Effect of flow field design and voltage change range on the dynamic behavior of PEMFCs

Data are presented to show that the dynamic behavior of a proton exchange membrane fuel cell (PEMFC) subjected to rapid changes in the voltage depends on the type of flow field and on the voltage range of the voltage change. These data consist of the responses of the current density when the flow rates are constant and at levels that result in operation between fuel stoichiometries of 1.2 and 1.1 (see Ref. 1 and 2 for other stoichiometries). The data expand an understanding of the previously observed pseudo-second-order dynamics of the current responding to a change in voltage. The results show that the undershoot of the final steady-state current that follows the resulting overshoot was observed with a standard triple-path serpentine flow field (SFF) but not with a single-path SFF. The results also show that the dimensionless peak current and the percentage of the overshoot current depend on the starting cell voltage and on the range of the voltage change. Evidence is presented to indicate that these peak heights are limited primarily by oxygen mass transfer, even though the PEMFC is operating at close to fuel-starved conditions. (c) 2005 The Electrochemical Society. All rights reserved.