Assessing the Performance of Transition Metals (M = Hf, Ti, and Zr) Decorated Silicon Carbide Nanotubes (M@SiCNTs) for Hydrogen Storage Applications: Insights from Theoretical Calculations

Abstract

This study conducted a thorough evaluation of the hydrogen storage capabilities exhibited by silicon carbide nanotubes (SiCNTs) functionalized with transition metals (Ti, Hf, and Zr). The investigation utilized dispersion-corrected D3(BJ) density functional theory (DFT) computational methods at the B3LYP/ def2svp level of theory. The primary objective was to evaluate the potential of metal-decorated nanotubes for efficient molecular hydrogen storage while also examining the impact of transition metals as adsorption sites. The electronic characteristics of the pristine SiCNT, featuring an energy gap of 3.447 eV, underwent significant improvement upon decoration with specific metals (Ti@SiCNT, Zr@SiCNT, and Hf@SiCNT). The resulting energy values were 2.419, 1.559, and 1.875 eV, respectively. We further investigated the adsorption energy and hydrogen storage capacity of Ti@SiCNT, Zr@SiCNT, and Hf@SiCNT in the adsorption process of the nH 2 (n = 1−4) molecule. The adsorption energies varied from −0.245 to 0.375 eV, falling well within the hydrogen storage material range suggested by the US Department of Energy. This research contributes valuable insights into the potential of transition metal-functionalized SiCNTs as promising candidates for hydrogen storage applications. As hydrogen molecules were stepwise adsorbed, the adsorption energy followed the order of Ti > Zr > Hf, highlighting Ti and Zr's superior performance in multiple hydrogen adsorption scenarios. To assess hydrogen storage capacity and release, gravimetric analysis, desorption temperatures, and energies were considered. The average desorption energies were calculated as −3.544, −3.324, and −3.537 eV for 4H 2 _Ti@SiCNT, 4H 2 _Zr@SiCNT, and 4H 2 _Hf@SiCNT, respectively. As additional hydrogen molecules were removed, the desorption energy became more negative, indicating a greater favorability for hydrogen release across all systems. Based on the calculated adsorption energy, electronic properties, desorption energy, and weight percent of the nanomaterials, which align with DoE standards, it can be concluded that the studied materials exhibit highly promising attributes for hydrogen storage applications.