Cobalt-doping in hierarchical Ni3S2 nanorod arrays enables high areal capacitance

Abstract

Areal capacitance is an important metrics for miniaturized capacitive energy storage devices due to the constraint of device area. In the present work, we proposed a free-standing hierarchical cobalt-doped Ni₃S₂ (Co-Ni₃S₂) nanorod arrays as a novel pseudocapacitive electrode to realize impressively high areal capacitance. With enhanced surface area donated by the introduction of cobalt, the Co-Ni₃S₂ nanorods exhibit an ultrahigh areal capacitance of 3.46 F cm⁻² at 8 mA cm⁻², which is more than three-fold over that of pristine Ni₃S₂. When coupled with an FeOOH anode, the fabricated Co-Ni₃S₂//FeOOH hybrid supercapacitor can deliver a large areal capacitance of 1.61 F cm⁻², a peak energy density of 0.73 mW h cm⁻², and a peak power density of 36.00 mW cm⁻². Besides, the as-fabricated hybrid supercapacitor also exhibits stable capacitive performance (83.5% capacity retention after 5000 cycles). The advanced and stable Co-Ni₃S₂ electrode developed in this work is highly desirable for micro supercapacitor devices.