Design of ordered-catalyst layers for polymer electrolyte membrane fuel cell cathodes

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 [2-4]. Recently, carbon nanotubes [5-9], carbon nanohorn [10], and carbon nanofibers [11-13] have been developed for Pt support materials for PEMFC cathodes, due to their high electronic conductivity and/or high catalytic activity of the oxygen-reduction reaction. For the catalyst-layer structure, ordered structures have higher potential than disordered structures, yielding improved cell performance due to oriented mass transport [9]. The design of ordered-catalyst layer structures with optimized carbon nanotube alignment, catalyst layer thickness, and proton conductive polymer content is needed to obtain high-performance PEMFCs. In this study, numerical simulations were used to determine the structure of ordered catalyst layers in PEMFC cathodes that yield maximum power density [14]. Ordered catalyst layers were composed of electron conducting tubes with Pt particles on their surface and polymer electrolyte thin films covering on them as shown in Fig. 1.