Enhanced Energetic Performance of Metal Nanoparticles and Metal/Polymer Composite Fuel with Multi-Functionalized Graphene

Metal fuels such as aluminum (Al) and boron (B) have been used for energetic applications ranging from space propulsion and exploration, and materials processing, to power generation for nano- and microdevices due to their high energy density and earth abundance. Recently, the ignition and combustion performance of Al and B particles were found to be improved by graphene-based additives, such as graphene oxide (GO) and graphene fluoride (GF), as their reactions provide heat to accelerate Al and B oxidation, gas to reduce particle agglomeration, and fluorine-containing species to remove native oxide shell. However, GF is not only expensive but also hydrophobic with poor mixing compatibility with metal particles. Herein, we report a multifunctional graphene-based additive for metal combustion, i.e., perfluoroalkyl-functionalized graphene oxide (CFGO), which integrates the benefits of GO and GF in one material. We compared the effects of CFGO to GO and GF on the ignition and combustion properties of Al and B nanoparticles using thermogravimetric analysis, differential scanning calorimetry, temperature-jump ignition, Xe flash ignition, time-of-flight mass spectrometry, and constant-volume combustion test. These experiments confirm that CFGO, with controllable oxygen and fluorine functional groups, generates fluorine-containing species, heat, and gases, which collectively lower the ignition threshold, augment the energy release rate, and reduce the combustion product agglomeration of nanosized Al and B particles, outperforming both GO and GF as additives. Moreover, this multi-functionalized graphene additive was further incorporated into boron/ hydroxyl-terminated polybutadiene composite, which is a typical composite fuel for air-breathing propulsion. The effect of CFGO on the burning and mechanical behaviors of the boron/polymer composite was also investigated. This work shows the great potential of using multi-functionalized graphene as an integrated additive for enhancing the energetic performance of metal nanoparticles and metal/polymer composite fuels for advanced propulsion and energy conversion applications.