Activity-Tuning of Supported Co–Ni Nanocatalysts via Composition and Morphology for Hydrogen Storage in MgH2

Xiaoli Ding,Hongfei Ding,Cuili Xiang,Qingan Zhang,Yun Song,Yongtao Li

doi:10.3389/fchem.2019.00937

Abstract

Developing cheap metal nanocatalysts with controllable catalytic activity is one of the critical challenges for improving hydrogen storage in magnesium (Mg). Here, it is shown that the activity of graphene-anchored Co–Ni nanocatalysts can be regulated effectively by tuning their composition and morphology, which results in significantly improved hydrogen storage in Mg. The catalytic activity of supported Co–Ni nanocatalysts is demonstrated to be highly dependent on their morphology and composition. When Ni was partly substituted by Co, the shape of these nanocatalysts was changed from spherical to plate-like, thus corresponding to a decrease in activity. These alterations intrinsically result in enhanced hydrogen storage properties of MgH2, i.e., not only does it exhibit a decreased peak desorption temperature but also a positive change in the initial activation for sorption. The results obtained provide a deep understanding of the tuning of catalytic activity via composition and morphology and further provide insights into improving hydrogen storage in Mg-based materials.

Highlights

Magnesium (Mg)-hydrides are considered promising hydrogen-storage materials due to their high theoretical hydrogen capacity of ∼7.6 wt%, low-cost, and good reversibility (Cao et al, 2015; Liu X. et al, 2015; Ding et al, 2017; Møller et al, 2017; Schneemann et al, 2018), even as compared to other high H-content complex hydrides
As solid-state hydrogen storage media, their application is still hampered by a large reaction enthalpy of ∼76 kJ· mol−1 H2 for desorption (Si et al, 2018), high activation barrier, and slow hydrogen atom diffusion (Paskevicius et al, 2010), which result in higher desorption temperature and sluggish kinetics
These results strongly suggest that the Co-Ni nanocatalysts can cause a significant enhancement in desorption and that the introduction of Co deteriorates the catalytic effect of Ni

Summary

Introduction

Magnesium (Mg)-hydrides are considered promising hydrogen-storage materials due to their high theoretical hydrogen capacity of ∼7.6 wt%, low-cost, and good reversibility (Cao et al, 2015; Liu X. et al, 2015; Ding et al, 2017; Møller et al, 2017; Schneemann et al, 2018), even as compared to other high H-content complex hydrides The dependence of the hydrogen sorption properties of MgH2 on the morphology, composition, and activity of supported nanocatalysts has not been established.

Results

Conclusion