Lattice strain and lattice expansion of nanoparticles of MgAl2O4 as a function of particle size

Harnessing morphological alteration from microflowers to nanoparticles and cations synergy (Co:Ni) in binder-free cobalt nickel vanadate thin film cathodes synthesized via SILAR method for hybrid supercapacitor devices

Electrode materials must be rationally designed with morphologies and electroactive sites manipulated through cations' synergy in bimetal compounds in order to maximize the performance of energy storage devices. Therefore, the present study emphasizes binder-free scalable preparation of cobalt nickel vanadate (CNV) thin films by a facile successive ionic layer adsorption and reaction (SILAR) approach with specific cations (Co:Ni) alternation. Increasing the Ni cation content in the CNV notably transforms its microflower structure comprising nanoflakes (252 nm) into nanoparticles (74 nm). An optimized S-CNV5 thin film cathode with Co:Ni molar ratio of ∼ 0.4:0.6 and a high specific surface area of 340 m2 g-1, provided the excellent specific capacitance (Csp) and capacity (Csc) of 1382 F g-1 and 691 C g-1, respectively at 1 A g-1 current density. A hybrid aqueous supercapacitor (HASc) device with positive and negative electrodes comprising optimized CNV and reduced graphene oxide (rGO), respectively, in a 1 M KOH electrolyte delivered a Csp of 133 F g-1 and a specific energy (SE) of 53 Wh kg-1 at a specific power (SP) of 2261 kW kg-1. Additionally, a fabricated hybrid solid-state supercapacitor (HSSc) device with the same electrodes applying PVA-KOH gel electrolyte displayed a Csp of 119 F g-1, and SE of 46 Wh kg-1 at SP of 1184 W kg-1. This boosted electrochemical activity is due to the synergetic effects of Ni and Co species in the CNV thin film electrodes, emphasizing the potential of CNV electrodes as cathodes in hybrid energy storage devices.