Search

Molybdenum carbides show great potential to replace platinum for electrocatalytic hydrogen evolution reaction (HER) to resolve the problem of hydrogen production, due to their high reserves, stability, low cost, and structural diversity. However, the effect of atomic configurations of different surfaces on HER is still lacking theoretical insights. In this work, the HER activity on 29 surfaces of seven phases is systematically explored by density functional theory, taking into account water effect. The exchange current for each surface is also given. Totally, there are nine surfaces which own high exchange current (>0.1 mA/cm2), especially the hydroxylated (014)-C and (010) of TiP-MoC, (110) of β-Mo2C, and (100)-C of α-Mo2C (1.410, 0.835, 0.687, and 0.464 mA/cm2, respectively). Combining with the stabilities of the surfaces for each phase, the phases with high HER activity could be also screened out. The electronic properties, including electron transfer to adsorbed hydrogen and the shift of the electronic states coupled by oxygen and adsorbed hydrogen orbitals, are applied to uncover the termination of surface and water effect on HER. Our results are expected to contribute to the understanding of the HER on different surfaces of molybdenum carbides and give some evidence for control synthesis of high HER activity surfaces.

Kagome materials have recently garnered substantial attention due to the intrinsic flat band feature and the stimulated magnetic and spin-related many-body physics. In contrast to their bulk counterparts, two-dimensional (2D) kagome materials feature more distinct kagome bands, beneficial for exploring novel quantum phenomena. Herein, we report the direct synthesis of an ultrathin kagome-structured Co-telluride (Co9Te16) via a molecular beam epitaxy (MBE) route and clarify its formation mechanism from the Co-intercalation in the 1T-CoTe2layers. More significantly, we unveil the flat band states in the ultrathin Co9Te16and identify the real-space localization of the flat band states by in situscanning tunneling microscopy/spectroscopy (STM/STS) combined with first-principles calculations. A ferrimagnetic order is also predicted in kagome-Co9Te16. This work should provide a novel route for the direct synthesis of ultrathin kagome materials via a metal self-intercalation route, which should shed light on the exploration of the intriguing flat band physics in the related systems.

Searching for none or less Pt-containing electrocatalytic materials for hydrogen evolution is a promising way to reduce the cost of hydrogen production. Thus, a computational screening of electrocatalytic materials for hydrogen evolution reaction (HER), Pt monolayer on transitional metals (Pt/TM), are carried out by DFT in this work. According to several prerequisites, including difficulty of synthesis, stability in electrochemical environment, HER activity, and economical cost, several stable, high activity, and low cost surfaces for HER are chosen. In detail, the Pt/TM(001)[TM = Fe, Mo, V, W or Nb], Pt/TM(111)[TM = Ag, Pd or Au], and Pt/Re(0001) moieties are found to have a predicted high activity comparable to pure Pt. In particular, the five Pt/TM(001) surfaces are economical and seldom reported. Even more, Pt/TM(001)[W, Nb, V, Fe] may be even much better than pure Pt, for both the suitable hydrogen adsorption ability and larger exchange current. Further DFT analysis indicates the HER activity on Pt/TM is related with the d-band center of the Pt layer, which could be tuned by the transition metal in substrate. Our results are expected to contribute to the understanding of the HER on Pt/TM and give theoretical evidence for corresponding experiments.

As an emerging member of monoelemental two-dimensional (2D) materials, 2D tellurium (tellurene) has recently attracted intensive attention due to its polymorphism arising from the multivalent nature and fascinating properties such as wide-range band gaps, high carrier mobilities, etc. Herein, we predict the formation of a rectangular-phase tellurene on Ni(111) by first-principles density functional theory (DFT) calculations and realize its direct syntheses and characterizations by molecular beam epitaxy (MBE) and scanning tunneling microscopy (STM). We reveal that the monolayer rectangular tellurene and underlying Ni(111) substrate are strongly coupled, along with good lattice registry along two mutually perpendicular directions, which serves as the key driving force for the tellurene formation. We also uncover the unique morphological transitions of Te/Ni(111) from rectangular tellurene monolayer, to uniform periodic striped patterns at the second layer, and then to thick striped patterns. This work should offer valuable insights for the substrate-mediated syntheses of monoelemental 2D materials, thus propelling their phase engineering and intriguing property explorations.

Collecting water from fog flow is emerging as a promising solution to the water shortage problem. This work demonstrated a novel environmentally responsive water collector made from a self-prepared Janus polyvinyl alcohol sponge in combination with a two-way shape memory alloy spring, which transforms the traditional manner of static water collection into a dynamic one. The unidirectional water transport of the Janus structure together with the dynamic collection approach correspond to a 30.8% increase in the water-collection rate (WCR). The resultant WCR is up to 5.1 g/h, which ranks relatively high compared to similar studies. The light- and thermal-response capability, easy fabrication, and good cycling performance indicate that our devices could be utilized in a variety of applications. In this work, an efficient, intelligent adaptive, simple-preparation, precision-guided, and economical fog-collecting devices are recommended. Our work provides new insights on the design of high-efficient water collectors with practicability.

Self-intercalation of native metal atoms in two-dimensional (2D) transition metal dichalcogenides has received rapidly increasing interest, due to the generation of intriguing structures and exotic physical properties, however, only reported in limited materials systems. An emerging type-II Dirac semimetal, NiTe2, has inspired great attention at the 2D thickness region, but has been rarely achieved so far. Herein, we report the direct synthesis of mono- to few-layer Ni-tellurides including 1T-NiTe2and Ni-rich stoichiometric phases on graphene/SiC(0001) substrates under ultra-high-vacuum conditions. Differing from previous chemical vapor deposition growth accompanied with transmission electron microscopy imaging, this work combines precisely tailored synthesis with on-site atomic-scale scanning tunneling microscopy observations, offering us visual information about the phase modulations of Ni-tellurides from 1T-phase NiTe2to self-intercalated Ni3Te4and Ni5Te6. The synthesis of Ni self-intercalated NixTeycompounds is explained to be mediated by the high metal chemical potential under Ni-rich conditions, according to density functional theory calculations. More intriguingly, the emergence of superconductivity in bilayer NiTe2intercalated with 50% Ni is also predicted, arising from the enhanced electron–phonon coupling strength after the self-intercalation. This work provides insight into the direct synthesis and stoichiometric phase modulation of 2D layered materials, enriching the family of self-intercalated materials and propelling their property explorations.