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Single-atom catalysts (SACs) have shown great potential in the electrochemical oxygen reduction reaction (ORR) toward hydrogen peroxide (H 2 O 2 ) production. However, current studies are mainly focused on 3d transition-metal SACs, and very little attention has been paid to 5d SACs. Here, a new kind of W SAC anchored on a porous O, N-doped carbon nanosheet (W 1 /NO-C) is designed and prepared via a simple coordination polymer-pyrolysis method. A unique local structure of W SAC, terdentate W 1 N 1 O 2 with the coordination of two O atoms and one N atom, is identified by the combination of aberrationcorrected scanning transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray absorption fine structure spectroscopy. Remarkably, the as-prepared W 1 /NO-C catalyzes the ORR via a 2epathway with high onset potential, high H 2 O 2 selectivity in the wide potential range, and excellent operation durability in 0.1 m KOH solution, superior to most of state-of-the-art H 2 O 2 electrocatalysts ever reported. Theoretical calculations reveal that the C atoms adjacent to O in the W 1 N 1 O 2 -C moiety are the most active sites for the 2e -ORR to H 2 O 2 with the optimal binding energy of the HOO* intermediate. This work opens up a new opportunity for the development of high-performance W-based catalysts for electrochemical H 2 O 2 production.

Molybdenum disulfide (MoS 2 ) is a promising layerstructured material for use in many applications due to its tunable structural and electronic properties in terms of its structural phases. Its performance including efficiency and durability is often dependent on its mechanical properties. To understand the effects of the structural phase on its mechanical properties, a comparative study on the mechanical properties of bulk 2H, 3R, 1T, and 1T′ MoS 2 was conducted using the first-principles density functional theory. Since considerable applications of MoS 2 are developed through strain engineering, the impact of the external pressure on its mechanical properties was also considered. Our results suggest a strong relationship between the mechanical properties of MoS 2 and the structural symmetry of its crystal. Accordingly, the impacts of the external pressure on the mechanical properties of MoS 2 also greatly vary with respect to the structural phases. Among all of the considered phases, the 2H and 3R MoS 2 have a larger bulk modulus, Young's modulus, shear modulus, and microhardness due to their higher stability. Conversely, 1T and 1T′ MoS 2 are less strong. As such, 1T and 1T′ MoS 2 can be a better candidate for strain engineering.

Mechanical properties of two dimensional (2D) materials are essential for their applications since they determine their stiffness and stability [1][2][3]. The 2D materials with superior mechanical properties, e.g. graphene with the bulk Young's modules of about 1 TPa, can be promising candidates as composite materials, protective coatings, fibers and energy storage materials [4]. To this end, numerous studies have been devoted to discovering strong 2D materials. A recent study by Lipatov et al experimentally demonstrates that the 2D Ti 3 C 2 T x MXene monolayer is a novel strong 2D material, which possess the similar in-plane planar Young's modulus of graphene. This work paved the avenue to search other strong 2D MXene monolayer for the similar applications. MXenes is a new family of 2D transition metal carbides and carbonitrides with more than 70 known species, which can be synthesized by the exfoliation of MAX phases [5,6]. MXenes have a general formula of M n+1 X n , where M and X represent a metal and C/N, respectively. Whereas, n can be 1, 2, or 3 in the known MXene materials [5]. In practicality, MXenes are too chemically active, which can be synthesized through the surface functionalization using terminal groups including -OH, -O and -F. The terminal groups are termed as T. As such, the surface functionalized MXenes are labelled as M n+1 X n T x [7,8]. The surface functionalized MXenes have further led to numerous technological applications, e.g. energy storage [9, 10], electromagnetic interference shielding [11,12], composite materials [13], catalysts [14] and sensors [15]. While the structural and electronic properties of M n+1 X n T x have

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The recent progress of multiscale numeric methods for investigating in-plane mechanical properties of 2D monolayers is reviewed.

Single-atoms (SAs) supported on various substrates have emerged as a new form of electrocatalysts for hydrogen evolution reaction (HER). The exfoliated MXenes possess rich defects/vacancies and surface oxygen groups, can be favorably utilized to anchor SAs. Here, we take advantage of the exfoliated Ti 3 C 2 T x to anchor Ru-SAs on Ti 3 C 2 T x through a wet-chemistry impregnation process. The obtained Ru SA @Ti 3 C 2 T x possesses excellent HER activity, especially under high current densities. Remarkably, Ru SA @Ti 3 C 2 T x can readily attain high current densities of 1 and 1.5 A cm À2 at low over potentials of 425.7 and 464.6 mV, respectively, demonstrating its potential for practical applications. The A 1g vibration frequency shift of the Raman spectrum is innovatively used to probe the surface OH coverage on Ti 3 C 2 T x , providing critical information for mechanistic studies. The experimental and theoretical studies reveal that the superior HER electrocatalytic activity of Ru SA @Ti 3 C 2 T x results from the Ru-SAs enhanced H 2 O adsorption and dissociation, and promoted H 2 formation.