[en] Inspired by the experimental synthesis of novel boron-doped graphene nanoribbon (BGNR), we have performed density functional theory (DFT) calculations to reveal the adsorption behaviors of lithium (Li) atoms on BGNR. We systematically studied the adsorption, diffusion and capacity of Li on BGNR with 7 carbon atoms in width. It is found that due to the doping effects of boron (B) atoms, BGNR exhibits a narrower band gap than graphene nanoribbon (GNR) with the same width. Individual Li atom exhibits much stronger binding on BGNR than that on GNR, attributing to the stronger LiC interaction caused by doping of B atoms. A zigzag diffusion path along the growth direction of BGNR is confirmed for diffusion of Li. The maximum theoretical storage capacity of Li on BGNR is determined as 783 mAh/g, which is 15 times than that on GNR with same width (52 mAh/g). Our results demonstrated that doping of B atoms greatly enhances the adsorption and storage performance of Li, which provides a theoretical foundation of researches on the novel BGNR and other similar structures for adsorption and storage of Li.

[en] This paper reports a theoretical study for the wurtzite phase (B4), rocksalt phase (B1) and transition intermediate phases hexagonal structure (Hexa) and tetragonal structure (Tetra) of AlN. Enthalpies of the different phases of AlN under different hydrostatic pressures have been calculated from the density functional theory (DFT). The transition pressure is obtained from the enthalpy curve crossings and determined to be 17.27 GPa between the B1 and B4 phases of AlN. The intermediate hexagonal structure is more stable at low pressure and the intermediate tetragonal structure remains more stable at high pressure. Our results show that the wurtzite phase (B4) is of direct bandgap (4.095 eV). The bandgap energy as a function of applied pressure fits a second - order polynomial and these values are in good agreement with the earlier first - principles calculations. (authors)

[en] The adsorption of small molecules (NH_3, N_2, H_2 and CH_4) on all-boron fullerene B_4_0 is investigated by density functional theory (DFT) and the non-equilibrium Green’s function (NEGF) for its potential application in the field of single-molecular gas sensors. The high adsorption energies (−1.09 to −0.75 eV) of NH_3 on different adsorption sites of the B_4_0 surface indicate that NH_3 strongly chemisorbs to B_4_0. The charge transfer induced by the NH_3 adsorption results in a modification of the density of states (DOS) of B_4_0 near the Fermi level, and therefore changes its electronic transport properties. For all possible adsorption sites, the adsorption of NH_3 exclusively leads to a decrease of the conductance of B_4_0. Taking into consideration that the non-polar gas molecules (e.g. N_2, H_2 and CH_4) are only physisorbed and show negligible effect on the conductance properties of B_4_0, we would expect that B_4_0 can be used as a single-molecular gas sensor to distinguish NH_3 from non-polar gas molecules at low bias. (paper)

[en] Core/shell nanowires (CSNWs) composed of Si, C, and SiC are promising systems for optoelectronic devices. Through computational investigations, we find that the band gaps (E_g) of these nanowires can be controlled not only by changing their composition, but also by adjusting the core/shell thickness ratio. For Si/SiC or SiC/C CSNWs with a fixed total number of layers, the dependence of E_g on the core/shell thickness ratio shows a bowing effect. E_g can be tuned from a few eV all the way to zero. These investigations provide direction for designing optoelectronic devices based on Earth-abundant elements. (paper)

[en] Recently, much attention has focused on less platinum alternative materials serving as the counter electrode material for dye-sensitized solar cells, while platinum itself has a lot of room for improvement. Herein, we introduce the earth-abundant silicon and combine it with Pt nanoparticles as the counter electrode in dye-sensitized solar cells to enlarge surface area and enhance the activity of Pt. Si-H bonds can reduce metal ions and enable small metal nanoparticles grown on the surface of silicon nanowires, which can effectively prevent metal nanoparticles from agglomeration in the catalysis. The density functional theory (DFT) calculation shows that the adsorption energy of I atom on the Pt/Si interface is −0.8 eV, which is the optimal adsorption energy for triiodide reduction, indicating that Pt/Si is a perfect material for the counter electrode. The electrochemical characterizations and the photocurrent-voltage performance experimentally confirm that Pt/SiNW is a better counter electrode material than other metal/SiNW composites and Pt, which is in accordance with DFT calculations. The power conversion efficiency of device based on the Pt/SiNW electrode is higher than that of the device based on Pt (8.23% vs.7.93%).

[en] Highlights: • Os/Si has a thermodynamically favorable hydrogen adsorption free energy. • Os/SiNW composites show a low Tafel slope of −24 mV dec⁻¹. • The performance of Os/SiNW catalysts exceeds Pt/C at high overpotentials. The development of highly efficient electrocatalysts for hydrogen evolution reaction is a fundamental undertaking of the hydrogen economy. Herein, we investigated the electrocatalytic performance of M/Si (M = Os, Rh, Pt, Pd, Re, Ru, Au or Ag) nanocomposites for hydrogen evolution reaction. The results show that Os/Si nanocomposites exhibit the best catalytic efficiency with a negligible onset overpotential (−25 mV), a small Tafel slope of −24 mV dec⁻¹ and remarkable long-term stability. Of most importance, at a current density of the typical industrial production (−1000 mA cm⁻²), the energy conversion efficiency of the Os/Si nanocomposite is 29.3% higher than that of the commercial 40 wt% Pt/C. The density functional calculations reveal that such outstanding catalytic activity of the Os/Si catalyst arises from the thermodynamically more favorable hydrogen adsorption free energy (ΔG_H* = −0.03 eV) at the osmium/silicon interfaces than that on platinum (ΔG_H* = −0.09 eV) or osmium (ΔG_H* = −0.26 eV).

[en] To fine-tune surface ligands towards high-performance devices, we developed an in situ passivation process for all-inorganic cesium lead iodide (CsPbI${}_3$) perovskite quantum dots (QDs) by using a bifunctional ligand, L-phenylalanine (L-PHE). Through the addition of this ligand into the precursor solution during synthesis, the in situ treated CsPbI${}_3$ QDs display significantly reduced surface states, increased vacancy formation energy, higher photoluminescence quantum yields, and much improved stability. Consequently, the L-PHE passivated CsPbI${}_3$ QDs enabled the realization of QD solar cells with an optimal efficiency of 14.62 % and red light-emitting diodes (LEDs) with a highest external quantum efficiency (EQE) of 10.21 %, respectively, demonstrating the great potential of ligand bonding management in improving the optoelectronic properties of solution-processed perovskite QDs. (© 2020 Wiley‐VCH GmbH)

[en] The catalytic decomposition of hydrazine (N₂H₄) could release lots of energy, and there have been extensive studies on metal surfaces as catalysts for this process. Here, we first reported the detailed mechanisms of adsorption and catalytic decomposition of N₂H₄ on metal-free nanomaterials with the carbon-based SiC₃ siligraphene (g-SiC₃) as substrate. By using density functional theory methods, it is found that N₂H₄ molecule chemically adsorbs on g-SiC₃, with the anti configuration as the most stable one. The following analysis show orbital hybridization between N₂H₄ and g-SiC₃. By analyzing the potential energy surfaces, it is revealed that the optimal decomposition pathway of N₂H₄ on g-SiC₃ is mainly the pre-adsorbed NH₂ intermediates assisted intermolecular decomposition, with N₂ and NH₃ as products. The rate determining step of the optimal decomposition pathway is ^*(N₂H₃+NH₂) → ^*(NNH₂+NH₃), which is different from the decomposition pathway of N₂H₄ on the extensively researched metal surfaces. Our results provide rational principles of metal-free carbon-based catalysts for adsorption and catalytic decomposition of N₂H₄.

[en] By using first-principles calculations, we investigate the structural stability of nitrogen-doped (N-doped) graphene with graphitic-N, pyridinic-N and pyrrolic-N, and the transition metal (TM) atoms embedded into N-doped graphene. The structures and energetics of TM atoms from Sc to Ni embedded into N-doped graphene are studied. The TM atoms at N_4V _2 forming a 4N-centered structure shows the strongest binding and the binding energies are more than 7 eV. Finally, we investigate the catalytic performance of N-doped graphene with and without TM embedding for O_2 dissociation, which is a fundamental reaction in fuel cells. Compared to the pyridinic-N, the graphitic-N is more favorable to dissociate O_2 molecules with a relatively low reaction barrier of 1.15 eV. However, the catalytic performance on pyridinic-N doped structure can be greatly improved by embedding TM atoms, and the energy barrier can be reduced to 0.61 eV with V atom embedded. Our results provide the stable structure of N-doped graphene and its potential applications in the oxygen reduction reactions

[en] Embedding transition-metal (TM) atoms into nonmagnetic nanomaterials is an efficient way to induce magnetism. Using first-principles calculations, we systematically investigated the structural stability and magnetic properties of TM atoms from Sc to Zn embedded into silicene with single vacancy (SV) and double vacancies (DV). The binding energies for different TM atoms correlate with the TM d-shell electrons. Sc, Ti, and Co show the largest binding energies of as high as 6 eV, while Zn has the lowest binding energy of about 2 eV. The magnetic moment of silicene can be modulated by embedding TM atoms from V to Co, which mainly comes from the 3d orbitals of TM along with partly contributions from the neighboring Si atoms. Fe atom on SV and Mn atom on DV have the largest magnetic moment of more than 3 μB. In addition, we find that doping of N or C atoms on the vacancy site could greatly enhance the magnetism of the systems. Our results provide a promising approach to design silicene-based nanoelectronics and spintronics device