Review—Advances in Scanning Electrochemical Microscopy (SECM)

Abstract

Scanning electrochemical microscopy (SECM) is unique among scanning probe methods in its quantitative rigor and in its ability to study samples in liquid environments with ease. SECM has become a popular and mature technique with a wide range of applications in electrochemical imaging, chemical kinetics, biological redox processes, and electrocatalytic reactions, among others. A major development in recent years is the ongoing shift from micrometer-scale experiments to the nanoscale. Recent advances in methodology have greatly increased the capacity of SECM to characterize interfaces at the nanoscale and to obtain molecular-level chemical information. The principles of SECM will be briefly introduced, and recent advances using this technique will be discussed. Scanning electrochemical microscopy (SECM) is a scanning probe technique and electrochemical tool that is widely used to probe surfaces and surface reactions. The instrumentation, theory, modes, and initial applications were developed in the Bard laboratories during the 1980's. SECM is now used worldwide and applications continue to be developed. A number of general reviews 1-21 and two monographs 22,23 have also been published. SECM differs from other scanning probe methods such as scanning tunneling (STM) and atomic force microscopy (AFM) in that welldeveloped electrochemical methods are used to quantitatively probe the chemistry of a substrate. SECM is based on the measurement of the current through an ultramicroelectrode (UME) tip, an electrode with a radius, a, on the order of a few nanometers to 25 μm, when it is held constant or moved in a solution in the vicinity of a substrate. Substrates range from solid surfaces, including glass, metal, polymer, and biological material, to liquids such as mercury and immiscible oil. The presence of a substrate perturbs the electrochemical response of the tip and this perturbation provides information about the nature and properties of the substrate with micrometer and nanometer resolution. SECM is also used in imaging and studying the uptake or release of chemical species from a surface, including processes in biological cells. SECM combines the virtues of electrochemistry at UMEs with the application of piezoelectric elements to position the tip in the x,y,z planes, as in STM. Steady-state SECM measurements are simpler than, but analogous to those with thin layer cells, 24-28 rotating ringdisk electrodes, 29,30 and arrays of interdigitated electrodes. 31 SECM Modes of OperationThere are several basic modes of operation of SECM that continue to be used in developing new applications. These include generation/collection and feedback modes. Most SECM measurements involve steady-state current measurements, though transient measurements are also made.Generation/collection modes.-In the generation/collection (G/C) modes of SECM, the tip is generally located at distances on the order of ten tip radii or less from the substrate and both tip, i T , and substrate, i S , currents are monitored. There are two types of SECM...

Probing the Speed Limits of Scanning Electrochemical Microscopy with In situ Colorimetric Imaging

“…Scanning electrochemical microscopy (SECM) is a scanning probe microscopy (SPM) technique that offers unique chemical imaging capabilities across a wide range of applications, but has traditionally suffered from slow imaging rates that reduce sample throughput . The relatively slow imaging rates in conventional SECM based on micron‐sized probes, commonly referred to as ultramicroelectrodes (UMEs), can usually be attributed to the large characteristic time constants associated with diffusive transport of electroactive species between the substrate and the probe .…”

Electrochemical Scanning Probe Microscopies in Electrocatalysis

“…Therefore, the technique permits the acquisition of local reactivity maps. In the most common substrate generation/tip collection (or tip generation/substrate collection) mode, a species electrochemically generated at the substrate is electrochemically detected at the tip (or vice versa) . The feedback mode is based on a redox couple: the oxidized species Ox is reduced at the substrate to form the species Red, which then diffuses to the tip, where it is reoxidized to Ox (or vice versa).…”

“…Ox can then diffuse back to the substrate, be reduced again, thus creating an electrochemical positive feedback loop. In the redox competition mode, both probe and substrate are competing for the same reactant species . At a higher substrate activity, less reactants are available for the reaction at the probe, thus the probe current decreases.…”

Mapping the antioxidant activity of apple peels with soft probe scanning electrochemical microscopy

“…The latter concept is related to the wellknown ferric ion reducing antioxidant power (FRAP) assay where Fe 3+ ions are reduced by AOs to Fe 2+ ions to determine the total AO's reducing capacity by a detectable color change of the iron complex [5,31]. Micrometer spatial resolution with electrochemical methods can be achieved by using scanning electrochemical microscopy (SECM) where microelectrodes are laterally translated in close vicinity to a substrate inside an electrolyte solution containing redox active species [32][33][34][35][36][37][38]. Typical SECM applications range from bio-imaging, surface reactivity mapping to the characterization of liquid-liquid interfaces [39][40][41][42].…”