Ultrahigh level heteroatoms doped carbon nanosheets as cathode materials for Zn-ion hybrid capacitor: The indispensable roles of B containing functional groups

Heavily heteroatoms doped carbons are highly attractive for electrochemical energy storage and electrocatalysis applications. We report herein a versatile coordination chemistry strategy for the producing of B, N co-doped carbon nanosheets (BCN-Mg) with an ultrahigh doping level (15.26 % for N, 10.18 % for O, and 3.21 % for B) though pyrolysis of nitrogen-rich Mg-based complex in the presence of boric acid . In this protocol, hexamethylenetetramine , which acts as both carbon and nitrogen source, can easily complex with magnesium ion to form a nitrogen-rich Mg-based complex in aqueous solution due to the presence of plentiful amino groups with strong complexation capability. Benefiting from the ultrahigh doping level and moderate specific surface area of 428 m 2 g −1 , the as-obtained B, N co-doped carbon nanosheets display a high specific capacity of 130.7 mA h g −1 (at 0.1 A g −1 ), and good stability of 87.3 % after 10,000 cycles when serves as the cathode for aqueous Zn-ion hybrid capacitors. More importantly, change details of the N and B containing functional groups during the charge-discharge process have been fully evaluated by ex-situ X-ray photoelectron spectroscopy characterization technique and density functional theory calculations. This work not only offers a new way to develop B, N co-doped carbon nanosheets with an ultrahigh doping level but also shed some new insight on the roles of heteroatoms containing functional groups for electrochemical energy storage applications.