Magnetic Enhancement for Hydrogen Evolution Reaction on Ferromagnetic MoS2 Catalyst.

Numerous efforts in improving the hydrogen evolution reaction (HER) performance of transition metal dichalcogenides mostly focus on active sites exposing, vacancy engineering, and phase engineering. However, little room is left for improvement in these approaches. It should be noted that efficient electron transfer also plays a crucial role in catalytic activity. In this work, by employment of an external vertical magnetic field, ferromagnetic bowl-like MoS2 flakes can afford electrons transmitting easily from a glassy carbon electrode to active sites to drive HER, and thus perform magnetic HER enhancement. The ferromagnetic bowl-like MoS2 flakes with an external vertical magnetic field can provide a roughly doubled current density compared to that without an external vertical magnetic field at a constant overpotential of -150 mV. Our work may provide a new pathway to break the bottleneck for further improvement of HER performance and also paves the way to utilize the magnetic enhancement in widely catalytic application.

Enhanced Thermoelectric Performance of p-type AgSbTe2 via Cu Doping.

Recently, the p-type semiconductor AgSbTe2 has received a great deal of attention due to its promising thermoelectric performance in intermediate temperatures (300-700 K). However, its performance is limited by the suboptimal carrier concentration and the presence of Ag2Te impurities. Herein, we synthesized AgSb1-xCuxTe2 (x = 0, 0.02, 0.04, and 0.06) and investigated the effect of Cu doping on the thermoelectric properties of AgSbTe2. Our results indicate that Cu doping suppresses the Ag2Te impurities, raises the carrier concentration, and results in an improved power factor (PF). The calculation reveals that Cu doping downshifts the Fermi energy level, reduces the energy band gap and the difference among several valence band maximums, and thereby explains the improvement of PF. In addition, Cu doping reduces the thermal conductivity, possibly attributed to the inhibition of Ag2Te impurities and the phonon softening of the AgSb1-xCuxTe2. Overall, Cu doping improves the ZT of AgSb1-xCuxTe2. Among all samples, AgSb0.96Cu0.04Te2 has a maximum ZT of ∼1.45 at 498 K and an average ZT of ∼1.11 from 298 to 573 K.

Laminated bilayer MoS2 with weak interlayer coupling.

Laminated bilayer MoS2 structures are prepared with MoS2 nanoparticles trapped between two individual MoS2 layers which can prevent the formation of a true stacking structure held together by van der Waals interaction. The laminated bilayer MoS2 clearly indicates a weak interlayer coupling with reduced van der Waals interaction between adjacent layers. As the interlayer coupling is insufficient to modify the band structure of MoS2, the laminated bilayer MoS2 can retain the direct bandgap structure of an isolated monolayer. Furthermore, by controlling the size of the MoS2 nanoparticles trapped in between, the interlayer distance and interlayer coupling of bilayer MoS2 structures can be engineered in a wide range, resulting in different bandgap behaviors. This finding is extremely important as it provides an effective approach to fabricate bandgap engineered bilayer MoS2 structures, which is a crucial step forward to making multi-layer MoS2-based p-n junctions and homo/hetero-structures, and thus advanced electronic devices, especially optoelectronic devices. This approach is applied to not only bilayer MoS2 structures, but also other layer structured two-dimensional materials.