Investigation of the Electrical Properties of Polymer/Carbon Composites Exposed to Joule Heating and Heat Treatment

Abstract

The bipolar plates are the essential part of Proton Exchange Membrane (PEM) fuel cells made of polymer-based-carbon composite or coated metallic materials. The composite type of bipolar plates has different microstructural and electrical properties that can considerably change under the operating conditions because of exposing to the high body temperature of the fuel cell and flowing the electric current from the parts named joule-heating effect. In this research, the different types of composites, containing phenolic resin as matrix and carbon fiber, graphite, and expanded graphite as filler, have been manufactured. The structural and electrical properties have been investigated by performing the heat-treatment (in three temperatures of 50, 100, and 150 • C) and joule-heating effect (in three induced powers 1.5, 5, and 10 W) tests. Here, the effect of time has been investigated too. Finally, SEM and optical microscopes, as well as DSC-TGA, electrical conductivity, and performance analyses are used for characterization. The results of electrical conductivity of different composites in the heat-treatment and joule heating effect tests showed that some of composite have a positive and some of them show negative temperature coefficient of resistivity. Bipolar plates are key components of Proton Exchange Membrane Fuel Cells (PEMFC). They are responsible for functions of vital importance to the long-term operation of these electrochemical devices. They play major roles in water and gas management, mechanical stability and electrical performance of fuel cells. 1-3Carbon-polymer (P) composites with either thermoplastic or thermoset matrices are advantageous over metallic materials with regard to corrosion resistance, low weight, and easy productablity.21 These carbon-polymer composites applied for bipolar plates usually contain the thermoset or thermoplastics as matrix and carbon fiber (CF), graphite (G), expanded graphite (EG), and carbon black (CB), carbon nanotube (CNT) as reinforcement.1-9 These fillers differ with together from the viewpoint of morphology and electrical conductivity. Therefore, it is anticipated that the electrical conductivity of their composites differs from each other. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] The electrical conductivity of composite bipolar plates is the most important properties of in DOE. There are some parameters influencing on the electrical conductivity of composites, such as filler content, filler length, filler aspect ratio, filler size, filler orientation, filler surface energy, matrix surface energy, and so on Ref. 7. Moreover, the body temperature of the fuel cell and passing electricity of different layers of the fuel cell during the operation can change the microstructural and electrical properties of composite layers such as bipolar plates and gas diffusion layer (GDL). It has been established that the passage of electrical conductivity and the high body temperature can influence on electrical conductivity of the composites, 21-24 the...

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