Design of metal-coordinated hypergolic materials: recent advances and perspectives

Space propulsion technology opens fascinating possibilities for exploring more distant regions of the universe. As a promising source of propulsion systems, hypergolic propellants can generate self-sustaining combustion upon contact with oxidizers, demonstrating significant superiorities in their system simplicity, cost-efficiency, restart capability, and precise thrust control. However, currently used hydrazine-based fuels and their liquid engine system have high toxicity and complex loading issues, making them unable to meet the growing demand for simplicity and controllability of advanced propulsion systems. The development of advanced hypergolic fuels has recently focused on metal-coordinated materials, with flexible metal-organic architectures providing superior tunability over traditional alternatives. The diversity in metal centers, organic ligands, and coordination geometries offers unprecedented opportunities for tailoring ignition behavior and energy release processes. Moreover, the well-defined atomic structures of these materials could provide an ideal platform for elucidating structure-activity relationships, supporting the rational design of high-performance hypergolic propellants through coordination chemistry. In this review, we document advancements in the field of metal-coordinated hypergolic materials, encompassing metal complexes, metal clusters, metal halides, and metal organic frameworks, focusing on understanding the crucial factors that regulate hypergolic activity. Through a critical analysis of the development of advanced metal-coordinated hypergolic materials, including structure design, machine learning assisted structure optimization, mechanism exploration, and practical adoption, this review offers valuable insights for future research in this field.