In situ growth of binder-free CoNi0.5-MOF/CC electrode for high-performance flexible solid-state supercapacitor application

Metal organic frameworks (MOFs) with binder-free electrodes have shown promise for portable electrochemical energy storage applications. However, their low specific capacitance and challenges associated with the attachment of active materials to the substrate constrain their practical utility. In this research, we prepared a CoNi_0.5-MOF/CC electrode by in situ growth of CoNi_0.5-MOF on an H₂O₂-pretreated carbon cloth (CC) without using any binder. It exhibits a higher specific capacitance of 1337.5 F g^-1 than that of CoNi_0.5-MOF (∼578 F g^-1) at a current density of 1 A g^-1 and an excellent rate ability of 88% specific capacitance retention at a current density of 10 A g^-1 after 6000 cycles. The as-assembled flexible asymmetric solid-state supercapacitor based on the CoNi_0.5-MOF/CC positive electrode and a nitrogen-doped graphene (N-Gr) negative electrode exhibits an energy density of 61.46 W h kg^-1 at a power density of 1244.56 W kg^-1 and holds a stable capacitance of ∼125 F g^-1 at 1 A g^-1 when the flexible supercapacitor is bent, showing great potential for flexible electronics application. The H₂O₂ is indicated to play an important role, enhancing the adhesion of CoNi_0.5-MOF on CC and reducing its charge transfer resistance by functionalizing the carbon fiber during the pretreatment of the CC matrix. The results provide a great way to prepare a flexible asymmetric solid-state supercapacitor with both high power density and high energy density for practical application.