Details of Nafion/polypyrrole composite formation have been obtained using electronic absorption spectroscopy.
Three distinct processmonomer loading, polymerization, and removal of unreacted monomerhave been
studied. Pyrrole loading displays a square root dependence on time, indicative of a diffusion controlled
partitioning process. Partitioning of pyrrole into Nafion, however, is complicated by protonation of pyrrole
and acid-catalyzed oxidation to give oligomeric and polymeric species. These processes are affected by the
presence of oxygen and are photosensitive. A variety of oxidizing agents have been used to effect polymerization
including Fe3+, H2O2, ammonium persulfate, and UV irradiation.
The synthesis and characterisation of two terpyridine based ruthenium/palladium heteronuclear compounds are presented. The photocatalytic behaviour of the Ru/Pd complex containing the linear 2,2′:5′,2′′-terpyridine bridge (1a) and its analogue the non-linear 2,2′:6′,2′′-terpyridine bridge (2a) are compared together with the respective mononuclear complexes 1 and 2. Irradiation of 1a with visible light (e.g., 470 nm) results in the photocatalytic generation of dihydrogen gas. Photocatalysis was not observed with complex 2a by contrast. A comparison with the photocatalytic behaviour of the precursors 1 and 2 indicates, that while for 1a the photocatalysis is an intramolecular process, for the mononuclear precursors it is intermolecular. The photophysical and electrochemical properties of the mono-and heterobinuclear compounds are compared. Raman spectroscopy and DFT calculations indicate that there are substantial differences in the nature of the lowest energy 3 MLCT states of 1a and 2a, from which the contrasting photocatalytic activities of the complexes can be understood.
A pyrazine bridged ruthenium/palladium bimetallic photocatalyst with peripheral 4,4'-dicarboxyethyl-2,2'-bipyridine ligands, EtOOC-RuPd, is reported, together with its 2,2'-bipyridine analogue. Upon irradiation with visible light, EtOOC-RuPd catalyses the production of hydrogen gas whereas the complex RuPd does not.
Nonprecious metal catalysts ͑NPMC͒ for the oxygen reduction reaction were prepared by surface modification of a carbon black with 5,6-diamino-1,10-phenanthroline through diazonium and benzimidazole coupling chemistry. Both methodologies covalently attach 1,10-phenanthroline to the surface. Oxygen-free cyclic voltammograms ͑CV͒ obtained for these modified carbons showed a clearly defined redox peak at ca. 650 mV versus normal hydrogen electrode, which we attribute to phenanthroline-type groups on the carbon surface. Introduction of Fe and subsequent pyrolysis at 700°C under a NH 3 /N 2 atmosphere yielded catalysts that were highly active toward the oxygen reduction reaction. The redox peak at 650 mV was present in the oxygen-free CVs for the most active catalysts, though less intense. Nevertheless, this indicates the presence pyridinic-type active sites in the heat treated catalysts and may be a useful tool in the study of NPMC.
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