The growing demand for portable electronic devices means that lightweight power sources are increasingly sought after. Electric double layer capacitors （EDLCs） are promising candidates for use in lightweight power sources due to their high power densities and outstanding charge/discharge cycling stabilities. Three-dimensional （3D） self-supporting carbon-based materials have been extensively studied for use in lightweight EDLCs. Yet, a major challenge for 3D carbon electrodes is the limited ion diffusion rate in their internal spaces. To address this limitation, hierarchically porous 3D structures that provide additional channels for internal ion diffusion have been proposed. Herein, we report a new chemical method for the synthesis of an ultralight （9.92 mg/cm3） 3D porous carbon foam （PCF） involving carbonization of a glutaraldehyde- cross-linked chitosan aerogel in the presence of potassium carbonate. Electron microscopy images reveal that the carbon foam is an interconnected network of carbon sheets containing uniformly dispersed macropores. In addition, Brunauer-Emmett-Teller measurements confirm the hierarchically porous structure. Electrochemical data show that the PCF electrode can achieve an outstanding gravimetric capacitance of 246.5 F/g at a current density of 0.5 A/g, and a remarkable capacity retention of 67.5% was observed when the current density was increased from 0.5 to 100A/g. A quasi-solid-state symmetric supercapacitor was fabricated via assembly of two pieces of the new PCF and was found to deliver an ultra-high power density of 25 kW/kg at an energy density of 2.8 Wh/kg. This study demonstrates the synthesis of an ultralight and hierarchically porous carbon foam with high capacitive performance.
Feng ZhanTianyu LiuGuihua HouTianyi KouLu YueRongfeng GuanYat Li
The microstructure and magnetic properties of Mn-doped ZnO films with various Mn contents,synthesized by magnetron sputtering at room temperature,are investigated in detail.X-ray diffraction(XRD) measurement results suggest that the doped Mn ions occupy the Zn sites successfully and do not change the crystal structure of the ZnO films.However,the microstructure of the Mn-doped ZnO films apparently changes with increasing the Mn concentration.Arrays of well-aligned nanoscale rods are found in the Mn-doped ZnO films with moderate Mn concentrations.Magnetic measurement results indicate that the ZnO films doped with moderate Mn concentration are ferromagnetic at room temperature.The possible origin of the ferromagnetism in our samples is also explored in detail.
