Designing Difunctional Promoters for Hypergolic Ignitions of Green Bipropellants Combining Ionic Liquids with H2O2

The emergence of tetrahydroborate (BH4-)/ cyanoborohydride (BH3CN-) anion-based ionic liquid fuels in combination with high test peroxide (>90%H2O2, HTP) oxidizers has accelerated the greening of bipropellants. However, most BH4- and BH3CN- anion-based ionic liquids are sensitive to water, making it difficult to store them. Here, novel difunctional promoters are designed for hypergolic ignition of BH4-/ BH3CN- anion-free ionic liquids with 90%H2O2. The transition metal in anions of promoters is expected to catalyze the exothermic decomposition of H2O2, and the substituted borohydride in cations of promoters acts as the ignition source. These novel difunctional promoters show good solubility in commercially available 1-allyl-3-methylimidazolium dicyanamide and 1-butyl-3 1-allyl-3-methylimidazolium dicyanamide 1-butyl-3methylimidazolium dicyanamide ionic liquid fuels, and the composite fuels exhibit high density, acceptable viscosity, and high thermostability. The addition of difunctional promoters ensures the smooth hypergolic ignition of BH4-/BH3CN- anion-free ionic liquid fuels with a minimum ignition delay time of 34.0 ms, and no apparent microexplosion and secondary combustion are observed during the ignition process. With the increase in the amount of the promoter, density specific impulses of the composite fuels improve gradually. This work provides a platform strategy for designing promoters by synergy of cations and anions and makes efforts to seek green bipropellants.