Single-point Attack of Two H2 O Molecules towards a Lewis Acid Site on the GaAl12 Clusters for Hydrogen Evolution.

The hydrogen evolution reaction (HER) of water with metallic aluminum-based materials provides an important way to address the global energy challenge; however, fundamental mechanism and reaction dynamics governing the chemical and electronic properties remain a debated research topic. Here we further study the HER mechanisms for water splitting on typical 13-atoms clusters, Al12 Ga and Al13 , by first-principles DFT calculations. We noted that the doping of a Ga atom into the Al13 cluster could reduce the transition state barrier for H2 O dissociation on the metal cluster. Furthermore, it is interesting that the second water molecule prefers to adsorb on the same metal site giving rise to both thermodynamically and kinetically favorable reaction pathways. Based on the well-established complementary active sites (CAS) mechanism for metal cluster reactivity, we provide insights into the reaction dynamics of such metal clusters with two water molecules, which also sheds light on the Eley-Rideal and Langmuir-Hinshelwood mechanisms in surface science. Natural bond orbitals (NBO) analysis was conducted to evaluate the donor-acceptor charge-transfer interactions between the cluster and the nucleophilic reagent. These results gain a better understanding of the mechanism for water reacting with aluminum-based materials.