Abnormal Performance Recovery During Long‐Term −30°C Cold Start Cycles: Mechanism and Engineering Strategies for a Metallic Bipolar Plate Proton Exchange Membrane Fuel Cell Stack

ABSTRACT

Driven by global carbon neutrality initiatives, proton exchange membrane fuel cells (PEMFCs) have emerged as a core zero‐emission power technology for transportation. However, their large‐scale application in cold regions is severely constrained by low‐temperature cold start capability, particularly the mandatory requirement of unassisted cold start at −30°C in road vehicle fuel cell regulations. A critical and previously unreported phenomenon—abnormal performance recovery during long‐term freeze–thaw cycles—has been identified in high‐power metallic bipolar plate (BPP) PEMFC stacks, which constitutes the core innovation of this work. Existing studies mostly focus on single cells or small‐scale stacks, with limited insights into the long‐term cold start cycle characteristics of high‐power metallic BPP stacks at −30°C, and the mechanism behind such abnormal performance recovery during freeze–thaw cycles remains poorly understood. In this work, a homemade 60 kW PEMFC stack with 154 cells and metallic BPPs was subjected to 40 repeated −30°C unassisted cold start cycles, combined with steady‐state polarization curve tests, multi‐condition electrochemical impedance spectroscopy (EIS), and ex situ microstructural characterizations. The results show that the metallic BPP stack achieved −30°C unassisted cold start within 153 s, exhibiting overwhelming advantages in low‐temperature adaptability. Most notably, the stack performance presented a distinct two‐stage non‐monotonic evolution that is unprecedented in existing research: continuous attenuation in the first 30 cycles (1.6% voltage degradation at 2.0 A cm ⁻² ), followed by full recovery to the initial level in Cycles 30–40, which was predominantly driven by a 30.6% reduction in concentration impedance. This abnormal performance recovery, the core innovation of this study, was verified to be a reversible effect derived from the dynamic balance between irreversible structural damage and reversible performance gains, including deep activation of the membrane electrode assembly (MEA), pore structure reconstruction of the catalyst layer (CL), and water management optimization within the stack. This reversible gain completely disappeared after accelerated calendar aging, accompanied by significant performance degradation with a 5.28% voltage decay at 2.0 A cm ⁻² . Severe irreversible damage occurred in the end cells due to the thermal edge effect, which became the core limitation of the stack's full‐life cycle lifetime. This work, for the first time, systematically reveals the abnormal non‐monotonic performance recovery phenomenon and its intrinsic mechanism in high‐power metallic BPP stacks during long‐term −30°C cold start cycles and proposes systematic engineering optimization strategies, providing critical theoretical and experimental support for the commercial application of automotive PEMFCs in cold regions.