Surface fractality and crystallographic texture properties of mixed and mono metallic MOFs as a new concept for energy storage devices

Herein, fractality, morphology and crystallography studies as a novel approach were introduced to evaluate the effect of inorganic nodes on energy storage device performances of Ni/Co-BTC and Ni/Zn-BTC mixed metallic (MM) and Ni-BTC, Zn-BTC, and Co-BTC mono metallic (mM) MOFs electrode materials. Through XRD data, crystallographic texture studies were pursued by calculating crystallite size (D), interplanar space (dhkl), strain and dislocation density (ε,δ), and texture coefficients (TC (hkl)). Besides statistical studies, the Areal Autocorrelation Function (AACF) via AFM analysis was developed to investigate morphological features. Fractality results of electrochemical and physical methods verified the reliability of these methods for describing the pseudocapacitive nature of MM-MOF and mM-MOF electrode materials. Based on our findings, compared with mM-MOFs, Ni/Co-BTC and Ni/Zn-BTC MM-MOF electrodes with the beneficiary of the synergistic effect of mixed-metallic cations, smaller crystallite size (D=21.53 nm), higher maximum height (Sz=21.64 nm) with larger fractal dimensions (Df=2.58), and more interface width roughness (RMS=2.65 nm) offers an impressive architecture capable of pseudocapacitance storing charge. Therefore, Ni/Co-BTC and Ni/Zn-BTC MM-MOF electrodes offer the specific capacity of 263.8 and 203.3 mA h g−1 at 2.5 A g−1 with a dominant contribution of battery-like features.