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Significant Progress in Advanced Magnesium based Nanocomposite Materials for Hydrogen Storage made by Prof. Jianxin Zou, Centre of Hydrogen Science, Shanghai Jiao Tong University

NOV 1,2021   

Recently, Prof. Jianxin Zou's team at the Centre of Hydrogen Science of Shanghai Jiao Tong University (SJTU) published their research work in the world-renowned journal ACS Nano on the utilization of MXenes to load nano sized magnesium hydride: "Nanoconfined and in Situ Catalyzed MgH2 Self-Assembled on 3D Ti3C2 MXene Folded Nanosheets with Enhanced Hydrogen Sorption Performances". Prof. Jianxin Zou is the sole corresponding author and PhD student Wen Zhu is the first author of the paper.

Magnesium hydride (MgH2) is a promising solid-state hydrogen storage material, which possesses high gravimetrical hydrogen storage density, low production cost, and considerable safety. However, its intrinsic high thermodynamic stability and slow hydrogen ab-/desorption kinetics severely restricts the scope of its application. "Nanoconfinement" has been considered as an effective approach to improve the performance of Mg-based hydrogen storage materials, such as enhancing their thermodynamic and kinetic performances. Conventional carbon matrix materials (e.g. activated carbon, carbon aerogels, carbon nanotubes, etc.) for "Nanoconfinement" could barely simultaneously retain both the high MgH2/Mg loading rates and excellent hydrogen ab-/desorption kinetics. Because of owning high specific surface areas, good chemical/physical stability, high thermal conductivity, and excellent catalytic effects, two-dimensional transition metal-carbon/nitride (e.g., MXenes) materials are considered as the ideal candidate for nanoconfinement of MgH2/Mg. However, due to the problems of interlayer stacking and oxidation caused by oxygen-containing chemical groups (-OH, -O, etc.) on the surface of MXenes, the utilization of MXenes loaded with MgH2 nanoparticles to improve their hydrogen storage performance has never been reported.

Fig. 1 (a-b) TEM images of the as-synthesized MgH2@Ti-MX, (c) isothermal

hydrogenation curves of MgH2@Ti-MX at different temperatures, (d) isothermal dehydrogenation curves of MgH2@Ti-MX at different temperatures.

In this study, Prof. Jianxin Zou's team adopted the electrostatic interaction between cetyltrimethylammonium bromide (CTAB) and Ti3C2Tx (MXene) to construct a three-dimensional folded structure, which could effectively suppress the interlayer stacking of MXenes. After annealing, the 3D folded Ti3C2Tx folded structure successfully served as a substrate that could homogeneously load MgH2 nanoparticles (Fig.1 a-b), and the resultant composite material (MgH2@Ti-MX) showed a high hydrogen storage capacity (4.1 wt%), fast hydrogen ab-/desorption kinetics at relatively low temperatures (Fig.1 c-d), and excellent cycling stability. For example, the 60MgH2@Ti-MX composite showed an onset hydrogen release temperature of 140 °C and was able to release approximately 3.0 wt% of hydrogen within 2.5 h at 150 °C, while demonstrated no significant decrease in hydrogen storage capacity and kinetic decay after 60 rapid hydrogen absorption and release cycles at 200 °C. It is worth noting that the hydrogen release temperatures are readily within the operating temperature range (80-200 °C) of high-temperature proton exchange membrane (HT-PEM) fuel cells, and therefore, the MgH2@Ti-MX hydrogen storage composite material can be integrated with the HT-PEM fuel cells to release hydrogen from low-grade waste heat generated in fuel cells, which shows promising applications in distributed power generation and fuel cell powered vehicles. In the whole composite system, Ti-MX not only provides a large number of confinement sites for Mg/MgH2 nanoparticles, but also exerts a significant catalytic effect on the hydrogen absorption and release of Mg/MgH2.

Fig. 2 (a) Typical HRTEM image of the 60MgH2@Ti-MX before electron beam radiation, (b−e) in situ HRTEM images showing the evolution of the microstructure upon hydrogen desorption induced by the electron beam irradiation, (f) XPS spectra of Ti 2P of Ti-MX and 60MgH2@Ti-MX at different states, and (g) schematic illustration of the proposed mechanism for the fast dehydrogenation.

Fig. 3 Schematic diagram of the hydrogen storage and release mechanism of MgH2@Ti-MX.

XRD, XPS, TEM, and in-situ HRTEM analyses (Fig. 2) further suggested that the in-situ generation of TiH2 nanophases at the MgH2(Mg)/Ti-MX interface played the key role in the hydrogen absorption and release processes. Under the electron beam irradiation, MgH2 decomposes to release hydrogen firstly in the vicinity of TiH2 nanodomains and then gradually expanding to the whole particle, and meanwhile, TiH2 gradually decomposes into TiH and Ti. Under the combined effects of "nanoconfinement" and "in-situ nanocatalysis" (Fig. 3), the MgH2@Ti-MX hydrogen storage composite material demonstrates excellent hydrogen storage performances. In summary, this work not only provides a strategy to enhance the hydrogen storage performance of MgH2, especially reducing its hydrogen release temperature, but also enables an insight for implementing "nanoconfinement" effect in other energy storage materials.

This work was supported by the Centre of Hydrogen Science at Shanghai Jiao Tong University, the National Natural Science Foundation of China, Shanghai Municipal Science and Technology Commission, and Shanghai Municipal Education Commission.


Paper link: https://pubs.acs.org/doi/abs/10.1021/acsnano.1c08343

Source: Centre of Hydrogen Science, Shanghai Jiao Tong University

800 Dongchuan Road, Minhang District, Shanghai, China Tel: +86-21-3420-3098