Large scale epitaxial growth and transfer of monolayer MoS has attracted great attention in recent years. Here, we report the wafer-scale epitaxial growth of highly oriented continuous and uniform monolayer MoS films on single-crystalline sapphire wafers by chemical vapor deposition (CVD) method. The epitaxial film is of high quality and stitched by many 0°, 60° domains and 60°-domain boundaries. Moreover, such wafer-scale monolayer MoS films can be transferred and stacked by a simple stamp-transfer process, and the substrate is reusable for subsequent growth. Our progress would facilitate the scalable fabrication of various electronic, valleytronic, and optoelectronic devices for practical applications.

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Replacing organic liquid electrolyte with inorganic solid electrolytes (SE) can potentially address the inherent safety problems in conventional rechargeable batteries. However, solid-state batteries (SSBs) have been plagued by the relatively low ionic conductivity of SEs and large charge-transfer resistance between electrode and SE. Here, a new design strategy is reported for improving the ionic conductivity of SE by self-forming a composite material. An optimized Na + ion conducting composite electrolyte derived from the Na 1+n Zr 2 Si n P 3−n O 12 NASICON (Na Super Ionic Conductor) structure is successfully synthesized, yielding ultrahigh ionic conductivity of 3.4 mS cm −1 at 25 °C and 14 mS cm −1 at 80 °C. On the other hand, in order to enhance the charge-transfer rate at the electrode/electrolyte interface, an interface modification strategy is demonstrated by utilization of a small amount of nonflammable and nonvolatile ionic liquid (IL) at the cathode side in SSBs. The IL acts as a wetting agent, enabling a favorable interface kinetic in SSBs. The Na 3 V 2 (PO 4 ) 3 /IL/SE/Na SSB exhibits excellent cycle performance and rate capability. A specific capacity of ≈90 mA h g −1 is maintained after 10 000 cycles without capacity decay under 10 C rate at room temperature. This provides a new perspective to design fast ion conductors and fabricate long life SSBs.

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We report a method for in situ atomic-scale observation of electrochemical delithiation in a working all-solid-state battery using a state-of-the-art chip based in situ transmission electron microscopy (TEM) holder and focused ion beam milling to prepare an all-solid-state lithium-ion battery sample. A battery consisting of LiCoO cathode, LLZO solid state electrolyte and gold anode was constructed, delithiated and observed in an aberration corrected scanning transmission electron microscope at atomic scale. We found that the pristine single crystal LiCoO became nanosized polycrystal connected by coherent twin boundaries and antiphase domain boundaries after high voltage delithiation. This is different from liquid electrolyte batteries, where a series of phase transitions take place at LiCoO cathode during delithiation. Both grain boundaries become more energy favorable along with extraction of lithium ions through theoretical calculation. We also proposed a lithium migration pathway before and after polycrystallization. This new methodology could stimulate atomic scale in situ scanning/TEM studies of battery materials and provide important mechanistic insight for designing better all-solid-state battery.

Bifunctional hydrogen electrocatalysis (hydrogen‐oxidation and hydrogen‐evolution reactions) in alkaline solution is desirable but challenging. Among all available electrocatalysts, Ni‐based materials are the only non‐precious‐metal‐based candidates for alkaline hydrogen oxidation, but they generally suffer from low activity. Here, we demonstrate that properly alloying Ni with Mo could significantly promote its electrocatalytic performance. Ni4Mo alloy nanoparticles are prepared from the reduction of molybdate‐intercalated Ni(OH)2 nanosheets. The final product exhibits an apparent hydrogen‐oxidation activity exceeding that of the Pt benchmark and a record‐high mass‐specific kinetic current of 79 A g−1 at an overpotential of 50 mV. A superior hydrogen‐evolution performance is also measured in alkaline solution. These experimental data are rationalized by our theoretical simulations, which show that alloying Ni with Mo significantly weakens its hydrogen adsorption, improves the hydroxyl adsorption and decreases the reaction barrier for water formation.

Flexible and self-supported carbon-coated FeS on carbon cloth films (denoted as FeS@C/carbon cloth) is prepared by a facial hydrothermal method combined with a carbonization treatment. The FeS@C/carbon cloth could be directly used as electrodes for Li-ion batteries (LIBs) and sodium-ion batteries (NIBs). The synthetic effects of the structure, highly electron-conductive of carbon cloth, porous structure for electrolyte access, and uniform carbon shell on FeS surface to accommodate the volume change lead to improved cyclability and rate capability. For lithium storage, the FeS@C/carbon cloth electrode delivers a high discharge capacity of 420 mAh g(-1) even after 100 cycles at a current density of 0.15 C and 370 mAh g(-1)at a high current density of 7.5 C (1 C = 609 mA g(-1). When used for sodium storage, it keeps a reversible capacity of 365 mAh g(-1)after 100 cycles at 0.15 C. Similar process can be utilized for the formation of various cathode and anode composites on carbon cloth for flexible energy storage devices.

Control of the precise lattice alignment of monolayer molybdenum disulfide (MoS ) on hexagonal boron nitride (h-BN) is important for both fundamental and applied studies of this heterostructure but remains elusive. The growth of precisely aligned MoS domains on the basal plane of h-BN by a low-pressure chemical vapor deposition technique is reported. Only relative rotation angles of 0° or 60° between MoS and h-BN basal plane are present. Domains with same orientation stitch and form single-crystal, domains with different orientations stitch and from mirror grain boundaries. In this way, the grain boundary is minimized and a continuous film stitched by these two types of domains with only mirror grain boundaries is obtained. This growth strategy is also applicable to other 2D materials growth.