Engineering the Activity and Stability of Pt-Alloy Cathode Fuel-Cell Electrocatalysts by Tuning the Pt-Pt Distance
Sputter-cleaned, polycrystalline Pt5Gd shows a five-fold increase in ORR activity , relative to Pt at 0.9 V in 0.1 M HClO4. The rest of the Pt5Ln (Ln = lanthanide) tested present at least a 3-fold enhancement in activity [4,5]. In all cases, a Pt overlayer with a thickness of few Pt layers is formed. Accordingly, the effect of alloying Pt is to impose strain onto the Pt overlayer [3,4]. It is likely that this strain would be relaxed by defects . Moreover, the activity of the Pt5Ln catalysts vs. the Pt-Pt distance shows a volcano relationship (Fig. A) . Pt5Ln electrocatalysts are highly stable, as shown in Fig. B . We show, for the first time, that the Pt-Pt distance not only controls the activity, but also the stability of these catalysts .
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Fig. (A) ORR kinetic current density at 0.9 V vs. RHE as a function of the lattice parameter and the Pt-Pt distance for Pt5Ln and Pt. (B) Kinetic current density of Pt5Ln and Pt before and after a stability test consisting of 10 000 cycles between 0.6 V and 1.0 V vs. RHE in an O2-saturated 0.1 M HClO4 electrolyte.