Evolution of “adsorption-insertion” K+ storage behaviors in flower-like carbons with tunable heteroatom doping and graphitic structure

Expanding the graphitic interlayer spacing and introducing heteroatoms into the carbon structure are the two key strategies for boosting the potassium storage performance. To fundamentally clarify the relation of graphitic...

Smart Designs of Mo Based Electrocatalysts for Hydrogen Evolution Reaction

As a sustainable and clean energy source, hydrogen can be generated by electrolytic water splitting (i.e., a hydrogen evolution reaction, HER). Compared with conventional noble metal catalysts (e.g., Pt), Mo based materials have been deemed as a promising alternative, with a relatively low cost and comparable catalytic performances. In this review, we demonstrate a comprehensive summary of various Mo based materials, such as MoO2, MoS2 and Mo2C. Moreover, state of the art designs of the catalyst structures are presented, to improve the activity and stability for hydrogen evolution, including Mo based carbon composites, heteroatom doping and heterostructure construction. The structure–performance relationships relating to the number of active sites, electron/ion conductivity, H/H2O binding and activation energy, as well as hydrophilicity, are discussed in depth. Finally, conclusive remarks and future works are proposed.

Preparation and Fluorescent Wavelength Control of Multi-Color Nitrogen-Doped Carbon Nano-Dots

It is known that, by taking advantage of heteroatom doping, the electronic states and transition channels in carbon nano-dots (CNDs) can be effectively modulated. Thus, the photoluminescence (PL) properties of CNDs can be changed. For potential applications of CNDs as advanced materials for optoelectronic devices, it is important and significant to develop the practical techniques for doping heteroatoms into CNDs. In this work, we synthesize the multi-color fluorescent by using a fast and effective microwave method where the CNDs are nitrogen-doped. We examine the influence of different ratios of the raw materials on the structure and optical properties of N-CNDs. The results show that the prepared N-CNDs can generate blue (445 nm), green (546 nm), and orange (617 nm) fluorescence or PL with the mass ratio of the raw materials at 1:1, 1:2 and 1:3, respectively. We find that the N content in N-CNDs leads to different surface/edge states in n−π∗ domain. Thus, the wavelength of the PL emission from N-CNDs can be tuned via controlling the N concentration doped into the CNDs. Moreover, it is shown that the intensity of the PL from N-CNDs is mainly positively related to the content of C-O groups attached on the surface/edges of the N-CNDs. This study provides an effective experimental method and technical way to improve the fluorescent emission, and to modulate the color of the PL emission from CNDs.

Regulating oxygen vacancies in Co3O4 by combining solution reduction and Ni2+ impregnation for oxygen evolution reaction

Oxygen vacancies are considered to be an important factor to influence the electronic structure and charge transport of electrocatalysts in the field of energy chemistry. Various strategies focused on oxygen vacancy engineering are proved to be efficient for further improving the electrocatalytic performance of Co3O4. Herein, an optimal Co3O4 with rich oxygen vacancies have been synthesized via a two-step process combining solution reduction and Ni2+ impregnation. The as-prepared electrocatalyst exhibits an enhanced oxygen evolution performance with the overpotential of 330 mV at the current density of 10 mA cm−2 in alkaline condition, which is 84 mV lower than that of pristine one. With the increasing of oxygen vacancies , the charge transfer efficency and surface active area are relatively enhanced reflected by the Tafel slope and double-layer capacitance measurement. These results indicate that combining solution reduction and heteroatom doping can be a valid way for efficient metal oxides-based electrocatalyst development by constructing higher concentration of oxygen vacancy.

Synthesis of Azepine- or Azocine-Embedded Hexabenzocoronene-Based Nanographenes

Classical polycyclic aromatic hydrocarbons (PAHs) are a large group of π-conjugated planar structures. To explore more properties of PAHs, new structures were designed including nonplanar topologies and heteroatom-doping moieties. As an important nanographene (NG) unit, hexabenzocoronene (HBC) and its derivatives have been intensively researched. Numbers of HBC-based nonplanar NGs were developed and the heteroatom-doped HBC-based NGs have been designed and synthesized as well. Herein, we synthetically summarized some synthetic methods for seven- or eight-membered ring containing HBC-based NGs, and discussed our newly synthesized azepine- or azocine-embedded NGs by using a modified synthetic route and a traditional Müllen’s synthetic method, respectively.

Photoelectric and Magnetic Properties of Boron Nitride Nanosheets with Turbostratic Structure and Oxygen Doping

Turbostratic and oxygen doping (3.7 atom % ) hexagonal boron nitride nanosheets (TO-BNNSs) with abundant defect sites, were synthesized by pyrolyzing the mixture of melamine cyanurate and boric acid. Systematic analyses reveal a highly disordered structures and covalent oxygen-doping in the TO-BNNSs. These features endow the product with increased unpaired electrons, localized charge asymmetry and spin polarization. While compared with bulk h-BN, the optical bandgap of TO-BNNSs drop down to ~5.2 from ~5.7 eV, dielectric constant raised from ~2.1 to ~2.4, the saturation magnetic moment increased from ~0.011 to ~0.033 emu/g, and the coercivity enlarged from ~73.56 to ~367.39 Oe. These results suggest that h-BN materials with turbostratic structure and heteroatom-doping have extensive application prospect in the fields of nanoscale optics, electronics and magnetics.