Doctor's Theses (authored and supervised):
G. Schmid:
"A hybrid hydrolytic hydrogen storage system based on catalyst sputter-coated hollow glass microspheres";
Supervisor, Reviewer: C. Eisenmenger-Sittner, G. Rupprechter;
Institut für Festkörperphysik,
2015;
oral examination: 2015-06-17.
English abstract:
Hydrogen pressurized hollow glass micro spheres in combination with NaBH4 (soda borohydride) hydrolysis bear the potential of storing hydrogen in feasible amounts and could reach storage densities up to 8-20 wt% or 30-50 kg/m³ (theoretically). Therefore, the approximately 20 μm diameter spheres are heated up and pressurized with hydrogen at 70 MPa, so hydrogen diffuses into the spheres. After the spheres are cooled down, hydrogen can be stored at room temperature without excessive security measures. To release the trapped hydrogen, heat has to be applied again to reach the temperatures of about 250 °C. To reach this temperature an exothermal chemical reaction can be used, in this case a NaBH4-water reaction, which produces hydrogen as a most welcome by-product. This chemical reaction has to be initialized by a catalyst deployed on the hollow glass microspheres.
To realise uniform coatings on the microspheres, an apparatus was designed with a special shaped coating vessel rotating beneath a deposition source, i.e. magnetron sputter source. However, in vacuum the particles tend to adhere to one another and to the surfaces of the containing vessel as coating proceeds, especially when depositing pure metal films. This prohibits most particles from being coated, since they are not exposed to the sputtering beam. To overcome these problems, a concussion mechanism was developed to break up the particle clusters. It will be shown that powder substrates of different kinds can be coated successfully.
Catalyst performance not only depends on the structure of the catalyst, but also on the support material of the catalyst. For the present application anatase phase TiO2 was chosen as support, which is why these films have been studied on plane glass substrate and hollow glass microspheres. The TiO2 films were reactively deposited with a bipolar pulsed DC power supply at different deposition pressures (Ar, O2), reverse times and frequencies. It will be shown that even though anatase films could be deposited on plane substrates, it was not possible to detect anatase films on hollow glass microspheres by X-ray diffraction.
In addition, results of the catalytic experiments of Ru, Pt, TiO2 films and combinations thereof will be presented. To characterise the catalyst the amount of released hydrogen and the reaction temperature were measured with a custom built experimental setup. Ruthenium films showed superior catalytic performance but inferior adhesion. The issue of adhesion was solved with multilayer and co-sputtered coatings. Since the activity of the catalysts decreased dramatically after the first test, a reactivation method had to be found. By hydrochloric acid treatment it was possible to repeatedly reactivate the catalyst.
In conclusion, a first step to realise a hybrid hydride hollow glass microsphere hydrogen storage system was taken. The next step would be experiments with hydrogen loaded microspheres.
Created from the Publication Database of the Vienna University of Technology.