Inorganic Chemistry

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

Roland Hermann Pawelke FOTEC Forschungs- und Technologietransfer GmbH

Abstract

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.

Version notes

V3: The discussion and the conclusion have been shortened so the manuscript is now 3000 words (Ockham´s razor).

Content

Thumbnail image of V3_Thermodyn_Overpotential_Manuscript.pdf
download asset V3_Thermodyn_Overpotential_Manuscript.pdf 1 MB [opens in a new tab]

Supplementary weblinks