Copper–Cobalt Oxide Nanoparticles with Tailored Cobalt Oxidation State and Lattice Oxygen Vacancy for Low-Temperature Ignition of Ammonium Dinitramide Monopropellants

Ammonium dinitramide (ADN) ionic liquid monopropellants are recognized as suitable green substitutes for hydrazine and have attracted considerable research interest. However, the cold-start capability of a monopropellant is a critical requirement in propulsion applications, and ADN monopropellants are not cold-start capable. In this study, we introduce non-noble metal oxide-based Cu-incorporated Co3O4 (Cu–Co3O4) spinel nanoparticles for the low-temperature catalytic ignition of an ADN-based liquid monopropellant variant, LMP 103X. The Cu incorporation reduces the particle size and enhances the surface properties of Co3O4. The catalytic activity of Cu–Co3O4 for the decomposition of LMP 103X monopropellant was investigated by using a simultaneous thermal analyzer. The Cu–Co3O4 nanoparticles enhanced the reaction rate and showed better catalytic performance by lowering the decomposition temperature from 178 to 132 °C, with sudden decomposition of the entire propellant sample. More grain boundaries observed in Cu–Co3O4 possibly enhanced the adsorption and transport of reactant species across the catalyst. The synergistic effect of the high Co3+/Co2+ ratio, oxygen vacancies, pore volume, grain boundaries, and segregation of CuO enhanced the catalytic activity of the Cu-incorporated Co3O4. The efficiency of the catalyst is analyzed by the oxidation states of the transition metals, the abundance of active sites, and oxygen vacancies appearing on their surfaces.