Unlocking the potential of optimal etching and ion exchange concentration in post-synthesis of binder-free NiCo-MOFs for high-performance supercapacitors

In this study, we synthesized binder-free NiCo-MOFs electrodes on a flexible stainless-steel substrate (abbreviated as NCMS) using a post-synthesis approach that involves etching and an ion-exchange method. Herein, different concentrations of the nickel precursor, specifically 0.01 M (NCMSA), 0.05 M (NCMSB), 0.10 M (NCMSC), and 0.15 M (NCMSD), were employed to optimize the concentrations of the nickel precursor involved in etching and ion exchange method for SCs. Structural, morphological, compositional, and electrochemical characteristics of NCMS electrodes were studied. Morphological investigation unveiled a porous interconnected sheet-like architecture of NiCo-MOFs electrodes which is highly advantageous for SCs. Notably, the NCMSB electrode exhibited outstanding electrochemical performance, achieving a highest specific capacity (Csp) of 206 mAh/g (1487 F/g) at 5 mV/s; along with a 54.42 % retention rate after 3000th cycles at 100 mV/s. Additionally, NCMSB demonstrated superior power density (Pd) and energy density (Ed) of 2500 W/kg and 43.68 Wh/kg respectively. The power law was employed to examine the charge storage kinetics of the NCMSB electrode. Moreover, a symmetric aqueous device fabricated and evaluated for its electrochemical performance, exhibiting maximum Cs of 22 F/g (9.01 mAh/g) at 10 mV/s. The device exhibited a good Pd of 389 W/kg and Ed of 3.14 Wh/kg at 1 A/g, maintaining 69 % retention over 3000th cycles at 15 A/g. The current findings highlight the significance of etching and ion-exchange concentrations of nickel precursor during the post-synthesis of NiCo-MOFs electrodes to achieve high supercapacitive performance.