Rapid hydrogen production from water using aluminum nanoclusters: A quantum molecular dynamics simulation study

Reaction Mechanisms and Dynamics of H2 Generation in Microhydrated Al Clusters: The Role of Oxo–Hydroxyl and Dioxo Structures in the Al17–·(H2O)2 System

“…It must be noted that the basic mechanism of Reber, Roach et al , involves a A 2 H 2 → A 2 + H 2 step [H 2 Al 17 (OH) 2 – → Al 17 (OH) 2 – + H 2 ] as the hydrogen generation process. Still, they pointed to other options for the H 2 -generating step, as did Day et al and Vashishta et al for the neutral cluster. Other H 2 -generating mechanisms have also been proposed for the reaction of Al 6 + and Al 13 with water.…”

“…We have also tried alternative adsorption options (see Figure SM_F10 of the SI and following figures), some of them previously considered by Reber et al 15 The second water molecule [that of the HAl 13,26 by that we mean that the corresponding saddle points are at least comparable in energy than the water-elimination products. However, we have found only one ER H 2 elimination saddle point which is comparable in energy with those of the H migration process or with the water elimination product; it is a structure already described by Day et al 26 Saddle points of the type described by Vashishta et al 71 (water assisted −Al••OH 2 − Al−H → −Al−OH−Al + H 2 processes) appear to be quite high in energy. At least in the system with a total of three water molecules, they are clearly higher than the water elimination products.…”

“…They distinguish between two types of mechanisms [Eley–Rideal (ER) and Langmuir–Hinshelwood (LH)]. Vashishta et al (for the neutral cluster) have considered an ER H 2 production mechanism in their studies about the reactivity of Al clusters covered by water shells, in which a surrounding water molecule participates in the mechanism; i.e., they consider a water-assisted process, where the extra water does not belong to the hydration chain.…”

“…Also there are some relatively old studies on the adsorption power of Al clusters toward simple molecules. − There are a number of other electronic structure studies on the Al­(H 2 O) n systems, − in addition to the more recent ones cited above. There are many structural studies on a number of Al clusters − and their interaction with several ligands, − including water, also on its reaction with water. − ,,, There are also some molecular dynamics (MD) simulation studies applied to Al m clusters ( m = {12, 17}) surrounded by several hydration shells. − The interaction with water molecules of a Al 100 cluster has been modeled by means of a reactive force field by Russo et al, who conclude that catalysis by water is an important effect. Two of the present authors have also concluded that water catalysis by Grothhuss-like mechanisms very much favors the water-splitting process in some Al m ·(H 2 O) n systems. , Finally, the dynamical aspects of H migration on the HAl 17 OH – system have been studied by two of the present authors .…”

Aluminum Nanoparticles from a Ga–Al Composite for Water Splitting and Hydrogen Generation

“…It is not just pristine Al that is reacting with water to produce hydrogen, it must be Al in its nanoform that is responsible for the splitting of water. At these nano-Al sites, a series of hydrogen-bond exchanges occur to liberate hydrogen. − The Al 2 O 3 byproduct is fibrous and gets swept away by the agitation of bubble formation, exposing a new surface of Al on the nanoparticles for further reaction. These observations are in qualitative agreement with the theoretical calculations previously reported in which Al nanoparticles can split water by the Grotthuss mechanism. − Density functional theory calculations on 13-atom clusters such as Al 13 and GaAl 12 , as well as an in-depth analysis of complementary Lewis acid/base pairs of these metal clusters, reveal that doping of Ga in an Al 13 cluster reduces the transition state barrier for the reduction of water via the simultaneous breaking of O–H and Al–H bonds.…”