ple of photocatalytic water splitting
Despite the great need for a technical realization of photoelectrochemical hydrogen production so far only the basic feasibility has been demonstrated in the laboratory. On an industrial scale, it is not yet possible to develop efficiently working cells. A thorough understanding as a basis for systematic development is missing.
In the department of "Sustainable Energy Technology" innovative techniques for fabrication of large area photoelectrodes are evaluated. In close cooperation with the Helmut-Schmidt-University, Hamburg, in particular the use of cold gas spraying for the production of electrodes is being tested. An important step towards enhancing the efficiency is an optimal structuring of the surface. Methods for structuring of the electrode surfaces from the nano to micro range are developed at the HZG.
Different electrodes manufactured with the CGS process (TiO2, Hematite, BiVO4)
For a commercially simple and economical fabrication of large area photoelectrodes it is necessary to transfer semiconductor powders (eg TiO2, WO3, Hämatit (α-Fe2O3)) to an efficiently working electrode structure.
Surface topography CGS electrodes
One of the main factors that determine the efficiency of the catalyst is the surface area availability for the catalytic water splitting. Our department is therefore working with structured electrodes that feature a much higher surface area compared to flat electrodes. We employ novel techniques for this structuring at different scales.
The coating of fabrics made from polymers or metals allows a simple process control and shows a significant increase of the surface area when using multilayers of fabric. By using different tissues, the electrode can be adapted to all requirements.
Titanium foams originating from the MIM process (made by the Department of Powder Technology) feature macropores that can be used to increase the surface area and to improve the gas management at the electrode.
The innovative cold gas spraying process allows - in contrast to the established wet chemical deposition methods - binding of the catalyst without the need to add binders and sintering steps. During the deposition, the particles have a high kinetic energy, so that fractures, micro-fine cracks and gaps arise. This significantly increases the available surface area. In addition, a significantly improved particle binding on the substrate is achieved.
Combinations of micro-, meso- and macroporous structures can be prepared by the use of inverse opal structures. This technique allows for a significant increase of the surface area. Also reproducible preparation of uniform structures that can be used for the basic study of transport mechanisms in photoelectrodes is possible.
The absorption of solar light can be controlled by the use of structures in equal dimensions of the light wavelength. Using reactive ion etching (in collaboration with the Molecular Foundry, Lawrence Berkeley National Labs) structures are designed and manufactured to control the absorption properties of the electrodes. Together with photo-active coatings (shown by the white coating in the SEM image on the left), the light yield can be increased dramatically.
Our department colaborates closely with other groups and institutions. These include the Helmholtz-Zentrum Berlin, the Molecular Foundry (Lawrence Berkeley National Laboratory), the Helmut Schmidt University and Monash University in Melbourne.
We have extensive equipment for the production and the photoelectrochemical characterization of surfaces.
Director of the Division "Materials Technology"
Institute of Materials Research - Materials TechnologyE-mail contact