Effect of Pt clusters on hydrogen adsorption behaviors of cup-stacked carbon nanotubes: a DFT study

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.