Kinetic patterns of charge transfer of Nb(V)/Nb(IV) redox couples in high-temperature chloride-fluoride melts

Le résumé fourni par la source

This work investigated the processes of complexation and electroreduction of niobium compounds in chloride and chloride-fluoride melts. Based on electrochemical measurements, it was established that the charge transfer between Nb(V) and Nb(IV) complexes is quasi-reversible and occurs mainly in the diffusion mode. The diffusion coefficients of niobium complexes and the activation energy of their diffusion in a wide temperature range were determined. It was shown that with an increase in the polarizing ability of cations and a decrease in their radius, the diffusion coefficients decrease, while the activation energy of the process increases. The results of quantum chemical calculations made it possible to establish the structure, energy characteristics, and features of the charge distribution in niobium complexes. It was found that the interaction of alkali and alkaline earth metal cations with the NbF72– anion is accompanied by a redistribution of the electron density and a weakening of the Nb–F bonds. The strengthening of the cation–anion interaction leads to a decrease in the mobility of the complexes in the melt and an increase in the activation energy of their diffusion. The combination of experimental data and calculation results indicates the formation of electrochemically active complexes of the type {Mn+[NbF7]2–} in the melts, which significantly affect the course of electrode processes and the transport properties of the system.

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