Abstract
The standard heterogeneous rate constants for the reduction of a series of viologen derivatives with a range of inter‐ring torsion angles were measured at Bi and Pt electrodes. The electrode potentials for the first one‐electron reduction of the viologens vary from −684 mV to −1070 mV vs. Ag/0.01 m Ag+; this enabled a comparison of the behaviour of metallic (Pt) and semi‐metallic (Bi) electrodes over a wide range of applied potentials. The differential capacitance (6.5 μF cm−2) of Bi/MeCN,TBAPF6 interfaces at the potential of zero charge (pzc=−0.60 V) is at least an order of magnitude greater than that calculated on the basis of the bulk Bi carrier density (3×1017 cm−3) and the differential capacitance (9.5 μF cm−2) of Pt/MeCN interfaces at their pzc (−0.43 V) is of the same order. The series of viologen derivatives exhibited simple one‐electron redox behaviour and showed similar rate constants at Pt (1.8×10−4–1.6×10−3 cm s−1) and Bi electrodes (1.1×10−4–1.9×10−3 cm s−1) after application of the Frumkin correction. These results demonstrate that the density of states at the Bi surface is much higher than in bulk. Finally, the Frumkin‐corrected standard rate constants were observed to be inversely correlated with the inter‐ring torsion angle of the viologens.
Highlights
The rate of heterogeneous electron transfer (ET) depends on both the nature of the redox couple and the electrode material
First we present the results of slow-scan cyclic voltammetry experiments and demonstrate that the one-electron reduction of the viologen derivatives is a well-behaved, simple electron transfer, we discuss the measurements of standard electrochemical rate constants by using fast-scan cyclic voltammetry (FSV), impedance spectroscopy (EIS) and steady-state microelectrode voltammetry
We are interested in the differential capacitance primarily to make the Frumkin correction for our heterogeneous electron-transfer rate data obtained by fast CV; we propose that the appropriate angular frequency is of the order of
Summary
The rate of heterogeneous electron transfer (ET) depends on both the nature of the redox couple and the electrode material. Attempts to study the rate in aqueous solvents have been made but they are complicated by adsorption phenomena and dimerisation of the reaction products.[43,44,45] Electrode fouling due to electrodeposition of the neutral form of the molecule has been observed in aqueous solvents.[46] We show that in acetonitrile, repeatable measurements of the standard rate constant may be obtained, free from such complications, by using fast scan voltammetry and convolution analysis.[47] First we present the results of slow-scan cyclic voltammetry experiments and demonstrate that the one-electron reduction of the viologen derivatives is a well-behaved, simple electron transfer, we discuss the measurements of standard electrochemical rate constants by using fast-scan cyclic voltammetry (FSV), impedance spectroscopy (EIS) and steady-state microelectrode voltammetry. Benniston (School of Chemistry, Newcastle University) and were prepared and purified as has been described previously.[30]
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