Diffusion effects on the evaluation of the kinetic parameters of the hydrogen oxidation

GENNERO DE CHIALVO, MARÍA ROSA; CHIALVO, ABEL CÉSAR

Thessaloniki (Grecia)

Congreso; 55th Annual Meeting of the International Society of Electrochemistry; 2004

International Society of Electrochemistry (ISE)

The kinetics of the electrochemical reaction of hydrogen oxidation is characterised by a marked effect of the mass transfer process of the reactant towards the reaction surface. Therefore, the evaluation of the kinetic parameters needs the knowledge of the dependence of the current density (j) on overpotential (h), as well as a parameter related to the fluid flow near the electrode surface, as the thickness of the diffusion layer, the flow rate, etc.             The present work analyses the hydrogen oxidation reaction (hor) considering theTafel-Heyrovsky-Volmer mechanism. In this context, it has been demonstrated that: (a) the Tafel-Volmer route always defines a maximum limiting current density less or equal to the diffusion limiting current density (jL); (b) the Heyrovsky-Volmer route always defines a diffusion limiting current density; (c) the simultaneous occurrence of the three steps (Tafel-Heyrovsky-Volmer) always defines a diffusion limiting current density al high overpotential values, although at low h can display a kinetic limiting current originated in the prevalence of the Tafel step (curve a in Fig. 1); (d) the Levich-Koutecky relationships are only strictly linear when they are evaluated in the h region corresponding to maximum j values and the origin intercept different from zero is only defined if the equilibrium reaction rate of the Heyrovsky step is very small.