Electrocatalysts remain vitally important for the rational management of intermediate polysulfides (LiPSs) in the realm of Li−S batteries. In terms of transition-metal-based candidates, in situ evolution of electrocatalysts in the course of an electrochemical process has been acknowledged; nevertheless, consensus has not yet been reached on their real functional states as well as catalytic mechanisms. Herein, we report an all-chemical vapor deposition design of the defective vanadium diselenide (VSe 2 )−vertical graphene (VG) heterostructure on carbon cloth (CC) targeting a high-performance sulfur host. The electrochemistry induces the sulfurization of VSe 2 to VS 2 at Se vacancy sites, which propels the adsorption and conversion of LiPSs. Accordingly, the VSe 2 −VG@CC/S electrode harvests an excellent cycling stability at 5.0 C with a capacity decay of only 0.039% per cycle over 800 cycles, accompanied by a high areal capacity of 4.9 mAh cm −2 under an elevated sulfur loading of 9.6 mg cm −2 . Theoretical simulation combined with operando characterizations reveals the key role played by the Se vacancy with respect to the electrocatalyst evolution and LiPS regulation. This work offers insight into the rational design of heterostructure sulfur hosts throughout defect engineering.

The growth of single‐crystal III‐nitride films with a low stress and dislocation density is crucial for the semiconductor industry. In particular, AlN‐derived deep‐ultraviolet light‐emitting diodes (DUV‐LEDs) have important applications in microelectronic technologies and environmental sciences but are still limited by large lattice and thermal mismatches between the epilayer and substrate. Here, the quasi‐van der Waals epitaxial (QvdWE) growth of high‐quality AlN films on graphene/sapphire substrates is reported and their application in high‐performance DUV‐LEDs is demonstrated. Guided by density functional theory calculations, it is found that pyrrolic nitrogen in graphene introduced by a plasma treatment greatly facilitates the AlN nucleation and enables fast growth of a mirror‐smooth single‐crystal film in a very short time of ≈0.5 h (≈50% decrease compared with the conventional process), thus leading to a largely reduced cost. Additionally, graphene effectively releases the biaxial stress (0.11 GPa) and reduces the dislocation density in the epilayer. The as‐fabricated DUV‐LED shows a low turn‐on voltage, good reliability, and high output power. This study may provide a revolutionary technology for the epitaxial growth of AlN films and provide opportunities for scalable applications of graphene films.

Witnessingc ompositional evolution and identifying the catalytically active moiety of electrocatalysts is of paramount importance in Li-S chemistry.N evertheless,t his field remains elusive.Wereport the scalable salt-templated synthesis of Se-vacancy-incorporated MoSe 2 architecture (SeVs-MoSe 2 ) and reveal the phase evolution of the defective precatalyst in working Li-S batteries.T he interaction between lithium polysulfides and SeVs-MoSe 2 is probed to induce the transformation from SeVs-MoSe 2 to MoSeS.F urthermore,o perando Raman spectroscopya nd ex situ X-rayd iffraction measurements in combination with theoretical simulations verify that the effectual MoSeS catalyst could help promote conversion of Li 2 S 2 to Li 2 S, thereby boosting the capacity performance.The Li-S battery accordingly exhibits asatisfactory rate and cycling capability even with and elevated sulfur loading and lean electrolyte conditions (7.67 mg cm À2 ; 4.0 mLmg À1 S ). This work elucidates the design strategies and catalytic mechanisms of efficient electrocatalysts bearing defects.

Single-crystalline GaN-based light-emitting diodes (LEDs) with high efficiency and long lifetime are the most promising solid-state lighting source compared with conventional incandescent and fluorescent lamps. However, the lattice and thermal mismatch between GaN and sapphire substrate always induces high stress and high density of dislocations and thus degrades the performance of LEDs. Here, the growth of high-quality GaN with low stress and a low density of dislocations on graphene (Gr) buffered sapphire substrate is reported for high-brightness blue LEDs. Gr films are directly grown on sapphire substrate to avoid the tedious transfer process and GaN is grown by metal-organic chemical vapor deposition (MOCVD). The introduced Gr buffer layer greatly releases biaxial stress and reduces the density of dislocations in GaN film and In Ga N/GaN multiple quantum well structures. The as-fabricated LED devices therefore deliver much higher light output power compared to that on a bare sapphire substrate, which even outperforms the mature process derived counterpart. The GaN growth on Gr buffered sapphire only requires one-step growth, which largely shortens the MOCVD growth time. This facile strategy may pave a new way for applications of Gr films and bring several disruptive technologies for epitaxial growth of GaN film and its applications in high-brightness LEDs.

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