Quasi-one-dimensional nanoribbons have great potential for applications in nanoelectronics and nanospintronics due to their unique quantum confinement effects. In this work, first-principles calculations are carried out to predict the stability as well as magnetic and electronic properties of MXene nanoribbons with either zigzag- or armchair-terminated edges. Three types of MXene recently realized experimentally, i.e. Ti2C, Ti3C2 and V2C, are considered to construct their corresponding MXene nanoribbons. In addition, the O-functionalized Ti2C and Ti3C2 nanoribbons are also investigated. The effect of functionalization is studied by comparing different functional groups including OH, F and O. Six zigzag and two armchair families are distinguished according to different ribbon edges. Our results show that all the investigated bare MXenes are metallic and exhibit certain magnetic moments in their ground states, irrespective of the ribbon width and ribbon type. Remarkable edge reconstructions are observed for all types of nanoribbon. We further show that hydrogen passivation can lead to the increase of the magnetic moments of Ti2C and V2C nanoribbons due to charge transfer. For O-functionalized Ti2C nanoribbons, our calculations indicate that some of them exhibit semiconducting properties dependent on edge configurations. In particular, the band gap of armchair Ti2CO2 nanoribbons with a width of 7.34 Å is found to be around 1.0 eV, which is significantly enhanced compared to the 0.4 eV of a pristine Ti2CO2 layer. The stabilities of these nanoribbons are evaluated by virtue of their binding energies, formation energies and edge energies and we show that functionalized MXene nanoribbons are more stable than bare ribbons. Our results thus provide strong evidence for the effectiveness of nanostructuring on the electronic and magnetic properties of MXenes.

The capacity and stability of the constituent electrodes critically determine the performance of Li-ion batteries (LIBs). In this study, density functional theory is employed to explore the potential application of the recently synthesized two dimensional phosphorene as an electrode material in LIBs. Our results show that Li atoms can bind strongly with the phosphorene monolayer and double layer with significant electron transfer. Besides, the structure of phosphorene is not influenced much by lithiation and the volume change is only 0.2%. After lithiation, a semiconductor-to-conductor transition is observed. The diffusion barrier values of Li are calculated to be 0.76 and 0.72 eV on monolayer and double layer phosphorene, respectively. We further demonstrate that the theoretical specific capacity of the phosphorene monolayer is 432.79 mA h g−1, which is larger than those of other commercial anode materials. The influence of Si and S implantation is also examined and our results indicate that Si-doped phosphorene greatly improves the binding of Li atoms, while the diffusion barrier is not affected. Our findings show that the high capacity, low open circuit voltage, small volume change and electrical conductivity of lithiated phosphorene make it a good candidate for application as an electrode material in batteries.

The performance of Li-ion batteries relies heavily on the capacity and stability of constituent electrodes. Recently synthesized 2D MXenes have demonstrated excellent Li-ion capacity with extremely high charging rates. In this work, first-principles calculations are employed to investigate the effects of external strain and Li concentration on the adsorption and diffusion of Li on Ti2C layer, a representative MXene. Our calculations demonstrate that the binding energy of Li atoms decreases monotonically with external strains, and the mechanical properties are not influenced by Li adsorption. For multiple Li atoms adsorption, their stable configurations show that the Li atoms tend to reside in one side first, in contrast with other 2D materials. We further show that the binding energy of Li is weakly dependent on the Li concentration. The diffusion barrier is calculated, and the results show that the strain and concentration have limited effects on the diffusion of Li atoms. Finally, the adsorption of Li atoms on two types of Ti2C double layer are considered. For all studied structures, their stabilities are examined by molecular dynamics simulations carried out at room temperature. The influence of Li adsorption on the electronic structures of Ti2C layer is also discussed. Our results suggest that Ti2C could be a promising electrode material for lithium ion batteries in terms of lithium storage capacity and stability at a high Li recycling rate.

The capacity and stability of the constituent electrodes critically determine the performance of Li-ion batteries (LIBs). In this study, density functional theory is employed to explore the potential application of the recently synthesized two dimensional phosphorene as an electrode material in LIBs. Our results show that Li atoms can bind strongly with the phosphorene monolayer and double layer with significant electron transfer. Besides, the structure of phosphorene is not influenced much by lithiation and the volume change is only 0.2%. After lithiation, a semiconductor-to-conductor transition is observed. The diffusion barrier values of Li are calculated to be 0.76 and 0.72 eV on monolayer and double layer phosphorene, respectively. We further demonstrate that the theoretical specific capacity of the phosphorene monolayer is 432.79 mA h g−1, which is larger than those of other commercial anode materials. The influence of Si and S implantation is also examined and our results indicate that Si-doped phosphorene greatly improves the binding of Li atoms, while the diffusion barrier is not affected. Our findings show that the high capacity, low open circuit voltage, small volume change and electrical conductivity of lithiated phosphorene make it a good candidate for application as an electrode material in batteries.

Quasi-one-dimensional nanoribbons have great potential for applications in nanoelectronics and nanospintronics due to their unique quantum confinement effects. In this work, first-principles calculations are carried out to predict the stability as well as magnetic and electronic properties of MXene nanoribbons with either zigzag- or armchair-terminated edges. Three types of MXene recently realized experimentally, i.e. Ti2C, Ti3C2 and V2C, are considered to construct their corresponding MXene nanoribbons. In addition, the O-functionalized Ti2C and Ti3C2 nanoribbons are also investigated. The effect of functionalization is studied by comparing different functional groups including OH, F and O. Six zigzag and two armchair families are distinguished according to different ribbon edges. Our results show that all the investigated bare MXenes are metallic and exhibit certain magnetic moments in their ground states, irrespective of the ribbon width and ribbon type. Remarkable edge reconstructions are observed for all types of nanoribbon. We further show that hydrogen passivation can lead to the increase of the magnetic moments of Ti2C and V2C nanoribbons due to charge transfer. For O-functionalized Ti2C nanoribbons, our calculations indicate that some of them exhibit semiconducting properties dependent on edge configurations. In particular, the band gap of armchair Ti2CO2 nanoribbons with a width of 7.34 Å is found to be around 1.0 eV, which is significantly enhanced compared to the 0.4 eV of a pristine Ti2CO2 layer. The stabilities of these nanoribbons are evaluated by virtue of their binding energies, formation energies and edge energies and we show that functionalized MXene nanoribbons are more stable than bare ribbons. Our results thus provide strong evidence for the effectiveness of nanostructuring on the electronic and magnetic properties of MXenes.