Investigation of hydrogen storage behavior of silicon nanoparticles

Porous Silicon (PS) freestanding film is a derivative of single crystal Si wafer. PS films obtained on electrochemical etching of p-type silicon (Si) wafer were used to synthesize Si nanoparticles by ultrasonication. 12 mu m thick and 29% porous freestanding PS films were sonicated for 4 h in 120 W ultrasonication bath at 42 kHz. HRTEM image shows Si nanoparticles in the range of 8-20 nm in size. In this paper we present results of hydrogen absorption experiments conducted on Si nanoparticles. Standard Seivert's type apparatus was used to carry out hydrogen absorption pressure composition isotherm measurements in the pressure range of 1-10 bar and in the temperature range of 29 degrees C-150 degrees C. Theoretically SiHx system has 3.44, 6.66 and 9.67 wt% of hydrogen for x = 1, 2, 3 respectively. Experimental results show maximum hydrogen uptake of 2.25 wt% at the temperature of 120 degrees C and at 9.76 bar pressure. Hydrogenation of Si nanoparticles exhibits frequency downshifts from 510.7 to 507.3 cm(-1) in Raman spectra. Raman peaks were de-convoluted in two bands to study effect of hydrogenation on FWHM, crystallanity and elastic strain of the nanoparticles. Bonding between Si, 0 and H atoms were investigated using Fourier transform infrared spectroscopy(FTIR) spectroscopy. UV-Vis spectra and Tauc plots were used to discuss the relation between hydrogenation and optical band gap of the Si nanoparticles. Optical band gap was found to increase from 1.6 to 2.25 eV on subjecting Si nanoparticles to hydrogenation. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Study of kinetics and thermal decomposition of ammonia borane in presence of silicon nanoparticles

Ammonia borane (AB, NH3BH3) is a promising material by virtue of its high gravimetic hydrogen storage capacity of 19.6 wt%. Hydrogen release from AB initiates at around 100 degrees C and as such is compatible to meet the present-day requirements of a PEM fuel cell. The thermal decomposition of AB is a complex process involving several reactions. Major issues include poor reaction kinetics, leading to delayed commencement of hydrogen generation i.e. long induction period, and the small amount of hydrogen released at optimal temperature. In the current paper the thermal decomposition of AB is studied at different temperatures. Further the effect of Si nanoparticles on the induction period and kinetics as well as the gas release reaction is studied in detail using different characterization techniques. It was found that the induction period reduced and the amount of gas released increased as a result of Si nanoparticle addition. This was facilitated by a reduction in the activation energy of decomposition and improved kinetics with the addition of silicon nanoparticles. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved