Activated carbons (ACs) were prepared by microwave−assisted heating of bituminous coal with KOH as activation agent in different gas media for supercapacitors. The pore structure parameters of ACs are obtained by using nitrogen adsorption technique. ACs prepared in static nitrogen, flowing nitrogen and carbon dioxide are denoted as ACStatic-N2, ACFlowing-N2, ACFlowing-CO2. The specific surface area of ACFlowing-N2 is the biggest among the three ACs, which reaches 1201 m2g-1 with total pore volume being at 0.64 cm3 g-1. The specific capacitance of ACFlowing-N2 electrode and energy density of ACFlowing-N2 capacitor is the biggest among the three AC samples with specific capacitance being at 302.6 F g-1 and energy density being at 10.1 Wh kg-1 after 400 cycles. The microwave−assisted KOH activation of coal is an efficient approach to the preparation of ACs for supercapacitors.
Activated carbons (ACs) from petroleum coke by microwave heating KOH activation are treated by microwave to investigate the effect of microwave−treatment power on AC properties. The electrochemical properties of AC electrodes for supercapacitors were investigated by cyclic voltammetry, constant current charge−discharge and electrochemical impedance spectroscopy. The results showed that specific surface area (SBET) and total pore volume of microwave−treated ACs, specific capacitance and energy density of microwave−treated AC electrodes decreased. The electrical conductivity and stability of AC electrodes for supercapacitors were improved. Fast microwave−treatment is an efficient method to obtain suitable ACs for supercapacitors.
Activated carbon (AC) was prepared from lignite by microwave heating ZnCl2. The pore structure parameters of AC are characterized by nitrogen adsorption technique. The AC and ruthenium oxide/AC composite are characterized by thermogravimetric analysis and transmission electron microscope. Electrochemical properties of ACs and ruthenium oxide/AC composite electrodes were investigated by cyclic voltammetry and constant current charge–discharge after AC was pre−oxidized by HNO3 solution. The results show that the specific surface area and total pore volume of AC from lignite reaches 1310 m2 g−1 and 0.80 cm3 g−1, respectively. The micropore volume of AC from lignite totals only 12.5%. AC and ruthenium oxide/AC composite electrodes with 5wt.% ruthenium oxide loading show high cycle stability. Compared to pristine AC electrode, specific capacitance of ruthenium/AC composite electrode and energy density of ruthenium/AC capacitor after 100 charge−discharge cycles increases 40.8% and 39.1%, respectively.
Direct preparation of activated carbon (AC) from coal was reported by microwave heating with potassium hydroxide as activation agent. Electrochemical properties of AC electrodes were investigated by cyclic voltammetry, constant current charge–discharge. The results show that functional groups on AC include –C=O, –O–H and –C–O. The micropore volume of AC from different coal totals 48.5–95.6%. The total pore volume of AC from different coal passes through a maximum with the decrease of volatile mater content in coal. The specific surface area and total pore volume of AC from Qing ting coal reach 1874 m2 g-1 and 1.00 cm3 g-1, respectively. The specific capacitance and energy density of AC from higher coal rank is usually bigger than that of AC from lower coal rank.
The high power light emitting diode (LED) array integrated with the microchannel heat sink is designed. Detailed theoretical analysis of the thermal resistance for the microchannel heat sink is obtained. The thermal resistance minimum is achieved by the heat sink structure optimization, the result of theoretical analysis is simulated by MATLAB software. The result shows that: the system acquired the best heat dissipation effect, when the total size of the radiator is fixed, the width of the cooling channel is 0.1mm, and the cooling water flow rate is 1 m/s, the minimum of thermal resistance is 0.019w/°C.
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