Hot-Tip Scanning Electrochemical Microscopy: Theory and Experiments Under Positive and Negative Feedback Conditions

Hot-tip scanning electrochemical microscopy (HT-SECM) is a novel surface characterization technique utilizing an alternating current (ac) polarized disk microelectrode as a probe. A high-frequency (∼100 MHz) ac waveform applied between the tip and a counter electrode causes the resistive heating of the surrounding electrolyte solution that leads also to the electrothermal fluid flow (ETF). The effects of the temperature and the convection driven by the ETF result in the increased rate of mass transfer of the redox species. In this paper, HT-SECM was studied in positive and negative feedback modes, for which approach curves and cyclic voltammograms were recorded. The experimental data showed that the use of a hot tip leads to a more pronounced feedback compared to that at room temperature. Numerical simulations performed in COMSOL Multiphysics supported the experimental findings. Additional analytical approximations were developed that could be used to predict the faradaic response in HT-SECM experiments. Finally, a possible contribution to the current from the Soret effect was studied theoretically. A good understanding of HT-SECM was achieved, both experimentally and theoretically, suggesting that this methodology could be applied to investigate electrode kinetics under the conditions of elevated temperature and increased rate of mass transfer.