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V1_AEP_Kinetics_manuscript.pdf (1.12 MB)

A Transition State Theory Perspective on the Relation of Reversible Metal Hydride First-Order Kinetics to Equilibrium Thermodynamics

preprint
submitted on 02.01.2021, 23:06 and posted on 04.01.2021, 13:26 by Roland Hermann Pawelke
In the event of hydrogen desorption from reversible metal hydrides, equilibrium thermodynamics exert a rate-limiting effect: if system pressure reaches equilibrium pressure, the reaction rate becomes zero. This is usually dealt with by an empiric term of either polynomial or logarithmic nature to first-order kinetics. This paper approaches the matter from a transition state theory perspective, combining the classic Eyring-Polyani equation with insights on reversible metal hydride chemical overpotential for scrutinizing the relation of Arrhenius first-order kinetics to van’t Hoff equilibrium pressure. The outcome, tested for the example of 4 mol % Ti-doped NaAlH4, suggests theoretical coherency and provides a method for identifying the factor by which an experiment deviates from ideal first-order kinetics. Adopting Arrhenius-Eyring-Polyani first-order kinetics as baseline for modelling kinetic behaviour of metal hydride sorption reactions not only covers a blind spot in the Arrhenius approach but creates a standard for result comparability.

Funding

European Space Agency grant 4000105330/12/NL/CLP

European Defence Agency grant A-1341-RT-GP

History

Email Address of Submitting Author

roland.pawelke@hushmail.com

Institution

FOTEC Forschungs- und Technologietransfer GmbH

Country

Austria

ORCID For Submitting Author

0000-0002-6944-2240

Declaration of Conflict of Interest

There are no conflicts of interest to declare.

Version Notes

V1: Initial version.

Exports