碳热还原活化扩孔提升介观结构碳纳米笼超级电容器性能

Boosting the Supercapacitance Performance of Mesostructured Carbon Nanocages by Enlarging Pore Sizes via Carbothermal Reduction

双电层电容器(EDLC)具有高功率密度和快速充/放电等优点,但能量密度较低.影响EDLC性能的主要因素包括:电极材料的比表面积、孔结构、导电性、浸润性,电解液的电压窗口和离子电导率.介观结构碳纳米笼(hCNC)新材料在超级电容器领域应用前景广阔.利用溶度积规则结合碳热还原,有效调变了hCNC壁上的通道数量和尺寸,在KOH和1-乙基-3-甲基咪唑四氟硼酸盐(EMIMBF4)电解液中电极材料均展现出优异的超级电容性能:在1 A·g^(-1)电流密度下优化样品的比电容分别为255和220 F·g^(-1),比常规的hCNC提高了50%和25.7%;在200 A·g^(-1)高电流密度下其比电容仍分别保持在179和129F·g^(-1)的高水平,比常规的hCNC提高了68.9%和33.0%;其能量密度分别可达12.8Wh·kg^(-1)@0.3k W·kg^(-1)和116Wh·kg^(-1)@0.97k W·kg^(-1).性能的提升归因于hCNC笼壁上引入了小尺寸介孔,同时增加了微孔的数量和尺寸,显著增加了比表面积,有利于离子在纳米笼内外的快速传输.本项研究为开发先进超级电容器电极材料提供了新的思路.

Electrical double layer capacitors(EDLCs)with the merits of high power density and fast charging/discharging have been widely used in the different fields,e.g.green energy and national defense,which is however limited by the unsatisfied energy density.The factors dominating the EDLCs performance mainly include the specific surface area,pore structure(i.e.,ion transport channel),conductivity and wettability of the electrode material,the working voltage window and ionic conductivity of the electrolyte.In recent years,mesostructured carbon nanocage have been attracting more and more attention as advanced platform materials for energy storage and conversion,which have a particularly broad application prospect in the field of supercapacitors.Based on the rule of solubility product and the carbothermal reduction method,herein we have developed a new route to regulate the pore size distribution of hierarchical carbon nanocages(hCNCs)and effectively increased the number and size of the channels across the shells of hCNCs.The optimized sample exhibits excellent supercapacitive performances in KOH and 1-ethyl-3-methylimidazolium tetrafluoroborate(EMIMBF4)electrolytes:the specific capacitance of 255 and 220 F•g^(-1) at 1 A•g^(-1)(50% and 25.7% higher than those of the pristine hCNCs);179 and 129 F•g^(-1) at a high current density of 200 A•g^(-1)(68.9% and 33.0% higher than those of the pristine hCNCs);energy density of 12.8 Wh•k^(-1)@0.3 kW•kg^(-1) and 116 Wh•kg^(-1)@0.97 kW•kg^(-1),respectively.Such excellent electrochemical performances can be attributed to the introduction of small-sized mesopores and the increase in number and size of micropores on the shells of hCNCs,which much increases the specific surface area and benefits the rapid transport of ions through the microchannels on the nanocage shells.This study provides a new thought to develop the advanced supercapacitor electrode materials.