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Hydrogen generation from aluminum-water systems

University of British Columbia

Aluminum is one of the most active metals with high affinity to oxygen. In reality however, its reactivity is drastically reduced by the presence of a nanometer-thin oxide film which prevents (or slows down) its corrosion in environments in which the pH ranges from about 4 to 9. Increased reactivity and uniform corrosion is observed typically only in high alkaline or high acidic solutions in which the film dissolves. It has been recently discovered at UBC that the passivation of aluminum in aqueous solutions of neutral and near-neutral pH can be prevented when Al is mechanically alloyed with a non-metallic second phase, such as alumina, carbon or metal oxides [1, 2]. In this work another variant of this system, the Al-WIS (Water-soluble Inorganic Salts such as KC1 or NaCl) system, is introduced. The rapid and massive corrosion reaction of the mechanically alloyed Al-WIS system, which takes place in tap (or marine, or ground) water, releases remarkably high amounts of hydrogen gas. This system can therefore be utilized as in situ, on demand hydrogen generation method through aluminum-assisted water split reaction. Al-WIS powders were prepared by high-energy ball-milling. Powder mixtures as well as salt-free (leached-out) Al powders were characterized using SEM, EDS, XRD, XPS and BET methods. Reaction enthalpy was determined using DSC and the pH shift during the reaction was monitored with a pH meter. The effects of WIS concentration, chemistry of other additives, powder particle size, temperature, and milling conditions on the reaction kinetics were investigated. The H₂ yield and Al- WIS reaction efficiency were high. From 1 g of mechanically alloyed Al powder, up to 1.25 litres of hydrogen gas were generated in the first hour of the reaction, i.e. efficiency up to 92% was achieved. Besides pure gaseous hydrogen, only pure solid aluminum hydroxides were formed as the reaction products. Bayerite (Al(OH)₃) was predominantly formed at T < 60°C whereas boehmite (AIOOH) at T > 100°C. Both phases were present in the temperature range between 60°C < T < 100°C.

Text

2010-01-16

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http://hdl.handle.net/2429/18402

Materials Engineering

University of British Columbia

UBCV

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