Study on the variation of impedance using one-dimensional alternating current scanning electrochemical microscopy

Abstract

The technique of the Alternating Current Scanning Electrochemical Microscopy (AC-SECM) is described. This method is based on the variation of the ac impedance according to the tip-substrate distance in a Scanning Electrochemical Microscopy (SECM) arrangement. The ac response can be used to obtain the informations of mass transport, kinetic parameters, the solution resistance, and the double-layer capacitance in close proximity of a substrate. Prior to the theoretical study, experimental trends are investigated in an AC-SECM configuration using a microdisk electrode and compared with the planar electrode case. As a disk electrode approaches a conductive substrate in the supported system, the finite-length-diffusion character of the Warburg impedance increases. Conversely, in case of an insulating substrate it decreases. When a supporting electrolyte is not in excess, the changes of the Warburg impedance due to migration and slow charge transfer kinetics were observed. The variation of the ac impedance is complicated with mass transfer and charge transfer, as a disk electrode approaches a conducting substrate in a low-ionic strength solution.