Analysis of the hydrogen electrode reaction mechanism in thin-layer cells. 1. Theory

This work develops the equations that relate the kinetic parameters of the hydrogen electrode reaction (HER) with the current density (j) vs. potential (E) dependences of a thin-layer cell (TLC). Two operation modes of the TLC are analyzed. The first one proposes to examine the j(E) dependence of the hydrogen evolution reaction (her) on one electrode while the paired electrode oxidized the dissolved H2 back to H+ under diffusion control. The second mode proposes to analyze the j(E) dependence of the hydrogen oxidation reaction (hor) on one electrode while the other generates dissolved H2 from H+ under diffusion control. In both cases, as very high mass-transport rates are reached for distances in the micrometer range, the j(E) curves are sensitive to the complete set of kinetic parameters even for very large reaction rates. Possible ways to incorporate these equations in the theoretical formalisms of well-established TLC-based techniques such as scanning electrochemical microscopy are discussed.