Measuring the Current Distribution with Submillimeter Resolution in PEFCs III. Influence of the Flow Field Geometry

The influence of the dimensions of the flow field's channels and ribs oil the local current generation at the submillimeter level and its correlation to the overall cell performance of polymer electrolyte fuel cells (PEFCs) were investigated. To measure the current and membrane resistance distribution oil the scale of channels and ribs, the recently developed method, introduced and discussed in the first two parts of this series, was applied using the current drain in the cell as an internal shunt resistor. Current and membrane resistance distributions were evaluated for a series of geometries with systematic variations in channel and rib dimensions. The general picture deduced from the results shows that in cells with wide channels, even on the scale of millimeter and submillimeter dimensions. water transport limitations and thus local membrane resistance differences are dominating the local and integral performance. With the use of wide ribs, reactant mass transport becomes the dominant limitation in particular for low oxygen partial pressure conditions. These local loss mechanisms can be related to the gradients along the channel of a technical cell, leading to the idea of adapting the channel/rib dimensions along the flow path front the inlet to the outlet to provide ail optimal geometry at every coordinate. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3187913] All rights reserved.