Ultrathin Nitrogen-Enriched Hybrid Carbon Nanosheets for Supercapacitors with Ultrahigh Rate Performance and High Energy Density

Flower-like NiO/ZnO hybrid coated with N-doped carbon layer derived from metal-organic hybrid frameworks as novel anode material for high performance sodium-ion batteries

Metal-organic hybrid frameworks are considered as the promising precursor to prepare high performance anode materials for sodium-ion batteries (SIBs). In the present work, flower-like NiO/ZnO@NC with hollow and porous structure was prepared via a facile solvothermal and calcination process. The hollow and porous structure not only improve the electron transport capability, and but also inhibits the aggregation and accommodates the volume change of NiO/ZnO@NC. Meanwhile, the coated amorphous carbon layer could also increase the electron conductivity and buffer the huge volume expansion of active material NiO/ZnO. When used as anode for SIBs, NiO/ZnO@NC demonstrates a high specific capacity of 300 mAh g^-1 with good cycling stability for 150 cycles, fast charge and discharge capability (154 mAh g^-1 at 2500 mA g^-1) and superior long cycling life at high current density for 2500 cycles. The strategy in this work should provide a new insight into fabrication novel structural anode materials for high performance SIBs.

Preparation of Porous Activated Carbons for High Performance Supercapacitors from Taixi Anthracite by Multi-Stage Activation

Coal-based porous materials for supercapacitors were successfully prepared using Taixi anthracite (TXA) by multi-stage activation. The characterization and electrochemical tests of activated carbons (ACs) prepared in different stages demonstrated that the AC from the third-stage activation (AC_III) shows good porous structures and excellent electrochemical performances. AC_III exhibited a fine specific capacitance of 199 F g⁻¹ at a current density of 1 A g⁻¹ in the three-electrode system, with 6 mol L⁻¹ KOH as the electrolyte. The specific capacitance of AC_III remained 190 F g⁻¹ even despite increasing the current density to 5 A g⁻¹, indicating a good rate of electrochemical performance. Moreover, its specific capacitance remained at 98.1% of the initial value after 5000 galvanostatic charge-discharge (GCD) cycle tests at a current density of 1 A g⁻¹, suggesting that the AC_III has excellent cycle performance as electrode materials for supercapacitors. This study provides a promising approach for fabricating high performance electrode materials from high-rank coals, which could facilitate efficient and clean utilization of high-rank coals.

Ultrathin 2D nitrogen-doped carbon nanosheets for high performance supercapacitors: insight into the effects of graphene oxides

Ultrathin 2D nitrogen-doped carbon nanosheets with a thickness of about 5 nm have been facilely synthesized from potato starch by using graphene oxides (GO) as the structure-directing agent. The pore structures and surface properties can be feasibly and rationally tailored by addition of a certain amount of GO in the precursor. The addition of GO to the potato starch can increase the surface areas and the pyridinic-N and pyrrolic-N ratios of the as-prepared 2D carbon nanosheets. The as-obtained ultrathin nitrogen-doped carbon nanosheets with the optimized amount of GO in potato starch (3 wt%) possess a unique 2D structure, a high N content, and high ratios of pyridinic-N and pyrrolic-N, exhibiting a high capacitance of 301 F g-1 at 0.5 A g-1, superior rate capability of 81% at 50 A g-1, and good cycling stability in 6 M KOH electrolyte. Experimental and theoretical results show that high pyridinic-N and pyrrolic-N ratios in the NCNSs are beneficial for improving the electrochemical performance. This work may provide helpful guidance for understanding the effect of the addition of GO to biomass precursors on the electrochemical performance of the 2D nitrogen-doped carbon electrodes for supercapacitors.

Polyhydroxyalkanoate-Modified Bacterium Regulates Biomass Structure and Promotes Synthesis of Carbon Materials for High-Performance Supercapacitors

Biomass-derived carbons have been extensively explored as electrode materials in supercapacitors. However, the type of biomass selected and its specific structure affects the synthesis of the advanced biomass-derived carbon materials. A green and facile method for the synthesis of carbon material with nanoscale and microscale porous structures for supercapacitors has been developed, based on regulating the original cell structure of the bacterial strain. The cell structure is modified in situ by regulating the accumulation of polyhydroxyalkanoate under controlled cultivation conditions. The novel bacterial in situ modification and nitrogen doping endow this hierarchically derived carbon material with improved performance. This material exhibits an extremely high specific capacitance (420 F g^-1 at 1 A g^-1 ) and long cycling stability (97 % capacitance retention after 10 000 cycles at 5 A g^-1 ) in aqueous electrolytes. More importantly, the symmetric supercapacitor delivers a superior energy density of 60.76 Wh kg^-1 at 625 W kg^-1 in an ionic liquid electrolyte system. Moreover, all components in the synthesis are low in cost, environmentally friendly, and biocompatible. With these unique features, the bacterial self-modification mode opens new avenues into the design and production of a wide range of hierarchical structures.

Self-Templating Synthesis of 3D Hollow Tubular Porous Carbon Derived from Straw Cellulose Waste with Excellent Performance for Supercapacitors

A three-dimensional hollow tubular porous carbon (SCPC) was prepared from straw cellulose waste through a self-templating method combined with NaOH activation. Straw cellulose acts both as carbon source and structural template. The obtained SCPC exhibits a 3D hierarchical porous network structure. SCPC has a high specific surface area, a high mesoporosity ratio, and a low resistivity, which make it display excellent electrochemical performance for supercapacitors. SCPC showed a high specific capacitance of 312.57 F g^-1 in 6 m KOH at 0.5 A g^-1 , an excellent rate performance of 281.32 F g^-1 even at 15 A g^-1 , and an outstanding cyclic stability of 92.93 % capacitance retention after 20 000 cycles at 1 A g^-1 . SCPC-based supercapacitors can deliver an energy density of 8.67 Wh kg^-1 at a power density of 3.50 kW kg^-1 in 6 m KOH and an energy density of 28.56 Wh kg^-1 at a power density of 14.09 kW kg^-1 in 1 m Et₄ NBF₄ /PC, which demonstrates the possibility of applying SCPC in supercapacitors. This research not only offers a facile and sustainable method for the preparation of hierarchical porous carbon for electrochemical energy storage devices but also provides a highly efficient method for the utilization of biomass waste.

Graphene oxide template-directed synthesis of porous carbon nanosheets from expired wheat flour for high-performance supercapacitors

2D N,S co-doped porous carbon nanosheets are prepared in the presence of GO from expired wheat flour.