Abstract: Transition metal selenides have attracted great interest in electrochemical energy storage applications because of their good electrochemical activity and conductivity properties. Herein, we reported the metal molybdenum selenide (MSe/Mo₃Se₄ (M: Zn, Mn, and Ni)) electrode materials on their morphological and electrochemical properties by varying the metal ions via a facile hydrothermal technique. The effects of the structural, morphological, and surface area properties of the prepared powder materials on their electrochemical performance were studied. Owing to the hierarchical porous and unique interconnected structure, the nickel molybdenum selenide nanosheet spheres (NMS NSSs)-based electrode material delivered an excellent specific capacity value of 252 mAh g^-1 at a current density of 1 A g^-1. Moreover, the optimized NMS NSSs electrode exhibited outstanding cycling stability with a capacity retention of 80% and a corresponding coulombic efficiency of 99% after 80,000 cycles. Additionally, a pouch-type hybrid supercapacitor (HSC) device was assembled using NMS NSSs material as a positive electrode and activated carbon as a negative electrode in 1 M aqueous KOH electrolyte. Furthermore, the assembled HSC device exhibited superior energy and power density values as well as magnificent cycling stability. For real-time practical applications, light-emitting diodes and a digital display were powered using two series-connected HSC devices. Therefore, the obtained tremendous results strongly suggest that the NiSe/Mo₃Se₄ NSSs-based materials could be a promising electrode for ultralong-life energy storage applications.

Key words: Nickel selenides, Molybdenum selenides, Nanosheet spheres, Ultralong-life cycling stability