Unleashing the Full\nPotential of Electrochromic Heterostructured\nNickel–Cobalt Phosphate for Optically Active High-Performance\nAsymmetric Quasi-Solid-State Supercapacitor Devices

Abstract

The rational design of hybrid systems that combine capacitor\nand\nbattery merits is crucial to enable the fabrication of high energy\nand power density devices. However, the development of such systems\nremains a significant barrier to overcome. Herein, we report the design\nof a Ni–Co phosphate (Ni_3–<i>x</i>Co_<i>x</i>(PO₄)₂·8H₂O) nanoplatelet-based system via a facile coprecipitation\nmethod at ambient conditions. The nanoplatelets exhibit multicomponent\nsynergy, exceptional charge storage capabilities, rich redox active\nsites (ameliorating the redox reaction activity), and high ionic diffusion\nrate/electron transfer kinetics. The designed Ni_3–<i>x</i>Co_<i>x</i>(PO₄)₂·8H₂O offered a respectable gravimetric specific\ncapacity and marvelous capability rate (966 and 595 C g^–1 at 1 and 15 A g^–1) over the Ni₃(PO₄)₂·8H₂O (327.3 C g^–1) and Co₃(PO₄)₂·8H₂O (68 C g^–1) counterparts. Additionally, the nanoplatelets\nshowed enhanced photoactive storage performance with a 9.7% increase\nin the recorded photocurrent density. Upon integration of Ni_3–<i>x</i>Co_<i>x</i>(PO₄)₂·8H₂O as a positive pole and commercial activated\ncarbon as a negative pole, the constructed hybrid supercapacitor device\nwith PVA@KOH quasi-gel electrolyte exhibits great energy and power\ndensities of 77.7 Wh kg^–1 and 15998.54 W kg^–1 with remarkable cycling stability of 6000 charging/discharging\ncycles and prominent Coulombic efficiency of 100%. Interestingly,\ntwo assembled devices are capable of glowing a red LED bulb for nearly\n180 s. This research paves the way to design and fabricate electroactive\nspecies via a facile approach for boosting the design of a plethora\nof supercapattery devices.