New Strategy for Improved Conductivity and Redox-Enhanced Supercapacitor Performance of Nickel Metal-Organic Framework

Owing to the high-surface area and macromolecular architecture, metal-organic frame (MOF) material has been referred to as an advanced system for supercapacitor applications. Indeed, poor electrical property and structural instability under electrified conditions are the major limitations. In this work, we wish to introduce a new strategy for marked enhancement in the electrical and redox property of the MOF by simple chemical mixing followed by ultrasonication of pristine MOF with low-cost carbon black (CB) material. As a model system, Ni-MOF, prepared using 2,2'-bipyridine and benzene-1,4-dicarboxylic acid (provides a rich source for pi-pi interaction with graphic carbon), functionalized CB, designated as CB@Ni-MOF, has been developed for improved energy storage application. Electrochemical studies of CB@Ni-MOF modified screen-printed carbon electrode showed about ten times enhanced peak current and surface excess value (24.8 nmol.cm(-2)) over the respective pristine Ni-MOF modified electrode (1.9 nmol.cm(-2)) in 1 M NaOH solution. Physicochemical and electrochemical characterization using TEM, X-ray, Raman, FTIR, BET Surface area and electrochemical impedance measurements collectively revealed that there are multiple hydrogen-bonding interactions between the oxygen functional groups of Ni-MOF and CB, and strong pi-pi interaction between the aromatic units of Ni-MOF and sp(2) carbon-graphitic sites of CB. These interactions help de-agglomeration and active-site inter-connection and a marked reduction in the multi-shell hollow structure of the CB (55nm -> 30nm). Capacitance measurement by galvanostatic charge and discharge (GCD) method yield value, 2700 F g(-1) at a biased-current, 2 A g(-1). It is about seven times higher than the values obtained with the respective pristine Ni-MOF (415 F g(-1)) and markedly higher than several literature-based MOF values. A GCD cyclic stability of the CB@Ni-MOF showed about 2% and 10% decrement at 2000 and 5000 cycles, respectively.