Multifunctional sulfur doping in cobalt-based materials for high-energy density supercapacitors

In this study, S-CCO@Co(OH)₂('CCO' representing CuCo₂O₄/Cu₂O; 'S-'representing sulfur doping) was synthesized by hydrothermal method followed by electrodeposition. The multiple effects of S doping were studied by S doping and constructing 3D core-shell structure. S doping induced the reduction of Cu²⁺and Co³⁺to Cu⁺and Co²⁺, respectively. Also, S partially replaces O and creates oxygen vacancies, which increases a number of active sites for the redox reaction enhancing the redox reaction activity. After the electrodeposition, S-Co bond is formed between the Co(OH)₂shell and the S-CCO core, which suggests a synergistic effect between S doping and core-shell structure. The formation of S-Co bond is conducive to electron and ion transport, thus improving electrochemical performance. After modification, the specific capacitance of S-CCO@Co(OH)₂is 4.28 times higher than CCO, up to 1730 Fg^-1. Furthermore, the assembled S-CCO@Co(OH)₂//activated carbon supercapacitor exhibits an energy density of 83.89 Whkg^-1at 848.81 Wkg^-1and a retention rate of 98.48% after 5000 charge and discharge cycles. Therefore, S doping and its mutual effect with the utilization of the core-shell structure considerably enhanced the electrochemical performance of the CCO-based electrodes, endowing its potential in further application.