Development of Mg²⁺Ion-Selective Microelectrodes for Potentiometric Scanning Electrochemical Microscopy Monitoring of Galvanic Corrosion Processes

Abstract

The fabrication of a solid-contact, micropipette-based magnesium ion-selective micro-tipped electrode (ISME) suitable for scanning electrochemical microscopy is reported and compared against a conventional micro-tipped ISME having a conventional aqueous internal reference electrode. Measurements showed that the solid-contact ISME had a lower internal resistance and a faster response time than the one with a liquid-contact. These advantages increased the spatial distribution and improved 2D images depicting concentration distributions of Mg 2+ . The ability of the microelectrode to image local ionic concentration has been tested over magnesium surfaces freely corroding or galvanically coupled to iron in aqueous chloride-containing solution. Scans of magnesium ion distribution, in the absence of corrosion currents, were also made over a micro-pipette source containing a concentrated magnesium chloride gel as a source of Mg 2+ and over a current source in the absence of Mg 2+ . From these measurements it was concluded that the potentiometric measurements over corroding surfaces were dominated by the changes in Mg 2+ distributions with small electric potential contributions due to corrosion current.

Electrochemical detection of cupric ions with boron-doped diamond electrode for marine corrosion monitoring

“…Boron-doped diamond (BDD) is increasingly of interest since its 29 outstanding chemical and physical properties are unparalleled in 30 comparison with other electrode materials [3][4][5][6][7]. The nil toxicity, 31 the high overpotentials for oxygen and hydrogen evolutions [8], 32 the high chemical and physical stability in addition to the low 33 capacitive current in aqueous solutions [9], make BDD an attractive 34 electrode material widely used in electroanalysis.…”

Applications of Scanning Electrochemical Microscopy (SECM) Coupled to Atomic Force Microscopy with Sub-Micrometer Spatial Resolution to the Development and Discovery of Electrocatalysts

“…SECM has been used to investigate various electrochemical reactions and electrode surfaces under diffusion-limited reaction conditions using a small probe electrode [12,[14][15][16][17][18][19][20][21][22][23]. The spatial and temporal resolution of SECM depends on the size of the probe electrode employed in the investigation, as described below [12].…”

“…The spatial and temporal resolution of SECM depends on the size of the probe electrode employed in the investigation, as described below [12]. Various approaches have been implemented for the fabrication of smaller electrodes to achieve electrochemical measurements with sub-micrometer resolution [14][15][16][17][18][19][20][21][22][23]. For example, a nanopipette and micropipette have been employed as ion-selective microelectrodes for SECM measurements [15,16].…”

Local Hydrogen Fluxes Correlated to Microstructural Features of a Corroding Sand Cast AM50 Magnesium Alloy

“…15,17 The potentiometric mode of SECM has also been extensively employed to characterize both pHs and Mg 2+ flux during corrosion of Mg alloys. 16,18,[33][34][35] The Mg 2+ is generated by anodic oxidation of the matrix phase (Equation 1) while the reduction of water occurs predominantly on the more noble alloy constituents (secondary phases) producing dissolved molecular H 2 and OH − species (Equation 2). Generation of OH − in the cathodic reaction leads to localized pH changes and the deposition of Mg(OH) 2 (Equation 3) on the alloy surface (K sp, Mg(OH) 2 = 5.61 × 10 −12 ).…”

“…15,17 The potentiometric mode of SECM has also been extensively employed to characterize both pHs and Mg 2+ flux during corrosion of Mg alloys. 16,18,[33][34][35] …”