Role of microporosity in hydrogen adsorption on templated nanoporous carbons M. Armandi a,c , B. Bonelli a,c , C. Otero Area ´n b , E. Garrone a,c, * a Dipartimento di Scienza dei Materiali ed Ingegneria Chimica, Politecnico di Torino, Corso Duca degli Abruzzi 24, I-10129 Torino, Italy b Departamento de Quı ´mica, Universidad de las Islas Baleares, 07122 Palma de Mallorca, Spain c INSTM Torino Politecnico Unit, Corso Duca degli Abruzzi 24, I-10129 Torino, Italy Received 27 July 2007; received in revised form 10 October 2007; accepted 11 October 2007 Available online 18 October 2007 Abstract Casting of inorganic templates is a viable method for obtaining porous carbons with tailored properties and with potential applica- tions in gas adsorption and storage. One of the most used inorganic templates is mesoporous SBA-15 silica, which presents a honeycomb structure, with microporous channels interconnecting mesopores, this three-dimensional structure allowing facile pores filling by the car- bon source. In this work, carbon replicas of SBA-15 silica were synthesized by using a sucrose solution as carbon source, and performing carbonization at different temperatures (800, 900 and 1000 °C). In all cases, partially graphitic carbons were obtained, with high surface areas and porous volumes, retaining the morphology of the silica template. Since the carbon replica pyrolised at 800 °C showed the high- est BET surface area, this was chosen for further post-synthesis treatments (physical or chemical) with the aim of improving textural and surface properties. H 2 adsorption isotherms at 77 K and sub-atmospheric pressure were measured, finding the highest hydrogen uptake, corresponding to 2.0 wt%, with chemically activated sample. Finally, a linear dependence was found between the hydrogen uptake and microporous volumes of the prepared carbons, as measured by the t-plot method, rather than with BET specific surface areas. Ó 2007 Elsevier Inc. All rights reserved. Keywords: Carbon replicas; Hydrogen; Microporous volume 1. 1.Introduction Though hydrogen is being considered as an ideal energy vector for replacing fossil fuels, several technological and scientific issues are still matter of studies and improve- ments, and in particular its storage is a challenge for mate- rial science [1]. To this purpose, four principal methods are proposed, each one presenting intrinsic limitations and technological problems: liquid hydrogen; compressed gaseous hydrogen; chemical hydrogen storage in atomic form (as with metal hydrides) and hydrogen physisorption. The latter has been considered by several authors as the most promising method [2] to meet the ambitious goals of the DOE (Department of Energy of the United States), consisting in the 6.5 wt% at ambient temperature and pressure to be achieved by 2010. In order to reach good performances through physisorption, materials are envisaged interacting only weakly with molecular hydrogen [1], but characterized by a huge specific surface area and limited specific weight, like activated or nanostructured carbon and carbon nano- tubes (CNTs) [3–14]. Bhatia and Myers [15] have shown that, for ambient temperature storage and delivery in the 30–1.5 bar pressure range, the optimum value for the adsorption enthalpy change is about 15 kJ mol 1 . With carbons, an average enthalpy change of 5.8 kJ mol 1 is found, and, consequently, an optimum operating tempera- ture of 115 K is predicted [15]. The same authors have shown that, though changing pore shapes and adsorption temperatures, the highest enthalpy of adsorption of 1387-1811/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2007.10.017 * Corresponding author. Tel.: +39 011 5644661; fax: +39 011 5644699. E-mail address: edoardo.garrone@polito.it (E. Garrone). www.elsevier.com/locate/micromeso Available online at www.sciencedirect.com Microporous and Mesoporous Materials 112 (2008) 411–418