Ultrathin electrodes, such as the 3M Nanostructured Thin Film (NSTF) electrode, provide a plausible pathway to reduce platinum cost in low temperature fuel cells. However, several operational shortcomings, involving relatively poor electrode proton conduction and tendencies to collect water in the cathode, were observed in our fuel cell tests. This can be greatly mitigated when a few-micron thick dispersed-catalyst layer is placed adjacent to the NSTF layer, forming a dispersed-catalyst/NSTF hybrid electrode. This dispersedcatalyst layer is also called the "interlayer" because it is located between the NSTF layer and the microporous layer of the cathode diffusion medium. In this study, development of the hybrid electrode was pursued. Emphasis on developing lab-scale fabrication methods that can easily translate to roll-to-roll manufacturing process was a key element of the hybrid electrode development. The fuel cell performance of the electrode showed high sensitivity to fabrication methods. When the dispersed-catalyst layer was coated directly on the NSTF electrode, voltage at high current density dropped significantly. The voltage loss was surmised to be caused by ionomer seepage into the NSTF layer during the coating process. This voltage loss could be eliminated by placing the dispersedcatalyst layer on the gas-diffusion layer and then located adjacent to the NSTF cathode. Interaction between the dispersed-catalyst and NSTF layers and how it affects the fuel cell performance is discussed.In a proton exchange membrane fuel cell (PEMFC), Pt or Pt alloy nanoparticles supported on high surface area carbon particles are generally used in the cathode. The highly dispersed nature of the catalyst allows for good utilization of the precious metal. However, the electrochemical stability of the carbon support as well as the dissolution of Pt nanoparticles raise concerns about the durability of the catalyst. 1-4 3M's Nanostructured Thin Film (NSTF) is an extended surface catalyst which consists of a thin film of Pt alloy coated on individual lath-shaped single crystalline whiskers of an organic compound, perylene red (PR149). 5-7 The ∼0.5-1 μm long support whiskers are electrically non-conductive, thereby greatly reducing their susceptibility to electro-oxidative corrosion. The continuous layer of Pt serves as the electrical conductor for the electrode. Due to the low curvature (smaller number of low-coordination-number Pt atoms) and bulk-like characteristics of Pt in this form, NSTF electrodes exhibit higher chemical and electrochemical stability and 5-10 times higher Pt-areaspecific ORR activity than dispersed carbon supported catalysts. 7-10 In addition, owing to its unique structure of an extended surface of Pt covering a support, one expects that the Pt or Pt-alloy layer thickness (and therefore the Pt loading) could be reduced while maintaining the electrochemical properties of the catalyst. 11 Therefore, NSTF catalyst technology provides a plausible pathway for achieving higher ORR activity using small amounts of ...