CATHODIC EVOLUTION OF HYDROGEN ON IRON DISILICIDE IN ALKALINE ELECTROLYTE

Abstract

The kinetics and mechanism of hydrogen evolution on the FeSi2 electrode in 0.25-1.0 M NaOH solutions have been studied by polarisation and impedance measurements. The cathodic polarisation curves of iron disilicide in the studied solutions are characterized by a Tafel region with constants α and β equal to (-0.78)-(-0.72) and (-0.133)-(-0.128) V, respectively. The impedance spectra of FeSi2 at the potentials of the Tafel region represent a capacitive semicircle with a displaced centre, which corresponds to an asymmetric maximum in the graph of phase angle dependence on the logarithm of the alternating current frequency; the magnitude of the electrode impedance in all solutions changes in accordance with the course of the polarization curves. To describe the hydrogen evolution reaction on iron disilicide, an equivalent electrical circuit was used, the Faraday impedance of which consists of series-connected charge-transfer resistances and a parallel circuit responsible for the adsorption of atomic hydrogen on the surface and its diffusion into the depth of the electrode material; the circuit also includes the electrolyte resistance and the double-layer capacitance impedance, which is modelled by a constant phase element. It is shown that the results of polarization and impedance measurements for the FeSi2 electrode are in satisfactory agreement with the discharge-electrochemical desorption mechanism, in which both stages are irreversible and have unequal transfer coefficients; for adsorbed atomic hydrogen, the Langmuir adsorption isotherm is satisfied; simultaneously with the reaction of hydrogen evolution, the reaction of hydrogen absorption by the electrode material proceeds with diffusion control. It has been found that iron disilicide in an alkaline electrolyte is characterised by the low overvoltage of hydrogen evolution, and it is a promising electrode material for the electrolytic production of hydrogen.