Electrochemical behavior of hexafluoroniobate, heptafluorotungstate, and oxotetrafluorovanadate anions in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide room temperature ionic liquid

Abstract

Electrochemical behavior of hexafluoroniobate (Nb(V)F_6[−]), heptafluorotungstate (W(VI)F_7[−]), and oxotetrafluorovanadate (V(V)OF_4[−]) anions has been investigated in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPyrTFSA) ionic liquid at 298 K by means of cyclic voltammetry and chronoamperometry. Cyclic voltammograms at a Pt electrode showed that Nb(V)F_6[−] anion is reduced to Nb(IV)F_6[2−] by a one-electron reversible reaction. Electrochemical reductions of W(VI)F_7[−] and V(V)OF_4[−] anions at a Pt electrode are quasi-reversible and irreversible reactions, respectively, according to cyclic voltammetry. The diffusion coefficients of Nb(V)F_6[−], W(VI)F_7[−] and V(V)OF_4[−] determined by chronoamperometry are 1.34 × 10[−7], 7.45 × 10[−8] and 2.49 × 10[−7] cm[2] s[−1], respectively. The Stokes radii of Nb(V)F_6[−], W(VI)F_7[−], and V(V)OF_4[−] in BMPyrTFSA have been calculated to be 0.23, 0.38, and 0.12 nm, from the diffusion coefficients and viscosities obtained.