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Figure 11.14 E versus time curve recorded during the ORR on a FePc/C gas diffusion
electrode ( j ΒΌ 225 mA cm 22 ). The FePc electrode was fed with ambient air without any
convection (temperature 20 8C) [Baranton et al., 2005].
was studied by Kirner's and Ballirano's groups [Kirner et al., 1976; Ballirano et al.,
1998]. These authors found that in the a-phase of the MPc, the macrocycles were
disposed in parallel stacks in the cell, whereas in the b-form, they were disposed in
perpendicular stacks. Figure 11.16 gives a representation of the structures viewed per-
pendicularly with respect to the (100) crystallographic plane. The authors also pointed
out that in the case of CoPc, the transition between the a- and b-forms led to increase
the Co - Co distance in the unit crystallographic cell: the Co - Co distance close
to 0.375 nm for a-CoPc increases to 0.479 nm for the b-phase. A similar value
of 0.479 nm between Fe centers was found for b-FePc. Moreover, Ballirano and
Figure 11.15 Schematic representation of co-facial cobalt porphyrins Co 2 FTF 4-2,1-NH
synthesized by Collman and co-workers [Collman et al., 1980].
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