Radicals are inevitable intermediates during the charging and discharging of organic redox electrodes. The increase of the reactivity of the radical intermediates is desirable to maximize the capacity and enhance the rate capability but is detrimental to cycling stability. Therefore, it is a great challenge to controllably balance the redox reactivity and stability of radical intermediates to optimize the electrochemical properties with a good combination of high specific capacity, excellent rate capability, and long-term cycle life. Herein, we reported the redox and tunable stability of radical intermediates in covalent organic frameworks (COFs) considered as high capacity and stable anode for sodium-ion batteries. The comprehensive characterizations combined with theoretical simulation confirmed that the redox of C−O• and α-C radical intermediates play an important role in the sodiation/desodiation process. Specifically, the stacking behavior could be feasibly tuned by the thickness of 2D COFs, essentially determining the redox reactivity and stability of the α-C radical intermediates and their contributive capacity. The modulation of reversible redox chemistry and stabilization mechanism of radical intermediates in COFs offers a novel entry to design novel high performance organic electrode materials for energy storage and conversion.

A porous and mat-like polyaniline/sodium alginate (PANI/SA) composite with excellent electrochemical properties was polymerized in an aqueous solution with sodium sulfate as a template. Ultraviolet-visible spectra, X-ray diffraction pattern, and Fourier transform infrared spectra were employed to characterize the PANI/SA composite, indicating that the PANI/SA composite was successfully prepared. The PANI/SA nanofibers with uniform diameters from 50 to 100 nm can be observed on scanning electron microscopy. Cyclic voltammetry and galvanostatic charge/discharge tests were carried out to investigate the electrochemical properties. The PANI/SA nanostructure electrode exhibits an excellent specific capacitance as high as 2093 F g(-1), long cycle life, and fast reflect of oxidation/reduction on high current changes. The remarkable electrochemical characteristic is attributed to the nanostructured electrode materials, which generates a high electrode/electrolyte contact area and short path lengths for electronic transport and electrolyte ion. The approach is simple and can be easily extended to fabricate nanostructural composites for supercapacitor electrode materials.

Despite great recent progress with graphene-based materials, the development of strong and cost-efficient multifunctional graphene-filled polymer composites has not yet to be achieved. A key challenge in the fabrication of nanoplatelet-filled polymer composites is the ability to realize the nanometer-level dispersion and the planar orientation of nanosheets in polymer matrices. In this report, ultrathin multilayer (PVA/GO) n films were successfully fabricated by bottom-up layer-by-layer (LBL) assembly of poly(vinyl alcohol) (PVA) and exfoliated graphene oxide (GO), in which exfoliated GO nanosheets were used as the building blocks. Typical tapping-mode atomic force microscope (AFM) and field emission scanning electron microscope (FESEM) images demonstrate an ordered arrangement of organic and inorganic layers. A significant enhancement of mechanical properties has been achieved, that is, a 98.7% improvement of elastic modulus (E r ) and a 240.4% increase of hardness. This may be attributed to the well-defined layered architecture with high degree of planar orientation and nanolevel assemblies of GO nanosheets in the polymer matrices.

No abstract

Free-standing three-dimensional hierarchical porous reduced graphene oxide foam (RGO-F) was first fabricated by a “dipping and dry” method using nickel foam as a template.