Influence of Pt Nanoparticle Electroless Deposition Parameters on the

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The Influence of Pt Nanoparticle Electroless Deposition Parameters on the Electrochemical Characteristics of Nafion-based Catalyst Coated Membrane Parisa Hosseinabadi, Mehran Javanbakht, Leila Naji, and Hossein Ghafarian-Zahmatkesh Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b03647 • Publication Date (Web): 08 Dec 2017 Downloaded from http://pubs.acs.org on December 8, 2017

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Industrial & Engineering Chemistry Research

The Influence of Pt Nanoparticle Electroless Deposition Parameters on the Electrochemical Characteristics of Nafion-based Catalyst Coated Membrane Parisa Hosseinabadi,† ,‡ Mehran Javanbakht,*,†,‡ Leila Naji† and Hossein GhafarianZahmatkesh† ,‡ † ‡

Department of Chemistry, Amirkabir University of Technology, Tehran, 1599637111, Iran

Fuel Cell and Solar Cell Laboratory, Renewable Energy Research Center, Amirkabir University of Technology, Tehran, 1599637111, Iran

*

Corresponding author at: Department of Chemistry, Amirkabir University of Technology, Tehran, Iran. Tel.: +98 21 645425806. Email address: [email protected] (M. Javanbakht).

1

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Graphical Abstract

ABSTRACT 2


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Platinum (Pt) catalyst coated membranes (CCMs) were prepared using controllable, low-cost, and low energy consumption electroless deposition methods and considered as a catalystelectrolyte for proton exchange membrane fuel cell. The influences of experimental conditions such as temperature, duration of absorption and reduction processes, type of solvent, pH of reaction, and ethylenediamine (EDA) as a modifier, on the structural, physicochemical, and electrochemical characteristics of CCMs were investigated for this method. The morphological analyses reveal that the smallest Pt nanoparticles (7.8 nm) were formed at 40 ºC, pH =14, and by means of EDA. This sample appeared to have the highest ionic conductivity, water uptake (WU) and capacitive characteristic. Cation-acceptation was observed for first time by modifying the surface of Nafion with EDA. Electrochemical active surface area for optimum CCM was 7.85 m2 g-1 and current density obtained at 0.5 V was 750 mA cm-2.

Key Words: Catalyst coated membrane; Modified Nafion; Platinum nanoparticle; Electroless deposition.

1. Introduction Fuel cells have been received more attention over the past decades because of ever-increasing demand for high energy/density system into the space program. Proton exchange membrane fuel cells (PEMFCs) are electrochemical devices that are preferred to be used in different applications 3



because of their outstanding properties such as quick startup, high power density and energy efficiency, acceptable oxygen reduction kinetics, rapid response to varying loads, relatively low operating temperature, small diffusional polarization, and their environmental friendly characteristics.1,2 Lots of efforts and researches have been conducted to fabricate PEMFCs at lower manufacturing cost.3 Investigations clearly showed that producing costs can be beneficially decreased using lower loading of catalyst without a decrease in cell efficiency.4 PEMFCs are comprised of a membrane electrode assembly (MEA) which is a proton exchange membrane mostly Nafion that has pressed between two gas diffusion electrodes (GDE).5 Platinum (Pt) is the most conventional metal used for the preparation of the electrocatalyst layer in PEMFC due to its unique properties, including catalytic activity, and permanence in the acidic medium during water electrolysis that depends on the preparation process.1,6

There are some essential factors effect on the efficiency of the catalyst layer include electrochemical surface area (ECSA) (surface to mass ratio), porosity and permeability to reactants (transmission of the reactants mass), proton conductivity (ionic conductivity), intermediate binding catalyst particles (electrical conductivity), and the proportion of catalyst particles which participate in the electrochemical reaction of electrode (capacity of the catalyst).7 With the aim of improving the electrochemical performance of Pt catalyst layer, various methods have been developed to increase the ECSA of Pt through a particle size reduction, increasing the interfaces among the catalyst, electrolyte, and reactants (three phase boundary). Application of Pt as a catalyst on gas diffusion layer (GDL) and on the ion-exchange membrane to form a catalyst coated membrane (CCM) are general methods for MEA fabrication. Excellent adhesion of Pt 4


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nanoparticles as electrocatalyst on the membrane is a critical characteristic for reducing ohmic resistance which has an undeniable role on the performance, current, and power densities of PEMFCs.8,9 CCM method is used to achieve high adhesion, uniform dispersion of Pt particles, low contact and internal resistance, high ECSA, and catalytic activity. When catalyst nanoparticles are directly grown on the ion-exchange membrane, the catalyst utilization would increase effectively. This has been achieved by chemical electroless deposition methods including impregnation–reduction (I-R), and reduction-permeation (T-T) methods. In I-R method, the cation-exchange membrane is soaked in an aqueous cationic metal solution, e.g. tetraamine platinum(II) ([Pt(NH3)4]2+), then is immersed in a reducing solution (e.g. sodium boro hydrate (NaBH4), and Hydrazine (NH2NH2)). Eventually, Pt ions are reduced to metal nanoparticles and locate firmly on the outer surface of the membrane. The electrodes prepared by this method have some special features such as low thickness, high porosity, good adhesion, and durability. It has been proved that the prolonged soaking of the ion-exchange membrane in the metal solution, leads to the greater depth of Pt deposition into the membrane.4,8–11 In the T-T method, an aqueous solution of metal anions such as platinum chloride ([PtCl6]2-), and a reducing agent (usually NaBH4) are exposed to opposite sides of a stationary membrane. [PtCl6]2- ions continuously penetrate the membrane and come into interaction with BH4- ions on the opposite side of the membrane, where the Pt ions are reduced to Pt metal nanoparticles at the membrane surface.12 The effects of adding alcohols in [PtCl6]2- solution on the morphology, electrochemical performance of the Pt-deposited Nafion membrane has been investigated.13 The result revealed that ethanol formed a thicker and well-dispersed Pt electrode layer, whereas methanol and npropanol produced thinner Pt electrodes than water. The ECSA of deposited Pt layer is also 5



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affected by the deposition time and temperature.4 Bessarabov et al.14,15 showed that the surface modification of the membrane with the ethylenediamine (EDA) results in a significant change in the distribution throughout the membrane. Xi et al.16 reveal that “Hot spots” – a kind of highly active site, which are unify of some unique units, especial, interfaces and catalyst particles– can affect the performance of nanomaterial.

Recently a novel controllable electroless deposition method of Pt nanoparticle catalyst onto Nafion membranes has been done.17,18 It has been shown that the hydration state of the Nafion has the most significant effect on constraining where Pt deposition happens on the Nafion membrane and with varying the pH of Pt solutions. In addition, the depth of the Pt deposition zone can be varied considerably.

In our previous works, we have investigated new proton exchange membranes based on polybenzimidazole,19-21

poly(vinyl

alcohol)/sulfonated

graphene

oxide

nanocomposite

membranes,22 aligned nanocomposite membranes containing sulfonated graphene oxide,23 and Nafion/Fe2TiO5 nanocomposite membrane.24

In the current work, for the first time to our knowledge, cation-acceptation in EDA-Nafion modified membrane was proved. As regards to the new method explained,17 allowing better control of deposition of Pt nanoparticles compared to I-R and T-T methods, CCMs were prepared by this method. The effect of temperature on morphology and nanoparticle's size was investigated. Due to the better performance of CCM prepared in higher temperature, studying of other factors was continued at this temperature. Another factor was the process duration. 6


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According to the results the best time was chosen for other CCMs investigations. Studying the effect of solvent in absorption step indicated that aqueous solvent has a positive impact on electroless deposition. Morphological, physical, and electrochemical investigations evidenced that Nafion membrane modification with EDA has affirmative effects on this method. A thinner and more porous Pt electrode structure was formed in modified Nafion membrane and in attendance of NaOH in reduction processes. These evidences have been revealed that cationacceptation in EDA-modified Nafion membrane accrues.

2. Experimental Section 2.1 Cleaning and preparation of Nafion membrane The roughened Nafion membrane was prepared through the following cleaning method.25 First, the membrane was boiled in 2 M HNO3 (Fisher scientific) solution at a temperature of 80 ºC for 2 h to exchange all cations on the sulfonate groups, for protons. The membrane was immersed in a 0.01 M solution of oxalic acid (M&B Ltd.) at room temperature for 24 h. Finally, to remove organic impurities and small polymer remains, the sample was immersed in a mixture of ethanolDI water 1:1 V/V in an ultrasonic bath for 2 h. The membrane was repeatedly boiled in DI water for 1 h to remove any residual HNO3, oxalic acid, and ethanol following each of steps.

7



2.2 Pt deposition on prepared Nafion membrane To evaluate the effect of different parameters on the physical and electrochemical characteristics of CCMs with low Pt loading, a controllable one-sided Pt deposition on Nafion was done. A deposition cell was designed and prepared of polycarbonate sheet; includes two compartments with 12 cm3 volume. In each experiment, Nafion was mounting between two compartments and sealed by four bolts. Figure1 shows the schematic illustration for the cell. One side of the Nafion was exposed to 0.9 mmol tetraamine platinum(II) chloride (Pt(NH3)4Cl2 99% purity, Alfa Aesar) solution, required for 0.4 mg cm-2 Pt loading on affected area of Nafion membrane (4.91 cm2). The pH of this solution was increased to 13 using KOH to prepared anionic site for Pt deposition. Another compartment, opposite side of the membrane was filled with aqueous solution of K2SO4 (0.013 M) and pH was decreased to 1 by H2SO4. This solution remained intact during the reaction. Deposition cell was placed on a heater magnetic stirrer and was stirred to avoid the formation of bubbles on the membrane surface. Afterward, the Pt solution was removed with a syringe, and this side of the membrane was washed with DI water and evacuated carefully using a syringe. Then, the compartment was re-filled by a 0.2 M NaBH4 (Aldrich) solution as reducing agent. The NaBH4 solution was refreshed every 20 min by the syringe. A light gray Pt layer was placed on the surface of the Nafion membranes.

8


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Figure 1. A schematic representation of electroless deposition process and cell, the radius of both cylindrical cell was 1.25 cm and volume was 11 cm3.

To evaluate the effect of temperature on the physical and electrochemical characteristics of CCMs, the controllable method was performed at 25 and 40 ºC. These samples were named CCM-T1 and CCM-T2, respectively. Results show that Pt nano particles prepared in 40 ºC possessed better performance in terms of physiochemical and electrochemical properties. Thus, the samples were prepared at 40 ºC to study the effect of other parameters. 9



In order to investigate the effect of time of adsorption and reduction process, three CCMs were prepared by varying the time of each step from 0.5, 1, and 2 h. These CCMs were named respectively CCM-D1, CCM-D2 (same as CCM-T2), and CCM-D3. CCM prepared at 1 h showed better characteristic. Thus, the duration of this method was set to 1 h for evaluating the effect of other factors.

The influence of alcohol co-solvent on the controllable method was studied by adding of methanol, ethanol, and 2-propanol (50:50 V/V) to the Pt solution during the adsorbing process. Fabricated CCMs was named CCM-S1, CCM-S2, and CCM-S3, respectively. Continued construction of CCMs was carried out with aqueous solutions due to reduced function of these samples.

Pre-clean Nafion membrane was immersed in an aqueous solution of EDA at room temperature for half an hour to functionalize the surface structure of the membrane with amine groups. The membrane was then washed with 0.4 M HCl and deionized water. CCMs prepared based on this surface modified membrane named as CCM-EDA.14,15

Furthermore, pH of the reducing agent was increased to 14 by adding NaOH (0.5 M) to the compartment containing NaBH4 solution. The effect of this parameter was studied on the Pt deposition on the surface modified Nafion membrane and prepared CCM was named as CCMEDA-A. The naming system and the fabrication conditions of the prepared CCMs are shown in Chart 1.

10


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Chart 1. Naming system and condition of fabrication of each CCMs.

Pt particles size, morphology, and also the thickness of the catalyst layer have a significant impact on the performance of the catalyst layer in MEA.4,11 Field emission scanning electron microscope FE-SEM (TESCAN MIRA3 MLU) was used for the investigation of the morphology of samples. The beam current was 15.00 kV. The cross-section of samples was then analyzed. 11



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For this purpose, Pt coated membranes were cooled in liquid nitrogen and fractured. All samples were coated with a very thin gold layer. The synthesized Pt particles were analyzed using X-ray diffraction (XRD), equation 1 (the Scherer formula) was used to estimate the nano particle size:

(1)

t=

where k is constant coefficient (≈1), ߣ is wavelength and b is peak breadth.11

Pt loading should be optimized; because high Pt loading causes to increase the cost of construction, decrease proton conductivity, and low Pt loading reduces the fuel cell performance. The amount of Pt deposition on the membrane was determined by inductively coupled plasmaatomic emission spectroscopy (ICP-AES) after treatment of the membrane with aqua regia a solution contains a ratio of 1:3 mixtures of concentrated HNO3 and HCl.18

2.3 Physicochemical characterization of the CCMs To evaluate the WU of the prepared CCMs, they were dried in a 65 ºC for 6 h and weighed to gain their dry weight (Wdry). Then the membranes were soaked in DI water for 6 h at room temperature and weighed (Wwet). The WU% was determined using equation (2):27

WU% =

(2)

× 100

12


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ATR-FTIR analysis was applied to study the effect of EDA on the chemical structure of Nafion membrane. For confirming the presence of ethylenediamine groups in the backbone of the polymer, the characteristic peaks were obtained by using ATR-FTIR (Bruker Alpha). The test was performed between 4000 and 550 cm-1 in transmittance mode.

2.4 Electrochemical characterization of CCMs In order to study the effect of various factors on proton conductivity (σ) and ECSA of CCMs, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were conducted.

The AC-EIS was investigated using a Potentiostat-Galvanostat, Autolab (PGSTAT302N, Netherland) at room temperature, over a frequency range of 100 mHz to 105 Hz and AC voltage amplitude of 50 mV. CCMs were soaked in DI water for 24 h to become fully hydrated and sandwiched between two Pt plates in 1×1 cm2 active area. Measurements were carried out at room temperature.

б

was obtained using equation (3), l is the measured thickness of the CCMs

(cm), Rs refers to the resistance (Ω), and A shows the area of CCMs (cm2).27

(3)

EIS data were analyzed by fitting results to suitable equivalent electrical circuit model by Z-view software.

13



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All CV experiments were performed at room temperature in a standard three-electrodes setup with a Pt wire as the counter electrode, Ag/AgCl as a reference electrode, and CCMs were used as working electrodes. The potential range and scan rate were -0.2-1 V and 0.1 V s-1, respectively. The 2 M solution of H2SO4 (Aldrich) was used as electrolyte solution and argon gas was bubbled into electrolyte.9 The ECSA of Pt was calculated using the equation (4):

(4)

ECSA=

where, QH (mC) is the charge due to the hydrogen adsorption/ desorption in the hydrogen region (0.05-0.40 V) resulted from the CV curve, 0.21 mC cm-2 is the electrical charge related to monolayer adsorption of hydrogen on Pt, and [Pt] is the amount of Pt loading onto CCMs.

The real surface area of catalyst layer can be estimated by roughness factor (Rf) shown in equation (5):4

(5) where, ReA is geometric area of the CCMs, respectively.

2.5 Fuel cell performance of fabricated CCMs In order to obtain the polarization curve of the catalyst coated membranes; selected CCMs was pressed between two GDE at 130 ºC under pressure of 1000 psi for 2 min. GDE comprise of 14


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diffusion layer and catalyst layer (contained a Pt loading of 0.2 mg cm-2 prepared by mixing 20% wt Pt/C, 5 ml isopropyl alcohol, and 0.1 g Nafion solution 5%.wt and sonicated for 15 min). Active surface area in this cell was 2.3×2.3 cm2. The Pt-coated surface of the CCMs was used for the cathode side. The CCM was mounted in the single cell and connected to the fuel cell tester (FCT-150, biologic, French). The performance of the cell was calculated by polarization curves obtaining at 70 °C by using wet H2 at the anode and wet air at the cathode. The gas flow rate was 300 mL min-1 under ambient pressure.4

3.

RESULT AND DISCUSSION

3.1 Concept In first step, the presences of KOH in Pt(NH3)4+2 help to create more anionic sites (-SO3-) on the surface of Nafion and make the membrane ready for more nucleation process. The concentration of KOH should be low enough to prevent occurring competitive reactions between Pt and potassium to occupy the anionic sites. According to this fact, the control of particles size and nucleation were dependent on this factor. The opposite side of the membrane was exposed to the acidic solution (pH =1). Pt(NH3)4+2 is moving through the membrane during the absorption step, this leads to distributed catalyst layer.17 H+ could pass through the membrane and prevent nucleation in depth of membrane by occupying anionic sites in the membrane. Therefore, thickness and density of the catalyst layer are related to the pH of the opposite side solution. In the second step (reducing step), where the Pt solution was replaced by NaBH4 solution, the presence of H+ ions in opposite side, led to the destruction of NaBH4 and creation of H2 nano15



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bubbles which caused to create finer particles with high porosity. Schematic process of deposition reaction has been shown in Figure 1. Reducing Pt on the membrane surface occurred according to the Schemes 1 - 6:14,28

Ion-exchange process in the

R-(SO3H)2 + Pt(NH3)42+ R-(SO3)2Pt(NH3)4 + 2H+

(1)

unmodified

R-SO2-N˙˙-CH2-CH2-NH2 + Pt(NH3)42+ R-SO2-N(Pt(NH3)42+)-CH2-CH2-NH2

(2)

Oxidation reaction

NaBH4 +8OH- BO2- + Na+ + 6H2O + 8e-

(3)

Reduction reaction

[Pt(NH3)4]2+ + 2e- Pt0 + 4NH3

(4)

Additional

NaBH4 + 2H2O NaBO2 + 4H2

Total reaction

NaBH4 + 4[Pt(NH3)4]2+ + 8OH- 4Pt0 (s) + 16NH3(g) + BO2- + Na+ +6H2O

and

modified

membranes

3.2 Physical and morphological characterization of CCMs As the electrocatalyst activity of Pt layer depends strongly on the morphology, particle size and distribution of Pt nanoparticles, CCMs were studied using FE-SEM.29 Figures 2 and 3 show longitudinal and cross-sectional images of each CCM in two part (x and x′). According to Figures 2a and 2b, when the temperature rises, nanoparticles have appeared in a smaller size and uniform deposition; that proved, rising in temperature caused to decrease in the size of the nanoparticles in this method.11,30 Figures 2a′ and 2b′ proved that better penetration and higher porosity of Pt particles accrue in a higher temperature. The thickness and the quality of Pt layer 16


(5) (6)

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depended on the duration of the process.31 As Figures 2c, 2c′, 2b, 2b′, 2d, and 2d′ demonstrate, in this method, with increasing the time of processes, size (because of agglomeration) and depth (due to more penetration) of nanoparticles were increased; however, in Figure 2c′ it was revealed that adhesion of catalyst layer which was formed at 0.5 h, was not desirable. It has been clarified that the time for soaking process affected the thickness and the quality of the prepared catalyst in this method.11,32 By comparing these three reaction times, it was proved that finer Pt structure formed in 1 h duration of the process. As the Figures 3a-3c′ show, the surface and cross-section morphology of the CCMs change considerably as a function of the solvent. In alcoholic solvent, the catalyst layer had no appropriate coherence to the Nafion membrane. It is due to the attendance of Ethanol, Methanol, and Propanol which caused to cracks and collapses in the catalyst layer, because of the membrane swelling.33 In Figures 3d and 3d′ uniform deposition of Pt nanoparticles, the acute-like and porous structure can be seen for modified Nafion with EDA. The total thickness of the Pt particles, consisting of Pt layer on the surface and within the bulk of the membrane, was between 8-9 µm (Figure 3d′). Those particles which were formed at the bulk of membrane had less access to three phase boundary for catalyst activity.34 In Figures 3e and 3e′, it seems that the application of NaOH in reducing agent decrease the penetration of Pt nanoparticles onto the bulk of comparing to CCM-EDA. This is due to the creation of electrostatic repulsion within the sulfonated hydrophilic regions of Nafion. As previously mentioned, Pt(NH3)4+ could pass through the membrane with a partition coefficient of 48, which was due to water carrying channels with the thickness of 2.5 nanometers. So, controlling the thickness of layering was an important principal in creating catalytic layers with desirable conditions.17,30,35 Comparison of the CCMs reveals the effect of each parameter on the 17



nanostructure of the Pt nanoparticle’s region. As the images show, the surface morphology of the CCMs changes considerably as a function of conditions. The most gilt-edged surface and thickness morphology are observed in CCM-EDA-A. It is important to note that the Pt particles were distributed deeper in the bulk of the modified membranes with EDA compared to the unmodified membranes. Using NaOH as electrostatic repulsion creator in CCM-EDA-A, caused to decrease the thickness to 4 µm this method (compare Figures 3d′ and 3e′). Pt nanoparticles, which occupied ionic clusters of the membrane, could prevent swelling of water absorption channels; therefore reduce proton conductivity.36

18


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Figure 2. Longitudinal and cross-sectional FE-SEM images of CCMs (a-a′) CCM-T1, (b-b′) CCM-T2, (c-c′) CCM-D1, (b-b′) CCM-D2, (d-d′) CCM-D3.

19



Figure 3. Longitudinal and cross-sectional FE-SEM images of CCMs (a-a′) CCM-S1, (b-b′) CCM-S2, (c-c′) CCM-S3, (d-d′) CCM-EDA, (e-e′) CCM-EDA-A.

Histograms of the CCM-C2, CCM-D3, CCM-EDA, and CCM-EDA-A are presented in Figure 4. It is clear that produce CCMs under condition of 40 ºC and 1 h (for each step) and using EDA as

20


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modifier lead to more uniform nucleation on the membrane. Adding NaOH in reduction agent bring forth the best features in terms of nanoparticle size and distribution properties.

Figure 4. histogram of CCM-D2, CCM-D3, CCM-EDA, and CCM-EDA-A.

The Pt catalytic activity significantly depends on its structure and particle’s size. XRD diffractogram of best CCMs are shown in Figure 5. For these CCMs, the diffraction peaks at 40º, 46º, 68º, and 82º are attributed to Pt (111), (200), (220) and (311) crystalline facet, respectively. It is proved that the sharpest peak indicating Pt-hexagonal (111) possess higher catalyst activity.28 From this peak the average size of Pt particles were estimated to be about 7, 12, 16, 17, and 18 nm for CCM-EDA-A, CCM-EDA, CCM-D2, CCM-D1, and CCM-T1, respectively. 21



These results are in good coordination with those of SEM and histogram. It is worth to point that the crystallite size calculating from XRD patterns, is related to the area of coherent diffraction and can be smaller than real particle’s size, therefore, these results are in good coordination with those of SEM and histogram.

Figure 5. XRD patterns of chosen CCMs.

Pt salt concentration in all samples was the same, but as can be seen in Table 1, Pt loading was affected by deposition condition. The faster replacement reaction of the Pt in higher temperature cause to more Pt-loading.31 Pt loading amount increased with the prolonging of the reaction time, due to amplification of cation exchange.11,28 As the result in Table 1 shows, with the prolonging 22


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time of reaction from 0.5 h to 1 h Pt loading had 12% growth and from 1 h to 2 h, considering the prolonging of the time is twice, Pt loading had just 3% increment. It can be assumed that after 1 h, the equilibrium of displacement reaction is reached. Pt loading decreased, in average to 267%, by the changing of the aqueous solvent to alcohol/water mixture solvent. The capacity of water to dissociation of ion pairs of Pt(NH3)4Cl2, against to ethanol, methanol and propanol is 82 to 24.3, 33.1, 21.8, respectively; so, the less loading of Pt can be proved in this method by accounting the aforementioned reasons.37 In CCM-EDA and CCM-EDA-A the amount of loading of Pt had a significant growing in comparison with the other samples, this growth comparing to CCM-D2 (as a reference sample) was about 17%. It can describe by bipolar junction in the membrane. Anion-rejection capacity has already been proven by Bessarabov et al.38 for EDA-modified Nafion membrane, but cation-acceptation capacity is demonstrated in this method by cationic precursor. Table 1 The amount of Pt loading (mg cm-2) and WU (%)

Parameters Sample

Pt loading

Temperature

Duration

Co-solvent

Modification

CCM-

CCM-

CCM-

CCM-

CCM-

CCM-

CCM-

CCM-

CCM-

CCM-

T1

T2

D1

D2

D3

S1

S2

S3

EDA

EDA-A

0.272

0.324

0.289

0.324

0.336

0.093

0.083

0.089

0.380

0.382

24.1

22.3

23.6

22.0

19.8

22.3

23.6

23.6

37.9

38.1

(mg cm-2) WU (%)

23



3.3 Physicochemical characterization of the CCMs Depth and density of catalyst layer had an extreme influence on the WU of the Pt-coated membrane.30,36 As it has been reported in specifications of the Nafion, ionic clusters which have been loaded by Pt had less water absorbing and this related to clogging absorbing water channels. According to Mauritz et al.35 each sulfonic groups on Nafion is responsible for adsorb 21 units of the water molecule. By occupying some of these sites by Pt particles, it was supposed to have a reduction in WU by raising Pt deposition. According to the results presented in Table 1, modified Nafion with EDA possessed higher WU compared to the pure Nafion membrane. This can ascribe to the formation of larger hydrophilic ionic clusters within these membranes and the better polarity on their surfaces.39 in comparing to CCM-D2 water absorption increased to 73%. Considering FE-SEM results in Figure 3 indicated high porosity of electrocatalyst layer in modified CCMs.

FT-ATR spectra of EDA-modified Nafion and non-modified membranes are compared in Figure 6. The –SO3− anion sites in both membranes had an absorption band at ∼1060 cm−1. The absorption bands in the regions of ∼1370 ± 10 and ∼3135 ± 105 cm−1 were characteristic features of the membranes modified with EDA. Chemical complex between the Nafion membrane and the EDA demonstrated a peak in the 1376 cm−1 region corresponded to antisymmetrical deformations of NH3+ ions.38 Stretching frequencies of NH3 + occurred in the region of 3135 ± 105 cm−1.

24


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Figure 6. Comparison of ATR spectra of pure Nafion and EDA-modified membranes.

3.4 Electrochemical characterization of CCMs Normalized-CV response of CCMs is compared in Figure 7 and its achieved results (ECSA and Rf) summarized in Table 2. It proved that activation cycle was necessary to activate the electrodes for higher performance. Ions moved through the membrane from the surface to double-layer when the potential of the electrode was varied. An electrically connected network between Pt nanoparticles (which are located in three phase boundary) and a shallow band within the near-surface region of the Nafion membrane seems to be suitable for electronic transport. The recognized potential of hydrogen adsorption, hydrogen desorption, was obvious as peaks in the voltammogram.39 As can be seen in Figure 7a and Table 2 the prepared catalysts layer in the 25



higher temperature has more performance because of more loading of Pt as catalyst and smaller nanoparticles’ size (shown in Table 1 and Figures 2, 3, and 4).11,28,29 Figure 7b and Table 2 have shown for CCM-D2 hydrogen adsorption–desorption peaks are observed more distinguished than CCM-D1 and CCM-D3; it can attribute to smaller Pt particle size, higher surface area and desirable thickness of CCM-D2 catalyst layer. According to the Figure 7c and Table 2 CCM-S1, CCM-S2 and CCM-S3 had low efficiency; it was predictable according to the SEM results. Figure 7d shows that foremost hydrogen adsorption–desorption peaks belong to CCM-EDA-A, since its great morphological properties due to using EDA as modifier and NaOH in reduction agent. As displayed in Figure 3, CCM-EDA and CCM-EDA-A have finer Pt particles and porosity that lead to higher electrochemical activity than other CCMs. Indeed, ECSA of the catalyst layer and Rf is an important parameter to determine the CCMs properties, which increases by temperature enhancement (40 ºC), apply appropriate duration of the process (1 h), using aqueous solvent, EDA-modification of the membrane and using NaOH in reducing agent, in this method. Because in this conditions, smaller and good distribution of nanoparticles have been formed. ECSA for CCM-EDA has increased comparing CCM-T2 (reference sample) to 31%. ECSA of CCM-EDA-A decreases 40% and 6.4% comparing to CCM-T2 and CCM-EDA, respectively, which related to high porosity and less thickness of this CCM (shown in Figure 3).4 There is some reason which may play role in CV curves. According to XRD patterns (Figure 5) polycrystalline-Pt particles formed on Nafion. Polycrystalline Pt particles electrode have indicated an oxidation mechanism, where Pt atoms as oxygen substitutes, in the surface layer, ejecting them into a lower density layer on top of the substrate. This exchange mechanism’s place is recognized as the double layer electric field. Electrochemical reduction of this oxide 26


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surface, leads to surface roughening; consequently, single cycle can completely disrupt the characteristic shape of the CV. For Pt(111) irreversible behavior in the CVs typically occurs at 1 V vs. Ag/AgCl reference, approximately. During Pt oxidation an underlying microscopic processes leads to roughness accumulating during potential cycling which is influences by the total transferred charge.40 Owing to polycrystalline structure broad hydrogen adsorptiondesorption peaks at 0.13 and 0.27 V. In the case of platinum, it is clear that the hydrogen adsorption-desorption process is very sensitive to the Pt particles’ structure; XRD pattern indicates the majority of Pt particles emerge as Pt (111) nano particles which proved to be a factor of broad hydrogen adsorption-desorption peaks in the range of 0.05–0.4 V, according to this fact and Figure 5 broadest peak for CCM-EDA-A seems logical. In the other side, ORR recognized as a multi-electron reaction correlated with the formation of many intermediates.41 Oxygen can be electrochemically reduced either directly to water (direct 4-electron reduction), or to hydrogen peroxide (H2O2) (series 2-electron reduction), depending on the structure of Pt particles, the mechanism for the ORR can be changed from series of reduction, with the 100% production of H2O2 on Pt (111) even in the cathode potential range (0.6–0.8 V) to almost 20% of H2O2 which may be formed on Pt/C, leading to difference in shape of CV curves.42 It is proved that. Uplift oxidation current appearing in 0.6 V approximately _ in some cases _ can be attributed to water splitting and remained Oxygen in acidic solvent because of not efficient Argon bubbling.

27



Figure 7. The effect of (a) temperature, (b) duration of reaction, (c) co-solvent (d) E DAmodification and pH increment and (e) comparison of voltammograms of the prepared CCMs, in a standard three-electrodes setup with Pt wire, Ag/AgCl and CCMs as counter, reference, and working electrodes in 2 M solution of H2SO4. 28


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Table 2 Variation of ECSA and Rf in different CCMs.

Parameters Sample

Temperature

Duration

Co-solvent

Modification

CCM-

CCM-

CCM-

CCM-

CCM-

CCM-

CCM-

CCM-

CCM-

CCM-

T1

T2

D1

D2

D3

S1

S2

S3

EDA

EDA-A

ECSA (m2 g-1)

5.32

6.51

5.64

6.51

5.17

3.15

3.65

3.32

7.35

7.85

Rf

1.08

1.35

1.16

1.35

1.06

0.65

0.75

0.69

1.53

1.63

Electrochemical reactions express the electron transfer at the electrode surface. In fact, this reaction is a function of mobility of ions in the electrolyte, attracted electroactive components, and double-layer capacitance at the Pt layer/Nafion interface.25,44,45 Interlinked hydrophilic pathways in Nafion structure, and porous nanostructure of Pt-catalyst creating near surface, provide proton transport. In Xi and Zhao46 it reveals that two ends of a single conductive nanowire possess more net surface charges than the middle part. Figure 8 shows Nyquist plots obtained by EIS for selected samples in each inquiry (based on previous results to prevent rehash). The frequency requirement for impedance can reveal the electrochemical processes in CCMs. In Figure 8 the semicircle in Nyquist plot is hardly distinguished in low-frequency region; that indicate high conductivity in these CCMs; however, the sharpest vertical line was observed for CCM-EDA-A indicating the highest charge storage capacity of this CCM. In high frequency, the greatest slope (the least semicircle radiant) area was detected for CCM-EDA-A, that indicates lower impedance (charge transfer resistance) in high frequency than other 29



CCMs;27,44,45,47 Achieved results of the EIS, indicated that Pt loading occupied ionic clusters of the membrane, also could prevent swelling of the water absorption channel, therefore reduced proton conductivity in un-modified CCMs.36 As it can be seen in Figure 3, CCM-EDA-A had the optimum particle size, distribution, and porosity; in another hand, it had the highest percent of WU because of using EDA as a modifier. The proton conductivity was closely related to the mobility of water molecules. Therefore, increasing the proton conductivity is attributed to the vehicle mechanism of hydrated cation cluster in the Nafion membrane; coordination between proton conductivity and WU in this study can be seen in Figure 9.

Figure 8. Comparing normalized Nyquist plots of selected hydrated-CCMs in full view and in the selected region in high frequency.

30


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EIS data were analyzed by fitting results to Randles equivalent electrical circuit model that includes a proton resistance (Rs), a double layer capacitor (Cdl) and a charge transfer resistance (Rct). Randles model and its Results are shown in Figure 10.44 As the results in Table 1 and Figures 9 and 10 indicate, with amplification in Pt loading, Nafion clusters were squeezed by the Pt particles and in consequences, the WU and proton conductivity were reduced in non-modified CCMs; but in higher amount of Pt loading in modified CCMs more polar groups were increased WU and proton conductivity.25 The interfacial resistance between the polymer electrolyte and the catalyst layer is one of the factors responsible for the proton resistance (versus to proton conductivity). In Nyquist plot, the high-frequency digit on the real axis (x-axis) was used to calculate the protonic conductivity of CCMs by using equation 3. The charge transfer resistance (Rct) estimated from the diameter of the semicircle was caused by electrochemical activity loss in the cathode catalyst. EIS results reveal EDA-modifying of Nafion membranes have an enhancing impact not only on the proton conductivity but also on the capacitive characteristic of the CCMs.

Figure 9. Water uptake and proton conductivity in different CCMs.

31



Figure 10. Randles model and variation in charge transfer resistance (Rct), double layer capacitance (Cdl) and ionic conductivity (σ) of CCMs.

3.5 Fuel cell performance of fabricated CCMs The current-voltage characteristics of CCMs were obtained by activating the electrodes, between open circuit potential and gradually increasing the current that is brought in Figure 11. It was proved that activation cycle is necessary to activate the catalyst for higher performance to avoid “reversible degradation” effect48. According to the prior results, best CCM of each inquiry was chosen to fuel cell performance analyzing as cathode. The OCV directly related to the mount of catalyst loading in cathode site. By a comparison between Pt loading and Cell voltage given in Table 1 and 3, it is clear that more Pt loading resulted in higher voltage cell. Cathode catalyst layer perform as catalysis of cathode reaction, oxygen transport to reaction sites, proton 32


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conduction from membrane to reaction sites, electron conduction from substrate to reaction zone, and water and heat generation removal from reactive zone into substrate. Activation process of cathode leads to a significant voltage drop in initiate current density (>100 mA). The slop of this region is affected by catalyst properties. It was observed that catalyst with less thickness, narrow distribution of particle size, more adhesion and porosity had lower slop in this region. As it has seen in Figures 2, 3, 4, and 5 Pt particle distributions in bulk of Nafion membrane for CCM-D3, CCM-D2, CCM-EDA and CCM-EDA-A are more suitable, respectively. The total Ionic resistance _which takes place inside the membrane electrolyte and catalyst where proton transport occurs_ controls the slope of the pseudo-linear middle portion of the I-V curve, whereupon, using same membrane (Nafion) in all samples resulted in almost equal slop in middle part of the curves. Figure 12 shows coordination of ECSA and current density of selected samples. Therefore, with the rising catalyst activity of Pt particles (ECSA), the current density increases too.49,50 This feature is ascribed to EDA-modified CCMs lead to an increment of proton conductivity (decrease of Ohmic resistance) and finally CCMs performance.30 In assessment, the effects of EDA-modifying and NaOH attendance in performance of CCMs are thinner thickness, good distribution of Pt particles in CCM-EDA-A which led to higher ECSA and proton conductivity and as a consequence increasing the maximum power density up to 29.7% and 6.6% compares with CCM-D2 and CCM-EDA, respectively. Although the fuel cell performance in this work was not higher than others study. This could be due to the rising of the electrical resistance of interfacial contact between the membrane, the catalyst layer and instrument.

33



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Figure 11. Polarization curve of the selected CCMs obtaining at 70 °C using wet H2 and air at the

anode and cathode by 300 mL min-1 follow rate, with 2.3×2.3 cm2 active area.

Table 3 Maximum power density, cell voltage and current density of selected CCMs.

Sample

Maximum power (mW cm-2)

Cell voltage (v)

Current density (mA cm-2)

CCM-D2

324

0.79

345

CCM-D3

290

0.85

290

CCM-EDA

385

0.95

594

CCM-EDA-A

412

0.96

753

34


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Figure 12. Comparison of ECSA and current density of single cells base on prepared CCMs.

4.

CONCLUSION

In the present work, we have optimized Pt-coated Nafion membrane for PEMFCs, using a controllable and one-sided method. This method provides condition to control and optimize the size of nano particles, distribution, and penetration onto the bulk of Nafion. Different conditions, including temperature, duration of the absorption and reduction process, kind of solvent, modification of membrane with ethylenediamine and effect of hydroxide attendance in reduction process was investigated. CCMs producing by EDA-modified Nafion in the temperature of 40º C, Pt(NH3) 4+2 aqueous solution, and 2-hour process (in sum), possess the best morphologically and electrochemically, among others. Adding hydroxide in reduction process leads to smaller Pt particle and more uniform distribution onto the membrane. By using EDA-modified membrane in cationic solvent, cation-acceptation has been proved. Creation new cationic site on Nafion membrane by EDA-modification and using Pt in form of cation resulted in more tendencies to 35



nucleation, simultaneously; adding hydroxide into reduction agent lead to create electrostatic repulsion within sulfunate-hydrophilic site into the membrane and prevent nucleation in depth of the balk where Pt particles have not access for electrocatalytic activation. It was proved an amount of the Pt which was toward to polymer electrolyte, was electrochemically active. Optimized CCM prepared has shown performance of 750 mA cm-2 @ 0.5 V and 7.85 m2 g-1 ECSA, this CCM possessed better performance compared to the other CCMs that fabricated in similar methods. Although the optimized CCM performance is less than that of recent works using CCM method with almost similar Pt loading (about 1000 mA cm-2 @ 0.5 V)51, but controllable and repeatable method for CCM procedure, make it the novel Pt catalyst, counter as a potential candidate for future studying of PEMFCs.

AUTHOR INFORMATION

Corresponding Author

*Tel.: +98 2164545806. E-mail: [email protected].

Acknowledgement

The authors are grateful to the Renewable Energy Research Center (Amirkabir University of Technology, Tehran, Iran) for the financial support of this work. 36


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REFRENCES

(1) Rao, C. R. K.; Trivedi, D. C. Chemical and electrochemical depositions of platinum group metals and their applications, Coord. Chem. Rev. 2005, 249, 613–631.

(2) Mehta, V.; Cooper, J. S. Review and analysis of PEM fuel cell design and manufacturing, J. Power Sources 2003, 114, 32–53.

(3) Tiwari, R.; Garcia, E.; The state of understanding of ionic polymer metal composite architecture: a review, Smart Mater. Struct. 2011, 208, 830–841.

(4) Rajalakshmi, N. H.; Ryu, Dhathathreyan, K. S. Platinum catalysed membranes for proton exchange membrane fuel cells - higher performance, Chemical Engineering Journal 2004, 102, 241–247.

(5) Cho, K. Y.; Yeom, Y. S.; Seo, H. Y.; Kumar, P.; Lee,A. S.; Baek, K. Y.; Yoon, H. G. Molybdenum-doped PdPt@ Pt Core-shell Octahedra Supported by Ionic Block Copolymer-functionalized Graphene as a Highly Active and Durable Oxygen Reduction Electrocatalyst, ACS Appl. Mater. Interfacess 2017, 9, 1524–1535.

(6) Ravichandran, S.; Venkatkarthick, R.; Sankari, A.; Vasudevan, S.; Davidson, D. J.; Sozhan, G. Platinum deposition on the nafion membrane by impregnation reduction using nonionic surfactant for water electrolysis e An alternate approach, Energy 2014, 68, 148–151.

(7) Lohrasbi, E.; Javanbakht, M.; Ahmadi, S. Synthesis of Graphene-Supported PtCoFe Alloy 37



with Different Thermal Treatment Procedures as Highly Active Oxygen Reduction Reaction Electrocatalysts for Proton Exchange Membrane Fuel Cells, Ind. Eng. Chem. Res. 2016, 34, 9154–9163.

(8) Weppner, W. Characterization and Sensing Property Studies of the Pt I Nation Electrode Prepared by the Chemical Reduction Method, Ionics 2005, 11, 177–183.

(9) Shen, M.; Roy, S.; Scott, K. Preparation and characterisation of Pt deposition on ion conducting membrane for direct methanol fuel cell electrodes, J. Appl. Electrochem. 2005, 35, 1103–1109.

(10) Fedkiw, P. S.; Her, W. An Impregnation-Reduction Method to Prepare Electrodes on Nafion SPE, J. Electrochem. Soc. 1989, 136, 899–900.

(11) Chabi, S.; Kheirmand, M. Applied Surface Science Electrocatalysis of oxygen reduction reaction on Nafion / platinum / gas diffusion layer electrode for PEM fuel cell, Appl. Surf. Sci. 2011, 257, 10408–10413.

(12) Takenaka, H.; Torikai, E.; Kawami, Y.; Wakabayashi, N.; City, I. Solid polymer electrolyte water electrolysis, Int. J. Hydrogen Energy 1982, 7, 397–403.

(13) Lee, J.; Yoo, Y. The Structure and Performance of Ionic Polymer-Metal Composite Actuators Prepared via Electroless Plating Process Using Various Alcohols, Macromol. Symp. 2007, 249, 56–60.

38


Page 38 of 58

Page 39 of 58 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(14) Bessarabov, D. G.; Michaels, W.C.; Popkov, Y.M. Galvanodynamic study of the electrochemical switching effect in perfluorinated cation-exchange membranes modified by ethylenediamine, J. Membr. Sci. 2001, 194, 81–90.

(15) Bessarabov, D. G.; Michaels, W.; Vermeulen, J. P.; Africa, S. Electroless Deposition of Platinum on Proton-Conductive Perfluorinated Membranes Modified with Ethylene Diamine, Ionics 1999, 5, 52–58.

(16) Xi, S.; Liu, X.; He, T.; Tian, L.; Wang, W.; Sun, R.; He, W.; Zhang, X.; Zhang, J.; Ni, W.; Zhou, X. “Hot spots” growth on single nanowire controlled by electric charge, Nanoscale 2016, 8, 12029–12034.

(17) Sode, A.; Ingle, N. J. C.; Mccormick, M.; Bizzotto, D.; Gyenge, E.; Ye, S. Controlling the deposition of Pt nanoparticles within the surface region of Nafion, J. Membr. Sci. 2011, 376, 162–169.

(18) Ingle, N. J. C.; Sode, A.; Martens, I.; Gyenge, E.; Wilkinson, D. P.; Bizzotto, D. Synthesis and characterization of diverse Pt nanostructures in Nafion, Langmuir 2014, 30, 1871– 1879.

(19) Shabanikia, A.; Javanbakht, M.; Salar Amoli, H.; Hooshyari, K. H.; Enhessari, M. Polybenzimidazole/strontium cerate nanocomposites with enhanced proton conductivity for proton exchange membrane fuel cells operating at high temperature, Electrochim. Acta 2015, 154, 370–378. 39



(20) Hooshyari, K.; Javanbakht, M.; Adibi, M. Novel composite membranes based on PBI and dicationic ionic liquids for high temperature polymer electrolyte membrane fuel cells, Electrochim. Acta 2016, 205, 142–152.

(21) Hooshyari, K.; Javanbakht, M.; Shabanikia, A. Fabrication BaZrO3 / PBI-based nanocomposite as a new proton conducting membrane for high temperature proton exchange membrane fuel cells, J. Power Sources 2015, 276, 62–72.

(22) Beydaghi, H.; Javanbakht, M. Aligned nanocomposite membranes containing sulfonated graphene oxide with superior ionic conductivity for direct methanol fuel cell application. Ind. Eng. Chem. Res. 2015, 54, 7028–7037.

(23) Beydaghi, H.; Javanbakht, M.; Kowsari, E. Synthesis and characterization of poly (vinyl alcohol)/sulfonated graphene oxide nanocomposite membranes for use in proton exchange membrane fuel cells (PEMFCs). Ind. Eng. Chem. Res. 2014, 43, 16621–16632.

(24) Hooshyari, K.; Javanbakht, M.; Naji, L.; Enhessari, M. Nanocomposite proton exchange membranes based on Nafion containing Fe2TiO5 nanoparticles in water and alcohol environments for PEMFC, J. Membr. Sci. 2014, 454, 74–81.

(25) Naji, L.; Safari, M.; Moaven, S. Fabrication of SGO/Nafion-based IPMC soft actuators with sea anemone-like Pt electrodes and enhanced actuation performance, Carbon 2016, 100, 243–257.

(26) Beydaghi, H.; Javanbakht, M.; Salar Amoli, H.; Badiei, A.; Khaniani, Y.; Ganjali, M. R.; 40


Page 40 of 58

Page 41 of 58 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Norouzi, P.; Abdouss, M. Synthesis and characterization of new proton conducting hybrid membranes for PEM fuel cells based on poly(vinyl alcohol) and nanoporous silica containing phenyl sulfonic acid, Int. J. Hydrogen Energy 2011, 36, 13310–13316.

(27) Yuan, X. Z.; Song, C.; Wang, H.; Zhang, J. Electrochemical impedance spectroscopy in PEM fuel cells: fundamentals and applications, Springer 2009.

(28) Jeon, J. H.; Yeom, S. W.; Oh, I. K. Fabrication and actuation of ionic polymer metal composites patterned by combining electroplating with electroless plating, Composites, Part A 2008, 39, 588–596.

(29) Lee, H.; Habas, S.E.; Kweskin, S.; Butcher, D.; Somorjai, G. A.; Yang, P. Morphological Control of Catalytically Active Platinum Nanocrystals13, Angew. Chem., Int. Ed. 2006, 45, 7824–7828.

(30) Lee, P.; Han, T.; Ouk, D.; Lee, J.; Kang, S.; Chung, C.; Lee, Y.; Cho, S. M.; Choi, H.; Kim, T.; Lee, E.; Nam, J. In situ formation of platinum nanoparticles in Nafion recast film for catalyst-incorporated ion-exchange membrane in fuel cell applications, J. Membr. Sci. 2008, 322, 441–445.

(31) Stoechiomotriques, N.; Cedex, O.; Mindrale, E.; Cedex, H.; Received, F. Preparation of solid polymer electrolyte composites: investigation of the ion-exchange process, J. Appl. Electrochem. 1995, 25, 227–232.

(32) Kim, T.; Yi, J.; Jung, C.; Jeong, E. Solvent effect on the Nafion agglomerate morphology in 41



the catalyst layer of the proton exchange membrane fuel cells, Int. J. Hydrogen Energy 2016, 42, 6–13.

(33) Hawut, W.; Pruksathorn, K. Platinum electroless deposition on Nafion membrane for PEM fuel cells, Korean J. Chem. Eng. 2006, 23, 555–559.

(34) Lufrano, F.; Passalacqua, E.; Squadrito, G.; Patti, A.; Giorgi, L. Improvement in the diffusion characteristics of low Pt-loaded electrodes for PEFCs, J. Appl. Electrochem. 1999, 29, 445–448.

(35) Moore, R. B.; Mauritz, K. A.; Moore, R. B. State of Understanding of Nafion State of Understanding of Nafion, Chem. Rev. 2004, 104, 4535–4586.

(36) Choi, P.; Jalani, N. H. Thermodynamics and Proton Transport in Nafion - II . Proton Diffusion Mechanisms and Conductivity, J. Electrochem. Soc. 2005, 152, 123–130.

(37) Arscott, P. G.; Wenner, J. R.; Bloomfield, V. A. DNA Condensation by Cobalt Hexaammine ( 111 ) in Alcohol- Water Mixtures : Dielectric Constant and Other Solvent Effects, Biopolymers 1995, 36, 345–364.

(38) Bessarabov, D. G.; Michaels, W.; Sanderson, R. D. Preparation and characterisation of chemically-modified perfluorinated cation-exchange platinum-containing membranes, J. Membr. Sci. 2000, 179, 221–229.

(39) Zhu, Z.; Chang, L.; Takagi, K.; Wang, Y.; Chen, H.; Li, D. Water content criterion for 42


Page 42 of 58

Page 43 of 58 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


relaxation deformation of Nafion based ionic polymer metal composites doped with alkali cations Water content criterion for relaxation deformation of Nafion based ionic polymer metal composites doped with alkali cations, Appl. Phys. Lett. 2014, 105, 1–4.

(40) Ruge, M.; Drnec, J.; Rahn, B.; Reikowski, F.; Harrington, D.A.; Carlà, F.; Felici, R.; Stettner, J.; Magnussen, O.M. Structural Reorganization of Pt (111) Electrodes by Electrochemical Oxidation and Reduction. J. Am. Chem. Soc. 2017, 139, 4532-4539.

(40) Inaba, M.; Ando, M.; Hatanaka, A.; Nomoto, A.; Matsuzawa, K.; Tasaka, A.; Kinumoto,T.; Iriyama, Y.; Ogumi, Z. Controlled growth and shape formation of platinum nanoparticles and their electrochemical properties. Electrochim. Acta 2006, 52, 1632-1638. (42) Stamenkovic, V.; Grgur, B.N.; Ross, P.N.; Markovic, N.M. Oxygen Reduction Reaction on Pt and Pt-Bimetallic Electrodes Covered by CO Mechanism of the Air Bleed Effect with Reformate. J. Electrochem. Soc. 2005, 152, 277-282. (43) Kucernak, A.R.; Muir, B. Analysis of the electrical and mechanical time response of solid polymer – platinum composite membranes, Electrochim. Acta 2001, 46, 1313–1322.

(44) Cho, Y.; Wan, J.; Sik, Y.; Cho, Y.; Kim, O.; Kwon, N.; Joong, O.; Yoon, W.; Choe, H.; Sung, Y. The dependence of performance degradation of membrane electrode assembly on platinum loading in polymer electrolyte membrane fuel cell, Int. J. Hydrogen Energy 2011, 37, 2490–2497.

(45) Safari, M.; Naji, L.; Baker, R. T.; Afshar, F. The enhancement effect of lithium ions on

43



actuation performance of ionic liquid-based IPMC soft actuators, Polymer 2015, 76, 140– 149.

(46) Xi, S.; Zhou, X., Multifunctions of Net Surface Charge in the Reaction on a Single Nanoparticle, J. Phys. Chem. C. 2016, 120, 16608-16616.

(47) Mohammad, S.; Niya, R.; Phillips, R. K.; Hoorfar, M. Process modeling of the impedance characteristics of proton exchange membrane fuel cells, Electrochim. Acta 2016, 191, 594-605.

(48) Ning, F.; He, X.; Shen, Y.; Jin, H.; Li, Q.; Li, D.; Li, S.; Zhan, Y.; Du, Y.; Jiang, J. Yang, H. Flexible and Lightweight Fuel Cell with High Specific Power Density, ACS nano 2017.

(49) Wang, C.; Zhang, Q.; Shen, S.; Xiaohui, Y.; Zhu, F.; Cheng, X. The respective effect of under-rib convection and pressure drop of flow fields on the performance of PEM fuel cells, Sci. Rep. 2017, 7, 1–9.

(50) Weiß, A.; Schindler, S.; Galbiati, S.; Danzer, M. A.; Zeis, R. Distribution of Relaxation Times Analysis of High-Temperature PEM Fuel Cell Impedance Spectra, Electrochim. Acta 2017, 23, 391-398.

(51) Sassin, M.B.; Garsany, Y.; Gould, B.D.; Swider-Lyons, K.E.; Fabrication Method for Laboratory-Scale High-Performance Membrane Electrode Assemblies for Fuel Cells, Anal. Chem. 2016, 511-518.

44


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Graphical abstract 151x159mm (300 x 300 DPI)



Chart 1 679x481mm (96 x 96 DPI)


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Figure 1 297x420mm (300 x 300 DPI)



Figure 2 674x1204mm (96 x 96 DPI)


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Figure 3 296x419mm (300 x 300 DPI)



Figure 4 254x190mm (96 x 96 DPI)


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Figure 5 203x222mm (300 x 300 DPI)



Figure 6 297x420mm (300 x 300 DPI)


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Figure 7 228x302mm (300 x 300 DPI)



Figure 8 297x420mm (300 x 300 DPI)


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Figure 9 297x420mm (300 x 300 DPI)



Figure 10 254x190mm (96 x 96 DPI)


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Figure 11 297x420mm (300 x 300 DPI)



Figure 12 254x190mm (96 x 96 DPI)


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Influence of Pt Nanoparticle Electroless Deposition Parameters on the

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