Modulation of electronic structure of Ni3S2 via Fe and Mo co-doping to enhance the bifunctional electrocatalytic activities for HER and OER.

Heazlewoodite nickel sulfide (Ni3S2) is advocated as a promising nonnoble catalyst for electrochemical water splitting because of its unique structure configuration and high conductivity. However, the low active sites and strong sulfur-hydrogen bonds (S-Hads) formed on Ni3S2 surface greatly inhibit the desorption of Hads and reduce the hydrogen and oxygen evolution reaction (HER and OER) activity. Doping is a valid strategy to stimulate the intrinsic catalytic activity of pristine Ni3S2 via modifying the active site. Herein, the Ni foam supported Fe and Mo co-doped Ni3S2 electrocatalysts (Fe-MoS2/Ni3S2@NF) have been constructed using Keplerate polyoxomolybdate {Mo72F30} as precursor through a facile hydrothermal process. Experimental results certificate that Fe and Mo co-doping can effectively tune the local electronic structure, facilitate the interfacial electron transfer, and improve the intrinsic activity. Consequently, the Fe-MoS2/Ni3S2@NF display more excellent HER and OER activity than MoS2/Ni3S2@NF and bare Ni3S2@NF by delivering the 10 and 50 mA cm-2 current densities at ultra-low overpotentials of 74/175 and 80/160 mV for HER and OER. Moreover, when coupled in an alkaline electrolyzer, Fe-MoS2/Ni3S2@NF approached the current of 10 mA cm-2 under a cell voltage of 1.60 V and exhibit excellent stability. The strategy to realize tunable catalytic behaviors via foreign metal doping provides a new avenue to optimize the water splitting catalysts.

Enhanced field-emission properties of buckled α-borophene by means of Li decoration: a first-principles investigation.

In this study, the structures and field-emission properties of Li-decorated buckled α-borophene (BBP) were investigated by first-principles density functional theory at the PW91 level. Using the computed binding energies, Hirshfeld- and electrostatic potential-derived charges, induced dipole moments, densities of states, and ionization potentials, we evaluated the influence of an applied electric field on the structural stability, work function, and field-emission current of the Li-decorated BBP nanostructures. Furthermore, we also explored the quantitative dependence of the emission current on the electric field, Li concentration, and molecular orbitals. The computed results indicated that increasing the electric field and Li concentration has a considerably positive effect on the field-emission performance of the Li-decorated BBPs. Besides advantages including small work functions and low ionization potentials, most remarkably, the field-emission current can be as high as 48.81 µA in Li4/BBP (supercell with 36 atoms only) under a rather small applied electric field of 0.05 V Å-1, which rivals the highest value of the graphene-BN nanocomposite among all the theoretical nanostructures presented to date. Our results highly support the fact that Li-decorated BBPs can be appealing field-emission cathode materials with an extremely high emission current.

In Situ Synthesis of Vertical Standing Nanosized NiO Encapsulated in Graphene as Electrodes for High-Performance Supercapacitors.

NiO is a promising electrode material for supercapacitors. Herein, the novel vertically standing nanosized NiO encapsulated in graphene layers (G@NiO) are rationally designed and synthesized as nanosheet arrays. This unique vertical standing structure of G@NiO nanosheet arrays can enlarge the accessible surface area with electrolytes, and has the benefits of short ion diffusion path and good charge transport. Further, an interconnected graphene conductive network acts as binder to encapsulate the nanosized NiO particles as core-shell structure, which can promote the charge transport and maintain the structural stability. Consequently, the optimized G@NiO hybrid electrodes exhibit a remarkably enhanced specific capacity up to 1073 C g-1 and excellent cycling stability. This study provides a facial strategy to design and construct high-performance metal oxides for energy storage.

Confirming the key role of Ar+ ion bombardment in the growth feature of nanostructured carbon materials by PECVD.

In order to confirm the key role of Ar+ ion bombardment in the growth feature of nanostructured carbon materials (NCMs), here we report a novel strategy to create different Ar+ ion states in situ in plasma enhanced chemical vapor deposition (PECVD) by separating catalyst film from the substrate. Different bombardment environments on either side of the catalyst film were created simultaneously to achieve multi-layered structural NCMs. Results showed that Ar+ ion bombardment is crucial and complex for the growth of NCMs. Firstly, Ar+ ion bombardment has both positive and negative effects on carbon nanotubes (CNTs). On one hand, Ar+ ions can break up the graphic structure of CNTs and suppress thin CNT nucleation and growth. On the other hand, Ar+ ion bombardment can remove redundant carbon layers on the surface of large catalyst particles which is essential for thick CNTs. As a result, the diameter of the CNTs depends on the Ar+ ion state. As for vertically oriented few-layer graphene (VFG), Ar+ ions are essential and can even convert the CNTs into VFG. Therefore, by combining with the catalyst separation method, specific or multi-layered structural NCMs can be obtained by PECVD only by changing the intensity of Ar+ ion bombardment, and these special NCMs are promising in many fields.

Thermal degradation of luminescence in inorganic perovskite CsPbBr3 nanocrystals.

The luminescence properties of inorganic perovskite CsPbBr3 nanocrystals (NCs) with emissions of 492 and 517 nm under thermal annealing treatment were studied by temperature-dependent photoluminescence (PL) spectroscopy. The CsPbBr3 NCs were annealed in vacuum at various temperatures. It was found that the NCs exhibited significant thermal degradation of PL at thermal annealing temperatures above 320 K. The transmission electron microscopy, X-ray diffraction and PL spectroscopy demonstrated that the size of NCs almost kept constant at thermal annealing temperatures below 360 K while it significantly enlarged at higher thermal temperatures above 380 K. The PL intensities, peak energies and linewidths of the annealed NCs, as a function of temperature, are discussed in detail. The PL degradation of the NCs was related to the formation of nonradiative recombination centers due to the loss of ligands and growth of NCs under thermal annealing.