Probing the effect of electrolyte ions on the electrochemical performance of nickel-based metal-organic frameworks

Understanding the influence of electrolyte ions dimension on electrochemical performance is essential for advancing the development of superior MOF-based devices. Nanosheet-type nickel metal-organic frameworks (Ni-BDC) have emerged as exceptional materials for next-generation supercapacitors. To address this, we investigate the energy storage performance of nickel-1,4-benzene dicarboxylate (Ni-BDC) via an elementary solvothermal approach. The primary objective of the present investigation was to elucidate the influence of distinct cationic components within aqueous electrolytes on the electrochemical efficiency of Ni-BDC. The electrochemical examination was performed using a three-electrode setup in different aqueous electrolytes, comprising LiOH, NaOH, and KOH, each with a concentration of 2 M. The calculated specific capacitance value of Ni-BDC increases in the order of 204 F/g (for LiOH) < 290 F/g (for NaOH) < 1526 F/g (for KOH) at 1 A/g due to the lowest hydration sphere radius, greater ionic mobility of K⁺ ion. The material performed better electrochemically in KOH electrolyte with 87 % capacitance preservation. Additionally, an asymmetric supercapacitor (ASSC) device was built using activated carbon (AC) as the negative electrode and nanosheet-like Ni-BDC as the positive electrode. The device, operating within a 1.4 V potential window, demonstrated a capacitance of 39.4 F/g at a current density of 1 A/g. The ASSC device maintained 85 % of its cyclic stability over 4000 charge-discharge cycles at a current density of 8 A/g. This study underscores the vital importance of selecting the optimal electrolyte to significantly enhance the electrochemical performance of Ni-BDC electrode material.