Application of organic compounds to metal-hydrogen systems as a technique for improving sorption properties: A new class of hydrogen absorbers

Abstract

A technique for using organic materials to improve the sorption properties of magnesium-based hydrogen storage media is presented. Two approaches are possible. First, Mg 2Ni and SmMg 3 reversibly absorb hydrogen under more moderate conditions when they have been modified with various organic compounds (anthracene, phenanthrene, chrysene, perylene, naphthacene, phthalonitrile, tetracyanoethylene or chloranil). The hydriding behaviour of modified Mg 2Ni and SmMg 3 is associated with the formation of electron donor-acceptor (EDA) complexes by charge transfer between the alloy particles and the organic modifiers. The process of hydrogen uptake is explained by “hydrogen spill-over”, in which hydrogen species in an atomiclike form which have been activated at the EDA sites rapidly migrate to react with the adjoining alloy particles. Second, small solvated magnesium particles formed by clustering in low temperature organic matrices (tetrahydrofuran, benzene, pentane or ethyl ether) are exceptionally active and immediately begin to absorb hydrogen without requiring “activation”. The hydrogen sorption characteristics of these magnesium-organic compound systems are elucidated. The exceptional activity of these systems can be partially interpreted in terms of their structural geometry compared with that of pure magnesium. The organic matrix in which the magnesium atoms are dispersed and in which crystal growth proceeds has pronounced effects on the shape, size and catalytic properties of the particles formed.