Scanning electrochemical microscopy electron transfer processes

The time range of the electrochemical measurements has been decreased considerably by using more powerful -> potentiostats, circuitry, -> microelectrodes, etc. by pulse techniques, fast -> cyclic voltammetry, -> scanning electrochemical microscopy the 10-6-10-1° s range has become available [iv,v]. The electrochemical techniques have been combined with spectroscopic ones (see -> spectroelectrochemistry) which have successfully been applied for relaxation studies [vi]. For the study of the rate of heterogeneous -> electron transfer processes the ILIT (Indirect Laser Induced Temperature) method has been developed [vi]. It applies a small temperature perturbation, e.g., of 5 K, and the change of the open-circuit potential is followed during the relaxation period. By this method a response function of the order of 1-10 ns has been achieved. 

Wei, C., Bard, A. J., Mirkin, M. V. Scanning electrochemical microscopy. 31. Application of SECM to the study of charge transfer processes at the liquid/liquid interface. J. Phys. Chem. 1995, 99, 16033. Tsionsky, M., Bard, A. J., Mirkin, M. V. Scanning electrochemical microscopy. 34. Potential dependence of the electron-transfer rate and film formation at the liquid/liquid interface. J. Phys. Chem. 1996, 100, 17881. 

FIGURE 5.2 Simulated feedback SECM transients with various rate constants for an irreversible heterogeneous process at the substrate. The upper and lower dashed curves correspond, respectively, to the limits A ijs ° and A [,s=0. The solid curves (from top to bottom) represent log A s=3.0, 1.5, 1.0, 0.5, 0, -0.5, and -1.0. RG=10. (Reprinted with permission from Bard, A.J., Mirkin, M.V., Unwin, P.R., and Wipf, D.O., Scanning electrochemical microscopy. 12. Theory and experiment of the feedback mode with finite heterogeneous electron-transfer kinetics and arbitrary substrate size, J. Phys. Chem., 96, 1861-1868, 1992. Copyright 1992 American Chemical Society.)... 

FIGURE 5.7 Schematic view of the processes involved in the SECM measurements of ET across an electroactive SAM. (A) Mediated ET, (B) direct electron tunneling through monolayer, and (C) ET through pinholes. (Adapted from Liu, B., Bard, A.J., Mirkin, M.V., and Creager, S.E., Electron transfer at self-assembled monolayers measured by scanning electrochemical microscopy, J. Am. Chem. Soc., 126, 1485-1492, 2004. Copyright 2004 American Chemical Society.)... 

Zhang, J., Unwin, P. R. Investigation of the kinetics of electron transfer process involving fuUerenes at liquid-liquid interfaces using scanning electrochemical microscopy Evidence of Marcus inverted region behaviour. J. Chem. Soc. Perkin Tran. 2001, 2, 1608-1612. 

---