"Direct electrochemical generation of supercooled sulfur microdroplets well below their melting temperature"

Nian Liu: Guangmin Zhou, Ankun Yang, Xiaoyun Yu, Feifei Shi, Jie Sun, Jinsong Zhang, Bofei Liu, Chun-Lan Wu, Xinyong Tao, Yongming Sun, Yi Cui, and Steven Chu; Proceedings of the National Academy of Sciences, 01/15/19.

Additional Authors: Guangmin Zhou, Ankun Yang, Xiaoyun Yu, Feifei Shi, Jie Sun, Jinsong Zhang, Bofei Liu, Chun-Lan Wu, Xinyong Tao, Yongming Sun, Yi Cui, and Steven Chu

Abstract:

Supercooled liquid sulfur microdroplets were directly generated from polysulfide electrochemical oxidation on various metalcontaining electrodes. The sulfur droplets remain liquid at 155 °C below sulfur’s melting point (Tm = 115 °C), with fractional supercooling change (Tm − Tsc)/Tm larger than 0.40. In operando light microscopy captured the rapid merging and shape relaxation of sulfur droplets, indicating their liquid nature. Micropatterned electrode and electrochemical current allow precise control of the location and size of supercooled microdroplets, respectively. Using this platform, we initiated and observed the rapid solidification of supercooled sulfur microdroplets upon crystalline sulfur touching, which confirms supercooled sulfur’s metastability at room temperature. In addition, the formation of liquid sulfur in electrochemical cell enriches lithium-sulfur-electrolyte phase diagram and potentially may create new opportunities for high-energy Li-S batteries.