The Thermodynamic Way of Assessing Reversible Metal Hydride Volume Expansion: Getting a Grip on Metal Hydride Formation Overpotential

Abstract

<p>The relative volume expansion of reversible metal hydride crystals upon formation is determined by means of the van’t Hoff reaction entropy and STP ideal gas parameters, the development of this approach leads to a general method for calculating metal hydride single-crystal density. These results allow highlighting the pressure requirement to hydride phase formation, shown by the example of Ti-NaAlH<sub>4</sub>.</p>

A Study of K/Ti-co-doped NaAlH4 on Thermodynamic Tailoring, Surplus Hydrogen Amount and Metal Hydride Molar Volume

“…It is reasonable to relate the effects caused by KH-doping with the next stable mixed alanate K 2 NaAlH 6 , 9 as KNa 2 AlH 6 is instable. 11,12 Its density is calculated by the entropy method, 10 on basis of the data of SØRBY et al, 13 as shown in equations 3a to 3c; the required NaH and Al densities base on Römpp's chemistry lexicon, 14,15 those of KH on data provided by American Elements. The doping effect in the sorbent is indirectly determined via gas phase thermodynamics: starting from a gas volume at IUPAC standard temperature and pressure (STP), introducing the sorbent phase entails hydrogen absorption respective hydride formation.…”

A Study of K/Ti-co-doped NaAlH₄ on Thermodynamic Tailoring, Surplus Hydrogen Amount and Metal Hydride Molar Volume

“…It is reasonable to relate the effects caused by KH-doping with the next stable mixed alanate K 2 NaAlH 6 , 9 as KNa 2 AlH 6 is instable. 11,12 Its density is calculated by the entropy method, 10 on basis of the data of SØRBY et al, 13 as shown in equations 3a to 3c; the required NaH and Al densities base on Römpp's chemistry lexicon, 14,15 those of KH on data provided by American Elements. The doping effect in the sorbent is indirectly determined via gas phase thermodynamics: starting from a gas volume at IUPAC standard temperature and pressure (STP), introducing the sorbent phase entails hydrogen absorption respective hydride formation.…”

“…A work primarily concerned with metal volume expansion upon hydride formation shows the conditional threshold pressure to hydride phase formation being given by the relation of equation 1, derived by means of the ideal gas law for the exemplary problem of [AlH 4 ]-formation in Ti-NaAlH 4 . 10 p > 4005 V m, NaAlH4 bar cm 3 (mol…”

“…This principle enables the assessment of metal volume expansion upon hydride formation on the sole basis of van't Hoff data as well as identifying the pressure requirements to the formation of a distinct hydride phase. 10 However, the principle reaches further as it must ultimately allow insight into how doping respective thermodynamic tailoring effects materialize in the sorbent phase: This paper examines that relation between dopant, sorbent phase molar volume and surplus hydrogen amount by the example of K/Ti-co-doped NaAlH 4 .…”