Enhanced hydrogen desorption properties of magnesium hydride by coupling non-metal doping and nano-confinement

摘要

Magnesium hydride (MgH_2) offers excellent capacity to store hydrogen, but it suffers from the high desorption temperature (＞283℃ for starting release hydrogen). In this work, we calculated the hydrogen desorption energy of Mg_(76)H_(152) clusters with/without non-metal dopants by density functional theory method. Phosphorus (P), as identified as the best dopant, can reduce the reaction energy for releasing one hydrogen molecule from 0.75 eV (bulk MgH_2) to 0.20 eV. Inspired by the calculation, P-doped ordered mesoporous carbon (CMK-3) was synthesized by one-step method and employed as the scaffold for loading MgH_2 nanoparticles, forming MgH_2@P/CMK-3. Element analysis shows that phosphorus dopants have been incorporated into the CMK-3 scaffold and magnesium and phosphorus elements are well-distributed in carbon scaffold hosts. Tests of hydrogen desorption confirmed that P-doping can remarkably enhance the hydrogen release properties of nanoconfined MgH_2 at low temperature, specifically ～1.5wt. % H_2 released from MgH_2@P/CMK-3 below 200 ℃. This work, based on the combination of computational calculations and experimental studies, demonstrated that the combined approach of non-metal doping and nano-confinement is promising for enhancing the hydrogen desorption properties of MgH_2, which provides a strategy to address the challenge of hydrogen desorption from MgH_2 at mild operational conditions.