Rational Construction of Cobalt Sulfide Nanoparticles Embedded in Hollow N, P, S Codoped Carbon Shells for Enhanced Supercapacitor Performance

An exquisitely designed nanostructure and hybridizing with heteroatom-doped carbon can significantly improve the electrochemical performance of the transition metal sulfides (TMSs). Herein, three-dimensional (3D) hollow N, P, S codoped carbon (NPSC) shells encapsulated with uniformly dispersed cobalt sulfide nanoparticles (Co_1-xS/HNPSCS) are synthesized for supercapacitors (SCs) by the sulfuration and carbonization of poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS)-functionalized cobalt-based zeolitic imidazolate framework-67 (ZIF-67). The PZS protects the ZIF-67 from collapsing and convert it in situ into NPSC shells, which are conducive to exposing abundant active sites and accelerating the kinetics of electrochemical reactions. As a result, the Co_1-xS/HNPSCS presents an unrivaled specific capacity of 1058.9 C g^-1 at 1 A g^-1. The assembled Co_1-xS/HNPSCS//AC hybrid SC (HSC) demonstrates a remarkable energy density of 57.8 W h kg^-1 at a power density of 375 W kg^-1. Density functional theory calculations show that the synergy between the Co_1-xS and NPSC can optimize the electronic configuration, improve the conductivity, and enhance the adsorption of OH^- on the surface of the electrode material. Besides, the quantum capacitance of the carbon layer is also increased by N, P, S codoping. This work exhibits an effective strategy to fabricate TMS/HNPSCS and offers theoretical and methodological guidance for the study of NPSC coating materials.