skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Predicting reaction equilibria for destabilized metal hydride decomposition reactions for reversible hydrogen storage

Abstract

Reversible storage of hydrogen still remains one of the biggest challenges for widespread use of hydrogen as a fuel. Light metal hydrides have high hydrogen content but are typically too thermodynamically stable. Destabilization of metal hydrides is an effective way to improve their thermodynamics. First principles calculations have proven to be effective for screening potential destabilized reactions, but these calculations have previously been limited to examining approximations for reaction enthalpies. We have used density functional theory calculations to calculate the reaction free energy and van’t Hoff plots for a variety of potential destabilized metal hydride reactions. Our calculations suggest a multistage approach for efficiently screening new classes of metal hydrides prior to experimental studies.

Authors:
; ;
Publication Date:
Research Org.:
National Energy Technology Laboratory (NETL), Pittsburgh, PA, Morgantown, WV, and Albany, OR
Sponsoring Org.:
USDOE - Office of Fossil Energy (FE)
OSTI Identifier:
937584
Report Number(s):
DOE/NETL-IR-2007-071; NETL-TPR-1561
Journal ID: ISSN 1932-7447; TRN: US200819%%268
DOE Contract Number:
DE-FC36-05G015066
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry C; Journal Volume: 111; Journal Issue: 4
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; APPROXIMATIONS; FREE ENERGY; FUNCTIONALS; HYDRIDES; HYDROGEN; HYDROGEN STORAGE; STORAGE; THERMODYNAMICS; CHEMISORPTION; PENTACENE; SILICON; SORPTIVE PROPERTIES; MORPHOLOGY; ADSORPTION HEAT

Citation Formats

Alapati, S.V., Johnson, J.K., and Sholl, D.S. Predicting reaction equilibria for destabilized metal hydride decomposition reactions for reversible hydrogen storage. United States: N. p., 2007. Web. doi:10.1021/jp065117.
Alapati, S.V., Johnson, J.K., & Sholl, D.S. Predicting reaction equilibria for destabilized metal hydride decomposition reactions for reversible hydrogen storage. United States. doi:10.1021/jp065117.
Alapati, S.V., Johnson, J.K., and Sholl, D.S. Thu . "Predicting reaction equilibria for destabilized metal hydride decomposition reactions for reversible hydrogen storage". United States. doi:10.1021/jp065117.
@article{osti_937584,
title = {Predicting reaction equilibria for destabilized metal hydride decomposition reactions for reversible hydrogen storage},
author = {Alapati, S.V. and Johnson, J.K. and Sholl, D.S.},
abstractNote = {Reversible storage of hydrogen still remains one of the biggest challenges for widespread use of hydrogen as a fuel. Light metal hydrides have high hydrogen content but are typically too thermodynamically stable. Destabilization of metal hydrides is an effective way to improve their thermodynamics. First principles calculations have proven to be effective for screening potential destabilized reactions, but these calculations have previously been limited to examining approximations for reaction enthalpies. We have used density functional theory calculations to calculate the reaction free energy and van’t Hoff plots for a variety of potential destabilized metal hydride reactions. Our calculations suggest a multistage approach for efficiently screening new classes of metal hydrides prior to experimental studies.},
doi = {10.1021/jp065117},
journal = {Journal of Physical Chemistry C},
number = 4,
volume = 111,
place = {United States},
year = {Thu Feb 01 00:00:00 EST 2007},
month = {Thu Feb 01 00:00:00 EST 2007}
}
  • Hydrides of period 2 and 3 elements are promising candidates for hydrogen storage, but typically have heats of reaction that are too high to be of use for fuel cell vehicles. Recent experimental work has focused on destabilizing metal hydrides through mixing metal hydrides with other compounds. A very large number of possible destabilized metal hydride reaction schemes exist, but the thermodynamic data required to assess the enthalpies of these reactions are not available in many cases. We have used density functional theory calculations to predict the reaction enthalpies for more than 300 destabilization reactions that have not previously beenmore » reported. The large majority of these reactions are predicted not to be useful for reversible hydrogen storage, having calculated reaction enthalpies that are either too high or too low, and hence these reactions need not be investigated experimentally. Our calculations also identify multiple promising reactions that have large enough hydrogen storage capacities to be useful in practical applications and have reaction thermodynamics that appear to be suitable for use in fuel cell vehicles and are therefore promising candidates for experimental work.« less
  • Favorable thermodynamics are a prerequisite for practical H2 storage materials for vehicular applications. Destabilization of metal hydrides is a versatile route to finding materials that reversibly store large quantities of H2. First principles calculations have proven to be a useful tool for screening large numbers of potential destabilization reactions when tabulated thermodynamic data are unavailable. We have used first principles calculations to screen potential destabilization schemes that involve Sc-containing compounds. Our calculations use a two-stage strategy in which reactions are initially assessed based on their reaction enthalpy alone, followed by more detailed free energy calculations for promising reactions. Our calculationsmore » indicate that mixtures of ScH2 + 2LiBH4, which will release 8.9 wt.% H2 at completion and will have an equilibrium pressure of 1 bar at around 330 K, making this compound a promising target for experimental study. Along with thermodynamics, favorable kinetics are also of enormous importance for practical usage of these materials. Experiments would help identify possible kinetic barriers and modify them by developing suitable catalysts.« less
  • One of the challenges of implementing the hydrogen economy is finding a suitable solid H{sub 2} storage material. Aluminium (alane, AlH{sub 3}) hydride has been examined as a potential hydrogen storage material because of its high weight capacity, low discharge temperature, and volumetric density. Recycling the dehydride material has however precluded AlH{sub 3} from being implemented due to the large pressures required (>10{sup 5} bar H{sub 2} at 25 C) and the thermodynamic expense of chemical synthesis. A reversible cycle to form alane electrochemically using NaAlH{sub 4} in THF been successfully demonstrated. Alane is isolated as the triethylamine (TEA) adductmore » and converted to unsolvated alane by heating under vacuum. To complete the cycle, the starting alanate can be regenerated by direct hydrogenation of the dehydrided alane and the alkali hydride (NaH) This novel reversible cycle opens the door for alane to fuel the hydrogen economy.« less