On the influence of exact exchange on transition metal superatoms

Vanadium Cluster Neutrals Reacting with Water: Superatomic Features and Hydrogen Evolution in a Fishing Mode

Hydrogen evolution reaction (HER) is known as the heart of various energy storage and conversation systems of renewable energy sources. Here we observe the cluster reactions of a light transition metal, vanadium, with water in a gas-phase flow tube reactor. While HER products of V₁ and V₂ were not observed, the effective HER of water on neutral V_n (n ≥ 3) clusters reveals reasonable and size-dependent reactivity of the vanadium clusters. Superatomic features and reaction dynamics of V₁₀, V₁₃, and V₁₆ are highlighted. Among the three typical superatoms, V₁₀ and V₁₆ exhibit an abnormal superatomic orbital energy level order, 1S|2S|1P|1D..., where the energy-reduced 2S orbital helps to accommodate the geometric structure and hence reinforce the cluster stability. In comparison, V₁₃ bears a less symmetrical structure and reacts readily with water, allowing for recombination of a hydroxyl atom with an adsorbed hydrogen atom, akin to a fishing-mode HER process. The joint experimental and theoretical study on neutral V_n clusters clarifies the availability of superatom chemistry for transition metals and appeals further development of cluster theory based on electronic cloud/orbital analysis instead of simply counting the valence electrons. Also, we provide insights into the HER mechanism of metal clusters and propose a strategy to design new materials for portable fuel cells of hydrogen energy.

Design of superatomic systems: exploiting favourable conditions for the delocalisation of d-electron density in transition metal doped clusters

The incorporation of transition metals into superatomic species has led to the proposal of highly tailorable systems, with the transition metal atoms typically acting as magnetic dopants. However, the extent to which d-electrons are able to delocalise from their ionic cores has not been fully recognised. In this work a variety of systems have been explored using a range of exchange-correlation functionals commonly used to explore cluster species, to test the extent of d-electron delocalisation under favourable conditions. Early transition metals have been shown to readily delocalise their valence d-electrons for superatomic shell closing, with higher period atoms showing a greater tendency for delocalisation. Our findings also provide the framework for the design of superatomic systems with large numbers of electrons being contributed from a single atom.