Cold start analysis of polymer electrolyte membrane fuel cells Kui Jiao, Xianguo Li* Department of Mechanical & Mechatronics Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada N2L 3G1 article info Article history: Received 21 July 2009 Received in revised form 2 September 2009 Accepted 2 September 2009 Available online 9 October 2009 Keywords: Cold start Polymer electrolyte membrane fuel cell Membrane thickness and ionomer volume fraction Potentiostatic and galvanostatic External heating abstract Cold start is critical to the commercialization of polymer electrolyte membrane fuel cell (PEMFC) for practical applications such as backup power and automotive applications. In this study, various numerically simulated PEMFC cold start processes are analyzed. The success of the cold start process depends on the competition between how fast the cell is heated up to the freezing point temperature and how fast ice is formed and built up in the pores of the cathode catalyst layer (CL) blocking oxygen transport to the reaction sites; the success of the cold start process thus depends on the product water (i) that is absorbed into the ionomer in the CL and membrane, (ii) that is taken away in vapour form by the gas flows (can be neglected), and (iii) that is frozen into ice in the CL pores. It is found that the membrane thickness and the ionomer volume fraction in the CL play pivotal roles in reducing the amount of ice formation. A thicker membrane leads to a larger water capacity but a slower water absorption process, and increasing the ionomer volume fraction in the CL enlarges the ion- omer water capacity and enhances the membrane water absorption. Starting the cell under the potentiostatic condition is confirmed to be superior to the galvanostatic condition. Heating up the external surfaces and the inlet air enhances the temperature increment of the cell. However, the external heating methods have negligible improvement in reducing the amount of ice formation. Even though heating the inlet air is more effective in increasing the cell temperature than heating the outer surfaces, the heat capacity of the inlet air is low. ª 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. 1. Introduction Successful startup from subzero temperatures is of paramount importance for the commercialization of polymer electrolyte membrane fuel cell (PEMFC) for practical applications such as backup power and automotive applications. Even though various external heating methods can be used to ensure the cold start capability, the volume and weight of the system, as well as the operation complexity and installation costs all increase with the increment of the external heating power requirement. Analysis of the various cold start processes to achieving optimal design and operating strategy is therefore critical to simplify or cast off the external heating system. The previous experimental and numerical studies [1–20] have indicated that the competition between the heat gener- ation and ice formation is the key factor that dominates the cold start performance. During a cold start process, heat is generated from the electrochemical reactions, electron and ion transport, and water phase change; and water is produced in the cathode catalyst layer (CL) at the three-phase contact interface (ionomer, catalyst and reactant gas). The product water can be absorbed by the ionomer in the CL and * Corresponding author. Tel.: þ1 519 888 4567x36843; fax: þ1 519 885 5862. E-mail addresses: kjiao@uwaterloo.ca (K. Jiao), x6li@uwaterloo.ca (X. Li). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he 0360-3199/$ – see front matter ª 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2009.09.004 international journal of hydrogen energy 35 (2010) 5077–5094