[en] Spinel transition metal oxide is a promising pseudocapacitive materials but the instability gives it narrow practical application. It is shown herein, that an effective remedy for these problems can be achieved by introducing highly conductive two dimensional (2D) reduced graphene oxide (rGO) substrate on which NiFe₂O₄ nanoparticles are well distributed. The rGO-NiFe₂O₄ hybrids with different NiFe₂O₄ contents were tailored to explore the source of the improvement in capacitance performance. It is found that rGO nanosheets in the hybrid can be used as a conductive substrate to accelerate the electron transport. Moreover, NiFe₂O₄ nanoparticles with a certain volume can simultaneously prevent the restacking of rGO and increase the pseudocapacitance. The G-N3 (30 wt% NiFe₂O₄) hybrid holds enhanced specific capacitance up to 210.9 F g⁻¹ at 0.5 A g⁻¹ far above that of pristine NiFe₂O₄ (50 F g⁻¹), and exhibits superior cycle stability with no obvious capacity loss even after 5000 cycles. This research indicates that a tailoring method can promote the electrochemical performance of NiFe₂O₄, and hopefully accelerate the commercialization of spinel transition metal oxides as electrode materials for supercapacitor.

[en] Spinel transition metal oxides are regarded as one of the finest pseudocapacitive materials, while unexpected stability hinders their practical application. For addressing such issue, herein, we use a simple hydrothermal method to grow NiFe₂O₄ nanoparticles on the surface of reduced graphene oxide (rGO). The rGO nanosheets in the hybrid can be used as a conductive substrate to accelerate the movement of electrons and ions, and they can also inhibit the aggregation of NiFe₂O₄. As the electrochemically active materials, the NiFe₂O₄ nanoparticles can reduce the self-stacking of rGO as well as increase the pseudocapacitance. The rGO-NiFe₂O₄ hybrid delivers improved specific capacitance of 215.7 F g⁻¹ at 0.5 A g⁻¹, and exhibits superior cycle stability with no obvious capacity loss after 10000 cycles. Our work demonstrates a method for effectively improving the electrochemical performance of NiFe₂O₄, and accelerating the commercialization of transition metal oxides as electrode materials for supercapacitors. (paper)

[en] The characteristics of multistep compound nuclear reactions with the giant resonances as doorway states are discussed in this Brief Report. A cross-section formula describing the above nuclear reactions is derived from the Feshbach-Kerman-Koonin theory with a proper modification of its basic assumptions. Parametrization of this formula leads to an extension of the conventional exciton model. As an application, the derived formula is used to calculate the cross sections of the photonuclear reactions exciting the giant dipole resonances in different nuclei, and the results are in good agreement with experimental data

[en] We investigate the dielectric properties of multi-walled carbon nanotubes (MWCNTs) and graphite filling in SiO₂ with the filling concentration of 2–20 wt.% in the frequency range of 10²–10⁷ Hz. MWCNTs and graphite have general electrical properties and percolation phenomena owing to their quasi-structure made up of graphene layers. Both permittivity ε and conductivity σ exhibit jumps around the percolation threshold. Variations of dielectric properties of the composites are in agreement with the percolation theory. All the percolation phenomena are determined by hopping and migrating electrons, which are attributed to the special electronic transport mechanism of the fillers in the composites. However, the twin-percolation phenomenon exists when the concentration of MWCNTs is between 5–10 wt.% and 15–20 wt.% in the MWCNTs/SiO₂ composites, while in the graphite/SiO₂ composites, there is only one percolation phenomenon in the graphite concentration of 10–15 wt.%. The unique twin-percolation phenomenon of MWCNTs/SiO₂ is described and attributed to the electronic transfer mechanism, especially the network effect of MWCNTs in the composites. The network formation plays an essential role in determining the second percolation threshold of MWCNTs/SiO₂

[en] We synthesize composite systems of multi-wall carbon nanotubes (MWCNTs)/SiO₂ by using the sol-gel method. The dielectric properties of the systems with different-concentration MWCNTs are studied. In our MWCNTs/SiO₂ inorganic systems, the twin-percolation phenomenon exists when the concentrations of MWCNTs are 5–10% and 15–20%. The permittivity and conductivity have jumping changes. The twin-percolation phenomenon is attributed to the special transfer mechanism of MWCNTs in the system, determined by hopping and migrating electrons. Variations of dielectric properties and conductance of the MWCNTs/SiO₂ systems are conformed to the percolation theory. The special percolation phenomenon and electric properties of MWCNTs/SiO₂ can help us comprehend the conductivity mechanism of the MWCNTs/SiO₂ systems effectively, and promote the development of a high performance function composite system. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

[en] screw-cone-like Zn₂GeO₄-ZnO particles with a base diameter of approximately 400 nm and a height of 400–800 nm or so were successfully synthesised by combustion oxidation of zinc and germanium powder at 960°C. No catalyst or carrier gases were used. XRD and SEM analyses reveal that Zn₂GeO₄ and ZnO grew to parasitic crystals evenly in interaction with each other. EDS images exhibit the homogeneity of the distribution of Ge and Zn. The formation mechanism is discussed and attributed to the unique growth process of the screw-cone-like Zn₂GeO₄-ZnO particles and its vapour-solid (VS) growth mechanism. In addition, the Zn₂GeO₄-ZnO particles could tune the energy level structure of nano-tetrapod ZnO, which leads to the emission peak redshift from 376 nm to 435 nm and enhances the light emission intensity in the visible light region

[en] We research the adsorption geometries and electronic structures of pristine graphene (p-GR) and Li-doped graphene (Li-GR) before and after CO adsorption by first-principles. The adsorption energies E_a_d of CO on p-GR and Li-GR are calculated. The results demonstrate that E_a_d of CO on Li-GR is from −3.3eV to −3.5eV, meanwhile Q is up to 0.13e, which indicate that strong electrostatic attractions occur between CO and Li-GR, while CO is physically adsorbed on p-GR. The obvious accumulated charge in electron density difference and increasing carrier density suggest that the conductivity of Li-GR is improved considerably after CO adsorption. An adsorption mechanism is also proposed. Our results provide a path to achieving CO sensors with high performance. (paper)

[en] The high-temperature permittivity of quartz fibre-reinforced silicon dioxide (SiO₂/SiO₂) nano-composites is studied on the basis of the multi-scale theoretical model. We obtain the permittivity of the SiO₂/SiO₂ at high temperature, which is dependent on the temperature by data-mining. The result shows that the permittivity and loss tangent obtained by data-mining are well consistent with the measured ones. The high-temperature permittivity can be well predicted for SiO₂/SiO₂ by the as-proposed model and the data-mining method. (condensed matter: electronic structure, electrical, magnetic, and optical properties)