Harnessing Electrochromic Heterostructured Nickel–Cobalt Phosphate for High-Performance Asymmetric Quasi-Solid-State Supercapacitors

The rational design of hybrid systems that combine capacitor and battery merits is crucial to fabricating high-energy and power-density devices. However, the development of such systems remains a significant barrier to overcome. Herein, we report the design of a Ni–Co phosphate (Ni_3–xCo_x(PO₄)₂.8H₂O) nanoplatelet-based system via a facile coprecipitation method at ambient conditions. The nanoplatelets exhibit multicomponent synergy, exceptional charge storage capabilities, rich redox active sites (ameliorating the redox reaction activity), and high ionic diffusion rate/electron transfer kinetics. The designed Ni_3–xCo_x(PO₄)₂.8H₂O offered a respectable gravimetric specific capacity 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 showed enhanced photoactive storage performance with a 9.7% increase in the recorded photocurrent density. Upon integration of Ni_3–xCo_x(PO₄)₂.8H₂O as a positive pole and commercial activated carbon as a negative pole, the constructed hybrid supercapacitor device with PVA@KOH quasi-gel electrolyte exhibits great energy and power densities of 77.7 Wh kg^–1 and 15998.54 W kg^–1 with remarkable cycling stability of 6000 charging/discharging cycles and prominent Coulombic efficiency of 100%. Interestingly, two assembled devices can glow a red LED bulb for nearly 180 s. This research paves the way for designing and fabricating electroactive species via a facile approach to boosting the design of a plethora of supercapattery devices.