Design strategy for metal–organic framework assembled on modifications of MXene layers for advanced supercapacitor electrodes

The poor electronic conductivity and instability of metal–organic framework (MOFs) nanomaterials have been considered as the main reasons that hinder their practical application. Here, the bimetallic NiCo-MOF is in-situ grown by two-dimension expanded MXene to construct promising hierarchical electrodes. Benefitting from the hydroxyl group on the surface of MXene attracts metal (Ni, Co) ions by weak coordination, leading to oxygen vacancies during NiCo-MOF formation. At the same time, the density functional theory (DFT) calculation displays that the redox active center of NiCo-MOF is guaranteed to possess excellent electron and ion transport performance. Moreover, the open morphology based on expanded MXene by the hard template method can solve the re-stacking problem of MXene and provide a larger growth area for NiCo-MOF. The electrode design engineering strategy significantly improves the capacitance performance by increasing the electrochemically active site and promoting the ion dynamics. Specifically, the integrated solid-state hybrid supercapacitor (HSC) with MXene@NiCo-MOF and activated carbon (AC) exhibits energy density of 40.23 Wh·kg−1 at a power density of 1495.07 W·kg−1 and 84.4 % capacitance retention after 10,000 cycles via adopting this strategy. The strategy also provides a new route to improve the performance of flexible MXene-based supercapacitors with polyvinyl alcohol hydrogel electrolytes.