Electrically Conductive CNT/PTFE Composite Film for Corrosion Resistant Coating on Bipolar Plate of Fuel Cell
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Electrically conductive CNT/PTFE composite film for corrosion resistant coating on bipolar plate of fuel cell Y. Show, K. Takahashi, R.Nishimura, K.Kohara, Y.Fukami and H.Murata Department of Electrical and Electronic Engineering, Tokai University 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292, JAPAN ABSTRACT Composite film of carbon nanotube (CNT) and polytetrafluoroethylene (PTFE) was formed with despersion fluid of CNT and PTFE. The film showed high electrical conductivity in the range of 5-13S/cm. This conductive film was applied on the stainless steel bipolar plate for the polymer electrolyte membrane fuel cell (PEMFC) as anticorrosion film. This coating decreased the contact resistance between the surface of bipolar plate and the membrane electrode assembly (MEA) of the PEMFC. Therefore, the output power of the fuel cell was increased by 1.6 times. INTRODUCTION Polymer electrolyte membrane fuel cells (PEMFC) are environmentally friendly and highly efficient power source. One of the applications is electric power source of automobiles [1,2]. The fuel cells for the automobile application are required to be miniaturization, high reliability and low cost. The bipolar plate is one of the high cost parts of the PEMFC, because more than hundred peaces of the bipolar plates are used in the PEMFC stack for automobile application. The stainless steel (SS) is a candidate material of the bipolar plate to reduce production cost of the PEMFC. Moreover, the SS bipolar plats achieve minimizing the PEMFC, since they are generally thinner than graphite bipolar plates. An ideal bipolar plate should be corrosion-resistant, because inside of the PEMFC is acid environment with pH of 3.7-4.1[3]. However, the SS bipolar plates are corroded during the operation of the PEMFC. Therefore, anticorrosion coating to the bipolar plates has been studied using carbon-based [4-7] and metal-based film[8]. In this study, the carbon nanotube and polytetrafluoroethylene (CNT/PTFE) composite film [9] was formed, and was coated on SS bipolar plates for the PEMFC as anticorrosion film, because this film is electrically conductive and chemically stable. Therefore, the contact resistance between the surface of the bipolar plate and the membrane electrode assembly (MEA) was decreased, and the output power of the fuel cell was increased. EXPERIMENT 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 (Ohashi Kasuga Tsusho Inc.) with 10nm in the diameter and 100µm in length. Cellulose derivatives were added to the water to disperse the CNT. This CNT dispersion was made by means of the technique reported in reference [10]. The CNT concentration in the dispersion fluid 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 (Daikin Industries, Ltd.) was used in this study. The PTFE particles in the water were 0.20-0.40µm in diameter. The PTFE c
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