What is the Upper Limit for the Standard Rate Constant of a Heterogeneous Electron Transfer Reaction?
Measuring the rates of rapid outer-sphere electron transfer (ET) reactions is of special interest because these mechanistically simple processes are used to check the ET theory.1 We investigated the kinetics of several fast heterogeneous electron transfer reactions by steady-state voltammetry at nanoelectrodes and scanning electrochemical microscopy (SECM) and addressed an intriguing question about possible differences between ET dynamics observed at macroscopic and nanometer-sized interfaces.2 The polished Pt electrodes (≥10 nm-radius) were prepared and used as tips for SECM experiments, so that a number of current vs. distance curves and voltammograms were obtained at the same tip without damaging it. This allowed us to characterize the tip geometry and then use it to obtain an extensive set of experimental data. In this way, nanoelectrochemical measurements of ET kinetics were made with reproducibility similar to that reported previously for micrometer-sized electrodes. The SECM cur
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