No abstract

No abstract

No abstract

In this work, a detailed electrochemical study of the molten LiF-CaF 2-ZrF 4 system is provided in the 810-920 • C temperature range, allowing the determination of the reduction potential, the diffusion coefficient and the reduction mechanism of dissolved Zr(IV) on an inert Ta electrode. Addition of CaO in the molten salt is shown to cause Zr(IV) precipitation into an equimolar mixture of solid compounds, most likely ZrO 2 and ZrO 1.3 F 1.4. Underpotential deposition of Zr on Cu and Ni electrodes is also evidenced and Gibbs energy of formation of Cu-Zr compounds calculated by open circuit chronopotentiometry.

The unique properties of 2D MXenes, such as metal‐like electrical conductivity and versatile surface chemistry, make them appealing for various applications, including energy storage. While surface terminations of 2D MXene are expected to have a key influence on their electrochemical properties, the conventional HF‐etching method limits the surface functional groups to F, OH, and O. In this study, O‐free, Cl‐terminated MXenes (noted as Ti3C2Clx) are first synthesized by a molten salt (FeCl2) etching route. Then, a substitution of surface termination from Cl to N is performed via post‐thermal treatment of Ti3C2Clx in Li3N containing molten salt electrolytes. While the Cl‐terminated pristine material does not show electrochemical activity, the surface‐modified, N‐containing Ti3C2Tx exhibits a unique capacitive‐like electrochemical signature in sulfuric acid aqueous electrolyte with rate performance—more than 300 F g−1 (84 mAh g−1) at 2 V s−1. These results show that control of the MXene surface chemistry enables the preparation of high‐performance electrodes in a previously not accessed limit of energy storage.

No abstract

No abstract

International audienceThe fluoroacidity of several alkaline fluoride media was studied by monitoring the concentration of electroactive species which is decreasing versus time due to a gas species release, such as silicon fluorides, as indicated by the reaction: SiF(4+x)x- = SiF4(g) + x F- This article relates the Si(IV) reaction study to define a relative fluoroacidity scale by studying the silicon ions stability in different melts. Electrochemical techniques allow the measurement of SiF4+xx- concentration evolution and thus the reaction rate constant to be calculated at different temperatures and for several fluoride media. The article shows that the free F- content depends on the fluoride mixture and that the rate values are correlated with the fluoroacidity allowing a qualitative estimation. Then a fluoride solvents fluoroacidity scale was proposed, scaling the different eutectic melts from basic melt to acidic one: NaF-KF < LiF-KF < NaF-MgF2 < NaF-CaF2 < LiF-NaF < LiF < LiF-CaF2