Xiujuan Qin

Synthesis of nitrogen-doped carbon cellular foam with ultra-high rate capability for supercapacitors

Three-dimensional (3D) interconnected N-doped porous carbons (NPCs) with different levels of pore structure are synthesized by a template method using MnOx as template and N-enriched pyrrole as carbon source. The fabricated materials show favorable pore size distribution in the range about 3–4 nm and moderate nitrogen content changing from 0.94 to 1.63 at%. Used as electrode material, the NPC originated from the optimum pyrolysis temperature of 750 °C demonstrates the best capacitance performance with a high specific capacitance of about 239.30 F g−1 at 0.5 A g−1. Moreover, it reveals an outstanding rate capability and the specific capacitance reaches 212.90 F g−1 at 10.0 A g−1 (up to 88.97% capacitance retention), as well as excellent cycling stability (∼10% capacitance loss after 5000 cycles) tested in 6 M KOH aqueous solution. Such exquisite performance may be ascribed to a unique combination of high specific surface area, suitable pore size distribution and introduction of nitrogen atoms.

Manganese oxide electrode with excellent electrochemical performance for sodium ion batteries by pre-intercalation of K and Na ions

Materials with a layered structure have attracted tremendous attention because of their unique properties. The ultrathin nanosheet structure can result in extremely rapid intercalation/de-intercalation of Na ions in the charge–discharge progress. Herein, we report a manganese oxide with pre-intercalated K and Na ions and having flower-like ultrathin layered structure, which was synthesized by a facile but efficient hydrothermal method under mild condition. The pre-intercalation of Na and K ions facilitates the access of electrolyte ions and shortens the ion diffusion pathways. The layered manganese oxide shows ultrahigh specific capacity when it is used as cathode material for sodium-ion batteries. It also exhibits excellent stability and reversibility. It was found that the amount of intercalated Na ions is approximately 71% of the total charge. The prominent electrochemical performance of the manganese oxide demonstrates the importance of design and synthesis of pre-intercalated ultrathin layered materials.

Nitrogen-oxygen co-doped corrugation-like porous carbon for high performance supercapacitor

Nitrogen-oxygen co-doped corrugation-like porous carbon (NO-PC) has been developed by direct pyrolysis of formaldehyde-melamine polymer containing manganese nitrate. The melamine, formaldehyde and manganese nitrate act as nitrogen, oxygen source and pore-foaming agent, respectively. NO-PC exhibits favorable porous architecture for efficient ion transfer and moderate heteroatom doping for additional pseudocapacitance, which synergistically enhances the electrochemical performance of the NO-PC-based supercapacitor. The electrode delivers specific capacitance of 240 F/g at 0.3 A/g when tested in 6 mol/L KOH electrolyte, good rate capability (capacitance retention of 83.3% at 5 A/g) as well as stable cycling performance (capacitance remains ~96% after 10000 cycles at 3 A/g). The facile synthesis with unique architecture and chemistry modification offers a promising candidate for electrode material of energy storage devices.

Facile synthesis of nitrogen-doped porous carbon for high-performance supercapacitors

Nitrogen-doped porous carbon (NCs) have been synthesized by direct pyrolysis of a mixture containing melamine, iron nitrate and ethylene diamine tetraacetic acid (EDTA). Both the addition of melamine and the carbonization temperature play critical roles in the formation of the unique structure. The results demonstrate that NC-700 shows the best electrochemical performance compared to the other samples. High specific capacitance (275 F g−1 at 0.3 A g−1) is obtained in 6 M KOH, and the capacitance still maintains 202 F g−1 when tested at 10 A g−1 (ca. 73.5% capacitance retention). Moreover, the NC-700 also possesses good cycling stability with only a loss of 2.0% after 10 000 cycles at 10 A g−1. The facile preparation method and good electrochemical performance render NCs a promising candidate for supercapacitor applications.