Al@pentacoordinated copper-based energetic metal ionic liquid core-shell fuel for enhanced propellant combustion

The pursuit of enhanced combustion performance in solid propellants has stimulated significant research focus on novel aluminum-based fuels. We report the synthesis of a novel copper-based metallic ionic liquid, [Cu(VIM)₅](BF₄)₂ (MetIL-Cu), achieved via fluorine-containing functional group incorporation. Comprehensive physicochemical characterization demonstrated exceptional safety parameters and energetic performance. Employing MetIL-Cu as a coating precursor yielded a core-shell structured fuel (Al@MetIL-Cu) with a dense, homogeneous encapsulation layer. Systematic characterization of composition, morphology, and thermal decomposition behavior validated the structural integrity of Al@MetIL-Cu and coating uniformity. Relative to Al, Al@MetIL-Cu displayed a 6.5 °C reduction in primary exothermic peak temperature along with a 118.1 °C decrease in exothermic peak width. Propellant applicability assessment commenced with theoretical performance calculations via Chemical Equilibrium with Applications (CEA). Computational results indicate that MetIL-Cu exceeds the efficacy of conventional additives. Propellant (CSP-2) containing Al@MetIL-Cu achieved a 9.5% enhancement in linear burning rate relative to pure aluminum-based counterparts, concurrently exhibiting significant amplification of flame area and intensity. Theory calculations revealed MetIL-Cu possesses: extended positive charge density distribution, a pronounced electropositive region, and a narrow bandgap (1.45 eV). These electronic properties synergistically facilitate electron transfer kinetics and elevate reactivity within Al@MetIL-Cu, establishing the electronic and kinetic mechanism for Al and AP thermal decomposition. Remarkably, Al@MetIL-Cu mediated a reduction in AP's high-temperature decomposition peak from 393.4 °C to 336.5 °C, compressed the exothermic peak width from 43.2 °C to 18.2 °C, and lowered apparent activation energy from 198.2 kJ·mol⁻¹ to 136.5 kJ·mol⁻¹. Collectively, Al@MetIL-Cu represents a novel high-performance fuel that concurrently optimizes the efficiency and peak width of Al and AP pyrolysis, delivering fundamental mechanistic insights and implementable strategies for enhancing solid propellant combustion performance.