Interweaving metal-organic framework-templated Co-Ni layered double hydroxide nanocages with nanocellulose and carbon nanotubes to make flexible and foldable electrodes for energy storage devices

Metal-organic frameworks (MOFs) and nanocellulose represent emerging and traditional porous materials, respectively. The combination of these two materials in specific ways could generate novel nanomaterials with integrated advantages and versatile functionalities. This study outlines the development of hierarchical porous and conductive nanosheets based on zeolitic imidazolate framework-67 (ZIF-67, a Co-based MOF)-templated Co-Ni layered double hydroxide (LDH) nanocages, Cladophora cellulose (CC) nanofibers, and multi-walled carbon nanotubes (CNTs). The LDH-CC-CNT nanosheets can be used as flexible and foldable electrodes for energy storage devices (ESDs). The electrodes are associated with a high areal capacitance of up to 1979 mF cm^-2 at a potential scan rate of 1 mV s^-1. A flexible, foldable, and hybrid ESD is assembled from LDH-CC-CNT and CC-CNT electrodes with a PVA/KOH gel. The entire device has an areal capacitance of 168 mF cm^-2 and an energy density of 0.6 mW h cm^-3 (60 μW h cm^-2), at a power density of 8.0 mW cm^-3 (0.8 mW cm^-2). These promising results demonstrate the potential of using MOFs and sustainable cellulose in flexible, foldable electronic energy storage devices.