In Operando Visualization of the Electrochemical Formation of Liquid Polybromide Microdroplets

Abstract

Zinc–bromine flow batteries are promising for stationary energy storage, and bromine‐complexing agents have been used to form phase‐separated liquid polybromide products. However, an understanding of the dynamics of polybromide nucleation is limited due to the beam sensitivity and complexity of polybromides. Here we report an in operando platform composed of dark‐field light microscopy and a transparent electrochemical cell to reveal the dynamics of polybromide formation in their native environment. Using our platform, we confirm and reveal the liquid nature, chemical composition, pinning effect (strong interaction with Pt), residual effect (residual charge products on the surface), self‐discharging, and over‐oxidation of the polybromide products. The results provide insights into the role of complexing agents and guide the future design of zinc–bromine flow batteries. Furthermore, our in operando platform can potentially be used to study sensitive species and phases in other electrochemical reactions.

Iodine Redox Chemistry in Rechargeable Batteries

“…The formation of a CoS 2 /CoS heterojunction by solvothermal treatment would result in an uneven distribution of surface charge, which could enhance the electrochemical activities through redox reactions of I − /I 3 − and S 2 − /S x 2− by improving the absorptivity of charged ions and promoting the charge‐transfer process [31] . The polysulfide/iodide flow battery with the CoS 2 /CoS heterojunction‐modified graphite felt (GF‐CoS 2 /CoS) electrode delivered a much higher power density of 86.2 mW cm −2 compared with the GF electrode (8.9 mW cm −2 ) and also exhibited an EE retention of 96 % after continuous working for 1000 h. Careful design of heterojunction electrocatalysts could offer an effective strategy to enhance the performance and competitiveness of rechargeable batteries.…”

Low‐Cost Titanium–Bromine Flow Battery with Ultrahigh Cycle Stability for Grid‐Scale Energy Storage

“…, n = 1-4) on the electrode during cycling. [19] Another possible reason could be that because MEP more strongly interacts with polybromides than CHA, electrochemical reactions are not facilitated during discharging. To confirm this assumption, the radii of the complexes as well as the Gibbs free energy changes during the reactions between the complexing agents and Br 3…”

Side‐View Operando Optical Microscopy Analysis of a Graphite Anode to Study Its Kinetic Hysteresis

“…For example, it allows us to utilize an electrochemical cell configuration similar to a real battery, which consists of liquid electrolytes and conventional electrodes fabricated on Cu or Al current collectors. Basically, in both cases, the interactions between charge transfer and diffusion of lithium ions are governed by the active materials in the electrodes rather than by the electrolytes . In contrast, the configurations of many spectroscopic analyses and scanning and transmission electron microscopes obfuscate this underlying mechanism owing to relatively large electrolyte contents in their minuscule devices, which lead to electrolyte‐dominant reactions during the operando analysis.…”