In this paper, the formation and characterization of Pt2, Pt3 as well as Pt4 atomic clusters in cup-stacked carbon nanotubes (CSCNTs) are evaluated by DFT to examine the adsorption capacity under the clusters. The results show that the Pt clusters move toward the bottom edge or form rings in the optimized stable structure. Pt far from the carbon substrate possesses more active electrons and adsorption advantages. The three clusters can adsorb up to 17, 18, and 16 hydrogen molecules. Loading metal clusters at the bottom edge maintains a relatively good adsorption property despite the low binding energy through comparative studies. The adsorption capacity does not increase with the number of Pt for metal aggregation reducing the hydrogen adsorption area thus impacting the hydrogen storage ability and the aggregation phenomenon limiting the action of Pt metal. During adsorption, chemisorption occurs only in the Pt2 cluster, while multiple hydrogen molecules achieve physiochemical adsorption in the Pt3 and Pt4 clusters. Compared with the atomic loading of the dispersion system in equal quantities, the dispersion system features higher molecular stability and can significantly reduce the energy of the carbon substrates, providing more sites for hydrogen adsorption in space.

Effect of Pt clusters on hydrogen adsorption behaviors of cup-stacked carbon nanotubes: a DFT study
    Abstract
        Graphical abstract
    1 Introduction
    2 Computational details
    3 Results and discussion
        3.1 Growth and properties of Pt-clusters on CGL
        3.2 Adsorption of nH2 on CGL-Pt clusters
        3.3 Comparative analysis of H2 adsorption on clusters and dispersed atoms
    4 Conclusions
    Acknowledgements 
    References

• Yongxin Wang(School of Environment, State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, People’s Republic of China)
• Jing Ding(School of Environment, State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, People’s Republic of China)
• Fengxia Deng(School of Environment, State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, People’s Republic of China)
• Huanpeng Liu(School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, People’s Republic of China)