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摘要
Alternating current (ac) voltammetry provides access to faster electrode kinetics than direct current (dc) methods. However, difficulties in ac and other methods arise when the heterogeneous electron-transfer rate constant (k(0)) approaches the reversible limit, because the voltammetric characteristics become insensitive to electrode kinetics. Thus, in this near-reversible regime, even small uncertainties associated with bulk concentration (C), diffusion coefficient (D), electrode area (A), and uncompensated resistance (R-u) can lead to significant systematic error in the determination of k(0) In this study, we have introduced a kinetically sensitive dual-frequency designer waveform into the Fourier-transformed large-amplitude alternating current (FTAC) voltammetric method that is made up of two sine waves having the same amplitude but with different frequencies (e.g., 37 and 615 Hz) superimposed onto a dc ramp to quantify the close-to-reversible Fc(0/+) process (Fc = ferrocene) in two nonhaloaluminate ionic liquids. The concept is that from a single experiment the lower-frequency data set, collected on a time scale where the target process is reversible, can be used as an internal reference to calibrate A, D, C, and R-u. These calibrated values are then used to calculate k(0) from analysis of the harmonics of the higher-frequency data set, where the target process is quasi-reversible. With this approach, k(0) values of 0.28 and 0.11 cm s(-1) have been obtained at a 50 mu m diameter platinum microdisk electrode for the close-to-diffusion-controlled Fe0/+ process in two ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonypimide and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, respectively.
- 出版日期2016-2-16
