Gittins Jamie W, Balhatchet Chloe J, Chen Yuan, Liu Cheng, Madden David G, Britto Sylvia, Golomb Matthias J, Walsh Aron, Fairen-Jimenez David, Dutton Siân E, Forse Alexander C
Yusuf Hamied Department of Chemistry, University of Cambridge Lensfield Road Cambridge CB2 1EW UK
Department of Chemistry, Imperial College London Exhibition Road London SW7 2AZ UK.
J Mater Chem A Mater. 2021 Jun 25;9(29):16006-16015. doi: 10.1039/d1ta04026j. eCollection 2021 Jul 27.
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 class of materials in EDLCs remain unanswered, including the effect of the identity of the metal node and organic linker molecule on capacitive performance, and the limitations of current conductive MOFs in these devices relative to traditional activated carbon electrode materials. Herein, we address both these questions a detailed study of the capacitive performance of the framework Cu(HHTP) (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with an acetonitrile-based electrolyte, finding a specific capacitance of 110-114 F g at current densities of 0.04-0.05 A g and a modest rate capability. By directly comparing its performance with the previously reported analogue, Ni(HITP) (HITP = 2,3,6,7,10,11-hexaiminotriphenylene), we illustrate that capacitive performance is largely independent of the identity of the metal node and organic linker molecule in these nearly isostructural MOFs. Importantly, this result suggests that EDLC performance in general is uniquely defined by the 3D structure of the electrodes and the electrolyte, a significant finding not demonstrated using traditional electrode materials. Finally, we probe the limitations of Cu(HHTP) in EDLCs, finding a limited stable double-layer voltage window of 1 V and only a modest capacitance retention of 81% over 30 000 cycles, both significantly lower than state-of-the-art porous carbons. These important insights will aid the design of future conductive MOFs with greater EDLC performances.
二维导电金属有机框架（MOFs）已成为用于双电层电容器（EDLCs）的有前景的模型电极。然而，关于这类材料在EDLCs中的行为仍有许多基本问题未得到解答，包括金属节点和有机连接分子的身份对电容性能的影响，以及相对于传统活性炭电极材料，当前导电MOFs在这些器件中的局限性。在此，我们通过对具有乙腈基电解质的框架Cu(HHTP)（HHTP = 2,3,6,7,10,11-六羟基三亚苯）的电容性能进行详细研究来解决这两个问题，发现在0.04 - 0.05 A g的电流密度下比电容为110 - 114 F g，且倍率性能一般。通过将其性能与先前报道的类似物Ni(HITP)（HITP = 2,3,6,7,10,11-六亚氨基三亚苯）直接比较，我们表明在这些近等结构的MOFs中，电容性能在很大程度上与金属节点和有机连接分子的身份无关。重要的是，这一结果表明，一般而言，EDLC性能由电极和电解质的三维结构唯一确定，这是使用传统电极材料未证明的重要发现。最后，我们探究了Cu(HHTP)在EDLCs中的局限性，发现其稳定的双电层电压窗口有限，为1 V，在30000次循环中电容保持率仅为适度的81%，两者均显著低于目前的多孔碳。这些重要见解将有助于设计未来具有更高EDLC性能的导电MOFs。
