Numerical investigation of low-temperature cold start in PEM fuel cell stacks: Effects of initial hydration and current loading strategies

Proton exchange membrane fuel cells (PEMFCs) are promising power sources for clean transportation and distributed generation due to their high efficiency and zero emissions. However, reliable self-start at subzero temperatures remains a major barrier to large-scale deployment in cold regions. During cold start, heat generation facilitates stack warming, while ice formation within the membrane electrode assembly (MEA) blocks reactant pathways, leading to voltage collapse and irreversible damage. In this study, a one-dimensional, stack-scale transient model is developed and experimentally validated at −10 °C. The model considers the electrochemistry, multiphase water transport, phase change, and heat transfer, enabling quantitative analysis of cold start dynamics under realistic conditions. Parametric studies are conducted to assess the effects of initial membrane hydration, maximum current density, current ramp rate, and current loading strategies. The results show that maximum current density acts as a tipping point for the trade-off between heat generation and ice blockage. Ramp rate governs the transient voltage response and the time duration of ice accumulation. Initial hydration serves as a bifurcation parameter, where both insufficient and excessive water content shrink the feasible startup window. By integrating these factors, a cold start strategy map is established to visualize the transition boundaries between success, partial failure, and complete failure at the stack level. The map provides direct design guidelines for robust and energy-efficient cold start control, bridging mechanistic insight with practical application. The proposed framework establishes mechanistic guidelines for selecting energy-efficient and durable startup protocols, supporting fuel-cell-powered vehicles and stationary systems operating in cold climates.