Abstract. The potential of a number of tetraaza-macrocyclic complexes of cobalt and nickel to mediate the photoreduction of carbon dioxide has been studied. Carbon monoxide and hydrogen are the main products, which result from illumination of an aqueous solution containing Ru(2,2'-bipyridine):+ as sensitizer, ascorbic acid as sacrificial eletron donor and a tetraaza-macrocyclic complex as relay. Their ratio strongly depends upon the relay compound used. The complexes can be used as electrocatalysts for CO, reduction at a mercury electrode since they lower the overpotential for CO, reduction showing turnover numbers/hour of approximately 3. A minimum potential is required to induce reaction of electrocatalysts and CO, (and H,O). Finally, the redox properties of the macrocyclic metal complexes at p-GaP and p-GaAs photocathodes in acetonitrile are compared with those observed at Pt.

Composites consisting of polymer matrix materials and natural or synthetic layered minerals e.g. clays were prepared by using special compatibilizing agents between these two intrinsically non‐miscible components. Block or graft copolymers combining one part of the polymer that is identically and/or completely miscible with the organic polymer and another part that is compatible with the natural mineral are applied to act as compatibilizer. The interaction between the first part of the compatibilizer is preferentially an ionic interaction or an interaction via hydrogen bonds. This interaction leads to a separation of the mineral into single sheets and/or small clusters containing approximately 2–10 sheets and a subsequent homogeneous incorporation of these clusters into the polymer matrix material.

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Biosensors based on Pt or Pt/Ir based needle-type microelectrodes have been successfully employed for continuous in vivo real-time brain biomonitoring of biomarkers such as glutamate and glucose. However, when implanted, these biosensors often bend, thereby damaging its surface and degrading its bioanalytical properties. In addition, downscaling of Pt and Pt/Ir needle-type biosensors, to improve the spatial resolution and decrease tissue damage, is technically challenging. In that sense, we investigated whether the use of a material with low malleability, tungsten (W), coated with a highly conductive material, gold (Au) could be as an alternative for conventional needle-type based biosensors.Therefore, we developed implantable needle-type (50 m Ø) gold coated tungsten (W-Au) amperometric microbiosensors. First, we evaluated electrochemically, the ability of W-Au microelectrodes (50 m Ø) to continuously monitor changes in H 2 O 2 . After, we functionalized, using a layer-by-layer assembly, the surface of W-Au microelectrodes. First with permselective membrane(s) (Nafion and Nafion-PPD) and after with an enzymatic hydrogel, containing an enzyme selective for glucose (glucose oxidase). Both the enzyme loading and the applied potential were optimized and the performance of functionalized W-Au microelectrodes and fully assembled biosensors was evaluated electrochemically. Additionally, the surface of bare and functionalized microelectrodes was also characterized by imaging techniques (scanning electron microscopy).In vivo experiments revealed that, W-Au based glucose biosensors, were able to accurately monitor, in real-time, changes in brain glucose in response to relevant pharmacological challenges.

Composites consisting of polymer matrix materials and natural or synthetic layered minerals e.g. clays were prepared by using special compatibilizing agents between these two intrinsically non-miscible components. Block or graft copolymers combining one part of the polymer that is identically and/or completely miscible with the organic polymer and another part that is compatible with the natural mineral are applied to act as compatibilizer. The interaction between the first part of the compatibilizer is preferentially an ionic interaction or an interaction via hydrogen bonds. This interaction leads to a separation of the mineral into single sheets and/or small clusters containing approximately 2 -10 sheets and a subsequent homogeneous incorporation of these clusters into the polymer matrix material.

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Electrical Properties / Electrochemistry / Materials Properties / Photoelectrochemistry 1 Semiconductors Polycrystalline Mg-doped (0.1 -5 at.%) Fe203 photoelectrodes have been prepared by annealing at 1573 K followed by slow cooling in air to ambient temperature. These materials are essentially single-phase at Mg concentrations not exceeding 0.5 at. %. Disk-shaped (photo)-electrodes were prepared, and their electric and photoelectrochemical (PEC) properties were measured. The positive sign of the photovoltage and of the thermoelectric power 8, confirmed the materials to be p-type semiconducting. -Carrier concentrations calculated from 8, revealed each Mg2+ to introduce one electron-hole up to about 0.1 at.% Mg. The a.c. conductivities, showing conductivity activation enthalpies of about 0.5 eV in the temperature region 300-800 K, are affected by grain growth and porosity. -The currentvoltage characteristics in the dark and under illumination, the spectral response, and the flatband potential (Vh = +2.2 V vs. SCE pH = 10) have also been determined. -PEC photocurrents in the visible region correspond to very low (-0.lY0) monochromatic quantum efficiency which is due to the low electron-hole mobility. The electronic transition in the visible region is indirect, and evidence has been found for this transition to be Fe-Fe charge transfer. Surface pretreatment is found to have a major effect on the photoelectrochemical properties as deduced from current-voltage curves. The stability of the a-Fe203 electrode in alkaline solution is discussed. IntroductionThe cleavage of water into hydrogen and oxygen in a photoelectrochemical (PEC) cell using a semiconductor photoelectrode has been well established [l -41. Optimal solar energy conversion requires a chemically inert semiconducting electrode material which shows photoconductivity far into the visible, and operates with high energy-conversion efficiencies.Recently, we have studied impurity doping of the stable wide bandgap materials n-type Ti02 and SrTi03 in order to extend their photoresponse into the visible part of the solar spectrum [5, 61. It appeared that with transition metal ion dopants efficient power-conversion efficiencies could only be reached under near uv irradiation. Besides these titanates, the potential applicability of other oxides as photoelectrodes in PEC cells has been studied.The photoelectrochemical properties of iron oxide, a-Fe2O3, have attracted wide-spread attention [7 -301 due to its relatively low bandgap energy of about 2.2 eV [18,31] which is close to the ideal value for optical solar energy absorption, its stability against chemical, and photochemical corrosion [7-9, 16, 191, its vast abundance, and its low cost of preparation.Aliovalent doping is required to render a-Fe2O3 semiconducting [15 -181. However, the flat-band potential of n-type iron oxide lies far below the hydrogen reduction potential [20,27].Hence, a PEC cell with this electrode requires an external bias of about 0.6 eV. While photoassisted electrolysis of water has been dem...