Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Thermal stability analysis of cold start processes in PEM fuel cells Weitong Pan a , Ping Li b , Quanquan Gan c , Xueli Chen a , Fuchen Wang a, ⁎ , Gance Dai b, ⁎ a Institute of Clean Coal Technology, East China University of Science and Technology, Shanghai 200237, China b State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China c Shanghai SinoFuelcell CO., Ltd., Shanghai 201401, China HIGHLIGHTS • Thermal stability analysis method for cold-start of PEM fuel cell is devel- oped. • Multiplicity features behind ice for- mation and thermal behavior are re- vealed. • Two startup modes and criteria for a successful one are proposed. • Temperature and concentration effects are clarified to improve operability. GRAPHICAL ABSTRACT ARTICLE INFO Keywords: Proton exchange membrane fuel cell Cold start criteria Steady-state multiplicity Thermal stability Mass transfer enhancement ABSTRACT Cold-start issue of proton exchange membrane (PEM) fuel cells is one of the major factors hindering its com- mercialization. The key element involved is the competition between ice formation and melting, behind which is the thermal behavior accompanied by nonlinear effects. In this work, the steady-state multiplicity feature during cold-start has been discovered based on the thermal stability analysis approach. The nonlinear heat generation term Q g and linear removal term Q r are separated from conservation equations and constructed against ice fraction. The plot thus obtained could identify the existence of multiplicity which is the intersection of the above two functions. Results indicate that one or two steady states arise for different operating conditions. The startup with only one steady state, namely the “extinguished” state is the worst condition and bound to fail. The startup with two steady states also incorporates an unstable one which denotes not only the critical transition from ice formation to melting but also the limit of the operational domain. Based on the theoretical analysis, simple and explicit criteria are quantitatively developed for the prediction of startup feasibility. Moreover, in order to ensure a reasonable and efficient operation, the impacts of key parameters are further summarized and discussed on the cold-start operability. The proposed approach that develops analytical expressions for the steady-state points provides a systematic yet simple way to reveal the essential physics of cold start. 1. Introduction Proton exchange membrane (PEM) fuel cell has been gaining much attention as one of the most promising energy conversion engines for transport, stationary and portable applications. The key benefits include the outstanding power density, high efficiency, low emissions and moderate operation [1–3]. However, restricted by the extremely cold weather in many regions, cold start operability of PEM fuel cell has become one of the major factors hindering its commercialization [4,5]. Cold start is defined as the startup from subzero temperature to the https://doi.org/10.1016/j.apenergy.2019.114430 Received 15 October 2019; Received in revised form 18 December 2019; Accepted 19 December 2019 ⁎ Corresponding authors. E-mail addresses: wfch@ecust.edu.cn (F. Wang), gcdai@ecust.edu.cn (G. Dai). Applied Energy 261 (2020) 114430 0306-2619/ © 2019 Elsevier Ltd. All rights reserved. T