Response of Specific Resistance Distribution in Electrolyte Membrane to Load Change at PEFC Operation

To understand the dynamic behavior of water content in a polymer electrolyte membrane (PEM) at load change in a polymer electrolyte fuel cell (PEFC), distribution profiles of specific resistance (p) at various portions of the PEM were investigated. Seven Pt potential probes were inserted into the PEM to monitor the transient change in the p between Pt probes. When the current density was stepped from 0.2 (stand-by condition) to 100, 200, or 300 mA cm -2 at the cell temperature of 80°C while supplying humidified H 2 and O 2 identically at 20% relative humidity (RH), it was found that the ratio of electro-osmotic drag (EOD) coefficient to water diffusion (WD) coefficient was constant irrespective of the current density. For the current step from 0.2 to 200 mA cm -2 when the reactant gases were humidified identically at 20, 40, or 60% RH, the EOD coefficient decreased or the WD coefficient increased with increasing RH, which might be caused by a structure change in the PEM.

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