Excellent Supercapacitor Performance of Robust Nickel-Organic Framework Materials Achieved by Tunable Porosity, Inner-Cluster Redox, and in Situ Fabrication with Graphene Oxide

Metal-organic frameworks have shown promising applications as electrode materials for supercapacitors because of the high porosity and tunable structures, but their poor water stability and conductivity limit their capacitance and efficiency. To demonstrate how to overcome these drawbacks, three isostructural Ni-organic frameworks with [(Ni2NiIII)-Ni-II(mu(3)-OH)(COO)(6)] trinuclear building blocks are selected. Taking advantage of high-connected architectures, absence of open metal sites, and effective inner-cluster redox process, three Ni-organic frameworks all are stable in KOH electrolyte and exhibit a pseudo-capacitor behavior with high specific capacitances up to 394, 426, and 465 F g(-1). The increasing porosity facilitates the diffusion of metal ions and electrons and thus increases their electrochemical performance. Furthermore, we demonstrate that the in situ fabrication of metal-organic frameworks with graphene oxide can effectively promote their supercapacitor performance. With a given 3% graphene oxide doping amount, the pseudo-capacitance values of the three compounds are improved to be 590, 576, and 504 F g(-1) respectively. The values surpass those of most of the reported metal-organic framework supercapacitors up to now. The excellent supercapacitor performance of these Ni-MOFs provides a new route to explore potential electrode material by utilizing robust metal-organic frameworks based on [M-3(mu(3)-OH)(COO)(6)] trinuclear building blocks.