Underwater self-sustaining combustion and micro-propulsion properties of Al@FAS-17/PTFE-based direct-writing nanothermite

•An underwater stable combustion is first achieved by hydrophobic thermite sticks.•These thermite sticks are extremely stable in both air or water environment.•The detailed combustion mechanism underwater is proposed.•A remarkable advantage of thermite sticks is found in micro-propulsion underwater.•The thermite stick can be employed to ignite explosives underwater.