Characterization of Uncoated Stainless Steel as Proton Exchange Membrane Fuel Cell Bipolar Plates Material ~ N. Caqué 1,2 *, M. Paris 1 , M. Chatenet 2 , E. Rossinot 1 , R. Bousquet 3 , E. Claude 1 1 Axane Fuel Cell Systems, 2 rue Clémencière, BP15, 38360 Sassenage, France 2 LEPMI, UMR 5279 CNRS/Grenoble-UNP/Univ. de Savoie/Univ. Joseph Fourrier 1130 rue de la piscine, BP 75, 38402 Saint Martin d’Hères, France 3 ArcelorMittal Stainless & Nickel Alloys, Avenue Jean Jaurès, BP1, 58160 Imphy, France Received May 10, 2011; accepted August 26, 2011 1 Introduction Bipolar plates (BPs) are key components of proton exchange membrane fuel cell (PEMFC) stacks. They enable most of the in/out processes occurring in a fuel cell, like reac- tant supply to both electrodes, electrical conduction between adjacent cells as well as evacuation of the produced heat and water. Furthermore, BPs represent a large part (11–45%) of the total cost of a stack [1]. Graphite and carbon/polymer composites are often chosen for BP but, with its good me- chanical stability, gas tightness, and electrical conductivity, thin metal strips can replace these classic materials, possibly yielding to increased power density [2]. Metal coils can also be easily stamped or hydroformed [3], resulting in cheaper plates than graphite and composite ones. However, the BP environment under the PEMFC operat- ing conditions is very aggressive: (i) the proton exchange membrane (PEM) ionomer is a superacid, while the (electro)- chemical conditions in the vicinity of the BP are (ii) very oxi- dant at the cathode (above 0.85 V vs. SHE, with high oxygen partial pressure), and (iii) very reductive at the anode (below 0.15 V vs. SHE with high hydrogen partial pressure) [4]. As a result, metal BP may rapidly degrade and contaminate the membrane electrode assemblies (MEA). Makkus et al. [5] showed that metallic cations generated by BP corrosion migrate and diffuse from the BP|gas diffusion layer (GDL) interface to the PEM. These metal cations interact with the sulfonic acid groups of the PEM, yielding to PEM ionic conductivity decrease and physical crosslinking [6–8]. Furthermore, LaConti et al. [9] for iron, as well as the group of Grenoble for platinum [6, 7], both showed that metallic cat- ions promote the degradation of the polymer chains of the PEM, by an increased radical production [10]. – [ * ] Corresponding author, nicolas.caque@airliquide.com Abstract Thanks to their high conductivity, important gas tightness, good corrosion resistance, and low-cost manufacturing path- ways, stainless steels are considered as good candidates for proton exchange membrane fuel cell (PEMFC) bipolar plates materials. In this study, a proprietary alloy was identified as very promising: its initial electrical contact resistance (ECR) with the gas diffusion layer was low, while its corrosion resistance in simulated PEMFC environment was sufficient. Furthermore, the ECR did not increase dramatically during long-term potentiostatic and potentiodynamic polarizations in simulated PEMFC cathode and anode environments. Finally, the stainless steel was successfully tested for 3,000 h in a commercial system using a 16-cell stack, without detri- mental cell voltage losses. Keywords: Bipolar Plates, Corrosion, Electrical Contact Resistance, Long-term Operation, PEMFC, Uncoated Stain- less Steels – ~ Paper presented at the “Fundamentals and Developments of Fuel Cells – Conference 2011”, January 19–21, 2011, Grenoble, France. 248 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim FUEL CELLS 12, 2012, No. 2, 248–255 ORIGINAL RESEARCH PAPER DOI: 10.1002/fuce.201100080