“Tandem-action” ferrocenyl iodocuprates promoting low temperature hypergolic ignitions of “green” EIL–H2O2 bipropellants

Abstract

The combination of Energetic Ionic Liquid (EIL) “green” fuels and high test peroxide (>90% H₂O₂; HTP), as a “green” oxidizer, is a very promising platform for the development of fully “green” bipropellants for space exploration. In this work, two new “tandem-action” promoters – [FcCH₂N(CH₃)₃⁺]₂[Cu₂I₄²⁻] (P1) and [FcCH₂N(CH₃)₃⁺]_n[Cu₂I₃⁻]_n (P2) – and two reference “single-action” promoters, [FcCH₂N(CH₃)₃⁺][H₃BCN⁻] (P3) and [CH₃N(CH₂CH₃)₃⁺]_n[Cu₂I₃⁻]_n (P4), were prepared, comprehensively characterized and evaluated for their ability to significantly shorten the Ignition Delay (ID) times of hypergolic reactions between a series of EILs and H₂O₂. These promoters exhibited high solubility and long-term chemical stability in a typical EIL fuel – 1-ethyl-3-methylimidazolium dicyanamide (F1). Upon screening the performance of promoter–EIL formulations, the best ID result of 31 ms was observed for the combination of 1-ethyl-3-methylimidazolium cyanoborohydride (F2) fuel and promoter P2 (10 wt%), with H₂O₂ (95%), whereas an ID time of 58 ms was observed for the F2/P2 formulation with commercially available H₂O₂ (70%), respectively. Remarkably, the latter formulation remained fully homogeneous even at −40 °C, and showed an ID time of 66 ms at this temperature with H₂O₂ (95%), indicating the advantages of our approach for the development of novel fully “green” bipropellants.