Al-assisted high frequency self-powered oscillations of liquid metal droplets.

It is of great scientific and practical significance to explore and imitate the rhythmic oscillating behaviors. Achieving oscillating behaviours via liquid metal is regarded as an excellent strategy and the "mercury beating heart" is a well-known representative. However, the oscillating behaviours achieved over the past few decades either require external power supply or exhibit low frequency. Here, intriguing Al-assisted high frequency self-powered oscillations of liquid metal droplets were discovered and the general mechanisms were interpreted. For this dynamic process, Al is added into the liquid metal for generating gas and activating liquid metal by forming countless tiny galvanic cells and an iron plate is used to passivate the liquid metal via electrochemical oxidation. Therefore, the high frequency self-fueled oscillations can be achieved due to the synergistic effect of these two factors. Furthermore, we predict and confirm that the oscillating behaviors can also be achieved on other eligible substrates (e.g., Ni plate) based on the proposed universal mechanism. The ability to achieve high frequency oscillations of liquid metal droplets promises rich opportunities in developing self-powered soft oscillators.