Home – Home – Jornals – Chemistry for Sustainable Development 2024 number 1

The kinetics and mechanism of hydrogen evolution on the MoSi₂ electrode in x M H₂SO₄ + (0.5-x ) M Na₂SO₄ ( x = 0.50; 0.35; 0.20) solutions have been studied. The cathodic polarization curves of MoSi₂ in the studied solutions are characterized by Tafel region with a slope of (-0.070)±0.002 V. The reaction order of the cathodic process with respect to hydrogen ions at the potentials of Tafel region is ~1.0; the derivative of the electrode potential with a change in electrolyte acidity is ~0.072 V. The impedance spectra of the MoSi₂ electrode in the studied potential range have the shape of a semicircle located in the capacitive half-plane, with the centre in the region of positive values of the imaginary impedance component; in the region of the highest frequencies, a short straight section is recorded on the impedance plots, indicating the presence of pores in the surface layer of the electrode. To describe the hydrogen evolution reaction on MoSi₂, we used an equivalent electrical circuit, the Faraday impedance of which consists of series-connected charge transfer resistance ( R₁) and a parallel R₂C₂Z_d-chain responsible for the adsorption of atomic hydrogen on the surface and its diffusion into the depth of the electrode material. The equivalent circuit also includes the solution resistance (R_s) and the double layer capacitance impedance, which is modeled by the constant phase element CPE₁. It is shown that the hydrogen evolution reaction on molybdenum disilicide in a sulphuric acid electrolyte proceeds along the discharge - recombination route with a quasi-equilibrium discharge stage when the Temkin logarithmic isotherm for adsorbed atomic hydrogen is fulfilled. The hydrogen evolution reaction is complicated by hydrogen absorption proceeding in the mode of solid-phase diffusion kinetics.