Hydrogen storage in graphene nanoplatelet incorporated silicon oxycarbides

Abstract

AbstractHighly porous materials having high specific surface areas are strong candidate materials for hydrogen storage by physisorption. However, the development of suitable adsorbents for hydrogen storage having chemical stability is still a challenge. Micro and mesoporous silicon oxycarbide (SiOC) ceramics due to their excellent chemical stability can overcome this constraint. Contrary with our expectations, the addition of graphene nanoplatelets (GNP) to SiOC ceramics resulted in a lower gravimetric density. A maximum gravimetric storage density of 1.58 wt.% was observed at 6 bar after adding 0.3 wt.% of GNP, whereas the pristine SiOC ceramic showed a gravimetric capacity of 2.07 wt.% at 6 bar. We have proposed a theoretical framework to quantify these phenomena in line with the existing structural model. We show that the addition of GNP results in an increase in the size of the silica nanodomain leading to an overall reduction in hydrogen uptake. Furthermore, we hypothesize that the addition of GNP beyond 3 wt.% could lead to an increase in the coordination of mixed bonds in the interface and subsequent loss of porosity in the composite. Our study confirms that the pore sizes are crucial in determining the hydrogen uptake in these composites.