Innovative Insight into O 2 /N 2 Permeation Behavior through an Ionomer Film in Cathode Catalyst Layers of Polymer Electrolyte Membrane Fuel Cells.

It is crucial to clarify the permeation behavior of O 2 through the ionomer film for enhancing local O 2 transport in cathodes of fuel cells. However, all existing studies mainly deal with pure O 2 rather than air. Herein, the permeation behavior of the O 2 /N 2 mixture through the ionomer film has been well explored in view of molecular bond length variations by molecular dynamics simulations. The bond lengths for O 2 and N 2 are shortened under a low hydration level when permeating through a dense layer with small free voids while no obvious change occurs at higher hydration. In the bulk ionomer region, O 2 molecules residing in water domains are energetically unstable because the bond lengths deviate far from the equilibrium length; thus, O 2 diffuses through the interfacial or hydrophobic regions. N 2 molecules show similar properties with O 2 . This study provides a novel perspective on the permeation behavior of O 2 and N 2 through the ionomer film, which definitely benefits enhancing local O 2 transport.