Preparation of N-Doped Supercapacitor Materials by Integrated Salt Templating and Silicon Hard Templating by Pyrolysis of Biomass Wastes

Abstract

For safe disposal and environmentally benign recycling, lignocellulosic biomass wastes are increasingly studied for use as precursors for the preparation of value-added porous carbon materials. However, conventional chemical vapor deposition is time consuming and difficult to perform on a large scale. Herein, we obtained nitrogen-doped porous carbon materials (NPCMs) with high supercapacitor performance by one-pot copyrolysis of a carbon precursor (wheat straw), nitrogen precursor (melamine), and salt templating (mixed salt of KCl/ZnCl₂ at 51:49). The NPCM with 7.78% nitrogen content exhibited an excellent gravimetric capacitance of 223.9 F g^–1, which is mainly attributed to the increase in surface area by the activation of salt templating and the decrease in ion-transport resistance by N doping of the NPCM. The removal of silicon in pyrolysis products efficiently enhanced the capacitance of materials, but there was a negative effect on capacitance if the silicon was removed from feedstocks before pyrolysis. The post-removal of the silicon greatly increased the cycle stability of NPCMs and maintained 91.4% of capacitance after 10,000 CV tests. BET and XPS analyses indicate that the silicon can improve the pore structure and facilitate the formation of reactive nitrogen species (N-5 and N-6) by hard template and catalysis functions during pyrolysis, which is mainly responsible for the high performance of as-prepared NPCM. This study provides a facile method for synthesizing biomass-based NPCMs, especially to utilize biomass waste that contains high silicon content.