Insulated π-Conjugated Azido Scaffolds for Stepwise Functionalization via Huisgen Cycloaddition on Metal Oxide Surfaces.

In organic-inorganic hybrid devices, fine interfacial controls by organic components directly affect the device performance. However, fabrication of uniformed interfaces using π-conjugated molecules remains challenging due to facile aggregation by their strong π-π interaction. In this report, a π-conjugated scaffold insulated by covalently linked permethylated α-cyclodextrin moiety with an azido group is synthesized for surface Huisgen cycloaddition on metal oxides. Fourier-transformed infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy confirm the successful immobilization of the insulated azido scaffold on ZnO nanowire array surfaces. Owing to the highly independent immobilization, the scaffold allows rapid and complete conversion of the surface azido group in Huisgen cycloaddition reactions with ethynyl-terminated molecules, as confirmed by FT-IR spectroscopy monitoring. Cyclic voltammetry analysis of modified indium tin oxide substrates shows the positive effects of cyclic insulation toward suppression of intermolecular interaction between molecules introduced by the surface Huisgen cycloaddition reactions. The utility of the scaffold for heterogeneous catalysis is demonstrated in electrocatalytic selective O2 reduction to H2O2 with cobalt(II) chlorin modified fluorine doped tin oxide electrode and photocatalytic H2 generation with iridium(III) dye-sensitized Pt-loaded TiO2 nanoparticle. These results highlight the potential of the insulated azido scaffold for a stepwise functionalization process, enabling precise and well-defined hybrid interfaces.

High Power Density of a Hydrogen Peroxide Fuel Cell Using Cobalt Chlorin Complex Supported on Carbon Nanotubes as a Noncorrosive Anode.

Hydrogen peroxide fuel cells (HPFCs) have attracted much attention due to their simple one-compartment structures and high availability under harsh conditions such as an anaerobic environment; however, catalysis improvement is strongly demanded for both anodes and cathodes in terms of activity and durability. Herein, we report the high catalytic activity of CoII chlorin [CoII(Ch)] for hydrogen peroxide (H2O2) oxidation with a low overpotential (0.21 V) compared to that of the CoII phthalocyanine and CoII porphyrin complexes, which have previously been reported as active anode catalysts. Linear sweep voltammograms and differential pulse voltammograms of the CoII complexes (CoIIL) and the corresponding ligands clearly showed that the CoIIIL species are the active species for H2O2 oxidation. Then, one-compartment HPFCs were constructed with CoII(Ch) supported on multiwalled carbon nanotubes (CNTs) as the anode together with FeII3[CoIII(CN)6]2 supported on CNTs as the cathode. The maximum power density of the HPFCs reached 151 µW cm-2 with an open circuit potential of 0.33 V when the coverage of CNT surfaces with CoII(Ch) exceeded ∼60% at the anode.