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

Abstract

Magnesium hydride (MgH 2) offers excellent capacity to store hydrogen, but it suffers from the high desorption temperature (>283 C 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 $1.5 wt. % H 2 released from MgH 2 @P/CMK-3 below 200 C. 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.

Carbon scaffold modified by metal (Ni) or non-metal (N) to enhance hydrogen storage of MgH2 through nanoconfinement

“…Accordingly, it is speculated that the observed improvement by the addition of N may come from the stabilization effect with the formation of N-Mg bonds, which has been supported by computational calculations. [49] Simultaneously, the introduced N atoms cover a part of unsaturated carbons (evidenced by XPS result, Figure 4d); as a result, Mg atoms bonded with unsaturated carbon are reduced as well and hydrogen released from Mg-C interface at low temperature becomes less. (Figure 7a-c) are analysed by using Jonhnson-Mehl-Avrami (JMA) theory, [50] the reacted fraction is given as function of time by β = 1-exp[-(kt) n ], where β is the reacted fraction, t is the desorption time, k = k(T) is the temperature dependent kinetic constant, and n is the JMA exponent (reaction order).…”

A review on design strategies for metal hydrides with enhanced reaction thermodynamics for hydrogen storage applications

“…In addition to metal‐based cationic additives, nonmetal‐based anionic additives have attracted attention for destabilizing metal hydrides . For instance, Yin et al employed the density functional theory (DFT) method to investigate the effect of F doping on the decomposition reaction thermodynamics of LiBH 4 .…”

“…They highlighted that the incorporation of N, which was highly electronegative, destabilized the metal hydride, resulting in the promotion of the thermodynamic properties of the metal hydride and the reduction of its dehydrogenation temperature. He et al investigated the hydrogen desorption properties of MgH 2 nanoclusters nanoconfined by P‐doped mesoporous carbon (CMK‐3) . The MgH 2 nanoparticles loaded into the P/CMK‐3 scaffold were bridged by the P dopant to form MgH 2 @P/CMK‐3.…”

“…In addition to metal-based cationic additives, nonmetal-based anionic additives have attracted attention for destabilizing metal hydrides. [85][86][87][88][89][90][91] For instance, Yin et al employed the density functional theory (DFT) method to investigate the effect of F doping on the decomposition reaction thermodynamics of LiBH 4 . 85 These calculations predicted that the substitution of H − by F − would reduce the reaction enthalpy for hydrogen release.…”

“…He et al investigated the hydrogen desorption properties of MgH 2 nanoclusters nanoconfined by P-doped mesoporous carbon (CMK-3). 88 The MgH 2 nanoparticles loaded into the P/CMK-3 scaffold were bridged by the P dopant to form MgH 2 @P/CMK-3. They observed that the dopant played a critical role in lowering the reaction energy for releasing 1 hydrogen molecule from 0.75 eV (pure MgH 2 ) to 0.20 eV (P-doped MgH 2 ).…”