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

Significance Since the first discovery of supercooling in 1724, the study of supercooled matter has been mainly limited to varying temperature or pressure. Here we demonstrate an electrochemical approach to generate and observe supercooled sulfur. Our methodology combines dark-field microscopy, a transparent electrochemical cell, and a fast camera to visualize the process at single microdroplet with millisecond time resolution. This platform may open up opportunities for studying supercooled liquids as the droplets approach either homogeneous nucleation to the crystalline state or enter into the glass transition. Relevant to understanding lithium-sulfur battery chemistry, liquid sulfur is observed to form in the electrochemical cell and elucidates a long-debated reaction pathway for sulfur redox reaction in this environment.