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We report boron nitride nanoflakes (BNNFs), for the first time, as a nanofiller for polymer electrolyte membranes in fuel cells. Utilizing the intrinsic mechanical strength of two-dimensional (2D) BN, addition of BNNFs even at a marginal content (0.3 wt %) significantly improves mechanical stability of the most representative hydrocarbon-type (HC-type) polymer electrolyte membrane, namely sulfonated poly(ether ether ketone) (sPEEK), during substantial water uptake through repeated wet/dry cycles. For facile processing with BNNFs that frequently suffer from poor dispersion in most organic solvents, we non-covalently functionalized BNNFs with 1-pyrenesulfonic acid (PSA). Besides good dispersion, PSA supports efficient proton transport through its sulfonic functional groups. Compared to bare sPEEK, the composite membrane containing BNNF nanofiller exhibited far improved long-term durability originating from enhanced dimensional stability and diminished chronic edge failure. This study suggests that introduction of properly functionalized 2D BNNFs is an effective strategy in making various HC-type membranes sustainable without sacrificing their original adventurous properties in polymer electrolyte membrane fuel cells.

We present a facile and simple method to fabricate a three-dimensional (3D) interface between a hydrocarbon-based polymer membrane and an electrode of a membrane–electrode assembly via solvent-vapor-annealed deposition (SVAD). SVAD not only increases the membrane proton conduction with nanophase-separated morphology but also reduces the interfacial resistance between the membrane and electrode with formation of nanoscale 3D interfaces. The enlarged interfacial area improves the power performance of fuel cells, originating from reduced interfacial resistances and increased electrochemical active surface area of the catalyst layer (CL) by ionomer impregnation into the tortuous nanopores of the nearest CL. Furthermore, the effect of the engineered 3D interface is investigated by measuring the mechanical durability by the wet–dry cycle and peel strength.

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Oxygen transport resistance, one of the causes of large polarization in the cathode catalyst layer (CL), is intensified in low‐Pt‐loaded polymer electrolyte membrane fuel cells (PEMFCs). In order to explore operation strategies and cathode design to mitigate the large oxygen transport resistance of low‐Pt‐loaded fuel cells, the influence of operating conditions and ionomer structure on oxygen transport in the CL is investigated. Remarkably, the oxygen transport resistance data for different operation conditions and ionomer structures lie on a single curve when they are plotted as a function of the water partial pressure of the feed. At a high water partial pressure of 80 kPa, the oxygen transport resistance of the low‐Pt‐loaded CL (0.14±0.03 mg−Pt cm−2) becomes comparable to that of the high‐Pt‐loaded CL (0.40±0.04 mg−Pt cm−2) as a result of the opposing influences of Pt loading on Knudsen and ionomer film diffusion. This emphasizes the importance of the water uptake in the ionomer film for reducing oxygen transport in the CL. From a fuel cell design perspective, the operation strategy and CL design to maintain high water partial pressure in the cathode CL are extremely important for realizing low‐Pt‐loaded fuel cells.