Technical Communication Hydrogen adsorption on Pd-modified carbon nanofibres: Influence of CNF surface chemistry and impregnation procedure Eva Dı´az, Marta Leo ´n, Salvador Ordo ´n ˜ ez* Department of Chemical Engineering and Environmental Technology, University of Oviedo, Julia ´n Claverı´a s/n, 33006 Oviedo, Spain article info Article history: Received 31 January 2010 Received in revised form 23 February 2010 Accepted 24 February 2010 Available online 26 March 2010 Keywords: Hydrogen storage Oxygen surface groups Graphitic carbon Palladium hydrides abstract Different carbon nanofibre (CNF) based materials (parent, oxidized, and impregnated with a palladium loading of 1 wt.% using different procedures) have been tested for hydrogen storage at ambient pressure. Parent CNF are completely free of oxygen surface groups, whereas treatment in nitric acid increases mainly the amount of surface anhydrides groups. Add to the surface functionalization, the solvent employed in the palladium impregnation was also varied, using both aqueous and organic precursor solutions. Thermogravimetric analyses of the hydrogen adsorption–desorption cycles suggest that the presence of theses functional groups hinders the adsorption. Concerning the presence of palladium, its influence strongly depends on the previous activation of the surface and on the solvent used for the palladium addition. The use of aqueous precursors and func- tionalized CNFs leads to increases in the adsorption capacity close to 100% compared to the parent CNF (12.6 vs. 6.7 cm 3 /g). ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. 1. Introduction The massive use of hydrogen as energy source requests the development of efficient storage procedures. Among these procedures, adsorption is considered as a very safe and effi- cient one. For this purpose, carbon materials have attracted a lot of interest because of their high adsorption capacity and reversibility, which is based on weak van der Waals force between H 2 and the surface of the materials [1]. Thus, carbon nanomaterials (such as carbon nanofibres) are of great prac- tical interest for hydrogen adsorption. Although typical values of hydrogen adsorption reached by carbon nanofibres are quite controvert, varying from 0.1 to 67 wt.% [2–4]; most recent studies showed that hydrogen store capacity is less than 0.05 wt.% at ambient temperature and 1 MPa [5]. One of the strategies for increasing this adsorption capacity is promoting spill-over effects [6]. Hydrogen spill- over effects involves the dissociation of the hydrogen mole- cule on a metal particle and the migration of the resulting atoms to the support surface. This migration is enhanced or hindered by the chemical nature of the support. Hydrogen spill-over is widely known and used in the development of catalysts for hydrogenation reactions, as mentioned (for the case of Pd/graphitic materials) by Amorim and Keane [7]. However, this effect is not so studied for the purpose of hydrogen storage, although the spill-over of hydrogen in carbon nanostructures can be an effective method to enhance their storage capacities [8,9]. One of the main features of the carbonaceous materials controlling both the current adsorp- tion and the spill-over effects is the presence and nature of the * Corresponding author. Tel.: þ34 985 103 437; fax: þ34 985 103 434. E-mail address: sordonez@uniovi.es (S. Ordo ´n ˜ ez). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 35 (2010) 4576–4581 0360-3199/$ – see front matter ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2010.02.119