Catalytic effect of carbon nanostructures on the hydrogen storage properties of MgH 2 eNaAlH 4 composite Ashish Bhatnagar a , Sunita K. Pandey a , Viney Dixit a , Vivek Shukla a , Rohit R. Shahi b , M.A. Shaz a , O.N. Srivastava a, * a Hydrogen Energy Centre, Department of Physics, Banaras Hindu University, Varanasi 221005, India b Department of Physics, MNNIT, Allahabad 211004, India article info Article history: Available online 17 June 2014 Keywords: MgH 2 NaAlH 4 Carbon nanostructures Catalytic effect abstract The present investigation describes the hydrogen storage properties of 2:1 molar ratio of MgH 2 eNaAlH 4 composite. De/rehydrogenation study reveals that MgH 2 eNaAlH 4 composite offers beneficial hydrogen storage characteristics as compared to pristine NaAlH 4 and MgH 2 . To investigate the effect of carbon nanostructures (CNS) on the de/rehydrogenation behavior of MgH 2 eNaAlH 4 composite, we have employed 2 wt.% CNS namely, single wall carbon nanotubes (SWCNT) and graphene nano sheets (GNS). It is found that the hydrogen storage behavior of composite gets improved by the addition of 2 wt.% CNS. In particular, catalytic effect of GNS þ SWCNT improves the hydrogen storage behavior and cyclability of the composite. De/rehydrogenation experiments performed up to six cycles show loss of 1.50 wt.% and 0.84 wt.% hydrogen capacity in MgH 2 eNaAlH 4 catalyzed with 2 wt.% SWCNT and 2 wt.% GNS respectively. On the other hand, the loss of hydrogen capacity after six rehydrogenation cycles in GNS þ SWCNT (1.5 þ 0.5) wt.% catalyzed MgH 2 eNaAlH 4 is diminished to 0.45 wt.%. Copyright ª 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Introduction Limited stocks of fossil fuel based energy resources and environmental problems have attracted global attention. Today, the whole world is looking towards the permanent solution to these problems. Hydrogen energy can be consid- ered as the permanent solution to the depletion of fossil fuel and environmental problem. But implementation of hydrogen economy has been largely hampered by the problems asso- ciated with storage of hydrogen [1]. Due to low volumetric density of hydrogen, it needs viable, efficient and safe media for storage [2e7]. Out of all the options available, solid-state storage of hydrogen is the promising option and offers various advantages over other modes of hydrogen storage [4]. Among the solid-state storage mode of hydrogen, elemental hydride (like MgH 2 ) and alanate-based complex metal hy- drides (like NaAlH 4 ) are the promising candidates as a hydrogen storage material. The promising elemental hydride MgH 2 desorbs hydrogen in a single step and releases 7.6 wt.% (<410  C) of hydrogen [8]. MgH 2 has already been studied by using various types of catalyst including CNS (i.e. SWCNT, Multi wall carbon nanotubes (MWCNT), planar graphitic nanofibre (PGNF), helical graphitic nanofibre (HGNF) etc) * Corresponding author. Tel.: þ91 0542 2368468. E-mail address: heponsphy@gmail.com (O.N. Srivastava). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 39 (2014) 14240 e14246 http://dx.doi.org/10.1016/j.ijhydene.2014.04.179 0360-3199/Copyright ª 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.