In polymer electrolyte membrane fuel cells (PEMFCs), because the reaction rate in the cathode is slower than that in the anode, the cathode catalyst layers require more catalyst loading than the anodes [1]. Much research has been focused on improving the catalytic activity in cathodes and simultaneously reducing the amount of Pt supported by carbon black, which is the most commonly used cathode catalyst [2] [3] [4] . Recently, carbon nanotubes [5-9], carbon nanohorn [10], and carbon nanofibers [11] [12] [13] have been