Scanning electrochemical microscopy imaging of rhodochrosite dissolution using gold amalgam microelectrodes

Abstract

Gold/mercury amalgam (Au/Hg) microelectrodes with a diameter of 25 µm were developed for the detection of environmentally relevant analytes such as manganese and iron by scanning electrochemical microscopy (SECM), and applied to investigate the controlled dissolution of manganese carbonate (MnCO₃; rhodochrosite) in acidic conditions. Characterization of the amalgam electrode geometry via approach curves recorded during SECM experiments revealed Au/Hg microelectrodes with sphere cap geometry. Quantitative determination of Mn²⁺ has been achieved by calibration of the Au/Hg microelectrode in bulk solution experiments. Subsequent SECM imaging experiments confirm the applicability of amalgam microelectrodes for imaging of Mn²⁺ production during dissolution of MnCO₃ at pH 3.9. This study confirms feasibility and provides the fundamental basis of SECM imaging with amalgam microelectrodes to address biogeochemically relevant questions.