Hybrid catalyst with monoclinic MoTe2 and platinum for efficient hydrogen evolution

© 2019 Author(s).Transition metal dichalcogenides (TMDs) are considered as promising catalysts for the hydrogen evolution reaction (HER) owing to their abundant active sites such as atomic vacancies and step edges. Moreover, TMDs have polymorphism, which has stimulated extensive studies on tuning of surface electronic structures for an active HER. The polymorphism in TMDs provides an opportunity for new hybrid catalysts with TMDs and other catalytic metals via surface engineering that can create a novel functional surface of the catalytic electrode for the active HER. Here, we report a hybrid catalyst with monoclinic MoTe2 and platinum (Pt) for the HER. Pt atoms were chemically bound to the surface of monoclinic MoTe2 that has an atomically distorted lattice structure, which produces a distinct Pt-Te alloy layer. The Pt/MoTe2 hybrid catalyst exhibits an active HER with a Tafel slope of 22 mV per decade and an exchange current density of 1.0 mA/cm2, which are the best values among those reported for TMD-based catalysts. The use of minimum amount of Pt on atomically distorted metallic TMDs realizes rich catalytic active sites on large basal planes for efficient hydrogen productio

Role of anionic vacancy for active hydrogen evolution in WTe2

© 2020Transition metal dichalcogenides (TMDs) have been investigated for use in a hydrogen evolution reaction (HER), mostly in the form of nano-sized flakes, due to the abundant active site formation by nanostructuring, surface functionalization, and phase engineering. However, the physical origin of the active HER on TMDs remains to be clarified. Here, we investigate the role of anion vacancies for the HER on the basal plane of single-crystalline tungsten dichalcogenide (WTe2), a group 6 metallic TMD. The WTe2 with a small amount of anionic (Te) vacancies shows an improved overpotential from –0.707 to –0.568 V and a constant Tafel slope of 154 mV/dec in the HER. Photoemission spectroscopy, combined with first-principle calculations, reveals that the work function of WTe2 is decreased by the anionic Te vacancies, which improves the bulk conductivity and the overpotential in the HER with the material. Moreover, the enlarged electrochemical active surface area with a large number of Te vacancies in the WTe2 critically improves the HER performance with decreases in the overpotential and the Tafel slope, –0.119 V and 79 mV/dec, respectively. Our results show that the modulation of work function and surface morphology is a promising way to improve the HER in TMDs11Nsciescopu

Lifshitz Transition and Non-Fermi Liquid Behavior in Highly Doped Semimetals

The classical Fermi liquid theory and Drude model have provided fundamental ways to understand the resistivity of most metals. The violation of the classical theory, known as non-Fermi liquid (NFL) transport, appears in certain metals, including topological semimetals, but quantitative understanding of the NFL behavior has not yet been established. In particular, the determination of the non-quadratic temperature exponent in the resistivity, a sign of NFL behavior, remains a puzzling issue. Here, a physical model to quantitatively explain the Lifshitz transition and NFL behavior in highly doped (a carrier density of ≈1022 cm−3) monoclinic Nb2Se3 is reported. Hall and magnetoresistance measurements, the two-band Drude model, and first-principles calculations demonstrate an apparent chemical potential shift by temperature in monoclinic Nb2Se3, which induces a Lifshitz transition and NFL behavior in the material. Accordingly, the non-quadratic temperature exponent in the resistivity can be quantitatively determined by the chemical potential shift under the framework of Fermi liquid theory. This model provides a new experimental insight for nontrivial transport with NFL behavior or sign inversion of Seebeck coefficients in emerging materials.11Nsciescopu

Active hydrogen evolution through lattice distortion in metallic MoTe2

Engineering surface atoms of transition metal dichalcogenides (TMDs) is a promising way to design catalysts for efficient electrochemical reactions including the hydrogen evolution reaction (HER). However, materials processing based on TMDs, such as vacancy creation or edge exposure, for active HER, has resulted in insufficient atomic-precision lattice homogeneity and a lack of clear understanding of HER over 2D materials. Here, we report a durable and effective HER at atomically defined reaction sites in 2D layered semimetallic MoTe2 with intrinsic turnover frequency (TOF) of 0.14 s(-1) at 0 mV overpotential, which cannot be explained by the traditional volcano plot analysis. Unlike former electrochemical catalysts, the rate-determining step of the HER on the semimetallic MoTe2, hydrogen adsorption, drives Peierls-type lattice distortion that, together with a surface charge density wave, unexpectedly enhances the HER. The active HER using unique 2D features of layered TMDs enables an optimal design of electrochemical catalysts and paves the way for a hydrogen economy113151sciescopu