Nitrogen-doped porous carbon with interconnected tubular structure for supercapacitors operating at sub-ambient temperatures

Operation of supercapacitors at sub-zero temperatures with reasonable performance is of great importance for their outdoor applications. Herein, the sub-zero performance of supercapacitors assembled from nitrogen-doped porous carbon electrodes with interconnected tubular structure using ionic liquid as electrolyte is reported. The carbon-based electrode materials are synthesized by pyrolysis of poly(1-vinylimidazole) networks in the presence of titanate nanotubes and potassium nitrate, followed by removal of titanate nanotubes. Benefiting from the interconnected hierarchically porous structure and large surface area, the synthesized electrode materials exhibits a gravimetric capacitance of 333 F.g(-1) under 1 A.g(-1) in a three-electrode system in 6.0 mol.L-1 KOH aqueous solution at room temperature. Symmetric supercapacitors assembled from the synthesized electrode deliver a specific energy of 32.7 Wh.kg(-1) under 1.30 Wkg(-1) using ionic liquid as electrolyte at room temperature. At -40 degrees C, the assembled device using ionic liquid as electrolyte possesses a specific energy of 48.3 Wh.kg(-1) under 1.75 kW.kg(-1) and 18.6 Wh.kg(-1) under 35.0 kW.kg(-1). In addition, the device retains 53.5% of its initial capacitance after 10,000 charge-discharge cycles at -40 degrees C under 10 A.g(-1).