Cathode Catalyst Layer as the Watershed in PEMFC

摘要

The full competition between mass transport and reaction in PEMFC unfolds in their cathode catalyst layers (CCLs).Recent models could provide vital relations between structure,composition and performance of CCLs.The CCL's key function in water removal is,however,rather unexplored.Studies of water balance in PEMFCs mostly focus on the other cell components.Notwithstanding this prioritization,a simple calculation shows that the CCL is the PEMFC's favourite medium for conversion of liquid water into vapor.Pore structure and wetting properties steer the interplay of evaporation,transport and reaction.A model will be presented,that links pore space morphology,composition,distributed properties (concentrations,pressures,reaction rates,and potential) with global performance (current voltage performance,critical phenomena in water management).It reveals how problems of flooding in the fuel cell could be mitigated by properly adjusting catalyst layer structure and operating conditions and under which conditions all liquid water arriving in the CCL would exit it over the CCL/GDL interface as vapor.Results,given here for a simple variant of the model,confirm the key role of the CCL for water management in PEMFC.Since critical liquid water formation seems to occur first in the middle of the CCL,it acts as a watershed for the whole cell.