Optimization of biomass-based carbon materials for hydrogen storage

Five biomass-based carbon samples have been successfully prepared through KOH activation procedure. The microstructure of the prepared materials was tuned by varying KOH/precursor weight ratio from 1:1 to 5:1, in order to optimize their hydrogen storage behavior and to clarify the storage mechanism. A careful physic-chemical characterization of the prepared sample (N₂ and CO₂ adsorption, X-ray diffraction, electron microscopy observations) showed that by increasing the activation ratio the nature of the carbons changes from microporous to micro-mesoporous. Thus, an increase in the surface area was observed which enhanced H₂ sorption capacity when high H₂ pressures were adopted (25-200 bar). At subatmospheric pressure, the role of active sites for H₂ adsorption, located in the oriented graphene sheets, was clearly elaborated. Finally, the optimal carbon sample has shown a capacity of 6wt% and 1.22 wt% at -196°C and 25°C respectively, and 200 bar. These results make biomass-based carbons promising materials for H₂ storage application.