The world is running out of fossil fuels and the products of their burning in air (mostly CO2) have already impacted global climate. Today it is clear that in near future we need to convert the global energy economy towards cleaner and renewable fuels (like hydrogen). However, to efficiently store hydrogen at ambient temperature and not too high pressures, we need to develop the hydrogen sorbent with simultaneously optimized specific surface and adsorption energy.
Here we report the first studies of the potential effectiveness of arc-discharge procedure to synthetize nanoporous, carbon based sorbents with characteristics required for hydrogen storage in vehicular applications. The arc-discharge, successfully used in the past to synthetize fullerenes and nanotubes, provides a relatively easy way to incorporate heteroatoms into pure carbon structures. Therefore we have assumed that we can adjust the synthesis parameters to prepare other graphene-based structures, with a variety of shapes, sizes, and interconnections between graphene fragments.
The properties of first boron-substituted carbons obtained by this method are promising: the prepared carbon soot contains a variety of organized, graphene based structures, and the HRTEM and NMR study confirm the presence of boron nanoclusters, partially incorporated into graphene layers. The energy of hydrogen adsorption is the highest ever observed experimentally in carbon-based sorbents: at least 10 % of adsorption sites adsorb hydrogen with the energy higher than 6.5 kJ/mol, and the strongest adsorption occurs with energy higher than 10 kJ/mol. These values are significantly larger than hydrogen adsorption energy in activated carbons (~4.5 kJ/mol). However, the specific surface of as-prepared samples is low (~ 200 m2/g), even after thermal activation. Therefore the samples are currently activated chemically (with KOH); this procedure should increase the surface accessible for adsorption by one order of magnitude.
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