MOFs And MOFs-derived Porous Carbon For Flexible Supercapacitor Electrode Materials

Flexible supercapacitors have become a research focus in recent years as a promising class of energy storage device and have attracted great attention due to their several important advantages including miniaturization,light-weight,flexibility,wearability and safety.With the rapid development of wearable electronic devices,the development of flexible supercapacitor with ultrahigh energy density and excellent mechanical robustness is urgently needed.One critical issue to construct promising flexible supercapacitors is engineering high-performance electrode materials with excellent mechanical flexibility.Metal-organic frameworks?MOFs?,a fascinating class of solid crystalline materials,consisting of metal ions and organic ligands assembled into periodically porous architecture,have been considered as promising candidates for electrode materials due to their intrinsic porous characteristics and extraordinarily large surface area.Nevertheless,the poor electrical conductivity of most MOFs has limited their application as electrode materials for supercapacitors.In this paper,a series of MOF-derivates and MOF composites based on three types of MOFs are fabricated,then they are used as electrode materials for flexible supercapacitors.The main contents of this paper are as follows:1.Novel three-dimensional?3D?interconnected hierarchical porous carbons?PCs?using Zn-based MOFs?Zn?tbip?,H₂tbip=5-tert-butyl isophthalate?with two distinct particle sizes as precursors were prepared via a one-step pyrolysis process.The size and carbonization temperature effects of the precursor on the porous architecture have been evaluated in detail.The porous carbon derived from small-sized Zn?tbip?at 900^oC?denoted as C-S-900?possesses a hierarchical porous structure with the highest specific surface area(1356 m² g^-1),which benefits ion immersion and retention.C-S-900 demonstrates an ultrahigh specific capacitance of 369 F g^-1 and 226 F g^-1 at10 and 400 mV s^-1 in 6 mol L^-1 KOH electrolyte,respectively.In addition,a symmetric flexible all-solid-state supercapacitor device was assembled with the electrode of C-S-900 and PVA/KOH gel electrolyte.The device can offer 96%capacity after 2000 stretching-bending cycles and operate micro-electronic devices displaying excellent mechanical robustness and cycling stability.The present work explored the relationship between the size and carbonization temperature effects of MOF precursors and the porous carbon architectures to optimize the performance of supercapacitors.2.Here,a simple and effective strategy that involves a“root-etch-wrap”process was developed to synthesize hollow core-shell hetero-structured electrodes.Specifically,ZnO hollow spheres take root on carbon cloth via an in situ growth routine,then are etched to aid the generation of a ZIF-8 shell.As-synthesized hollow core-shell ZnO@ZIF-8 is wrapped by PANI nanocoating,resulting in a flexible conductive porous electrode?denoted as PANI/ZnO@ZIF-8-CC?.The optimized electrode exhibits an ultrahigh areal capacitance(4839-3987 mF cm^-2 at 5-30 mA cm^-2),which is at least 3 times higher than that of PANI-CC and ZnO@ZIF-8-CC owing to the synergistic effect.In addition,a symmetric flexible supercapacitor fabricated by PANI/ZnO@ZIF-8-CC and PVA/KCl gel electrolyte exhibits a high energy density of 0.137-0.0891 mWh cm^-3(at a power density of 1.421-23.629Wcm^-3)and a good long-term cycling ability(87%for 10 000 cycles at 5 mA cm^-2).All of these results make unique core-shell structured PANI/ZnO@ZIF-8-CC a promising electrode material for advanced energy storage and conversion applications.3.In this work,we present a controllable“anchor-etch-calcine”approach to produce core-shell heterostructured MOF-derived porous carbon/CoO composite in conductive substrate?NF@CoO@Co/N-C?.The novel CoO as core assembled by highly ordered nanowire array contain numerous accessible active sites.The unique MOF-derived porous carbon as shell with Co-and N-codoped structure possesses large surface area,porosity,outstanding stability,excellent conductivity and compatibility.These characteristics enhance electrochemical performance and alleviate volume expansion effectively.The NF@CoO@Co/N-C electrode exhibits an ultrahigh areal capacitance of 4.24 F cm^-2 at 2 mA cm^-2,which is at least two-fold higher than its corresponding oxide.Notably,an asymmetric flexible all-solid-state supercapacitor fabricated by NF@CoO@Co/N-C delivers high volumetric capacity(9.32 F cm^-3),high energy density(3.29 mWh cm^-3)and remains above 96%of the initial capacitance even after 10000 cycles at 10 mA cm^-2.This study provides rational guidance toward the design of transitional metal oxides?TMOs?electrode materials with extended-life energy storage performance duo to the effectively alleviated volume expansion.