Redox Reactions of Ag(I)/Ag and Ferrocenium/Ferrocene in 1-Butyl-1-methylpyrrolidinium Bis(fluorosulfonyl)amide Ionic Liquid

The electrode reactions of Ag(I)/Ag and ferrocenium/ferrocene (Fc(+)/Fc) were investigated in an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA). The potential of Ag(I)/Ag depended on the logarithm of the concentration of Ag(I), as predicted by the Nernst equation, indicating the Ag(I)/Ag can be used as a reference electrode reaction in BMPFSA. The reversible electrode reaction of Fc(+)/Fc was observed in BMPFSA by cyclic voltammetry. The donor number of BMPFSA was estimated to be 13 from the difference in the formal potentials of Ag(I)/Ag and Fc(+)/Fc, indicating the coordination ability of FSA(-) was slightly stronger than that of bis(trifluoromethylsulfonyl)amide (TFSA(-)). The diffusion coefficients (D) of Fc and Fc(+) were (5.7 +/- 0.7) and (3.3 +/- 0.2) x 10(-7) cm(2) s(-1), respectively. The ratio of D of Fc(+) against that of Fc was smaller than those in TFSA(-)-type ionic liquids, reflecting the higher charge density of FSA(-). The standard rate constant (k(0)) of Fc(+)/Fc was estimated to be (5.4 +/- 1.1) x 10(-3) cm s(-1). The apparent activation energy for k(0) was close to the activation energy for D, suggesting the electrode reaction of Fc(+)/Fc can be regarded as the outer sphere electron transfer reaction with a very small reorganization energy. (c) 2023 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.