In this work, we investigate the cold-start operation of polymer electrolyte fuel cells (PEFCs) through high-resolution neutron radiography, experimental testing, theoretical evaluation, and comparison with model prediction. Ice formation location, voltage evolution, and loss of the electro-catalyst surface area (ECSA) are examined. A dimensionless parameter , characterizing the spatial variation of the reaction rate across the cathode catalyst layer, is discussed at subfreezing temperature using newly determined membrane ionic conductivity. The evaluation identifies the operating range that the reaction rate can be treated uniform across the catalyst layer, in which the model is valid. © 2012 Elsevier Ltd. All rights reserved.

The ability of polymer electrolyte fuel cells (PEFCs) to startup at subfreezing temperatures is governed by whether it is able to overcome the freezing point (0°C) before product ice prevents the electrochemical reactions. In this work, we experimentally investigated the coulombs of charge Qc transferred in PEFCs under subfreezing operation before the output voltage drops to 0.0V. PEFCs with various membranes and catalyst-layer thicknesses, ionomer-carbon ratios, operating current density, and initial hydration of PEFCs were studied, and their influences on cold-start performance and coulombs of charge were experimentally measured. We find that subfreezing temperature, ionomer-catalyst ratio, and catalyst-layer thickness, significantly affect the amount of charge transferred before operational failure, whereas the membrane thickness and initial hydration level have limited effect for the considered cases. © 2013 The Electrochemical Society.

This work presents an in situ study on the water-content measurement in polymer electrolyte fuel cells (PEFCs) using neutron imaging. The effects of several important operating and design parameters on water content are examined, including the relative humidity (RH), the polytetraflouroethylene (PTFE) loadings in gas diffusion media including the microporous layer (MPL), current density, and flow field configurations including single-/quad-serpentine channels and co-/counter-flow configurations. Efforts are also made to distinguish water contents between the channel and land projected areas, and obtain the water profile along the gas flow path. We find that the highest water content occurs at a low current density for fixed operational stoichiometry, and liquid water emerges downstream at low humidity and increases rapidly after on-set. © 2012 Elsevier Ltd. All rights reserved.