Combined electrochemical/surface science investigations of Pt/Cr alloy electrodes Page: 8 of 21
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The behavior of Pt0.2Cr0,8 when cycled to high positive potentials is
unique among these alloys. In general it is observed [5] that the oxidation
state of Pt does not change greatly with electrochemical treatment. At most,
in samples cycled to high positive potentials, the Pt(4f) B.E. falls a few
tenths of an eV, consistent with the loss of Cr and the corresponding shift in
the metallic Pt level as per Figs. 1 and 2. However, when Pt0.2Cr0.8 is cycled
to +1.6 V, a new Pt(4f) signal appears at 74.6 eV B.E., characteristic of
Pt *, as sh own in Fig. 4 [13,14]. The appearance of such highly oxidized Pt
was unique to this alloy for cycling to +1.6 V. Thus, it appears that the high
chromium content in some way catalyzes the formation of Pt4+. Note that Pt4+
has :lso appeared when a pure Pt electrode was held at +2.0 V vs SHE or higher
in 1N H2SO4 [14J. In that case, careful analysis indicated that Pt4+ was pres-
ent as an hydroxide, Pt(OH)4 [14J. We have no reason to change this interpre-
tation for the Pt/Cr alloys, but only to point out that Pt4+ appears at much
lower voltages here.
To compare directly with these experiments, the Pt0.2Cr0.8 alloy was
treated using the same procedure, i.e., the alloy was first cycled times to
the upper voltage limit, then held there for 15 min, and removed from solution
at that voltage under potentiostatic control. (The Sample was then washed as
usual,) The only difference here is in our solution, 85% H3 '4 instead of
.N Fys4. The results are shown in Fig. 4. Already at +1.4 V, the Pt4' peak
has appeared, and it predominates by +1.6 V. Since increasing pH will only
dejtaibilize the oxidized states o' Pt [15J, we cafn conclude that alloying with
80 Cr dec"eaies thu potential for generation of Pt surface species by abJot
0.6 V.
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Daube, K. A.; Paffett, M. T.; Gottesfeld, S. & Campbell, C. T. Combined electrochemical/surface science investigations of Pt/Cr alloy electrodes, article, January 1, 1985; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1054134/m1/8/?rotate=90: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.