## 1 Introduction  
Aluminum, Al, is the most abundant metal in the earth's crust. When Al reacts with water, it produces H\({}_{2}\) gas and aluminum hydroxide, Al(OH)\({}_{3}\)[1]. The H\({}_{2}\) produced can be harnessed as a clean, ecologically friendly energy source, making it a desirable fuel for many applications [2, 3, 4, 5, 6]. The development of methods for H\({}_{2}\) production is motivated by a vision to move away from fossil fuels due to their finite availability and the environmental damage caused by their combustion [7, 8, 9, 10]. There are many ways to generate H\({}_{2}\) including water electrolysis [11], chemical reactions [12], steam reforming of hydrocarbons [13], and from biological sources [14]. These methods are not amenable to portable-use systems, as they are either too expensive or initiated under extreme conditions. Transporting pure H\({}_{2}\) has challenges with its low volumetric energy density and high flammability. Thus, it is necessary to develop safe and economically feasible H\({}_{2}\) delivery systems that can be utilized on-demand. Aluminum is deemed as a possible source of energy storage for direct H\({}_{2}\) generation as long as its surface is passivated efficiently, effectively and safely [15]. Pure aluminum spontaneously reacts with water due to its high reduction potential (\(E^{\circ}=-1.66\) V) but can easily form a thin oxide layer when in contact with air, which leads to remarkably low reactivity [16]. This thin oxide layer develops into a 75 to 100 nm thick layer in a few months. It is also insoluble in, and impermeable to, water and prevents contact between the metal and water, hindering access to the energy-rich aluminum metal core [17]. Thus, \(\mu\)Al powders remain almost unhydrolyzed due to the thick oxide layer formation [18, 19]. Because of this, it is important to find a method to activate the surface of \(\mu\)Al to allow access to the energetically rich and reactive metallic core. This problem can be solved by mixing organic capped Al nanoparticles (Al NPs) with \(\mu\)Al. Strategies for the activation of aluminum and aluminum alloys also have importance in additive manufacturing processes [20]. When the problems related to surface oxidation and agglomeration are overcome, Al NPs demonstrate fast reaction rates, exceptional combustion efficiency, and higher volumetric energy densities in comparison to conventional materials [21; 22]. Due to their high surface-to-volume ratio, nanoparticles can have exceptionally strong interactions with other components in a nanocomposite. Thus, nanoaluminum surfaces may be stabilized by passivation and surface coated with organic polymers or polymerizable substrates to control their size and safety in energetics applications [23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40]. Our lab has previously reported that epoxyalkane-capped Al NPs demonstrated moderate air stability, as well as high active aluminum content [41; 42; 43]. Of these, epoxyhexane-capped Al NPs have the least protective cap owing to the shorter alkyl side-chain and react rapidly and completely with water to generate H\({}_{2}\) at room temperature, and produce basic conditions that can be exploited for the benefit of \(\mu\)Al hydrolytic activation. Thus the Al NPs could work as an indirect promoter by generating Al(OH)\({}_{3}\) to facilitate H\({}_{2}\) production from \(\mu\)Al at room temperature. [PERSON] et al. have previously reported that Al(OH)\({}_{3}\) could catalytically promote H\({}_{2}\) generation from the \(\mu\)Al-water system and was more effective compared with other promoters [44; 45; 46; 47]. Several composite samples of \(\mu\)Al and Al NPs were prepared with a variety of ratios by mass and analyzed for their hydrogen generation efficiency upon hydrolysis. pH measurements and pH-dependent speciation modelling were used to determine whether to attribute the \(\mu\)Al activation to the exothermicity of the Al NPs' hydrolysis or the resulting pH change.