Chemical Gardens as Electrochemical Systems: In Situ Characterization of Simulated Prebiotic Hydrothermal Vents by Impedance Spectroscopy.

In an early earth or planetary chimney systems, hydrothermal fluid chemistry and flow durations play a large role in the chimney's ability to drive electrochemical reactions for the origin of life. We performed continuous electrochemical impedance spectroscopy (EIS) characterization on inorganic membranes representing prebiotic hydrothermal chimney vents in natural seafloor systems, by incorporating an electrode array into a chimney growth experiment. Localized potential and capacitances profiles in the chimney reveal a dynamic system where redox processes are driven by transport phenomena, increasing rapidly due to disequilibrium until achieving equilibrium at about 100 mV and 1000 µF/cm2 . The impedance in the chimney interior is three orders of magnitude lower (100 Ohms/cm2 vs 100 KOhms/cm2 ) than at the ocean or the ocean/chimney interface. The calculated peak dissipation factor (DF) values are more than ten times higher (40.0 vs 3.0) and also confirm the elevated chemical reactivity in the chimney interior.

In Situ Polysulfide Detection in Lithium Sulfur Cells.

Lithium sulfur batteries promise significant improvements in specific energy compared to Li-ion, but are limited by capacity fade upon cycling. Efforts to improve durability have focused on suppressing the solubility of intermediate polysulfides in the electrolyte. Here we describe an in situ electrochemical polysulfide detection method based on the cyclic volatmmetric response. The voltammetric peaks correlate with increased discharge, consistent with increased polysulfide species in the electrolyte as demonstrated by prior literature measurements using spectroscopic methods. We verified that adding metal sulfide species to the sulfur cathode and ceramic-coatings on the polyolefin separator result in reduced polysulfide concentration, consistent with improved cycle life reported earlier. Further, the use of highly concentrated electrolytes produces no detectable dissolved polysulfide species. Future advances in Li/S technology could utilize this method to determine the polysulfide contents in the electrolyte, and thus quantify the efficacy of the sulfur-sequestering strategies.