Effects of p- and n-type Doping in Inorganic Fullerene MoS2on the Hydrogen Evolution Reaction

Implantation of Gallium into Layered WS2 Nanostructures is Facilitated by Hydrogenation

Bombarding WS2 multilayered nanoparticles and nanotubes with focused ion beams of Ga+ ions at high doses, larger than 1016 cm-2 , leads to drastic structural changes and melting of the material. At lower doses, when the damage is negligible or significantly smaller, the amount of implanted Ga is very small. A substantial increase in the amount of implanted Ga, and not appreciable structural damage, are observed in nanoparticles previously hydrogenated by a radio-frequency activated hydrogen plasma. Density functional calculations reveal that the implantation of Ga in the spaces between adjacent layers of pristine WS2 nanoparticles is difficult due to the presence of activation barriers. In contrast, in hydrogenated WS2 , the hydrogen molecules are able to intercalate in between adjacent layers of the WS2 nanoparticles, giving rise to the expansion of the interlayer distances, that in practice leads to the vanishing of the activation barrier for Ga implantation. This facilitates the implantation of Ga atoms in the irradiation experiments.

Graphitic Carbon Cloth-Based Hybrid Molecular Catalyst: A Non-conventional, Synthetic Strategy of the Drop Casting Method for a Stable and Bifunctional Electrocatalyst for Enhanced Hydrogen and Oxygen Evolution Reactions

Hydrogen energy production through water electrolysis is envisaged as one of the most promising, sustainable, and viable alternate sources to cater to the incessant demands of renewable energy storage. Germane to our effort in this field, we report easily synthesizable and very cost-effective isoperthiocyanic acid (IPA) molecular complexes as electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under acidic and alkaline conditions. The Pd(II)IPA, Co(II)IPA, and Ni(II)IPA complexes were synthesized and were evaluated for HER and OER applications. These complexes when embedded onto graphitized carbon cloth (GrCC) exhibited a significant enhancement in the HER activity in contrast to their pristine counterparts. The hybrid electrocatalyst Pd(II)IPA among the three showed an extremely low overpotential of 94.1 mV to achieve a current density of 10 mA cm^-2, while Co(II)IPA and Ni(II)IPA complexes showed overpotentials of 367 and 394 mV, respectively, to achieve a current density of 10 mA cm^-2. These complexes on carbon cloth showed decreased charge transfer resistance compared to that of pristine metal complexes. The enhanced catalytic activity of the complexes on carbon cloth can be attributed to the porous and conducting nature of the graphitized carbon cloth. For OER activity, the Pd(II)IPA complex showed an excellent performance with an overpotential value of 210 mV, while Co(II)IPA and Ni(II)IPA exhibited overpotentials of 400 and 270 mV, respectively, to drive a current density of 10 mA cm^-2 in 0.1 M KOH. This work further widens the scope and application of molecular complexes in combination with an excellent carbon support for renewable energy storage applications.

Topology of transition metal dichalcogenides: the case of the core-shell architecture

Non-planar architectures of the traditionally flat 2D materials are emerging as an intriguing paradigm to realize nascent properties within the family of transition metal dichalcogenides (TMDs). These non-planar forms encompass a diversity of curvatures, morphologies, and overall 3D architectures that exhibit unusual characteristics across the hierarchy of length-scales. Topology offers an integrated and unified approach to describe, harness, and eventually tailor non-planar architectures through both local and higher order geometry. Topological design of layered materials intrinsically invokes elements highly relevant to property manipulation in TMDs, such as the origin of strain and its accommodation by defects and interfaces, which have broad implications for improved material design. In this review, we discuss the importance and impact of geometry on the structure and properties of TMDs. We present a generalized geometric framework to classify and relate the diversity of possible non-planar TMD forms. We then examine the nature of curvature in the emerging core-shell architecture, which has attracted high interest due to its versatility and design potential. We consider the local structure of curved TMDs, including defect formation, strain, and crystal growth dynamics, and factors affecting the morphology of core-shell structures, such as synthesis conditions and substrate morphology. We conclude by discussing unique aspects of TMD architectures that can be leveraged to engineer targeted, exotic properties and detail how advanced characterization tools enable detection of these features. Varying the topology of nanomaterials has long served as a potent methodology to engineer unusual and exotic properties, and the time is ripe to apply topological design principles to TMDs to drive future nanotechnology innovation.

Theoretical investigation on the hydrogen evolution reaction mechanism at MoS2 heterostructures: the essential role of the 1T/2H phase interface

DFT calculations have been performed to study the HER mechanism at 1T/2H MoS₂ heterostructures. The HER activity along the 1T/2H phase interface is comparable with those at the Mo-edge of 2H MoS₂ and the basal plane of 1T MoS₂.

Electrochemical Hydrogen Evolution over Hydrothermally Synthesized Re-Doped MoS2 Flower-Like Microspheres

In this research, we report a simple hydrothermal synthesis to prepare rhenium (Re)- doped MoS₂ flower-like microspheres and the tuning of their structural, electronic, and electrocatalytic properties by modulating the insertion of Re. The obtained compounds were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Structural, morphological, and chemical analyses confirmed the synthesis of poorly crystalline Re-doped MoS₂ flower-like microspheres composed of few stacked layers. They exhibit enhanced hydrogen evolution reaction (HER) performance with low overpotential of 210 mV at current density of 10 mA/cm², with a small Tafel slope of 78 mV/dec. The enhanced catalytic HER performance can be ascribed to activation of MoS₂ basal planes and by reduction in charge transfer resistance during HER upon doping.

Manganese Doping of MoSe2 Promotes Active Defect Sites for Hydrogen Evolution

Transition-metal dichalcogenides (TMDs) are being widely pursued as inexpensive, earth-abundant substitutes for precious-metal catalysts in technologically important reactions such as electrochemical hydrogen evolution reaction (HER). However, the relatively high onset potentials of TMDs relative to Pt remain a persistent challenge in widespread adoption of these materials. Here, we demonstrate a one-pot synthesis approach for substitutional Mn-doping of MoSe₂ nanoflowers to achieve appreciable reduction in the overpotential for HER along with a substantial improvement in the charge-transfer kinetics. Electron microscopy and elemental characterization of our samples show that the MoSe₂ nanoflowers retain their structural integrity without any evidence for dopant clustering, thus confirming true substitutional doping of the catalyst. Complementary density functional theory calculations reveal that the substitutional Mn-dopants act as promoters, rather than enhanced active sites, for the formation of Se-vacancies in MoSe₂ that are known to be catalytically active for HER. Our work advances possible strategies for activating MoSe₂ and similar TMDs by the use of substitutional dopants, not for their inherent activity, but as promoters of active chalcogen vacancies.