Metal oxide nanoparticles for Solar cells and Catalysis

New precursors and solution processes are developed and studied to get a better understanding of the factors that control particle sizes, surface faceting, crystallographic quality and doping of complex oxide semi-conductors. The systems studied aim at applications in three areas that have similar requirements:

  1. Photo-catalytic decomposition of organics into CO2 and H2O for self-cleaning surfaces, cleaning of water and air from organic and bio-toxics.
  2. Photo-catalytic decomposition of water to H2 and O2 (water splitting) for use as renewable carbon free fuel.
  3. Solar-cells for generation of renewable electricity.

Photo-catalytic semi-conductors absorb photons from the solar light exiting the electron to a higher energy band, leaving a positive “hole”. The electron and hole then move to the surface where the absorbed energy is used for molecular reactions; decomposition of organic toxic substances or decomposition of water into H2 and O2. Hence, optimization of a photo-catalyst requires optimized band-structures, high crystal quality and optimized particle size to let the charges can move to the surface, rather than recombine, as well as good surface sites for molecular reactions. Most non-oxide materials break down during use. To achieve good enough efficiency for application, probably it is required a combination of a good light absorber and a surface structure, optimized for the chemical reactions. Thus very complex wire or particle structures in mixed phase or core-shell structures are required, and for real application, they must still be prepared at low cost and high through-put.

New solution based routes are developed for preparation of complex nano-structures based on doped and non-doped TiO2, ZnO, WO3 and Fe2O3. Here control of the particles sizes, phases and surface structures is in focus, as well as doping for control of band-structures. Much extended doping ranges compared to more conventional processes have been achieved, as well as wire and core-shell structures including e.g. metal nano-particle studded shells. The physical and electronic structures, and surface reactions are studied in great detail, often within collaborations; IR, TEM, SEM, TGA/DSC, XRD, in-situ IR, Raman spectroscopy, XAS, XES, XPS, PES, RIXS.

TiO2 anatase and WO3 as, from left; mixed phase, core-shell and wire structures.

Detailed studies of TiO2 (anatase, rutile, brookite) has shown e.g. that an anatase photo-catalyst with optimized size and surface facets yield 15 times higher decomposition rate than P25. It was also shown that ZrO2 doped anatase yielded a highly time-stable catalyst with a high decomposition rate, as well as improved solar-cell efficiency.

Some collaborators are; K. Jansson (SU), L. Österlund (UU/FOI), O. Karis (UU), LBNL Berkeley, USA, and NIMS, Tsukuba, Japan.

Examples of publications

  • L. Österlund, G. Westin, and M. Leideborg. “Highly reactive photocatalytic material and manufacture thereof”, Swedish patent application. IPC SE09501-9.
  • A. Mattson, M. Leideborg, L. Persson, G. Westin, and L. Österlund, Oxygen diffusion and photodegradation of acetone on Zr and Nb doped TiO2 nanoparticles, J. Phys. Chem. C., 113, 3810-3818, 2009.
  • J.H. Richter, P.G. Karlsson, G. Westin, J. Blomquist, P. Uvdal, H. Siegbahn and A. Sandell, Ultra-high Vacuum Li Insertion in sol-gel prepared Mn doped TiO2 studied by Electron Spectroscopy, J. Phys. Chem. C, 111, 3459-3466, 2007.
  • A. Mattson, M. Leideborg, K. Larsson, G. Westin, L. Österlund, Solar light decomposition of acetone on TiO2 and Nb-doped TiO2 thin films, J. Phys. Chem. B., 110, 1210-1220, 2006.

Contact: Gunnar Westin