DFT study on Pt-decorated (9,0) single-walled carbon nanotubes: hydrogen adsorption and sensing

Abstract

Context

Carbon nanotubes are commonly used for hydrogen detection. However, pure carbon nanotubes exhibit limitations in this application. The Pt-decorated carbon nanotubes are considered to have the potential of hydrogen adsorption and sensing. The adsorption of H₂ on the outside wall of (9,0) single-walled carbon nanotubes (SWCNT(9,0)) were studied using density functional theory (DFT) calculations. The tiny adsorption energy (0.023 eV) implied a high barrier of the adsorption of H₂ on the outer wall of pure SWCNT, so metal atom (Pt, Fe, Ni) was used to decorate SWCNT. The result showed that Pt-SWCNT(9,0) exhibited the highest hydrogen adsorption capacity (0.791 eV) and meanwhile as the most stable catalyst structure. The hydrogen molecule underwent adsorption and dissociation on all three systems. Furthermore, the electronic structures of Pt-SWCNT(9,0) and H₂/Pt-SWCNT(9,0) were discussed. It is interesting that the interaction between Pt atom and SWCNT(9,0) changed the electronic state of carbon nanotubes and enhanced the adsorption energy of H₂. In the configurations involving multiple H₂ molecules, most molecules exhibited physical adsorption on Pt-SWCNT(9,0), whereas only one molecule was chemical adsorption. The electron transfer of Pt was promoted with the enhancement of orbital hybridization. In addition, the HOMO–LUMO gap (E_g) increased and the conductivity (σ) of Pt-SWCNT(9,0) changed after the adsorption of H₂, which was according with the experimental studies. Our calculations reveal that Pt-decorated SWCNT(9,0) has the capabilities of hydrogen adsorption and sensing. In the future, the design of the material structure will tune the conductivity for better H₂ sensor.

Methods

All DFT calculations were performed using the Gaussian 16 software. GaussView 6.0 software was utilized to visualize the molecular models, molecular orbitals, and electrostatic potential (ESP) of all relevant species. Multiwfn 3.8 software was utilized to plot localized orbital locator (LOL) graph and electron localization function (ELF) distribution maps. The DFT method was the B3LYP-D3BJ. The 6-31G(d,p) basis set was utilized for the C, H atoms, and Lanl2dz basis set for the Pt, Fe, and Ni atoms. No extraneous computational parameters were used in the structure optimization and frequency calculation that could affect calculation accuracy in the gas phase.