IDENTIFICATION OF A CRITICAL INITIAL TEMPERATURE WINDOW FOR PEMFC COLD START UNDER LINEAR 25 S LOADING BASED ON A ONE-DIMENSIONAL MULTIPHASE MODEL

The low-temperature cold-start capability of proton exchange membrane fuel cells (PEMFCs) is strongly influenced by the initial temperature and the water-thermal coupling behavior within the stack. In this study, a one-dimensional multiphase cold-start model was developed based on a lumped-parameter approach. A 5 kW stack consisting of 30 single cells was investigated under a unified linear 25 s loading strategy, in which the current density was linearly increased from 0 to 0.5 A·cm -2 and then maintained constant. The cold-start evolution characteristics were systematically analyzed over an initial temperature range from -4 °C to -20 °C. The simulation results reveal the existence of a distinct critical initial temperature interval (approximately -12 °C to -14 °C) under the prescribed loading protocol, with the upper and lower bounds corresponding to two fundamentally different evolutionary pathways. When the initial temperature exceeds the lower bound of this interval, the stack establishes a stable positive thermo-electrical coupling feedback, enabling voltage recovery and sustained operation. In contrast, when the initial temperature falls below this interval, the system progressively enters an irreversible degradation trajectory and ultimately becomes unstable. Further analysis indicates that the decisive factor governing cold-start success is not the overall heat generation level, but whether the edge cells can surpass the freezing point and complete ice melting within a critical time window. These findings provide a theoretical basis for cold-start boundary identification and strategy optimization.