First-principles quantum insights into phonon dynamics and thermophysical potential of MgH2 and MgH2:Mo for enhanced thermoelectricity and hydrogen energy applications

Abstract

Amidst the growing world population and depletion of conventional energy sources and their harmful impact, there is an urgent need for a sustainable energy-paradigm shift from fossil fuels to renewable and alternative clean energy sources. In this context, hydrogen and thermoelectric energy sources hold great promise and could be the best substitute for fossil fuels. However, hydrogen generation, storage, and transport under ambient conditions remain challenging due to high costs and safety concerns. The competitive relation between thermoelectric properties is a big hindrance in harnessing the thermoelectric materials of high thermal efficiency. This urges scientists to search for energy-efficient thermoelectric and hydrogen-storage solid materials, with enormous ability to convert thermal energy into electricity and store and release hydrogen on demand. Despite being a potential hydrogen storage material owing to high hydrogen storage density, poor thermodynamic kinetics of magnesium hydride (MgH₂) with high stability under normal conditions hinder its domestic and industrial-scale usage. The possible solutions are alloying, nanostructuring, clustering, and doping of MgH₂ with transition metals. This study reports on the investigation of a systematic analysis on phonon dynamics, thermodynamic, and thermoelectric properties of MgH2 and Mg $H_2$:Mo(10 wt% Mo), employing the density functional theory within the generalized gradient approximation. The Quasi-harmonic Debye-Gruneisen model is executed to compute thermodynamic properties, while the Boltzmann theory is employed to compute the key thermoelectric properties. Besides enhanced thermodynamic properties for (de)hydrogenation, the computed results yield a high thermoelectric performance with the figure of merit of order 1.2.