Hydrothermally synthesized nickel copper phosphate thin film cathodes for high-performance hybrid supercapacitor devices

Abstract

Transition metal phosphate (TMP) based materials are developing as advanced type electrode materials for hybrid supercapacitors (SCs) due to their unprecedented conductivity, and rich redox activity. Attracted by these fabulous physicochemical characteristics of metal phosphates, binder-free nickel copper (Ni-Cu) phosphate thin films directly grown on stainless steel (SS) substrate by hydrothermal method. The morphological alteration from microplates like nickel phosphate to microrods like copper phosphate is detected with increasing copper content in Ni-Cu phosphate thin films. The optimal 1:1 ratio of nickel and copper in Ni-Cu phosphate (Ni1.62Cu1.35(PO4)2·H2O) thin film illustrates high specific capacitance (Cs) (capacity (Cc)) of 711 F g−1 (355.5 C g−1) at 1.5 A g−1. More significantly, a hybrid aqueous SC (HASC) and all-solid-state SC (HASSC) electrochemical energy storage devices (ESDs) have been fabricated. The HASC device showed superior Cs (85 F g−1 at 0.8 A g−1) with specific energy (SE) of 30 Wh kg−1 at 1.27 kW kg−1 specific power (SP). Additionally, HASSC device offers a higher Cs (52 F g−1 at 0.6 A g−1) with 18.53 Wh kg−1 SE at 1.64 kW kg−1 SP. Also, both HASC and HASSC devices exhibit excellent long-term durability of 84.81 and 80.83 %, respectively, after 5000 GCD cycles. Moreover, HASSC device brightens a panel of 201 red light-emitting diodes (LEDs) illustrating its commercial practicability to next-generation hybrid energy storage devices.