On the Common Ground of Thermodynamics and Kinetics: How to Pin Down Overpotential to Reversible Metal Hydride Formation and the Complete Ideal Gas Theory of Reversible Chemical Hydrogen Storage

20 January 2021, Version 3
This content is a preprint and has not undergone peer review at the time of posting.


Ti-doped NaAlH4 requires at 125 °C for [AlH4] formation more than twice the equilibrium pressure; while it is straightforward to relate this conditional surplus in hydrogenation pressure respective chemical potential to kinetic hindrance, it appears strange that this matter has not been duly theoretically addressed in literature to this day. The interest in identifying such overpotentials is not of purely academic interest but touches a problem of very practical significance as the maximum applied pressure is an important threshold to metal hydride tank design. A theory-based tool would be a resource-efficient complement or even alternative to PCI measurements. This paper tracks the formation overpotential issue down to its root and outlines a simple yet accurate general method based on Arrhenius and van’t Hoff data. Rather unexpectedly, the result is also the final missing piece towards a comprehensive understanding of reversible chemical hydrogen storage with regard to attainable hydrogen storage capacity.


metal hydrides
reversible reactions
hydrogen storage
hydrogen storage capacity
equilibrium thermodynamics
Kinetic analysis
Thermodynamic Modeling
Thermodynamics analyses
sodium alanate

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