Construction of highly dispersed mesoporous bimetallic-sulfide nanoparticles locked in N-doped graphitic carbon nanosheets for high energy density hybrid flexible pseudocapacitors

Abstract

Mixed bimetallic sulfides have attracted significant research attention as favorable pseudocapacitive materials for supercapacitors due to their high specific capacitance and suitable work function. However, the low conductivity and inferior energy density hinder their practical applications. Herein, bimetallic sulfide (Zn_xCo_1−xS) nanoparticle-embedded in nitrogen-doped carbon directly grown on a flexible carbon cloth (Zn_xCo_1−xS-NC) as a binder-free electrode with high pseudocapacitive charge storage and excellent stability was designed. This unique hierarchical mesoporous composite structure was simply derived from a metal–organic framework (MOF) precursor, followed by calcination and a tuned sulfurization process. The optimized binder-free Zn_0.76Co_0.24S-NC electrode exhibits excellent pseudocapacitive performance, including the record high specific capacitance of 2133.2 F g⁻¹ (354.53 mA h g⁻¹) at 1.25 A g⁻¹ for metallic sulfides and exceptionally high rate capability and cycling stability (95.63% over 10 000 cycles) in an aqueous electrolyte. Asymmetric flexible solid-state supercapacitors based on Zn_0.76Co_0.24S-NC as the positive electrode and bimetallic MOF-derived nitrogen-doped mesoporous carbon (MPC) as the negative electrode (ZCS//MPC-ASC) were assembled and exhibited excellent capacitance of 290 F g⁻¹ at 1 A g⁻¹ and high energy density of 92.59 W h kg⁻¹, which exceeded those of most of the previous solid-state symmetric and asymmetric SCs based on carbon materials and single/bimetallic oxides and sulfides. Furthermore, our ZCS//MPC-ASC device displays an inspiring cycling stability by retaining 91.82% of its initial capacitance after 5000 cycles.