Insights Into the Electric Double-Layer Capacitance of the Two-Dimensional Electrically Conductive Metal-Organic Framework Cu3(HHTP)2

Abstract

Two-dimensional electrically conductive metal-organic frameworks (MOFs) have emerged as promising model electrodes for use in electric double-layer capacitors (EDLC). Here, we demonstrate the high capacitive performance of the framework Cu<sub>3</sub>(HHTP)<sub>2</sub> (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with an organic electrolyte and compare its behaviour with the previously reported analogue, Ni<sub>3</sub>(HITP)<sub>2</sub> (HITP = 2,3,6,7,10,11-hexaiminotriphenylene). At low current densities of 0.04 – 0.05 A g<sup>−1</sup>, Cu<sub>3</sub>(HHTP)<sub>2</sub> electrodes exhibit a specific capacitance of 110 – 114 F g<sup>−1</sup> and show 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> and suggesting that capacitive performance is largely independent of the identity of the metal node and organic linker molecule. However, we find a limited cell voltage window of 1.3 V and only moderate capacitance retention (86 %) over 30,000 cycles at a moderate current density of 1 A g<sup>−1</sup>, both significantly lower than state-of-the-art porous carbons. These important insights will aid the design of future conductive MOFs with improved performance in EDLCs.