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