The Master Key to the Problem of Reversible Chemical Hydrogen Storage is 12 kJ (mol H2)-1

Abstract

<p>This article outlines a potent theoretical formalism illuminating the boundaries to reversible solid hydrogen storage based on the ideal gas law and classic equilibrium thermodynamics. A global picture of chemical reversible hydrogen sorption is unveiled including a thermodynamic explanation of partial reversibility. This is utilized to elucidate a multitude of issues from metal hydride chemistry: Highlights are why the substitution of a mere 4 mol % Na by K in Ti-doped NaAlH<sub>4</sub> raises the reversible storage capacity by 42 % and elaboration of the reaction pathway in (Rb/K)H-doped Mg(NH<sub>2</sub>)<sub>2</sub>/2LiH. The findings of this work allow for a change of paradigm towards the understanding of reversible chemical energy storage and provide a hitherto missing tool of ample analytic and predictive power, complementary to experiment.</p>

See the Forest, Ignore the Trees: A Minimalist Approach to Metal Hydride Tank Modelling Maximizing General Practical Usability

“…By outcome, this is an easily passable shortcut to a result that otherwise is obtainable only by an indefinitely more complex transient simulations of the temperature distribution inside the metal hydride bed. The deeper implications of the constraining role of equilibrium thermodynamics towards the thermodynamic domain of metal hydride hydrogen storage have been outlined recently; 8 this article does a job in kind for kinetics. With regard to the under-valued role of the all-governing principle of self-regulation in the perception of the subject to date, the way how the problem is perceived, understood and addressed may be more important than the actual result itself.…”

“…Hydrogen at typical metal hydride sorption reaction conditions (T > 300 K, p ≤ 100 bar) shows near-ideal behaviour and the self-constraining nature is the Leitmotif to reversible chemical hydrogen storage: On one hand, it provides a thermodynamic reason for the otherwise ill-explainable phenomenon of partial reversibility of metal hydrides. 8 Thermodynamics are universal and there is a further-reaching fundamental significance towards reversible chemical energy storage respective reversible mass transfer due to the normative role of hydrogen electrode potentials in electrochemistry. 9 At the other hand, the same principle has a dominant effect on the kinetics of hydrogen release inside a metal hydride tank.…”

A Simple Method for Identifying the Thermodynamic Limits to the Specific Energy of Electrochemical Energy Storage Systems

“…The Nernst equation bases on the transfer of charge, not mass; yet since it measures by SHE potential excursions, it can be by principle calibrated for the maximum reversible mass transfer on the basis of previous work. 1 Starting from equation 1, that objective is achievable in five-steps.…”

“…Since 1 mole of hydrogen provides 2 moles of electrons, the irreducible voltage change E 1%°° associated with the ideal reversible transfer of 1 % w/w nuclear particle mass figures to -0.06235 (7) V as shown on equation 9 (taking up the original figures from the reasoning towards µ 1%°° at T° = 273.15 K) 1 .…”

“…The successful unveiling of the invisible yet manifest empirical boundaries to reversible chemical hydrogen sorption by means of fundamental thermodynamics entails the conclusion that not only reversible hydrogen but all reversible mass transfer is limited by the same thermodynamic principle. 1 The initial concept bases on ideal hydrogen transfer in a twophase gas-sorbent system which is a sound theoretical base for tackling the issue because of two reasons: first reason, the ideal gas law approximates hydrogen behaviour well at typical metal hydride sorption reaction conditions. Second reason, the ideal gas law makes for a suitable theoretical base describing the ultimate thermodynamic limits because there cannot be a less hindered mass transfer across phase boundaries.…”