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G. Schmid, J. Bauer, C. Eisenmenger-Sittner:
"Magnetron sputtered catalytic coatings on hollow glass microspheres for a H2-storage system";
Vortrag: Int. Conf. for Metallurgical Coatings and Thin Films, San Diego, CA, USA; 20.04.2015 - 24.04.2015.

Hydrogen pressurized hollow glass micro spheres in combination with NaBH4 (sodaborohydrid) hydrolysis bear the potential of storing hydrogen in feasible amounts and could reach storage densities up to 12 wt% or 85 kg/m³ (theoretically). Therefore the approximately 40 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 120 °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 deposited on the hollow glass microspheres.
To apply the catalytic coatings on the hollow glass microspheres by magnetron sputtering a special coating system was used. The catalytic behaviour, the film thickness and the film durability of Ru, Pt, Ti, TiO2 and combinations from them were investigated. To characterise the catalyst the amount of released hydrogen and the reaction temperature were measured with a custom built experimental setup. After one test the spheres were washed, dried and reused to investigate the stability of the catalyst. Since the activity of the catalyst decreased a method to reactivate it was needed to be found.
Ruthenium films showed the best catalytic performance of the tested coatings, e.g. 90% H2-yield with ruthenium as compared to 20% H2-yield with Pt. However, it became clear that ruthenium films have very bad adhesion behaviour, which was solved with an interlayer between the catalyst and the hollow sphere. Current work focuses on the long time stability of the catalyst and on finding an inexpensive catalyst material.

This work was supported by the Austrian Science Fund (FWF), project "CatSphere", grant number P-22718.