Electrochemistry

This study reports a rapid electrochemical synthesizing method and its mechanisms of todorokite, achieved within 30 minutes using Mn2+(aq) in 1 M MgCl2 at pH 8.5 and room temperature. We demonstrate that structured Mn(III), which exhibits Jahn-Teller distortion, forms through comproportionation at pH 8.5 and subsequently rearranges to create the todorokite framework. In addition, we found that aqueous Mg2+ species, specifically Mg(OH)+, stabilizes the structured Mn(III) and contributes to the formation of the todorokite framework during electrodeposition. Our facile and direct synthesis method of todorokite promises to enhance its utility in engineering applications, offer an approach for synthesizing and controlling the crystalline structure of Mn oxides through the principles of sustainable chemistry, and advance the fundamental understanding of the natural occurrence of todorokite in environmental chemistry. 

This study employs a novel electrochemical method to mimic the cyclic redox reactions occurring over long geological timescales in accelerated manner. The results revealed that the kinetics and electron flux of the cyclic redox reaction are key to the layer-to-tunnel structure transformation of Mn oxides, provided new insights for natural biotic and abiotic redox reactions and explained the dominance of todorokite in nature.

Because a Li metal battery stores at least ten times more electricity than a Li-ion battery, it is promising a next generation rechargeable battery system. However, during routine charging and discharging cycles, Li dendrites grow on the Li metal electrode, degrade the battery’s performance, and even cause short-circuits. Using transmission mode grazing incidence small angle X-ray scattering, I found that an increase of current density resulted in a smaller radius for Li primary particles, e.g., 5.4 nm at 0.1 mA/cm2, 4.5 nm at 0.5 mA/cm2, and 3.5 nm at 2.0 mA/cm2. I also demonstrated the fractal-similarity of Li dendrites in nanoscale to microscale observations. Our nanoscale observations, which have not been reported, could shed light on diverse nanoengineering routes to control the interface at the Li metal anode and solve the Li dendrite formation problem.