Fluorinated metal-coordinated ionic-liquid-coated aluminum powder: enhanced combustion performance in solid propellants

The development of novel aluminum-based fuels is critical for advancing solid propellant performance for clean and efficient energy applications. We synthesized a fluorine-functionalized metal ionic liquid, Cu(AIM)₄(PF₆)₂ (FMIL-Cu), which exhibits excellent safety and high energy density (26.36 kJ cm⁻³). Using FMIL-Cu as a shell material, we prepared the core–shell Al@FMIL-Cu fuel with a dense, uniform coating on Al particles. Microstructural and thermal analyses confirmed the coating's uniformity and chemical integrity, with Al@FMIL-Cu decomposing 62.0 °C earlier than pristine Al. We then fabricated a solid propellant (CSP-2) using Al@FMIL-Cu and tested its performance. Compared to the control (CSP-0), CSP-2 showed a 13.4 °C earlier decomposition temperature, 25.0% higher burning rate, and enhanced flame area/light intensity. The combustion products of CSP-2 exhibited minimal noticeable agglomeration, with the D₉₀ decreasing from 89.3 µm to 11.2 µm and the average particle size reducing from 50.3 µm to 16.6 µm, resulting in more complete energy conversion and fewer solid residues. Computational studies revealed FMIL-Cu's large positive electrostatic potential, broad electropositive distribution, and a narrow bandgap (4.61 eV), which enhance Al@FMIL-Cu's electron transfer and reactivity. Fluorine groups in FMIL-Cu reacted with the Al combustion intermediate AlO (ΔG = −142.1 kJ mol⁻¹), thereby facilitating the reaction process thermodynamically and improving CSP-2's performance. Our integrated experimental and theoretical study demonstrates Al@FMIL-Cu as a novel high-performance fuel with great potential for advanced solid propellants toward sustainable energy utilization.