Optimisation of mechanical activation of aluminium for an economical on-demand hydrogen production

Hydrogen gas, H2 is generated when aluminium metal is reacted with water. Due to
the protective oxide layer, the reaction does not take place at ambient conditions.
Different activation schemes are possible however most are either expensive or not
very practical for H2 generation. This work attempted to address this issue of
activation of aluminium particles by means of a reactive ball milling technique. A
number of studies based on the activation (preparing it to react with water without
the aid of any external heat or catalyst) of aluminium Al, by this method, was
reported previously where the energy investment was substantial. This gap in
knowledge motivated us to perform milling with a different approach. Milling
protocols were identified and devised and presented a milling programme which
aided in reducing the energy investment considerably. The motivation behind this
work is to use the Al powder prepared by milling in a hydrogen generator connected
to fuel cells for in situ generation. Due to the sensitive nature of fuel cell, it was
necessary to produce hydrogen gas at a steady rate. It was found that the powder
made up of a mixture of metal oxides and salt prepared in-house, provided an
excellent base to achieve this. It was also seen that milling of the Al particles to 40
µm proved to perform the best for hydrogen production with yield reaching 85 %
in 3 hrs reaction time using only 0.3 g of activated aluminium at ambient conditions.
Reaction time can be improved by increasing milling time it would not be
economically attractive. After reactive milling and reactions were examined/
inspected using SEM, EDX and XRD techniques for in-depth analysis of Al particle
crystalline structure, morphology and size. Milling modifies the surface of the
aluminium particles promoting hydrogen gas production. It was also noted that this
reaction does not require any heat and that it can generate hydrogen gas at the
ambient conditions. It was noticed that when the initial temperature of the solution
is increased the reaction rate first improves up to 32 oC than it declines at 45 oC and
beyond when larger Al particles are used. This work revealed that reaction requires
agitation throughout the process in order to maintain a high yield of hydrogen.
While this presented work used deionised water, it should be mentioned that other
solvents (aqueous solutions) may be used for hydrogen production as shown in the
research. However, the highest amount of yield was produced when deionised water
and urea solution was used at 25 oC. “If we had a hydrogen economy worldwide, every nation on earth could create
its own energy source to support its economy and the threat of war over
diminishing resources would just evaporate” - Dennis Weaver