The mass transport in porous transport layers (PTLs) with pores exclusively in the through-plane direction was investigated using in operando X-ray radiography and electrochemical performance analysis. We observed via synchrotron X-ray imaging that through pores that are under the lands are inaccessible by liquid water. We thereby observed the limited in-plane mass transport that takes place in PTLs with pores exclusively in the through-plane direction. Additionally, a thicker layer of gas was observed with the use of the PTL with through pores under both the channels and the lands (PTL_(Ch,L)) when compared to the PTL with through pores only under the channels (PTL_(Ch)). This corresponded to the PTL_(Ch,L) exhibiting a higher mass transport overpotential than the PTL_(Ch). Finally, the limited in-plane mass transport in the PTL with through pores led to a relatively dehydrated catalyst layer and higher ionic resistance with increasing current density.
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