Use of Nutrient Rich Hydrophytes to Create N,P-Dually Doped Porous Carbon with Robust Energy Storage Performance.

The optimal strategy for the safe disposal of large amounts of hydrophyte biomass with enriched levels of N and P is challenging. In this study, we proposed and illustrated a facile pyrolysis approach to prepare an N, P-dually doped porous carbon (NPC) material with robust energy storage performance using a thermochemical self-doping process and a widely distributed hydrophyte biomass (Typha angustifolia). As a supercapacitor electrode material for electrochemical energy storage, the NPC shows a maximum capacitance of 257 F g and energy density of 19.0 Wh kg and only 3% capacitance loss after 6000 times of cyclic use, which places the NPC among the best porous carbon supercapacitors known previously. Multiple characterizations (BET, SEM, XPS, and Raman) provide evidence that NPC's excellent energy storage performance involves a pseudocapacitive contribution due to the Faradaic redox reactions of the N and P functional groupsand a capacitive contribution from the formation of the electrical double layer. The external nitrogen resource cannot improve the supercapacitor performance of NPC, suggesting a role for the assimilated nitrogenof plants. In contrast, an external phosphorus resource can significantly increase the specific capacitance from 257 to 375 F g of NPC. These findings provide useful information for effective energy storage utilization of biomass wastes with differentconcentrations of N and P by fast pyrolysis and activation processes.