Nitrogen-doped porous carbon via ammonothermal carbonization for supercapacitors

Abstract: In this study we demonstrate a cheap and sustainable ammonothermal approach towards nitrogen-doped porous carbons. Sodium borate (borax) is employed as a catalyst during the synthesis resulting in the formation of small interconnected primary particles of <100 nm in size. Microporosity is created in these nitrogen-doped, ammonothermal carbon samples by a synchronous activation and post carbonization procedure at 850 °C, while the interconnected primary particles offer larger interstitial void spaces including mesopores. Variation of the starting ammonia concentration allows for the facile adjustment of the final nitrogen content, reaching up to 7 wt.% after post carbonization. Electrochemical characterization is carried out in two and three electrode modes by means of cyclic voltammetry and galvanostatic cycling at different scan rates and current densities, respectively. The sample prepared at a high glucose-to-ammonia ratio shows high specific capacitance of 185 and 144 F g⁻¹ at 0.2 and 20 A g⁻¹, respectively (271 F g⁻¹ in a three electrode mode at 1 A g⁻¹). All samples demonstrate a very stable capacitance over the tested 5000 cycles at 10 A g⁻¹ with no degradation and an excellent coulombic efficiency of >99%. Comparison of different pore systems indicates that a continuous pore size distribution may explain improved rate performances. [Figure not available: see fulltext.]