Hydrogen is an alternative future energy carrier. However, the drawback associated with its compact storage is still a scientific and technological challenge. Metal hydrides offer a suitable combination weighing both safety and cost. In particular, magnesium hydride (MgH2) is an ideal candidate with a high gravimetric capacity of 7.6 wt %, low cost, and abundance in nature. However, the high stability of Mg-H is a significant limitation for practical application. Although, recently, interface and strain induced-modification is proposed as a strategy to reduce the MgH2 stability in Mg nanoalloys. Nonetheless, they are not well understood in Mg nanoalloys. Moreover, understanding and interpreting these effects on a single nanoparticle (NP) from bulk measurement techniques is a significant problem. Since the effect of averaging and low spatial resolution plagues the collected data, it prevents in resolving the intrinsic impact of size, strain, and interface on a structure-property relationship of single NPs. Therefore, we propose (i) to use STEM-EELS with insitu gas holder(H2) at operando conditions in an aberration-corrected microscope to unravel the metal-hydride phase transition of individual Mg nanoalloys. (ii) apply state of the art iDPC and 4D-STEM to resolve the role of the interface and precise measurement of strain to identify the effect of destabilization on individual Mg nanoalloys. Moreover, advanced training on insitu TEM at DTU, iDPC, and 4D-STEM techniques @secondment and other transferable skills will diversify my competence further and positively impact my future career prospects and networking across Europe. The infrastructure/expertise at DTU, my experience, and knowledge in NP synthesis and hydrogen storage, along with the DTU support office, will ensure the successful implementation of the proposal. Finally, disseminating research and communication to the stakeholders and the general public will ensure the maximum impact of the project's results.