Decoding the nonlinear degradation behavior of 12‐ <scp>kW PEMFC</scp> stacks under complex operating conditions

Abstract Hydrogen fuel cells are promising electrochemical energy conversion devices with high efficiency and zero emissions, making them attractive for transportation and other applications. However, their commercialization remains hindered by insufficient durability and the high cost of platinum‐based catalysts. This study investigates the degradation behavior of a 22‐cell short stack with an effective area of 367 cm 2 operated for over 700 h under idle, start–stop, rated load, and variable load conditions. Offline multi‐condition analyses focusing on membrane electrode assembly components, including the catalyst layer, gas diffusion layer, and proton exchange membrane, reveal distinct degradation pathways. Catalyst activity loss arises from carbon support corrosion and platinum oxidation under high‐potential conditions (OCV &gt;0.85 V per cell); the proton exchange membrane undergoes microporous structure deterioration driven by combined mechanical and chemical stresses; and the gas diffusion layer experiences porosity reduction due to multiphase flow effects. These findings provide mechanistic insights into stack degradation and establish a theoretical basis for enhancing durability and supporting the engineering application of fuel cell technology.