The high capacity hydrogen storage material of Y-doped B40: A theoretical study

Structural transformation in Pd nanoclusters induced by Cu doping: an ADFT study

CONTEXT

Transition metal nanoparticles have gained great importance due to their promising applications in various fields such as energy, electronics, medicine, and agriculture. For these applications, materials with outstanding properties are currently required. Therefore, different strategies have been established to improve the properties of pure nanoparticles such as alloying, doping, and formation of composites. Among these strategies, doping is gaining great importance because it has been demonstrated that doped nanoparticles have better properties than pure nanoparticles. Therefore, it is essential to know the role of doping on the structures and properties of clusters with more than 16 atoms. Consequently, in this study, we propose a theoretical study of structures and properties focusing on pure Pd19, Cu-doped Pd18 (Pd18Cu), and Cu2-doped Pd17 (Pd17Cu2) nanoclusters and thus elucidate the role of Cu atoms on the structures and properties of larger doped Pd nanoclusters than those already presented in the literature. We have selected a nanocluster with 19 atoms since the most stable structure of this system is characterized by defined shapes such as octahedron or double-icosahedron.

METHODS

Ground state structures and properties of Pd19, Pd18Cu, and Pd17Cu2 nanoclusters were studied using the auxiliary density functional theory (ADFT), as implemented in the deMon2k code. For obtaining the ground state structures of Pd19, Pd18Cu, and Pd17Cu2 nanoclusters, several dozen initial structures were taken along Born-Oppenheimer molecular dynamics (BOMD) trajectories and subsequently optimized without symmetry restrictions. The optimizations were performed with the revised PBE functional in combination with TZVP-GGA for the Cu atoms and using an 18-electron QECP|SD basis set for the Pd atoms. Different energetic and electronic properties were calculated for the most stable structures of Pd19, Pd18Cu, and Pd17Cu2 nanoclusters. Interestingly, when the Pd nanocluster is doped with two Cu atoms (Pd17Cu2), there is a structural transition, because the most stable structures for Pd19 and Pd18Cu are icosahedral. While the Pd17Cu nanocluster is characterized for a double-icosahedral-base structure. The binding energy per atom increases when the Cu concentration in the nanoclusters increases. According to the HOMO-LUMO gap, the chemical reactivity of the nanoclusters tends to increase as the Cu content in the nanoclusters increases.

First-Principles Study of Titanium-Doped B7 Cluster for High Capacity Hydrogen Storage

The geometrical structure, stability, electronic properties, and hydrogen storage capabilities of a titanium-doped B7 cluster was calculated using density functional theory computations. The results show that the TiB7 cluster is predicted to be stable under near-ambient conditions based on an ab initio molecular dynamic simulation. The transition state analysis found that the H2 molecule can dissociate on the TIB7 cluster surface to form a hydride cluster. The Ti atom within the TiB7 cluster demonstrates an impressive capacity to adsorb up to five H2 molecules, achieving a peak hydrogen storage mass fraction of 7.5%. It is worth noting that the average adsorption energy of H2 molecules is 0.27-0.32 eV, which shows that these configurations are suited for reversible hydrogen storage under mild temperature and pressure regimes. In addition, calculations found that both polarization and hybridization mechanisms play pivotal roles in facilitating the adsorption of H2 molecules onto the TiB7 cluster. Our research results show that the TiB7 cluster has potential for hydrogen storage applications under near-ambient conditions.

Spectral properties of B40 enhanced by small molecule adsorption

The luminescence characteristics of small molecule excited B40 have not been studied yet, and it may have a potential application value in quantum dot luminescence. Herein, the adsorption and fluorescence emission spectra of small molecules (pyridine, pyrazine and benzene) adsorbed on B40 are studied using first-principles. The results show that the absorption of pyridine and pyrazine on B40 can form stable chemisorption structures pyridine-B40 and pyrazine-B40, while benzene adsorption can form physisorption structure benzene-B40. Moreover, the adsorbed pyridine can enhance the intensity of emission spectra of B40. And the pyrazine adsorbed can obviously enhance the intensity of absorption and emission spectra of B40 and cause the spectra to redshift to the visible light range. And the adsorption of benzene has almost no enhancement effect on absorption and emission spectra of B40. In addition, the influence of different computational basis sets on spectra characteristics has also been discussed and the results show that the main peaks of absorption and emission spectra calculated by the diffuse function augmented basis sets are redshifted relatively. This finding provides a strategy for quantum dot luminescence and a theoretical reference for experimental research.