McGill Researchers have made rocket fuel that is much cleaner and safer than the hypergolic fuels that are commonly used today. And still just as effective. The new fuels use simple chemical “triggers” to unlock the energy of one of the hottest new materials, a class of porous solids known as metal-organic frameworks, or MOFs. MOFs are made up of clusters of metal ions and an organic molecule called a linker.
They induce hypergolic behavior in MOFs by using acetylene and vinyl substituents to unlock the latent energetic properties of electron-deficient linkers in a ZIF. This strategy also uses the formation of coordination bonds to enhance the hypergolic reactivity of the ligand, which is intrinsically different from approaches used to design other types of energetic (e.g., explosive and pyrotechnic) MOFs, where the formation of an extended structure often leads to ligand stabilization, in the form of reduced heat and shock sensitivity, sometimes accompanied by increased heat of detonation due to an energetic ligand being trapped in a nonpreferred conformation. The modularity of MOFs permits modification of the hypergolic properties (ID, flame color, and duration) of the fuel, including achieving ultrashort IDs, without changing its overall structure. Note that the acetylene or vinyl triggers induce hypergolicity without major changes to the overall energetic content of the ZIF structure. The ability to achieve and fine-tune hypergolic performance, combined with the absence of hydrazine-based carcinogens or explosive components, should make hypergolic MOFs promising candidates for safer, environmentally friendly propellants. We are currently investigating the use of other transition metals besides cobalt and zinc as nodes to facilitate the discovery of new MOF hypergols and understand the relationship between the choice of metal node and hypergolic behavior.
Science Advances – Hypergolic zeolitic imidazolate frameworks (ZIFs) as next-generation solid fuels: Unlocking the latent energetic behavior of ZIFs
Hypergolic materials, capable of spontaneous ignition upon contact with an external oxidizer, are of critical importance as fuels and propellants in aerospace applications (e.g., rockets and spacecraft). Currently used hypergolic fuels are highly energetic, toxic, and carcinogenic hydrazine derivatives, inspiring the search for cleaner and safer hypergols. Here, we demonstrate the first strategy to design hypergolic behavior within a metal-organic framework (MOF) platform, by using simple “trigger” functionalities to unlock the latent and generally not recognized energetic properties of zeolitic imidazolate frameworks, a popular class of MOFs. The herein presented six hypergolic MOFs, based on zinc, cobalt, and cadmium, illustrate a uniquely modular platform to develop hypergols free of highly energetic or carcinogenic components, in which varying the metal and linker components enables the modulation of ignition and combustion properties, resulting in excellent hypergolic response evident by ultrashort ignition delays as low as 2 ms.