investigation of these new class of catalysts. However, we anticipate that a proper
test of stability should be conducted on nanoparticles and in a fuel cell if possible.
Furthermore there is so far no direct comparison between the stability of Pt alloys
based on early transition metals and late transition metals. A proper test should
be strictly performed under the same conditions and with similar preparation techniques.
Figure 1.8: Experimental ORR activity (expressed as kinetic current density at 0.9 V vs.
RHE normalized per geometric surface area) of various polycrystalline alloys of Pt and early
transition metals. ORR polarization curves were acquired at 20 mV s1, while they were
acquired at 50 mV s1 for the other activities reported in the following chapters of this
thesis. Figure adapted from 6.
On the basis of the encouraging results on Pt3Y and Pt3Sc surfaces, other polycrystalline
alloys of Pt and early transition metals have been tested with the same
methodology 6, 98. Figure 1.8 summarizes the ORR activities of all the alloys
of Pt and early transition metals tested in our group prior to the work of this thesis:
following the rank of activities, Pt3Y, Pt5Y, Pt5La, Pt3Sc, Pt3Hf, Pt3Zr, Pt2Y, PtY.
Among these, the Pt-Y phases with very high Y content (Pt2Y, PtY) were found to
corrode in acid; Pt3Hf, Pt3Zr exhibited the formation of Hf oxide and Zr oxide on
the surface of Pt, explaining the low activity enhancement compared to Pt. Pt3Sc
also showed a rather small increase. On the other hand, both Pt5Y and Pt5La were
at least 3 times more active than polycrystalline Pt and considerably more active
than alloys such as Pt3Co and Pt3Ni prepared in similar conditions 37. Pt5La in
particular was the first alloy of Pt and a lanthanide metal tested as an ORR catalyst.
Together with the results of Kim and co-workers on Pt-La thin films 99 that also
exhibited high activity and stability, it motivated the study of a large number of
other Pt5Ln alloys (with Ln indicating a generic lanthanide metal) in the present