## 3 Results and Discussion
### Hydrolysis Activation Study  
In the absence of any catalytic promoter, \(\mu\)Al particles hydrolyze so slowly as to be unobservable. Al NPs, on the other hand, react rapidly and completely with water to form Al(OH)\({}_{3}\) (\(s\)) (Equation (1)). We hypothesize that the Al(OH)\({}_{3}\) produced in this more rapid reaction then promotes the observable acceleration of the \(\mu\)Al reaction with water (Equation (2)). Alternatively, the exothermicity of Al NP hydrolysis in Equation (1) could be the driver for the pursuant reaction in Equation (2); the following will discern which of these is the more likely. \[\text{2 Al NPs }(s)+6\text{H}_{2}\text{O }(l)\rightarrow\text{2 Al}(\text{OH})_{3} \left(s\right)+3\text{H}_{2}\left(g\right) \tag{1}\]  
\[\text{2}\mu\text{Al }(s)+6\text{H}_{2}\text{O }(l)\overset{\text{ Catalytic Al}(\text{OH})_{3}}{ \rightarrow}2\text{Al}(\text{OH})_{3}\left(s\right)+3\text{H}_{2}\left(g\right) \tag{2}\]  
Experiments were thus designed where \(\mu\)Al and Al NPs were combined with various mass ratios, from 10 to 90% Al NPs, and then their hydrolysis reactions were studied using a gas burette assembly shown in Figure 1. Any measured volume of hydrogen produced, \(V_{mix}\), at atmospheric pressure, \(P\), was deemed to have originated only from active Al\({}^{0}\), either from the Al NPs (primary source) or from the \(\mu\)Al (secondary source) and was therefore the sum of \(V_{1}\) and \(V_{2}\), respectively (Equation (3)). To calculate \(V_{2}\), the reaction to produce H\({}_{2}\) (with volume \(V_{1}\)) by the hydrolysis of the same quantity of Al NPs without the \(\mu\)Al present was also carried out. Volume \(V_{2}\) was then used to determine the number of moles, \(n_{2}\), of Al\({}^{0}\) reacting from the \(\mu\)Al only, according to the ideal gas law (Equation (4)). Finally, the 'activated \(\mu\)Al' was quantified as the stochiometric equivalent mole amount of \(\mu\)Al\({}^{0}\) that reacted to produce the \(n_{2}\) moles of H\({}_{2}\) relative to the total quantity of \(\mu\)Al used in the experiment, \(n_{\mu\text{Al}}\) (Equation (5)) and expressed as a percentage. Allowing for oxide passivation, the latter quantity was adjusted by coefficient \(f\), the mass fraction of active Al\({}^{0}\) (\(\mathcal{M}_{Al}\) g/mol) in the mass of \(\mu\)Al used, \(m_{\mu\text{Al}}\), which was calculated to be 0.99 based on a spherical core volume fraction for 30 \(\upmu\)m particles with a 100 nm thick oxide shell. The 'activated \(\mu\)Al' was plotted versus the mass % of Al NPs used in the mixed \(\mu\)Al/Al NPs samples and is shown in Figure 2.  
\[V_{mix}=V_{1}+V_{2} \tag{3}\]  
\[n_{2}=\frac{PV_{2}}{RT}=\frac{P(V_{mix}-V_{1})}{RT} \tag{4}\]  
\[\text{Activated }\mu\text{Al}=\frac{\frac{3}{2}n_{2}}{n_{\mu\text{Al}}}\times 1 00\%=\frac{\frac{3}{2}P(V_{mix}-V_{1})\times\mathcal{M}_{Al}}{RT\times fm_{ \mu\text{Al}}}\times 100\% \tag{5}\]The inset bar chart of Figure 2 shows that in the absence of Al NPs, there was no activation toward hydrolysis with less than 1% of the \(\upmu\)Al reacting. Integration with just 10% Al NPs by mass incurred substantial activation with ca. 52% of the \(\upmu\)Al consumed by the time H\({}_{2}\) generation appeared to have visually ceased. As the proportion of Al NPs was raised, a steady increase in \(\upmu\)Al activation was observed, reaching ca. 59% corresponding to 90% Al NPs by mass. As the main plot in Figure 2 shows, there is a simple linear relationship between these two quantities between 10 and 90% Al NPs by mass. The activation range thus spans only 7% and given the need to maximize H\({}_{2}\) production with the minimum incorporation of Al NPs, our results suggest that a composite 9:1 \(\upmu\)Al/Al NPs material (by mass) is the best possible formulation. Indeed, when the total moles of active \(\upmu\)Al\({}^{0}\) per unit mass of Al NPs is considered (Figure 3), it can be seen that this was highest at 0.204 mol/g for the 9:1 \(\upmu\)Al/Al NPs sample and decreased rapidly before becoming steady at ca.