Journal of Power Sources 438 (2019) 227013 Available online 14 August 2019 0378-7753/© 2019 Elsevier B.V. All rights reserved. Facile synthesis of nitrogen self-doped hierarchical porous carbon derived from pine pollen via MgCO 3 activation for high-performance supercapacitors Liu Wan * , Ping Song, Jiaxing Liu, Dequan Chen, Rui Xiao, Yan Zhang, Jian Chen, Mingjiang Xie, Cheng Du ** Hubei Key Lab for Processing and Application of Catalytic Materials, College of Chemical Engineering, Huanggang Normal University, Huanggang, 438000, China HIGHLIGHTS G R A P H I C A L ABSTRACT � Hierarchical porous carbon is produced from pine pollen. � Magnesium carbonate is employed as an effective activating agent. � The obtained carbon electrode shows a high specifc capacitance of 419.6 F g 1 . � Symmetric supercapacitor delivers a high energy density of 34.9 Wh kg 1 . A R T I C L E INFO Keywords: Nitrogen self-doping Hierarchical porous carbon Pine pollen Supercapacitor ABSTRACT The development of simple and green synthetic strategies to obtain porous carbon with both high energy density and power density for carbon-based supercapacitors has motivated the utilization of sustainable biomass ma- terials, due to their unique microstructures and high heteroatom contents. Herein, a novel, green and effcient activation agent magnesium carbonate is proposed to prepare nitrogen self-doped hierarchical porous carbon materials derived from pine pollen for superior carbon-based supercapacitors. The obtained carbon has a large surface area of 1311.2 m 2 g 1 , hierarchical porous structure with interconnected meso-/macropores and high nitrogen, oxygen contents. When applied as supercapacitor electrode in a three-electrode system, the carbon- based electrode exhibits a high specifc capacitance of 419.6 F g 1 at a current density of 1 A g 1 , good rate retention of 60.3% from 1 to 100 A g 1 and superior long-term cycling stability with 2.6% loss of its initial capacitance after 10,000 cycles in 6 M KOH aqueous electrolyte. Additionally, the assembled symmetric supercapacitor can work at a high voltage of 2.0 V in 1 M Na 2 SO 4 aqueous electrolyte, and deliver an ultrahigh energy density of 34.9 Wh kg 1 at a power density of 181.0 W kg 1 . * Corresponding author. ** Corresponding author. E-mail addresses: wanliuok2006@163.com (L. Wan), ducheng20141020@163.com (C. Du). Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour https://doi.org/10.1016/j.jpowsour.2019.227013 Received 10 May 2019; Received in revised form 19 July 2019; Accepted 12 August 2019