INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 13, No. 12, pp. 2183-2186 DECEMBER 2012 / 2183 © KSPE and Springer 2012 Graphite Foil Based Assembled Bipolar Plates for Polymer Electrolyte Fuel Cells Sanghoon Ji 1 , Yong-Sheen Hwang 2 , Taehyun Park 3 , Yoon Ho Lee 3 , Jun Yeol Paek 3 , Ikwhang Chang 1 , Min Hwan Lee 4 , and Suk Won Cha 3,# 1 Department of Intelligent Convergence Systems, Seoul National University, Daehak-dong, Gwanak-gu, Seoul, South Korea, 151-742 2 Fuel Cell Vehicle Team, Hyundai Motor Company, 104 Mabuk-dong, Giheung-gu, Yongin, South Korea, 446-912 3 School of Mechanical and Aerospace Engineering, Seoul National University, Daehak-dong, Gwanak-gu, Seoul, South Korea, 151-742 4 School of Engineering, University of California, Merced, 5200 North Lake Road, Merced, CA 95343, USA # Corresponding Author / E-mail: swcha@snu.ac.kr, TEL: +82-2-880-8050, FAX: +82-2-880-1696 KEYWORDS: Assembled bipolar plate, Graphite foil, Polycarbonate, Current collector, Support, Polymer electrolyte fuel cell (PEFC) Graphite foil has been considered as a promising bipolar plate material in polymer electrolyte fuel cells due to its high electrical conductance and high corrosion resistance as well as low manufacturing costs. However, the highly flexible character of graphite foil led to physical deformation under external mechanical and thermal stimuli during fuel cell operations. In this study, we show a modified bipolar plate to overcome the weakness by combining with a mechanically sturdy component – polycarbonate plate. A unit cell with the assembled bipolar plates showed stable powering behaviors under thermal cycling. There was no significant difference in ohmic resistance between a unit cell with the assembled bipolar plates and a unit cell with graphite plates. Manuscript received: July 2, 2012 / Accepted: August 17, 2012 1. Introduction Polymer electrolyte fuel cells (PEFCs) have gained much attention as a next-generation renewable energy conversion device due to their high energy efficiency and low operating temperature. 1 By many researches related to physical and chemical properties, an electro- chemical performance of PEFCs reached close to the commercial level. However, their high manufacturing cost is still impeding their active commercialization. 2-6 Particularly, graphite plates widely used as separators in PEFCs comprise more than 20% of the PEFC stack manufacturing cost for large volume manufacturing. 7-9 Graphite foil has been considered a prospective bipolar plate material due to the excellent electrical and thermal properties, and its low manufacturing cost. 10,11 However, graphite foil bipolar plates can be easily deformed by clamping forces applied to ensure decent fuel cell performance. 12 Moreover, repetitive start and stop operations can cause deformations of the bipolar plates, which result in non-uniform pressure at the interface with the membrane electrode assembly (MEA). 13 Therefore, it is highly required to find effective ways to prevent graphite foil from being deformed by external mechanical and thermal stimuli. In this study, we designed bipolar plates that are assembled by combining graphite foils and polycarbonate plates. Graphite foil with flow-fields acts as a current collector and polycarbonate plate supports structure of the graphite foil. To investigate the effect of thermal cycle on cell performance, start/stop operations were conducted for 3 days. The feasibility of the assembled bipolar plate in PEFCs was studied by comparing polarization and ohmic resistances of a unit cell with the assembled bipolar plates (using a graphite foil) with those of a unit cell with graphite bipolar plates only (we call it the reference cell). 2. Experimental Procedure A unit cell having an active area of 25 cm 2 with membrane electrode assembly (MEA; 7-layer series, 3 M Corp.) was clamped by applying a torque of 30 kgf·cm and sealed with silicon-based sealants. 14 Heating of cells was carried out by conductive cartridge heater units. Table 1 shows the experimental conditions and features of the MEA used for the study. All MEAs were activated at 60 o C for six hours with fully humidified hydrogen and air, which allegedly caused little changes in the voltage behaviors with test time until a performance degradation occurred. 15 Custom-made station was used to evaluate electrochemical performance of cells. Fig. 1 shows a schematic dia- gram of the station. Fully humidified hydrogen and air were supplied with a flow rate of 0.2 and 1.0 lpm, respectively. The discharge of cells was controlled by direct current electronic loader DOI: 10.1007/s12541-012-0289-7