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

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 Fe_xS_y. 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 Ni_xFe_1-xS bimetallic sulfide. With the synergy effect produced by the bimetal, the Ni_0.5Fe_0.5S 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.