Ferrocenium hexafluorophosphate (FcPF6) of 1 mM (M ≡ mol dm -3 ) with LiPF6 of 1000, 100, 10, 1 and 0 mM as the supporting electrolyte dissolved in propylene carbonate (PC) was prepared. Each of these solutions is denoted as 𝐶 sup ≡ 𝑐 LiPF 6 𝑐 Fc + ⁄ = 1000, 100, 10, 1, 0 (𝑐 i : concentration of i). Pt disk ( = 3 mm) and wire were used as the working and counter electrodes, respectively, and a double junction Ag|Ag + electrode as the reference electrode. Measurements were carried out under thermostatic conditions at 30 °C in an Ar-filled glove box. The potential was swept in the range between 𝐸°′ ± 0.25 V (𝐸°′: formal potential) at a sweep rate of 1 V s -1 .