Electrocatalysis at Platinum and Bimetallic Alloys - Fuel Cell Catalysis: A Surface Science Approach - page 328

Figure 10.10 Temperature dependence of H 2 O 2 yield P(H 2 O 2 ) at Nafion - Pt(4.8 nm)/CB
(W), Nafion2Pt(2.6 nm)/CB (D), Nafion2Pt(1.6 nm)/CB (S), Nafion - Pt(2.6 nm)/CB with
the same Pt loading as 1.6 nm catalyst (A), Nafion - Pt(bulk) ( † ), and Pt(bulk) without
Nafion coating ( 5 ). U m ¼ 50 cm s 21 . (From Yano et al. [2006b], reproduced by permission
of the PCCP Owner Societies.)

Nafion) [Wakabayashi et al., 2005a], the Nafion coating on Pt is the major reason for
triggering H 2 O 2 production in a practical potential region E . 0.70 V. It has been
reported that DQ H at Nafion - Pt(bulk) decreases by about 10% compared with a
Pt(bulk) (without Nafion) electrode [Lawson et al., 1988; Chu et al., 1989; Zecevic
et al., 1997; Chu, 1998]. This reduction is probably due to a specific adsorption of sul-
fonate groups in Nafion, as observed by in situ FTIR spectroscopy [Ayato et al., 2006].
Therefore, sulfonate groups in Nafion could be the species strongly adsorbed on Pt sur-
face, modifying the surface property.

10.3.1.2 Arrhenius Plots of k app The value of I k at a given potential E is deter-
mined in the same manner as described in Section 10.2.4. Because the contribution of
two-electron reduction to the production of H 2 O 2 (compared with the overall ORR)
was very low, we can evaluate an apparent rate constant k app at a constant applied
potential from the following equation [Wakabayashi et al., 2005a, b]:

I k
4FS Pt

¼ k app [H þ ][O 2 ] (10 : 8)