"tandem-action" ferrocenyl iodocuprates promoting low temperature hypergolic ignitions of "green" EIL-H₂O₂bipropellants

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.