Membrane-electrode-assemblies (MEAs) were fabricated with electrospun nanofiber electrodes containing Johnson-Matthey (JM) HiSpec 4000 catalyst and a Nafion 212 membrane. MEA performance was evaluated in a hydrogen/air fuel cell, where power output was correlated with cathode Pt loading (0.029-0.107 mg(Pt)/cm(2)) and changes in fuel cell temperature (60 degrees C and 80 degrees C), pressure (up to 3.0 atm), and feed gas flow rates. In all experiments, the nanofiber anode had a fixed Pt loading of 0.10 mg/cm(2). The mass activity (0.16 A/mg(Pt) at 0.9 V) and electrochemical surface area (similar to 41 m(2)/g) of nanofiber cathodes were very high and more power was generated from nanofiber electrode MEAs than from a conventional MEA with decal electrodes. Thus, the maximum power density for H-2/air fuel cell operation at 80 degrees C, 1 atm (ambient) pressure, 125 sccm H-2, and 500 sccm air was 437 mW/cm(2) for a nanofiber cathode at 0.065 mg(Pt)/cm(2) vs. 400 mW/cm(2) for a decal MEA with cathode/anode Pt loadings of 0.104/0.40 mg/cm(2). Similarly, an electrospun cathode with a Pt loading of 0.055 mg/cm(2) produced a maximum power density of 906 mW/cm(2) at 80 degrees C and 3 atm pressure with 2000 sccm fully humidified air and 500 sccm H-2. (C) 2013 The Electrochemical Society. All rights reserved.