Enhanced electrochemical capacitive performance of zinc and cobalt metal-organic frameworks derived electrodes in redox additive electrolyte and their application in electrocatalytic water splitting

Herein, three MOF-derived freestanding oxide electrodes are synthesized via in-situ grown MOFs on nickel foam (NF) followed by thermal treatment for supercapacitor and electrochemical water-splitting. Amongst, ZnCo 2 O 4 @NF exhibits superior electrochemical performance due to its ultra-thin structure, favorable surface properties, and dual-metal active centers (Zn 2+ /Co 2+ , Co 3+ ), achieving a specific capacity of 115.5 C g −1 at 2 A g −1 . To enhance performance, redox additives (KBr, LiOH) are introduced into a 3 M KOH electrolyte. The optimized 0.2 M LiOH + 3 M KOH electrolyte improves specific capacity to 560.8 C g −1 at 2 A g −1 , while 0.2 M KBr + 3 M KOH results in 346.6 C g −1 at 1 A g −1 . An asymmetric supercapacitor (ASC) using ZnCo 2 O 4 @NF and activated charcoal (AC) exhibits an energy density of 84.7 W h kg −1 at 2250 W kg −1 in 0.2 M LiOH + 3 M KOH, surpassing 76 W h kg −1 at 1500 W kg −1 with 0.2 M KBr. In electrocatalysis, ZnCo 2 O 4 @NF shows overpotentials of 500 mV (OER) and 55 mV (HER) at 10 mA cm −2 in 1 M KOH. A full water-splitting cell using ZnCo 2 O 4 @NF as both electrodes delivers 10 mA cm −2 at 1.63 V. • MOF-derived oxides offer large surface area and high porosity. • Dual metals boost conductivity and electrochemical performance. • Redox additives improve supercapacitive performance via redox reactions. • Freestanding MOF electrodes serve as supercapacitors and electrocatalysts.