Oxygen reduction in acid media: influence of the heat treatment on the FeNPc(1–20 isomer mixture impregnated on carbon blacks and active charcoals
Oxygen reduction with the aid of a number of FeNPc(1–2) impregnated carbon supports in sulphuric acid solutions has been investigated. 
 
Loading of the carbon samples amounted to about 10 wt.%. After a 10 day stay in the aerated solutions the samples were investigated with rotating disk electrode and X-ray photoelectron spectroscopy techniques. The most active and stable samples correspond to mono- or submonolayers of FeNPc deposited on high dibutylphthalate adsorption carbon blacks. Comparison with data obtained previously on Norit BrX impregnations emphasizes the role of the electron density on the inner nitrogen atoms rather than that on the iron centres.
Is nitrogen important in the formulation of Fe-based catalysts for oxygen reduction in solid polymer fuel cells?
The role of nitrogen and iron in the generation of catalysts for oxygen reduction in acidic media has been investigated by using two independent organic precursors. The Fe and N precursors were polyvinylferrocene adsorbed on carbon black and acetonitrile vapor, respectively. These precursors were pyrolyzed at 1000 degrees C. A catalyst is obtained only if Fe and N are present together in the reactor during pyrolysis. Inactive Fe clusters surrounded by a protective graphitic envelope are produced when adsorbed polyvinylferrocene is pyrolyzed alone at 1000 degrees C. The latter material may, however, be activated by a second pyrolysis in acetonitrile vapor. The characterization of the catalyst indicates that the iron is oxidized (Fe-II and Fe-III), but no strong Fe-N-x bonds were unequivocally detected by ToF SIMS. Lifetime testing of the catalyst in a polymer electrolyte fuel cell demonstrated stable currents for at least 300 h. The current density measured with a catalyst containing 1 wt% Fe was about 1/3 of that measured with a commercial Pt-based catalyst containing 2 wt% metal loading. (C) 1997 Published by Elsevier Science Ltd.
Reversible oxidation and rereduction of entire thin films of transition-metal phthalocyanines
Thin films (1000 to 2000A thick) of iron(II) (Fe), cobalt(II) (Co), nickel(II) (Ni), copper(II) (Cu), and zinc(II) (Zr) phthalocyanines (Pc) on gold or indium oxide electrodes undergo stoichiometric oxidation and rereduction. Except for FePc and CoPc, the process is essentially reversible. Chronocoulometry showed that ZnPc films oxidized to the extent of 1.21 electrons per ZnPc molecule; CoPc required 1.92 electrons per molecule. Charge compensation is attained upon oxidation by uptake of anions from the electrolyte and by expulsion of anions upon reduction. Auger electron spectrometry allowed detection of the ions and characterization of their distributions. In partially oxidized films, the anions appear to be homogeneously distributed. Oxidation seems to proceed at all grains with equal probability, with anions entering and departing along grain boundaries. Smaller anions allow full oxidation at rapid rates; larger ones inhibit the oxidation with respect to rate. Optical spectroscopy showed evidence for reorganizaton of the crystalline lattices. The rereduced form is not the same as the original material, but it can be restored to the original form by annealing at 125/sup 0/C. In cyclic oxidations and rereductions, there is a gradual loss of charge-consuming ability, apparently related to electrical isolation of small domains, perhaps grains. Themore » oxidations and rereductions are electrochromic, and the various color changes are described. 10 figures, 1 table.« less