Phase engineering has a profound effect on the chemical bonding and electric configuration, which play significant roles in regulating the activities of catalysts. The metallic phases of transition-metal dichalcogenides (TMDs) have been proposed to show more excellent performance in electrocatalysis over their semiconductor phase; however, the controllable phase engineering for these compounds remains a challenge. In this work, filmlike 1T′ MoTe 2 (F-1T′ MoTe 2 ), filmlike 1T′/ 2H MoTe 2 , porous 1T′ MoTe 2 , small granular 1T′ MoTe 2 , and large granular 1T′ MoTe 2 were successfully synthesized on a flexible carbon cloth (CC) substrate with 3D network structure by chemical vapor deposition (CVD). The high activity of the assynthesized F-1T′ MoTe 2 /CC electrode for HER in 1 M H 2 SO 4 solution was demonstrated by the small onset overpotential of −230.7 mV, a low Tafel slope of 127.1 mV dec −1 , and robust electrochemical durability. The enhanced electrocatalytic activity and stability of F-1T′ MoTe 2 /CC benefit from excellent catalytically active sites and remarkable conductivity of the F-1T′ MoTe 2 . The results demonstrate an efficient route to designing and constructing metallic-phase TMD catalysts for high-performance electrocatalytic devices. KEYWORDS: 1T′ MoTe 2 , carbon cloth, CVD, H 2 SO 4 , HER

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Using the first-principles calculation, we systematically studied the electronic properties of the bilayer transition metal dichalcogenides (TMDs) MX 2 (M = Mo, W; X = S, Se, Te) with replacing one, two, three or four layers of X atoms as Y atoms (X ≠ Y = S, Se, Te). By comparison, it is found that when the inner two layers of chalcogenide atoms are different, the system has both valence band offset (VBO) and conduction band offset (CBO). Among them, values of the band offsets reach maxima when the inner one layer of X atoms is replaced by Y atoms, namely forming the asymmetric Janus bilayer XMX/YMX. We take SMoS/SeMoS as an example to analyze the formation of the band offsets and the improvement of optoelectronic properties. Importantly, it is also found that both external electric field and biaxial strain can regulate electronic structures of asymmetric Janus bilayer TMDs with noticeable modulation of the values of band offsets. When the external electric field changes from negative to positive continually, CBO decreases and VBO increases. While when the biaxial strain changes from compression to stretch continually, CBO increases and VBO decreases. These findings enrich the study of bilayer TMDs that can be used as optoelectronic, nanoelectronic and valleytronic devices.

Searching for ideal two-dimensional (2D) topological insulators (TIs) with large bandgaps is significant for the realization of the quantum spin Hall effect (QSHE) at room temperature. By employing ab initio calculations based on the density functional theory, we predict a novel 2D TI, semi-oxidized phosphorus thallium O-PTl, which harbors a series of excellent properties, such as high flexibility, chemical stability, and a large tunable 2D TI bandgap. In contrast to the monolayer PTl, semi-oxidation on one side of P induces a large TI bandgap of 403 meV, which can be further enlarged to 460 meV by biaxial strain, far exceeding the temperature required for practical application. Due to the semi-oxidation on one side of P, the material is chemically stable against surface oxidization when grown on suitable substrates forming heterostructures. For the O-PTl/BN and O-PTl/graphane heterostructures, we find that the nontrivial topological bandgap of O-PTl is almost not affected by substrate, which is crucial to the experimental realization of QSHE. Our results demonstrate a new type of 2D TI materials and provide a new alternative strategy to devise topological electronic devices operating at room temperature.