Résumé
The intensive use of fossil fuels and the emission of combustion products (mostly CO2) to air have already impacted global climate. We urgently need to find a technological solution to convert the global energy economy towards cleaner and renewable fuels. A possible solution consists in using hydrogen as energy vector. Today this technology is limited by the absence of material that could efficiently store hydrogen at ambient temperature and moderate pressures. We still need to conceive and synthetize a hydrogen adsorbent with simultaneously optimized specific surface and hydrogen binding energy. In this work we explore the possibility to prepare a new material for reversible hydrogen storage by physisorption: boron-substituted nanoporous carbons. We show that electric arc discharge synthesis (Fig.1) may be optimized to produce graphitized structures with a variety of graphene fragment sizes, forms, and interconnections between them. The morphology, structure, chemical composition, and homogeneity of boron distribution over the carbon samples were characterized using MEB, HRTEM, EELS, and XRD microscopies, and HR solid state NMR. The porosity and adsorption parameters were determined from isotherms of nitrogen adsorption at T = 77 K and from calorimetric measurements. Two parameters that are essential for efficient hydrogen storage at ambient conditions are sorbent specific surface and the energy of gas adsorption at this surface. The energy of hydrogen adsorption in our samples is twice as high as in all-carbon materials (~9 kJ/mol). However, the specific surface of as prepared samples is low (~200 m2/g We show that material specific surface can be controlled and increased by thermal and/or chemical activation of the samples.