The kinetics of hydrogen evolution reaction accompanied by hydrogen absorption reaction with consideration of subsurface hydrogen as an adsorbed species: Faradaic impedance

•Subsurface hydrogen as a separate species influences the Faradaic impedance.•New equivalent circuit for combination of H2 evolution and H absorption is proposed.•The model provides good fit to impedance spectra of TiFe and TiFe2 electrodes. An equation has been obtained for the Faradaic impedance of the hydrogen evolution reaction (HER), parallel to which the hydrogen absorption reaction (HAR) occurs, taking into account subsurface hydrogen (hydrogen atoms between the first and second layers of metal atoms) as a separate state. A new equivalent electrical circuit for the HER + HAR process has been proposed. It has been shown that the improvement in the quality of approximation of the impedance spectra of TiFe and TiFe2 cathodes in 0.5 M H2SO4 when using this equivalent circuit is statistically significant. Based on the impedance data, a HER + HAR mechanism is suggested for the TiFe electrode. The interactions in the layer of adsorbed hydrogen atoms and in the subsurface layer are discussed qualitatively.