Exceptional Pseudocapacitive Behavior of 2D NiS and CoS Electrodes for Supercapacitors

ABSTRACT The practical application of NiS and CoS powders in supercapacitor electrodes is often hindered by stacking and agglomeration effects. This study introduces a simplified, energy‐efficient strategy for fabricating 2D NiS and CoS electrodes with enhanced electrochemical performance. A single‐stage hydrothermal procedure was used to directly grow NiS and CoS on Ni foam. XRD and FESEM analyses confirmed the formation of a single‐phase hexagonal NiS with nanoleaf morphology, while CoS exhibited an amorphous structure composed of wall‐like nanosheet architectures. Electrochemical characterization revealed that the redox behavior of NiS was dominated by the Ni 3+ /Ni 2+ couple, whereas CoS displayed redox transitions involving both Co 4+ /Co 3+ and Co 3+ /Co 2+ couples. NiS and CoS delivered exceptional specific capacitances of 3386 and 2166 F g −1 at 1 A g −1 , respectively. Notably, CoS retained 93% of its capacity for over 4000 cycles at 2 A g −1 and delivered consistent performance at current densities of up to 200 A g −1 . The synergistic effect of EDLC and faradaic reactions enhanced CoS's cycling stability and capacitance beyond previously reported values. This simple synthesis strategy enables high‐performance NiS and CoS electrodes without complex doping or heterostructure engineering, offering strong potential for next‐generation hybrid supercapacitors.