Boron containing energetic ionic liquids: Sustainable propellants for green aerospace propulsion

Boron containing energetic ionic liquids (BCEILs) are promising sustainable alternatives to toxic hydrazine-based hypergolic fuels. Over 200 BCEILs with varied structures have been synthesized. Research advances including their classification, preparation methods, physicochemical properties, fuel–oxidizer compatibility, hypergolicity, and reaction mechanisms are reviewed. Key physicochemical parameters include phase-transition/decomposition temperatures, density, viscosity, heat values, and specific impulse. Compatibility with oxidizers like white/red fuming nitric acids, N 2 O 4 , H 2 O 2 and ionic liquids is analyzed. Hypergolicity is primarily assessed via drop tests measuring ignition delay, though limitations exist in simulating real combustion. Analyses on hypergolicities of typical BCEILs reveal the molecular structure and combustion organization are both important to give full play to the performance of these fuels. Computational chemistry studies using natural bond orbital wavefunction analysis, density functional theory, and quantitative structure–property relationship models have elucidated initial reaction paths, yet comprehensive mechanistic understanding across fuel-oxidizer systems remains incomplete. Challenges include scalable production, sustainable oxidizers, and mechanistic studies. Future work should optimize modular molecular design, comprehensive property databases, and advanced hypergolic testing for practical propulsion applications. • Overview of BCEILs as promising sustainable alternatives to toxic hypergolic fuels. • Description of their molecular design, preparation methods, and properties. • Detailed analysis of their compatibility, hypergolicity, and reaction mechanisms. • In-depth synthesis of current knowledge and informed speculation for future research.