Realization of a half-metallic state on bilayer WSe2 using doping transition metals (Cr, Mn, Fe, Co, Ni) in its interlayer

Construction of Bimetallic Heterojunction Based on Porous Engineering for High Performance Flexible Asymmetric Supercapacitors

It remains a great challenge to design and manufacture battery-type supercapacitors with satisfactory flexibility, appropriate mechanical property, and high energy density under high power density. Herein, a concept of porous engineering is proposed to simply prepare two-layered bimetallic heterojunction with porous structures. This concept is successfully applied in fabrication of flexible electrode based on CuO-Co(OH)₂ lamella on Cu-plated carbon cloth (named as CPCC@CuO@Co(OH)₂ ). The unique structure brings the electrode a high specific capacity of 3620 mF cm^-2 at 2 mA cm^-2 and appropriate mechanical properties with Young's modulus of 302.0 MPa. Density functional theory calculations show that porous heterojunction provides a higher intensity of electron state density near the Fermi level (E-E_f  = 0 eV), leading to a highly conductive CPCC@CuO@Co(OH)₂ electrode with both efficient charge transport and rapid ion diffusion. Notably, the supercapacitor assembled from CPCC@CuO@Co(OH)₂ //CC@AC shows high energy density of 127.7 W h kg^-1 at 750.0 W kg^-1 , remarkable cycling performance (95.53% capacity maintaining after 10 000 cycles), and desired mechanical flexibility. The methodology and results in this work will accelerate the transformative developments of flexible energy storage devices in practical applications.

meta-Position synergistic effect induced by Ni-Mo co-doped WSe2 to enhance the hydrogen evolution reaction

Transition metal dichalcogenides have been the most attractive two-dimensional layered materials for electrocatalytic hydrogen evolution due to their unique structure and multi-phase electronic states. However, the enhancement of the WSe₂ electrocatalytic hydrogen evolution reaction (HER) performance by bimetal co-doping has been rarely reported. Herein, the NiMo-WSe₂ catalyst has been synthesized by a one-step hydrothermal reaction, with lower overpotentials of 177 and 188 mV at a current density of 10 mA cm^-2 in 0.5 M H₂SO₄ and 1 M KOH, respectively. The large specific surface area and thinner edge morphology provide more active sites for hydrogen production, thereby significantly improving the charge transfer kinetics. Density functional theory calculation results show that under acidic conditions the ΔG_H* values of NiMo-WSe₂ with different structures and hydrogen adsorption sites are also different, when the hydrogen adsorption site was located at the top of the Se-Ni bond, the meta NiMo-WSe₂ has a ΔG_H* value (-0.04 eV) that is closest to 0. Meanwhile, NiMo-WSe₂ (meta) also has a minimum of ΔG_H* under alkaline conditions. DOS confirmed that Ni doping has a large impact on the electronic states at the WSe₂ Fermi level, while NiMo co-doping greatly reduces the potential energy barrier of the HER reaction, jointly increasing the current density, and thus improving the HER performance.

Coexisting unconventional Rashba- and Zeeman-type spin splitting in Pb-adsorbed monolayer WSe2

Based on first-principles calculations, the unconventional Rashba- and Zeeman-type spin splitting can simultaneously coexist in the Pb-adsorbed monolayer WSe₂system. The first two adsorption configurationst₁andt₂show remarkable features under the spin-orbit coupling, in which two split energy branches show same spin states at the left or right side of Γ, and the spin polarization is reversed for both Rashba band branches. For the second adsorption configuration, an energy gap was observed near the unconventional spin polarization caused by the repelled Rashba bands for avoid crossing, and this gap can produce non-dissipative spin current by applying the voltage. The results fort₂configuration with spin reversal show that the repel band gap and Rashba parameter can be effectively regulated within the biaxial strain range of -8% to 6%. By changing the adsorption distancedbetween Pb and the neighboring Se atom layer, the reduceddcaused the transfer from Rashba-type to Zeeman-type spin splitting. This predicted adsorption system would be promising for spintronic applications.

The electronic and magnetic properties of h-BN/MoS2 heterostructures intercalated with 3d transition metal atoms

We performed density functional theory calculations to investigate the electronic and magnetic properties of h-BN/MoS2 heterostructures intercalated with 3d transition-metal (TM) atoms, including V, Cr, Mn, Fe, Co, and Ni atoms. It was found that metal and magnetic semiconductor characteristics are induced in the h-BN/MoS2 heterostructures after intercalating TMs. In addition, the results demonstrate that h-BN sheets could promote charge transfer between the TMs and the heterogeneous structure. Specifically, the h-BN/MoS2 heterostructure transforms from an indirect semiconductor to a metal after intercalating V or Cr atoms in the interlayers. For Mn, Fe, and Co atoms, the bandgaps of the intercalated heterojunction systems become smaller when the spin polarization is 100% at the highest occupied molecular orbital level. However, the system intercalated with Ni atoms exhibits no spin polarization and non-magnetic character. Strong covalent-bonding interactions emerged between the intercalated TMs and the nearest S atom of the h-BN/MoS2 heterostructure. In addition, the magnetic moments of the TM atoms show a decreasing trend for all the interstitial intercalated heterostructures compared with their free-standing states. These results reveal that h-BN/MoS2 heterostructures with intercalated TMs are promising candidates for application in multifarious spintronic devices.

Half-metal state of a Ti2C monolayer by asymmetric surface decoration

Searching for two-dimensional (2D) ferromagnetic materials is one of the key steps in 2D spintronics. 2D metal carbide/nitride materials (MXene) are widely regarded as promising candidates for this kind of material. However, when the surfaces are saturated with some functional groups during the preparation, the ground states of most of the MXenes transit from ferromagnetic (FM) to antiferromagnetic (AFM) or non-magnetic (NM) states. In this article, we propose a new method to avoid this problem by adopting asymmetric decoration of the MXene surface, which can make MXenes ferromagnetic ground states. Based on hybrid density functional theory calculations, our results show asymmetrical adsorption of negative ions or metal atoms makes the Ti atoms have different valence states, such as one sublayer Ti4+ and another Ti+, which prefer FM ground states. This research will deepen our understanding of the magnetic properties of 2D materials and contribute to the design of new 2D ferromagnetic materials.

Electronic and magnetic properties of a black phosphorene/Tl2S heterostructure with transition metal atom intercalation: a first-principles study

Using density functional theory calculations, the structural, electronic and magnetic properties of a black phosphorene/Tl₂S heterostructure (BP/Tl₂S) and the BP/Tl₂S intercalated with transition metal atoms (TMs) have been detailed investigated. It is demonstrated that the BP/Tl₂S is a type-I van der Waals (vdW) heterostructure with an indirect band gap of approximately 0.79 eV. The BP/Tl₂S experiences a transition from type-I to type-II when various strains are applied. In addition, the BP/Tl₂S intercalated with TMs (TM-BP/Tl₂S) exhibits various kinds of meaningful electronic and magnetic properties. Several TM-BP/Tl₂S systems are still non-magnetic ground states and six TM-BP/Tl₂S (Ti-, V-, Cr-, Mn-, Fe-, Tc-) systems are ferromagnetic. Interestingly, three TM-BP/Tl₂S (V-, Cr-, Mn-) systems display half-metallic character. The Fe-BP/Tl₂S and Tc-BP/Tl₂S are dilute magnetic semiconductors (DMSs), while TM-BP/Tl₂S (Mo-, Pd-, Ni-) systems are semiconductors. The other TM-BP/Tl₂S systems become metals. These results may open a new avenue for application of the BP/Tl₂S in future spintronic and electronic devices.

Using density functional theory calculations, the structural, electronic and magnetic properties of a black phosphorene/Tl₂S heterostructure (BP/Tl₂S) and the BP/Tl₂S intercalated with transition metal atoms (TMs) have been detailed investigated.