Carbon nanostructures as catalyst for improving the hydrogen storage behaviour of complex aluminium hydride

Abstract

The present paper reports the catalytic effect of carbon nanostructures, particularly graphitic nanofibres (GNFs) with different structure morphology, namely helical GNFs (HGNFs) and planar GNFs (PGNFs) as the catalyst for complex aluminium hydride. HGNFs and PGNFs were synthesized by catalytic thermal decomposition of acetylene (C2H2). The growth of HGNFs was achieved by employing faceted Ni nanoparticles, whereas spherical Ni nanoparticles produce PGNFs. It has been observed that HGNFs posses superior catalytic activity than PGNFs in improving the desorption kinetics and decreasing the desorption temperature of complex aluminium hydride (NaAlH 4, LiAlH4 and LiMg(AlH4)3). Temperature programmed desorption (TPD) reveals that HGNFs admixed alanates undergo hydrogen desorption at a much lower temperature than PGNFs admixed material. Thus for the heating rate of 2°C/min, the peak desorption temperature corresponds to initial step desorption of NaAlH4 admixed with 8 mol% HGNFs and 8 mol% PGNFs has been lowered to 143.6°C and 152.6°C, respectively. In addition to the enhancement in desorption kinetics, the GNFs admixed NaAlH4 also undergoes rehydrogenation at the moderate condition. In order to get supportive evidence for our experiment, we have carried out abinitio studies by calculating hydrogen removal energy from alanates with planar and helical model of GNF. It becomes clear that from both experiment and ab-initio calculations, that catalytic effect of GNFs is curvature dependent. Thus HGNF with higher helicity helps to lower the energy needed to remove hydrogen from alanates.