Stainless steel bipolar plate coated with carbon nanotube (CNT)/polytetrafluoroethylene (PTFE) composite film for proton exchange membrane fuel cell (PEMFC)

doi:10.1016/j.jpowsour.2009.01.027

Journal of Power Sources

Volume 190, Issue 2, 15 May 2009, Pages 322-325

https://doi.org/10.1016/j.jpowsour.2009.01.027 Get rights and content

Abstract

Composite film of carbon nanotube (CNT) and polytetrafluoroethylene (PTFE) was successfully formed by using their dispersion fluids. This CNT/PTFE composite film was electrically conductive in the range of 10 S cm⁻¹. The proton exchange membrane fuel cell (PEMFC) was assembled with the stainless steel bipolar plate coated with the CNT/PTFE composite film. This coating decreased the contact resistance between the surface of the bipolar plate and the membrane electrode assemble (MEA). Therefore, the output power of the fuel cell increased by 1.6 times.

Introduction

The proton exchange membrane fuel cell (PEMFC) is an ideal candidate for automotive propulsion application, because it has high efficiency and cleanliness as a power source. Graphite bipolar plate has excellent natures in terms of chemical stability and electrical conductivity. However, it contributes significantly to the weight and cost of PEMFC although automotive application requires miniaturization and low cost. Metals such as stainless steel have been considered as alternative materials to graphite bipolar plate, because they are produced using chemical etching or press processes. Moreover, they are generally thinner than graphite bipolar plates thus resulting in a fuel cell stack that is both light in weight and small in volume.

An ideal bipolar plate material should be corrosion-resistant, because pH in fuel cell has a low value of 3.7–4.1 [1]. However, metal bipolar plates were corroded in the strong acidic environment in PEMFC. Therefore, carbon-based [2], [3], [4], [5] and metal-based [6] coating on metal bipolar plates has been studied to improve corrosion resistance and conductivity. Although amorphous carbon film coating on the metal bipolar plates increases the output power of fuel cell [2], [3], this technique is far from the practical application, because its coating cost using the chemical vapor deposition (CVD) method is of high value.

In this study, electrically conductive composite film consisting of carbon nanotube (CNT) and polytetrafluoroethylene (PTFE) was coated on stainless steel bipolar plates. Moreover, the contact resistance between the surface of the bipolar plate and the membrane electrode assembly (MEA), and the output power of the fuel cell were investigated.

Section snippets

Formation of CNT/PTFE composite film

CNT/PTFE composite film was formed from CNT and PTFE dispersion fluids. The CNT dispersion fluid was made from multi-walled type CNTs. Cellulose derivatives were added to the water to disperse the CNT. This CNT dispersion was made by means of the technique reported in Ref. [7]. The CNT concentration in the dispersion fluids was 3%. The CNTs were well-dispersed in the water even when the CNT concentration was of a high value. Water-based commercial PTFE dispersion was used in this study. The

Result and discussion

Fig. 1 shows the mixed dispersion fluids of CNT and PTFE made by two kinds of the methods. Fig. 1(a) shows the fluid which made by mixing the powdered CNT and the PTFE dispersion as a reference. When the powdered CNT was used, both the CNT and the PTFE were settled to the bottom of the bottle. Clear supernatant fluid was appeared at the top. Fig. 1(b) shows the dispersion fluid made by mixing dispersion fluids of the CNT and the PTFE. The CNT was well-dispersed in the PTFE dispersion. The CNT

Summary

The CNT/PTFE composite film was formed by using the dispersion fluids of the CNT and the PTFE. This film showed properties of electrical conduction facilitated by the CNTs within the film. The conductivity of the composite film increased with an increase in the CNT concentration. The film having the conductivity of 12 S cm⁻¹ was observed at the CNT concentration of 75%. The fuel cell assembled with the stainless steel bipolar plates, which was coated with this composite film, showed higher output

Acknowledgements

This work is supported by the research and study promotion program in Tokai University and the coordinate project for application and promotion of intellectual property by Foundation of Kanagawa Academy of Science and Technology. The authors would like to thank Mr. Y. Miyamoto of the Technical Service Coordination Office, Tokai University for the TEM investigations.

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Citation Excerpt :
Therefore, the MEA with the CNT interlayer was found to be durable for at least 24 h. Corrosion, referring to the oxidation of carbon or a metal, must be prevented in PEMFCs as they have acidic, oxidizing nature in the cathode. CNTs have superior corrosion resistance [36–40,44], which are comparable to those of other candidate components for preventing corrosion. Although even the multi-walled CNT begins oxidation from relatively higher temperatures (>400 °C) [36,44]; however, this is likely not to be a severe problem in PEMFCs considering their operating temperature.
Carbon nanotube (CNT) sheet was sandwiched between the cathodic GDBL and a bipolar plate of polymer electrolyte membrane fuel cells (PEMFCs). The CNT sheets were synthesized through the direct spinning method and investigated their morphological characteristics. The electrochemical performances of MEA with CNT interlayer were measured via polarizations, iR-free, and electrochemical impedance spectra (EIS) compared to the conventional MEA under elevating backpressure. The performance of the MEA with CNT interlayer at 1.0 bar_g was enhanced by 91.8% (364 mW cm⁻² at 0.7 V), which was higher than the peak power density improvement of 13.0% (850 mW cm⁻² at 0.48 V). We also identified that corresponding ohmic and charge-transfer resistances were reduced. Especially, the ohmic resistance was decreased by up to 42.2% with increasing operating pressure compared to the conventional MEA due to better hydration and interfacial contact. Notwithstanding that the performance was ameliorated with increased pressure, we found that the mass transport loss tends to become more sensitive at the high current density region, and thus optimum operating conditions were proposed. We concluded that the CNT sheet as a functional interlayer would be advantageous in improving the performance of commercialized PEMFCs.
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Short communicationStainless steel bipolar plate coated with carbon nanotube (CNT)/polytetrafluoroethylene (PTFE) composite film for proton exchange membrane fuel cell (PEMFC)

Abstract

Introduction

Section snippets

Formation of CNT/PTFE composite film

Result and discussion

Summary

Acknowledgements

Electrochim. Acta

Surf. Coat. Technol.

Diamond Relat. Mater.

J. Power Sources

Short communication
Stainless steel bipolar plate coated with carbon nanotube (CNT)/polytetrafluoroethylene (PTFE) composite film for proton exchange membrane fuel cell (PEMFC)