Single-Wall Carbon Nanohorns Supporting Pt Catalyst in Direct Methanol Fuel Cells

We made high-power direct methanol fuel cells (DMFCs) by using single-wall carbon nanohorns (SWNHs) to support the Pt catalyst. The unique structure of the SWNH aggregate is advantageous to support the fine Pt catalysts. To prevent the growth of Pt particles even under high-Pt-content conditions, defects were intentionally created on the surface of SWNHs by oxidizing them with H₂O₂. This reduced the mean diameter of the Pt particles supported on the SWNHs to 2.9 nm, which is roughly ²/₃ that of the Pt particles on as-grown SWNHs, for 60 wt % Pt content. We also improved the process used to make a membrane electrode assembly (MEA) by immersing the catalyst electrodes in 50 vol % MeOH before the hot-pressing process. This increased the active surface area of the Pt catalysts to nearly 100% of the Pt surface and strengthened the joint between the electrodes and the membrane. These improvements enabled us to obtain a power density of 76 mW/cm² at 0.4 V for a passive-type DMFC operated at 40 °C.