Supported and isolated metal atoms and clusters as models for understanding the hydrogen economy.

Hydrogen is a clean, convenient, renewable, and versatile energy carrier that could replace fossil fuels. It could be transformed into the desired energy form without releasing greenhouse gases like CO or other harmful species, playing promising roles in combating the global energy crisis and realizing carbon neutrality. The so-called hydrogen economy consists of three parts: hydrogen generation, storage, and re-electrification. Reactivity studies of metal atoms and atomically precise metal clusters, either in isolation or on supports, contribute to the understanding of basic physical principles and chemical processes underlying the hydrogen economy. In this review, we discuss the state-of-the-art laser vaporization and gas aggregation technique in precisely synthesizing the desired metal atoms and clusters. Their performance for catalytic hydrogen generation and hydrogen adsorption was studied through mass spectrometry and infrared spectroscopy. We focus on our novel approach to investigate the structural and reactive properties of fullerene-metal clusters towards water splitting and hydrogen storage, aiming to provide a fundamental understanding of the involved active sites, reaction pathways, and metal-support interactions. The ultimate goal is to obtain atomic-level reaction mechanisms for hydrogen generation and storage of carbon-metal-based materials.