Ferrocene-modified azole-borane complexes achieve efficient hypergolic ignition with hydrogen peroxide via a dual-pathway mechanism

Abstract

The operational safety of hydrogen peroxide is intrinsically linked to its concentration, making the development of hypergolic fuels capable of spontaneous ignition with low-concentration H₂O₂ (e.g., 70%), a significant yet challenging goal. Currently, most conventional fuels are constrained by inherent reactivity limitations and fail to achieve hypergolic ignition with 70% H₂O₂. To address this, we developed an “all-in-one” molecular design strategy to synthesize a novel series of high-activity complexes (Fc 4–7) by integrating ferrocene's catalytic functionality with the hypergolicity of imidazole/triazole-borane. All the synthesized complexes demonstrated hypergolic ignition with 70% H₂O₂. Notably, Fc-6 exhibited the shortest ignition delay time (46 ms). To further enhance hypergolicity performance, lithium nitrate (LiNO₃) was introduced as an additive into 70% H₂O₂, which successfully shortened the ignition delay time to a remarkable 27 ms. The specific impulse calculation results showed that Fc-6 exhibited the highest specific impulse of 249.9 s when paired with 70% H₂O₂ + 30% LiNO₃. Moreover, the hypergolic ignition mechanism revealed a dual-pathway ignition process: (1) ferrocene-mediated electron transfer accelerated H₂O₂ decomposition into OH radicals and (2) the B–H bond reacted vigorously with OH radicals, releasing substantial heat that ignited the surrounding flammable small molecules.