Superior catalytic activity and high chemical stability of inexpensive electrocatalysts for the hydrogen evolution reaction (HER) are crucial to the large-scale production of hydrogen from water. The nonprecious two-dimensional MoSe materials emerge as a potential candidate, and the improvement of their catalytic activity depends on the optimization of active reaction sites at both the edges and the basal plane. Herein, the structural stability, electrocatalytic activity, and HER mechanisms on a series of MoSe catalytic structures including of point defects, holes, and edges have been explored by using first-principles calculations. Our calculated results demonstrate that thermodynamically stable defects (e.g., V, V, Se, and V) and edges (e.g., Mo-R and Se-R) in MoSe are very similar to the case of MoS, but their HER activity is higher than that of the corresponding structures in MoS, which is in good agreement with experimental observations. Furthermore, a Fermi-abundance model is proposed to explain the fundamental correlation between the HER activity of various MoSe catalysts and their intrinsic electronic structures, and this model is also applicable for assessing the HER activity of other types of catalysts, such as MoS and Pt. Moreover, two different HER mechanisms have been revealed in the MoSe catalytic structures: the Volmer-Tafel mechanism is preferred for the V and V structures, whereas the Volmer-Heyrovsky mechanism is more favorable for other MoSe catalytic structures. The present work suggests that MoSe with appropriate defects and edges is able to compete against the Pt-based catalysts and also opens a route to design highly active electrocatalysts for the HER.

Two-dimensional VS2 nanomaterials have emerged as highly efficient and inexpensive electrocatalysts for the hydrogen evolution reaction (HER), and the further improvement of their HER performance depends on the understanding of the catalytic mechanism and activity in various pristine and defective structures. Here, structural stability, electronic properties, and HER activity of monolayer VS2 nanosheets with various intrinsic point defects are studied by using first-principles calculations. Compared to the most-studied 2H-phase MoS2 basal plane, both 2H- and 1T-phase VS2 basal planes exhibit superior catalytic activity due to their metallic properties. With the introduction of intrinsic point defects onto VS2 basal planes, we find that there are four types of stable defects in the 2H phase (i.e., Sad, Svac, Vad, and VS) and three types of stable defects in the 1T phase (i.e., Sad, Svac, and Vad). Moreover, the formation of Svac, Vad, and VS structures in the 2H phase and Vad in the 1T phase can enhance the HER activity of basal planes, which implies that the synthesis of VS2 nanosheets at the V-rich condition facilitates the achievement of high HER performance. The HER activity of pristine and defective VS2 structures can be well understood by a Fermi-abundance model that is also suitable to describe a broad class of electrocatalytic HER systems. This work provides a deep insight into the HER activity of single-layer VS2 and the guidance for synthesizing highly active electrocatalysts in transition-metal dichalcogenides.

Based on the experimental evidence and DFT calculations, a Pd–carbon nanotube interface facilitates the rate-determining step in the formic acid dehydrogenation reaction.

Shape-specific copper oxide nanostructures have attracted increasing attention due to their widespread applications in energy conversion, sensing, and catalysis. Advancing our understanding of structure, composition, and surface chemistry transformations in shaped copper oxide nanomaterials during changes in copper oxidation state is instrumental from both applications and preparative nanochemistry standpoints. Here, we report the study of structural and compositional evolution of amorphous copper (II) hydroxide nanoparticles under hydrazine reduction conditions that resulted in the formation of crystalline Cu2O and composite Cu2O-N2H4 branched particles. The structure of the latter was influenced by the solvent medium. We showed that hydrazine, while being a common reducing agent in nanochemistry, can not only reduce the metal ions but also coordinate to them as a bidentate ligand and thereby integrate within the lattice of a particle. In addition to shape and composition transformation of individual particles, concurrent interparticle attachment and ensemble shape evolution were induced by depleting surface stabilization of individual nanoparticles. Not only does this study provide a facile synthetic method for several copper (I) oxide structures, it also demonstrates the complex behavior of a reducing agent with multidentate coordinating ability in nanoparticle synthesis.

Chiral linear assemblies of plasmonic nanoparticles with chiral optical activity often show low asymmetry factors. Systematic understanding of the structure-property relationship in these systems must be improved to facilitate rational design of their chiroptical response. Here we study the effect of large-area interparticle gaps in chiral linear nanoparticle assemblies on their chiroptical properties using a tetrahelix structure formed by a linear face-to-face assembly of nanoscale Au tetrahedra. Using finite-difference time-domain and finite element methods, we performed in-depth evaluation of the extinction spectra and electric field distribution in the tetrahelix structure and its dependence on various geometric parameters. The reported structure supports various plasmonic modes, one of which shows a strong incident light handedness selectivity that is associated with large face-to-face junctions. This works highlights the importance of gap engineering in chiral plasmonic assemblies to achieve g-factors greater than 1 and produce structures with a handedness-selective optical response.