page_title: Scanning electrochemical microscopy
section_title: Ionic dissolution
hierarchical_section_title: Scanning electrochemical microscopy / Applications / Solid/Liquid Interface / Ionic dissolution
caption_attribution_description: English: Fig. 10. Scheme of SECM-induced ionic crystal dissolution.
context_page_description: Scanning electrochemical microscopy is a technique within the broader class of scanning probe microscopy that is used to measure the local electrochemical behavior of liquid/solid, liquid/gas and liquid/liquid interfaces. Initial characterization of the technique was credited to University of Texas electrochemist, Allen J. Bard, in 1989.
  Since then, the theoretical underpinnings have matured to allow widespread use of the technique in chemistry, biology and materials science. Spatially resolved electrochemical signals can be acquired by measuring the current at an ultramicroelectrode tip as a function of precise tip position over a substrate region of interest. Interpretation of the SECM signal is based on the concept of diffusion-limited current. Two-dimensional raster scan information can be compiled to generate images of surface reactivity and chemical kinetics.
  The technique is complementary to other surface characterization methods such as surface plasmon resonance, electrochemical scanning tunneling microscopy, and atomic force microscopy in the interrogation of various interfacial phenomena.
context_section_description: The dissolution of ionic crystals in aqueous environments is fundamentally important to the characterization of a host of naturally occurring and synthetic systems. The high spatial resolution and three-dimensional mobility provided by the UME allows one to probe the dissolution kinetics on specific faces of single ionic crystals, whereas previous characterization techniques relied on a bulk or ensemble average measurement. Due to the high mass transfer rates associated with UMEs in the SECM configuration, it is possible to quantify systems defined by very fast reaction kinetics. In addition, UMEs allow monitoring over a wide dynamic range, making possible the study of ionic solids with large differences in solubility.
  Early examples demonstrating the utility of SECM to extract quantitative rate data from such systems was carried out on CuSO₄ crystals in an aqueous solution saturated with Cu²⁺ and SO²⁻
  ₄ ions. By positioning an UME in the SECM configuration approximately one-electrode radius away from the (100) face of a CuSO₄ crystal, it was possible to perturb the dissolution equilibrium by locally reducing Cu²⁺ at the UME surface. As the crystal face locally dissolved into copper and sulfate ions, a visible pit was formed and the chronoamperometric signal could be monitored as a function of distance between the UME and the crystal. Assuming first or second order kinetic behavior, the dissolution rate constant could then be extracted from the data. Similar studies have been performed on additional crystal systems without a supporting electrolyte.
caption: Ionic dissolution of crystal by local reduction of Mn+
exif: {}