Synthesis and Characterization of Organic Dyes Containing Various Donors and Acceptors

(1)

Synthesis and characterization of novel nanocomposite membrane of

sodium titanate/Nafion

®

Yongsheng Wei

a

, Liangbo Shen

b

, Fanghui Wang

c

, Wein-Duo Yang

d

, Hong Zhu

c,

⁎

,

Zhongming Wang

c

, Kefei Han

c

a

School of Science, Beijing Jiaotong University, Beijing 100044, PR China

b

Beijing No. 4 High School, Beijing 100034, PR China

c

Institute of Modern Catalysis, Department of Organic Chemistry, State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, PR China

d

Department of Chemical and Materials Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung 807, Taiwan, ROC

a b s t r a c t

a r t i c l e i n f o

Article history:

Received 8 November 2010 Accepted 25 February 2011 Available online 3 March 2011 Keywords:

Nanocomposite membrane Sodium titanate nanotubes FTIR

Nanocomposites Fuel cell

Novel nanocomposite membrane of sodium titanate/Naﬁon based on sodium titanate nanotubes with Naﬁon®

were prepared by solvent casting techniques. Nanotubes of sodium titanate were synthesized by hydrothermal method. TEM, XRD, and FTIR were employed to characterize the crystal phase, microstructure, and other physicochemical properties of the membrane and the nanotube samples. FTIR results showed us that the nanotube material of Na2Ti3O7has existed in the nanocomposite membrane of Na2Ti3O7/Naﬁon. The

existence of sodium titanate nanotubes in Naﬁon®_{improves the methanol crossover and makes promising}

practical value of blocking methanol in direct methanol fuel cells.

1. Introduction

Fuel cells have recently attracted considerable attention as an alternative energy-conversion technology that meets the demand of

sustainable development [1,2]. Direct methanol fuel cell (DMFC)

using an aqueous solution of methanol as fuel is one kind of PEMFC and is thought to be the most promising power generating system for

applications in portable electronic devices[3–5]. Proton exchange

membrane is one of key materials whether in DMFC. Presently,

commercially available perﬂuorinated membranes including Naﬁon®

have the problem of methanol crossover and reduce the performance of DMFC, which slowed the commercial process of direct methanol

fuel cell[6,7].

After literatures study, we found that modi_{ﬁcation of the}

perﬂuorinated sulfonic membrane is a doable method. It is a new

direction to prepare organic/inorganic composite membrane this way. Nanotubes of sodium titanate showed the special performance of conductivity and the water holding, which meets the requirements of

proton exchange membrane for better performance[8,9].

In this study, the sodium titanate nanotubes of micro-diameter

were synthesizedﬁrst, and then they were casted with Naﬁon®_to

change the structure of the novel nanocomposite membrane.

2. Experimental 2.1. Materials

Naﬁon®_{solution (5 wt.%) was purchased from DuPont, USA. N,}

N-dimethylformamide (DMF) was purchased from Beijing Yili Fine Chemicals Ltd., China. Methanol and pure sulfuric acid were purchased from Beijing Chemicals Ltd., China. Deionized water was used throughout the study.

2.2. Synthesis of sodium titanate nanotubes (Na2Ti3O7)

2 kg of anatase TiO2 (80–200 nm) is weighed into a ﬂask, and

15 ml of 10 M NaOH solution is added and then stirred with ultrasound for 2 h. The mixture is transferred into a high-pressure

reaction kettle lined with Teﬂon on the inner wall and sealed. The

water-heated mixture is allowed to react at 130 °C for 3 days. The reaction kettle was then cooled under natural condition to room

temperature and taken out, and the contentﬁltered. A white solid was

obtained, which was then washed with deionized water until the pH was 7 and dried to yield sodium titanate nanotubes.

2.3. Preparation of sodium titanate/Naﬁon®_{nanocomposite membranes}

Sodium titanate/Naﬁon® _{nanotube composite membrane was}

prepared. The base membranes were prepared by a solvent casting

technique in which the low-boiling-point alcohols in Naﬁon®

solution Materials Letters 65 (2011) 1684–1687

⁎ Corresponding author. Tel.: +86 10 82161887. E-mail address:zhuho128@126.com(H. Zhu).

Contents lists available atScienceDirect

Materials Letters

(2)

plays important role of net, which can prevent the methanol go

through the Naﬁon membrane and reduce the methanol crossover.

3.6. Water uptake

For most proton conductive polymers, water acts as the carrier for proton transportation through the membrane. Thus, adequate hydration of electrolyte membranes is crucial for high proton

conductivity. The results of water uptake for the Na2Ti3O7/Naﬁon®

composite membrane with different quality of nanotubes at room

temperature at different temperatures are shown inFig. 5-a. Water

uptake increases with the quality of the nanotubes. The water uptake

of the Na2Ti3O7/Naﬁon®composite membrane is higher than that of

Naﬁon®_{112 which is 10.4 wt.% at room temperature. It is believed that}

Ti–OH and H2O can form hydrogen bonds, which increases the

absorption of water. Besides, the nanotubes have a very high speciﬁc

surface area and may also lead to higher water adsorption. Overall, these results show that the composite membrane has higher water uptake and may lead to better performance in a fuel cell.

3.7. Swelling degree

The swelling degree of composite membrane affects the mem-brane performance. Too large a swelling degree will adversely affect the mechanical properties of the membrane and may crack the fuel cell and shorten its life.

The water swelling results of composite membranes of different

nano-material contents are shown inFig. 5-b. The swelling degree

increases with the nano-material content. Generally speaking, the change of nano-material content has little effect on the dimensions of the membrane. This indicates that composite membranes have good resistance to swelling. The reason is that there are abundant hydroxyl groups on the surface of nanotubes and these hydroxyl groups are highly hydrophilic. After the sodium titanate nanotubes have been

added to Naﬁon®_{and acidi}_{ﬁed, the sodium ions are replaced by the}

smaller hydrogen ions. The collapse of the original tubular structure leaves more space to accept water molecules without affecting the membrane volume. The introduction of water molecules provides the physical foundation for proton conductivity in the membrane.

4. Conclusions

Novel nanocomposite membranes of Na2Ti3O7/Naﬁon®for direct

methanol fuel cell are prepared by solvent casting techniques. The base material of sodium titanate nanotubes was synthesized by hydrothermal method. TEM and SEM test results show us that the diameter of nanotubes is in nanometer orders of magnitude and lies

the same direction as the nanocomposite membrane of Na2Ti3O7/

Naﬁon®_{. Introduction of nanotubes of Na}

2Ti3O7 affect the proton

conductivity of the nanocomposite membrane of Na2Ti3O7/Naﬁon®.

More meaning is that the methanol crossover can be improved. The nanotubes have dual role of blocking methanol crossover and better

ability in water holding. Na2Ti3O7/Naﬁon®composite membrane is

expected to have better performance and further promising in direct methanol fuel cell applications.

Acknowledgements

The authors gratefully acknowledge the ﬁnancial support from

International S&T Cooperation Program of China (No. 2006DFA61240 and No. 2009DFA63120), the National Science Foundation of China (No. 50674006, No. 20876013, and Key Program No. 20636060).

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1 3 5 7 10 10 15 20 25 T = 298 K Na2Ti3O7/Nafion

Water Uptake (w

t.%)

Na

2

Ti

3

O

7

content (wt.%)

1 3 5 7 10 10 11 12 13 14 15

T = 298 K

Na2Ti3O7/Nafion

Swelling degree (%)

Na

2

Ti

3

O

7

content (wt.%)

Blank Nafion

b

a

Fig. 5. (5-a) Water uptake of composite membranes with for different nanotubes contents at room temperature. (5-b) Swelling degree of composite membranes at room temperature.

1687 Y. Wei et al. / Materials Letters 65 (2011) 1684–1687