A hybrid hydrolytic hydrogen storage system based on catalyst-coated hollow glass microspheres

Abstract

Hydrogen-pressurized hollow glass microspheres (HGMs) in combination with a hydride bear the potential of storing hydrogen in feasible amounts. Therefore, the approximately 20-µm diameter spheres are heated up and pressurized with hydrogen at a pressure of 85 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 stored hydrogen, heat has to be applied again to reach temperatures of about 250 °C (523.15 K). To reach this temperature, it is suggested in this work to use an exothermal chemical reaction, which produces hydrogen as a by-product. In this case, an NaBH4–water reaction will be discussed, which has to be initialized by a catalyst deployed on the HGMs. It will be shown that hydrogen storage densities of up to 20 wt% and 50 kg/m3 can be theoretically achieved with the proposed hydrogen storage system consisting of hydrogen-pressurized HGMs and a hydride, that is, NaBH4. Volumetric storage density and other aspects, such as water management, temperature restriction, stoichiometric restriction and hydrogen diffusion through glass, will be discussed. Due to resulting high water vapour pressures, a pressure vessel will still be needed in the concept. This paper shall give an overview of theoretically achievable storage densities with the proposed system. Experiments were carried out regarding catalytic promoted hydrolysis with HGMs, and resulting storage densities were determined. These experiments show good agreement with theory. However, they will be addressed only briefly in the outlook of the paper because a detailed discussion would go beyond the scope of this work. Copyright © 2016 John Wiley & Sons, Ltd.