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). 

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. Sultan et al., Curr. Opi Electrochem., 2023, 41:101350

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. Han et al., J. Electrochem. Soc., 2017, 164:C952