Transition metal dichalcogenides (TMDs) exhibit promising catalytic properties for hydrogen generation, and several approaches including defect engineering have been shown to increase the active catalytic sites. Despite preliminary understandings in defect engineering, insights on the role of various types of defects in TMDs for hydrogen evolution catalysis are limited. Screw dislocation-driven (SDD) growth is a line defect and yields fascinating spiral and pyramidal morphologies for TMDs with a large number of edge sites, resulting in very interesting electronic and catalytic properties. The role of dislocation lines and edge sites of these spiral structures on their hydrogen evolution catalytic properties is unexplored. Here we show that the large number of active edge sites connected together by dislocation lines in the vertical direction for a spiral WS 2 domain results in exceptional catalytic properties toward hydrogen evolution reaction. A micro-electrochemical cell fabricated by photo-and electron beam-lithography processes is used to study the electrocatalytic activity of a single spiral WS 2 domain, controllably grown by chemical vapor deposition. Conductive atomic force microscopy studies show improved vertical conduction for the spiral domain, which is compared with monolayer and mechanically exfoliated thick WS 2 flakes. The obtained results are interesting and shed light on the role of SDD line defects, which contribute to large number of edge sites without compromising the vertical electrical conduction, on the electrocatalytic properties of TMDs for hydrogen evolution.

Spiral and pyramidal WS2 domains controllably synthesized through chemical vapour deposition technique exhibit interesting optical properties.

Transition metal dichalcogenides (TMDs) exhibit unique properties and show potential for promising applications in energy conversion. Mono/few-layered TMDs have been widely explored as active electrocatalysts for the hydrogen evolution reaction (HER). A controlled synthesis of TMD nanostructures with unique structural and electronic properties, leading to highly active sites or higher conductivity, is essential to achieve enhanced HER activity. Here, we demonstrate a new approach to controllably synthesize highly catalytically active oxygen-incorporated 1T and 2H WS2 nanoclusters from oxygen deficient WO3 nanorods, following chemical exfoliation and ultrasonication processes, respectively. The as-synthesized 1T nanoclusters, with unique properties of tailored edge sites, and enhanced conductivity resulting from the metallic 1T phase and oxygen incorporation, have been identified as highly active and promising electrocatalysts for the HER, with a very low Tafel slope of 47 mV per decade and a low onset overpotential of 88 mV, along with exceptionally high exchange current density and very good stability. The study could be extended to other TMD materials for potential applications in energy conversion and storage.

Exploring highly efficient and low-cost electrocatalysts for the oxygen evolution reaction (OER) is very important for the development of renewable energy conversion and storage systems. Layered metal hydroxides have been studied with great interest owing to their high electrochemical activity and stability toward OER. Herein, we demonstrate an efficient approach to engineer the surface active sites in β-Co­(OH)2 for enhanced electrocatalysis of OER. We employ a single-step bipolar electrochemical technique for the exfoliation of pristine β-Co­(OH)2(Co­(OH)2-Bulk) into thinner and smaller sheets. The as-synthesized Co­(OH)2 nanostructures with improved active sites exhibit enhanced electrocatalytic activity toward OER with a very low overpotential of 390 mV at 10 mA cm–2 and a Tafel slope of 57 mV dec–1 in alkaline media. The results provide a promising lead for the development of efficient and economically viable electrode materials for oxygen evolution electrocatalysis.

Transition metal oxysulfides (TMOS) exhibit promising catalytic properties for hydrogen evolution reactions (HER). However, the development of facile and controllable routes for obtaining nanostructured TMOS under ambient conditions still remains a significant challenge. Here we report a simple and controllable route to synthesize nanoparticles of tungsten oxysulfides (WO x S y ) that exhibit enhanced electrocatalytic activity toward HER with outstanding stability. The sulfur-rich tungsten oxysulfides with engineered anionic species can offer multiple functionalities, including abundant active sites and improved conductivity that synergistically contribute to enhanced electrocatalytic activity for HER. The optimized WO x S y electrocatalyst shows low overpotential of 103 mV at a current density of 10 mA cm–2, along with a Tafel slope of 54 mV decade–1 and 5.89 × 10–2 mA cm–2 exchange current density. Density functional theory (DFT) based calculations further establish the improved catalytic activity of tungsten oxysulfide (WO x S y ), compared to the pristine 1T-WS2, based on the free energy calculations. The present work demonstrates a highly promising approach toward the development of cost-effective, efficient, and durable electrocatalysts to replace precious metals for electrocatalytic hydrogen generation.

We present helicity resolved photoluminescence (PL) measurements of WS 2 spiral (SPI) nanostructures. We show that very high degree of circular polarization (DCP) (~94 ± 4%) is obtained from multilayer SPI samples at room temperature upon excitation with a circularly polarized laser at a wavelength near-resonant with the A-exciton (633 nm). TEM analysis showed that these SPI nanostructures have AB stacking in which the inversion symmetry is broken, and hence this leads to very high DCP. Comparison with PL from monolayer and bi-layer WS 2 samples, along with polarization resolved PL studies provide evidence for suppression of interlayer/intravalley scattering in the multilayer SPI samples.

The development of earth-abundant and highly efficient electrocatalysts for hydrogen evolution reaction (HER) in alkaline media is essential for practical alkaline water electrolysis. The possibility of tuning the electrocatalytic activity of alkaline HER electrocatalysts through various approaches, such as interfacial engineering or doping, has been recently explored. In this work, electrochemically exfoliated Co­(OH)2 and chemically derived 1T-MoS2 nanostructures are electrostatically coupled to form a synergistic nanostructured two-dimensional heterostructure, which is shown to remarkably improve the HER activity in an alkaline medium. The Co­(OH)2/1T-MoS2 heterostructure with an optimal 1:5 ratio (Co1Mo5) showed a low overpotential of 151 mV at a current density of 10 mA cm–2 and a Tafel slope of 94 mV dec–1 in alkaline media. The shift in the overpotential achieved for the heterostructure (>250 mV) compared to the individual MoS2 component is remarkably high, as per the earlier reports.

Enhancement of fluorescence emission from singlephoton quantum emitters on plasmonic nanomaterials using surface plasmon-coupled emission (SPCE) platforms has seen significant advancements. In parallel, there has also been an exponential rise in applications involving two-dimensional (2D) transition-metal dichalcogenides (TMDs) that exhibit unique exciton−plasmon interactions. Although both these Frontier research areas have impacted the development of sensor and sensing technologies, no study coalesces these two arenas for translational applications. In this work, we use thin WS 2 nanosheets for realizing 1000-fold fluorescence enhancement on the SPCE platform. Structure-dependent fluorescence enhancement exhibited by WS 2 provides new insight into the use of TMDs and exciton−plasmon coupling in SPCE substrates. Cellphone-based detection of the emitting dipole is another unique aspect of this work that presents a low-cost alternative in comparison with high-end detectors.