In this experiment, we aim to investigate the density as well as the electronic, elastic and thermodynamic properties of hydrogen-bearing Fe-Si-alloys at pressures above 300 GPa and temperatures up to several thousands of degrees. Therefore, nuclear inelastic scattering (NIS) and powder x-ray diffraction (XRD) are planned to be used. Applying the NIS technique brings the advantage of studying the lattice dynamics in order to gain the thermodynamic sample characterization. The measured phonon density of states provides the Debye phonon average velocity (vD), which is necessary to calculate the compressional (vp) and shear velocity (vs) of the material, in combination with the density and bulk modulus obtained by XRD. The measurements and following calculations will allow us to refine the amount of hydrogen and silicon in the Earth’s core, to explain its observed seismic parameters.