Synthesis and characterization of air-stable aluminum nanoparticles and its application for hydrogen storage

Abstract

Air stable aluminum nanoparticles for generation of hydrogen were synthesized by wet chemical process. Aluminum hydride (alane) was prepared using aluminum chloride to replace expensive alane solution. Oleic acid was applied to form organic layer on surface of aluminum nanoparticles, called passivation. The size and distribution of aluminum nanoparticles are controlled by concentration of capping agent and catalyst. XRD (X-ray Diffraction), SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy), FTIR (Fourier Transform Infrared Spectroscopy) were used to study the surface analysis. Simple floating test and ignition test were developed to identify organic passivated aluminum nanoparticles. TGA (Thermogravimetric Analysis) and measurement volume of hydrogen generation were suggested to study active aluminum content in aluminum nanoparticles. $AlCl_3$ and $LiAlH_4$ were reacted with a molar ratio of 1:3 AlH3 in diethyl ether for more than 12 hr and produced AlH3 which was decomposed to aluminum by titanium isopropoxide (TTIP). The average size of aluminum particles 100 nm by adding optimized amount of TTIP (18 mM). The time of alane decomposition reaction also affected on formation of particles, and optimized reaction time was 40 min. The concentration of capping agent had a little impact on particle size, but it was sure that excess amount of capping agent caused agglomeration of particles in spite of washing. TEM images showed that smooth organic coating layer was formed on aluminum surface in the case of organic-passivated aluminum, whereas air-passivated aluminum had rough surface with oxide layer. Both cases showed the thickness of layer was 2-3 nm. The hydrogen generation by the aluminum nanoparticles was investigated and developed to measure active aluminum content in particles.