Liquid-metal transfer from an anode to a cathode without short circuiting

Abstract

Droplets of liquid metals attached to an anode in an electrochemical cell move toward the cathode since electrochemical oxidation lowers the interfacial tension of the metal. When the droplet reaches the cathode, it wraps around the cathode but does not touch it despite the electrostatic attraction between the positively charged liquid metal and the negatively charged cathode. The combination of electrochemical oxidation of the liquid-metal anode and hydrogen production on the cathode prevents contact, thus avoiding a short circuit between the two electrodes. Consequently, the liquid metal continues to flow toward the cathode and surrounds it until finally the metal completely detaches from the anode and transfers to the cathode. Such manipulation depends on the distance between the cathode and the liquid metal; only the closest liquid-metal droplet will detach and transfer. During this process, the liquid can adopt surprising shapes that resemble tentacles. We demonstrate and characterize the unique ability to detach and transfer liquid metal using a low applied voltage. Positively charged anodes should short circuit when they are brought into contact with a cathode. The authors demonstrate that a liquid-metal anode can naturally flow toward the cathode, completely surround it and ultimately transfer to the cathode without short circuiting in an electrochemical cell.