Nitrogen and Sulfur Codoped Hierarchical Porous Carbon Derived from Lignin for High-Performance Zinc Ion Capacitors

As electrode materials for zinc ion capacitors (ZICs), porous carbons are an important factor affecting the electrochemical behavior of ZICs. Heteroatom doping is an efficient approach to adjust the pore structure, regulate the electronic structure, increase the surface wettability, and provide pseudo capacitance. In this work, hierarchical porous N/S codoped activated carbon (N/S-AC) materials were prepared from lignin using urea and thiourea as the dopants. The preparation process consisted of first step charring and second step activation with codoping to yield N/S-AC, which exhibited hierarchical pore structure, suitable for providing abundant active sites. The use of N/S-AC as cathode materials for ZIC delivered an outstanding specific capacitance of 307 F g–1 at 1 A g–1 and a remarkable capacity retention of 99.72% after 20,000 cycles at 10 A g–1. The device also exhibited a high energy density of 108.8 Wh kg–1 at 2880 W kg–1 and 65.8 Wh kg–1 at 115200 W kg–1. The excellent electrochemical properties were attributed to the synergistic effect of nitrogen and sulfur elements, and hierarchical porous structure. In sum, these findings are promising for development of ZIC electrode materials with high energy density.