Kinetics of heterogeneous electron transfer

Cyclic voltammetry is the most widely used technique for acquiring qualitative information about electrochemical reactions. The power of cyclic voltammetry results from its ability to rapidly provide considerable information on the thermodynamics of redox processes, on the kinetics of heterogeneous electron-transfer reactions, and on coupled chemical reactions or adsorption processes. Cyclic voltammetry is often the first experiment performed in an electroanalytical study. In particular, it offers a rapid location of redox potentials of the electroactive species, and convenient evaluation of the effect of media upon the redox process. 

Electrochemical studies on SAMs have proven invaluable in elucidating the impact of various molecular parameters such as bridge structure, molecular orientation or the distance between the electroactive species and electrode surface. As described above in Section 5.2.1, the kinetics of heterogeneous electron transfer have been studied as a function of bond length for many systems. Similarly, the impact of bridge structure and inter-site distances have been studied for various supramolecu-lar donor-acceptor systems undergoing photoinduced electron transfer in solution. In both types of study, electron transfer is observed to increase as the distance between the donor and acceptor decreases. As discussed earlier in Chapter 2, the functional relationship between the donor-acceptor distance and the electron transfer rate depends on the mechanism of electron transfer, which in turn depends on the electronic nature of the bridge. 

It has been shown very recently that l,3,5-tris(4-(ALphenyl-AL3-methylphenyl)phenyl) benzene (56), when studied in DMF and dichloromethane solutions, forms two and three reversible one-electron anodic waves, respectively92. The kinetics of heterogeneous electron transfers has recently been studied using the high speed microband channel electrode in solutions containing 0.1 M TBAP as electrolyte it was possible to find standard potentials E°, transfer coefficients a and, finally, standard rate constants k°. The obtained data, labeled by subscripts 1, 2 and 3 for the first, second and third electron transfer, respectively, are collected in Table 2. 

The kinetics of heterogeneous electron transfer reaction in the presence of insonation at the electrode surface has been quantified by analyzing the wave shape of the sonovoltammetric signal. Huck [18] investigated one-electron redox systems such as Pe3-i-/2-i- and reported... 

Ding ZF, Quinn BM, Bard AJ (2001) Kinetics of heterogeneous electron transfer at liquidAiquid interfaces as studied by SECM. J Phys Chem B 105 (27) 6367-6374. doi 10.1021/jp0100598... 

Cyclic voltammetry (CV) can provide information about the thermodynamics of the redox process, kinetics of heterogeneous electron transfer reactions and coupled chemical reactions [32]. The reversible electron transfer steps inform us about the compound s ability to accept electrons however, experimental conditions, such as solvent and temperature also influence the voltammogram. The structure of the lowest unoccupied molecular orbital (LUMO) levels of the compound can be determined from the number of CV waves and reduction potentials ( 1/2)- Moreover, the CV can serve as a spectroscopy as demonstrated by Heinze [32], since the characteristic shapes of the waves and their unequivocal positions on the potential scale are effectively a fingerprint of the individual electrochemical properties of the redox system. 

Horrocks, B. R., Mirkin, M. V., Bard, A. J. Scanning electrochemical microscopy. 25. Application to investigation of the kinetics of heterogeneous electron transfer at semiconductor (WSej and Si) electrodes, J. Phys. Chem. 1994, 98, 9106-9114. 

Xie, S., Meng, X., Liang, Z., Li, B., Chen, Z., Zhu, Z., Li, M., Shao, Y. Kinetics of heterogeneous electron transfer reactions at the externally polarized water/o-nitrophenyl octyl ether interface. J. Phys. Chem. C 2008,112,18117-18124. 

Z. Ding, B. M. Quinn, and A. J. Bard, /. Phys. Chem. B., 105, 6367 (2001). Kinetics of Heterogeneous Electron Transfer at Liquid/Liquid Interfaces as Studied by SECM. 

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