Thomas W. Tighe

Water Transport Mechanisms in PEMFC Gas Diffusion Layers

Understanding how water produced in the cathode catalyst layer is removed during proton exchange membrane fuel cell (PEMFC) operation is critical for optimization of materials and model development. The present work combines in situ and ex situ experiments designed to elucidate the dominant water discharge mechanism when considering capillary and vapor transport at normal PEMFC operating conditions. The flux of water vapor driven by the thermal gradient in the cathode diffusion layer can alone be sufficient to remove product water at high current densities even with saturated gas in the delivery channels. The role of an intermediate microporous layer and its impact in vapor vs liquid transport is also considered. We propose that the primary role of the microporous layer is to prevent condensed water from accumulating on and blocking oxygen access to the cathode catalyst layer. .

Investigation of Fundamental Transport Mechanism of Product Water From Cathode Catalyst Layer in PEMFCs

Understanding how water produced in the cathode catalyst layer is removed during PEMFC operation can be critical for materials optimization and representative models. The present work combines in-situ and ex-situ experiments to determine the dominant water discharge mechanism when considering capillarity and vapor transport. Water flux of vapor driven by the thermal gradient in the cathode diffusion layer is shown to be sufficient to remove product water at high current densities with saturated gas in the gas delivery channels. The role of an intermediate microporous layer and its impact in vapor versus liquid transport is also considered. Through novel experimental techniques and capturing all key physical interactions it is concluded that vapor diffusion is the fundamental mechanism by which water is removed from the cathode catalyst layer.Copyright

Hydrogen-Water Flow Regime Transitions Applied to Anode Flow Phenomena in a PEMFC

Although water is produced on the cathode side of a polymer electrolyte membrane fuel cell (PEMFC), it is known to migrate to the anode, where the two-phase hydrogen-water interactions become critical to keep the channels clear for effective reactant delivery. Hydrogen-water flow regime transitions were experimentally investigated and compared to air-water transitions in a 1.0 mm square channel. Gas superficial velocities were evaluated for an anode stoichiometric ratio of 2.0 over a current density range from 0.1 A/cm2 to 2.0 A/cm2 . Liquid superficial velocities were controlled at the corresponding cathodic water production rate. It is shown that the annular transition in a hydrogen system occurs at as much as twice the gas velocity required for the same transition in an air system. At the low liquid flux expected in the anode channels of a PEMFC, a transition from slug to annular two-phase flow will occur at an unobtainable velocity for efficient fuel cell operation.© 2005 ASME