Pillared-layer Ni-MOF nanosheets anchored on Ti3C2 MXene for enhanced electrochemical energy storage

The poor conductivity, unsatisfactory stability and easy aggregation of metal-organic framework (MOF) nanomaterials have been recognized as the main reasons that prevent their practical application. Here, we report the highly conductive and cyclic-stable Ti3C2 MXene@pillared-layer [Ni(thiophene-2,5-dicarboxylate)(4,4'-bipyridine)]n MOF composites (MXene@Ni-MOF). Based on the hard-soft-acid-base principle, the pillared-layer Ni-MOF porous structure with Ni-N coordination bonds confer better structural stability. The Ni-MOF nanosheets are immobilized by the MXene, leading to fast charge transfer between the Ni-MOF and MXene, solving the problem of poor conductivity of Ni-MOF, while avoiding the agglomeration of Ni-MOF nanosheets. Moreover, the strong interaction between the organic ligands of Ni-MOF and surface functional groups of MXene plays a key role: it reduces the exposure of surface groups of MXene, limits the oxidation of MXene, and increases its layer spacing, thus facilitating the rapid ion transport. The MXene@Ni-MOF exhibits a high specific capacitance (979 F g-1 at 0.5 A g-1) and the new aqueous asymmetric supercapacitor device displays an excellent cycling property with only 2% decay after 5000 cycles.