Energy harvesting from NiCo₂S₄/CoS nanoflakes: a two-fold strategy by morphology control and using redox-additive...

Designing materials with an appropriate (nano) architecture could prove to be an effective strategy to improve several electrochemical properties to yield high-energy storage devices for their practical applications. Here, a two-fold approach of choosing an appropriate synthesis method (pulsed electrodeposition) and a redox-additive electrolyte has been adopted for this purpose. A customized pulsed electrodeposition technique, used for obtaining macroporous NiCo₂S₄/CoS nanoflakes, has been designed, which shows improved energy storage (as pseudocapacitors) application. Specific capacitance, when used in electrode form, has been further enhanced by choosing an optimized electrolyte consisting of 1 M KOH and 0.05 M K₃[FeCN₆], where the latter has been used as a redox-additive electrolyte. The multifunctional electrode shows a high capacitance of ∼7000 mF cm^-2. The addition of the redox-additive material to the electrolyte increases the diffusion coefficient (4-fold), which in turn increases the energy storage properties of the material. The improved electrochemical properties have been utilized in designing a prototype solid-state symmetric supercapacitor device, which shows a capacitance value of 380 F g^-1 with a high power density and energy density. Additionally, the device exhibits an exceptionally high capacitance retention of 100% after 2000 continuous switchings at high current density. The device performance under real-life on-field conditions has also been demonstrated. This work significantly shows that surface morphology modification by adopting a custom pulsed electrodeposition technique and redox-additive electrolyte optimization is an effective strategy to enhance the electrochemical energy storage performance.