A high recoverable energy storage density polymer composite film has been designed in which the ferroelectric-paraelectric 0.85 (K0.5Na0.5NbO3)-0.15SrTiO3 (abbreviated as KNN-ST) solid solution particles were introduced into polyvinylidene fluoride (PVDF) polymer as functional fillers. The effects of the polarization properties of K0.5Na0.5NbO3 (KNN) and KNN-ST particles on the energy storage performances of KNN-ST/PVDF film were systemically studied. And the introduction of SrTiO3 (ST) was effective in reducing the remnant polarization of the particles, improving the dielectric properties and recoverable energy storage density of the KNN-ST/PVDF films. Compared to KNN/PVDF films, the dielectric permittivity of composite films was enhanced from 17 to 38 upon the introduction of ST. A recoverable energy storage density of 1.34 J/cm3 was achieved, which is 202.60% larger than that of the KNN/PVDF composite films. The interface between the particles and the polymer matrix was considered to the enhanced dielectric permittivity of the films. And the reduced remnant polarization of the composites was regarded as the improving high recoverable energy storage density. The results demonstrated that combing ferroelectric- paraelectric particles with polymers might be a key method for composites with excellent dielectric permittivity, high energy storage density, and energy efficiency.

In this paper, the distribution of the charge trap levels in polyimide (PI) films was investigated by using photo-stimulated discharge (PSD) technique, which was to explore the effect of photoconductivity on photo-stimulated discharge current. The PSD spectra show that the photo-stimulated discharge current of the PI films is mainly distributed in the range of 649–320 nm, but there are two significant current peaks when the wavelength is 300 nm and 244 nm, respectively. By studying the reason of generating two current peaks, it is concluded that the two current peaks are not generated by trapped charge de-trapping but generated by photoconductivity of charge-transfer complex in the PI films. According to the research, it is concluded that the trap levels in PI films are mainly distributed in the range of 1.92 eV–3.88 eV.

No abstract

We have comparatively investigated the adsorption behaviors of atomic platinum on the internal and external surfaces of single walled pristine and doped carbon nanotubes using density functional theory calculations. The equilibrium adsorption geometries, binding energy (E b ), and density of states of the Pt on these CNTs were calculated at the PBEPBE/LanL2DZ level. Our results reveal that the binding abilities of atomic Pt onto the internal and external surfaces of the CNTs are in following orders by dopant:The binding energy of O-CNT towards atomic Pt more than doubles that of pristine CNT, which can be attributed to the active carbon sites created by C-O bond breaking, while N-CNT demonstrates the smallest enhancement due to its similar binding configuration for Pt with pristine CNT. In contrast, as a result of the confined space of nanotube, Pt has two more bonding sites inside the B-and Be-CNT, while the external counterparts prefer the double coordinated C-X bridge site. In this respect, Pt atom in Pt@X-CNT (X = B and Be) presents more delocalized and bonding states than Pt/X-CNT, though the binding energy of the former is smaller than the latter.

PBEPBE-D3 calculations were performed to investigate how platinum (Pt) interacts with the internal and external surfaces of single-walled pristine, Si-, Ge-, and Sn-doped (6,6) carbon nanotubes (CNTs). Our calculations showed that atomic Pt demonstrates stronger binding strength on the external surfaces than the internal surface adsorption for the same type of nanotube. In cases of external surface adsorptions, Si-, Ge-, and Sn-doped CNTs show comparable binding energies for Pt, at least 1.40 eV larger than pristine CNT. This enhancement can be rationalized by the strong covalent interactions between Pt and XAC (X 5 Si, Ge, and Sn) pairs based on struc-tural and projected density of states analysis. In terms of internal surface adsorptions, Ge and Sn doping could significantly enhance the binding of Pt. Pt atom shows much more delocalized and bonding states inside Ge-and Sn-doped CNTs, indicating multiple-site interaction pattern when atomic Pt is confined inside the nanotubes. However, the internal surface of Si-doped CNT presents limited enhancement in Pt adsorption with respect to that of pristine CNT because of their similar binding geometries.

No abstract

No abstract

Dynamic characteristics of discharge particles are described within the framework of a two-dimensional photoionization-hydrodynamic numerical model for the discharge process of SF6-N2-CO2 gas mixtures at atmospheric pressure, under a uniform DC applied field. The finite difference-flux corrected transport (FD-FCT) algorithm is used in the numerical implementation for improving the accuracy and efficiency. Then the tempo-spatial distributions of the gap-space electric field and electron velocity are calculated from the microscopic mechanism, and the dynamic behaviors of charged particles are obtained in detail. Meanwhile, the tempo-spatial critical point of the avalanche-to-streamer in this model is discovered, and several microscopic parameters are also investigated. The results showed that the entire gap discharge process can be divided into two phases of avalanche and streamer according to Raether-Meek criterion; the electron density within the discharge channel is lower compared to that of positive and negative ions; space charge effect is a dominant factor for the distortion of spatial electric field, making the discharge channel expand toward both electrodes faster; photoionization provides seed electrons for a secondary electron avalanche, promoting the formation and development speed of the streamer.