Regulated micro-leaf like nickel pyrophosphate as a cathode electrode for asymmetric supercapacitor

In present work, nickel pyrophosphate (Ni₂P₂O₇.8H₂O) thin film on stainless steel substrate synthesized using facile chemical bath deposition method and used as cathode electrode for asymmetric supercapacitor. Three compositions of nickel phosphate with varying of nickel:phosphate (2:1, 1:1 and 1:2) molar ratio are prepared to study composition effect on microstructure and subsequently on supercapacitive performance. Morphology changes with composition from microflower to leaf like, consequently supercapacitive performance influences with increasing phosphate content in material. The well dispersed leaf like microstructure (nickel:phosphate;1:2) of nickel pyrophosphate offers more active sites and it shows maximum specific capacitance of 482 F g⁻¹ at current density of 3 mA cm^-2 along with 99.73% capacitive retention over 2500 cycles. Moreover, an asymmetric device fabricated using nickel pyrophosphate and reduced graphene oxide as a positive and negative electrode, respectively. Prepared asymmetric supercapacitor offers specific capacitance of 74.81 F g^-1 at 0.9 mA cm^-2 current density with 26.6 Wh kg^-1 energy density at a moderately high power density of 870.6 W kg^-1. Also, exhibits 87.35% of capacitive retention over 5500 cycles at 4 mA cm^-2 current density.