
        Metal hydrides, with their inherently high gravimetric and volumetric densities, present a compelling platform for hydrogen storage for mobile applications. However, several fundamental barriers have persistently impeded technological progress. This perspective provides an overview of the current hurdles plaguing metal hydride technology and the novel approaches recently adopted that may potentially surmount these challenges. In particular, nanocomposites, a homogenous matrix of two or more components synergistically integrated for enhanced material performance, is emerging as a new and promising class of material for hydrogen storage. This perspective highlights the potential of nanocomposites, specifically magnesium nanocomposites, for hydrogen storage. First, the existing challenges of metal hydrides are reviewed, followed by the progress achieved thus far by metal hydride size reduction to the nanoscale, and incorporation in a matrix material. Lastly, a novel nanocomposite synthesized by confining magnesium nanocrystals within a gas-selective polymer matrix is highlighted and the potential for improvement is discussed. This metal-polymer nanocomposite holds great promise as a general approach for future work on hydrogen-storage composites, as it simultaneously provides air-stability, high hydrogen storage density, and rapid hydrogenation kinetics.
