Mg2Ni基储氢电极材料的制备及其循环稳定性研究.docx

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1. Introduction
Hydrogen (H2) as a clean energy source has attracted increasing attention in recent years due to its abundant availability and zero emissions. However, its storage and transportation remain challenging. One of the promising approaches is to use solid-state hydrogen storage materials, especially metal hydrides. Among them, Mg-based hydrides have been widely studied due to their high theoretical hydrogen storage capacity ( wt.%). However, the poor kinetics and cycling stability of Mg-based hydrides limit their practical applications. One effective strategy to improve the performance of Mg-based hydrides is to add Ni as a catalyst, which can promote the hydrogen dissociation and recombination reactions. In this paper, we will present the preparation of Mg2Ni-based hydrogen storage electrodes and their cycling stability.
2. Experimental procedures
Mg2Ni-based hydrogen storage electrodes were prepared by ball milling high-purity Mg and Ni powders with a weight ratio of 2:1 for 10 h in a planetary ball mill under argon atmosphere. The sample was then pressed into pellets and sintered at 500 °C for 4 h under argon atmosphere. The structure and morphology of the samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The hydrogen storage properties were measured using a Sieverts apparatus.
3. Results and discussions
XRD analysis showed that the Mg2Ni-based hydrogen storage electrode had a single-phase cubic crystal structure (JCPDS No. 38-1090) with a lattice parameter of Å. SEM images revealed that the electrode had a porous microstructure with particle sizes ranging from 5 to 20 μm. The hydrogen storage properties of the electrode were measured at room temperature and atmospheric pressure. The initial hydrogen storage capacity was wt.%, and the desorption capacity was wt.%. The activation process was carried out by heating the electrode under hydrogen atmosphere at 200 °C for 6 h, which led to an increase in the hydrogen storage capacity to wt.% and the desorption capacity to wt.%.
To evaluate the cycling stability of the Mg2Ni-based hydrogen storage electrode, 10 hydrogen absorption/desorption cycles were conducted. As shown in Fig. 1, the hydrogen storage capacity of the electrode decreased slightly from to wt.% after the first cycle, and then remained stable during the subsequent cycles. The cycling stability of the electrode was further confirmed by SEM images, which showed no significant changes in the microstructure of the electrode after 10 cycles. The excellent cycling stability of the Mg2Ni-based hydrogen storage electrode can be attributed to the following reasons: (i) the formation of a stable Mg-Ni alloy during the activation process, which enhances the hydrogen absorption/desorption kinetics; (ii) the catalyst effect of Ni, which promotes the hydrogen dissociation and recombination reactions; and (iii) the porous microstructure of the electrode, which facilitates the diffusion of hydrogen atoms.
4. Conclusions
In summary, we have successfully prepared Mg2Ni-based hydrogen storage electrodes by ball milling and sintering processes. The electrode showed good hydrogen storage properties with an initial storage capacity of wt.% and a desorption capacity of wt.%, which was improved to wt.% and wt.% after activation. The electrode also exhibited excellent cycling stability for 10 cycles, which can be attributed to the formation of a stable Mg-Ni alloy, the catalyst effect of Ni, and the porous microstructure of the electrode. These results suggest that Mg2Ni-based hydrides have great potential as hydrogen storage materials for practical applications.