Temperature Gradient Design for Elevated Performance in Proton Exchange Membrane Fuel Cells (PEMFCs) under High Current Density

High current density (HCD) operation in proton exchange membrane fuel cells (PEMFCs) presents significant water and thermal management challenges, mainly due to excessive production and uneven distribution of water and heat. Constructing an in-plane temperature difference (TD) in the cathode to match the water–gas state variations is a promising approach. This study innovatively reconstructs the cathode liquid cooling channels of a hydrogen-air PEMFC to create an in-plane TD, experimentally investigating various designs across different inlet relative humidities (RH), with deeper mechanism analysis, including electrochemical impedance spectroscopy (EIS) and local current density distribution. Results show that a positive temperature difference (PTD) enhances HCD performance, improving voltage and current uniformity by 10% and 2% at 2100 mA/cm2, while the enhancement weakens with increasing inlet humidity. Reverse temperature differences (RTDs) persistently have an adverse effect, which worsens with higher difference amplitude and RH. Mechanism exploration for TDs reveals that PTD improves membrane hydration upstream and reduces flooding downstream under low humidity conditions while tending to cause flooding upstream under high humidity conditions. RTD causes drying upstream and exacerbates downstream flooding, which is more pronounced at higher humidity. This research provides novel insights into optimizing thermal management at HCDs in low-humidity environments like automotive applications and high-humidity environments.