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Reaction mechanisms of the H2 oxidation/evolution reaction

Electrocatalysis

The hydrogen oxidation/evolution reaction

  1. M. W. Breiter

Published Online: 15 DEC 2010

DOI: 10.1002/9780470974001.f204027

Handbook of Fuel Cells

Handbook of Fuel Cells

How to Cite

Breiter, M. W. 2010. Reaction mechanisms of the H2 oxidation/evolution reaction. Handbook of Fuel Cells. .

Author Information

  1. Institut für Technische Elektrochemie und Festkörperchemie, Vienna, Austria

Publication History

  1. Published Online: 15 DEC 2010

Abstract

The mechanisms of the H2 oxidation/evolution are discussed on basis of the classical pathways (Volmer–Tafel reactions and Volmer–Heyrovsky reactions). For simplicity the discussion is given for acidic systems under the assumption of Langmuirian adsorption of the atomic hydrogen, adsorbed on the electrode surface. The modifications necessary for alkaline systems are indicated.

The conditions are outlined when one of the pathways is predominant. Control by a single step is then discussed. The possible effect of mass transport is considered. The dependence of the exchange current densities of the individual reactions upon the coverage with atomic hydrogen is derived.

The experimental observation that relationships between the logarithm of the exchange current density and the M[BOND]H bond strength appear to possess a volcano shaped curve is discussed in detail under consideration of how the hydrogen atoms are bonded. The question of which type of hydrogen atoms is involved in the H2 oxidation/evolution on platinum metals is briefly considered.

Finally, a more complex reaction is treated in which either one or several products are formed. The differences in the kinetics of such reactions to that of the simpler H2 oxidation/evolution are pointed out.

Keywords:

  • reaction mechanisms for hydrogen electrode;
  • Volmer–Tafel mechanism;
  • Volmer Heyrovsky mechanism;
  • Langmuirian adsorption;
  • Tafel equation;
  • exchange current densities;
  • diffusion overpotential;
  • underpotential deposition