On the Mechanism of Scanning Electrochemical Potential Microscopy

Abstract

Scanning electrochemical potential microscopy (SECPM) is a type of probe microscopy, in which a sharp tip similar to those employed in electrochemical tunnelling microscopy is connected to a high impedance amplifier, but the tip potential instead of tip current is used as the signal in the feedback loop. SECPM has been found to provide much higher spatial resolution than would be expected on the basis of a mechanism in which the tip responds to the local electrochemical potential of the solution; in fact, it can obtain atomic resolution similar to STM, but is a superior technique for imaging electronically insulating objects such as proteins on a metal surface. We suggest a mechanism for these high‐resolution images based on electron exchange between tip and substrate coupled to faradaic processes at the tip/solution interface. This mechanism operates alongside the conventional mechanism in which the tip responds to the local potential in the diffuse layer of the substrate and allows a simple description of the sigmoidal tip potential−distance curves that have been reported.

Electrochemical Scanning Probe Microscopies in Electrocatalysis

“…The profiles obtained agreed with expectations from Gouy–Chapman theory at large probe–WE separation, but deviated at small distances explained by overlapping of the double layers and the occurrence of tunneling currents. If the tunneling currents are balanced by faradaic and leakage currents, however, the sigmoidal profile shape of the approach curve in close distance to the electrode can be theoretically confirmed …”

“…On the one hand, leakage currents due to the experimental setup were suggested as closing the current loop . On the other hand, coupling of the tunneling current to faradaic processes at the tip/electrolyte interface was suggested recently as another closing mechanism …”

“…Thus, aside from the effects related to tip shape and overlapping of the double layer, at small tip–probe separation another factor needs to be considered: tunneling currents between the tip and the substrate . A high spatial resolution similar to STM can be reached in SECPM: this as well as the shape of the approach curves has been considered as an indication toward tunneling .…”

The mechanism of water oxidation using transition metal-based heterogeneous electrocatalysts

“…Scanning microscopy serves as an influential instrument for visualizing surface properties and localized electrochemical activity on an atomic scale in situ or even operando , thus playing a pivotal role in investigating heterogeneous electrocatalysis mechanisms. 312,313 Bard's team proposed an in situ scanning electrochemical microscopy (SECM) technique to obtain chemical information by measuring the local current response on the electrode surface. The technique has contributed significantly to the basic understanding of the electrocatalytic OER mechanism in recent decades.…”