Carbon nanostructures as catalyst for improving the hydrogen storage behavior of sodium aluminum hydride

Abstract

The present paper reports the catalytic effect of carbon nanomaterials, particularly carbon nanotubes (CNTs) and graphitic nanofibres (GNFs) with two different structure morphology, namely planar GNFs (PGNFs) and helical GNFs (HGNFs) as the catalyst for improving the dehydrogenation and rehydrogenation behavior of sodium aluminum hydride (NaAlH 4). It has been observed that HGNFs posses superior catalytic activity than other carbon nanoforms in improving the desorption kinetics and decreasing the desorption temperature of NaAlH 4. Temperature programmed desorption (TPD) reveals that HGNFs admixed NaAlH 4 undergo hydrogen desorption at a much lower temperature than PGNFs and CNTs (SWCNTs and MWCNTs) admixed NaAlH 4. Thus for the heating rate of 2 °C/min, the peak desorption temperature corresponds to initial step decomposition of NaAlH 4 admixed with 2 wt.% HGNFs and 2 wt.% PGNFs has been lowered to 143.6 °C and 152.6 °C, respectively (for pristine NaAlH 4, it is ∼170 °C). In addition to the enhancement in desorption kinetics, the HGNFs admixed NaAlH 4 undergoes fast rehydrogenation at the moderate condition. Microstructural investigation reveals that the HGNFs were present on the surface of NaAlH 4 grains, whereas CNTs were tunneled into the grains of NaAlH 4 suggesting a distinct catalytic behavior of different carbon nanovariants.