Defect engineering of P doped Fe7S8 porous nanoparticles for high-performance asymmetric supercapacitor and oxygen evolution electrocatalyst

Transition metal sulfides are promising battery-type materials for electrochemical energy storage and a great electrocatalyst for oxygen evolution reaction (OER). However, the poor conductivity and sluggish reaction kinetic as well as the deficiency of electrochemically active sites hinder the practical application of FexSy. Herein, we design Fe7S8 porous nanoparticles with surface phosphate ions and enriched sulfur-vacancies (P-Fe7S8), which is reported as a new high-specific-capacity material for asymmetric supercapacitor. Benefiting from the merits of substantially improved electrical conductivity and increased active sites, the optimized P-Fe7S8 negative electrode delivers ultra-high specific capacitance of 804.7F/g at 0.4 mA. Moreover, the assembled NiS//P-Fe7S8 ASC presents an impressive specific capacitance of 335.9F/g at 1.2 A/g, a high energy density of 134.8 Wh/kg at a power density of 1042.1 W/kg, and great flexibility under different bending angles. Furthermore, the one-step vulcanization process is provided with universal applicability for the synthesis of NixFe1-xS bimetallic sulfide. With the synergy effect produced by the bimetal, the Ni0.5Fe0.5S hollow porous nanoparticles exhibit the remarkable activity of oxygen evolution reaction with a low overpotential of 174 mV at 10 mA cm-2 and Tafel slope of 41 mV dec-1. This simple method provides new insight into the synthesis of novel multifunctional metal sulfide nanomaterials.