Junxian Zhang

Nitrogen‐Doped Carbon Membrane Derived from Polyimide as Free‐Standing Electrodes for Flexible Supercapacitors

Nitrogen-doped carbon materials have attracted great interest in the energy storage due to the better electrochemical performances than the pristine carbon materials. In this work, a heterocyclic polyimide containing benzopyrrole and benzimidazole rings is carbonized to fabricate the free-standing and flexible carbon membrane (CarbonPI ) with a high packing density (0.89 cm(-3)), in which the location of nitrogen atoms in the doped configurations is easily controlled. XPS analysis indicates that quaternary nitrogen is the predominant nitrogen-doped configurations. The high content of nitrogen effectively improves the wettability of the electrode materials. The CarbonPI membrane exhibits excellent volumetric capacitance (159.3 F cm(-3) at 1 A g(-1)), high rate capability (127.5 F cm(-3) at 7 A g(-1)), and long cycle life. TEM images reveal the very slight change of the microstructure of graphitic nanosheet of CarbonPI during the long charge/discharge cycles.

A top-down approach for fabricating free-standing bio-carbon supercapacitor electrodes with a hierarchical structure

Biomass has delicate hierarchical structures, which inspired us to develop a cost-effective route to prepare electrode materials with rational nanostructures for use in high-performance storage devices. Here, we demonstrate a novel top-down approach for fabricating bio-carbon materials with stable structures and excellent diffusion pathways; this approach is based on carbonization with controlled chemical activation. The developed free-standing bio-carbon electrode exhibits a high specific capacitance of 204 F g−1 at 1 A g−1; good rate capability, as indicated by the residual initial capacitance of 85.5% at 10 A g−1; and a long cycle life. These performance characteristics are attributed to the outstanding hierarchical structures of the electrode material. Appropriate carbonization conditions enable the bio-carbon materials to inherit the inherent hierarchical texture of the original biomass, thereby facilitating effective channels for fast ion transfer. The macropores and mesopores that result from chemical activation significantly increase the specific surface area and also play the role of temporary ion-buffering reservoirs, further shortening the ionic diffusion distance.

Rational design of polyaniline/MnO2/carbon cloth ternary hybrids as electrodes for supercapacitors

Two types of ternary composites were fabricated by reversing the deposition sequence of polyaniline (PANI) and MnO2 layers on plasma treated carbon cloth (m-CC), i.e., PANI@MnO2@m-CC and MnO2@PANI@m-CC. By comparison, PANI@MnO2@m-CC displayed a unique porous structure and possessed a better electrochemical performance than that of MnO2@PANI@m-CC. The morphological transformation of MnO2 petals into nanoparticles while anchoring PANI nanorods increases the interactions between the two pseudoactive materials. An asymmetric supercapacitor was fabricated by using PANI@MnO2@m-CC as the positive electrode and activated microwave exfoliated graphite oxide (‘a-MEGO’)@m-CC as the negative electrode. The asymmetric supercapacitor showed a maximum energy density of 33.9 W h kg−1 (at a power density of 319.0 W kg−1) and power density of 17.2 kW kg−1 (at an energy density of 14.3 W h kg−1) at an operating voltage of 2.0 V, suggesting PANI@MnO2@m-CC is a promising electrode candidate for supercapacitors.

Vapor-phase polymerization of poly(3, 4-ethylenedioxythiophene) nanofibers on carbon cloth as electrodes for flexible supercapacitors

In this study, an evaporative vapor-phase polymerization approach was employed to fabricate vertically aligned poly(3, 4-ethylenedioxythiophene) (PEDOT) nanofibers on the surface of carbon cloth (CC). Optimized reaction conditions can obtain well distributed and uniform layers of high-aspect-ratio PEDOT nanofibers on CC. The hierarchical PEDOT/CC structure as a freestanding electrode exhibits good electrochemical properties. As a flexible symmetric supercapacitor, the PEDOT/CC hybrid electrode displays a specific areal capacitance of 201.4 mF cm(-2) at 1 mA cm(-2), good flexibility with a higher value (204.6 mF cm(-2)) in the bending state, and a good cycling stability of 92.4% after 1000 cycles. Moreover, the device shows a maximum energy density of 4.0 Wh kg(-1) (with a power density of 3.2 kW kg(-1)) and a maximum power density of 4.2 kW kg(-1) (with an energy density of 3.1 Wh kg(-1)). The results demonstrate that PEDOT may be a promising material for storage devices through a simple and efficient vapor-phase polymerization process with precisely controlled reaction conditions.