Demonstration of Controlled Hydrogen Release Using Rh@GQDs during Hydrolysis of NH₃BH₃

Achieving the controlled release of H₂ through an effective approach still faces many challenges. Herein, high-quality graphene quantum dots (GQDs) are synthesized from a new precursor, 1,2,4-trihydroxy benzene, and a multifunctional platform of Rh@GQDs is further developed for the controlled H₂ evolution upon the hydrolysis of NH₃BH₃ (AB). More importantly, the designing concepts of multistep and stepless speed controls have been introduced in the domains of both H₂ evolution for the first time. Through a novel designing protocol, the rate of H₂ evolution can be freely regulated and constantly varied on demand by means of chelation between Zn²⁺ and ethylene diamine tetraacetic acid (EDTA). The density functional theory calculation indicates that Zn²⁺ has the priority to be adsorbed onto Rh(100) due to its larger adsorption energy (107.98 kcal·mol^-1) than that of AB (36.36 kcal·mol^-1). A controlling mechanism is presented such that Zn²⁺ will cover the active sites of the nanocatalyst to prevent the H₂ evolution, and EDTA can chelate Zn²⁺ to reactivate the nanocatalyst for the production of H₂, greatly facilitating use of this strategy in other catalytic reactions. Moreover, it is demonstrated that the protocol is equally valid for diverse hydrogen storage materials. Therefore, this work not only establishes whole new concepts for the controlled production of H₂ but also explains their mechanism, thus remarkably advancing the utilization of H₂ energy and significantly enlightening the controlled process of catalysis.