Polymer electrolyte membrane fuel cell transient voltage characteristic considering liquid water imbibition and drainage in gas diffusion layer

The transient water transport problem within polymer electrolyte membrane fuel cell (PEMFC) makes its dynamic behavior unpredictable occasionally, bringing uncertainties to the water management. In this work, a novel experimental methodology is proposed, where the dynamic processes of gas diffusion layer (GDL) imbibition-drainage are accomplished by galvanostatic discharge and alterable air feeding, meanwhile, the PEMFC voltage characteristic is measured as an external state to derive stoichiometry-voltage curve (lambda-V curve). The other transient processes within PEMFC, including membrane sorption/desorption, catalyst surface covering/uncovering and gas channel blocking/unblocking, are also analyzed by high frequency resistance (HFR) measurement, air & oxygen feeding comparison, and pressure drop measurement, respectively. Taking a commercial PEMFC for example, the liquid water's transient capillary transport within GDL is found to dominate PEMFC's lambda-V hysteresis under the condition of high humidification. For the first time, three cycles of GDL imbibition/drainage are in-situ accomplished on the PEMFC, demonstrating: (a) V(lambda) during 1st imbibition is lower than V(lambda) during 2nd and 3rd imbibition, which agree closely, implying 'water pathways' built after 1st imbibition improve PEMFC's performance. (b) V(lambda) during drainage is always higher than V(lambda) during imbibition, despite the steady-existing 'water pathways'. (c) 'Water pathways' in GDL are established within 24 min.