Influence of the chemical potential on the hydrogen sorption kinetics of Mg2Ni/TM/Pd (TM = transition metal) trilayers

The optical switching from shiny metallic to black absorbing states of 30 nm Mg2Ni/50 nm TM/10 nm Pd (TM = Ti, V, Cr, Mn, Fe, Co, Ni, Pd) trilayer thin films upon hydrogenation is used to determine the hydrogen absorption/desorption kinetics at moderate H-2 pressure and room temperature. A strong correlation is observed between these kinetics and the enthalpies of solution of H in TM. A diffusion model based on chemical potentials of hydrogen in metals has been developed that agrees qualitatively with the experimental data, both from kinetics and hydrogen concentration profile points of view. The influences of the solution enthalpy and the diffusion coefficient of H in TM and that of the TM layer thickness are discussed with respect to this model. Finally, we conclude with potential applications of these trilayers, from optical hydrogen detection to reinvestigation of diffusion coefficients of H in TM.