Upgrading Structural Conjugation in Three-Dimensional Ni-Based Metal–Organic Frameworks for Promoting Electrical Conductivity and Specific Capacitance

Metal-organic frameworks (MOFs) have emerged as promising candidates for electrochemical energy storage and conversion due to their high specific surface areas, abundant active sites, and excellent chemical and structural tunability. However, the direct utilization of MOFs as electrochemical materials is a challenge because of the poor electroconductivity induced by the insulating nature of most organic linkers. Herein, a conjugated three-dimensional Ni-MOF {Ni(HBTC)(BPE)}_<i>n</i> (<b>Ni-BPE</b>) with a 2-fold interpenetrating structure was developed via the coordination polymerization of Ni²⁺, a H₃BTC ligand (1,3,5-benzenetricarboxylic acid), and a vinyl-functionalized bipyridine linker (1,2-di(4-pyridyl)ethylene, BPE). <b>Ni-BPE</b> displayed an enhanced conjugation system compared to analogous and insulated <b>Ni-BPY</b> that is constructed by the Ni-BTC layer and ordinary bipyridine linker (4,4'-bipyridine, BPY). Notably, upgrading structural conjugation promoted a dramatical ∼204 times increase in the electroconductivity of <b>Ni-BPE</b> compared to <b>Ni-BPY</b>. More importantly, <b>Ni-BPE</b> displayed a higher specific capacitance of 633.2 F g^-1 (316.6 C g^-1) at 1 A g^-1, which exhibited a significant ∼1.5-fold enhancement than <b>Ni-BPY</b>. Furthermore, the asymmetric supercapacitor can reach a good energy density of 25.2 Wh kg^-1 with a reasonable cycle stability of 71.0% over 5000 cycles. This work provides an effective method for optimizing the structure of insulating MOFs to enhance the electroconductivity and specific capacitance.