Hydrogen release from a single water molecule on V_n⁺ (3 ≤ n ≤ 30)

Water and its interactions with metals are closely bound up with human life, and the reactivity of metal clusters with water is of fundamental importance for the understanding of hydrogen generation. Here a prominent hydrogen evolution reaction (HER) of single water molecule on vanadium clusters V_n⁺ (3 ≤ n ≤ 30) is observed in the reaction of cationic vanadium clusters with water at room temperature. The combined experimental and theoretical studies reveal that the wagging vibrations of a V-OH group give rise to readily formed V-O-V intermediate states on V_n⁺ (n ≥ 3) clusters and allow the terminal hydrogen to interact with an adsorbed hydrogen atom, enabling hydrogen release. The presence of three metal atoms reduces the energy barrier of the rate-determining step, giving rise to an effective production of hydrogen from single water molecules. This mechanism differs from dissociative chemisorption of multiple water molecules on aluminium cluster anions, which usually proceeds by dissociative chemisorption of at least two water molecules at multiple surface sites followed by a recombination of the adsorbed hydrogen atoms.