Contact : Junsoo Han

Atomic emission spectroelectrochemistry (AESEC) was first developed for aqueous corrosion research in the early 1990s (https://doi.org/10.1149/1.1393433) by Professor Kevin Ogle at l'Institut de Recherche de la SIDérurgie (IRSID). At LISE, different analytic techniques are coupled with AESEC such as electrochemical impedance spectroscopy (EIS), electrochemical quartz crystal microbalance (EQCM), and gravimetric gas measurement.

 

Basic principles

Element-resolved dissolution rates during electrochemical measurement are monitored in real-time by an inductively coupled plasma - atomic emission spectrometer (ICP-AES, Ultima 2C, Horiba France). The electrolyte carrying dissolved species from electrochemical reaction in a specially designed electrochemical cell transported to the plasma with 6 000 – 10 000 K where all species are atomized and exited by collisions with electrons and argon ions. 

             

Fig. 1

The dissolved species in the electrolyte after the electrochemical reactions are transported to an ICP-AES downstream of a specially designed electrochemical flow cell. The dissolved species M are all atomized and excited to an energy state of M*. The excited atoms M* emit electromagnetic radiation with elemental specific wavelengths when they decay to the ground energy state. The atomic intensity of the radiation of an element M at a specific wavelength λ, I_M,λ, is proportional to the concentration of the element in the electrolyte. In ICP-AES, the intensity is detected by a polychromator composed of multiple exit slits detecting more than 30 pre-selected elements, and by a monochromator with non-predefined wavelength giving a high spectral resolution of a single element. The elemental dissolution rate, v_M, can be calculated from the elemental concentration, CM, by the following reactions:

C_M = (I_M,λ – I_M,λ°) / κ_λ                       [1]

v_M = f C_M / A                                  [2]

where I_M,λ° is the background intensity of M, κ_λ is the sensitivity factor of M at λ determined from a separate standard calibration measurement, A is the exposed surface area, and f is the flow rate of the electrolyte controlled by a peristaltic pump.

Elemental dissolution rate is often presented in equivalent elemental current density, j_M, using Faraday’s law to facilitate direct comparison between electrical current density and spectroscopic elemental dissolution rate as:

j_M = z_M F v_M / M_M                                 [3]

where M_M is the atomic mass of M, F is the Faraday constant (96485 C mol^-1) and z_M is the valence of the dissolving ions for oxidation, e.g., M à M^z+ + z_M e^-.

An example of the AESEC dissolution profile of the anodic dissolution of an MgZn₂ intermetallic phase is given in Fig. 2 to show the analytical capability of the AESEC technique. The convoluted electric current density, j_e^*, is presented for a direct comparison of the electric signal with the spectroscopic signal with identical time resolution for both datasets.3,10 A nearly congruent and faradaic anodic dissolution is indicated when comparing the faradaic electrical current (j_e^*) and the sum of two elemental equivalent current densities (j_Σ). The ratio of j_Zn/j_Mg reached a value of 1.92 ± 0.03 in 50 s, close to the stoichiometry of the MgZn₂ intermetallic phase assuming z_Mg = z_Zn = 2. The dissolution was nearly faradaic in that j_Σ / j_e^* = 0.97 ± 0.02, close to 1, indicating that almost all reaction contributed to electric current without forming insoluble species. Fig. 2. Potentiostatic transient experiment of MgZn₂ intermetallic phase at E_ap = -0.80 V vs. SCE in deaerated 30 mM NaCl, pH = 10.1. The horizontal dashed line is j = 0 and the vertical dashed line is t = 0 when the electrolyte comes into contact with the specimen.

Fig. 2