Electrochemical reaction orders: Applications to the hydrogen- and oxygen-evolution reactions☆
Abstract
The problem of deduction of electrochemical reaction orders is discussed for two- and multi-step reactions, particularly for conditions under which the type of isotherm (eg Langmuir and Temkin) governing the adsorption of electrochemically formed intermediates eg H, and OH and O in the hydrogen- and oxygen-evolution reactions, respectively, may change with the extent of coverage. In multi-step reactions, the reaction orders can lead to distinction of kinetic pathways under Temkin adsorption conditions where Tafel slopes can be ambiguous. The reaction orders also depend on the relative coverages by the two intermediates OH and O usually considered in the oxygen-evolution reaction. Applications are made to experimental data for the hydrogen evolution reaction at Pt and Hg. For the latter metal, reaction-order considerations render the H2+-ion -discharge mechanism unlikely as also indicated by H/D separation-factor calculations. The slow H2+-ion-neutralization mechanism is shown to lead to dia chemisorbed and not in equilibrium with H2+ ions in solution.
Résumé
Discussion des méthodes de déduction de l'ordre d'une réaction electrochimique à deux ou plusieurs étapes, particuliéerement pour les conditions où le type d'isotherme d'adsorption (Langmuir on Temkin) des intermédiaires engendrés electrochimiquement (H, OH, O dans les réactions d'évolution de H2 on O2) pourrait se modifier avec l'étendue de recouvrement. Pour les réactions à plusieurs étapes, les ordres de réaction peuvent suggérer des chemins cinétiques, sous des conditions d'adsorption de Temkin, pour lesquers les pentes de Tafel seraient ambigües. Applications aux données expérimentales obtenues pour l'évolution de H2 sur Pt et Hg. Pour ce second métal, la considération de l'ordre reactionnel rénd improbable le mécanisme par décharge de l'ion H2+, comme l'indique aussi le facteur de séparation H/D.
Zusammenfassung
Das Problem der Ableitung von elektrochemischen Reaktionsordnungen wird für Zwei- und Mehrstufenreaktionen diskutiert, speziell für Bedingungen bei welchen der Isothermentyp (z.B. Langmuir oder Tempkin), welcher die Absorption der elektrochemisch gebildeten Produkte (z.B. H, OH und O) beschreibt, sich mit dem Bedeckungsgrad ändern kann.
In Mehrstufenreaktionen können die Reaktionsordnungen zur Unterscheidung von kinetischen Reaktionswegen unter Tempkin-Bedingungen führen, wo Tafel-Steigungen mehrdeutig sein können. Die Reaktionsordnungen hängen bei der Sauerstoff-Abscheidungsreaktion ebenfalls von den relativen Bedeckungen durch die gewöhnlich in Betracht gezogenen Zwischenprodukte O und OH ab.
Es wird Bezug, genommen auf experimentelle Werte für die Wasserstoffabscheidung an Platin und Quecksilber. Für das letztere Elektrodenmetall führen Reaktionsordnungs-Betrachtungen dazu, den H2+-Ionen-Entladungsmechanismus als unwahrscheinlich anzusehen, auf was auch H/D-Trennfaktoren-Berechnungen hindeuten. Man zeigt, dass der langsame H2+-Ionen-Neutralisations-Mechanismus zu diagnostisch unterschiedlichen Ergebnissen führt gegenüber der früher angenommenen Atom + Ion-Desorptionsstufe, wenn das H2+-Ion chemiesorbiert und nicht im Gleichgewicht mit H2+-Ionen in der Lösung ist.
References (48)
- B.E. Conway
Trans. Roy. Soc. Canada
(1960) - R. Parsons
- K.J. VetterK.J. Vetter
Z. phys. Chem.
(1950) - A.N. Frumkin
Z. phys. Chem.
(1933) - O. Stern
Z. Electrochem.
(1924) - R. Parsons
- J.O'M. Bockris
J. Chem. Phys.
(1956)J.O'M. Bockris - J.O'M Bockris et al.
J. Phys. Chem.
(1961)J.O'M. Bockris et al.J. Electrochem. Soc.
(1952) - S. Levina et al.
Acta Phys.-Chim. URSS
(1937) - V. Bagotzki et al.
Zh. Fiz. Khim.
(1949)
Dokl. Akad. Nauk SSSR
Trans. Faraday Soc.
Canad. J. Chem.
J. Chem. Phys.
Trans. Faraday Soc.
Trans. Faraday. Soc.
Acta Phys.-Chim. URSS
Trans. Faraday Soc.
Zh. Fiz. Khim.
J. Phys. Chem.
J. Res. Inst. Catalys. Hokkaido
Sci. Pap. Inst. Phys. Chem. Res., Tokyo
J. Res. Inst. Catalys. Hokkaido
J. Phys. Chem.
Ber. Bunsenges
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Manuscript received 14 January 1964.