Wangsheng Chu

Metallic Nickel Nitride Nanosheets Realizing Enhanced Electrochemical Water Oxidation

Exploring efficient and inexpensive oxygen evolution reaction (OER) electrocatalysts is of great importance for various electrochemical energy storage and conversion technologies. Ni-based electrocatalysts have been actively pursued because of their promising activity and earth abundance. However, the OER efficiency for most of the developed Ni-based electrocatalysts has been intrinsically limited due to their low electrical conductivity and poor active site exposure yield. Herein, we report metallic Ni3N nanosheets as an efficient OER electrocatalyst for the first time. The first-principles calculations and electrical transport property measurements unravel that the Ni3N is intrinsically metallic, and the carrier concentration can be remarkably improved with dimensional confinement. The EXAFS spectra provide solid evidence that the Ni3N nanosheets have disordered structure resultant of dimensional reduction, which then could provide more active sites for OER. Benefiting from enhanced electrical conductivity with metallic behavior and atomically disordered structure, the Ni3N nanosheets realize intrinsically improved OER activity compared with bulk Ni3N and NiO nanosheets. Our finding suggests that metallic nitride nanosheets could serve as a new group of OER electrocatalysts with excellent property.

Ultrathin nickel hydroxide and oxide nanosheets: synthesis, characterizations and excellent supercapacitor performances.

High-quality ultrathin two-dimensional nanosheets of α-Ni(OH)2 are synthesized at large scale via microwave-assisted liquid-phase growth under low-temperature atmospheric conditions. After heat treatment, non-layered NiO nanosheets are obtained while maintaining their original frame structure. The well-defined and freestanding nanosheets exhibit a micron-sized planar area and ultrathin thickness (<2 nm), suggesting an ultrahigh surface atom ratio with unique surface and electronic structure. The ultrathin 2D nanostructure can make most atoms exposed outside with high activity thus facilitate the surface-dependent electrochemical reaction processes. The ultrathin α-Ni(OH)2 and NiO nanosheets exhibit enhanced supercapacitor performances. Particularly, the α-Ni(OH)2 nanosheets exhibit a maximum specific capacitance of 4172.5 F g−1 at a current density of 1 A g−1. Even at higher rate of 16 A g−1, the specific capacitance is still maintained at 2680 F g−1 with 98.5% retention after 2000 cycles. Even more important, we develop a facile and scalable method to produce high-quality ultrathin transition metal hydroxide and oxide nanosheets and make a possibility in commercial applications.

Single-Atom Pt as Co-Catalyst for Enhanced Photocatalytic H2 Evolution

Isolated single-atom platinum (Pt) embedded in the sub-nanoporosity of 2D g-C3 N4 as a new form of co-catalyst is reported. The highly stable single-atom co-catalyst maximizes the atom efficiency and alters the surface trap states of g-C3 N4 , leading to significantly enhanced photocatalytic H2 evolution activity, 8.6 times higher than that of Pt nanoparticles and up to 50 times that for bare g-C3 N4 .

Atomically Dispersed Iron–Nitrogen Species as Electrocatalysts for Bifunctional Oxygen Evolution and Reduction Reactions

Rational design of non-noble materials as highly efficient, economical, and durable bifunctional catalysts for oxygen evolution and reduction reactions (OER/ORR) is currently a critical obstacle for rechargeable metal-air batteries. A new route involving S was developed to achieve atomic dispersion of Fe-Nx species on N and S co-decorated hierarchical carbon layers, resulting in single-atom bifunctional OER/ORR catalysts for the first time. The abundant atomically dispersed Fe-Nx species are highly catalytically active, the hierarchical structure offers more opportunities for active sites, and the electrical conductivity is greatly improved. The obtained electrocatalyst exhibits higher limiting current density and a more positive half-wave potential for ORR, as well as a lower overpotential for OER under alkaline conditions. Moreover, a rechargeable Zn-air battery device comprising this hybrid catalyst shows superior performance compared to Pt/C catalyst. This work will open a new avenue to design advanced bifunctional catalysts for reversible energy storage and conversion devices.

Strain Dynamics of Ultrathin VO2 Film Grown on TiO2 (001) and the Associated Phase Transition Modulation

Tuning the metal insulator transition (MIT) behavior of VO2 film through the interfacial strain is effective for practical applications. However, the mechanism for strain-modulated MIT is still under debate. Here we directly record the strain dynamics of ultrathin VO2 film on TiO2 substrate and reveal the intrinsic modulation process by means of synchrotron radiation and first-principles calculations. It is observed that the MIT process of the obtained VO2 films can be modulated continuously via the interfacial strain. The relationship between the phase transition temperature and the strain evolution is established from the initial film growth. From the interfacial strain dynamics and theoretical calculations, we claim that the electronic orbital occupancy is strongly affected by the interfacial strain, which changes also the electron-electron correlation and controls the phase transition temperature. These findings open the possibility of an active tuning of phase transition for the thin VO2 film through the interfacial lattice engineering.

Phase-Transformation Engineering in Cobalt Diselenide Realizing Enhanced Catalytic Activity for Hydrogen Evolution in an Alkaline Medium.

Phase-transformation engineering is successfully applied in designing an alkaline hydrogen evolution reaction (HER) electrocatalyst. Benefiting from phase-transformation engineering, which endows higher electrical conductivity, ideal water adsorption energy, and faster transformation efficiency of Hads into hydrogen, cubic-phase CoSe2 realizes an enhanced electrocatalytic activity for HER under alkaline conditions.

Stable Metallic 1T‐WS2 Nanoribbons Intercalated with Ammonia Ions: The Correlation between Structure and Electrical/Optical Properties

Stable metallic 1T-WS2 nanoribbons with zigzag chain superlattices, highly stabilized by ammonia-ion intercalation, are produced using a facile bottom-up process. The atomic structure of the nanoribbons, including W-W reconstruction and W-S distorted octahedral coordination, results in distinctive electrical transport and optical Raman scattering properties that are very different from semiconducting 2H-WS2 . The correlations between structure and properties are further confirmed by theory calculations.

Engineering the Electronic State of a Perovskite Electrocatalyst for Synergistically Enhanced Oxygen Evolution Reaction

A surface hydrogen effect to modulate the pure electronic-state transition in perovskite Ca0.9 Yb0.1 MnO3 synergistically generates a more suitable eg electron filling status and better conductivity. This achieves 100 times higher catalytic activity compared to that of a pristine sample.

Growth and phase transition characteristics of pure M-phase VO2 epitaxial film prepared by oxide molecular beam epitaxy

VO2 epitaxial film with large size has been prepared by oxide-molecular beam epitaxy method on Al2O3 (0001) substrate. The VO2 film shows a perfect crystal orientation, uniformity, and distinct metal-insulator phase transition (MIT) characteristics. It is observed that the MIT character is closely associated with the crystal defects such as oxygen vacancies. By controlling the growth condition, the MIT temperature can be tuned through modifying the content of oxygen vacancies. The role of the oxygen vacancies on the phase transition behavior of this VO2 film is discussed in the framework of the hybridization theory and the valence state of vanadium.

Heterogeneous Lollipop-like V2O5/ZnO Array: A Promising Composite Nanostructure for Visible Light Photocatalysis

ZnO/V(2)O(5) core-shell nanostructures have been prepared by a two-step synthesis route through combined hydrothermal growth and magnetron sputtering. After annealing under oxygen ambience, a ZnO/V(2)O(5) heterogeneous lollipop-like nanoarray formed. The microstructure and crystal orientation of those nanolollipops were investigated by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), which show single crystal structure. The optical properties were characterized by UV-vis spectroscopy and showed quite different absorption curves for the as-deposited and annealed samples. The ZnO/V(2)O(5) nanolollipops demonstrated excellent photocatalytic activity in terms of decomposing 2,6-dichlorophenol (2,6-DCP) under visible light, indicating their promising potential as catalysts for industrial wastewater and soil pollution treatments.