Standard rate constants of charge transfer for Nb(V)/Nb(IV) redox couple in chloride-fluoride melts: Experimental and calculation methods.

Standard rate constants k_s of charge transfer for Nb(V)/Nb(IV) redox couple in NaCl-KCl (the equimolar mixture) -K₂NbF₇, KCl-K₂NbF₇, and CsCl-K₂NbF₇ melts are determined by using cyclic voltammetry. An unconventional series of the standard rate constants is found: k_s (KCl) < k_s (CsCl) < k_s (NaCl-KCl). Ab initio calculations carried out by using a PC Gamess/Firefly quantum-chemical program showed that the charge transfer activation energy can change not monotonically in the Na-K-Cs series, in compliance with the reorganization energy relationship. This leads, in its turn, to nonmonotonic change in the charge transfer rate constants. [ABSTRACT FROM AUTHOR]