Thermodynamic properties of hydrogen in quasi-two-dimensional vanadium lattices

The solubility and thermodynamics of hydrogen in quasi-two-dimensional vanadium lattices have been investigated. The quasi-two-dimensional character of the vanadium lattices were obtained by growing alternating layers of molybdenum and vanadium in Mo/V superlattice structures. The hydrogen solubility was found to be higher in the thin V layers than in bulk vanadium. The enthalpy change, Delta H_H, reached a value of -0.42 eV per H atom after a steep increase from the infinite-dilution limit (-0.28 eV per H atom). The entropy change, Delta S_H, is found to decrease for the thin V layers compared to bulk vanadium for hydrogen concentrations up to H/V=0.2. Above 0.2, Delta S_H reached the bulk values.