Nitrogen and Sulfur Codoped Porous Carbon Directly Derived from Potassium Citrate and Thiourea for High-Performance Supercapacitors

Abstract

By introducing a heteroatom into carbon material, an effective improvement in capacitance can be realized owing to surface oxidation and reduction reactions of pseudocapacitors. Herein, a simple one-pot carbonization activation method was proposed to convert potassium citrate into three-dimensional interconnected porous carbon (PC). Then, an effective double heteroatom doping method by thiourea was used to prepare nitrogen–sulfur-doped PC (N,S-PC). This porous structure facilitates the storage of a large number of ions and reduces their diffusion path. The synthesized N,S-PC nanomaterial has a capacitance of 674 F/g at 1 A/g in a 1 M H2SO4 electrolyte, can retain 94.41% of the initial capacitance after 10 000 cycles at 5 A/g, and has a long cycle life. More importantly, a symmetric supercapacitor assembled with this material can exhibit an energy density of up to 32.6 (W·h)/kg at a high-power density of 750 W/kg. This is due to the high performance of N,S-PC in supercapacitor electrode materials.

N-Doped Yolk–Shell Carbon Nanospheres with “Carbon Bridges” for Supercapacitors

“…N doping can modulate the chemical and electronic environment, which provided pseudocapacitance through surface redox reactions. 40 The yolk−shell C@C-2 nanospheres with a high surface area ensured sufficient active sites for ion adsorption. Besides, N doping also introduced various defects for extra ion storage, contributing to excellent electrochemical performance.…”

“…With the elevated scanning rate, the contribution from the capacitance-controlled process rose to 67.8, 71.9, 75.7, and 78.6%, indicating the essential role of capacitive charge storage in the electrode’s total capacity, particularly at high scan rates (Figure c). N doping can modulate the chemical and electronic environment, which provided pseudocapacitance through surface redox reactions . The yolk–shell C@C-2 nanospheres with a high surface area ensured sufficient active sites for ion adsorption.…”

“…36−39 A higher electronegativity (3.5) of N is observed in comparison to that of carbon (3.0), so the nitrogen-doped (N-doped) carbon materials are conductive to the introduction of pseudocapacitors, which can deliver greater specific capacities. 40 Meanwhile, nitrogen doping can also effectively advance electrochemical properties and keep excellent cyclability through enhancing surface wettability and electron-donor tendencies of carbon materials. 41,42 Resorcinol-formaldehyde (RF) resin, with its easy polymerization, low cost, and high carbon residue, has been used as a familiar carbon source for preparing carbon nanospheres with yolk−shell structures.…”

Rapid Synthesis of Oxygen-Enriched Porous Carbon through a Microwave Method and Its Application in Supercapacitors

“…As a new generation of energy-storage devices, supercapacitors are preferred by researchers because of their high power density, high energy density, fast charging and discharging, and excellent cycle stability. − Carbon supercapacitors store charge mainly through non-Faraday charging of the carbon/electrolyte double layer because ions are adsorbed on the electrode/electrolyte interface through electrostatic interactions to form an electric double layer capacitor (EDLC) . Carbon electrode materials have a large interconnected pore structure and exhibit excellent electrical conductivity for charge storage . Therefore, carbon materials such as activated carbon, − carbon nanotubes, carbon fibers, and graphene have large specific surface areas, high electrical conductivity, and low cost, and they have been used as electrode materials for EDLC .…”

“…Carbon electrode materials have a large interconnected pore structure and exhibit excellent electrical conductivity for charge storage . Therefore, carbon materials such as activated carbon, − carbon nanotubes, carbon fibers, and graphene have large specific surface areas, high electrical conductivity, and low cost, and they have been used as electrode materials for EDLC . The introduction of nitrogen (N), oxygen (O), and phosphorus (P) heteroatoms into PC is an effective strategy for improving the electrochemical performance of PC .…”