Facile one-step electrodeposition synthesis of binder-free CoxFe3-xSe4 ultrathin nanosheet arrays towards high-performance quasi-solid-state supercapacitors

In this report, binder-free ultrathin nanosheet arrays of Co2FeSe4 (CFS) are prepared for the first time via the potentiostatic electrodeposition method for three minutes. Various physiochemical characterizations are performed to study the effect of Co and Fe in CoxFe3-xSe4. Ultrathin porous nanosheet arrays of the optimized CFS-2 (using 2 mmol CoCl2 center dot 6H(2)O) facilitate the electrolytic diffusion to the core electroactive sites, resulting in enhanced capacitive property of the electrode. As per the obtained results, the as-prepared CFS-2 delivers the maximum areal capacitance of 3393 mF cm(-2) at a current density of 3 mA cm(-2) in 1 M KOH with excellent capacitance retention of 96.4% even after 10,000 charge-discharge cycles. Furthermore, the CFS-2 is employed to fabricate poly(vinyl alcohol)-KOH gel electrolyte-based quasi-solid-state asymmetric supercapacitor device. The fabricated supercapacitor exhibits outstanding energy and power densities of 157.3 mWh cm(-2) and 2250 mW cm(-2), respectively and demonstrates excellent long cycling stability (85.8% capacitance retention) and columbic efficiency (101.8%) after 10,000 charge-discharge cycles. The overall three-minute electrodeposition synthesis enabling facile upscale route and excellent electrochemical properties suggests the potential of CFS-2 to be applicable in advanced energy storage systems and portable electronics.