(704a) MOF-Derived Metal Oxide Composites for High Performance Energy Storage

Metal-organic frameworks (MOFs) are crystalline porous structures composed of metal ion centers and organic linkers coupled through coordination bonding. The intrinsic high specific surface area, controllable pore size and good thermal stability of MOF structures makes them good candidates to be used as porous templates. Through a novel coordination modulation method, it is possible to control the size, morphology, and structural properties of MOF structures by incorporating secondary ligands to modulate the coordination equilibrium with the same chemical functionality as the primary organic linkers to act as capping agents and to adjust the coordination interactions between metal ions and organic linkers and thus resulting modulated MOFs in terms of morphology and crystal size. This paves the way to develop and synthesize MOF structures with favorable characteristics to be used as sacrificial templates to synthesize interconnected porosity and high surface area.

The advanced approaches to develop high performance electroactive materials mainly focus on introducing more electrochemically active sites, shortening ionic pathways, faster charge transfer kinetics. This will be only achieved by careful selection of appropriate electroactive material as well as rational design of hybrid electrode architecture using conductive scaffolds such as graphene. We tend to focus more on exploiting methods to improve the electrochemical performance of metal oxides composites by trying to understand better the metal oxide composite formation and the metal oxide/graphene interfacial interactions and its effect the electrochemical kinetics of our composite structure.

In this work, we adopt a rational strategy to synthesize NiCo₂O₄/Co₃O₄ metal nanostructures. Highly porous ZIF-67 nanocrystals are firstly produced through coordination modulation process. By carefully etching these structures, ZIF-67/Ni-Co layered double-hydroxide template is formed. The as-prepared templates are subsequently calcinated to obtain the NiCo₂O₄/Co₃O₄ metal nanostructures. Later, to prevent the agglomeration and improve the charge transfer properties of our structures, the surface of as-prepared nanostructures is functionalized using a silanization process and mixed with graphene oxide dispersion to form self-assembled NiCo₂O₄/Co₃O₄-rGO composite structures. We report NiCo₂O₄/Co₃O₄-rGO composite structure with a capacity of 969 F g^-1 at current density of 1 A g^-1 showing a remarkable stability of showing 93% of initial capacitance after 10000 cycles of charge-discharge using electrodes with a high mass loading (~4 mg cm^-2).