Enhancing the Electrochemical Energy Storage of Metal-Organic Frameworks: Linker Engineering and Size Optimization

The electric conductivity and charge transport efficiency of metal-organic frameworks (MOFs) dictate the effective utilization of built-in redox centers and electrochemical redox kinetics and therefore electrochemical performance. Reticular chemistry and the tunable microcosmic shape of MOFs allow for improving their electric conductivity and charge transfer efficiency. Herein, we synthesized two Ni-MOFs (Ni-tdc-bpy and Ni-tdc-bpe) by the solvothermal reaction of Ni²⁺ ions with 2,5-thiophenedicarboxylic acid (H₂tdc) in the presence of conjugated 4,4'-bipyridyl (bpy) and 1,2-di(4-pyridyl)ethylene (bpe) coligands, respectively. We also synthesized two thinning Ni-MOFs (Ni-tdc-bpy(0.5) and Ni-tdc-bpe(0.5)) by adjusting the amounts of bpy and bpe, respectively. Experimental investigations revealed that linker engineering by tuning the delocalization of the N-donor dipyridyl coligands and size optimization by controlling the amount of the coligand rendered the Ni-MOF with significantly improved electrical conductivity and charge transport efficiency. Among them, Ni-tdc-bpe(0.5) possessing the bpe coligand with more strong delocalization and an optimized size exhibited an enhanced specific capacitance of 650 F g^-1 at 0.5 A g^-1. Moreover, the hybrid supercapacitor constructed from Ni-tdc-bpe(0.5) and activated carbon delivered an excellent energy density of 33.6 Wh kg^-1 at a power density of 232.6 W kg^-1.