Octahydrotriborate (B3H8-) based hypergolic ionic liquids as ultra-fast ignition propellant fuels with superior decomposition efficiency

s Hypergolic ionic liquids (HILs) have been investigated to replace traditional toxic hydrazine fuels. Among numerous HILs, borohydride ionic liquids have demonstrated excellent ignition performance and have the potential to be used as a new generation of propellants. In this work, a series of HILs were synthesized for the first time utilizing the octahydrotriborate (B 3 H 8 – ) anion, paired with cations featuring nitrogen-rich functional groups derived from imidazole, triazole, and pyridine. Comprehensive characterization of all resulting ionic liquids was performed using 1 H and 13 C NMR, IR spectroscopy, and high-resolution mass spectrum. Key properties including melting points (-17.8∼131.9 o C), decomposition temperatures (95.4∼196.1 o C), thermal kinetic parameters, and heats of formation were measured or calculated. Consistent with expectations, these HILs demonstrated ultra-fast ignition delay (ID) times upon contact with white fuming nitric acid (WFNA), accompanied by significantly high specific impulse ( I sp ). Furthermore, the [B 3 H 8 ] – anion also exhibited superior decomposition efficiency compared to the boron cage structure.