B-substituted nanoporous carbons for hydrogen storage: from computer simulations to experimental verification
Résumé
Hydrogen is considered to be the preferred successor to gasoline due to its clean combustion, but its efficient and save storage remains the bottle-neck and one of the main challenges in hydrogen based technologies, especially those addressing mobile applications.
Among different storage methods, reversible physical adsorption of molecular hydrogen in nanoporous materials is considered as the one of most attractive options. However, despite of more than 20 years of intensive experimental research no existing porous structures – from traditional activated carbons to porous polymer networks or metal organic frameworks - possess the required adsorbing properties.
Therefore, we used computer simulations to explore the experimental options toward the most promising solutions. We showed that boron substituted graphene-based nanoporous structures may reach necessary storage performance if both key parameters defining the storage capacity of a sorbent (its specific surface and the energy of hydrogen adsorption) will be optimized. A potentially effective way to synthetize such optimized structures is arc-discharge procedure, successfully used in the past to synthetize fullerenes and nanotubes. We have assumed that the synthesis parameters can be modified to prepare graphene-based structures with a variety of substitution sites, shapes, sizes, and interconnections between graphene fragments.
The first boron-substituted carbons prepared in this way show promising properties: they contain a variety of organized, graphene based structures decorated with boron nanoclusters, partially incorporated into graphene layers. The strongest adsorption occurs with the binding energy higher than 10 kJ/mol, and at least 10 % of adsorption sites adsorb hydrogen with the energy higher than 6.5 kJ/mol, significantly larger than in activated carbons (~4.5 kJ/mol). The specific surface of as-prepared samples is low (~ 200 m2/g). To increase it, both physical (heating in O2 reach atmosphere) and chemical (with KOH) activation are currently in progress.