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

摘要

Electrochemical behavior of hexafluoroniobate (Nb(V)F6~), 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 x 10~(-7), 7.45 x 10~(-8) and 2.49 x 10~(_7)cm~2s~(-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.