Two-dimensional electrically conductive metal-organic frameworks (MOFs) have emerged as promising model electrodes for use in electric double-layer capacitors (EDLCs). However, a number of fundamental questions about the behaviour of this...
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Metal-organic frameworks (MOFs) are among the most promising materials for next-generation energy storage systems. However, the impact of particle morphology on the energy storage performances of these frameworks is poorly...
Two-dimensional
electrically conductive metal-organic frameworks (MOFs) are candidate electrode
materials for use in electric double-layer capacitor (EDLC) structure-property
investigations due to their well-defined crystalline structures. Their promising
capacitive performance was first illustrated by EDLCs constructed with the
layered framework Ni<sub>3</sub>(HITP)<sub>2 </sub>(HITP = 2,3,6,7,10,11-hexaiminotriphenylene)
and an organic electrolyte. Despite
this promise, there have been few follow-up
studies on the use of these frameworks in EDLCs, raising questions about the
generality of the results. Here, we demonstrate the high capacitive performance of
the layered framework Cu<sub>3</sub>(HHTP)<sub>2</sub> (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene)
in EDLCs with an organic electrolyte and compare its performance with Ni<sub>3</sub>(HITP)<sub>2</sub>.
Cu<sub>3</sub>(HHTP)<sub>2</sub> exhibits a specific capacitance of 110
– 114 F g<sup>–1 </sup>at low current densities of 0.04 – 0.05 A g<sup>–1</sup>
and shows modest capacitance retentions (66 %) at current densities up to 2 A g<sup>–1</sup>,
mirroring the performance of Ni<sub>3</sub>(HITP)<sub>2</sub>. However, we also
explore the limitations of Cu<sub>3</sub>(HHTP)<sub>2</sub> in EDLCs, finding a
limited cell voltage window of 1.3 V and only moderate capacitance retention over
30,000 cycles. This illustrates that these materials require further
development to improve their EDLC performance, particularly to reach similar cycling
performance levels as porous carbons. Despite this, our work underscores the
utility of framework materials in EDLCs and suggests that capacitive
performance is largely independent of the identity of the metal node and
organic linker molecule, instead being dictated by the three-dimensional
structure of the framework. These important insights will aid the design of
future conductive MOFs for use in EDLCs.
Metal-organic frameworks (MOFs) are among the most promising materials for next-generation energy storage systems, including supercapacitors. Few studies, however, have examined the impact of particle morphology and degree of agglomeration on the energy storage performances of these materials. To address this, here we use coordination modulation to synthesise three samples of the conductive MOF Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with distinct microstructures. Evaluation of the performances of these samples in symmetric supercapacitors with organic and ionic liquid electrolytes demonstrated that samples with weakly agglomerated ‘flake-like’ particles, with short pores and many pore openings, display superior capacitive performances than samples with either weakly agglomerated ‘rod-like’ particle morphologies or strongly agglomerated ‘flake-like’ particles. The results of this study provide a target microstructure for conductive MOFs for energy storage applications.
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