Aluminum+Reacting+with+Water+producing+H

The purpose of this White Paper is to describe and evaluate the potential of aluminum-water reactions for the production of hydrogen for on-board hydrogen-powered vehicle applications. Although the concept of reacting aluminum metal with water to produce hydrogen is not new, there have been a number of recent claims that such aluminum-water reactions might be employed to power fuel cell devices for portable applications such as emergency generators and laptop computers, and might even be considered for possible use as the hydrogen source for fuel cell-powered vehicles.

In the vicinity of room temperature, the reaction between aluminum metal and water to form aluminum hydroxide and hydrogen is the following: 2Al + 6H2O = 2Al(OH)3 + 3H2. The gravimetric hydrogen capacity from this reaction is 3.7 wt.% and the volumetric hydrogen capacity is 46 g H2/L.

Although this reaction is thermodynamically favorable, it does not proceed due to the presence of a coherent and adherent layer of aluminum oxide which forms on the surface of aluminum particles which prevents water from coming into direct contact with the aluminum metal. The key to inducing and maintaining the reaction of aluminum with water near room temperature is the continual removal and/or disruption of this coherent/adherent aluminum oxide layer.

A number of reaction-promoting approaches have been investigated for the aluminum-water reaction. These include additions of hydroxide promoters such as NaOH, oxide promoters such as Al2O3, and salt promoters such as NaCl. These additions act to disrupt the aluminum oxide layer on the aluminum metal. In addition, the reaction of water with molten aluminum alloys such as aluminum-lithium and aluminum-gallium has been studied. In this case, the molten nature of the alloy prevents the development of a coherent and adherent aluminum oxide layer. However, none of these approaches have proven commercially viable to date. https://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/aluminium_water_hydrogen.pdf