A study of the effect of the second coordination sphere on the standard rate constants of charge transfer (k(s)) for the Nb(V)/Nb(IV) redox couple in chloride, chloride-fluoride and fluoride melts has been presented. By using cyclic voltammetry, the standard rate constants of charge transfer were determined for chloride melts: k(s) (CsCl) < k(s) (KCl). The redox process in the NaCl-KCl (equimolar mixture) - NbCl5 melt was reversible. The standard rate constants of charge transfer were experimentally determined for chloride-fluoride melts: k(s) (KCl) < k(s) (CsCl) < k(s) (NaCl-KCl). The dependence of the standard rate constants was obtained for pure fluoride melts: k(s) (CsF) < k(s) (KF) < k(s) (NaF-KF). The influence of the first coordination sphere composition on the charge transfer standard rate constants was found experimentally: k(s) (fluoride melts) < k(s) (chloride-fluoride melts) < k(s) (chloride melts), both at glassy carbon and platinum electrodes. It was found that the k(s) increases with the temperature increase and substitution of a glassy-carbon electrode for a platinum one. (C) 2015 The Electrochemical Society.