Kun Tao

N-doped WS2 nanosheets: a high-performance electrocatalyst for the hydrogen evolution reaction

Non-Pt-based catalysts are urgently required to produce abundant hydrogen in electrochemical water splitting, in order to make the hydrogen evolution reaction (HER) feasible and energy efficient. Here, N-doped WS2 nanosheets were synthesized by a one step sol–gel process, which are electrochemically active toward the HER with a low onset potential of 86 mV, a large cathodic current density (100 mA cm−2 at an overpotential of 197 mV) and long-term durability. We anticipate that this synthetic method will be a powerful tool for creating high-performance electrocatalysts from other transition metal dichalcogenides.

Metallic Ni3N nanosheets with exposed active surface sites for efficient hydrogen evolution

Ni-Based catalysts have been considered as promising non-noble-metal hydrogen evolution reaction (HER) electrocatalysts for future clean energy devices. Here, atomically thin metallic Ni3N nanosheets are fabricated as the hydrogen evolution cathode, which exhibit remarkable HER activity close to that of a commercial Pt/C electrode. The Ni3N nanosheet catalyst shows an electrocatalytic current density of 100 mA cm2 at a low overpotential of 100 mV vs. RHE, a high exchange current density of 0.32 mA cm−2, a Tafel slope of 59.79 mV dec−1 and remarkable durability (little activity loss >5000 cycles) in acidic media as well as high HER activity in neutral and alkaline media. Through systematic theoretical calculations, the active surface sites of the Ni3N nanosheets are explicitly identified. The Ni atoms accompanied by surrounding N atoms on the N–Ni surface demonstrate a small ΔGH* of 0.065 eV due to the Ni–N co-effect, which act as the most active HER sites. This finding broadens our vision to realize the HER activity of 2D metallic electrocatalysts and paves the way for exciting opportunities in exploring and optimizing advanced catalysts for future energy production.

High temperature ferromagnetism in Cu-doped MoS2 nanosheets

The synthesis of 2D metal chalcogenide based on ferromagnetic nanosheets is in high demand for modern electronics and spintronics applications. Herein, Cu-doped MoS2 nanosheets were successfully prepared by a hydrothermal method. Magnetic measurement results indicate that the doping of Cu ions can introduce ferromagnetism into MoS2 nanosheets, where saturate magnetization increases with increased Cu concentration. Further, the hysteresis curves measured at different temperatures demonstrate a high Curie temperature of 930 K for the Cu-doped MoS2 nanosheets. This result opens a new path to exploring spintronics in pristine 2D nanostructures by non-magnetic atom doping.

A series of unexpected ferromagnetic behaviors based on the surface-vacancy state: an insight into NiO nanoparticles with a core–shell structure

Antiferromagnetic nanoparticles as ultimate low-dimensional materials potentially give novel magnetic properties that differ from their bulk form due to strong quantum and surface effects. Herein, we propose that the observed anomalous ferromagnetic behavior of NiO nanoparticles is due to the formation of a ferromagnetic particle shell that is oxygen-vacancy related. A novel self-consistent estimation of the saturation magnetization further confirmed our proposal. The samples, synthesized by a thermal decomposition method, exhibit diversely anomalous ferromagnetic behavior, such as hysteresis curves, large coercivities, exchange bias and spin-glass behavior. A large saturation magnetization of 0.536 emu g−1 exists in the 6 nm NiO sample and it is found to decrease with increasing crystal size. Neither impurity element nor change of valence state has been found in the samples, through X-ray photoelectron, X-ray diffraction or selected-area electron diffraction measurements. Remarkably, a large amount of oxygen vacancies exists, which was verified by X-ray photoelectron spectrum fitting results and Raman spectroscopy. A post-hydrogen-annealing process strongly elevates ferromagnetic ordering, as a result of surface defect enhancement. Moreover, our estimation of the saturation magnetization based on first principle calculation results is in agreement with the experimental conclusion, which reveals the significance of surface states in mediating anomalous magnetic properties in low-dimensional antiferromagnetic materials.

P dopants induced ferromagnetism in g-C3N4 nanosheets: Experiments and calculations

Outstanding magnetic properties are highly desired for two-dimensional (2D) semiconductor nanosheets due to their potential applications in spintronics. Metal-free ferromagnetic 2D materials whose magnetism originated from the pure s/p electron configuration could give a long spin relaxation time, which plays the vital role in spin information transfer. Here, we synthesize 2D g-C3N4 nanosheets with room temperature ferromagnetism induced by P doping. In our case, the Curie temperature of P doped g-C3N4 nanosheets reaches as high as 911 K and the precise control of the P concentration can further adjust the saturation magnetization of the samples. First principles calculation results indicate that the magnetic moment is primarily due to strong hybridization between p bonds of P, N, and C atoms, giving the theoretical evidence of the ferromagnetism. This work opens another door to engineer a future generation of spintronic devices.Outstanding magnetic properties are highly desired for two-dimensional (2D) semiconductor nanosheets due to their potential applications in spintronics. Metal-free ferromagnetic 2D materials whose magnetism originated from the pure s/p electron configuration could give a long spin relaxation time, which plays the vital role in spin information transfer. Here, we synthesize 2D g-C3N4 nanosheets with room temperature ferromagnetism induced by P doping. In our case, the Curie temperature of P doped g-C3N4 nanosheets reaches as high as 911 K and the precise control of the P concentration can further adjust the saturation magnetization of the samples. First principles calculation results indicate that the magnetic moment is primarily due to strong hybridization between p bonds of P, N, and C atoms, giving the theoretical evidence of the ferromagnetism. This work opens another door to engineer a future generation of spintronic devices.

Adjustable ferromagnetic behavior in iron-doped two-dimensional MoS2 multilayer nanosheets

Robust ferromagnetism of two-dimensional (2D) semiconductors has been achieved in recent years. In this study, 2D MoS2 nanosheets doped with Fe ions were prepared and characterized. The results indicated that the prepared samples had no other impurities induced by Fe doping. M–H curves measured under different temperatures suggested that robust ferromagnetism occurred in the MoS2 nanosheets after Fe doping and that the nanosheets had a high Curie temperature above 930 K. This experiment provides an effective method for manipulating the magnetic properties of MoS2 nanosheets via doping with Fe ions.