Metalloporphyrin Catalysts of Oxygen Reduction - Fuel Cell Catalysis: A Surface Science Approach - page 647

Figure 18.9 Chemical structures of simple Fe porphyrins whose catalytic properties in the
ORR have been studied extensively. These properties are tabulated in Collman et al. [2004a].
the catalytic properties of Co porphyrins has been studied [Hutchison et al., 1997;
Yamazaki et al., 2005]. Nonetheless, valuable generalizations can still be inferred
from the literature data:
† Electrocatalytic reduction of both O 2 and H 2 O 2 starts at potentials close to that of
the Fe III/II couple in the absence of a substrate (which for most porphyrins is
about 0.2 - 0 V with respect to a normal hydrogen electrode (NHE) at pH 6;
the exception being Fe(TMPyP), E 0.5 V). Catalytic reduction of H 2 O 2 by
simple ferric porphyrins is too slow to be detectable in typical electrocatalytic
experiments; whereas ferrous porphyrins catalyze rapid reduction of H 2 O 2 ,