Effects of the difference in electrical resistance under the land and channel in a PEM fuel cell

Previous studies have shown experimentally that the current density in a proton exchange membrane (PEM) fuel cell can be significantly higher under the land than under the channel in most practical operating cell voltage ranges [14]. In order to determine if the difference in electrical resistances under the land and the channel is a major cause for the observed local current density differences, a dedicated experimental study has been conducted to separately measure the electrical resistance under the land and channel and to isolate the in-plane (lateral) resistance from the total resistance of the gas diffusion electrode (GDE). First, a special test fixture is designed such that the electron paths under both the land and the channel are identical to those in a real operating fuel cell and the electrical resistance under each area can be measured separately. Using this test fixture, the total electrical resistances under the land and the channel are measured separately. The results show that the total electrical resistance under the channel is much higher than that under the land except in the case with very narrow channels. Secondly, in order to determine the source(s) of the difference in electrical resistance under the different areas, the in-plane resistances of the GDE and the gas diffusion layer (GDL) are measured. The results show that the difference in lateral resistance between the areas under the land and the channel is negligibly small. Thirdly, basic analyses show that the difference in direct voltage loss caused by the higher electrical resistance under the channel is significant; besides, the resistance difference can result in a large enough variations in local overpotential to cause significant local current density differences. Therefore, the difference in local electrical resistance under the land and channel is large enough to be a major cause for the observed local current density differences. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.