Electrospun carbon nanofiber catalyst layers for polymer electrolyte membrane fuel cells: Structure and performance

Carbon nanofiber-based fuel cell catalyst layers are prepared by electrospinning random and orthogonally-aligned structures using various structural and compositional parameters. Specifically, the influence of the level of fiber alignment, Platinum (Pt) loading, ionomer loading and distribution, deposition methods, and fiber support carbonization temperature on the support microstructure and fuel cell performance are studied and characterized by physicochemical methods. The effects of these controlled fabrication parameters were evaluated in-situ, specifically in the activation, ohmic, and mass transport overpotential regions. SEM/TEM observations reveals continuous fibrous conductive network formed by ionomer bridges between the fibers. It is found that ionomer/carbon of 0.158 with a thickness of ∼60 nm achieved the highest current density under normal operating conditions. Thicker ionomer layer resulted in high oxygen transport resistance, decreasing performance at high potentials. Carbon nanofiber (CNF) samples with 157 μg cm−2 Pt loading and I/C 0.158 achieve 5× higher current density compared to conventional V50 carbon black at 600 mV. Although the effect of orthogonally organized fibers is not clear, the results prove the advantage of using CNF as a catalyst support with tailorable material properties. Further process optimization may advance the CNF/Pt structure, while developing an understanding of the role of microstructure and organization.