(63i) Supercooled Water in PEM Fuel Cells

Polymer Electrolyte Membrane Fuel Cells (PEMFCs) face three hurdles for widespread automotive commercialization: cost, cathode catalyst durability and freeze tolerance. This research seeks to understand water mobility during and after freeze of a hydrogen PEMFC. During the process of freezing in a fuel cell, the water inherently present in the membrane electrode assembly undergoes phase transition from liquid to solid. The acidic nature of Nafion® and its presence in the catalyst layer (more specifically the agglomerate) causes supercooled water to appear during the freezing process which is mobile within the membrane, catalyst layer and agglomerate. The cells were conditioned with varying %RH under load and then frozen. Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) were performed after freeze. For cells under no load, EIS shows a high frequency intercept (HFI), and generally both high and low frequency arcs (HFA,LFA). Varying %RH did not change the LFA but did change HFI and HFA. A thermal gradient on the cell fixture was used to simulate the end of a stack during freeze. Regression was used to fit circles to the HFA and LFA.