Ferrocene-functionalized room-temperature ionic liquids as green bipropellant hypergolic fuels

Abstract

It is well-established that numerous metallic compounds accelerate hydrogen peroxide (H₂O₂) decomposition, significantly decreasing the ignition delay (ID) time of hydrocarbon fuels. However, such catalysts, particularly ferrocene derivatives, are typically solid-state materials, rendering them incompatible with liquid–liquid bipropellant systems where ID correlates critically with additive solubility. To address this limitation, we synthesized a novel class of ferrocene-based room-temperature ionic liquids (ILs) through systematic modulation of alkyl chain lengths on the ferrocenium cation paired with anion volume optimization. These tailored ILs exhibited hypergolic ignition upon contact with 90% H₂O₂. Furthermore, blending the synthesized ILs with 1-amino-4-methylpiperazine (PIP) markedly decreased ID. Notably, the compound [FcCH₂N(CH₃)₂CH₂CHCH₂]⁺[IM-BH₂CN]⁻ (F6) achieved the most pronounced ID reduction, with its ID decreasing from 358 ms to 115 ms.