Binder-free metal–organic framework-based core–shell arrays for supercapacitors

Supercapacitors (SCs) are regarded as promising electrochemical energy storage devices, where the electrodes are vital in determining the performance of the devices. Metal-organic frameworks (MOFs) have recently emerged as suitable electrode materials or templates/precursors of electrode materials for SCs. The key to utilizing MOF-based electrode materials is to address their low electronic conductivity and poor stability issues. Therefore, rational design and fabrication of binder-free MOF/MOF derivative arrays is considered the most promising strategy to address these challenges. Another way to overcome the above limitations is to combine MOF-based materials with secondary electrochemically active materials to form composites with delicate architectures, such as core-shell structures, where the complementary and synergetic effects of different components give rise to enhanced energy storage capability. There are growing numbers of studies on MOF-based core-shell hybrid arrays directly constructed on current collectors. In this frontier review, we first introduce two synthesis strategies of constructing MOF-based core-shell arrays: growing MOFs on transition metal oxide (TMO) arrays and on a reactive hard template. Subsequently, core-shell arrays using MOF derivatives as core or shell materials are summarized. Finally, the potential challenges in binder-free core-shell array electrodes and possible solutions to these challenges are also discussed.