We tune the thermodynamics of hydrogen absorption in Mg by means of elastic clamping. The loading isotherms measured by hydrogenography show that Mg films covered with Mg-alloy-forming elements, such as Pd and Ni, have hydrogen plateau pressures more than 2 orders of magnitude higher than bulk Mg at the same temperature. An elastic model allows us to interpret the Mg thickness dependence of the hydrogen plateau pressure. Our results suggest an alternative route for the development of new hydrogen storage materials with optimized thermodynamic properties.

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We investigated the influence of the substrate on the thermodynamic properties of metal hydride thin films by hydrogenography, using PdH_x as a model system. After appropriate hydrogen cycling, reproducible hydrogenation properties are found at the same equilibrium pressure for all substrates studied. Comparing these thin films with free-standing films-measured both by hydrogenography and by Sievert's method-we find a very similar behavior. Hence, thin films can be used to study the hydrogenation behavior of the corresponding bulk materials.

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Hydrogenography is a new optical thin film combinatorial method that follows hydrogenation and determines its associated thermodynamic properties. Due to clamping to the substrate, stresses generated in thin films are larger than in bulk. This must be taken into account for a comparison between these two types of systems. In this article, we follow the microstructure, surface morphology and in-plane stress changes of thin polycrystalline PdH_x films upon several hydrogen ab/desorption cycles and correlate them to the evolution in shape and hysteresis of pressure-optical transmission isotherms (PTIs) recorded by hydrogenography. The in-plane stress in the first instance is relaxed inhomogeneously by buckling, and a more complete, homogeneous relaxation is only reached after the creation of a buckle-and-crack network that is the two-dimensional analogue of bulk decrepitated grains. This sequence of changes is clearly visible in the PTIs, demonstrating another useful facet of hydrogenography for characterizing metal-hydrogen systems.

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A multisite lattice gas approach is used to model pressure-optical- transmission isotherms (PTIs) recorded by hydrogenography on Mgy Ti1-y Hx sputtered thin films. The model reproduces the measured PTIs well and allows us to determine the chemical short-range order parameter s. The s values are in good agreement with those determined from extended x-ray absorption fine structure measurements. Additionally, the PTI multisite modeling yields a parameter L that accounts for the local lattice deformations with respect to the average Mgy Ti1-y lattice given by Vegard's law. It is thus possible to extract two essential characteristics of a metastable alloy from hydrogenographic data.@en