Tailoring moldy-mulberry-derived carbons for ionic liquid-based supercapacitors with ultrahigh energy density

Abstract

Developing low cost and renewable materials for energy storage is becoming critical for modern society. Biomass-derived porous carbons are promising candidates for constructing high-performance supercapacitors and batteries. To overcome challenges such as the low energy density of carbon, herein three-dimensional interconnected N/P/O co-doped hierarchical porous carbon is fabricated from moldy mulberry/melamine mixture, which possesses a large specific surface area, enhanced surface wettability and fast ions transportation. The thus-improved microstructural properties of N/P/O co-doped carbon boost their supercapacitive performances in aqueous and ionic liquid electrolytes, where specific capacitance of 340 F g−1 at 1.0 A g−1 in KOH solution and capacitance retention of 95.0 % after 25,000 cycles are achieved. Symmetric supercapacitors assembled with such carbon electrodes produce an energy density of 15.5 Wh kg−1 at the power density of 162.3 W kg−1 in KOH solution, and an ultrahigh energy density of 147.6 Wh kg−1 at 900 W kg−1 in EMIMBF4 electrolyte. DFT calculations illustrate that the high N/P doping enhances the electrical conductivity and promotes binding sites for EMIM+ adsorption, hence greatly boosting their supercapacitive capability. These gratifying results demonstrate the feasibility of significantly enhancing electrochemical properties of biomass-derived hierarchical porous carbons with a simple and scalable doping method.