Catalytic ignition of the [BMIM]DCA-H2O2 propellant with the Cu(vim)2(DCA)2 complex

Abstract

An ionic liquid (IL)-H₂O₂ propellant offers a green alternative to the traditional hydrazine-N₂O₄ system. Due to the weak oxidizing ability of H₂O₂, typical ILs cannot be spontaneously ignited. To address this issue, catalytic ignition was proposed, and a series of metal complex catalysts with the formula M(vim)₂(DCA)₂ (M = Mn, Fe, Co, and Cu) were synthesized. Single-crystal X-ray diffraction analysis shows that the Mn, Fe and Co complexes adopt an octahedral geometry, while the Cu complex exhibits a planar quadrilateral geometry. The physicochemical properties (T_d, ΔH_c, ΔH_f, and I_sp) of the fuels (10 wt% M(vim)₂(DCA)₂ + 90 wt% [BMIM]DCA) were evaluated. Dynamic light scattering and UV-vis spectroscopy analyses confirm that the four complexes disperse well in [BMIM]DCA. Ignition tests reveal that Cu(vim)₂(DCA)₂ exhibits the best catalytic performance for the ignition of [BMIM]DCA with H₂O₂, achieving t_id as short as 21 ms. EPR studies indicate that Cu(vim)₂(DCA)₂ catalyzes H₂O₂ to generate reactive oxygen species (·OH, ·O₂⁻, and ¹O₂), which subsequently induce the spontaneous ignition of [BMIM]DCA. DFT calculations reveal that the zero-dimensional geometry of Cu(vim)₂(DCA)₂ features an unsaturated Cu center and electron-rich ligand framework. This typical structure enables efficient electron transfer to activate H₂O₂, boosting ROS generation and ignition. This work clarifies the crucial role of the metal center in the IL-H₂O₂ system and provides an important insight into the catalytic ignition of the “double-green” propellants.