Intercalation-type pseudocapacitive clustered nanoparticles of nickel–cobalt phosphate thin films synthesized via electrodeposition as cathode for high-performance hybrid supercapacitor devices

Abstract

The binder-free synthesis of nickel–cobalt phosphate electrodes has attracted tremendous attention in hybrid energy storage devices due to their significant electrochemical activity based on the synergy between Ni and Co cations. As such, the present work describes a facile scalable synthetic approach using the potentiostatic electrodeposition (PED) of binder-free nickel–cobalt phosphate electrodes with varying Ni : Co composition. Alteration in Ni : Co composition leads to amorphous-to-crystalline structural conversion and the microsphere-to-nanosheet-like morphological evolution of nickel–cobalt phosphate electrodes. The optimal ∼1 : 1 (Ni : Co) composition nickel–cobalt phosphate electrode with clustered nanoparticle-like morphology exhibits intercalation pseudocapacitive behavior and demonstrates a maximum specific capacitance (capacity) of 2228 F g⁻¹ (891 C g⁻¹) at 1.5 A g⁻¹ current density. Moreover, the fabricated aqueous hybrid asymmetric supercapacitor (AHAS) device delivers a high specific capacitance of 185 F g⁻¹, possessing an energy density of 65.7 W h kg⁻¹ at 2.2 kW kg⁻¹ power density with 97% retention. Furthermore, the solid-state hybrid asymmetric supercapacitor (SHAS) device displays a maximum specific capacitance of 90 F g⁻¹ with 32 W h kg⁻¹ energy density at 0.32 kW kg⁻¹ power density and exhibits 89% capacitive retention. The present study establishes a scalable synthesis of binder-free nickel–cobalt phosphate electrodes as cathodes in hybrid energy storage devices for practical applications.