State-of-the-art Pt/C catalysts

The stability of electrocatalysts for PEMFCs is increasingly a key topic as commercial applications become nearer. The DoE has set challenging near-term durability targets for fuel cell technology (automotive 5,000 h by 2010 stationary 40,000 h by 2011) and has detailed the contribution of the (cathode) catalyst to these. In particular, for automotive systems as well as steady-state stability, activity after simulated drive cycles and start-stop transients has been considered. In practice, both these treatments have been found to lead to severe degradation of the standard state-of-the-art Pt/C catalyst, as detailed next. 

Mathias et al. showed that a 30% Ft alloy on a corrosion-resistant support gave an initial performance 50 mV below that of a standard 50% Pt/C catalyst. Although the Pt alloy catalyst showed much greater stability at 1.2 V, this large discrepancy in activity is unacceptable. Therefore, fhe challenge is to develop Pf (and Pf alloy) cafalysfs wifh high stabilify and similar activities to that shown by state-of-the-art Pt/C catalysts. 

Fig. 9.7 (a) MEA polarization and (b) power density curves for (squares) state-of-the-art Pt/C catalyst, (stars) NPMC based on metal-organic framework, and (circles) NPMC based on Black Pearls 2000 carbon support (reprinted with permission from Macmillan Publishers Ltd [44], copyright 2011)... 

In order to achieve ORR activity target of fourfold increase over the state-of-the-art Pt/C catalyst, one could either increase the Pt dispersion or increase the area-specific activity of the catalysts. It was shown that there are several pathways to the requirement. Some electrocatalysts prepared via these approaches have shown promising initial ORR activities, but none of them have yet been demonstrated to retain high activity throughout life. Loss of Pt surface area due to particle-size growth and partial loss of the less-noble metal from alloy catalysts are common phenomena. 

Pt(lll) surface, and 90 times more active than the current state-of-the-art Pt/C catalysts [17]. 

In 2007, Markovic et al. reported a single-crystalline study showing that the PtsNiClll) surface is tenfold more active in the oxygen reduction reaction (ORR) than the corresponding Pt(lll) surface and 90-fold more active than the current state-of-the-art Pt/C catalysts, as shown in Fig. 2.8 [40]. This beautiful study stimulated the synthesis of nanoparticles consisting of the PtsNiCl 11) surface and, 3 years later, the synthesis of PtsNi nanooctahedra and the results for the ORR activity test were reported [26]. 

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