Amorphous, hydrous nickel phosphate thin film electrode prepared by SILAR method as a highly stable cathode for hybrid asymmetric supercapacitor

To achieve higher supercapacitive performance of active material, several materials with precise structures and properties have been prepared using different chemical synthesis methods. Recently, amorphous materials are gaining much attention as an electrode in supercapacitor application as it provides superior electrochemical properties due to disorder in structure. So, in this investigation, a facile, binder free successive ionic layer adsorption and reaction (SILAR) method is adopted for the preparation and deposition of amorphous, hydrous nickel phosphate thin films on stainless steel substrates. The amorphous nickel phosphate shows mesoporous, clusters of particles like morphology. In the electrochemical study, the amorphous, hydrous nickel phosphate electrode demonstrates a superior specific capacitance of 1700 F g⁻¹ (specific capacity- 814 C g⁻¹) at 0.5 mA cm⁻² current density along with excellent capacitive retention (96.55%) and coulombic efficiency (98.62%) over 5000 cycles. Furthermore, fabricated hybrid supercapacitor device using the nickel phosphate as cathode and reduced graphene oxide as anode exhibits specific capacitance of 113.5 F g⁻¹ at 3 mA cm⁻² current density with a high 40.37 Wh kg⁻¹ energy density at 1.689 kW kg⁻¹ power density alongwith excellent cyclic stability (95.09% retention after 5000 cycles). The obtained results illustrate that the amorphous, hydrous nature of nickel phosphate is a beneficial and superior choice as a cathode material in high-performing hybrid asymmetric supercapacitor devices.