Yuan Sun

Monolayer MoS2 quantum dots as catalysts for efficient hydrogen evolution

Monolayer MoS2 quantum dots (QDs) with lateral size around 3 nm were prepared through an effective multi-exfoliation based on lithium (Li) intercalation. The effects of the number of exfoliation on the microstructures and electrocatalytic activities of hydrogen evolution reaction (HER) for MoS2 nanosheets were examined. The lateral size of the nanosheets decreases rapidly with increasing the number of exfoliation. The obtained monolayer MoS2 QDs exhibit improved HER catalytic activities with a low overpotential of approximately 120 mV and a relatively small Tafel slope of 69 mV dec−1. Both the ultrathin structure and the abundance of exposed active edge sites make monolayer MoS2 QDs a promising HER electrocatalyst for practical application.

MoS2-Based Mixed-Dimensional van der Waals Heterostructures: A New Platform for Excellent and Controllable Microwave-Absorption Performance

It is widely recognized that constructing multiple interface structures for enhanced interface polarization is beneficial to microwave absorption. Here, we report our work of achieving excellent microwave-absorption performance and controlling better-defined interfaces in vertically stacked two-dimensional (2D) MoS2 with other dimensional building blocks. The optimal reflection loss and effective absorbing bandwidth (reflection loss <-10 dB) of several mixed-dimensional van der Waals heterostructures are as follows: (i) for 2-0 type (2D MoS2/zero-dimensional Ni nanoparticles), -19.7 dB and 2.92 GHz; (ii) for 2-1 type (2D MoS2/one-dimensional carbon nanotubes), -47.9 dB and 5.60 GHz; and (iii) for 2-3 type (2D MoS2/three-dimensional carbon layers), -69.2 dB and 4.88 GHz. As a result, by selected synthesis of different types of microstructures, we can regulate and control microwave-absorption properties in MoS2 mixed-dimensional van der Waals heterostructures. In addition, attributing to the better-defined interfaces generated in mixed-dimensional van der Waals heterostructures, we found an alternative strategy to improve microwave attenuation properties of 2-0, 2-1, and 2-3 samples by controlling interfacial contacts. The results indicate that mixed-dimensional van der Waals heterostructures provide a new stage for the next generation of microwave-absorbing materials.

An efficient Co 3 S 4 /CoP hybrid catalyst for electrocatalytic hydrogen evolution

The development of efficient, universal and inexpensive electrocatalysts for hydrogen evolution reaction (HER) is central to the area of sustainable energy conversion. Considering the Co-based sulfides/phosphides have the same catalytic mechanism with the hydrogenases occurring in nature. Here, a new catalyst based on Co3S4/CoP hybrid that is comprised entirely cheap and earthabundant elements, was first synthesized via a two-step method, the Co(CO3)0.5(OH)·0.11H2O precursor was prepared by a hydrothermal method, followed by phosphidation and sulphidation under Ar atmosphere simultaneously. The resulting Co3S4/CoP hybrid material possessed porous core-shell structure with a homogeneous element distribution and large electroactive surface area (~21.04 mF cm−2). More importantly, the nanostructured Co3S4/CoP electrode exhibits excellent HER properties in acid medium with a low onset overpotential of 34 mV, a small Tafel slope of 45 mV dec−1, as well as a large exchange current density of 150 μA cm−2. These results obtained in this study indicate that the Co3S4/CoP hybrid nanorod is promising replacement to the Pt-based catalysts for H2 production. Moreover, the synthetic method presented in this work can provide an efficient way to synthesis other nanocomposites.

Solvent-directed and anion-modulated self-assemblies of nanoparticles: a case of ZnO

Self-assembly of nanoparticles is one of the most appealing fields in nanoscience. In the present article, we demonstrate solvent-directed and anion-modulated self-assemblies of ZnO recrystallized from layered basic zinc acetate nanoflakes by heat treatment in liquid media. Diverse controllable ZnO patterns, including nanodots, nanodisks, twinned mesocrystals, mesoporous nanospheres, unprecedented triangular nanoprisms and porous nanosheets, have been achieved from the same precursor, indicating a fascinating platform for studies of self-assembly. It is confirmed that polar protic solvents such as water, alcohol and methanol not only provide liquid media to disperse the precursor nanoflakes but also force their decomposition under mild conditions without basic additives and direct self-assemblies of the resulting ZnO. Both the physicochemical property and the structure of the solvent play important roles. Due to the anion exchange reactions of zinc hydroxide salts and face-selective electrostatic interactions between the added anions and wurtzite ZnO, the conversion and self-assembly process can be effectively modulated by the addition of anions. When the affinity of added anions to the zinc hydroxide layers is weak, the conversion process will be slackened and the preferential assembly direction of ZnO will be modified. However, when the affinity is strong, other stable zinc hydroxide salts instead of ZnO will be obtained. Our findings give new insights into the solid-phase transformation and assembly from the precursor nanoflakes to ZnO. In addition, the outstanding light scattering feature of the resulting ZnO mesocrystals confers application significance on them.