SECM

SECM, or Scanning Electrochemical Microscopy, is a scanning probe technique used to map the electrochemical reactivity of surfaces with high spatial resolution. In SECM, a microelectrode tip, typically an ultramicroelectrode, is positioned very close to a substrate in an electrolyte solution. A controlled potential is applied to the tip relative to a reference electrode, and the resulting current is recorded as the tip scans over the surface. The local electrochemical behavior of the substrate is inferred from how the tip current responds to changes in distance and surface properties.

Principles and modes: SECM relies on the interaction between the tip and the substrate to modulate the flux of electroactive species in the solution. In the common feedback mode, a conductive surface near the tip increases the current (positive feedback), while an insulating area decreases it (negative feedback). Other modes include generator-collector and redox competition, where species generated at the tip participate in reactions at the substrate or vice versa, enabling more complex measurements and imaging of coupled processes.

Instrumentation and operation: The setup uses a working electrode tip, a counter electrode, and a reference electrode in an electrolytic cell. The tip is scanned over the surface by a piezoelectric stage, and the tip–surface distance is controlled by monitoring approach curves or maintaining a specified current setpoint. The resulting electrochemical map reflects local reactivity, diffusion characteristics, and surface morphology.

Applications: SECM is used for surface mapping of catalytic activity, corrosion studies, battery electrode characterization, sensor development, and investigations in biology, including single cells and membranes. It provides noncontact, in situ, label-free electrochemical imaging in liquid environments.

History: SECM was developed in the late 1980s and 1990s by researchers including Allen J. Bard and colleagues, and has since evolved with variations such as SECCM and three-dimensional imaging.