ABSTRACT
Scanning electrochemical microscopy (SECM) is a powerful electrochemical tool to investigate heterogeneous electron transfer (ET) reactions at interfaces. The major advantages of SECM against other electrochemical methods reside in its high time and spatial resolutions as well as the wide range of its applicability to various interfaces. Subsequently, SECM enables more advanced assessment of ET theories and mechanisms and more detailed evaluation of diverse electroactive interfaces. For instance, the extremely rapid kinetics of a heterogeneous ET reaction can be probed without a diffusion limitation under steady states by employing high mass transport conditions achieved in the SECM-based thin-layer cell with the short separation distance, d, between the substrate and the inlaid disk ultramicroelectrode (UME) tip (Figure 6.1). Moreover, the laterally heterogeneous electroactivity of the substrate surface can be probed by scanning the tip to obtain an electrochemical image with high spatial resolution determined by the small tip radius, a. In standard SECM kinetic
6.1 Introduction .......................................................................................................................... 127 6.2 SECM Tip Voltammetry of Heterogeneous ET Reactions ................................................... 128
6.2.1 Principle .................................................................................................................... 128 6.2.2 Applications .............................................................................................................. 130
6.2.2.1 Nanotip Voltammetry of Rapid ET Reactions ........................................... 130 6.2.2.2 Room Temperature Ionic Liquid ................................................................ 131
6.3 SECM of Heterogeneous ET Reactions at Various Substrates ............................................. 132 6.3.1 Principle .................................................................................................................... 132
6.3.1.1 Feedback and SG/TC Modes ..................................................................... 132 6.3.1.2 Irreversible Substrate Reactions................................................................. 133 6.3.1.3 Reversible and Quasireversible Substrate Reactions ................................. 135 6.3.1.4 Unbiased Substrates ................................................................................... 136 6.3.1.5 Reaction-Rate Imaging .............................................................................. 137
6.3.2 Applications .............................................................................................................. 139 6.3.2.1 Single-Walled Carbon Nanotube Network ................................................ 139 6.3.2.2 Individual One-Dimensional Nanostructures ............................................ 141 6.3.2.3 Boron-Doped Diamond Electrode ............................................................. 144 6.3.2.4 Monolayer-Mediated ET ............................................................................ 146 6.3.2.5 Electroactive Polymer Film ....................................................................... 149
6.4 Conclusions and Future Perspectives.................................................................................... 153 Acknowledgments .......................................................................................................................... 153 References ...................................................................................................................................... 153
measurements, both tip and substrate are biased externally using a bipotentiostat to independently control ET rates at the respective interfaces. Alternatively, a SECM tip can drive and monitor a heterogeneous ET reaction at a substrate without a bias from an external circuit to characterize an electroactive substrate material in a pristine state or on an insulating support.
