Switching the thermodynamics of MgH2 nanoparticles through polystyrene stabilisation and oxidation

Abstract

Magnesium is a promising material for hydrogen storage purposes; however, modifying the thermodynamic properties of the magnesium/hydrogen reaction remains important for practical application. Herein, we report an exciting finding that allows switching the thermodynamic properties of polystyrene stabilised magnesium nanoparticles via simple exposure to air. The magnesium nanoparticles stabilised with polystyrene were synthesised by direct hydrogenolysis of di-n-butylmagnesium. Polystyrene was found to significantly influence the nucleation and growth process leading to nanoparticles of ∼100 nm with thermodynamic properties similar to that of bulk magnesium. However, upon partial oxidation and hydrogen cycling, these nanoparticles were found to undergo a significant morphological reconstruction and particle size reduction leading to a drastic shift in thermodynamic properties with both enthalpy and entropy decreasing to 52.3 ± 3.2 kJ mol⁻¹ H₂ and 101.3 ± 4.5 J mol⁻¹ K⁻¹ H₂, respectively. Such a shift in thermodynamics demonstrates the possibility of tuning the thermodynamics of magnesium through the use of appropriate external factors such as partial oxidation while maintaining a reasonable storage capacity.