Nanoporous carbons remain the most promising candidates for effective hydrogen storage by physisorption in currently foreseen hydrogen-based scenarios of the world’s energy future. An optimal sorbent meeting the current technological requirement has not been developed yet. Here we first review the storage limitations of currently available nanoporous carbons, then we discuss possible ways to improve their storage performance. We focus on two fundamental parameters determining the storage (the surface accessible for adsorption and hydrogen adsorption energy). We define numerically the values nanoporous carbons have to show to satisfy mobile application requirements at pressures lower than 120 bar. Possible necessary modifications of the topology and chemical compositions of carbon nanostructures are proposed and discussed. We indicate that pore wall fragmentation (nano-size graphene scaffolds) is a partial solution only, and chemical modifications of the carbon pore walls are required. The positive effects (and their limits) of the carbon substitutions by B and Be atoms are described. The experimental ‘proof of concept’ of the proposed strategies is also presented. We show that boron substituted nanoporous carbons prepared by a simple arc-discharge technique show a hydrogen adsorption energy twice as high as their pure carbon analogs. These preliminary results justify the continuation of the joint experimental and numerical research effort in this field.

Hydrogen is considered to be the preferred successor to gasoline due to its clean combustion.However, efficient and save storage of hydrogen remains the bottle-neck and one of the main challenges in hydrogen-basedtechnologies. In the past we have justified [1] the necessary conditions (materials physical properties) the hydrogenadsorbents MUST simultaneously fulfilled to be used in mobile applications: it must exhibit the specific surface at least ofthe order of 5000–7000 m2/g, have the average binding energy above 10 kJ/mol, and the density above 0.6 kg/m3. This setof parameters put so strict constrains on possible solutions that such systems are neither yet known nor seem easy tosynthesize.Here we explored the possibility to prepare boron-substituted nanoporous carbons, cheap, light and save material that wassupposed [2,3] to reversibly store hydrogen by physisorption at room temperatures and moderated pressure (< 120 bar). Weshowed that electric arc discharge between graphite electrodes may be optimized to produce graphitized structures with avariety of graphene fragment sizes, forms, and interconnections between them. It also allows to introduce boron heteroatominto graphite-like structure. The as-synthetized material shows the hydrogen binding energy twice as high as unsubstitutedcarbons, but requires post-treatment (activation) as the its surface is low (~200 m2/g).

Here we explored the possibility to prepare boron-substituted nanoporous carbons, cheap, light and save material that wassupposed [2,3] to reversibly store hydrogen by physisorption at room temperatures and moderated pressure (< 120 bar). Weshowed that electric arc discharge between graphite electrodes may be optimized to produce graphitized structures with avariety of graphene fragment sizes, forms, and interconnections between them. It also allows to introduce boron heteroatominto graphite-like structure. The as-synthetized material shows the hydrogen binding energy twice as high as unsubstitutedcarbons, but requires post-treatment (activation) as the its surface is low (~200 m2/g).

L'utilisation intensive des combustibles fossiles et l’émission des produits de leur combustion (principalement du CO2) dans l'air ont déjà impacté le climat mondial. Trouver des solutions technologiques permettant la conversion de l'économie mondiale aux carburants propres et renouvelables devient urgent. Une de possibilités consiste en utilisation de l’hydrogène comme un vecteur d’énergie. Aujourd’hui elle est limitée par l’absence d’un matériau permettant son stockage à des températures ambiantes et à des pressions modérées.Dans ce projet, nous explorons la possibilité de préparer un nouveau matériau pour un stockage réversible de l’hydrogène par physisorption : les carbones nanoporeux substitués au bore. Nous montrons que la synthèse en arc électrique peut être optimisée pour produire des structures graphitisées, avec la variété de tailles, de formes et d'interconnexions entre les fragments de graphène. Leur morphologie, structure, composition chimique et homogénéité de la distribution de l’hétéroatome dans la structure carbonée ont été caractérisés par les techniques SEM, HRTEM, EELS, XRD et spectroscopie RMN. La porosité et propriétés adsorptives ont été étudiées en utilisant les mesures d’adsorption de l’azote à T= 77 K.Les deux paramètres essentiels pour un stockage efficace de l’hydrogène dans les conditions ambiantes sont la surface spécifique de l’adsorbant et l’énergie avec laquelle les molécules du gaz sont adsorbées sur cette surface. Nous montrons que la surface spécifique d’adsorption peut être contrôlée et augmentée par une activation thermique ou chimique pour optimiser le stockage, et que la présence du bore dans les structures carbonées permet de doubler l’énergie d'adsorption d'hydrogène du matériau.

The systematic usage of fossil fuels and the emission of their combustion products (mostly CO2) in the air have already impacted global climate. Therefore, new technological solutions to drug the global energy economy towards cleaner and renewable fuels, in particular for mobile applications, are urgently needed. In particular the efficient storage of hydrogen, a clean energy vector, requires to develop an adequate sorbent operating at ambient temperature and moderated pressures, with simultaneously optimized specific surface and hydrogen binding energy. In this project we explore the potential effectiveness of arc-discharge procedure to synthesize carbon-based nanoporous sorbents with characteristics fulfilling the requirements of vehicular applications. We show that by adjusting the synthesis parameters is possible to prepare numerous graphene-based structures of different forms, sizes, and interconnections between them. The arc-discharge technique provides also a relatively easy way to incorporate heteroatoms (like boron or nitrogen) into pure carbon structures. The as-synthesized boron-substituted carbon nanostructures are characterized in term of texture (using nitrogen adsorption and spectroscopic measurements) and homogeneity of boron (using energy filtered transmission electron microscopy). The calorimetric study at different temperatures were performed to quantify the material’s capacity to adsorb hydrogen.The obtained results are promising. The energy of hydrogen adsorption in our samples is the highest ever observed experimentally in carbon-based sorbents. However, the specific surface of as prepared samples is low. Therefore, the thermal and chemical activation procedure have been applied to increase the surface accessible for adsorption and micropore volume, and in consequence, the samples’ capacity to store hydrogen.

The world is running out of fossil fuels and the products of their burning in air (mostly CO2) have already impacted global climate. Therefore, we still need a lot effort to search how to convert the global energy economy towards cleaner and renewable fuels (like hydrogen), in particular, for mobile applications. It is clear now, that to efficiently store hydrogen at ambient temperature and not too high pressures, we need to develop hydrogen sorbent and optimize simultaneously both its specific surface and adsorption energy. In this project we propose to explore the potential effectiveness of arc-discharge procedure to synthetize nanoporous, carbon based sorbents with characteristics required in vehicular applications. The technique was successfully used in the past to synthetize fullerenes and nanotubes. Therefore we have assumed that we can adjust the synthesis parameters to prepare other graphene-based structures, with a variety graphene fragment sizes, forms, and interconnections between them. In addition, arc-discharge technique provides a relatively easy way to incorporate heteroatoms into pure carbon structures.The first characterizations of boron-substituted carbons obtained by this method are promising: the energy of hydrogen adsorption is the highest ever observed experimentally in carbon-based sorbents. However, the specific surface is relatively low, ~ 200 m2/g, suggesting that the samples need to be activated to increase their accessible for adsorption surface and, in consequence, their capacity to store hydrogen.