Interface reactions and stability of a hydride composite (NaBH4 + MgH2)

• Published in: Physical chemistry chemical physics : PCCP Vol. 14; no. 23; pp. 836 - 8368
• Main Authors: Kato, Shunsuke, Borgschulte, Andreas, Bielmann, Michael, Züttel, Andreas
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 21.06.2012
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Surface physical chemistry; Hydrogen; Enthalpy; In situ; Entropy; Hydrides; X ray; Review; Composite material; Mechanism; Thermodynamics; Photoelectron spectrometry; Interface reaction; Composition; Stability; Thermodesorption; Desorption; Equilibrium; Sorption; Adsorption; Isotherm; Kinetics; Thermodynamic properties; Comparative study; Interface; X-ray photoelectron spectra
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c2cp23491b

The use of the interaction of two hydrides is a well-known concept used to increase the hydrogen equilibrium pressure of composite mixtures in comparison to that of pure systems. The thermodynamics and reaction kinetics of such hydride composites are reviewed and experimentally verified using the example NaBH 4 + MgH 2 . Particular emphasis is placed on the measurement of the kinetics and stability using thermodesorption experiments and measurements of pressure-composition isotherms, respectively. The interface reactions in the composite reaction were analysed by in situ X-ray photoelectron spectroscopy and by simultaneously probing D 2 desorption from NaBD 4 and H 2 desorption from MgH 2 . The observed destabilisation is in quantitative agreement with the calculated thermodynamic properties, including enthalpy and entropy. The results are discussed with respect to kinetic limitations of the hydrogen desorption mechanism at interfaces. General aspects of modifying hydrogen sorption properties via hydride composites are given. The hydrogen desorption pathway of the reactive hydride composite is determined by the thermodynamic parameters, i.e. the reaction enthalpy Δ H , the reaction entropy Δ S , and the migration of Mg at the interfaces.