, we developed a new approach to design the low-Pt electrocatalysts for the cathode. This approach involves pressing Pt-coated Nafion membrane on diffusion layer to prepare new membrane electrode with low platinum loading. The Pt deposition of the cation-exchange membranes was achieved by the several methods for example, mechanically pressing, electrochemical deposition, chemical reduction and impregnation-reduction method [14–16]. The chemical deposition method and the impregnation-reduction method are both electroless deposition method [17]. The method of electroless deposition involves the deposition of a metallic coating from an aqueous bath onto a substrate by a controlled chemical reduction reaction which is catalyzed by the metal or alloy being deposited or reduced. The basic electroless deposition process is an electronic exchange [13]. In particular, after a substrate is immersed in the plating bath, the substrate surface catalyzes oxidation of the reducing agent. This oxidation causes a release of electrons that, in turn, reduce metal platinum ions in the bath at the substrate surface. These reduced metal ions are then deposited onto the substrate and, over time, generate a metal shell around the substrate [13]. The main advantages of electroless deposition are the deposition selectivity, high metal purity, low operating temperature, planar topography, good working characteristics, low cost, simplicity and applicability for mass production [14,18–20].

S. Chabi, M. Kheirmand / Applied Surface Science 257 (2011) 10408–10413

It was demonstrated that variables such as membrane modification and the use of surfactant, different reducing agents and applied external activation during the deposition process [18], play important roles in the modification of the morphology of the Pt deposition, improvement in the catalytic activity of the Pt deposition and optimization of the Pt deposition of cation-exchange membranes [16,20]. The electroless reduction of platinum salts has been already used, for example, for the deposition on Ti, Si, SnO2 substrate, aluminum electrode and Nafion membrane [14,15,21,22]. Takenaka and co-workers was first reported a chemical reduction route, to deposit platinum on Nafion membrane. In this method, solutions of platinum anions, such as chloroplatinate (PtCl6 2− ), and a reducing agent, typically tetrahydroborate ion (BH4 − ), are exposed to opposite sides of a stationary SPE (solid polymer electrolyte) membrane [15]. Fedkiw and Her used impregnation-reduction method, to prepare platinum-coated Nafion membrane. In this method Nafion was impregnated with Pt(NH3 )4 Cl2 before reducing the metal salt with the reducing agent NaBH4 [23]. It was shown that the longer the time of electroless, the greater is the depth of Pt deposition into Nafion [17]. Bessarabov et al. investigated the influence of the membrane modification by using ethylene diamine (EDA) on the process of the Pt deposition in these membranes. They showed that modification of the membranes with EDA resulted in an increase in membrane electrical resistances [17]. Hawut et al. investigated the effects of electroless time (30–90 min) and Pt:N2 H4 ratio on the PEMFC performance. They demonstrated that platinum deposition increased when the Pt:N2 H4 ratio decreased. However, the loading of platinum that they used was not low. The maximum current density was 80 mA cm−2 at 0.3 V and the loading of platinum was 0.79 mg cm−2 [24]. Liang and Zhao [25] fabricated a Pt–Nafion integrated electrode for DMFC. They used electrochemical method to deposit platinum nanowires on the Nafion membrane. According to their findings, The DMFC with this new anode structure demonstrated a lower rate of methanol crossover as the result of the incorporation of Pt nanowires into the hydrophilic pores of the Nafion membrane. It is believed that the MEA with the integrated electrode would have an elongated lifetime compared with the conventional MEA. The delamination of the MEA has been identified as a major problem in the DMFC performance degradation. The delamination mainly takes place at the anode due to different swelling degrees of the anode and the Nafion membrane. The integrated anodic electrode, however, has a larger binding force, thereby the delamination is unlikely. Lee et al. [26] synthesized platinum nanoparticles inside a Nafion membrane for fuel cell applications. The synthesized nanoparticles, caused increment in the proton conductivity of the Nafion membrane. The problem with these works is that the value of 4 mg cm−2 for platinum loading that they used was so high, and in many of these works the catalyst was used both in Nafion membrane and GDE. But in our work the platinum electrocatalyst was just dispersed in the Nafion membrane. However, to our knowledge platinum coated Nafion/gas diffusion electrode for PEM fuel cell has not been reported. In this work membrane electrode, with low loading of platinum, based on platinum-coated Nafion membrane was fabricated. The Pt deposition of the Nafion membrane was achieved by electroless method. Pt coated membrane was characterized with SEM and XRD techniques. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV) were used

10409

to analyze the oxygen reduction reaction kinetics on platinum coated Nafion membranes.

2. Experimental In the present study, Pt-coated Nafion membranes are fabricated through three steps, which include surface treatment, activation step and platinum deposition. A saturated NaCOOH solution was used as reducing agent.

2.1. Treatment of Nafion membrane Before the treatment of the Nafion membranes, the Nafion 117 films (Aldrich) were cut into circular discs with 1.3 cm2 surface area for electroless plating. In order to remove organic and metallic impurities, the membranes were treated by immersion them at 80 ◦ C for 1 h in following solutions, respectively: 3% H2 O2 (30% Merck), deionized water, 0.5 mol dm−3 H2 SO4 (Merck), and deionized water [5,27].

2.2. Sensitivity and activation of the Nafion membrane After the treatment stage, the Nafion membranes were immerged in 0.1 mol dm−3 SnCl2 –HCl (Merck) solution for 2 h. The membranes were then washed with 0.1 mol dm−3 HCl solution to remove any absorbed SnCl2 . Finally the membranes were immerged for 30 min in 0.0014 mol dm−3 PdCl2 –0.25 mol dm−3 HCl solutions to produce active membranes. When palladium is deposited on Nafion membrane, not only palladium is formed on the Nafion membrane but also palladium particles can be formed on the Nafion membrane by impregnating the pores [10]. The observed increment in the catalytic activity of the Pt monolayer surfaces on Pd substrates compared with those on Pt, may also partly reflects the decreased formation of PtOH on Pd-supported Pt monolayer [6].

2.3. Deposition of platinum on the Nafion membrane Impregnation-reduction method was used to produce Ptlayered Nafion membranes. In this method the treated Nafion membranes were immerged in different concentrations of H2 PtCl6 solution (15 ml, Merck) in room temperature. Then a saturated NaCOOH solution was added as a reducing agent and the resulting solution was heated to 50 ◦ C. At which point the platinum ions are reduced to platinum metal at the membrane surface according to the redox reaction: − − PtCl2− 6 + 4e → Pt + 6Cl

(1)

The thickness and quality of metallic platinum plated on the membrane surface depends on immersion time of the membrane in the plating solution and the concentration of H2 PtCl6 in the solution [22,28,29]. Typically the substrate remains in the plating bath for about 1–2 min. Platinum reduction occurs rapidly and a color change in the membrane is seen immediately upon initiation of reduction. Following this initial color change, a deposit of platinum could be observed to be formed on the membrane slowly, and by the end of the reduction process, platinum emerged on the membrane surface [29]. Table 1 gives the loading of platinum for different concentrations of H2 PtCl6 . The loading of platinum was obtained by Nafion weighting before and after the platinum deposition.

10410

S. Chabi, M. Kheirmand / Applied Surface Science 257 (2011) 10408–10413

-0.015

Table 1 Loading of platinum on Nafion for different concentration of H2 PtCl6 . Pt loading (mg cm−2 )

0.04 0.05 0.06 0.07

0.080 0.120 0.153 0.200

2.4. Preparation of gas diffusion layer To prepare the gas diffusion layer, a mixture comprised of a homogeneous suspension of 13 wt.% PTFE, carbon Vulcan (Cabot), glycerol (Merck), 2-propanol (Merck) and distilled water was homogenized using a sonicator (Misonix model S-3000) for 15 min and then painted onto carbon paper (TGP-060H Electro chem.). The resulting composite structure was dried in air at room temperature, and then heated in an oven at 80 ◦ C for 30 min to remove the dispersion agent contained in the PTFE, and finally sintered at 330 ◦ C for 30 min. The pores of the diffusion layer must allow mass flow of the reactant (fuel and oxidant) to and of products from the wetted pores of the active layer, where the electrochemical reactions take place [30]. The loading of diffusion layer was about 2 mg cm−2 . 2.5. Pressing the Nafion membrane on the gas diffusion layer Since the Nafion membrane is a solid type, the contact between Pt-coated Nafion membrane and diffusion layer becomes an important factor in order to obtain high performance. Hence after preparation of diffusion layer and platined the Nafion membrane, Pt-coated Nafion membrane was hot-pressed on the diffusion layer at temperature 130 ◦ C for 90 s. And the new electrode was prepared. 2.6. Chemical and electrochemical studies of GDEs The morphology of GDEs was characterized via scanning electron microscopy (SEM) and X-ray diffraction (XRD). Electrochemical behaviors of the GDEs were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) measurement in 2 M H2 SO4 . A three electrode system with an Ag/AgCl electrode, as the reference electrode, a Pt electrode as the counter electrode, was used to perform electrochemical experiments. The GDE was mounted in a Teflon body having the provision for a gas supply at the back of electrode. The electrochemical cell was connected to a potentiostat–galvanostat (EG&G 273A). Potentials are reported with respect to the reference electrode. 3. Results and discussion 3.1. Electrochemical measurements of the GDEs In order to investigate the electrochemistry characteristics such as the electrochemical surface area (ESA) and roughness factor (RF ) of the electrodes, CV measurements were carried out in N2 atmosphere. Fig. 1 shows the CV curves of electrodes in 2 M H2 SO4 in the potential range of −0.3 to 1 V. The scan rate was 40 mV s−1 . As the potential of the electrode is varied, ions move to the surface to form a double-layer. The established features of hydrogen adsorption, hydrogen desorption, are evident as peaks in the voltammogram [13,22]. As can be seen in Fig. 1a, the GDE that was prepared by 0.06 mol dm−3 H2 PtCl6 has higher peak than other electrodes. The charge associated with this peak was 55.8 mC cm−2 . In comparison with other electrodes, this electrode clearly shows hydrogen adsorption–desorption peak. Due to Nafion membrane resistance and poor platinum, some electrodes do not show good features of

-0.01 -0.005 0

I/A cm-2

[H2 PtCl6 ] (mol dm−3 )

0.005

0.05 M H2PtCl6

0.01

0.06M H2PtCl6

0.015

0.07 M H2PtCl6

0.04 M H2PtCl6

0.02 0.025 -0.3 0.03

-0.1

0.1

0.3

0.5

0.7

0.9

1.1

E/V Fig. 1. Cyclic voltammograms of electrodes for different concentration of H2 PtCl6 . The electrolyte solution is 2 M H2 SO4 and the scan rate is 40 mV s−1 .

hydrogen adsorption–desorption on the surface of the electrodes. For high loadings of Pt, the Nafion clusters were likely squeezed by the synthesized Pt nanoparticles and as a result the water uptake and proton conductivity and then hydrogen adsorption–desorption peaks were decreased [35]. It is assumed that each surface platinum atom is associated with one chemisorbed hydrogen atom, allowing the charge corresponding to the area under the strong and weak hydrogen adsorption peaks, QH (␮C) to be converted to the real electrochemical surface area. The columbic charge for hydrogen desorption was used to calculate the active surface area of each electrode [13,30]. To obtain electrochemical surface area from the value of QH , assumption must be made about the atoms on the surface are accessible to hydrogen adsorption. Assuming one Had per Pt surface atoms, a theoretical charge associated with a monolayer of hydrogen formed on the bases of: H+ + e− → Had , Q0 has been commonly taken as 210 ␮C cm−2 estimated as follows: nF Q0 = A NA

(2)

where n is the number of Pt atoms (1.3 × 1015 cm−2 ) and NA is Avogadro constant, A, is real area and F is the Faraday constant [22,31]. The roughness factor (RF ) was calculated by dividing the ESA by the geometric area (1.3 cm2 ) of the electrode. Comparison of the calculated values of the real electrochemical surface area, roughness factor and specific surface area (S) for different electrodes (Table 2) reveals that the use of 0.06 M H2 PtCl6 gives improvements in all of these characteristics. On the other hand, for low and high concentrations of H2 PtCl6 , weak peaks were obtained. Fig. 2 shows the polarization curves for different electrodes. As can be seen in this graph, the electrode with 0.06 M H2 PtCL6 has higher current in the −220 mV than other electrodes, which indicates that the performance of this electrode is much better than Table 2 Electrochemical surface area (ESA), roughness factor (RF ) and specific surface area (S) of the constructed electrodes. [H2 PtCl6 ] (mol dm−3 )

ESA (cm2 )

RF (cm2 Pt cm−2 )

S (m2 g−1 )

0.05 0.06 0.07

80.95 265.7 86.2

62.27 204.38 66.3

51.89 133.58 47.35

S. Chabi, M. Kheirmand / Applied Surface Science 257 (2011) 10408–10413

10411

20

1.2 1

0.06MH2PtCl6

18

0.04 M H2PtCl6

0.04MH2PtCl6

0.07 M H2PtCl6

16

0.06M H2PtCl6

0.07MH2PtCl6

0.05M H2PtCl6

0.8

14

0.05MH2PtCl6

12

-Z (im)

E/V

0.6 0.4

10 8

0.2

6 4

0

2

-0.2 -0.02

0.00

0.02 I/ A cm-2 0.04

0.06

0.08

0

0

5

Fig. 2. Potential vs. current density for different electrodes in 2 M H2 SO4 solution; in the potential range of 1.2–0.3 V; sweep rate: 1 mV s−1 .

10

15

Z (Re)

20

25

30

Fig. 3. Impedance spectra at a potential of 0.3 V for different electrodes. Frequency range: 100 kHz to 10 mHz.

other electrodes. At low current density the current is limited by reaction kinetics, whereas, at high current density, the current is limited by reactants diffusion [32]. The OCP value for this optimum electrode is 0.63 V, and over hours this electrode shows very little loss in the initial value of OCP, which indicate the good stability of this electrode [33]. The kinetic parameters of the ORR for electrodes can be obtained from the polarization data. The kinetics data were obtained using the semi-empirical equations: E = E0 − b log i − Ri

(3)

E0 = Er + b log i0

(4)

where Er is the reversible potential for the electrode; i0 is the exchange current density for the ORR, b is the Tafel slope, and R represents the total contributions of polarization components. Table 3 gives the Tafel slopes and exchange current densities for different electrodes. Tafel slope provides a visual understanding of the activation polarization of a fuel cell. It was being noted that, the resistance related to Nafion membrane was about 10  cm−2 [9]. As can be seen in Table 3, the electrode prepared by using 0.06 mol dm−3 concentration of H2 PtCl6 has lower Tafel slop than other electrodes. The exchange current density for this electrode was 4.1 × 10−3 A cm−2 . The exchange current density was calculated by the linear portions of the Tafel plots. It is apparent that this electrode has the highest electrochemical activity toward the ORR in the acid solution among the four electrodes. The loading of platinum for this electrode was 0.153 mg cm−2 . When the concentration of H2 PtCl6 was increased from 0.06 to 0.07 mol dm−3 , the Tafel slope was increased from 102 mV dec−1 to 120 mV dec−1 and the electrode performance was decreased. Typically the increase of the time of electroless deposition ensures the decrease of both forward and reverse currents [21]. In order to get more information about electrochemical behavior of electrodes, the a.c. impedance spectrum of each electrode was

obtained at potential of 0.3 V. AC Impedance measurements were carried out in the presence of O2 . The Nyquist plots of the different electrodes are shown in Fig. 3. The results of this test are in good accordance with other tests. As seen the spectrum of best electrode takes the form of a single semi-circular curves. The diameter of the semi-circle for electrode that prepared with 0.06 M H2 PtCl6 is lower than other electrodes, which means that this electrode has lower charge transfer resistance (Rct ) and then the better performance than other electrodes. The charge transfer resistance (Rct ) for this optimum electrode is 15 . 3.2. XRD results XRD diffractogram of best sample was shown in Fig. 4. For this sample, extra peaks corresponding to metallic polycrystalline platinum are observed. The diffraction peaks at 40◦ , 46◦ , 68◦ and 82◦ are attributed to Pt (1 1 1), (2 0 0), (2 2 0) and (3 1 1) crystalline facet, respectively. The characteristic diffraction peaks of the FCC Pt demonstrate that a successful reduction of Pt precursor to metallic form has been achieved [1,15]. This graph shows a peak at 40◦ (2) that corresponding to Pt (1 1 1). The amorphous band at ca. 18◦ related to the crystalline peak of Nafion [10]. The Scherer formula is used to assess the particle size. t=

n b cos 

where n is constant coefficient,  is wavelength and b is peak breadth.

Table 3 Tafel parameters obtained from Eq. (3) for different electrodes. [H2 PtCl6 ] (mol dm−3 )

i0 (mA cm−2 )

b (mV dec−1 )

0.04 0.05 0.06 0.07

1.8 2.58 4.1 2.8

138 122 102 120

(5)

Fig. 4. XRD pattern for GDE prepared with 0.06 M H2 PtCl6 .

10412

S. Chabi, M. Kheirmand / Applied Surface Science 257 (2011) 10408–10413

Fig. 5. SEM micrographs of surface of GDEs: (a) 0.04 M, (b) 0.05 M and (c) 0.06 M of H2 PtCl6 .

From the extent of the line broadening of (1 1 1) at 2 of 39.5◦ , the average platinum particle size of this sample was estimated to be about 3 nm. The size of particle can be controlled by manipulating the synthesis temperature, and with the increase of temperature, a smaller size can be achieved [34]. 3.3. SEM results The characteristics of platinum coated on the Nafion membrane were examined by means of scanning electron microscopy (SEM). Fig. 5 shows scanning electron micrograph for different electrodes. Scanning electron microscopic analyses indicated good adhesion between the metallic electrode and the Nafion polymer. The mean grain size of the platinum particle was found. The SEM images for all surfaces showed that some cracks formed on the surface of the Ptlayered Nafion membrane. It was believed that some of the cracks might be caused by the residual stress between the plated Pt layer and Nafion membrane. When the Nafion membrane was taken out from water and dried, the Nafion membrane shrunk to a degree, so some cracks were developed eventually in the Pt films. Some of the cracks might be produced when SEM samples were prepared [10,35].

Besides, platinum nanoparticles synthesized differently on both electrode and as a result different amount of platinum atoms participate in ORR. Electrochemical measurements indicated that in comparison with traditional electrode, new electrode has lower Tafel slope (102 mV vs. 138 mV per decade) and higher OCP than traditional electrode. And it means that the activity of oxygen reduction reaction, which is determined by the rate determining step, is higher than the activity of ORR in traditional electrode. This feature can be attributed to the separated paths for electrons and protons in new electrode. Separation between electron and proton paths leads in high catalyst utilization of the electrode. The electrode containing Pt-coated Nafion membrane has lower overpotential, by minimizing ohmic resistance, charge transfer and mass transport limitations than traditional GDE.

1.2 1

For comparison, a traditional GDE that prepared with Pt/C (10 wt.% ETEK) and has a pure Nafion membrane on its surface was fabricated [28]. A comparison of the LSV curves of new GDE and traditional GDE with the same Pt loading was illustrated in Fig. 6. The Pt loading for two GDE was 0.153 mg cm−2 . As can be seen in Fig. 6 the new GDE, with Pt-coated Nafion membrane, gives better currents than other GDE. And even at low over potential and activation region, the behavior of two electrodes is different. At activation region, new electrode shows better performance. Activation resistance plays a significant role at low current density, it implies that traditional electrode has a low potential to prompt the oxidation–reduction reaction. While the new electrode, with platinum on Nafion membrane has less activation resistance [26,35].

E/V

4. Comparison between new GDE and traditional GDE

0.8

Pt on nafion membrane

0.6

Pt on Catalyst layer

0.4 0.2 0 -0.2 -0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

I/A cm -2 Fig. 6. Comparison of LSV curves between GDE with Pt on Nafion membrane and GDE with Pt on catalyst layer, for the same loading.

S. Chabi, M. Kheirmand / Applied Surface Science 257 (2011) 10408–10413

5. Conclusion A Pt layer modified Nafion membrane was obtained by electroless plating. The SEM results showed clearly the formation of platinum nanoparticles on the Nafion membrane surface. Electrochemical results such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV), showed that, as the concentration of H2 PtCl6 increased, the oxygen reduction reaction rate increased until a concentration was reached where the reduction reaction was limited by the problem of mass transport. It was apparent that the electrode with 0.06 M H2 PtCl6 has the highest electrochemical activity toward the ORR among the four electrodes. Compared with traditional gas diffusion electrode, with platinum on catalyst layer, the new gas diffusion electrode, with Pt-coated Nafion membrane, exhibit improved polarization performance. The loading of platinum, for these two electrodes was the same and it was 0.153 mg cm−2 . The results illustrate that placing a Pt layer on Nafion membrane is an attractive way of designing O2 reduction electrocatalysts with very low Pt contents. References [1] E. Antolin, Recent developments in polymer electrolyte fuel cell electrodes, J. Appl. Electrochem. 34 (2004) 563–576. [2] N. Rajalakshmi, H. Ryu, K.S. Dhathathreyan, Platinum catalysed membranes for proton exchange membrane fuel cells–higher performance, Chem. Eng. J. 102 (2004) 241–247. [3] D.-H. Son, R.K. Sharma, Y.-G. Shul, H. Kim, Preparation of Pt/zeolite-Nafion composite membranes for self-humidifying polymer electrolyte fuel cells, J. Power Sources 165 (2007) 733–738. [4] B. Smitha, S. Sridhar, A.A. Khan, Solid polymer electrolyte membranes for fuel cell applications, J. Membr. Sci. 259 (2005) 10–26. [5] S.M. Rao, Y. Xing, Simulation of nanostructured electrodes, for polymer electrolyte membrane fuel cells, J. Power Sources 185 (2008) 1094–1100. [6] J. Zhang, M.B. Vukmirovic, K. Sasaki, F. Uribe, R.R. Adzic, Platinum monolayer electrocatalysts for oxygen reduction: effect of substrate, and long-term stability, J. Serb. Chem. Soc. 70 (2005) 513–525. [7] H. Zhong, H. Zhang, G. Liu, Y. Liang, J. Hu, B. Yi, A novel non-noble electrocatalyst for PEM fuel cell based on molybdenum nitride, Electrochem. Commun. 8 (2006) 707–712. [8] S. Lister, G. Mclean, PEM fuel cell electrodes, J. Power sources 130 (2004) 61–67. [9] M.D. Bennett, D.J. Leo, Manufacture and characterization of ionic polymer transducers employing non-precious metal electrodes, Smart Mater. Struct. 12 (2003) 424–436. [10] D.-H. Son, R.K. Sharma, Y.-G. Shul, H. Kim, Preparation of Pt/zeolite–Nafion composite membranes for self-humidifying polymer electrolyte fuel cells, J. Power Sources 165 (2007) 733–738. [11] S.M. Rao, Y. Xing, Simulation of nanostructured electrodes for polymer electrolyte membrane fuel cells, J. Power Sources 185 (2008) 1094–1100. [12] H. Sun, et al., Pd electroless plated Nafion membrane for high concentration DMFCs, J. Membr. Sci. 259 (2005) 27–33. [13] A.S. Koslov, T. Palaniamy, D. Narasimhan, Electroless autocatalytic platinum plating, US Patent 6,391,477 (2002). [14] R. Diaz, J. Arbiol, F. Sanz, J.R. Morante, Electroless addition of platinum to SnO2 nanopowders, Chem. Mater. 14 (8) (2002) 3277–3283.

10413

[15] S.-A. Sheppard, S.A. Campbell, J.R. Smith, G.W. Lloyd, T.R. Ralph, F.C. Walsh, Electrochemical and microscopic characterization of platinum-coated perfluorosulfonic acid (Nafion 117) materials, The Analyst (1998). [16] D.G. Bessarabov, W. Michaels, R.D. Sanderson, Preparation and characterisation of chemically-modified perfluorinated cation-exchange platinum-containing membranes, J. Membr. Sci. 179 (2000) 221–229. [17] D.G. Bessarabov’, W. Michaels, J.P. Vermeulen, Electroless deposition of platinum on proton-conductive perfluorinated membranes modified with ethylene diamine, in: Ionic5(1999), the 5th Euroconference on Solid State Ionics, Benalmddena, Spain, September 13–20, 1998. [18] A. Nidola, G. Martelli, Deposition of catalytic electrodes on ion-exchange membranes, US Patent 4,364,803 (1982). [19] T.D. Gierke, G.E. Munn, F.C. Wilson, The morphology in Nafion perfluorinated membrane products, as determined by wide- and small-angle X-ray studies, J. Polym. Sci. B: Polym. Phys. 19 (1981) 687. [20] J.J. Pak, S.-E. Cha, H.-J. Ahn, S.-K. Lee, Fabrication of Ionic Polymer Metal Composites by Electroless Plating of Pt, Nano-Bioelectronics & Systems Research Center, 2000. [21] G.V. Kuznetsov, V.A. Skryshevsky, T.A. Vdovenkova, A.I. Tsyganova, P. Gorostiza, F. Sanz, Platinum electroless deposition on silicon from hydrogen fluoride solutions, J. Electrochem. Soc. 148 (8) (2001) C528–C532. [22] M.H. Pournaghi-Azar, B. Habibi, Preparation of a platinum layer-modified aluminum electrode by electrochemical and electroless cemenations and its use for the electrooxidation of methanol, J. Electroanal. Chem. 580 (2005) 23–34. [23] P.S. Fedkiw, W. Her, An impregnation-reduction method to prepare electrodes on Nafion SP, J. Electrochem. Soc. 136 (1989) 899. [24] W. Hawut, M. Hunsom, K. Pruksathorn, Platinum electroless deposition on nafion membrane for PEM fuel cells, Kor. J. Chem. Eng. 23 (4) (2006) 555–559. [25] Z.X. Liang, T.S. Zhao, New DMFC anode structure consisting of platinum nanowires deposited into a Nafion membrane, J. Phys. Chem. C 111 (2007) 8128–8134. [26] P.-C. Lee, et al., In situ formation of platinum nanoparticles in Nafion recast film for catalyst-incorporated ion-exchange membrane in fuel cell applications, J. Membr. Sci. 322 (2008) 441–445. [27] H.-k. Lee, J.-h. Park, D.-Y. Kim, T.-H. Lee, A study on the characteristics of the diffusion layer thickness and porosity of the PEMFC, J. Power Sources 131 (2004) 200–206. [28] M. Ludvigsson, J. Lindgren, J. Tegenfeldt, FTIR study of water in cast Nafion films, J. Electrochem. Soc. 147 (4) (2000) 1303–1305. [29] M. Siripong, S. Fredholm, Q.A. Nguyen, B. Shih, J. Itescu, J. Stolk, A Cost-Effective Fabrication Method for Ionic Polymer-Metal Composites, College of Engineering Olin Way, 2000. [30] H. Gharibi, M. Zhiani, A.A. Entezami, R.A. Mirzaie, M. Kheirmand, K. Kakaei, Study of polyaniline doped with trifluoromethane sulfonic acid in gas-diffusion electrodes for proton-exchange membrane fuel cells, J. Power Sources 155 (2006) 138–144. [31] C.W.B. Bezerraa, et al., A review of heat-treatment effects on activity and stability of PEM fuel cell catalysts for oxygen reduction reaction, J. Power Sources 173 (2007) 891–908. [32] L.R. Jordan, A.K. Shulka, T. Behrsing, N.R. Avery, B.C. Muddle, M. Forsyth, Effect of diffusion-layer morphology on the performance of polymer electrolyte fuel cells operating at atmospheric pressure, J. Appl. Electrochem. 30 (2000) 641–646. [33] C. Hamon, G. Purdy, Y.S. Kim, B. Pivovar, P. Zelenay, Novel process for improved long-term stability of DMFC membrane electrode assembly, ECS Proceedings Journal 206th Electrochemical Society Meeting, Hawaii. 2004. [34] X. Wang, I.-M. Hsing, Surfactant stabilized Pt and Pt alloy electrocatalyst for polymer electrolyte fuel cells, Electrochim. Acta 47 (2002) 2981–2987. [35] J. Prabhuram, T.S. Zhao, Z.X. Liang, H. Yang, C.W. Wong, Pd and Pd–Cu alloy deposited Nafion membranes for reduction of methanol crossover in direct methanol fuel cells, J. Electrochem. Soc. 152 (7) (2005) A1390–A1397.