Researchers working in the area of rocket propulsion strive for environmental friendliness, low toxicity, and overall operability, as well as a performance level comparable with current propellant combinations such as hydrazine and N 2 O 4 . Maintaining high performance while lowering hazards is extremely difficult.All rocket oxidizers are hazardous by their very nature, and so reduction of those hazards, even though the resulting materials might not be completely harmless, is at the heart of green initiatives in propulsion. The corrosivity of nitric acid is well known, and, although N 2 O 4 is much less corrosive, it combines high toxicity with high vapor pressure. A significant step to a lower-toxicity bipropulsion system would be the demonstration of hypergolicity (spontaneous ignition) between an ionic liquid (IL), which is a paragon of low vapor toxicity, and a safer oxidizer. Apart from cryogens, hydrogen peroxide seems to be especially promising because of its high performance, less-toxic vapor and corrosivity, and its environmentally benign decomposition products, [1] which make handling this oxidizer considerably less difficult than N 2 O 4 or nitric acid.A high fuel performance can be fostered by light metals with large combustion energies and relatively light products. Elements with considerable performance advantages and nontoxic products are aluminum and boron. The need for light combustion products through the production of hydrogen gas and water vapor is fulfilled by a high hydrogen content. Aluminum and boron are well known for their ability to serve as hydrogen carriers in neutral and ionic molecules. Defense research in the 1960s focused extensively on the development of hydrogen-containing fuels with boron, aluminum, and other metals, [2] but was mainly concerned with neutral compounds that have high vapor toxicity. Their rich anionic chemistry combined with the design flexibility of ILs presage novel materials that have the potential to overcome problems that caused these promising propellants to be abandoned.To date, no IL has been reported to be hypergolic with H 2 O 2 , and first-generation hypergolic ILs based on dicyanamide, nitrocyanamide, and azide anions lack high hydrogen content. [3] We tested ILs from each class with 90 % and 98 % H 2 O 2 , and all failed to ignite. This result is hardly surprising since fuels that are hypergolic with nitric acid vastly outnumber those that ignite with N 2 O 4 . For many years, hydrazine was the only fuel hypergolic with H 2 O 2 . [4] Since solutions of lithium aluminum hydrides and LiBH 4 in ethers have demonstrated H 2 O 2 hypergolicity, [5] the same behavior from ILs with metal hydride anions might be expected. However, the development of energetic roomtemperature ILs (RTILs) with metal hydride anions involves a number of technical challenges. Simple metal hydride anions are poor liquefying agents. Furthermore, heterocyclic, unsaturated salts that feature imidazolium, triazolium, pyridinium, and other common IL cations are reduced by BH 4 À ions,...
