A perspective on influences of cathode material degradation on oxygen transport resistance in low Pt PEMFC

A large-scale industrial application of proton exchange membrane fuel cells (PEMFCs) greatly depends on both substantial cost reduction and continuous durability enhancement. However, compared to effects of material degradation on apparent activity loss, little attention has been paid to influences on the phenomena of mass transport. In this review, influences of the degradation of key materials in membrane electrode assemblies (MEAs) on oxygen transport resistance in both cathode catalyst layers (CCLs) and gas diffusion layers (GDLs) are comprehensively explored, including carbon support, electrocatalyst, ionomer in CCLs as well as carbon material and hydrophobic polytetrafluoroethylene (PTFE) in GDLs. It is analyzed that carbon corrosion in CCLs will result in pore structure destruction and impact ionomer distribution, thus affecting both the bulk and local oxygen transport behavior. Considering the catalyst degradation, an eventual decrease in electrochemical active surface area (ECSA) definitely increases the local oxygen transport resistance since a decrease in active sites will lead to a longer oxygen transport path. It is also noted that problems concerning oxygen transport caused by the degradation of ionomer chemical structure in CCLs should not be ignored. Both cation contamination and chemical decomposition will change the structure of ionomer, thus worsening the local oxygen transport. Finally, it is found that the loss of carbon and PTFE in GDLs lead to a higher hydrophilicity, which is related to an occurrence of water flooding and increase in the oxygen transport resistance.