Charge‐carrier transport in organic materials is the fundamental physical process behind devices such as laser printers. Charge‐carrier mobility data are presented for hexabutyloxytriphenylene (H4T), which exhibits an unusually high charge‐carrier mobility, which can be traced to the formation of a plastic discotic phase. The Figure shows the normal discotic hexagonal texture with six‐fold symmetry observed for H4T at 144°C; this symmetry disappears at lower temperatures (see also the cover). magnified image
Direct methanol fuel cells (DMFCs) have the major advantage of the high energy density of the methanol (4.33 kWh/l) they use as a liquid fuel, although their costs remain too high due to the high quantity of Pt needed as a catalyst for oxygen reduction in the presence of methanol. Pt−Ni core−shell catalysts are promising candidates for improved oxygen reduction kinetics as shown in hydrogen fuel cells. The novelty in this work is due to the fact that we studied these catalysts in DMFC cathodes where oxygen must be reduced and membrane-permeating methanol oxidized at the same time. In spite of many attempts to overcome these problems, high amounts of Pt are still required for DMFC cathodes. During measurements over more than 3000 operating hours, the performance of the core−shell catalysts increased so substantially that a similar performance to that obtained with five times the amount of commercial platinum catalyst was achieved. While catalyst degradation has been thoroughly studied before, we showed here that these catalysts exhibit a self-protection mechanism in the DMFC cathode environment and prolonged operation is actually beneficial for performance and further stability due to the formation of a distinct Pt-rich shell on a PtNi core. The catalyst was analyzed by transition electron microscopy to show how the catalyst structure had changed during activation of the core−shell catalyst.
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