Rice husk derived graphene-like material: Activation with phosphoric acid in the absence of inert gas for hydrogen gas storage

In this study, the effect of concentration of phosphoric acid (H₃PO₄) towards the physicochemical properties of rice husk derived graphene (GRHA) in the absence of inert gas was investigated. From TGA analysis, it was found that GRHA 1:3 possessed the highest weight loss (24.66%) due to the highest reactivity towards H₃PO₄. The FTIR shows that graphene-like material was obtained as the –OH groups were vanished in GRHA structure after activation. Raman spectroscopy and XRD analysis indicated that the produced GRHA is in amorphous state and has few layers of graphene. GRHA 1:3 showed the greatest improvement in their porous structure including the highest surface area (315.07 m²/g) with the largest pore volume (0.2069 cm³/g) as compared to other samples. From the static adsorption test, it was confirmed that GRHA 1:3 stored the highest amount of hydrogen compared to other samples with 1.95 wt % contributed by its excellent porosity and surface area. To further understand the kinetics of hydrogen adsorption on GRHA, pseudo-first model and pseudo-second model was plotted. Pseudo second model was the best fitted model which indicated that the gas molecule adsorbed in the GRHA material via chemisorption. Additionally, from the kinetic study it was found that the adsorption process of GRHA 1:3 was controlled by multi-step adsorption process.