Tafel-Horiuti mechanism

The Tafel-Horiuti mechanism corresponds to fast discharge and slow hydrogen recombination ... 

The initial step, reaction (20), in the HER is charge transfer, leading to the formation of an adsorbed intermediate MH containing the metal M. The MH can either recombine to form molecular hydrogOT by reaction (21) or interact with H+ and an electron to form hydrogen by reaction (22). The former step is termed the recombination or Tafel reaction and the latter, 4he electrdchemical desorption or Horiuti-Heyrovsky mechanism. 

Erdey-Gruz and Volmer and Butler/ to whom we owe a rate expression for charge transfer processes. Later, Frumkin " took into account the potential distribution at the electrode-electrolyte interface and its influence upon the process of discharge of ions. Experimentally observable quantities other than the Tafel constants have also been employed since then in elucidating the mechanism. For example, experimental observations of and attempts of theoretical interpretation of the electrolytic hydrogen-deuterium separation factor were presented by Topley and Eyring, Horiuti, " and others, " as briefly reviewed elsewhere. ... 

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