Photocatalytic splitting of water was carried out in a two-phase system. The efficiencies of different types of nanocrystalline semiconductors were investigated and compared with commercialised TiO2 nanopowder. Genera...Photocatalytic splitting of water was carried out in a two-phase system. The efficiencies of different types of nanocrystalline semiconductors were investigated and compared with commercialised TiO2 nanopowder. Generated hydrogen was chemically stored by use of a quinoid system, which seems to be useable for fuel cells. Solar light sensitive nanocomposites of CdSe/TiO2 and CdSxSey/TiO2 type were prepared and their good photocatalytic performance was demonstrated. In the visible range of 400 - 600 nm CdSxSey/TiO2 composites show comparable good results as in the UV range, which is very promising for their use as solar light water splitters. The concept of sensitising TiO2 with different kind of semiconductor nanoparticles, which is already known from quantum dot sensitised solar cells (QDSC), was demonstrated here for water splitting as well. Furthermore the kinetics of the storage reaction was investigated by UV-Vis spectroscopy and found to proceed via a consecutive reaction with an 1:1 charge transfer complex of quinone and hydroquinone as intermediate. The electron transfer process via a Fe2+/Fe3+ redox couple was investigated by UV-Vis spectroscopy as well as by a dye reaction on the TiO2 surface. A light microscopic view of the surface of larger aggregates of TiO2 nanoparticles indicated different areas of photocatalytic activity with photocatalysis preferentially at catalyst edges. The global electron transfer process could be traced by following the dye colour in real time.展开更多
Gr?tzel cells were prepared by using CdSe- and CdSxSey-nanoparticles as sensitizer. The quantum dots were incorporated in various sizes and concentrations in a TiO2 nanoparticle layer by a simple mixing procedure. The...Gr?tzel cells were prepared by using CdSe- and CdSxSey-nanoparticles as sensitizer. The quantum dots were incorporated in various sizes and concentrations in a TiO2 nanoparticle layer by a simple mixing procedure. The advantage of this method compared to anchoring of nanoparticles to TiO2 by linker molecules or chemical bath deposition is that we are able to control the ratio between TiO2 and CdSe or CdSxSey more precisely and over a larger range of concentrations. TiO2 solar cells sensitized by this technique achieved photon-to-current conversion efficiencies (IPCE) of ~40% in the range of 300 - 500 nm with a maximum IPCE of ~70% at 400 nm (sulphide/sulphate electrolyte). The best results at wavelengths above 500 nm were achieved with CdSxSey/TiO2 cells at a molar ratio of 6:1 (S:Se) with IPCE of 40% at 500 nm and still 15% at 800 nm. Quantum efficiencies obtained with iodine/iodide electrolyte were lower and lead to an overall efficiency of 0.32%. The CdSxSey sensitized solar cells show enhanced stability compared to CdSe based systems and the use of the iodine/iodide electrolyte increases cell endurance further.展开更多
文摘Photocatalytic splitting of water was carried out in a two-phase system. The efficiencies of different types of nanocrystalline semiconductors were investigated and compared with commercialised TiO2 nanopowder. Generated hydrogen was chemically stored by use of a quinoid system, which seems to be useable for fuel cells. Solar light sensitive nanocomposites of CdSe/TiO2 and CdSxSey/TiO2 type were prepared and their good photocatalytic performance was demonstrated. In the visible range of 400 - 600 nm CdSxSey/TiO2 composites show comparable good results as in the UV range, which is very promising for their use as solar light water splitters. The concept of sensitising TiO2 with different kind of semiconductor nanoparticles, which is already known from quantum dot sensitised solar cells (QDSC), was demonstrated here for water splitting as well. Furthermore the kinetics of the storage reaction was investigated by UV-Vis spectroscopy and found to proceed via a consecutive reaction with an 1:1 charge transfer complex of quinone and hydroquinone as intermediate. The electron transfer process via a Fe2+/Fe3+ redox couple was investigated by UV-Vis spectroscopy as well as by a dye reaction on the TiO2 surface. A light microscopic view of the surface of larger aggregates of TiO2 nanoparticles indicated different areas of photocatalytic activity with photocatalysis preferentially at catalyst edges. The global electron transfer process could be traced by following the dye colour in real time.
文摘Gr?tzel cells were prepared by using CdSe- and CdSxSey-nanoparticles as sensitizer. The quantum dots were incorporated in various sizes and concentrations in a TiO2 nanoparticle layer by a simple mixing procedure. The advantage of this method compared to anchoring of nanoparticles to TiO2 by linker molecules or chemical bath deposition is that we are able to control the ratio between TiO2 and CdSe or CdSxSey more precisely and over a larger range of concentrations. TiO2 solar cells sensitized by this technique achieved photon-to-current conversion efficiencies (IPCE) of ~40% in the range of 300 - 500 nm with a maximum IPCE of ~70% at 400 nm (sulphide/sulphate electrolyte). The best results at wavelengths above 500 nm were achieved with CdSxSey/TiO2 cells at a molar ratio of 6:1 (S:Se) with IPCE of 40% at 500 nm and still 15% at 800 nm. Quantum efficiencies obtained with iodine/iodide electrolyte were lower and lead to an overall efficiency of 0.32%. The CdSxSey sensitized solar cells show enhanced stability compared to CdSe based systems and the use of the iodine/iodide electrolyte increases cell endurance further.
