No abstract

Organic/inorganic hybrid membranes based on poly(vinyl alcohol) (PVA) and sulfonated polyhedral oligosilsesquioxane (sPOSS), crosslinked by ethylenediaminetetraacetic dianhydride (EDTAD), were prepared as candidate materials for proton exchange membranes in direct methanel fuel cell (DMFC) applications. Fourier transform infrared (FT-IR) spectroscopy and ion exchange capacity measurements for the prepared networks clearly revealed sPOSS incorporation. We found that proton conductivity increased and methanol permeability decreased with increasing sPOSS content in the hybrid membrane. In particular, our hybrid membranes demonstrated proton conductivities as high as 0.042 S/cm, which is comparable to that of Nafion TM , while exhibiting two orders of magnitude lower methanol permeability as compared to Nafion TM . We postulate that the polar sulfonic acid groups of the incorporated sPOSS cages assemble to provide ion conduction paths while the hydrophobic portions of the same sPOSS cages combine to form a barrier to methanol permeation with improved thermal stability of the hybrid membrane.

The O2 and NO reactivity of a Cr(II) complex bearing a 12-membered tetraazamacrocyclic TMC ligand, [CrII(12-TMC)(Cl)]+ (1), and the NO reactivity of its peroxo derivative, [CrIV(12-TMC)(O2)(Cl)]+ (2), are described. By contrast to the previously reported Cr(III)-superoxo complex, [CrIII(14-TMC)(O2)(Cl)]+, a Cr(IV)-peroxo complex (2) is formed in the reaction of 1 and O2. Full spectroscopic and X-ray analysis reveals that 2 possesses a side-on η2-peroxo ligation. A quantitative reaction of 2 with NO affords a reduction in Cr oxidation state and production of a Cr(III)-nitrato complex, [CrIII(12-TMC)(NO3)(Cl)]+ (3). The latter is suggested to form via a Cr(III)-peroxynitrite intermediate. A Cr(II)-nitrosyl complex, [CrII(12-TMC)(NO)(Cl)]+ (4), derived from 1 andNO could also be synthesized; however, it does not react with O2.

Reaction of a nonheme iron(III)-peroxo complex, [FeIII(14-TMC)(O2)]+, with NO+, a transformation which is essentially isoelectronic with that for nitric oxide dioxygenases [Fe(III)(O2•−) + NO], affords an iron(IV)-oxo complex, [FeIV(14-TMC)(O)]2+, and nitrogen dioxide (NO2), followed by conversion to an iron(III)-nitrato complex, [FeIII(14-TMC)(NO3)(F)]+.